Sonya L. Heath

Initial antibodies binding to HIV-1 gp41 in acutely infected subjects are polyreactive and highly mutated

Many HIV-1 envelope-reactive antibodies shortly after HIV-1 transmission may arise from crow-reactive memory B cells previously stimulated by non-HIV-1 host or microbial antigens

Immune Suppression by Neutrophils in HIV-1 Infection: Role of PD-L1/PD-1 Pathway

HIV-1 infection is associated with a progressive loss of T cell functional capacity and reduced responsiveness to antigenic stimuli. The mechanisms underlying T cell dysfunction in HIV-1/AIDS are not completely understood. Multiple studies have shown that binding of program death ligand 1 (PD-L1) on the surface of monocytes and dendritic cells to PD-1 on T cells negatively regulates T cell function. Here we show that neutrophils in the blood of HIV-1-infected individuals express high levels of PD-L1. PD-L1 is induced by HIV-1 virions, TLR-7/8 ligand, bacterial lipopolysaccharide (LPS), and IFNα. Neutrophil PD-L1 levels correlate with the expression of PD-1 and CD57 on CD4+ and CD8+ T cells, elevated levels of neutrophil degranulation markers in plasma, and increased frequency of low density neutrophils (LDNs) expressing the phenotype of granulocytic myeloid-derived suppressor cells (G-MDSCs). Neutrophils purified from the blood of HIV-1-infected patients suppress T cell function via several mechanisms including PD-L1/PD-1 interaction and production of reactive oxygen species (ROS). Collectively, the accumulated data suggest that chronic HIV-1 infection results in an induction of immunosuppressive activity of neutrophils characterized by high expression of PD-L1 and an inhibitory effect on T cell function.

Interleukin-21-Producing HIV-1-Specific CD8 T Cells Are Preferentially Seen in Elite Controllers

ABSTRACT A hallmark of human immunodeficiency virus type 1 (HIV-1) pathogenesis is the rapid loss of CD4 T cells leading to generalized immune dysfunction, including an exhausted CD8 T cell phenotype. Understanding the necessary factors that govern the functional quality and protective potential of antiviral T cell responses would facilitate rational vaccine design and improve therapeutic strategies to combat persistent infections. Mouse models of chronic viral infection demonstrate that interleukin-21 (IL-21), produced primarily by CD4 T cells, is required for the generation and maintenance of functionally competent CD8 T cells and viral containment. We reasoned that preserved IL-21 production during HIV-1 infection would be associated with enhanced CD8 T cell function, allowing improved viral control. Here we analyzed the ability of CD4 and CD8 T cells to produce several cytokines in addition to IL-21 ex vivo following stimulation with overlapping HIV-1 peptides. Both CD4 and CD8 T cells were able to produce IL-21 in response to HIV-1 infection, with the latter cell type more closely associated with viral control. Furthermore, IL-21-producing HIV-1-specific CD4 T cells (compared to those producing other cytokines) were the best indicator of functional CD8 T cells. Our results demonstrate that HIV-1-specific IL-21-producing CD8 T cells are induced following primary infection and enriched in elite controllers, suggesting a critical role for these cells in the maintenance of viremia control.

CD8 T cell response and evolutionary pressure to HIV-1 cryptic epitopes derived from antisense transcription

Retroviruses pack multiple genes into relatively small genomes by encoding several genes in the same genomic region with overlapping reading frames. Both sense and antisense HIV-1 transcripts contain open reading frames for known functional proteins as well as numerous alternative reading frames (ARFs). At least some ARFs have the potential to encode proteins of unknown function, and their antigenic properties can be considered as cryptic epitopes (CEs). To examine the extent of active immune response to virally encoded CEs, we analyzed human leukocyte antigen class I–associated polymorphisms in HIV-1 gag, pol, and nef genes from a large cohort of South Africans with chronic infection. In all, 391 CEs and 168 conventional epitopes were predicted, with the majority (307; 79%) of CEs derived from antisense transcripts. In further evaluation of CD8 T cell responses to a subset of the predicted CEs in patients with primary or chronic infection, both sense- and antisense-encoded CEs were immunogenic at both stages of infection. In addition, CEs often mutated during the first year of infection, which was consistent with immune selection for escape variants. These findings indicate that the HIV-1 genome might encode and deploy a large potential repertoire of unconventional epitopes to enhance vaccine-induced antiviral immunity.

Interleukin-2 Production by Polyfunctional HIV-1-Specific CD8 T-cells is Associated with Enhanced Viral Suppression

Background: Assays to measure the induction of HIV-1-specific CD8 T-cell responses often rely on measurements of indirect effector function such as chemokine and cytokine production, which may not reflect direct elimination of an invading pathogen. Assessment of the functional ability of CD8 T cells to suppress HIV-1 replication has been viewed as a surrogate marker of an effectual immune response. To further investigate this, we measured the capacity of virus-specific CD8 T cells to inhibit HIV-1 replication in an in vitro suppression assay. Methods: We expanded 15 epitope-specific CD8 T-cell lines from peripheral blood mononuclear cells of chronically HIV--infected progressors (n = 5) and controllers (n = 4) who were not on antiretroviral therapy. Cell lines were tested for their ability to produce effector molecules (CD107a, IL-2, IFN-γ, TNF-α, perforin) and suppress virus replication in autologous CD4 T cells. Results: CD8 T-cell lines from both progressors and controllers had largely similar effector function profiles as determined by intracellular cytokine staining. In contrast, we observed that CD8 T-cell lines derived from controllers show enhanced virus suppression when compared with progressors. Virus suppression was mediated in an major histocompatibility complex-dependent manner and found to correlate with a polyfunctional IL-2+ CD8 T-cell response. Conclusions: Using a sensitive in vitro suppression assay, we demonstrate that CD8 T-cell-mediated suppression of HIV-1 replication is a marker of HIV-1 control. Suppressive capacity was found to correlate with polyfunctional IL-2 production. Assessment of CD8 T-cell-mediated suppression may be an important tool to evaluate vaccine-induced responses.

Functionally Competent Antigen-Specific CD127hi Memory CD8+ T Cells Are Preserved Only in HIV-Infected Individuals Receiving Early Treatment

The importance of functional CD4+ T cells and antigen control in the maintenance of CD127 expression on antigen-specific CD8+ T cells is poorly understood in humans. We compared CD127 expression on antigen-specific CD8+ T cells in 4 groups of human immunodeficiency virus (HIV)-infected patients. This analysis demonstrated that HIV-specific CD8+ CD127(hi) T cells are maintained as long-lived memory cells only in HIV-infected individuals treated early with antiretroviral therapy (ART). This population of CD127(hi) T cells fluctuates with viral load (VL) such that the antigen-specific T cell pool oscillates from a CD127(hi) memory to a CD127(lo) effector phenotype depending on the levels of plasma VL. In individuals with chronic infection, the CD127(hi) pool diminishes or is lost with time despite virologic control while receiving ART. These studies show that functionally competent subsets of antigen-specific memory CD8+ T cells in HIV-infected individuals are maintained but only if control of viremia is attained early during the course of infection.

HIV-Specific CD8+ T Cells from Elite Controllers Are Primed for Survival

ABSTRACT HIV-specific cytotoxic T lymphocytes (CTL) are preferentially primed for apoptosis, and this may represent a viral escape mechanism. We hypothesized that HIV-infected individuals that control virus to undetectable levels without antiretroviral therapy (ART) (elite controllers [EC]) have the capacity to upregulate survival factors that allow them to resist apoptosis. To address this, we performed cross-sectional and longitudinal analysis of proapoptotic (cleaved caspase-3) and antiapoptotic (Bcl-2) markers of cytomegalovirus (CMV) and HIV-specific CD8 T cells in a cohort of HIV-infected subjects with various degrees of viral control on and off ART. We demonstrated that HIV-specific CTL from EC are more resistant to apoptosis than those with pharmacologic control (successfully treated patients [ST]), despite similar in vivo conditions. Longitudinal analysis of chronically infected persons starting ART revealed that the frequency of HIV-specific T cells prone to death decreased, suggesting that this phenotype is partially reversible even though it never achieves the levels present in EC. Elucidating the apoptotic factors contributing to the survival of CTL in EC is paramount to our development of effective HIV-1 vaccines. Furthermore, a better understanding of cellular markers that can be utilized to predict response durability in disease- or vaccine-elicited responses will advance the field.

Association of Macrophage Inflammation Biomarkers With Progression of Subclinical Carotid Artery Atherosclerosis in HIV-Infected Women and Men

Background Monocytes and monocyte-derived macrophages promote atherosclerosis through increased inflammation and vascular remodeling. This may be especially true in chronic human immunodeficiency virus (HIV) infection. Methods We examined 778 women (74% HIV+) in the Womens Interagency HIV Study and 503 men (65% HIV+) in the Multicenter AIDS Cohort Study who underwent repeated B-mode carotid artery ultrasound imaging in 2004-2013. We assessed baseline associations of the serum macrophage inflammation markers soluble (s)CD163, sCD14, galectin-3 (Gal-3), and Gal-3 binding protein (Gal-3BP) with carotid plaque formation (focal intima-media thickness >1.5 mm) over 7 years. Results Marker levels were higher in HIV+ persons versus HIV- persons. Presence of focal plaque increased over time: from 8% to 15% in women, and 24% to 34% in men. After adjustment for demographic, behavioral, and cardiometabolic factors, and CRP and interleukin-6, each standard deviation increase in sCD14 was associated with increased plaque formation (risk ratio [RR] 1.24, 95% confidence interval [CI] 1.07-1.43). This pattern was consistentby sex. sCD163 was associated with plaque formation in virally suppressed HIV+ men (RR 1.52, 95% CI 1.04-2.22); Gal-3BP and Gal-3 were not associated with increased plaque. Conclusions sCD14 and sCD163 may play important roles in atherogenesis among HIV+ persons.

HLA Class-II Associated HIV Polymorphisms Predict Escape from CD4+ T Cell Responses

Antiretroviral therapy, antibody and CD8+ T cell-mediated responses targeting human immunodeficiency virus-1 (HIV-1) exert selection pressure on the virus necessitating escape; however, the ability of CD4+ T cells to exert selective pressure remains unclear. Using a computational approach on HIV gag/pol/nef sequences and HLA-II allelic data, we identified 29 HLA-II associated HIV sequence polymorphisms or adaptations (HLA-AP) in an African cohort of chronically HIV-infected individuals. Epitopes encompassing the predicted adaptation (AE) or its non-adapted (NAE) version were evaluated for immunogenicity. Using a CD8-depleted IFN-γ ELISpot assay, we determined that the magnitude of CD4+ T cell responses to the predicted epitopes in controllers was higher compared to non-controllers (p<0.0001). However, regardless of the group, the magnitude of responses to AE was lower as compared to NAE (p<0.0001). CD4+ T cell responses in patients with acute HIV infection (AHI) demonstrated poor immunogenicity towards AE as compared to NAE encoded by their transmitted founder virus. Longitudinal data in AHI off antiretroviral therapy demonstrated sequence changes that were biologically confirmed to represent CD4+ escape mutations. These data demonstrate an innovative application of HLA-associated polymorphisms to identify biologically relevant CD4+ epitopes and suggests CD4+ T cells are active participants in driving HIV evolution.

CD8 T-cell proliferative capacity is compromised in primary HIV-1 infection.

Understanding the correlates of immunity that control HIV-1 infection is imperative to our understanding of HIV-1 disease and vaccine development. HIV-1-specific cytotoxic T lymphocytes are fundamental to the control of viremia; however, which T-cell repertoire components enact this control remains unclear. We hypothesize that polyfunctional HIV-1-specific CD8 T cells capable of viral control are present in most patients early in infection and these cells are distinguished by their ability to secrete interleukin (IL)-2 and proliferate. We examined HIV-1-specific CD8 T-cell proliferation and cytokine secretion in primary HIV-1 infection (PHI) using known HIV-1 cytotoxic T-cell epitopes to exclude CD4 bystander effect. We found that only a subset of patients with PHI demonstrated “CD4-independent” CD8 proliferation ex vivo. The remainder of the patients lacked HIV-1-specific CD8 T cells with proliferative capacity, even after the addition of exogenous IL-2. Among the proliferators, IL-2 production from the total HIV-specific CD8 T-cell population correlated with proliferation. Surprisingly, though, we did not routinely detect both IL-2 secretion and proliferative capacity from the same antigen-specific CD8 T cells. Thus, there are distinct and heterogeneous populations of CD8 T cells, phenotypically characterized by either proliferation or IL-2 secretion and few with dual capacity. Generation of these responses may be an important measure of HIV-1 control but are not universal after PHI. Furthermore, the heterogeneity of this population suggests that a simple measure of an effective vaccine response remains elusive.