Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Hum Vaccin. Author manuscript; available in PMC 2010 April 1.
Published in final edited form as:
Hum Vaccin. 2009 April; 5(4): 268–271.
PMCID: PMC2729359

HIV-1 vaccine design: Harnessing diverse lymphocytes to conquer a diverse pathogen


In the Fall of 2007, the HIV-1 research field received news that their front-runner vaccine was not protective. In response to this disappointment, scientists are now reviewing the intricacies of the immune response toward HIV-1 to develop new and better strategies for vaccine development. Decades ago, researchers recognized the impressive amino acid and carbohydrate diversity of HIV-1, and the associated obstacles to vaccine development. At first glance, the diversity and other unique features of HIV-1 may seem insurmountable, but attention to vaccine successes in other fields serves to renew optimism. The newly-licensed rotavirus and papillomavirus cocktail vaccines remind scientists that diverse pathogens can be conquered and that the chronic nature of a virus infection need not thwart successful vaccine design. Here we describe current efforts to gain insights from other vaccine fields and to adopt a cocktail vaccine approach for the prevention of HIV-1 infections in humans.

Keywords: Multi-envelope, diversity, HIV-1 vaccine, B-lymphocytes, T-lymphocytes, cocktail, prevention


HIV-1 vaccine development has met with much disappointment 1-3, as the virus presents more than one obstacle to the research scientist. First, the virus is highly diverse. Second, the virus establishes a chronic infection when an exposure occurs in the context of an unprimed immune system. Each of these features must be acknowledged by vaccine developers, but need not thwart vaccine success. Here, we will describe a multi-envelope vaccine strategy designed to tackle a diverse pathogen with diverse lymphocytes and to prevent HIV-1 infections in humans.

HIV-1 diversity

HIV-1 is characterized by highly diverse proteins, both external and internal, due to the function of an error-prone reverse transcriptase and a lack of polymerase-related proofreading function4. The envelope protein, which contains five regions of hyper-variability, differs not only in terms of amino acid sequences, but also in terms of length and sites of glycosylation5 (glycosylation accounts for more than half of the molecular weight of the HIV-1 envelope protein). Variable regions are frequent targets of immune activity6;7 while conserved regions are often masked; some conserved regions are hidden within the three dimensional structure of HIV-1 while others mimic ‘self’ antigens, against which humans are tolerant 8. While vaccine developers often strive to elicit immune responses toward the conserved regions of HIV-1, this strategy has yielded disappointing results thus far in clinical trials1.

One might be inclined to describe the diversity of HIV-1 proteins as limitless, but certain constraints are dictated by function. For example, the envelope protein must bind the highly conserved human CD4 molecule. Envelope must also bind co-receptors (e.g. CCR5)9 and must mediate the fusion of virus and host cell membranes. Thus, while protein diversity at the amino acid level may appear enormous, the number of mutually exclusive, functional three-dimensional structures need not be vast.

A diverse immune response can counter pathogen diversity

The human immune system consists of billions of lymphocytes, subdivided into B- and T-cell populations. As lymphocytes develop, each undergoes a sophisticated process of recombination/splicing at the nucleic acid level that leads to expression of a unique cell surface receptor (B-cells express antibodies while T-cells express T-cell receptors (TCR))10. Antibodies can bind pathogens directly while T-cell receptors bind antigenic peptides in association with major histocompatibility proteins. In each case, a structural lock-and-key type interaction is necessary for the lymphocyte receptor to engage its target. Because of the impressive diversity of receptors in the human immune system, virtually every pathogen can be countered by a ‘specific’ set of B-cell and T-cell populations.

Successful vaccines against diverse pathogens have been produced in other fields by grouping pathogens based on antigenic structure. Cocktails are formulated to encompass a representative antigen or antigenic complex from each group and to activate respective B-cell and T-cell populations. In this context, the antigens might be termed ‘immunotypes’ in that they activate different lymphocyte subsets. Lymphocytes responsive to each vaccine component then function in unison to conquer the breadth of diverse pathogens in nature.

As an example, developers of the influenza virus vaccine have recognized that the hemagglutinin molecules on virus surfaces can have variable structures (e.g. hemagglutinin H1 and hemagglutinin H3 antigens are structurally distinct and mark different groups of influenza viruses). Scientists therefore include representatives of the different hemagglutinin antigens in current vaccine cocktails; each immunogen elicits a different population of B-cells and respective antibodies. The ‘immunotype-specific’ antibodies (ISabs) need not be ‘broadly-neutralizing’ (i.e. H1-specific antibodies need not recognize H3 and vice versa) provided that the antibodies function together to target diverse hemagglutinin molecules.

Similar approaches have been used to formulate the pentavalent rotavirus vaccine11, the quadrivalent papillomavirus vaccine12 and the 23-component pneumococcus vaccine13. To date, the strategy has not been fully tested in the HIV-1 field. Although HIV-1 vaccines sometimes encompass more than one envelope, components have often been selected based on sequence (clade or subtype) rather than structure14;15 and clinical efficacy trials have been limited. Possibly, the application of this proven approach to HIV-1 vaccine development may be required for production of a successful product.

Will the chronic nature of HIV-1 infection hamper vaccine development?

The development of vaccines against papillomavirus and Varicella zoster virus (VZV) shows that the chronic nature of a virus infection need not hamper vaccine success. Accomplishments in other vaccine fields also illustrate the importance of establishing a robust immune response before (not after) a virus infection has been established. When the virus is encountered before the immune system is primed, it may sequester in privileged sites and remain hidden from B-cell and T-cell surveillance. Then, when immune cells are finally activated by virus in the periphery, they cannot reach the sequestered target. Often the viruses that are associated with chronic infection co-exist with the host’s immune response for years without incident. If, however, the immune system is compromised (as may be mediated by an unrelated insult), virus re-activation can overwhelm the host (e.g. shingles can result when VZV reactivates in an immunodeficient individual). The best way to avoid late-stage disease is to induce immune responses prior to virus exposure, and thus block virus at its site of entry 16.

Has an immune response toward an immunodeficiency virus ever been protective?

The ability of activated immune cells to prevent immunodeficiency virus infection was demonstrated approximately two decades ago17;18. As one example, Hu et. al. prepared a vaccine comprising envelope glycoprotein (the outer coat protein) of simian immunodeficiency virus (SIV). One group of macaques was vaccinated with the envelope-based vaccine while another group of macaques served as controls. When later challenged with an infectious clone of SIV that expressed an envelope protein identical to that in the vaccine, all vaccinated animals were protected from infection 18. This result showed that the primate immune system is fully capable of preventing infection with an immunodeficiency virus provided that the vaccine and virus are antigenically matched.

Protection from superinfection has also been demonstrated in HIV/SIV systems in non-human primates. In other words, an animal is often infected when exposed to HIV or SIV for the first time, but resistant to infection when exposed to a second virus at a later date 19-24. Why is this so? The protection is likely because virus is sequestered in privileged sites (similar to the situation for VZV and papillomavirus) and over the course of months, mutates extensively to naturally prime the immune system against a cocktail of antigens25. Even though the second virus challenge may present new viral sequences, the antigens are similar to those seen following the first infection. Virus is therefore conquered by the previously-primed immune system.

In studies of HIV-1 infected humans, superinfection is also ‘rare’ in that it is difficult to document (although this is a topic of considerable controversy 26-28). For example, a recent survey of HIV-1-infected individuals within stable sero-concordant relationships revealed no transmission events27. Possibly, HIV-1 superinfections occur most frequently in humans during early and late stages of infection, either when the immune system is relatively naïve to HIV29, or when activated HIV-1-specific lymphocytes are destroyed by disease. Otherwise, similar to the case in macaques, it appears that the priming of immune cells with one virus (and its associated escape mutants) may be sufficient to confer protection against a second virus challenge.

Advancing a cocktail approach for vaccine development

A number of independent research groups have thus far studied vaccine cocktails with an intent to capture the diversity of HIV-1 in one vaccine7;15;30-33. The creation of antigenic cocktails has generally been centered around HIV-1 envelope proteins or fragments, as envelope elicits both neutralizing antibodies and T-cell function (although diversity should also be considered when vaccines target internal HIV-1 proteins). Cocktails of envelopes have ranged in component size from 3 to >50 15;30-33. The number of components must be large enough to represent the diversity of functional HIV-1 structures (perhaps greater than 3), but small enough to facilitate the manufacture of vaccines for world-wide distribution. The qualitative improvement in immune responses toward cocktail versus single-component vaccines has been repeatedly demonstrated 31;34-36. Even when an envelope contributes to only 1% of a mixed vaccine, it is capable of eliciting a unique population of responding cells37.

At a time when research funds are shifting toward HIV vaccine discovery38;39, there may be a renewed opportunity to conduct a more comprehensive study of envelope immunotypes and their respective ISabs. Systematic side-by-side comparisons of single-envelope and mixed-envelope vaccines in research animals could advance the current understanding of HIV-1 immunogens, and improve the design of second-generation cocktail vaccines. A variety of assays (both B-cell and T-cell)40-45 might be employed to define immunogen-specific activities, as there is currently no assay for which a clear correlate of protection against HIV-1 can be demonstrated. Results of systematic studies in research animals might then promote the testing of cocktails in advanced clinical trials and the ultimate prevention of HIV-1 infections in humans.


The recent front-runner vaccine in the HIV-1 field was specifically designed to elicit T-cell responses toward the internal proteins gag, pol and nef, each from a different clade B-isolate of HIV-146. The failure of this and other T-cell focused strategies 1;3 encourages researchers to expand the capacities of future vaccines. To date, most successful vaccines have partnered B-cell and T-cell activities and many have activated a breadth of immune specificities and functions11-13;47;48. Vaccine successes have demonstrated that a manageable cocktail of antigens can protect against infection and disease by diverse pathogens; cocktails are generally created by grouping pathogens by structure and representing each group by a different component in the vaccine cocktail. With views of harnessing the full capacity of a highly sophisticated immune system, researchers may gain optimism that similar efforts could yield a successful vaccine for human protection against HIV-1.


Multi-envelope HIV-1 vaccine design has been funded in part by NIH Cancer Center Support Core Grant P30-CA21765, NIH NIAID-P01 AI45142, the Mitchell Fund, the Carl C. Anderson Sr. and Marie Jo Anderson Charitable Foundation, the Pendleton Fund, the Pioneer Fund, and the American Lebanese Syrian Associated Charities.

Reference List

1. News in Brief. HIV vaccine failure prompts Merck to halt trial. Nature. 2007;449(7161):390. [PubMed]
2. Berman PW, Gray AM, Wrin T, et al. Genetic and immunologic characterization of viruses infecting MN-rgp120-vaccinated volunteers. J Infect Dis. 1997;176:384–397. [PubMed]
3. Cohen J. AIDS vaccines. HIV dodges one-two punch. Science. 2004;305(5690):1545–1547. [PubMed]
4. Roberts JD, Bebenek K, Kunkel TA. The accuracy of reverse transcriptase from HIV-1. Science. 1988;242(4882):1171–1173. [PubMed]
5. Lockey TD, Hurwitz JL. Size-heterogeneous sequences mark hot spots for asparagine, serine, and threonine insertions in HIV type 1 envelope. Aids Res Hum Retroviruses. 1998;14(8):717–719. [PubMed]
6. Pinter A, Honnen WJ, Kayman SC, Trochev O, Wu Z. Potent neutralization of primary HIV-1 isolates by antibodies directed against epitopes present in the V1/V2 domain of HIV-1 gp120. Vaccine. 1998;16(19):1803–1811. [PubMed]
7. Nyambi PN, Nadas A, Mbah HA, et al. Immunoreactivity of intact virions of human immunodeficiency virus type 1 (HIV-1) reveals the existence of fewer HIV-1 immunotypes than genotypes. J Virol. 2000;74(22):10670–10680. [PMC free article] [PubMed]
8. Haynes BF, Fleming J, St Clair EW, et al. Cardiolipin polyspecific autoreactivity in two broadly neutralizing HIV-1 antibodies. Science. 2005;308(5730):1906–1908. [PubMed]
9. Siciliano SJ, Kuhmann SE, Weng Y, et al. A critical site in the core of the CCR5 chemokine receptor required for binding and infectivity of human immunodeficiency virus type 1. J Biol Chem. 1999;274(4):1905–1913. [PubMed]
10. Murphy K, Travers P, Walport M. Janeway’s Immunobiology. 7. Garland Science; New York, NY: 2008.
11. Clark HF, Offit PA, Plotkin SA, Heaton PM. The new pentavalent rotavirus vaccine composed of bovine (strain WC3) -human rotavirus reassortants. Pediatr Infect DIs J. 2006;25(7):577–583. [PubMed]
12. Krogstad P, Cherry JD. Quadrivalent human vaccine - a call to action and for additional research. Pediatr Res. 2007;62(5):527. [PubMed]
13. Biagini RE, Schlottmann SA, Sammons DL, et al. Method for simultaneous measurement of antibodies to 23 pneumococcal capsular polysaccharides. Clin Diagn Lab Immunol. 2003;10(5):744–750. [PMC free article] [PubMed]
14. Catanzaro AT, Roederer M, Koup RA, et al. Phase I clinical evaluation of a six-plasmid multiclade HIV-1 DNA candidate vaccine. Vaccine. 2007;25(20):4085–4092. [PubMed]
15. Brave A, Boberg A, Gudmundsdotter L, et al. A new multi-clade DNA prime/recombinant MVA boost vaccine induces broad and high levels of HIV-1-specific CD8(+) T-cell and humoral responses in mice. Mol Ther. 2007;15(9):1724–1733. [PubMed]
16. Goldman GS. Incidence of herpes zoster among children and adolescents in a community with moderate varicella vaccination coverage. Vaccine. 2003;21(2730):4243–4249. [PubMed]
17. Berman PW, Gregory TJ, Riddle L, et al. Protection of chimpanzees from infection by HIV-1 after vaccination with recombinant glycoprotein gp120 but not gp160. Nature. 1990;345:622–625. [PubMed]
18. Hu S-L, Abrams K, Barber GN, et al. Protection of macaques against SIV infection by subunit vaccines of SIV envelope glycoprotein gp160. Science. 1992;255:456–459. [PubMed]
19. Shibata R, Siemon C, Cho MW, et al. Resistance of previously infected chimpanzees to successive challenges with a heterologous intraclade B strain of human immunodeficiency virus type 1. J Virol. 1996;70(7):4361–4369. [PMC free article] [PubMed]
20. Wyand MS, Manson K, Montefiori DC, et al. Protection by live, attenuated simian immunodeficiency virus against heterologous challenge. J Virol. 1999;73(10):8356–8363. [PMC free article] [PubMed]
21. Stahl-Hennig C, Dittmer U, Nisslein T, et al. Rapid development of vaccine protection in macaques by live-attenuated simian immunodeficiency virus. J Gen Virol. 1996;77(Pt 12):2969–2981. [PubMed]
22. Cranage MP, Whatmore AM, Sharpe SA, et al. Macaques infected with live attenuated SIVmac are protected against superinfection via the rectal mucosa. Virology. 1997;229(1):143–154. [PubMed]
23. Stephens EB, Joag SV, Atkinson B, et al. Infected macaques that controlled replication of SIVmac or nonpathogenic SHIV developed sterilizing resistance against pathogenic SHIV(KU-1) Virology. 1997;234(2):328–339. [PubMed]
24. Titti F, Sernicola L, Geraci A, et al. Live attenuated simian immunodeficiency virus prevents super-infection by cloned SIVmac251 in cynomolgus monkeys. J Gen Virol. 1997;78(Pt 10):2529–2539. [PubMed]
25. Wrin T, Crawford L, Sawyer L, et al. Neutralizing antibody responses to autologous and heterologous isolates of human immunodeficiency virus. J Acquir Immune Defic Syndr. 1994;7:211–219. [PubMed]
26. Casado C, Pernas M, Alvaro T, et al. Coinfection and superinfection in patients with long-term, nonprogressive HIV-1 disease. J Infect Dis. 2007;196(6):895–899. [PubMed]
27. Chakraborty B, Valer L, De MC, Soriano V, Quinones-Mateu ME. Failure to detect human immunodeficiency virus type 1 superinfection in 28 HIV-seroconcordant individuals with high risk of reexposure to the virus. Aids Res Hum Retroviruses. 2004;20(9):1026–1031. [PubMed]
28. Gonzales MJ, Delwart E, Rhee SY, et al. Lack of detectable human immunodeficiency virus type 1 superinfection during 1072 person-years of observation. J Infect Dis. 2003;188(3):397–405. [PMC free article] [PubMed]
29. Otten RA, Ellenberger DL, Adams DR, et al. Identification of a window period for susceptibility to dual infection with two distinct human immunodeficiency virus type 2 isolates in a Macaca nemestrina (pig-tailed macaque) model. J Infect Dis. 1999;180(3):673–684. [PubMed]
30. Zhan X, Martin LN, Slobod KS, et al. Multi-envelope HIV-1 vaccine devoid of SIV components controls disease in macaques challenged with heterologous pathogenic SHIV. Vaccine. 2005;23(4647):5306–5320. [PubMed]
31. Seaman MS, Xu L, Beaudry K, et al. Multiclade human immunodeficiency virus type 1 envelope immunogens elicit broad cellular and humoral immunity in rhesus monkeys. J Virol. 2005;79(5):2956–2963. [PMC free article] [PubMed]
32. Pal R, Kalyanaraman VS, Nair BC, et al. Immunization of rhesus macaques with a polyvalent DNA prime/protein boost human immunodeficiency virus type 1 vaccine elicits protective antibody response against simian human immunodeficiency virus of R5 phenotype. Virology. 2006;348(2):341–353. [PubMed]
33. Azizi A, Anderson DE, Torres JV, et al. Induction of broad cross-subtype-specific HIV-1 immune responses by a novel multivalent HIV-1 peptide vaccine in cynomolgus macaques. J Immunol. 2008;180(4):2174–2186. [PubMed]
34. Hurwitz JL, Slobod KS, Lockey TD, et al. Application of the Polyvalent Approach to HIV-1 Vaccine Development. Curr Drug Targets Infect Disord. 2005;5(2):143–156. [PubMed]
35. Kong W-P, Huang Y, Yang Z-Y, et al. Immunogenicity of multiple gene and clade human immunodeficiency virus type 1 DNA vaccines. J Virol. 2003;77:12764–12772. [PMC free article] [PubMed]
36. Ljungberg K, Rollman E, Eriksson L, Hinkula J, Wahren B. Enhanced immune responses after DNA vaccination with combined envelope genes from different HIV-1 subtypes. Virology. 2002;302(1):44–57. [PubMed]
37. Zhan X, Slobod KS, Surman S, et al. Minor components of a multi-envelope HIV vaccine are recognized by type-specific T-helper cells. Vaccine. 2004;22:1206–1213. [PubMed]
38. Fauci AS, Johnston MI, Dieffenbach CW, et al. HIV vaccine research: the way forward. Science. 2008;321(5888):530–532. [PubMed]
39. Berkley SF, Koff WC. Scientific and policy challenges to development of an AIDS vaccine. Lancet. 2007;370(9581):94–101. [PubMed]
40. Gomez-Roman VR, Florese RH, Patterson LJ, et al. A simplified method for the rapid fluorometric assessment of antibody-dependent cell-mediated cytotoxicity. J Immunol Methods. 2006;308(12):53–67. [PubMed]
41. Forthal DN, Landucci G, Cole KS, et al. Rhesus macaque polyclonal and monoclonal antibodies inhibit simian immunodeficiency virus in the presence of human or autologous rhesus effector cells. J Virol. 2006;80(18):9217–9225. [PMC free article] [PubMed]
42. Polonis VR, Brown BK, Rosa BA, et al. Recent advances in the characterization of HIV-1 neutralization assays for standardized evaluation of the antibody response to infection and vaccination. Virology. 2008;375(2):315–320. [PubMed]
43. Brown SA, Stambas J, Zhan X, et al. Clustering of Th cell epitopes on exposed regions of HIV envelope despite defects in antibody activity. J Immunol. 2003;171(8):4140–4148. [PubMed]
44. Forthal DN, Landucci G, Phan TB, Becerra J. Interactions between natural killer cells and antibody Fc result in enhanced antibody neutralization of human immunodeficiency virus type 1. J Virol. 2005;79(4):2042–2049. [PMC free article] [PubMed]
45. Holl V, Peressin M, Decoville T, et al. Nonneutralizing antibodies are able to inhibit human immunodeficiency virus type 1 replication in macrophages and immature dendritic cells. J Virol. 2006;80(12):6177–6181. [PMC free article] [PubMed]
46. McElrath MJ, De Rosa SC, Moodie Z, et al. HIV-1 vaccine-induced immunity in the test-of-concept Step Study: a case-cohort analysis. Lancet. 2008;372(9653):1894–1905. [PMC free article] [PubMed]
47. Demkowicz WE, Jr, Littaua RA, Wang J, Ennis FA. Human cytotoxic T-cell memory: long-lived responses to vaccinia virus. J Virol. 1996;70(4):2627–2631. [PMC free article] [PubMed]
48. Crotty S, Felgner P, Davies H, et al. Cutting edge: long-term B cell memory in humans after smallpox vaccination. J Immunol. 2003;171(10):4969–4973. [PubMed]