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1.  HIV-1 Vaccine-Induced C1 and V2 Env-Specific Antibodies Synergize for Increased Antiviral Activities 
Journal of Virology  2014;88(14):7715-7726.
The RV144 ALVAC/AIDSVax HIV-1 vaccine clinical trial showed an estimated vaccine efficacy of 31.2%. Viral genetic analysis identified a vaccine-induced site of immune pressure in the HIV-1 envelope (Env) variable region 2 (V2) focused on residue 169, which is included in the epitope recognized by vaccinee-derived V2 monoclonal antibodies. The ALVAC/AIDSVax vaccine induced antibody-dependent cellular cytotoxicity (ADCC) against the Env V2 and constant 1 (C1) regions. In the presence of low IgA Env antibody levels, plasma levels of ADCC activity correlated with lower risk of infection. In this study, we demonstrate that C1 and V2 monoclonal antibodies isolated from RV144 vaccinees synergized for neutralization, infectious virus capture, and ADCC. Importantly, synergy increased the HIV-1 ADCC activity of V2 monoclonal antibody CH58 at concentrations similar to that observed in plasma of RV144 vaccinees. These findings raise the hypothesis that synergy among vaccine-induced antibodies with different epitope specificities contributes to HIV-1 antiviral antibody responses and is important to induce for reduction in the risk of HIV-1 transmission.
IMPORTANCE The Thai RV144 ALVAC/AIDSVax prime-boost vaccine efficacy trial represents the only example of HIV-1 vaccine efficacy in humans to date. Studies aimed at identifying immune correlates involved in the modest vaccine-mediated protection identified HIV-1 envelope (Env) variable region 2-binding antibodies as inversely correlated with infection risk, and genetic analysis identified a site of immune pressure within the region recognized by these antibodies. Despite this evidence, the antiviral mechanisms by which variable region 2-specific antibodies may have contributed to lower rates of infection remain unclear. In this study, we demonstrate that vaccine-induced HIV-1 envelope variable region 2 and constant region 1 antibodies synergize for recognition of virus-infected cells, infectious virion capture, virus neutralization, and antibody-dependent cellular cytotoxicity. This is a major step in understanding how these types of antibodies may have cooperatively contributed to reducing infection risk and should be considered in the context of prospective vaccine design.
PMCID: PMC4097802  PMID: 24807721
2.  Nonneutralizing Functional Antibodies: a New “Old” Paradigm for HIV Vaccines 
Animal and human data from various viral infections and vaccine studies suggest that nonneutralizing antibodies (nNAb) without neutralizing activity in vitro may play an important role in protection against viral infection in vivo. This was illustrated by the recent human immunodeficiency virus (HIV) RV144 vaccine efficacy trial, which demonstrated that HIV-specific IgG-mediated nNAb directed against the V2 loop of HIV type 1 envelope (Env) were inversely correlated with risk for HIV acquisition, while Env-specific plasma IgA-mediated antibodies were directly correlated with risk. However, tier 1 NAb in the subset of responders with a low level of plasma Env-specific IgA correlated with decreased risk. Nonhuman primate simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) challenge studies suggest that Env-mediated antibodies are essential and sufficient for protection. A comparison of immune responses generated in human efficacy trials reveals subtle differences in the fine specificities of the antibody responses, in particular in HIV-specific IgG subclasses. The underlying mechanisms that may have contributed to protection against HIV acquisition in humans, although not fully understood, are possibly mediated by antibody-dependent cell-mediated cytotoxicity (ADCC) and/or other nonneutralizing humoral effector functions, such as antibody-mediated phagocytosis. The presence of such functional nNAb in mucosal tissues and cervico-vaginal and rectal secretions challenges the paradigm that NAb are the predominant immune response conferring protection, although this does not negate the desirability of evoking neutralizing antibodies through vaccination. Instead, NAb and nNAb should be looked upon as complementary or synergistic humoral effector functions. Several HIV vaccine clinical trials to study these antibody responses in various prime-boost modalities in the systemic and mucosal compartments are ongoing. The induction of high-frequency HIV-specific functional nNAb at high titers may represent an attractive hypothesis-testing strategy in future HIV vaccine efficacy trials.
PMCID: PMC4135913  PMID: 24920599
3.  Are anti-HIV IgAs good guys or bad guys? 
Retrovirology  2014;11(1):109.
An estimated 90% of all HIV transmissions occur mucosally. Immunoglobulin A (IgA) molecules are important components of mucosal fluids. In a vaccine efficacy study, in which virosomes displaying HIV gp41 antigens protected most rhesus monkeys (RMs) against simian-human immunodeficiency virus (SHIV), protection correlated with vaginal IgA capable of blocking HIV transcytosis in vitro. Furthermore, vaginal IgG exhibiting virus neutralization and/or antibody-dependent cellular cytotoxicity (ADCC) correlated with prevention of systemic infection. In contrast, plasma IgG had neither neutralizing nor ADCC activity. More recently, a passive mucosal immunization study provided the first direct proof that dimeric IgAs (dIgAs) can prevent SHIV acquisition in RMs challenged mucosally. This study compared dimeric IgA1 (dIgA1), dIgA2, or IgG1 versions of a human neutralizing monoclonal antibody (nmAb) targeting a conserved HIV Env epitope. While the nmAb neutralization profiles were identical in vitro, dIgA1 was significantly more protective in vivo than dIgA2. Protection was linked to a new mechanism: virion capture. Protection also correlated with inhibition of transcytosis of cell-free virus in vitro. While both of these primate model studies demonstrated protective effects of mucosal IgAs, the RV144 clinical trial identified plasma IgA responses to HIV Env as risk factors for increased HIV acquisition. In a secondary analysis of RV144, plasma IgA decreased the in vitro ADCC activity of vaccine-induced, Env-specific IgG with the same epitope specificity. Here we review the current literature regarding the potential of IgA – systemic as well as mucosal – in modulating virus acquisition and address the question whether anti-HIV IgA responses could help or harm the host.
PMCID: PMC4297362  PMID: 25499540
IgA; Dimeric IgA1 (dIgA1); dIgA2; Secretory IgA (SIgA); HIV/SHIV; Mucosal transmission; Passive immunization; Non-human primate models; RV144 trial; AIDS vaccine development
4.  Antibody-Dependent Cellular Cytotoxicity-Mediating Antibodies from an HIV-1 Vaccine Efficacy Trial Target Multiple Epitopes and Preferentially Use the VH1 Gene Family 
Journal of Virology  2012;86(21):11521-11532.
The ALVAC-HIV/AIDSVAX-B/E RV144 vaccine trial showed an estimated efficacy of 31%. RV144 secondary immune correlate analysis demonstrated that the combination of low plasma anti-HIV-1 Env IgA antibodies and high levels of antibody-dependent cellular cytotoxicity (ADCC) inversely correlate with infection risk. One hypothesis is that the observed protection in RV144 is partially due to ADCC-mediating antibodies. We found that the majority (73 to 90%) of a representative group of vaccinees displayed plasma ADCC activity, usually (96.2%) blocked by competition with the C1 region-specific A32 Fab fragment. Using memory B-cell cultures and antigen-specific B-cell sorting, we isolated 23 ADCC-mediating nonclonally related antibodies from 6 vaccine recipients. These antibodies targeted A32-blockable conformational epitopes (n = 19), a non-A32-blockable conformational epitope (n = 1), and the gp120 Env variable loops (n = 3). Fourteen antibodies mediated cross-clade target cell killing. ADCC-mediating antibodies displayed modest levels of V-heavy (VH) chain somatic mutation (0.5 to 1.5%) and also displayed a disproportionate usage of VH1 family genes (74%), a phenomenon recently described for CD4-binding site broadly neutralizing antibodies (bNAbs). Maximal ADCC activity of VH1 antibodies correlated with mutation frequency. The polyclonality and low mutation frequency of these VH1 antibodies reveal fundamental differences in the regulation and maturation of these ADCC-mediating responses compared to VH1 bNAbs.
PMCID: PMC3486290  PMID: 22896626
5.  Enhancing Exposure of HIV-1 Neutralization Epitopes through Mutations in gp41 
PLoS Medicine  2008;5(1):e9.
The generation of broadly neutralizing antibodies is a priority in the design of vaccines against HIV-1. Unfortunately, most antibodies to HIV-1 are narrow in their specificity, and a basic understanding of how to develop antibodies with broad neutralizing activity is needed. Designing methods to target antibodies to conserved HIV-1 epitopes may allow for the generation of broadly neutralizing antibodies and aid the global fight against AIDS by providing new approaches to block HIV-1 infection. Using a naturally occurring HIV-1 Envelope (Env) variant as a template, we sought to identify features of Env that would enhance exposure of conserved HIV-1 epitopes.
Methods and Findings
Within a cohort study of high-risk women in Mombasa, Kenya, we previously identified a subtype A HIV-1 Env variant in one participant that was unusually sensitive to neutralization. Using site-directed mutagenesis, the unusual neutralization sensitivity of this variant was mapped to two amino acid mutations within conserved sites in the transmembrane subunit (gp41) of the HIV-1 Env protein. These two mutations, when introduced into a neutralization-resistant variant from the same participant, resulted in 3- to >360-fold enhanced neutralization by monoclonal antibodies specific for conserved regions of both gp41 and the Env surface subunit, gp120, >780-fold enhanced neutralization by soluble CD4, and >35-fold enhanced neutralization by the antibodies found within a pool of plasmas from unrelated individuals. Enhanced neutralization sensitivity was not explained by differences in Env infectivity, Env concentration, Env shedding, or apparent differences in fusion kinetics. Furthermore, introduction of these mutations into unrelated viral Env sequences, including those from both another subtype A variant and a subtype B variant, resulted in enhanced neutralization susceptibility to gp41- and gp120-specific antibodies, and to plasma antibodies. This enhanced neutralization sensitivity exceeded 1,000-fold in several cases.
Two amino acid mutations within gp41 were identified that expose multiple discontinuous neutralization epitopes on diverse HIV-1 Env proteins. These exposed epitopes were shielded on the unmodified viral Env proteins, and several of the exposed epitopes encompass desired target regions for protective antibodies. Env proteins containing these modifications could act as a scaffold for presentation of such conserved domains, and may aid in developing methods to target antibodies to such regions.
Julie Overbaugh and colleagues analyze an HIV strain with high susceptibility to antibody neutralization and identify two gp41 envelope mutations that confer this sensitivity by exposing multiple neutralization epitopes.
Editors' Summary
In 1984 when scientists identified human immunodeficiency virus (HIV)—the cause of acquired immunodeficiency syndrome (AIDS)—many experts believed that a vaccine against HIV infection would soon be developed. Nearly 25 years later, there is still no such vaccine and with about 2.5 million new HIV infections in 2007, an effective vaccine is urgently needed to contain the AIDS epidemic. Vaccines provide protection against infectious diseases by priming the immune system to deal quickly and effectively with viruses and other pathogens. Vaccines do this by exposing the immune system to an immunogen—a fragment or harmless version of the pathogen. The immune system mounts a response against the immunogen and also “learns” from this experience so that if it is ever challenged with a virulent version of the same pathogen, it can quickly contain the threat. Many vaccines work by stimulating an antibody response. Antibodies are proteins made by the immune system that bind to molecules called antigens on the surface of pathogens. Antibodies that inactivate the invader upon binding to it are called “neutralizing” antibodies.
Why Was This Study Done?
Several characteristics of HIV have hampered the development of an effective vaccine. An “envelope” protein consisting of two subunits called gp120 and gp41 covers the outside of HIV. Many regions of this protein change rapidly, so the antibody response stimulated by a vaccine containing the envelope protein of one HIV variant provides little protection against other variants. However, other regions of the protein rarely change, so a vaccine that stimulates the production of antibodies to these “conserved” regions is likely to provide protection against many HIV variants. That is, it will stimulate the production of broadly neutralizing antibodies. Unfortunately, it has been difficult to find HIV vaccines that do this, because these conserved regions are often hidden from the immune system by other parts of the envelope protein. In this study, the researchers investigate the envelope protein of an HIV-1 variant they have isolated that is highly susceptible to inactivation by antibodies specific for these conserved regions. Comparing the envelope protein of this sensitive virus to closely related envelope proteins that are resistant to neutralization could identify features that might, if included in an envelope protein immunogen, produce a vaccine capable of generating broadly neutralizing antibodies.
What Did the Researchers Do and Find?
The researchers isolated a subtype A HIV-1 variant from a newly infected woman in Kenya that was efficiently neutralized by monoclonal antibodies (antibodies made by cells that have been cloned in the laboratory). These antibodies were specific for several different conserved regions of gp41 and gp120. The isolate was also neutralized by antibodies in blood from HIV-1-infected people. The envelope protein of the sensitive variant was the same as that of a resistant variant isolated at the same time from the woman, except for four amino acid changes in conserved regions of gp41 (proteins are made from long strings of amino acids). Using a technique called site-directed mutagenesis, the researchers introduced these amino acid changes into envelope proteins made in the laboratory and determined that just two of these changes were responsible for the neutralization sensitivity of the HIV-1 variant. The introduction of these two changes into the neutralization resistant variant and into the unrelated envelope sequences of another subtype A (common in Africa) HIV-1 variant and a subtype B HIV-1 (common in Europe and the Western Hemisphere) variant increased the sensitivity of all these viruses to antibody neutralization.
What Do These Findings Mean?
These findings show that two amino acid changes in gp41 of a neutralization-sensitive HIV-1 variant are responsible for the sensitivity of this variant to several neutralizing antibodies. The finding that the inclusion of these changes in the envelope protein of neutralization-resistant HIV-1 variants greatly increases their sensitivity to neutralizing antibodies indicates that the normally shielded regions of the protein are somehow made accessible to antibody by these changes. One possibility is that the amino acid changes might modify the overall shape of the envelope protein, thus exposing multiple, normally hidden regions in the HIV-1 envelope protein to antibodies. Importantly, these findings open up the possibility that the inclusion of these modifications in envelope-based immunogens might improve the ability of vaccines to generate broadly neutralizing antibodies against HIV-1.
Additional Information.
Please access these Web sites via the online version of this summary at
Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS
HIVInSite has comprehensive information on all aspects of HIV/AIDS, including links to resources dealing with HIV vaccine development
Information is available from Avert, an international AIDS charity, on all aspects of HIV and AIDS, including HIV vaccines
The US Centers for Disease Control and prevention provides information on HIV/AIDS including information on its HIV vaccine unit (in English and some information in Spanish)
The AIDS Vaccine Clearinghouse provides clear information about HIV vaccine science, research and product development
The International AIDS Vaccine Initiative also provides straightforward information about the development of HIV vaccines
PMCID: PMC2174964  PMID: 18177204
6.  Plasma IgG to Linear Epitopes in the V2 and V3 Regions of HIV-1 gp120 Correlate with a Reduced Risk of Infection in the RV144 Vaccine Efficacy Trial 
PLoS ONE  2013;8(9):e75665.
Neutralizing and non-neutralizing antibodies to linear epitopes on HIV-1 envelope glycoproteins have potential to mediate antiviral effector functions that could be beneficial to vaccine-induced protection. Here, plasma IgG responses were assessed in three HIV-1 gp120 vaccine efficacy trials (RV144, Vax003, Vax004) and in HIV-1-infected individuals by using arrays of overlapping peptides spanning the entire consensus gp160 of all major genetic subtypes and circulating recombinant forms (CRFs) of the virus. In RV144, where 31.2% efficacy against HIV-1 infection was seen, dominant responses targeted the C1, V2, V3 and C5 regions of gp120. An analysis of RV144 case-control samples showed that IgG to V2 CRF01_AE significantly inversely correlated with infection risk (OR= 0.54, p=0.0042), as did the response to other V2 subtypes (OR=0.60-0.63, p=0.016-0.025). The response to V3 CRF01_AE also inversely correlated with infection risk but only in vaccine recipients who had lower levels of other antibodies, especially Env-specific plasma IgA (OR=0.49, p=0.007) and neutralizing antibodies (OR=0.5, p=0.008). Responses to C1 and C5 showed no significant correlation with infection risk. In Vax003 and Vax004, where no significant protection was seen, serum IgG responses targeted the same epitopes as in RV144 with the exception of an additional C1 reactivity in Vax003 and infrequent V2 reactivity in Vax004. In HIV-1 infected subjects, dominant responses targeted the V3 and C5 regions of gp120, as well as the immunodominant domain, heptad repeat 1 (HR-1) and membrane proximal external region (MPER) of gp41. These results highlight the presence of several dominant linear B cell epitopes on the HIV-1 envelope glycoproteins. They also generate the hypothesis that IgG to linear epitopes in the V2 and V3 regions of gp120 are part of a complex interplay of immune responses that contributed to protection in RV144.
PMCID: PMC3784573  PMID: 24086607
7.  Vaccine-Induced IgG Antibodies to V1V2 Regions of Multiple HIV-1 Subtypes Correlate with Decreased Risk of HIV-1 Infection 
PLoS ONE  2014;9(2):e87572.
In the RV144 HIV-1 vaccine efficacy trial, IgG antibody (Ab) binding levels to variable regions 1 and 2 (V1V2) of the HIV-1 envelope glycoprotein gp120 were an inverse correlate of risk of HIV-1 infection. To determine if V1V2-specific Abs cross-react with V1V2 from different HIV-1 subtypes, if the nature of the V1V2 antigen used to asses cross-reactivity influenced infection risk, and to identify immune assays for upcoming HIV-1 vaccine efficacy trials, new V1V2-scaffold antigens were designed and tested. Protein scaffold antigens carrying the V1V2 regions from HIV-1 subtypes A, B, C, D or CRF01_AE were assayed in pilot studies, and six were selected to assess cross-reactive Abs in the plasma from the original RV144 case-control cohort (41 infected vaccinees, 205 frequency-matched uninfected vaccinees, and 40 placebo recipients) using ELISA and a binding Ab multiplex assay. IgG levels to these antigens were assessed as correlates of risk in vaccine recipients using weighted logistic regression models. Levels of Abs reactive with subtype A, B, C and CRF01_AE V1V2-scaffold antigens were all significant inverse correlates of risk (p-values of 0.0008–0.05; estimated odds ratios of 0.53–0.68 per 1 standard deviation increase). Thus, levels of vaccine-induced IgG Abs recognizing V1V2 regions from multiple HIV-1 subtypes, and presented on different scaffolds, constitute inverse correlates of risk for HIV-1 infection in the RV144 vaccine trial. The V1V2 antigens provide a link between RV144 and upcoming HIV-1 vaccine trials, and identify reagents and methods for evaluating V1V2 Abs as possible correlates of protection against HIV-1 infection.
Trial Registration NCT00223080
PMCID: PMC3913641  PMID: 24504509
8.  HIV-1 Specific IgA Detected in Vaginal Secretions of HIV Uninfected Women Participating in a Microbicide Trial in Southern Africa Are Primarily Directed Toward gp120 and gp140 Specificities 
PLoS ONE  2014;9(7):e101863.
Many participants in microbicide trials remain uninfected despite ongoing exposure to HIV-1. Determining the emergence and nature of mucosal HIV-specific immune responses in such women is important, since these responses may contribute to protection and could provide insight for the rational design of HIV-1 vaccines.
Methods and Findings
We first conducted a pilot study to compare three sampling devices (Dacron swabs, flocked nylon swabs and Merocel sponges) for detection of HIV-1-specific IgG and IgA antibodies in vaginal secretions. IgG antibodies from HIV-1-positive women reacted broadly across the full panel of eight HIV-1 envelope (Env) antigens tested, whereas IgA antibodies only reacted to the gp41 subunit. No Env-reactive antibodies were detected in the HIV-negative women. The three sampling devices yielded equal HIV-1-specific antibody titers, as well as total IgG and IgA concentrations. We then tested vaginal Dacron swabs archived from 57 HIV seronegative women who participated in a microbicide efficacy trial in Southern Africa (HPTN 035). We detected vaginal IgA antibodies directed at HIV-1 Env gp120/gp140 in six of these women, and at gp41 in another three women, but did not detect Env-specific IgG antibodies in any women.
Vaginal secretions of HIV-1 infected women contained IgG reactivity to a broad range of Env antigens and IgA reactivity to gp41. In contrast, Env-binding antibodies in the vaginal secretions of HIV-1 uninfected women participating in the microbicide trial were restricted to the IgA subtype and were mostly directed at HIV-1 gp120/gp140.
PMCID: PMC4108330  PMID: 25054205
9.  HIV Impairs Opsonic Phagocytic Clearance of Pregnancy-Associated Malaria Parasites 
PLoS Medicine  2007;4(5):e181.
Primigravid (PG) women are at risk for pregnancy-associated malaria (PAM). Multigravid (MG) women acquire protection against PAM; however, HIV infection impairs this protective response. Protection against PAM is associated with the production of IgG specific for variant surface antigens (VSA-PAM) expressed by chondroitin sulfate A (CSA)-adhering parasitized erythrocytes (PEs). We hypothesized that VSA-PAM-specific IgG confers protection by promoting opsonic phagocytosis of PAM isolates and that HIV infection impairs this response.
Methods and Findings
We assessed the ability of VSA-PAM-specific IgG to promote opsonic phagocytosis of CSA-adhering PEs and the impact of HIV infection on this process. Opsonic phagocytosis assays were performed using the CSA-adherent parasite line CS2 and human and murine macrophages. CS2 PEs were opsonized with plasma or purified IgG subclasses from HIV-negative or HIV-infected PG and MG Kenyan women or sympatric men. Levels of IgG subclasses specific for VSA-PAM were compared in HIV-negative and HIV-infected women by flow cytometry. Plasma from HIV-negative MG women, but not PG women or men, promoted the opsonic phagocytosis of CSA-binding PEs (p < 0.001). This function depended on VSA-PAM-specific plasma IgG1 and IgG3. HIV-infected MG women had significantly lower plasma opsonizing activity (median phagocytic index 46 [interquartile range (IQR) 18–195] versus 251 [IQR 93–397], p = 0.006) and levels of VSA-PAM-specific IgG1 (mean fluorescence intensity [MFI] 13 [IQR 11–20] versus 30 [IQR 23–41], p < 0.001) and IgG3 (MFI 17 [IQR 14–23] versus 28 [IQR 23–37], p < 0.001) than their HIV-negative MG counterparts.
Opsonic phagocytosis may represent a novel correlate of protection against PAM. HIV infection may increase the susceptibility of multigravid women to PAM by impairing this clearance mechanism.
Based on a comparison of HIV-negative or HIV-infected primigravid and multigravid women, Kevin Kain and colleagues suggest that opsonic phagocytosis might protect against pregnancy-associated malaria, and that HIV infection might impair this parasite clearance mechanism.
Editors' Summary
Every year, malaria kills more than one million people—mostly young children. Among adults, pregnant women are most affected by malaria, a parasitic disease spread by mosquitos. In areas of Africa where malaria is widespread, about 10,000 women die because of pregnancy-associated malaria (PAM) each year. In PAM, red blood cells containing parasites (parasitized erythrocytes or PEs) collect in the woman's placenta. These PEs, which stick to a placental molecule called chondroitin sulfate A (CSA), are covered with parasitic proteins known as variant surface antigens of PAM (VSA-PAM). Women in their first pregnancy (primigravid women) are particularly susceptible to PAM, but multigravid women are more resistant unless they are also infected with HIV (the virus that causes AIDS), in which case they are extremely susceptible to PAM. Protection against PAM in multigravid women is associated with the production of immunoglobulins (proteins made by the immune system that circulate in the blood and bind to foreign proteins or antigens) that recognize VSA-PAM. These immunoglobulins or antibodies are called VSA-PAM-specific IgG and their production increases with each pregnancy
Why Was This Study Done?
It is unclear how VSA-PAM-specific IgG protects multigravid women against PAM or how HIV infection impairs this protective response. One possibility is that VSA-PAM-specific IgG coats the PEs in the placenta to enable immune system cells called macrophages to recognize and ingest them, a process called opsonic phagocytosis. In this study, the researchers have investigated whether opsonic phagocytosis provides multigravid women with protection against PAM and whether a failure of this form of protective immunity underlies the susceptibility of HIV-infected multigravid women to PAM.
What Did the Researchers Do and Find?
The researchers collected plasma (the fluid part of blood) from primigravid and multigravid women (some of whom were infected with HIV) living in a Kenyan region where malaria is common soon after they gave birth and from men living in the same area. They then purified IgG1, IgG2, IgG3, and IgG4 from the plasma samples. These four IgG subclasses have different immune functions—only IgG1 and IgG3 participate in opsonic phagocytosis. To measure the ability of the plasma samples and purified IgGs to promote opsonic phagocytosis, the researchers mixed each sample with a laboratory isolate of CSA-binding PEs and macrophages and counted how many PEs the macrophages ingested. Plasma from HIV-negative multigravid women but not primigravid women or men promoted opsonic phagocytosis and, in the plasma from multigravid women, this activity depended on IgG1 and IgG3. HIV-infected multigravid women, however, had less opsonizing activity in their plasma than HIV-negative multigravid women and the level of this activity correlated with the levels of VSA-PAM-specific IgG1 and IgG3 (measured using a technique called flow cytometry) in the plasma samples of these two groups of women.
What Do These Findings Mean?
These findings support the hypothesis that VSA-PAM-specific IgG1 and IgG3 promote opsonic clearance of CSA-binding PEs. Thus, opsonic immune mechanisms may be involved in the protective response to PAM seen in multigravid women. However, because all the measurements of opsonic phagocytosis in this study used a laboratory isolate of PEs, these findings need to be confirmed using PEs isolated from placentas to check that they are generalizable. Other findings reported here suggest that HIV-positive multigravid women are more susceptible to PAM than HIV-negative multigravid women because reduced amounts of VSA-PAM-specific IgG in their plasma reduce the ability of opsonic phagocytosis to clear PEs from their placenta. Overall, these results may have implications for the development of vaccines against PAM. For example, they suggest that vaccines should be designed to stimulate the production of VSA-PAM-specific antibodies of the IgG1 and IgG3 subclasses. They also suggest that, provided the link between opsonic phagocytosis and protection against PAM can be confirmed in population-based studies, new vaccines could be evaluated for their potential to protect women against PAM by seeing whether the plasma of vaccinees promotes opsonic phagocytosis of CSA-binding PEs.
Additional Information.
Please access these Web sites via the online version of this summary at
US Centers for Disease Control and Prevention information on malaria and malaria during pregnancy (in English and Spanish)
World Health Organization information on malaria, including a feature on malaria in pregnancy (in English, Spanish, French, Arabic, Chinese and Russian)
Special Program for Research and Training in Tropical Diseases (TDR) information on malaria and research into the disease
Roll Back Malaria Partnership fact sheets on all aspects of malaria, including malaria in pregnancy (in English, French and Portuguese)
HIV Insite, information from the University of California at San Francisco on malaria and HIV
PMCID: PMC1880852  PMID: 17535103
10.  Mucosal Immunization of Lactating Female Rhesus Monkeys with a Transmitted/Founder HIV-1 Envelope Induces Strong Env-Specific IgA Antibody Responses in Breast Milk 
Journal of Virology  2013;87(12):6986-6999.
We previously demonstrated that vaccination of lactating rhesus monkeys with a DNA prime/vector boost strategy induces strong T-cell responses but limited envelope (Env)-specific humoral responses in breast milk. To improve vaccine-elicited antibody responses in milk, hormone-induced lactating rhesus monkeys were vaccinated with a transmitted/founder (T/F) HIV Env immunogen in a prime-boost strategy modeled after the moderately protective RV144 HIV vaccine. Lactating rhesus monkeys were intramuscularly primed with either recombinant DNA (n = 4) or modified vaccinia virus Ankara (MVA) poxvirus vector (n = 4) expressing the T/F HIV Env C.1086 and then boosted twice intramuscularly with C.1086 gp120 and the adjuvant MF59. The vaccines induced Env-binding IgG and IgA as well as neutralizing and antibody-dependent cellular cytotoxicity (ADCC) responses in plasma and milk of most vaccinated animals. Importantly, plasma neutralization titers against clade C HIV variants MW965 (P = 0.03) and CAP45 (P = 0.04) were significantly higher in MVA-primed than in DNA-primed animals. The superior systemic prime-boost regimen was then compared to a mucosal-boost regimen, in which animals were boosted twice intranasally with C.1086 gp120 and the TLR 7/8 agonist R848 following the same systemic prime. While the systemic and mucosal vaccine regimens elicited comparable levels of Env-binding IgG antibodies, mucosal immunization induced significantly stronger Env-binding IgA responses in milk (P = 0.03). However, the mucosal regimen was not as potent at inducing functional IgG responses. This study shows that systemic MVA prime followed by either intranasal or systemic protein boosts can elicit strong humoral responses in breast milk and may be a useful strategy to interrupt postnatal HIV-1 transmission.
PMCID: PMC3676124  PMID: 23596289
11.  FCGR2C polymorphisms associate with HIV-1 vaccine protection in RV144 trial 
The Journal of Clinical Investigation  2014;124(9):3879-3890.
The phase III RV144 HIV-1 vaccine trial estimated vaccine efficacy (VE) to be 31.2%. This trial demonstrated that the presence of HIV-1–specific IgG-binding Abs to envelope (Env) V1V2 inversely correlated with infection risk, while the presence of Env-specific plasma IgA Abs directly correlated with risk of HIV-1 infection. Moreover, Ab-dependent cellular cytotoxicity responses inversely correlated with risk of infection in vaccine recipients with low IgA; therefore, we hypothesized that vaccine-induced Fc receptor–mediated (FcR-mediated) Ab function is indicative of vaccine protection. We sequenced exons and surrounding areas of FcR-encoding genes and found one FCGR2C tag SNP (rs114945036) that associated with VE against HIV-1 subtype CRF01_AE, with lysine at position 169 (169K) in the V2 loop (CRF01_AE 169K). Individuals carrying CC in this SNP had an estimated VE of 15%, while individuals carrying CT or TT exhibited a VE of 91%. Furthermore, the rs114945036 SNP was highly associated with 3 other FCGR2C SNPs (rs138747765, rs78603008, and rs373013207). Env-specific IgG and IgG3 Abs, IgG avidity, and neutralizing Abs inversely correlated with CRF01_AE 169K HIV-1 infection risk in the CT- or TT-carrying vaccine recipients only. These data suggest a potent role of Fc-γ receptors and Fc-mediated Ab function in conferring protection from transmission risk in the RV144 VE trial.
PMCID: PMC4151214  PMID: 25105367
12.  Comprehensive Sieve Analysis of Breakthrough HIV-1 Sequences in the RV144 Vaccine Efficacy Trial 
PLoS Computational Biology  2015;11(2):e1003973.
The RV144 clinical trial showed the partial efficacy of a vaccine regimen with an estimated vaccine efficacy (VE) of 31% for protecting low-risk Thai volunteers against acquisition of HIV-1. The impact of vaccine-induced immune responses can be investigated through sieve analysis of HIV-1 breakthrough infections (infected vaccine and placebo recipients). A V1/V2-targeted comparison of the genomes of HIV-1 breakthrough viruses identified two V2 amino acid sites that differed between the vaccine and placebo groups. Here we extended the V1/V2 analysis to the entire HIV-1 genome using an array of methods based on individual sites, k-mers and genes/proteins. We identified 56 amino acid sites or “signatures” and 119 k-mers that differed between the vaccine and placebo groups. Of those, 19 sites and 38 k-mers were located in the regions comprising the RV144 vaccine (Env-gp120, Gag, and Pro). The nine signature sites in Env-gp120 were significantly enriched for known antibody-associated sites (p = 0.0021). In particular, site 317 in the third variable loop (V3) overlapped with a hotspot of antibody recognition, and sites 369 and 424 were linked to CD4 binding site neutralization. The identified signature sites significantly covaried with other sites across the genome (mean = 32.1) more than did non-signature sites (mean = 0.9) (p < 0.0001), suggesting functional and/or structural relevance of the signature sites. Since signature sites were not preferentially restricted to the vaccine immunogens and because most of the associations were insignificant following correction for multiple testing, we predict that few of the genetic differences are strongly linked to the RV144 vaccine-induced immune pressure. In addition to presenting results of the first complete-genome analysis of the breakthrough infections in the RV144 trial, this work describes a set of statistical methods and tools applicable to analysis of breakthrough infection genomes in general vaccine efficacy trials for diverse pathogens.
Author Summary
We present an analysis of the genomes of the HIV viruses that infected some participants of the RV144 Thai trial, which was the first study to show efficacy of a vaccine to prevent HIV infection. We analyzed the HIV genomes of infected vaccine recipients and infected placebo recipients, and found differences between them. These differences coincide with previously-studied genetic features that are relevant to the biology of HIV infection, including features involved in immune recognition of the virus. The findings presented here generate testable hypotheses about the mechanism of the partial protection seen in the Thai trial, and may ultimately lead to improved vaccines. The article also presents a toolkit of methods for computational analyses that can be applied to other vaccine efficacy trials.
PMCID: PMC4315437  PMID: 25646817
13.  Targeting HIV-1 Envelope Glycoprotein Trimers to B Cells by Using APRIL Improves Antibody Responses 
Journal of Virology  2012;86(5):2488-2500.
An HIV-1 vaccine remains elusive, in part because various factors limit the quantity and quality of the antibodies raised against the viral envelope glycoprotein complex (Env). We hypothesized that targeting Env vaccines directly to B cells, by fusing them to molecules that bind and activate these cells, would improve Env-specific antibody responses. Therefore, we fused trimeric Env gp140 to A PRoliferation-Inducing Ligand (APRIL), B-cell Activating Factor (BAFF), and CD40 Ligand (CD40L). The Env-APRIL, Env-BAFF, and Env-CD40L gp140 trimers all enhanced the expression of activation-induced cytidine deaminase (AID), the enzyme responsible for inducing somatic hypermutation, antibody affinity maturation, and antibody class switching. They also triggered IgM, IgG, and IgA secretion from human B cells in vitro. The Env-APRIL trimers induced higher anti-Env antibody responses in rabbits, including neutralizing antibodies against tier 1 viruses. The enhanced Env-specific responses were not associated with a general increase in total plasma antibody concentrations, indicating that the effect of APRIL was specific for Env. All the rabbit sera raised against gp140 trimers, irrespective of the presence of CD40L, BAFF, or APRIL, recognized trimeric Env efficiently, whereas sera raised against gp120 monomers did not. The levels of trimer-binding and virus-neutralizing antibodies were strongly correlated, suggesting that gp140 trimers are superior to gp120 monomers as immunogens. Targeting and activating B cells with a trimeric HIV-1 Env-APRIL fusion protein may therefore improve the induction of humoral immunity against HIV-1.
PMCID: PMC3302291  PMID: 22205734
14.  Complement Lysis Activity in Autologous Plasma Is Associated with Lower Viral Loads during the Acute Phase of HIV-1 Infection 
PLoS Medicine  2006;3(11):e441.
To explore the possibility that antibody-mediated complement lysis contributes to viremia control in HIV-1 infection, we measured the activity of patient plasma in mediating complement lysis of autologous primary virus.
Methods and Findings
Sera from two groups of patients—25 with acute HIV-1 infection and 31 with chronic infection—were used in this study. We developed a novel real-time PCR-based assay strategy that allows reliable and sensitive quantification of virus lysis by complement. Plasma derived at the time of virus isolation induced complement lysis of the autologous virus isolate in the majority of patients. Overall lysis activity against the autologous virus and the heterologous primary virus strain JR-FL was higher at chronic disease stages than during the acute phase. Most strikingly, we found that plasma virus load levels during the acute but not the chronic infection phase correlated inversely with the autologous complement lysis activity. Antibody reactivity to the envelope (Env) proteins gp120 and gp41 were positively correlated with the lysis activity against JR-FL, indicating that anti-Env responses mediated complement lysis. Neutralization and complement lysis activity against autologous viruses were not associated, suggesting that complement lysis is predominantly caused by non-neutralizing antibodies.
Collectively our data provide evidence that antibody-mediated complement virion lysis develops rapidly and is effective early in the course of infection; thus it should be considered a parameter that, in concert with other immune functions, steers viremia control in vivo.
Antibody-mediated complement lysis of HIV virions develops rapidly and is effective already early in the course of HIV infection.
Editors' Summary
If untreated, most people who become infected with the human immunodeficiency virus (HIV) eventually develop acquired immunodeficiency syndrome (AIDS). Over time, HIV infects and kills their CD4 T lymphocytes—immune system cells that stimulate B lymphocytes to make antibodies (proteins that recognize and destroy infectious agents) and that help CD8 T lymphocytes to kill cells that contain viruses and bacteria. The loss of CD4 T lymphocytes—a central player in “adaptive immunity”—leaves patients very susceptible to infections. However, the immune system does not die quietly. It does its best to fight HIV infection by mounting a cell-mediated immune response in which T lymphocytes attack HIV-infected cells. It also mounts a “humoral” immune response in which antibodies that recognize HIV are made. Some of these are neutralizing antibodies, which prevent HIV entering its host cells and replicating. Other antibodies may limit viral spread by inducing destruction of the virus. One way they can do this is by activating another part of the immune system called the complement system, which can break open and kill viruses (this is known as antibody-mediated complement lysis). In addition, antibodies and complement can coat the HIV virus particles so that phagocytes (for instance macrophages—yet another type of immune system cell) engulf and destroy the virus.
Why Was This Study Done?
The role that humoral immunity plays in fighting HIV infection is complex and poorly understood. In particular, it is not clear whether the complement system helps to stop the spread of HIV or whether it inadvertently helps it to spread by facilitating its entry into host cells. It is important to understand as much as possible about the humoral immune response to HIV infection so that vaccines can be designed to provide maximum protection against HIV. In this study, the researchers have investigated whether antibody-mediated complement lysis controls the amount of virus in the blood of patients infected with HIV.
What Did the Researchers Do and Find?
The researchers collected plasma (the liquid part of blood that contains circulating antibodies) from patients recently infected with HIV (acute infection) and patients who had been infected for some time (chronically infected). They also isolated HIV from each of the patients—so-called autologous virus. They then used a sensitive molecular biology assay to test each plasma sample for its ability to lyse the autologous virus (and also a standard virus) when supplied with complement from a healthy donor. Most of the plasma samples were able to lyse HIV, although the samples taken from chronically infected patients generally caused more lysis than those from acutely infected patients. In the chronically infected patients, the level of lysis induced was not related to the amount of virus in the patients' blood (viremia). However, plasma taken from acutely infected patients with higher viral loads was less active in the lysis assay than plasma taken from patients with lower viral loads. Finally, the researchers showed that the levels of antibodies in the various plasma samples to the two envelope proteins of HIV correlated strongly with the ability of each sample to lyse the standard virus and that these antibodies were mainly non-neutralizing antibodies.
What Do These Findings Mean?
By showing that antibody-mediated complement lysis of HIV in the laboratory is inversely related to the patients' viral loads during acute infection, these findings suggest (but do not prove) that antibody-mediated complement lysis of HIV contributes to the control of viremia early in HIV infections. But, the importance of this form of humoral immunity in combating HIV infections remains uncertain, since complement has the potential to enhance as well as block viral spread. Further work is needed to unravel which of these effects is dominant in patients and to characterize fully the antibodies that activate complement. Nevertheless, the results of this study suggest that complement-activating antibodies should be considered in future attempts to design an effective HIV vaccine.
Additional Information.
Please access these Web sites via the online version of this summary at
National Institute of Allergy and Infectious Diseases fact sheet on HIV infection and AIDS
US Department of Health and Human Services information on AIDS, including information on vaccines
US Centers for Disease Control and Prevention information on HIV/AIDS
Aidsmap information on HIV and the immune system provided by the charity NAM
Wikipedia pages on the complement system (note: Wikipedia is a free online encyclopedia that anyone can edit)
PMCID: PMC1637124  PMID: 17121450
15.  HIV-Specific Antibodies Capable of ADCC Are Common in Breastmilk and Are Associated with Reduced Risk of Transmission in Women with High Viral Loads 
PLoS Pathogens  2012;8(6):e1002739.
There are limited data describing the functional characteristics of HIV-1 specific antibodies in breast milk (BM) and their role in breastfeeding transmission. The ability of BM antibodies to bind HIV-1 envelope, neutralize heterologous and autologous viruses and direct antibody-dependent cell cytotoxicity (ADCC) were analyzed in BM and plasma obtained soon after delivery from 10 non-transmitting and 9 transmitting women with high systemic viral loads and plasma neutralizing antibodies (NAbs). Because subtype A is the dominant subtype in this cohort, a subtype A envelope variant that was sensitive to plasma NAbs was used to assess the different antibody activities. We found that NAbs against the subtype A heterologous virus and/or the woman's autologous viruses were rare in IgG and IgA purified from breast milk supernatant (BMS) – only 4 of 19 women had any detectable NAb activity against either virus. Detected NAbs were of low potency (median IC50 value of 10 versus 647 for the corresponding plasma) and were not associated with infant infection (p = 0.58). The low NAb activity in BMS versus plasma was reflected in binding antibody levels: HIV-1 envelope specific IgG titers were 2.2 log10 lower (compared to 0.59 log10 lower for IgA) in BMS versus plasma. In contrast, antibodies capable of ADCC were common and could be detected in the BMS from all 19 women. BMS envelope-specific IgG titers were associated with both detection of IgG NAbs (p = 0.0001)and BMS ADCC activity (p = 0.014). Importantly, BMS ADCC capacity was inversely associated with infant infection risk (p = 0.039). Our findings indicate that BMS has low levels of envelope specific IgG and IgA with limited neutralizing activity. However, this small study of women with high plasma viral loads suggests that breastmilk ADCC activity is a correlate of transmission that may impact infant infection risk.
Author Summary
In the absence of intervention, only about one third of infants born to HIV-1 infected mothers who are continuously exposed to maternal breast milk over prolonged periods get infected. This observation raises the possibility that immune factors in infected women play a role in limiting HIV-1 transmission. Identifying factors associated with reduced HIV-1 transmission risk will improve our understanding on the potential correlates of protection that should be the focus of generating effective immunogens and vaccination protocols. Here we assessed the functional role of breast milk antibodies in a group of women with high plasma viral loads and systemic NAbs and determined that overall, breast milk contains low levels of neutralizing antibodies when compared to plasma. In contrast, we observed a robust non-neutralizing activity in breast milk that was associated with infant infection status. Our study adds to the growing evidence of a potential role of non-neutralizing antibodies in limiting HIV-1 transmission and calls for more attention to this arm of the HIV-1 response.
PMCID: PMC3375288  PMID: 22719248
16.  Prevention of SIV Rectal Transmission and Priming of T Cell Responses in Macaques after Local Pre-exposure Application of Tenofovir Gel 
PLoS Medicine  2008;5(8):e157.
The rectum is particularly vulnerable to HIV transmission having only a single protective layer of columnar epithelium overlying tissue rich in activated lymphoid cells; thus, unprotected anal intercourse in both women and men carries a higher risk of infection than other sexual routes. In the absence of effective prophylactic vaccines, increasing attention is being given to the use of microbicides and preventative antiretroviral (ARV) drugs. To prevent mucosal transmission of HIV, a microbicide/ARV should ideally act locally at and near the virus portal of entry. As part of an integrated rectal microbicide development programme, we have evaluated rectal application of the nucleotide reverse transcriptase (RT) inhibitor tenofovir (PMPA, 9-[(R)-2-(phosphonomethoxy) propyl] adenine monohydrate), a drug licensed for therapeutic use, for protective efficacy against rectal challenge with simian immunodeficiency virus (SIV) in a well-established and standardised macaque model.
Methods and Findings
A total of 20 purpose-bred Indian rhesus macaques were used to evaluate the protective efficacy of topical tenofovir. Nine animals received 1% tenofovir gel per rectum up to 2 h prior to virus challenge, four macaques received placebo gel, and four macaques remained untreated. In addition, three macaques were given tenofovir gel 2 h after virus challenge. Following intrarectal instillation of 20 median rectal infectious doses (MID50) of a noncloned, virulent stock of SIVmac251/32H, all animals were analysed for virus infection, by virus isolation from peripheral blood mononuclear cells (PBMC), quantitative proviral DNA load in PBMC, plasma viral RNA (vRNA) load by sensitive quantitative competitive (qc) RT-PCR, and presence of SIV-specific serum antibodies by ELISA. We report here a significant protective effect (p = 0.003; Fisher exact probability test) wherein eight of nine macaques given tenofovir per rectum up to 2 h prior to virus challenge were protected from infection (n = 6) or had modified virus outcomes (n = 2), while all untreated macaques and three of four macaques given placebo gel were infected, as were two of three animals receiving tenofovir gel after challenge. Moreover, analysis of lymphoid tissues post mortem failed to reveal sequestration of SIV in the protected animals. We found a strong positive association between the concentration of tenofovir in the plasma 15 min after rectal application of gel and the degree of protection in the six animals challenged with virus at this time point. Moreover, colorectal explants from non-SIV challenged tenofovir-treated macaques were resistant to infection ex vivo, whereas no inhibition was seen in explants from the small intestine. Tissue-specific inhibition of infection was associated with the intracellular detection of tenofovir. Intriguingly, in the absence of seroconversion, Gag-specific gamma interferon (IFN-γ)-secreting T cells were detected in the blood of four of seven protected animals tested, with frequencies ranging from 144 spot forming cells (SFC)/106 PBMC to 261 spot forming cells (SFC)/106 PBMC.
These results indicate that colorectal pretreatment with ARV drugs, such as tenofovir, has potential as a clinically relevant strategy for the prevention of HIV transmission. We conclude that plasma tenofovir concentration measured 15 min after rectal administration may serve as a surrogate indicator of protective efficacy. This may prove to be useful in the design of clinical studies. Furthermore, in vitro intestinal explants served as a model for drug distribution in vivo and susceptibility to virus infection. The finding of T cell priming following exposure to virus in the absence of overt infection is provocative. Further studies would reveal if a combined modality microbicide and vaccination strategy is feasible by determining the full extent of local immune responses induced and their protective potential.
Martin Cranage and colleagues find that topical tenofovir gel can protect against rectal challenge with SIV in a macaque model, and can permit the induction of SIV-specific T cell responses.
Editors' Summary
About 33 million people are now infected with the human immunodeficiency virus (HIV), which causes AIDS by killing immune system cells. As yet, there is no cure for AIDS, although HIV infections can be held in check with antiretroviral drugs. Also, despite years of research, there is no vaccine available that effectively protects people against HIV infection. So, to halt the AIDS epidemic, other ways of preventing the spread of HIV are being sought. For example, pre-exposure treatment (prophylaxis) with antiretroviral drugs is being investigated as a way to prevent HIV transmission. In addition, because HIV is often spread through heterosexual penile-to-vaginal sex with an infected partner, several vaginal microbicides (compounds that protect against HIV when applied inside the vagina) are being developed, some of which contain antiretroviral drugs.
Why Was This Study Done?
Because HIV can cross the membranes that line the mouth and the rectum (the lower end of the large intestine that connects to the anus) in addition to the membrane that lines the vagina, HIV transmission can also occur during oral and anal sex. The lining of the rectum in particular is extremely thin and overlies tissues rich in activated T cells (the immune system cells that HIV targets), so unprotected anal intercourse carries a high risk of HIV infection. Anal intercourse is common among men who have sex with men but is also more common in heterosexual populations than is generally thought. Tenofovir (an antiretroviral drug that counteracts HIV after it has entered human cells) given by mouth partly protects macaques against rectal infection with simian immunodeficiency virus (SIV; a virus that induces AIDS in monkeys and apes) so the researchers wanted to know whether this drug might be effective against rectal SIV infection if applied at the site where the virus enters the body.
What Did the Researchers Do and Find?
To answer this question, the researchers rectally infected several macaques with SIV up to 2 h after rectal application of a gel containing tenofovir, after rectal application of a gel not containing the drug, or after no treatment. In addition, a few animals were treated with the tenofovir gel after the viral challenge. Most of the animals given the tenofovir gel before the viral challenge were partly or totally protected from SIV infection, whereas all the untreated animals and most of those treated with the placebo gel or with the drug-containing gel after the viral challenge became infected with SIV. High blood levels of tenofovir 15 min after its rectal application correlated with protection from viral infection. The researchers also collected rectal and small intestine samples from tenofovir-treated macaques that had not been exposed to SIV and asked which samples were resistant to SIV infection in laboratory dishes. They found that only the rectal samples were resistant to infection and only rectal cells contained tenofovir. Finally, activated T cells that recognized an SIV protein were present in the blood of some of the animals that were protected from SIV infection by the tenofovir gel.
What Do These Findings Mean?
These findings, although based on experiments in only a few animals, suggest that rectal treatment with antiretroviral drugs before rectal exposure to HIV might prevent rectal HIV transmission in people. However, results from animal experiments do not always reflect what happens in people. Indeed, clinical trials of a potential vaginal microbicide that worked well in macaques were halted recently because women using the microbicide had higher rates of HIV infection than those using a control preparation. The finding that immune-system activation can occur in the absence of overt infection in animals treated with the tenofovir gel additionally suggests that a combination of a local antiretroviral/microbicide and vaccination might be a particularly effective way to prevent HIV transmission. However, because HIV targets activated T cells, viral rechallenge experiments must be done to check that the activated T cells induced by the virus in the presence of tenofovir do not increase the likelihood of infection upon re-exposure to HIV before this potential microbicide is tried in people.
Additional Information
Please access these Web sites via the online version of this summary at
Read the accompanying PLoS Medicine Perspective by Florian Hladik
An overview of HIV infection and AIDS is available from the US National Institute of Allergy and Infectious Diseases
HIVInSite has comprehensive information on all aspects of HIV/AIDS, including an article on safer sex, which includes information on the risks associated with specific types of sex and on microbicides and other methods to prevent the sexual transmission of HIV
Information on all aspects of HIV/AIDS is available from Avert, an international AIDS charity, including information on HIV prevention and on microbicides
The World Health Organization has a fact sheet on microbicides
The UK charity NAM also provides detailed information on microbicides
PrEP Watch is a comprehensive information source on pre-exposure prophylaxis for HIV prevention
Global Campaign for Microbicides is an international coalition of organisations dedicated to accelerating access to new HIV prevention options
PMCID: PMC2494562  PMID: 18684007
17.  Insensitivity of Paediatric HIV-1 Subtype C Viruses to Broadly Neutralising Monoclonal Antibodies Raised against Subtype B 
PLoS Medicine  2006;3(7):e255.
A Phase I clinical trial has been proposed that uses neutralising monoclonal antibodies (MAbs) as passive immunoprophylaxis to prevent mother-to-child transmission of HIV-1 in South Africa. To assess the suitability of such an approach, we determined the sensitivity of paediatric HIV-1 subtype C viruses to the broadly neutralising MAbs IgG1b12, 2G12, 2F5, and 4E10.
Methods and Findings
The gp160 envelope genes from seven children with HIV-1 subtype C infection were cloned and used to construct Env-pseudotyped viruses that were tested in a single-cycle neutralisation assay. The epitopes defining three of these MAbs were determined from sequence analysis of the envelope genes. None of the seven HIV-1 subtype C pseudovirions was sensitive to 2G12 or 2F5, which correlated with the absence of crucial N-linked glycans that define the 2G12 epitope and substitutions of residues integral to the 2F5 epitope. Four viruses were sensitive to IgG1b12, and all seven viruses were sensitive to 4E10.
Only 4E10 showed significant activity against HIV-1 subtype C isolates, while 2G12 and 2F5 MAbs were ineffective and IgG1b12 was partly effective. It is therefore recommended that 2G12 and 2F5 MAbs not be used for passive immunization experiments in southern Africa and other regions where HIV-1 subtype C viruses predominate.
Editors' Summary
AIDS is caused by HIV. By killing the cells of the body's immune system, HIV infection makes people vulnerable to many potentially fatal bacterial and viral diseases. HIV is most commonly spread through unprotected sex with an infected partner but it can also pass from mother to child during late pregnancy or birth, or through breast milk. At least one in four infected women will transmit HIV to their babies if left untreated. But if infected women are treated with drugs that fight HIV—so-called antiretrovirals—during late pregnancy and if breastfeeding does not occur, only one to two babies in 100 will become infected with HIV. In addition, elective Caesarian section has been found to be protective against HIV infection. Implementation of this approach has greatly reduced mother-to-child transmission in developed countries, but most HIV-infected women live in developing countries where access to antiretrovirals is limited. In these cases, treatment of pregnant women (during pregnancy and delivery) and their newborn babies with a single dose of one antiretroviral drug, which can halve HIV transmission, is used, even though WHO/UNAIDS recommends simple antenatal, intrapartum, and postnatal antiretroviral regimens to achieve levels of less than 5% transmission in resource poor settings. These strategies will not have an impact on breastmilk transmission, which accounts for half the transmissions in these settings.
Why Was This Study Done?
One way to reduce breastmilk transmission of HIV might be by “passive immunization.” In this, newborn babies would be injected with HIV-specific antibodies—proteins that stick to molecules on the surface of HIV. Because the virus uses these molecules to invade the baby's immune cells, injected antibodies might stop HIV from the mother becoming established in her offspring. Four antibodies have been made in the laboratory—so-called human monoclonal antibodies—that bind to the surface of HIV subtype B, which is found mainly in Europe and North America, and stop HIV from killing human cells. However, most HIV isolated in Africa is subtype C, so in this study researchers have tested whether these antibodies prevent HIV subtype C killing cells grown in the laboratory. It is important, they argue, that antibodies should be shown to work outside the body before testing passive immunization in babies.
What Did the Researchers Do and Find?
The researchers isolated several subtype C viruses from babies born in Johannesburg, South Africa, and made artificial viruses (known as “pseudotyped” viruses) from them. These artificial viruses could then be used in tests to see whether the human monoclonal antibodies could prevent the viruses infecting human cells in a laboratory test, that is, whether the viruses were “sensitive” to the antibodies. All the viruses were insensitive to two of the antibodies (2G12 and 2F5), and the researchers show that this was because the viruses lacked the specific parts of the HIV surface molecules recognized by these antibodies. Four of the viruses were sensitive to an antibody called IgG1b12, and all were sensitive to antibody 4E10, albeit at high concentrations that might be difficult to achieve in people. Finally, the researchers report that the sensitivity of the viruses was not enhanced by using all four antibodies at the same time.
What Do These Findings Mean?
Given these results, the researchers warn against using 2G12 and 2F5 antibodies for passive immunization to prevent mother-to-child transmission, in particular postnatal transmission, in areas where most people are infected with HIV subtype C viruses. Furthermore, because animal studies have indicated that only combinations of at least three monoclonal antibodies with activity against HIV in laboratory tests provide complete protection against HIV infection, the researchers question whether any clinical trials on passive immunization should be started with currently available antibodies. Their doubts about such trials are heightened by observations that 4E10 and 2F5 react against antigens present on human cells, which might make them unsafe for use in people, although so far no adverse effects have been seen in adults treated with these antibodies. However, these experiments used an artificial laboratory-based assay and it's possible that these antibodies might kill HIV subtype C more effectively in people; other components of the immune system might help them deal with the virus. If clinical studies of these antibodies do go ahead, it is essential that the babies in these trials must be carefully monitored to ensure that the antibodies are safe, and they and their mothers should also be given access to optimal antiretroviral prophylaxis according to WHO/UNAIDS guidelines. In a related PLoS Medicine Perspective paper (, Miroslaw Gorny1 and Susan Zolla-Pazner discuss the study further and stress the critical need to determine if passive immunization with such antibodies could decrease mother-to-child transmission of HIV, and if so what the best antibodies would be.
Additional Information.
Please access these Web sites via the online version of this summary at
•  National Institute of Allergy and Infectious Diseases fact sheets on HIV infection and AIDS
•  US Department of Health and Human Services information on HIV/AIDS, including clinical guidelines and fact sheets on preventing transmission from mother to child
•  US Centers for Disease Control and Prevention information on HIV/AIDS, including pages on the prevention of mother-to-child transmission
•  MedlinePlus encyclopedia entry on HIV/AIDS
•  Preventing mother-to-child transmission of HIV Web page
Assessment of viruses from seven children with HIV-1 subtype C infection showed generally poor sensitivity to four monoclonal antibodies proposed for a trial of passive immunoprophylaxis to prevent mother-to-child transmission.
PMCID: PMC1502151  PMID: 16834457
18.  Polyclonal B Cell Differentiation and Loss of Gastrointestinal Tract Germinal Centers in the Earliest Stages of HIV-1 Infection 
PLoS Medicine  2009;6(7):e1000107.
Studying the effects of early HIV infection on human antibody responses, M. Anthony Moody and colleagues find rapid polyclonal B cell differentiation and structural damage to gut-associated lymphoid tissue.
The antibody response to HIV-1 does not appear in the plasma until approximately 2–5 weeks after transmission, and neutralizing antibodies to autologous HIV-1 generally do not become detectable until 12 weeks or more after transmission. Moreover, levels of HIV-1–specific antibodies decline on antiretroviral treatment. The mechanisms of this delay in the appearance of anti-HIV-1 antibodies and of their subsequent rapid decline are not known. While the effect of HIV-1 on depletion of gut CD4+ T cells in acute HIV-1 infection is well described, we studied blood and tissue B cells soon after infection to determine the effect of early HIV-1 on these cells.
Methods and Findings
In human participants, we analyzed B cells in blood as early as 17 days after HIV-1 infection, and in terminal ileum inductive and effector microenvironments beginning at 47 days after infection. We found that HIV-1 infection rapidly induced polyclonal activation and terminal differentiation of B cells in blood and in gut-associated lymphoid tissue (GALT) B cells. The specificities of antibodies produced by GALT memory B cells in acute HIV-1 infection (AHI) included not only HIV-1–specific antibodies, but also influenza-specific and autoreactive antibodies, indicating very early onset of HIV-1–induced polyclonal B cell activation. Follicular damage or germinal center loss in terminal ileum Peyer's patches was seen with 88% of follicles exhibiting B or T cell apoptosis and follicular lysis.
Early induction of polyclonal B cell differentiation, coupled with follicular damage and germinal center loss soon after HIV-1 infection, may explain both the high rate of decline in HIV-1–induced antibody responses and the delay in plasma antibody responses to HIV-1.
Please see later in the article for Editors' Summary
Editors' Summary
Acquired immunodeficiency syndrome (AIDS) has killed more than 25 million people since 1981 and more than 30 million people are now infected with the human immunodeficiency virus (HIV), which causes AIDS. HIV infects and kills a type of immune system cell called CD4+ T lymphocytes. These cells are needed to maintain a vigorous immune response, so people infected with HIV eventually become susceptible to other infections and develop full-blown AIDS. However, early during HIV infection, other parts of the immune system attempt to fight off the virus. Soon after infection, immune system cells called B lymphocytes begin to produce HIV-specific antibodies (proteins that recognize viral molecules called antigens). The first antibodies to HIV usually appear two to seven weeks after infection; from about 12 weeks after infection, antibodies are made that can kill the specific HIV type responsible for the infection (neutralizing antibodies).
Why Was This Study Done?
Unfortunately, by this time, it is too late for the antibody (“humoral”) immune response to clear HIV from the body. Indeed, the humoral immune response to HIV is very slow; for most viruses, neutralizing antibodies appear within days of infection. To help them design an effective HIV vaccine, scientists need to understand how the virus delays humoral responses to HIV infection (and how it later causes the production of HIV-specific antibodies to decline). Little is known, however, about the early effects of HIV infection on B lymphocytes. These cells are born and mature in the bone marrow. “Naïve” B lymphocytes, each of which carries an antigen-specific receptor (a protein that binds to a specific antigen), then enter the blood and circulate around the body, passing through the “peripheral lymphoid organs”. Exposure to antigens in these organs, which include lymph nodes and gut-associated lymphoid tissues, activates the subset of B lymphocytes that recognize the specific antigens that are present. Finally, with the help of activated T lymphocytes, the activated B lymphocytes proliferate and change (differentiate) into antibody-secreting cells and memory B lymphocytes (which respond more quickly to antigen than naïve B lymphocytes). In this study, the researchers investigate the effects of early HIV-1 infection on B lymphocytes in blood and in gut-associated lymphoid tissues.
What Did the Researchers Do and Find?
The researchers collected blood from patients as early as 17 days after HIV-1 infection and tissue samples from the lower portion of the small intestine (a region rich in gut-associated lymphoid structures called Peyer's patches) from 47 days after infection onward. When they analyzed the B lymphocytes in these samples (which were collected during two trials organized by the US Center for HIV/AIDS Vaccine Immunology [CHAVI]), they found that HIV-1 infection rapidly induced the activation of many different B cells that recognized a variety of antigens (polyclonal activation), as well as the appearance of differentiated B cells in blood and in gut-associated lymphoid tissue. The B lymphocytes that were activated in the gut made HIV-specific antibodies but also antibodies against unrelated antigens (such as flu virus proteins). Finally, the structure of Peyer's patches was altered early in HIV-1 infection. More specifically, most of the lymphoid follicles (organized collections of lymphocytes and antigen-presenting cells) in the Peyer's patches showed signs of damage and T- and B-lymphocyte death and the number of germinal centers (regions in lymphoid follicles in which B lymphocytes proliferate) was reduced.
What Do These Findings Mean?
Although the depletion of gut-associated CD4+ T lymphocytes in early HIV-1 infection is well known, these new results demonstrate the effects of early HIV-1 infection on gut-associated and circulating B lymphocytes. The results of this study are limited by the methods used to analyze the antibodies induced by HIV infection and by only taking tissue samples from one region of the gut. Nevertheless, the findings of polyclonal B-cell activation and damage to gut-associated lymphoid follicles soon after HIV-1 infection may have implications for HIV-1 vaccine design. Specifically, these findings suggest that an effective HIV-1 vaccine will need to ensure that significant levels of neutralizing antibodies are present in people before HIV-1 infection and that other protective immune defenses are fully primed so that, in the event of HIV-1 infection, the virus can be dealt with effectively before it disables any part of the immune system.
Additional Information
Please access these Web sites via the online version of this summary at
Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS
HIV InSite has comprehensive information on all aspects of HIV/AIDS, including an article about how HIV-1 infection affects the immune system
Information is available from Avert, an international AIDS charity on many aspects of HIV/AIDS, including information on the stages of HIV infection, and on AIDS vaccines (in English and Spanish)
The US Center for HIV/AIDS Vaccine Immunology (CHAVI) Web site provides information on research designed to solve major problems in HIV vaccine development and design
PMCID: PMC2702159  PMID: 19582166
19.  Contribution of non-neutralizing vaccine-elicited antibody activities to improved protective efficacy in rhesus macaques immunized with Tat/Env compared to multigenic vaccines 
Previously, chronic phase protection against SHIV89.6P challenge was significantly greater in macaques primed with replicating adenovirus type 5 host range mutant (Ad5hr)-recombinants encoding HIVtat and env and boosted with Tat and Env protein compared to macaques primed with multigenic Ad-recombinants (HIVtat, HIVenv, SIVgag, SIVnef) and boosted with Tat, Env and Nef proteins. The greater protection was correlated with Tat and Env binding antibodies. As the macaques lacked SHIV89.6P neutralizing activity pre-challenge, we investigated whether antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cell mediated viral inhibition (ADCVI) might exert a protective effect. We clearly show that Tat can serve as an ADCC target, although the Tat-specific activity elicited did not correlate with better protection. However, Env-specific ADCC activity was consistently higher in the Tat/Env group, with sustained cell killing post-challenge exhibited at higher levels (p < 0.00001) for a longer duration (p = 0.0002) compared to the multigenic group. ADCVI was similarly higher in the Tat/Env group, and significantly correlated with reduced acute phase viremia at weeks 2 and 4 post-challenge (p = 0.046 and 0.011, respectively). Viral specific IgG and IgA antibodies in mucosal secretions were elicited but did not influence the outcome of the intravenous SHIV89.6P challenge. The higher ADCC and ADCVI activities seen in the Tat/Env group provide a plausible mechanism responsible for the greater chronic phase protection. As Tat is known to enhance cell-mediated immunity to co-administered antigens, further studies should explore its impact on antibody induction so that it may be optimally incorporated into HIV vaccine regimens.
This is an author-produced version of a manuscript accepted for publication in The Journal of Immunology (The JI). The American Association of Immunologists, Inc. (AAI) publisher of The JI, holds the copyright to this manuscript. This manuscript has not yet been copyedited or subjected to editorial proofreading by The JI; hence it may differ from the final version published in The JI (online and in print). AAI (The JI) is not liable for errors or omissions in this author-produced version of the manuscript or in any version derived from it by the United States National Institutes of Health or any other third party. The final, citable version of record can be found at “”
PMCID: PMC2744397  PMID: 19265150
AIDS; Vaccination; Other animals; Viral; Antibodies
20.  HIV-Specific Functional Antibody Responses in Breast Milk Mirror Those in Plasma and Are Primarily Mediated by IgG Antibodies ▿ 
Journal of Virology  2011;85(18):9555-9567.
Despite months of mucosal virus exposure, the majority of breastfed infants born to HIV-infected mothers do not become infected, raising the possibility that immune factors in milk inhibit mucosal transmission of HIV. HIV Envelope (Env)-specific antibodies are present in the milk of HIV-infected mothers, but little is known about their virus-specific functions. In this study, HIV Env-specific antibody binding, autologous and heterologous virus neutralization, and antibody-dependent cell cytotoxicity (ADCC) responses were measured in the milk and plasma of 41 HIV-infected lactating women. Although IgA is the predominant antibody isotype in milk, HIV Env-specific IgG responses were higher in magnitude than HIV Env-specific IgA responses in milk. The concentrations of anti-HIV gp120 IgG in milk and plasma were directly correlated (r = 0.75; P < 0.0001), yet the response in milk was 2 logarithm units lower than in plasma. Similarly, heterologous virus neutralization (r = 0.39; P = 0.010) and ADCC activity (r = 0.64; P < 0.0001) in milk were directly correlated with that in the systemic compartment but were 2 log units lower in magnitude. Autologous neutralization was rarely detected in milk. Milk heterologous virus neutralization titers correlated with HIV gp120 Env-binding IgG responses but not with IgA responses (r = 0.71 and P < 0.0001, and r = 0.17 and P = 0.30). Moreover, IgGs purified from milk and plasma had equal neutralizing potencies against a tier 1 virus (r = 0.65; P < 0.0001), whereas only 1 out of 35 tested non-IgG milk fractions had detectable neutralization. These results suggest that plasma-derived IgG antibodies mediate the majority of the low-level HIV neutralization and ADCC activity in breast milk.
PMCID: PMC3165739  PMID: 21734046
21.  Antibody-Dependent Cellular Cytotoxicity against Primary HIV-Infected CD4+ T Cells Is Directly Associated with the Magnitude of Surface IgG Binding 
Journal of Virology  2012;86(16):8672-8680.
Antibody (Ab)-dependent cellular cytotoxicity (ADCC) is thought to potentially play a role in vaccine-induced protection from HIV-1. The characteristics of such antibodies remain incompletely understood. Furthermore, correlates between ADCC and HIV-1 immune status are not clearly defined. We screened the sera of 20 HIV-1-positive (HIV-1+) patients for ADCC. Normal human peripheral blood mononuclear cells were used to derive HIV-infected CD4+ T cell targets and autologous, freshly isolated, natural killer (NK) cells in a novel assay that measures granzyme B (GrB) and HIV-1-infected CD4+ T cell elimination (ICE) by flow cytometry. We observed that complex sera mediated greater levels of ADCC than anti-HIV-1 envelope glycoprotein (Env)-specific monoclonal antibodies and serum-mediated ADCC correlated with the amount of IgG and IgG1 bound to HIV-1-infected CD4+ T cells. No correlation between ADCC and viral load, CD4+ T cell count, or neutralization of HIV-1SF162 or other primary viral isolates was detected. Sera pooled from clade B HIV-1+ individuals exhibited breadth in killing targets infected with HIV-1 from clades A/E, B, and C. Taken together, these data suggest that the total amount of IgG bound to an HIV-1-infected cell is an important determinant of ADCC and that polyvalent antigen-specific Abs are required for a robust ADCC response. In addition, Abs elicited by a vaccine formulated with immunogens from a single clade may generate a protective ADCC response in vivo against a variety of HIV-1 species. Increased understanding of the parameters that dictate ADCC against HIV-1-infected cells will inform efforts to stimulate ADCC activity and improve its potency in vaccinees.
PMCID: PMC3421757  PMID: 22674985
22.  Pre-Clinical Development of a Recombinant, Replication-Competent Adenovirus Serotype 4 Vector Vaccine Expressing HIV-1 Envelope 1086 Clade C 
PLoS ONE  2013;8(12):e82380.
There is a well-acknowledged need for an effective AIDS vaccine that protects against HIV-1 infection or limits in vivo viral replication. The objective of these studies is to develop a replication-competent, vaccine vector based on the adenovirus serotype 4 (Ad4) virus expressing HIV-1 envelope (Env) 1086 clade C glycoprotein. Ad4 recombinant vectors expressing Env gp160 (Ad4Env160), Env gp140 (Ad4Env140), and Env gp120 (Ad4Env120) were evaluated.
The recombinant Ad4 vectors were generated with a full deletion of the E3 region of Ad4 to accommodate the env gene sequences. The vaccine candidates were assessed in vitro following infection of A549 cells for Env-specific protein expression and for posttranslational transport to the cell surface as monitored by the binding of broadly neutralizing antibodies (bNAbs). The capacity of the Ad4Env vaccines to induce humoral immunity was evaluated in rabbits for Env gp140 and V1V2-specific binding antibodies, and HIV-1 pseudovirus neutralization. Mice immunized with the Ad4Env160 vaccine were assessed for IFNγ T cell responses specific for overlapping Env peptide sets.
Robust Env protein expression was confirmed by western blot analysis and recognition of cell surface Env gp160 by multiple bNAbs. Ad4Env vaccines induced humoral immune responses in rabbits that recognized Env 1086 gp140 and V1V2 polypeptide sequences derived from 1086 clade C, A244 clade AE, and gp70 V1V2 CASE A2 clade B fusion protein. The immune sera efficiently neutralized tier 1 clade C pseudovirus MW965.26 and neutralized the homologous and heterologous tier 2 pseudoviruses to a lesser extent. Env-specific T cell responses were also induced in mice following Ad4Env160 vector immunization.
The Ad4Env vaccine vectors express high levels of Env glycoprotein and induce both Env-specific humoral and cellular immunity thus supporting further development of this new Ad4 HIV-1 Env vaccine platform in Phase 1 clinical trials.
PMCID: PMC3849430  PMID: 24312658
23.  The role of the humoral immune response in the molecular evolution of the envelope C2, V3 and C3 regions in chronically HIV-2 infected patients 
Retrovirology  2008;5:78.
This study was designed to investigate, for the first time, the short-term molecular evolution of the HIV-2 C2, V3 and C3 envelope regions and its association with the immune response. Clonal sequences of the env C2V3C3 region were obtained from a cohort of eighteen HIV-2 chronically infected patients followed prospectively during 2–4 years. Genetic diversity, divergence, positive selection and glycosylation in the C2V3C3 region were analysed as a function of the number of CD4+ T cells and the anti-C2V3C3 IgG and IgA antibody reactivity
The mean intra-host nucleotide diversity was 2.1% (SD, 1.1%), increasing along the course of infection in most patients. Diversity at the amino acid level was significantly lower for the V3 region and higher for the C2 region. The average divergence rate was 0.014 substitutions/site/year, which is similar to that reported in chronic HIV-1 infection. The number and position of positively selected sites was highly variable, except for codons 267 and 270 in C2 that were under strong and persistent positive selection in most patients. N-glycosylation sites located in C2 and V3 were conserved in all patients along the course of infection. Intra-host variation of C2V3C3-specific IgG response over time was inversely associated with the variation in nucleotide and amino acid diversity of the C2V3C3 region. Variation of the C2V3C3-specific IgA response was inversely associated with variation in the number of N-glycosylation sites.
The evolutionary dynamics of HIV-2 envelope during chronic aviremic infection is similar to HIV-1 implying that the virus should be actively replicating in cellular compartments. Convergent evolution of N-glycosylation in C2 and V3, and the limited diversification of V3, indicates that there are important functional constraints to the potential diversity of the HIV-2 envelope. C2V3C3-specific IgG antibodies are effective at reducing viral population size limiting the number of virus escape mutants. The C3 region seems to be a target for IgA antibodies and increasing N-linked glycosylation may prevent HIV-2 envelope recognition by these antibodies. Our results provide new insights into the biology of HIV-2 and its relation with the human host and may have important implications for vaccine design.
PMCID: PMC2563025  PMID: 18778482
24.  Vaccine-Induced HIV-1 Envelope gp120 Constant Region 1-Specific Antibodies Expose a CD4-Inducible Epitope and Block the Interaction of HIV-1 gp140 with Galactosylceramide 
Journal of Virology  2014;88(16):9406-9417.
Mucosal epithelial cell surface galactosylceramide (Galcer) has been postulated to be a receptor for HIV-1 envelope (Env) interactions with mucosal epithelial cells. Disruption of the HIV-1 Env interaction with such alternate receptors could be one strategy to prevent HIV-1 entry through the mucosal barrier. To study antibody modulation of HIV-1 Env-Galcer interactions, we used Galcer-containing liposomes to assess whether natural- and vaccine-induced monoclonal antibodies can block HIV-1 Env binding to Galcer. HIV-1 Env gp140 proteins bound to Galcer liposomes with Kds (dissociation constants) in the nanomolar range. Several HIV-1 ALVAC/AIDSVAX vaccinee-derived monoclonal antibodies (MAbs) specific for the gp120 first constant (C1) region blocked Galcer binding of a transmitted/founder HIV-1 Env gp140. Among the C1-specific MAbs that showed Galcer blocking, the antibody-dependent cellular cytotoxicity-mediating CH38 IgG and its natural IgA isotype were the most potent blocking antibodies. C1-specific IgG monoclonal antibodies that blocked Env binding to Galcer induced upregulation of the gp120 CD4-inducible (CD4i) epitope bound by MAb 17B, demonstrating that a conformational change in gp120 may be required for Galcer blocking. However, the MAb 17B itself did not block Env-Galcer binding, suggesting that the C1 antibody-induced gp120 conformational changes resulted in alteration in a Galcer binding site distant from the CD4i 17B MAb binding site.
IMPORTANCE Galactosyl ceramide, a glycosphingolipid, has been postulated to be a receptor for the HIV-1 envelope glycoprotein (Env) interaction with mucosal epithelial cells. Here, we have mimicked this interaction by using an artificial membrane containing synthetic Galcer and recombinant HIV-1 Env proteins to identify antibodies that would block the HIV-1 Env-Galcer interaction. Our study revealed that a class of vaccine-induced human antibodies potently blocks HIV-1 Env-Galcer binding by perturbing the HIV-1 Env conformation.
PMCID: PMC4136246  PMID: 24920809
25.  SIVmac239 MVA Vaccine with and without a DNA Prime, Similar Prevention of Infection by a Repeated Dose SIVsmE660 Challenge Despite Different Immune Responses 
Vaccine  2011;30(9):1737-1745.
Vaccine regimens using different agents for priming and boosting have become popular for enhancing T cell and Ab responses elicited by candidate HIV/AIDS vaccines. Here we use a simian model to evaluate immunogenicity and protective efficacy of a recombinant modified vaccinia Ankara (MVA) vaccine in the presence and absence of a recombinant DNA prime. The simian vaccines and regimens represent prototypes for candidate HIV vaccines currently undergoing clinical testing.
Recombinant DNA and MVA immunogens expressed simian immunodeficiency virus (SIV)mac239 Gag, PR, RT, and Env sequences. Vaccine schedules tested inoculations of MVA at months 0, 2, and 6 (MMM regimen) or priming with DNA at months 0 and 2 and boosting with MVA at months 4 and 6 (DDMM regimen). Twelve weekly rectal challenges with the heterologous SIV smE660 were initiated at 6 months following the last immunization.
Both regimens elicited similar 61–64% reductions in the per challenge risk of SIVsmE660 transmission despite raising different patterns of immune responses. The DDMM regimen elicited higher magnitudes of CD4 T cells whereas the MMM regimen elicited higher titers and greater avidity Env-specific IgG and more frequent and higher titer SIV-specific IgA in rectal secretions. Both regimens elicited similar magnitudes of CD8 T cells. Magnitudes of T cell responses, specific activities of rectal IgA Ab, and the tested specificities for neutralization and antibody-dependent cellular cytotoxicity did not correlate with risk of infection. However, the avidity of Env-specific IgG had a strong correlation with the per challenge risk of acquisition, but only for the DDMM group.
We conclude that for the tested immunogens in rhesus macaques, the simpler MMM regimen is as protective as the more complex DDMM regimen.
PMCID: PMC3278564  PMID: 22178526
Vaccine; Immunodeficiency virus; Simian immunodeficiency virus; DNA vaccine MVA vaccine; avidity in protection

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