HIV-specific CD8+ T cell responses in infected infacts enrolled on a study of early highly active antiretroviral treatment (HAART) and supervised treatment interruption (STI).

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.The manifestation of HIV-1 infection is different in children and adults. Most of the children who acquire HIV perinatally progress to disease within the first two years of life, while adults can remain asymptomatic for up to ten years. However, a small minority group of children can control the virus for years in the absence of antiretroviral therapy. We characterized CD8+ T cell responses critical for the containment of HIV infection in a cohort of infants HIV infected from birth using IFN- γ ELISPOT, multicolour flow cytometry and viral sequencing of the Gag protein. We investigated whether the age at the time of infection, specificity and functionality of the generated responses, genetic make up and the maternal immune responses to HIV, influenced disease progression in the child. We found that the majority of in-utero infected infants mounted CD8+ T cell responses from the first days of life. In contrast to chronically infected children or adults, the specificity of the initial response in acutely infected infants was directed towards Env and Rev proteins and CD4+ T cell responses were minimal during the first 6 months of life. Slow progression to disease was associated with possession of one of the protective HLA-B alleles by either the mother or the child (P=0.007) and targeting of Gag epitopes presented by the protective HLA-B alleles. Mothers who expressed protective alleles but whose children did not possess these alleles, transmitted less fit viruses that benefited their children. Furthermore, slow progressor children had more polyfunctional CD8+ T cell responses in early infection when compared to rapid progressors (P=0.05). The ability of infants to induce CD8+ T cell responses early in life is encouraging for vaccine interventions. The differences in the specificity of the initial responses between adults and children, insufficient priming of these responses as a result of minimal CD4+ T cell help during infancy and possession of non-protective HLA alleles shared between mother and child, may explain the rapid disease progression generally noted in most infants. However, slow progression to disease in the minority group of children may be attributed to functional capacity of the CD8+ T cells generated by the child, mediation by protective HLA alleles, acquisition of low fitness viruses from the mother or de novo attenuation of the virus by the child’s own immune responses

Neutrophil Effector Functions Are Not Impaired in Duffy Antigen Receptor for Chemokines (DARC)-Null Black South Africans

Neutrophils are well-recognized for their pathogen killing mechanisms and disorders of neutrophil count and function are associated with recurrent infections. The Duffy Antigen Receptor for Chemokines (DARC)-null genotype is predominant in sub-Saharan African ancestry populations and is the major genetic determinant of benign ethnic neutropenia which has been associated with increased risk of Human Immunodeficiency Virus (HIV)-1 acquisition and mother-to-child transmission. However, the impact of DARC-null-linked neutropenia on HIV disease progression remains controversial. While the DARC-null genotype is associated with low numbers of circulating neutrophils, the effects of the polymorphism on neutrophil functions is unknown. We investigated the impact of the DARC-null trait and lower absolute neutrophil counts (ANCs) on key neutrophil effector functions [proteolytic activity within the phagosome following Fc receptor-mediated phagocytosis, reactive oxygen species (ROS) production, and neutrophil extracellular trap (NET) formation] in 20 HIV negative and 22 HIV-1 chronically infected black South Africans. Phagosome maturation was measured by flow cytometry following Fc-mediated uptake of IgG opsonized beads; ROS production was measured by chemi-luminescence after activation of neutrophils with phorbol 12-myristate 13-acetate (PMA). Activated neutrophils were also visualized by fluorescent microscopy for NET quantification. Study subjects were genotyped for the DARC trait using TaqMan allelic discrimination assays and ANCs were measured by full blood count. As expected, the DARC-null polymorphism was highly prevalent in our participant cohort (69%) and was strongly associated with lower ANCs in uninfected (p = 0.0007) and HIV-1 infected (p = 0.03) subjects. We observed enhanced proteolytic activity within the phagosome in the absence of DARC at 10 min (p = 0.05 and p = 0.009) and 60 min (p = 0.05 and p = 0.07) in uninfected and HIV-1 infected subjects, respectively. ROS was unaffected by DARC trait irrespective of HIV status. Furthermore, formation of NETs was reduced in neutrophils from DARC-null subjects (p = 0.04) following prolonged in vitro stimulation, but only in HIV-1 infected subjects. The data indicate differential neutrophil function in the absence of DARC that may be moderately modulated by HIV-1 infection but overall, the data suggest that DARC-null trait is not deleterious to neutrophil effector functions in African populations

Interleukin 1-Beta (IL-1β) production by innate cells following TLR stimulation correlates with TB recurrence in art-treated HIV-infected patients.

CAPRISA, 2017.Abstract available

Low Immune Activation in Early Pregnancy Is Associated With Preterm But Not Small-for-gestational-age Delivery in Women Infected With Human Immunodeficiency Virus Initiating Antiretroviral Therapy in Pregnancy: A Prematurity Immunology in HIV-infected Mothers and their Infants Study (PIMS) Case-control Study in Cape Town, South Africa.

BACKGROUND: Mechanisms underlying an association between human immunodeficiency virus (HIV) or antiretroviral therapy (ART) during pregnancy with risk of preterm delivery (PTD) and small-for-gestational-age (SGA) remain unclear. We explored the association between cellular immune activation and PTD or SGA in women with HIV initiating ART during or before pregnancy. METHODS: Women with HIV enrolled at median 15 weeks' gestation, were analyzed for immune markers, and matched on ART initiation timing (15 women initiated pre- and 15 during pregnancy). There were 30 PTD (delivery 25th percentile) as outcomes. Lymphocytes, monocytes, and dendritic cell populations and their activation status or functionality were enumerated by flow cytometry. RESULTS: PTD cases initiating ART in pregnancy showed decreased CD8+ T cell, monocyte, and dendritic cell activation; increased classical (CD14+CD16-) and intermediate (CD14+CD16+) monocyte frequencies; and decreased inflammatory monocytes (CD14dimCD16+) compared with SGA cases and term controls (all P < .05). Allowing for baseline viral load, the immune markers remained significantly associated with PTD but only in women initiating ART in pregnancy. Lower monocyte activation was predictive of PTD. TLR ligand-induced interferon-α and macrophage inflammatory protein-1β levels in monocytes were significantly lower in PTD women initiating ART in pregnancy. CONCLUSION: Low immune activation, skewing toward anti-inflammatory monocytes, and lower monocyte cytokine production in response to TLR ligand stimulation were associated with PTD but not SGA among women initiating ART in, but not before, pregnancy, suggesting immune anergy to microbial stimulation as a possible underlying mechanism for PTD in women initiating ART in pregnancy

Transmission and accumulation of CTL escape variants drive negative associations between HIV polymorphisms and HLA

Human immunodeficiency virus (HIV)-1 amino acid sequence polymorphisms associated with expression of specific human histocompatibility leukocyte antigen (HLA) class I alleles suggest sites of cytotoxic T lymphocyte (CTL)-mediated selection pressure and immune escape. The associations most frequently observed are between expression of an HLA class I molecule and variation from the consensus sequence. However, a substantial number of sites have been identified in which particular HLA class I allele expression is associated with preservation of the consensus sequence. The mechanism behind this is so far unexplained. The current studies, focusing on two examples of “negatively associated” or apparently preserved epitopes, suggest an explanation for this phenomenon: negative associations can arise as a result of positive selection of an escape mutation, which is stable on transmission and therefore accumulates in the population to the point at which it defines the consensus sequence. Such negative associations may only be in evidence transiently, because the statistical power to detect them diminishes as the mutations accumulate. If an escape variant reaches fixation in the population, the epitope will be lost as a potential target to the immune system. These data help to explain how HIV is evolving at a population level. Understanding the direction of HIV evolution has important implications for vaccine development

Slow progression of pediatric HIV associates with early CD8+ T cell PD-1 expression and a stem-like phenotype

HIV non-progression despite persistent viraemia is rare among antiretroviral therapy (ART)-naïve adults, but relatively common among ART-naïve children. Previous studies indicate that ART-naïve paediatric slow-progressors (PSPs) adopt immune evasion strategies similar to those described in the SIV natural hosts. However, the mechanisms underlying this immunophenotype are not well understood. In a cohort of early-treated infants who underwent analytical treatment interruption (ATI) after 12 months of ART, expression of PD-1 on CD8+ T-cells immediately prior to ATI was the main predictor of slow progression during ATI (r=0.77, p=0.002). PD-1+ CD8+ T-cell frequency was also negatively correlated with CCR5 (r=-0.74, p=0.005) and HLA-DR (r=-0.63, p=0.02) expression on CD4+ T-cells and predicted stronger HIV-specific T-lymphocyte responses. In the CD8+ T-cell compartment of PSPs, we identified an enrichment of stem-like TCF-1+PD-1+ memory cells, whereas paediatric progressors and viraemic adults were populated with a terminally exhausted PD-1+CD39+ population. TCF-1+PD-1+ expression on CD8+ T-cells was associated with higher proliferative activity (r=0.41, p=0.03) and stronger Gag-specific effector functionality. These data prompt the hypothesis that the proliferative burst potential of stem-like HIV-specific cytotoxic cells could be exploited in therapeutic strategies to boost the antiviral response and facilitate remission in early-ART-treated infants with a preserved and non-exhausted T-cell compartment

CD8+ T cell breadth and ex vivo virus inhibition capacity distinguish between viremic controllers with and without protective HLA class I alleles.

CAPRISA, 2016.Abstract available in PDF file

Slow progression of pediatric HIV associates with early CD8 + T cell PD-1 expression and a stem-like phenotype

HIV nonprogression despite persistent viremia is rare among adults who are naive to antiretroviral therapy (ART) but relatively common among ART-naive children. Previous studies indicate that ART-naive pediatric slow progressors (PSPs) adopt immune evasion strategies similar to those described in natural hosts of SIV. However, the mechanisms underlying this immunophenotype are not well understood. In a cohort of early-treated infants who underwent analytical treatment interruption (ATI) after 12 months of ART, expression of PD-1 on CD8 + T cells immediately before ATI was the main predictor of slow progression during ATI. PD-1 + CD8 + T cell frequency was also negatively correlated with CCR5 and HLA-DR expression on CD4 + T cells and predicted stronger HIV-specific T lymphocyte responses. In the CD8 + T cell compartment of PSPs, we identified an enrichment of stem-like TCF-1 + PD-1 + memory cells, whereas pediatric progressors and viremic adults had a terminally exhausted PD-1 + CD39 + population. TCF-1 + PD-1 + expression on CD8 + T cells was associated with higher proliferative activity and stronger Gag-specific effector functionality. These data prompted the hypothesis that the proliferative burst potential of stem-like HIV-specific cytotoxic cells could be exploited in therapeutic strategies to boost the antiviral response and facilitate remission in infants who received early ART with a preserved and nonexhausted T cell compartment

Immunodominant HIV-1 Cd4+ T Cell Epitopes in Chronic Untreated Clade C HIV-1 Infection

Background: 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. Conclusions/Significance: 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

Discordant Impact of HLA on Viral Replicative Capacity and Disease Progression in Pediatric and Adult HIV Infection

HLA class I polymorphism has a major influence on adult HIV disease progression. An important mechanism mediating this effect is the impact on viral replicative capacity (VRC) of the escape mutations selected in response to HLA-restricted CD8+ T-cell responses. Factors that contribute to slow progression in pediatric HIV infection are less well understood. We here investigate the relationship between VRC and disease progression in pediatric infection, and the effect of HLA on VRC and on disease outcome in adult and pediatric infection. Studying a South African cohort of >350 ART-naïve, HIV-infected children and their mothers, we first observed that pediatric disease progression is significantly correlated with VRC. As expected, VRCs in mother-child pairs were strongly correlated (p = 0.004). The impact of the protective HLA alleles, HLA-B*57, HLA-B*58:01 and HLA-B*81:01, resulted in significantly lower VRCs in adults (p<0.0001), but not in children. Similarly, in adults, but not in children, VRCs were significantly higher in subjects expressing the disease-susceptible alleles HLA-B*18:01/45:01/58:02 (p = 0.007). Irrespective of the subject, VRCs were strongly correlated with the number of Gag CD8+ T-cell escape mutants driven by HLA-B*57/58:01/81:01 present in each virus (p = 0.0002). In contrast to the impact of VRC common to progression in adults and children, the HLA effects on disease outcome, that are substantial in adults, are small and statistically insignificant in infected children. These data further highlight the important role that VRC plays both in adult and pediatric progression, and demonstrate that HLA-independent factors, yet to be fully defined, are predominantly responsible for pediatric non-progression