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1.  Co-Operative Additive Effects between HLA Alleles in Control of HIV-1 
PLoS ONE  2012;7(10):e47799.
HLA class I genotype is a major determinant of the outcome of HIV infection, and the impact of certain alleles on HIV disease outcome is well studied. Recent studies have demonstrated that certain HLA class I alleles that are in linkage disequilibrium, such as HLA-A*74 and HLA-B*57, appear to function co-operatively to result in greater immune control of HIV than mediated by either single allele alone. We here investigate the extent to which HLA alleles - irrespective of linkage disequilibrium - function co-operatively.
Methodology/Principal Findings
We here refined a computational approach to the analysis of >2000 subjects infected with C-clade HIV first to discern the individual effect of each allele on disease control, and second to identify pairs of alleles that mediate ‘co-operative additive’ effects, either to improve disease suppression or to contribute to immunological failure. We identified six pairs of HLA class I alleles that have a co-operative additive effect in mediating HIV disease control and four hazardous pairs of alleles that, occurring together, are predictive of worse disease outcomes (q<0.05 in each case). We developed a novel ‘sharing score’ to quantify the breadth of CD8+ T cell responses made by pairs of HLA alleles across the HIV proteome, and used this to demonstrate that successful viraemic suppression correlates with breadth of unique CD8+ T cell responses (p = 0.03).
These results identify co-operative effects between HLA Class I alleles in the control of HIV-1 in an extended Southern African cohort, and underline complementarity and breadth of the CD8+ T cell targeting as one potential mechanism for this effect.
PMCID: PMC3477121  PMID: 23094091
2.  Limited Immunogenicity of HIV CD8+ T-Cell Epitopes in Acute Clade C Virus Infection 
The Journal of Infectious Diseases  2011;204(5):768-776.
Background. Human immunodeficiency virus type 1 (HIV-1)–specific CD8+ responses contribute to the decline in acute peak viremia following infection. However, data on the relative immunogenicity of CD8+ T-cell epitopes during and after acute viremia are lacking.
Methods. We characterized CD8+ T-cell responses in 20 acutely infected, antiretroviral-naive individuals with HIV-1 subtype C infection using the interferon-γ enzyme-linked immunosorbent spot assay. Eleven of these had not fully seroconverted at the time of analysis. Viruses from plasma were sequenced within defined cytotoxic T-lymphocyte (CTL) cell epitopes for selected subjects.
Results. At approximately 28 days after estimated initial infection, CD8+ T-cell responses were directed against an average of 3 of the 410 peptides tested (range, 0–6); 2 individuals had no detectable responses at this time. At 18 weeks, the average number of peptides targeted had increased to 5 (range 0–11). Of the 56 optimal Gag CTL epitopes sequenced, 31 were wild-type in the infecting viruses, but only 11 of 31 elicited measurable CD8+ T-cell responses.
Conclusions. These data demonstrate that the majority of CD8+ responses are not elicited during acute HIV infection despite the presence of the cognate epitope in the infecting strain. There is a need to define factors that influence lack of induction of effective immune responses and the parameters that dictate immunodominance in acute infection.
PMCID: PMC3156105  PMID: 21844303
3.  Short Communication: CD8+ T Cell Polyfunctionality Profiles in Progressive and Nonprogressive Pediatric HIV Type 1 Infection 
AIDS Research and Human Retroviruses  2011;27(9):1005-1012.
Pediatric HIV-1 infection is characterized by rapid disease progression and without antiretroviral therapy (ART), more than 50% of infected children die by the age of 2 years. However, a small subset of infected children progresses slowly to disease in the absence of ART. This study aimed to identify functional characteristics of HIV-1-specific T cell responses that distinguish children with rapid and slow disease progression. Fifteen perinatally HIV-infected children (eight rapid and seven slow progressors) were longitudinally studied to monitor T cell polyfunctionality. HIV-1-specific interferon (IFN)-γ+ CD8+ T cell responses gradually increased over time but did not differ between slow and rapid progressors. However, polyfunctional HIV-1-specific CD8+ T cell responses, as assessed by the expression of four functions (IFN-γ, CD107a, TNF-α, MIP-1β), were higher in slow compared to rapid progressors (p=0.05) early in infection, and was associated with slower subsequent disease progression. These data suggest that the quality of the HIV-specific CD8+ T cell response is associated with the control of disease in children as has been shown in adult infection.
PMCID: PMC3332389  PMID: 21288139
4.  Lack of Association between HLA Class II Alleles and In Vitro Replication Capacities of Recombinant Viruses Encoding HIV-1 Subtype C Gag-Protease from Chronically Infected Individuals 
Journal of Virology  2012;86(2):1273-1276.
It is unknown whether favorable HLA class II alleles may attenuate HIV-1 through selection pressure in a manner similar to that of protective HLA class I alleles. We investigated the relationship between HLA class II alleles and in vitro replication capacities of recombinant viruses encoding HIV-1 subtype C Gag-protease from chronically infected individuals. No associations were found between individual alleles and lower replication capacity, suggesting no significant HIV-1 attenuation by HLA class II-restricted Gag-specific CD4+ T cell immune pressure.
PMCID: PMC3255856  PMID: 22090116
5.  Impairment of CD1d-Restricted Natural Killer T Cells in Chronic HIV Type 1 Clade C Infection 
Recent studies suggest that natural killer T (NKT) cells play a role in early antiviral pathogenesis and are rapidly depleted in chronic human immunodeficiency virus type 1 (HIV-1) clade B infection. We aimed to characterize the phenotypic and functional characteristics of NKT cells in HIV-1 clade C-infected Africans at different stages of HIV-1 disease. NKT cell frequencies, subsets, and ex vivo effector functions were assessed using multiparametric flow cytometry in a cross-sectional analysis of cryopreserved peripheral blood mononuclear cells from a cohort of 53 HIV-1 clade C chronically infected South African adults with CD4 T cell counts ranging from 94 to 839 cells/μl. We observed a significant decline of NKT cell numbers in advanced HIV-1 disease as well as activation and functional impairment of NKT cells in individuals with low CD4 T cell counts. The loss of NKT cells was largely driven by a reduction in the CD4+ and CD4–CD8– NKT cell subsets in advanced disease. These findings demonstrate significant impairment of the NKT cell compartment in progressive HIV-1 clade C disease that might play an important role in the modulation of immune function in HIV-1 infection.
PMCID: PMC3083726  PMID: 20942750
6.  Possession of HLA Class II DRB1*1303 Associates with Reduced Viral Loads in Chronic HIV-1 Clade C and B Infection 
The Journal of Infectious Diseases  2011;203(6):803-809.
Background.The HLA class II molecules play a central role in the generation of human immunodeficiency virus (HIV)–specific CD4+ T-helper cells, which are critical for the induction of cytotoxic CD8+ T cell responses. However, little is known about the impact of HLA class II alleles on HIV disease progression.
Methods.In this study we investigated the effect of HLA class II alleles on HIV disease outcome and HIV-specific T cell responses in a cohort of 426 antiretroviral therapy–naive, HIV-1 clade C–infected, predominantly female black South Africans.
Results.The HLA class II allele DRB1*1303 was independently associated with lower plasma viral loads in this population (P = .02), an association that was confirmed in a second cohort of 1436 untreated, HIV-1 clade B–infected, male European Americans, suggesting that DRB1*1303-mediated protection is independent of ethnicity, sex, and viral clade. Interestingly, DRB1*1303 carriage was not associated with an increased frequency of interferon (IFN) γ–positive HIV-specific CD4+ T cell responses.
Conclusions.These data demonstrate the independent effect of an HLA class II allele, DRB1*1303, on HIV disease progression, in the absence of increased IFN-γ–positive HIV-specific CD4+ T cell frequencies, suggesting that the protective activity of DRB1*1303 may be mediated via an alternative mechanism.
PMCID: PMC3071131  PMID: 21257739
7.  Gag-Protease-Mediated Replication Capacity in HIV-1 Subtype C Chronic Infection: Associations with HLA Type and Clinical Parameters▿ †  
Journal of Virology  2010;84(20):10820-10831.
The mechanisms underlying HIV-1 control by protective HLA class I alleles are not fully understood and could involve selection of escape mutations in functionally important Gag epitopes resulting in fitness costs. This study was undertaken to investigate, at the population level, the impact of HLA-mediated immune pressure in Gag on viral fitness and its influence on HIV-1 pathogenesis. Replication capacities of 406 recombinant viruses encoding plasma-derived Gag-protease from patients chronically infected with HIV-1 subtype C were assayed in an HIV-1-inducible green fluorescent protein reporter cell line. Viral replication capacities varied significantly with respect to the specific HLA-B alleles expressed by the patient, and protective HLA-B alleles, most notably HLA-B*81, were associated with lower replication capacities. HLA-associated mutations at low-entropy sites, especially the HLA-B*81-associated 186S mutation in the TL9 epitope, were associated with lower replication capacities. Most mutations linked to alterations in replication capacity in the conserved p24 region decreased replication capacity, while most in the highly variable p17 region increased replication capacity. Replication capacity also correlated positively with baseline viral load and negatively with baseline CD4 count but did not correlate with the subsequent rate of CD4 decline. In conclusion, there is evidence that protective HLA alleles, in particular HLA-B*81, significantly influence Gag-protease function by driving sequence changes in Gag and that conserved regions of Gag should be included in a vaccine aiming to drive HIV-1 toward a less fit state. However, the long-term clinical benefit of immune-driven fitness costs is uncertain given the lack of correlation with longitudinal markers of disease progression.
PMCID: PMC2950592  PMID: 20702636
8.  Immunodominant HIV-1-specific HLA-B- and HLA-C-restricted CD8+ T cells do not differ in polyfunctionality 
Virology  2010;405(2-3):483-491.
HIV-1 specific HLA-B-restricted CD8+ T cell responses differ from HLA-C-restricted responses in antiviral effectiveness. To investigate possible reasons for these differences, we characterized the frequency and polyfunctionality of immmunodominant HLA-B*57/B5801- and HLA-Cw*07-restricted CD8+ T cells occurring concurrently in nine study subjects assessing IFN-γ, TNF-α, IL-2, MIP-1β, and CD107a by flow cytometry and analyzed sequence variation in targeted epitopes. HLA-B*57/5801 and HLA-Cw*07 restricted CD8+ T cells did not differ significantly in polyfunctionality (p = 0.84). Possession of three or more functions correlated positively with CD4+ T cell counts (r = 0.85; p = 0.006) and monofunctional CD8+ T cells inversely correlated with CD4 cell counts (r = −0.79; p = 0.05). There were no differences in polyfunctionality of CD8+ T cells specific to wildtype versus mutated epitopes. These results suggest that loss of polyfunctionality and increase in monofunctional HIV-1-specific CD8+ T cells are associated with disease progression independent of restricting HLA allele. Furthermore, sequence variation does not appear to significantly impact CD8+ T cell polyfunctionality in chronic HIV-1 infection.
PMCID: PMC2954365  PMID: 20638093
HLA-B*57/5801; HLA-C; HIV-1 chronic infection; CD8+ T cells; Polyfunctionality
9.  Impact of select immunologic and virologic biomarkers on CD4 decline in chronic HIV-1 subtype C infection: Results from Sinikithemba longitudinal population-based cohort, Durban, South Africa 
The extent to which immunologic and clinical biomarkers influence HIV outcomes remains incompletely characterized, particularly for non-B subtypes. Based on data supporting in vitro HIV protein-specific CD8 T-lymphocyte responses as correlates of immune control in cross-sectional studies, we assessed the relationship of these responses, along with established HIV biomarkers, with rates of CD4 decline in subtype-C infection.
Bi-variate and multivariate mixed effects models were used to assess the relationship of baseline CD4, plasma viral load (pVL), HLA class I alleles, and HIV protein-specific CD8 responses with rate of CD4 decline in a longitudinal population-based cohort of 300 therapy-naïve, chronically infected adults with baseline CD4>200 cells/mm3 and pVL>500 copies/ml, over a median 25 months follow-up.
In bi-variate analyses, baseline CD4, pVL and possession of a protective HLA allele correlated significantly with rate of CD4 decline. No relationship was observed between HIV protein-specific CD8 responses and CD4 decline. Results from multivariate models, incorporating baseline CD4 (201–350 and >350), pVL (≤100,000 and >100,000), HLA (protective vs. not), yielded the ability to discriminate CD4 declines over a 10-fold range: the highest rate of decline was observed among individuals with CD4>350, pVL>100,000 with no protective HLA alleles (−59 cells/mm3/year), while the slowest decline was observed in individuals with CD4 201–350, pVL≤100,000 and a protective allele (−6 cells/mm3/year).
The combination of plasma viral load and HLA class I type, but not in vitro HIV protein-specific CD8 responses, differentiates rates of CD4 decline in chronic subtype-C infection better than either marker alone.
PMCID: PMC2777678  PMID: 19663693
HIV subtype C; disease progression; CD4 decline; HLA class I; HIV-specific CTL responses
10.  Impact of HLA in Mother and Child on Disease Progression of Pediatric Human Immunodeficiency Virus Type 1 Infection▿  
Journal of Virology  2009;83(19):10234-10244.
A broad Gag-specific CD8+ T-cell response is associated with effective control of adult human immunodeficiency virus (HIV) infection. The association of certain HLA class I molecules, such as HLA-B*57, -B*5801, and -B*8101, with immune control is linked to mutations within Gag epitopes presented by these alleles that allow HIV to evade the immune response but that also reduce viral replicative capacity. Transmission of such viruses containing mutations within Gag epitopes results in lower viral loads in adult recipients. In this study of pediatric infection, we tested the hypothesis that children may tend to progress relatively slowly if either they themselves possess one of the protective HLA-B alleles or the mother possesses one of these alleles, thereby transmitting a low-fitness virus to the child. We analyzed HLA type, CD8+ T-cell responses, and viral sequence changes for 61 mother-child pairs from Durban, South Africa, who were monitored from birth. Slow progression was significantly associated with the mother or child possessing one of the protective HLA-B alleles, and more significantly so when the protective allele was not shared by mother and child (P = 0.007). Slow progressors tended to make CD8+ T-cell responses to Gag epitopes presented by the protective HLA-B alleles, in contrast to progressors expressing the same alleles (P = 0.07; Fisher's exact test). Mothers expressing the protective alleles were significantly more likely to transmit escape variants within the Gag epitopes presented by those alleles than mothers not expressing those alleles (75% versus 21%; P = 0.001). Reversion of transmitted escape mutations was observed in all slow-progressing children whose mothers possessed protective HLA-B alleles. These data show that HLA class I alleles influence disease progression in pediatric as well as adult infection, both as a result of the CD8+ T-cell responses generated in the child and through the transmission of low-fitness viruses by the mother.
PMCID: PMC2748050  PMID: 19605475
11.  Immunodominant HIV-1 Cd4+ T Cell Epitopes in Chronic Untreated Clade C HIV-1 Infection 
PLoS ONE  2009;4(4):e5013.
A dominance of Gag-specific CD8+ T cell responses is significantly associated with a lower viral load in individuals with chronic, untreated clade C human immunodeficiency virus type 1 (HIV-1) infection. This association has not been investigated in terms of Gag-specific CD4+ T cell responses, nor have clade C HIV-1–specific CD4+ T cell epitopes, likely a vital component of an effective global HIV-1 vaccine, been identified.
Methodology/Principal Findings
Intracellular cytokine staining was conducted on 373 subjects with chronic, untreated clade C infection to assess interferon-gamma (IFN-γ) responses by CD4+ T cells to pooled Gag peptides and to determine their association with viral load and CD4 count. Gag-specific IFN-γ–producing CD4+ T cell responses were detected in 261/373 (70%) subjects, with the Gag responders having a significantly lower viral load and higher CD4 count than those with no detectable Gag response (p<0.0001 for both parameters). To identify individual peptides targeted by HIV-1–specific CD4+ T cells, separate ELISPOT screening was conducted on CD8-depleted PBMCs from 32 chronically infected untreated subjects, using pools of overlapping peptides that spanned the entire HIV-1 clade C consensus sequence, and reconfirmed by flow cytometry to be CD4+ mediated. The ELISPOT screening identified 33 CD4+ peptides targeted by 18/32 patients (56%), with 27 of the 33 peptides located in the Gag region. Although the breadth of the CD4+ responses correlated inversely with viral load (p = 0.015), the magnitude of the response was not significantly associated with viral load.
These data indicate that in chronic untreated clade C HIV-1 infection, IFN-γ–secreting Gag-specific CD4+ T cell responses are immunodominant, directed at multiple distinct epitopes, and associated with viral control.
PMCID: PMC2661367  PMID: 19352428
13.  Compensatory Mutation Partially Restores Fitness and Delays Reversion of Escape Mutation within the Immunodominant HLA-B*5703-Restricted Gag Epitope in Chronic Human Immunodeficiency Virus Type 1 Infection▿  
Journal of Virology  2007;81(15):8346-8351.
HLA-B*5703 is associated with effective immune control in human immunodeficiency virus type 1 (HIV-1) infection. Here we describe an escape mutation within the immunodominant HLA-B*5703-restricted epitope in chronic HIV-1 infection, KAFSPEVIPMF (Gag 162-172), and demonstrate that this mutation reduces viral replicative capacity. Reversion of this mutation following transmission to HLA-B*5703-negative recipients was delayed by the compensatory mutation S165N within the same epitope. These data may help explain the observed association between HLA-B*5703 and long-term control of viremia.
PMCID: PMC1951305  PMID: 17507468

Results 1-13 (13)