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1.  Differential gene expression in HIV/SIV-associated and spontaneous lymphomas 
Diffuse large B-cell lymphoma (DLBCL) is more prevalent and more often fatal in HIV-infected patients and SIV-infected monkeys compared to immune-competent individuals. Molecular, biological, and immunological data indicate that virus-associated lymphomagenesis is similar in both infected hosts. To find genes specifically overexpressed in HIV/SIV-associated and non-HIV/SIV-associated DLBCL we compared gene expression profiles of HIV/SIV-related and non-HIV-related lymphomas using subtractive hybridization and Northern blot analysis. Our experimental approach allowed us to detect two genes (a-myb and pub) upregulated solely in HIV/SIV-associated DLBCLs potentially involved in virus-specific lymphomagenesis in human and monkey. Downregulation of the pub gene was observed in all non-HIV-associated lymphomas investigated. In addition, we have found genes upregulated in both non-HIV- and HIV-associated lymphomas. Among those were genes both with known (set, ND4, SMG-1) and unknown functions. In summary, we have demonstrated that simultaneous transcriptional upregulation of at least two genes (a-myb and pub) was specific for AIDS-associated lymphomas.
PMCID: PMC1252723  PMID: 16239949
non-Hodgkin's lymphoma; diffuse large B-cell lymphoma; HIV/SIV-associated lymphomas; spontaneous; differentially expressed genes; subtractive hybridization
2.  Immune surveillance and lymphoid malignancy in immunocompromised host 
Immune surveillance is a dynamic process that involves an intact immune system to identify and protect the host against tumor development. The increased understanding of the genetics, infections and hematological malignancies in congenital immune deficiency states supports the concept that impaired T cells and Natural-killer/T cells leads to B-cell lymphoma. Furthermore, severe combined immunodeficient mice are prone to spontaneous tumor development and therefore serve as experimental models. Here we discuss the acquired conditions and mechanisms involved in dysregulation of the immune system that lead to lymphoma. Preemptive strategies to improve immune regulation and response and restore a competent immune system may lead to a decrease in lymphoid malignancies.
PMCID: PMC3649811  PMID: 23675561
Lymphoma; immune surveillance; immune deficiency
3.  Developing strategies for HIV-1 eradication 
Trends in immunology  2012;33(11):554-562.
Highly active antiretroviral therapy (HAART) suppresses HIV-1 replication, transforming the outlook for infected patients. However, reservoirs of replication-competent forms of the virus persist during HAART, and when treatment is stopped, high rates of HIV-1 replication return. Recent insights into HIV-1 latency, as well as a report that HIV-1 infection was eradicated in one individual, have renewed interest in finding a cure for HIV-1 infection. Strategies for HIV-1 eradication include gene therapy and hematopoietic stem cell transplantation, stimulating host immunity to control HIV-1 replication, and targeting latent HIV-1 in resting memory CD4+ T cells. Future efforts should aim to provide better understanding of how to reconstitute the CD4+ T cell compartment with genetically engineered cells, exert immune control over HIV-1 replication, and identify and eliminate all viral reservoirs.
PMCID: PMC3963166  PMID: 22867874
reservoir; eradication; latency; HIV-1; cure
4.  EBV, HHV8 and HIV in B cell non Hodgkin lymphoma in Kampala, Uganda 
B cell non Hodgkin lymphomas account for the majority of lymphomas in Uganda. The commonest is endemic Burkitt lymphoma, followed by diffuse large-B-cell lymphoma (DLBCL). There has been an increase in incidence of malignant lymphoma since the onset of the HIV/AIDS pandemic. However, the possible linkages of HHV8 and EBV to the condition of impaired immunity present in AIDS are still not yet very clearly understood.
1. To describe the prevalence of Epstein-Barr virus, Human Herpes virus 8 and Human Immunodeficiency Virus-1 in B cell non Hodgkin lymphoma biopsy specimens in Kampala, Uganda.
2. To describe the histopathology of non Hodgkin lymphoma by HIV serology test result in Kampala, Uganda
Tumour biopsies specimens from 119 patients with B cell non Hodgkin lymphoma were classified according to the WHO classification. Immunohistochemistry was used for detection of HHV8 and in situ hybridization with Epstein Barr virus encoded RNA (EBER) for EBV. Real time and nested PCR were used for the detection of HIV.
The patients from whom the 1991-2000 NHL biopsies had been taken did not have HIV serology results therefore 145 patients biopsies where serology results were available were used to describe the association of HIV with non Hodgkin lymphoma type during 2008-2009.
In this study, the majority (92%) of the Burkitt lymphomas and only 34.8% of the diffuse large B cell lymphomas were EBV positive. None of the precursor B lymphoblastic lymphomas or the mantle cell lymphomas showed EBV integration in the lymphoma cells.
None of the Burkitt lymphoma biopsies had HIV by PCR. Of the 121 non Hodgkin B cell lymphoma patients with HIV test results, 19% had HIV. However, only 1(0.04%) case of Burkitt lymphoma had HIV. All the tumours were HHV8 negative.
The majority of the Burkitt lymphomas and two fifths of the diffuse large B cell lymphomas had EBV. All the tumours were HHV8 negative. Generally, the relationship of NHL and HIV was weaker than what has been reported from the developed countries. We discuss the role of these viruses in lymphomagenesis in light of current knowledge.
PMCID: PMC2907314  PMID: 20591151
5.  T-helper 1 versus T-helper 2 lymphocyte immunodysregulation is the central factor in genesis of Burkitt lymphoma: hypothesis 
The HIV epidemic has challenged our previous understanding of endemic Burkitt's lymphoma. Despite the strong association of Burkitt's lymphoma and HIV infection in the Developed world, and against previous postulations that the cancer is due to immunosupression among African children, the HIV epidemic in the Malaria belt has not been associated with a corresponding increase in incidence of childhood Burkitt's lymphoma. Even outside the context of HIV infection, there is substantial evidence for a strong but skewed immune response towards a TH2 response in genesis of Burkitt lymphoma.
Presentation of the hypothesis
Rather than a global and/or profound immunosupression, the final common pathway in genesis of Burkitt's lymphoma is the dysregulation of the immune response towards a TH2 response dominated by B-lymphocytes, and the concomitant suppression of the TH1 cell-mediated immune surveillance, driven by various viral/parasitic/bacterial infections.
Testing the hypothesis
Case control studies comparing TH2 and TH1 immune responses in Burkitt lymphoma of different etiological types (sporadic, HIV-related, endemic and post-transplant) to demonstrate significant dominance of TH2 immune response in presence of poor CMI response as a common factor. Immunological profiling to evaluate differences between immune states that are associated (such as recurrent Malaria infection) and those that are not associated (such as severe protein-energy malnutrition) with Burkitt lymphoma. Prospective cohorts profiling chronology of immunological events leading to Burkitt lymphoma in children with EBV infection.
Implications of the hypothesis
The dysregulation of the immune response may be the missing link in our understanding of Burkitt lymphomagenesis. This will provide possibilities for determination of risk and for control of development of malignancy in individuals/populations exposed to the relevant infections.
PMCID: PMC1884132  PMID: 17509139
6.  Patients with Epstein Barr virus positive lymphomas have decreased CD4+ T cell responses to the viral nuclear antigen 1 
Epstein Barr virus (EBV) causes lymphomas in immune competent and, at increased frequencies, in immune compromised patients. In the presence of an intact immune system, EBV associated lymphomas express in most cases only three or fewer EBV antigens at the protein level, always including the nuclear antigen 1 of EBV (EBNA1). EBNA1 is a prominent target for EBV specific CD4+ T cell and humoral immune responses in healthy EBV carriers. Here we demonstrate that patients with EBV associated lymphomas, primarily Hodgkin's lymphoma, lack detectable EBNA1 specific CD4+ T cell responses and have slightly altered EBNA1 specific antibody titers at diagnosis. In contrast, the majority of EBV negative lymphoma patients had detectable IFNγ expression and proliferation by CD4+ T cells in response to EBNA1, and carry EBNA1 specific immunoglobulins at levels similar to healthy virus carriers. Other EBV antigens, which were not present in the tumors, were recognized in less EBV positive, than negative lymphoma patients, but detectable responses reached similar CD8+ T cell frequencies in both cohorts. Patients with EBV positive and negative lymphomas did not differ in T cell responses in influenza specific CD4+ T cell proliferation and in antibody titers against tetanus toxoid. These data suggest a selective loss of EBNA1 specific immune control in EBV associated lymphoma patients, which should be targeted for immunotherapy of these malignancies.
PMCID: PMC2605183  PMID: 18781564
EBNA1; CD4+ T cells; Hodgkin's lymphoma
7.  The BAF complex and HIV latency 
Transcription  2012;3(4):171-176.
The persistence of a reservoir of transcriptionally competent but latent virus in the presence of antiviral regimens presents the main impediment to a curative therapy against HIV. Therefore it is critical to understand the molecular mechanisms, which lead to the establishment and maintenance of HIV latency, and which contribute to the reversal of this process and mediate HIV transcriptional activation in response to T cell activation signals. Here I discuss features of the nucleosomal landscape of the HIV promoter or 5'LTR in controlling HIV transcription. I emphasize on the emerging understanding of the role of the ATP dependent SWI/SNF chromatin remodelling complexes in modulating the chromatin architecture at the HIV LTR and how this leads to a tight regulation of LTR transcription.
PMCID: PMC3654765  PMID: 22771990
BAF; HIV-1; SWI/SNF; chromatin structure; nucleosome positioning; transcription factors
8.  The effect of different immune responses on the evolution of virulent CXCR4-tropic HIV. 
We use mathematical models to determine possible mechanisms contributing to the evolution and rise of virulent CXCR4-tropic HIV in vivo. The models predict that the ability of the virus to specialize on a given target cell type depends on the exact fitness landscape of the viral mutants. Because this fitness landscape varies between people, this may explain why the evolution of fully CXCR4-tropic strains only occurs in about 50% of infected patients. Assuming that CXCR4-tropic HIV may evolve, we investigate the effect of different immune responses on the rise of such virulent strains. If we assume that CXCR4-tropic HIV is more cytopathic than CCR5-tropic virus, virulent CXCR4-tropic mutants remain suppressed at low levels both in the absence of an immune response, and in the presence of responses that act on the virus before integration into the host genome. On the other hand, this difference in cytopathogenicity is reduced by the presence of immune responses acting on infected cells, allowing CXCR4-tropic HIV to coexist with the CCR5-tropic virus. These results may help to interpret experimental data and are discussed with reference to the literature.
PMCID: PMC1689517  PMID: 9872003
9.  Packaging Limits and Stability of HIV-1 Sequences in a Coxsackievirus B Vector 
Vaccine  2009;27(30):3992-4000.
Enteroviruses elicit protective mucosal immune responses that could be harnessed as part of a strategy to prevent sexual transmission of the human immunodeficiency virus-1 (HIV-1). We report the construction of replication competent recombinant vectors of coxsackievirus B3 (CVB3) that express one or more portions of the HIV-1 Gag protein. Vectors containing the capsid domain of Gag were initially genetically unstable with protein expression lost after brief passage in tissue culture. Codon modification to increase the G/C content of the HIV-1 capsid sequence resulted in enhanced genetic stability of CVB3 vectors during in vitro passage. Cells infected with a vector expressing the matrix (MA) subunit of the HIV-1 Gag protein were susceptible to lysis by CD8 T cell clones specific for the SL9 epitope found within MA. These studies suggest that CVB3 vectors may be useful as vaccine vector candidates, if hurdles in class I antigen presentation and stability can be overcome.
PMCID: PMC2745320  PMID: 19389440
HIV-1; Vaccine; Coxsackievirus B3
10.  Relationship Between the Competence Antigen and the Competence-Activator Substance in Pneumococci 
Journal of Bacteriology  1965;90(5):1226-1232.
Tomasz, Alexander (The Rockefeller Institute, New York, N.Y.), and Samuel M. Beiser. Relationship between the competence antigen and the competence-activator substance in pneumococci. J. Bacteriol. 90:1226–1232. 1965.—Antisera prepared against pneumococci in their competent phase inhibit deoxyribonuoleic acid (DNA)-mediated genetic transformation as well as binding of radioactive DNA by the cells. The same sera do not inhibit transformation of competent Haemophilus influenzae and Bacillus subtilis cells, but transformation of a Streptococcus strain genetically related to pneumococci is inhibited. The kinetics of immune inhibition of transformation resembles the inactivation of bacteriophage by phage-neutralizing antisera. The appearance of the competence antigen on the surface of pneumococci can be induced by the competence-activator substance. Antisera prepared against competent pneumococci can also inhibit the conversion of incompetent cells to competence by the competence-activator substance. The possibility is considered that part of the new antigenic determinant appearing on the cell surface during competence may be the activator itself.
PMCID: PMC315806  PMID: 4379003
11.  Estimating the individualized HIV-1 genetic barrier to resistance using a nelfinavir fitness landscape 
BMC Bioinformatics  2010;11:409.
Failure on Highly Active Anti-Retroviral Treatment is often accompanied with development of antiviral resistance to one or more drugs included in the treatment. In general, the virus is more likely to develop resistance to drugs with a lower genetic barrier. Previously, we developed a method to reverse engineer, from clinical sequence data, a fitness landscape experienced by HIV-1 under nelfinavir (NFV) treatment. By simulation of evolution over this landscape, the individualized genetic barrier to NFV resistance may be estimated for an isolate.
We investigated the association of estimated genetic barrier with risk of development of NFV resistance at virological failure, in 201 patients that were predicted fully susceptible to NFV at baseline, and found that a higher estimated genetic barrier was indeed associated with lower odds for development of resistance at failure (OR 0.62 (0.45 - 0.94), per additional mutation needed, p = .02).
Thus, variation in individualized genetic barrier to NFV resistance may impact effective treatment options available after treatment failure. If similar results apply for other drugs, then estimated genetic barrier may be a new clinical tool for choice of treatment regimen, which allows consideration of available treatment options after virological failure.
PMCID: PMC2921410  PMID: 20682040
12.  Epstein-Barr virus-specific cytotoxic T cell responses in HIV-1 infection: different kinetics in patients progressing to opportunistic infection or non-Hodgkin's lymphoma. 
Journal of Clinical Investigation  1997;99(7):1525-1533.
Although the high incidence of EBV-associated diffuse large cell lymphomas (DLCL) in HIV-1 infection is believed to be related to loss of immune control due to HIV-induced immune deficiency, it has been claimed that cytotoxic T lymphocyte (CTL) responses to EBV are longer lasting in HIV-1-infected persons than CTL directed against HIV-1 itself. We approached this apparent paradox by performing the first longitudinal study into the kinetics of EBV and HIV-specific CTL responses in HIV-infected patients progressing either to AIDS with non-Hodgkin's lymphoma (NHL) or AIDS with opportunistic infection (OI). Multiple samples were tested from HIV-1 seroconversion to AIDS-diagnosis. Four out of six patients that were either long-term asymptomatic or progressing to OI showed declining HIV-1 CTL precursor (CTLp) frequencies whereas EBV-CTLp remained stable, suggestive for HIV-1-specific immune exhaustion. In two patients rapidly progressing to AIDS-OI, a parallel decline of HIV-1- and EBV-CTL responses was seen, indicative for total collapse of cellular immunity. In all these six patients EBV-load remained low. However, in four out of five patients that progressed to DLCL, EBV-load was high and increasing several months preceding the NHL. In all five patients, EBV-CTLp decreased before the emergence of the NHL. Thus, our data show that in HIV-1 infection loss of HIV-1-specific T cell immunity is not necessarily paralleled by loss of EBV-specific T cell responses. The occurrence of AIDS-related DLCL is preceded by decreasing EBV-CTLp and increasing EBV load. Failing EBV-control might therefore be an important step in the pathogenesis of AIDS-related DLCL.
PMCID: PMC507972  PMID: 9119996
13.  Clinical Significance of Enteric Protozoa in the Immunosuppressed Human Population 
Clinical Microbiology Reviews  2009;22(4):634-650.
Summary: Globally, the number of immunosuppressed people increases each year, with the human immunodeficiency virus (HIV) pandemic continuing to spread unabated in many parts of the world. Immunosuppression may also occur in malnourished persons, patients undergoing chemotherapy for malignancy, and those receiving immunosuppressive therapy. Components of the immune system can be functionally or genetically abnormal as a result of acquired (e.g., caused by HIV infection, lymphoma, or high-dose steroids or other immunosuppressive medications) or congenital illnesses, with more than 120 congenital immunodeficiencies described to date that either affect humoral immunity or compromise T-cell function. All individuals affected by immunosuppression are at risk of infection by opportunistic parasites (such as the microsporidia) as well as those more commonly associated with gastrointestinal disease (such as Giardia). The outcome of infection by enteric protozoan parasites is dependent on absolute CD4+ cell counts, with lower counts being associated with more severe disease, more atypical disease, and a greater risk of disseminated disease. This review summarizes our current state of knowledge on the significance of enteric parasitic protozoa as a cause of disease in immunosuppressed persons and also provides guidance on recent advances in diagnosis and therapy for the control of these important parasites.
PMCID: PMC2772358  PMID: 19822892
14.  EBNA3B-deficient EBV promotes B cell lymphomagenesis in humanized mice and is found in human tumors 
The Journal of Clinical Investigation  2012;122(4):1487-1502.
Epstein-Barr virus (EBV) persistently infects more than 90% of the human population and is etiologically linked to several B cell malignancies, including Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and diffuse large B cell lymphoma (DLBCL). Despite its growth transforming properties, most immune-competent individuals control EBV infection throughout their lives. EBV encodes various oncogenes, and of the 6 latency-associated EBV-encoded nuclear antigens, only EBNA3B is completely dispensable for B cell transformation in vitro. Here, we report that infection with EBV lacking EBNA3B leads to aggressive, immune-evading monomorphic DLBCL-like tumors in NOD/SCID/γc–/– mice with reconstituted human immune system components. Infection with EBNA3B-knockout EBV (EBNA3BKO) induced expansion of EBV-specific T cells that failed to infiltrate the tumors. EBNA3BKO-infected B cells expanded more rapidly and secreted less T cell–chemoattractant CXCL10, reducing T cell recruitment in vitro and T cell–mediated killing in vivo. B cell lines from 2 EBV-positive human lymphomas encoding truncated EBNA3B exhibited gene expression profiles and phenotypic characteristics similar to those of tumor-derived lines from the humanized mice, including reduced CXCL10 secretion. Screening EBV-positive DLBCL, HL, and BL human samples identified additional EBNA3B mutations. Thus, EBNA3B is a virus-encoded tumor suppressor whose inactivation promotes immune evasion and virus-driven lymphomagenesis.
PMCID: PMC3314448  PMID: 22406538
15.  Humoral, mucosal, and cellular immunity in response to a human immunodeficiency virus type 1 immunogen expressed by a Venezuelan equine encephalitis virus vaccine vector. 
Journal of Virology  1997;71(4):3031-3038.
A molecularly cloned attenuated strain of Venezuelan equine encephalitis virus (VEE) has been genetically configured as a replication-competent vaccine vector for the expression of heterologous viral proteins (N. L. Davis, K. W. Brown, and R. E. Johnston, J. Virol. 70:3781-3787, 1996). The matrix/capsid (MA/CA) coding domain of human immunodeficiency virus type 1 (HIV-1) was cloned into the VEE vector to determine the ability of a VEE vector to stimulate an anti-HIV immune response in mice. The VEE-MA/CA vector replicated rapidly in the cytoplasm of baby hamster kidney (BHK) cells and expressed large quantities of antigenically identifiable MA/CA protein. When injected subcutaneously into BALB/c mice, the vector invaded and replicated in the draining lymphoid tissues, expressing HIV-1 MA/CA at a site of potent immune activity. Anti-MA/CA immunoglobulin G (IgG) and IgA antibodies were present in serum of all immunized mice, and titers increased after a second booster inoculation. IgA antibodies specific for MA/CA were detected in vaginal washes of mice that received two subcutaneous immunizations. Cytotoxic T-lymphocyte responses specific for MA/CA were detected following immunization with the MA/CA-expressing VEE vector. These findings demonstrate the ability of a VEE-based vaccine vector system to stimulate a comprehensive humoral and cellular immune response. The multifaceted nature of this response makes VEE an attractive vaccine for immunization against virus infections such as HIV-1, for which the correlates of protective immunity remain unclear, but may include multiple components of the immune system.
PMCID: PMC191432  PMID: 9060663
16.  Oral Immunization with a Live Coxsackievirus/HIV Recombinant Induces Gag p24-Specific T Cell Responses 
PLoS ONE  2010;5(9):e12499.
The development of an HIV/AIDS vaccine has proven to be elusive. Because human vaccine trials have not yet demonstrated efficacy, new vaccine strategies are needed for the HIV vaccine pipeline. We have been developing a new HIV vaccine platform using a live enterovirus, coxsackievirus B4 (CVB4) vector. Enteroviruses are ideal candidates for development as a vaccine vector for oral delivery, because these viruses normally enter the body via the oral route and survive the acidic environment of the stomach.
Methodology/Principal Findings
We constructed a live coxsackievirus B4 recombinant, CVB4/p24(733), that expresses seventy-three amino acids of the gag p24 sequence (HXB2) and assessed T cell responses after immunization of mice. The CVB4 recombinant was physically stable, replication-competent, and genetically stable. Oral or intraperitoneal immunization with the recombinant resulted in strong systemic gag p24-specific T cell responses as determined by the IFN-γ ELISPOT assay and by multiparameter flow cytometry. Oral immunization with CVB4/p24(733) resulted in a short-lived, localized infection of the gut without systemic spread. Because coxsackieviruses are ubiquitous in the human population, we also evaluated whether the recombinant was able to induce gag p24-specific T cell responses in mice pre-immunized with the CVB4 vector. We showed that oral immunization with CVB4/p24(733) induced gag p24-specific immune responses in vector-immune mice.
The CVB4/p24(733) recombinant retained the physical and biological characteristics of the parental CVB4 vector. Oral immunization with the CVB4 recombinant was safe and resulted in the induction of systemic HIV-specific T cell responses. Furthermore, pre-existing vector immunity did not preclude the development of gag p24-specific T cell responses. As the search continues for new vaccine strategies, the present study suggests that live CVB4/HIV recombinants are potential new vaccine candidates for HIV.
PMCID: PMC2932689  PMID: 20824074
17.  Long-term experimental evolution in Escherichia coli. XI. Rejection of non-transitive interactions as cause of declining rate of adaptation 
Experimental populations of Escherichia coli have evolved for 20,000 generations in a uniform environment. Their rate of improvement, as measured in competitions with the ancestor in that environment, has declined substantially over this period. This deceleration has been interpreted as the bacteria approaching a peak or plateau in a fitness landscape. Alternatively, this deceleration might be caused by non-transitive competitive interactions, in particular such that the measured advantage of later genotypes relative to earlier ones would be greater if they competed directly.
To distinguish these two hypotheses, we performed a large set of competitions using one of the evolved lines. Twenty-one samples obtained at 1,000-generation intervals each competed against five genetically marked clones isolated at 5,000-generation intervals, with three-fold replication. The pattern of relative fitness values for these 315 pairwise competitions was compared with expectations under transitive and non-transitive models, the latter structured to produce the observed deceleration in fitness relative to the ancestor. In general, the relative fitness of later and earlier generations measured by direct competition agrees well with the fitness inferred from separately competing each against the ancestor. These data thus support the transitive model.
Non-transitive competitive interactions were not a major feature of evolution in this population. Instead, the pronounced deceleration in its rate of fitness improvement indicates that the population early on incorporated most of those mutations that provided the greatest gains, and subsequently relied on beneficial mutations that were fewer in number, smaller in effect, or both.
PMCID: PMC134600  PMID: 12443537
18.  Viral quasispecies profiles as the result of the interplay of competition and cooperation 
Viral quasispecies can be regarded as a swarm of genetically related mutants. A common approach employed to describe viral quasispecies is by means of the quasispecies equation (QE). However, a main criticism of QE is its lack of frequency-dependent selection. This can be overcome by an alternative formulation for the evolutionary dynamics: the replicator-mutator equation (RME). In turn, a problem with the RME is how to quantify the interaction coefficients between viral variants. Here, this is addressed by adopting an ecological perspective and resorting to the niche theory of competing communities, which assumes that the utilization of resources primarily determines ecological segregation between competing individuals (the different viral variants that constitute the quasispecies). This provides a theoretical framework to estimate quantitatively the fitness landscape.
Using this novel combination of RME plus the ecological concept of niche overlapping for describing a quasispecies we explore the population distributions of viral variants that emerge, as well as the corresponding dynamics. We observe that the population distribution requires very long transients both to A) reach equilibrium and B) to show a clear dominating master sequence. Based on different independent and recent experimental evidence, we find that when some cooperation or facilitation between variants is included in appropriate doses we can solve both A) and B). We show that a useful quantity to calibrate the degree of cooperation is the Shannon entropy.
In order to get a typical quasispecies profile, at least within the considered mathematical approach, it seems that pure competition is not enough. Some dose of cooperation among viral variants is needed. This has several biological implications that might contribute to shed light on the mechanisms operating in quasispecies dynamics and to understand the quasispecies as a whole entity.
PMCID: PMC2885392  PMID: 20459709
19.  APOBEC3G induces a hypermutation gradient: purifying selection at multiple steps during HIV-1 replication results in levels of G-to-A mutations that are high in DNA, intermediate in cellular viral RNA, and low in virion RNA 
Retrovirology  2009;6:16.
Naturally occurring Vif variants that are unable to inhibit the host restriction factor APOBEC3G (A3G) have been isolated from infected individuals. A3G can potentially induce G-to-A hypermutation in these viruses, and hypermutation could contribute to genetic variation in HIV-1 populations through recombination between hypermutant and wild-type genomes. Thus, hypermutation could contribute to the generation of immune escape and drug resistant variants, but the genetic contribution of hypermutation to the viral evolutionary potential is poorly understood. In addition, the mechanisms by which these viruses persist in the host despite the presence of A3G remain unknown.
To address these questions, we generated a replication-competent HIV-1 Vif mutant in which the A3G-binding residues of Vif, Y40RHHY44, were substituted with five alanines. As expected, the mutant was severely defective in an A3G-expressing T cell line and exhibited a significant delay in replication kinetics. Analysis of viral DNA showed the expected high level of G-to-A hypermutation; however, we found substantially reduced levels of G-to-A hypermutation in intracellular viral RNA (cRNA), and the levels of G-to-A mutations in virion RNA (vRNA) were even further reduced. The frequencies of hypermutation in DNA, cRNA, and vRNA were 0.73%, 0.12%, and 0.05% of the nucleotides sequenced, indicating a gradient of hypermutation. Additionally, genomes containing start codon mutations and early termination codons within gag were isolated from the vRNA.
These results suggest that sublethal levels of hypermutation coupled with purifying selection at multiple steps during the early phase of viral replication lead to the packaging of largely unmutated genomes, providing a mechanism by which mutant Vif variants can persist in infected individuals. The persistence of genomes containing mutated gag genes despite this selection pressure indicates that dual infection and complementation can result in the packaging of hypermutated genomes which, through recombination with wild-type genomes, could increase viral genetic variation and contribute to evolution.
PMCID: PMC2657108  PMID: 19216784
20.  Stress-Induced Tradeoffs in a Free-Living Lizard across a Variable Landscape: Consequences for Individuals and Populations 
PLoS ONE  2012;7(11):e49895.
Current life history theory suggests that the allocation of energetic resources between competing physiological needs should be dictated by an individual’s longevity and pace of life. One key physiological pathway likely to contribute to the partitioning of resources is the vertebrate stress response. By increasing circulating glucocorticoids the stress response can exert a suite of physiological effects, such as altering immune function. We investigated the effects of stress physiology on individual immunity, reproduction and oxidative stress, across an urban landscape. We sampled populations in and around St. George, Utah, examining corticosterone in response to restraint stress, two innate immune measures, reproductive output, and the presence of both reactive oxygen metabolites and antioxidant binding capacity, in populations of common side-blotched lizards (Uta stansburiana) experiencing variable levels of environmental stress. Additionally, using capture-mark-recapture techniques, we examined the relationships between these physiological parameters and population-level differences. Our results reveal elevated physiological stress corresponds with suppressed immunity and increased oxidative stress. Interestingly, urban populations experiencing the most physiological stress also exhibited greater reproductive output and decreased survival relative to rural populations experiencing less physiological stress, demonstrating a tradeoff between reproduction and life maintenance processes. Our results suggest that environmental stress may augment life history strategy in this fast-paced species, and that shifts in life history strategy can in turn affect the population at large. Finally, the urban environment poses definite challenges for organisms, and while it appears that side-blotched lizards are adjusting physiologically, it is unknown what fitness costs these physiological adjustments accrue.
PMCID: PMC3502225  PMID: 23185478
21.  Phages and HIV-1: From Display to Interplay 
The complex hide-and-seek game between HIV-1 and the host immune system has impaired the development of an efficient vaccine. In addition, the high variability of the virus impedes the long-term control of viral replication by small antiviral drugs. For more than 20 years, phage display technology has been intensively used in the field of HIV-1 to explore the epitope landscape recognized by monoclonal and polyclonal HIV-1-specific antibodies, thereby providing precious data about immunodominant and neutralizing epitopes. In parallel, biopanning experiments with various combinatorial or antibody fragment libraries were conducted on viral targets as well as host receptors to identify HIV-1 inhibitors. Besides these applications, phage display technology has been applied to characterize the enzymatic specificity of the HIV-1 protease. Phage particles also represent valuable alternative carriers displaying various HIV-1 antigens to the immune system and eliciting antiviral responses. This review presents and summarizes the different studies conducted with regard to the nature of phage libraries, target display mode and biopanning procedures.
PMCID: PMC3344243  PMID: 22606007
phage display; HIV-1; epitope mapping; mimotopes; HIV-1 inhibitor; HIV-1 vaccine; gp120; gp41; CXCR4; CCR5
22.  An equilibrium for phenotypic variance in fluctuating environments owing to epigenetics 
The connection between random environments and genetic and phenotypic variability has been a major focus in the population genetic literature. By providing differential access to the underlying genetic information, epigenetic variation could play an important role in the interaction between environmental and phenotypic variation. Using simulation, we model epigenetic plasticity during development by investigating the dynamics of genetic regulators of the epigenetic machinery that change the variance of the phenotype, while having no effect on the phenotype's mean. Previous studies have found that increased phenotypic variance is selected for if the environment is fluctuating. Here, we find that when a variance-increasing allele achieves a sufficiently high frequency, it can be out-competed by a variance-reducing allele, with the consequence that the population evolves to an equilibrium phenotypic variability. This equilibrium is shown to be robust to different initial conditions, but to depend heavily on parameters of the model, such as the mutation rate, the fitness landscape and the nature of the environmental fluctuation. Indeed, if there is no mutation at the genes controlling the variance of the phenotype, reduction of this variance is favoured.
PMCID: PMC3284130  PMID: 21849387
epigenetics; epigenetic variation; phenotypic variation; fluctuating environments; evolution
23.  Acute kidney injury and inflammatory immune reconstitution syndrome in mixed genotype (A/E) hepatitis B virus co-infection in HIV-associated lymphoma 
We report a first case of HIV-associated lymphoma (HAL) presenting with acute kidney injury (AKI) and inflammatory immune reconstitution syndrome (IRIS). A 39-year-old male, treated with nonsteroidal anti-inflammatory drugs (NSAIDs) for one month prior to admission, developed AKI, left testicular tumor, and recurrent swelling of the right parotid gland. A resected testicular tumor exhibited features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma. Renal biopsy showed hydro-degeneration of renal tubules, interstitial inflammatory cells, and a small number of lymphoma cells in the sub-capsule, compatible with acute interstitial nephritis. His renal dysfunction rapidly recovered following chemotherapy and combination antiretroviral therapy (cART). He developed pneumonia concomitantly with a decrease in HIV-RNA level and an increase in CD4+ cells after the first cycle of chemotherapy, which spontaneously resolved after the second cycle of chemotherapy without additional anti-infection drugs; thus, his pneumonia fulfilled the diagnostic criteria for IRIS. We suggest that IRIS may frequently develop during chemotherapy for HAL, but may be overlooked. He was coinfected with hepatitis B virus (HBV), which genotypes known as is associated with liver-related mortality and response to antiviral therapy; recently, an intimate interplay between HIV and HBV in the onset of lymphoma has been reported. Therefore, we addressed the HBV genotype in the patient. The analysis revealed that he exhibited a mixed genotype (A/E) not native to Japan and primarily found in Europe and North America or West Africa. These findings suggest that universal vaccination for juveniles against HBV is warranted in Japan.
PMCID: PMC3563184  PMID: 23411777
Hepatitis B virus; HIV; genotype; immune reconstitution inflammatory syndrome; acute kidney injury; ptosis
An important component of pathogen evolution at the population level is evolution within hosts. Unless evolution within hosts is very slow compared to the duration of infection, the composition of pathogen genotypes within a host is likely to change during the course of an infection, thus altering the composition of genotypes available for transmission as infection progresses. We develop a nested modeling approach that allows us to follow the evolution of pathogens at the epidemiological level by explicitly considering within-host evolutionary dynamics of multiple competing strains and the timing of transmission. We use the framework to investigate the impact of short-sighted within-host evolution on the evolution of virulence of human immunodeficiency virus (HIV), and find that the topology of the within-host adaptive landscape determines how virulence evolves at the epidemiological level. If viral reproduction rates increase significantly during the course of infection, the viral population will evolve a high level of virulence even though this will reduce the transmission potential of the virus. However, if reproduction rates increase more modestly, as data suggest, our model predicts that HIV virulence will be only marginally higher than the level that maximizes the transmission potential of the virus.
PMCID: PMC3906838  PMID: 24094332
Epidemiology; evolution; nested model; pathogen; transmission-virulence trade-off; virulence
25.  AIDS related systemic non-Hodgkin's lymphoma 
Sexually Transmitted Infections  2000;76(5):335-341.
Objective: To review the current literature on HIV associated non-Hodgkin's lymphoma.
Methods: A comprehensive Medline/Pubmed search of articles pertaining to HIV associated non-Hodgkin's lymphoma as well as personal experience from the treatment of over 200 patients at the Chelsea and Westminster Hospital, one of the largest centres for the management of HIV disease in Europe.
Conclusion: High grade B cell non-Hodgkin's lymphoma is the second commonest tumour affecting people with HIV. The incidence of this tumour is not declining following the introduction of highly active antiretroviral therapy. Chemotherapy has been employed with modest success in this group of patients; however, the prognosis remains worse than for immunocompetent patients. Advances in molecular genetics and virology have led to a greater understanding of the biology of these tumours. However, these advances have yet to be translated into improvements in the clinical management of patients with AIDS associated non-Hodgkin's lymphoma.
Key Words: AIDS; HIV; non-Hodgkin's lymphoma
PMCID: PMC1744226  PMID: 11141847

Results 1-25 (196791)