A significant challenge to HIV eradication is the elimination of viral reservoirs in germinal center (GC) T follicular helper (Tfh) cells. However, GCs are considered to be immune privileged for antiviral CD8 T cells. Here, we show a population of simian immunodeficiency virus (SIV)-specific CD8 T cells express CXCR5 (C-X-C chemokine receptor type 5, a chemokine receptor required for homing to GCs) and expand in lymph nodes (LNs) following pathogenic SIV infection in a cohort of vaccinated macaques. This expansion was greater in animals that exhibited superior control of SIV. The CXCR5+ SIV-specific CD8 T cells demonstrated enhanced polyfunctionality, restricted expansion of antigen-pulsed Tfh cells in vitro,and possessed a unique gene expression pattern related to Tfh and Th2 cells. The increase in CXCR5+ CD8 T cells was associated with the presence of higher frequencies of SIV-specific CD8 T cells in the GC. Following TCR-driven stimulation in vitro, CXCR5+ but not CXCR5– CD8 T cells generated both CXCR5+ as well as CXCR5– cells. However, the addition of TGF-β to CXCR5– CD8 T cells induced a population of CXCR5+ CD8 T cells, suggesting that this cytokine may be important in modulating these CXCR5+ CD8 T cells in vivo. Thus, CXCR5+ CD8 T cells represent a unique subset of antiviral CD8 T cells that expand in LNs during chronic SIV infection and may play a significant role in the control of pathogenic SIV infection.

Chronic HIV infection is associated with accumulation of germinal center T follicular helper cells (GC-Tfh) in the lymphoid tissue. The GC-Tfh cells can be heterogeneous based on the expression of chemokine receptors associated with T helper lineages such as CXCR3 (Th1), CCR4 (Th2), and CCR6 (Th17). However, the heterogeneous nature of GC-Tfh cells in the lymphoid tissue and its association with viral persistence and antibody production during chronic SIV/HIV infection is not known. To address this, here we characterized the expression of CXCR3, CCR4, and CCR6 on GC-Tfh in lymph nodes following SIVmac251 infection in rhesus macaques (RMs). In SIV naïve RM, only a small fraction of GC-Tfh expressed CXCR3, CCR4 and CCR6. However, during chronic SIV infection, the majority of GC-Tfh cells expressed CXCR3, while the proportion of CCR4+ cells did not change and CCR6+ cells decreased. CXCR3+ but not CXCR3− GC-Tfh produced IFN-γ (Th1 cytokine) and IL-21 (Tfh cytokine) while both subsets expressed CD40L following stimulation. Immunohistochemistry analysis demonstrated an accumulation of CD4+ IFN-γ+ T cells within the hyperplastic follicles during chronic SIV infection. CXCR3+ GC-Tfh also expressed higher levels of ICOS, CCR5 and α4β7, contained more copies of SIV DNA compared to CXCR3− GC-Tfh cells. However, both CXCR3+ and CXCR3− GC-Tfh delivered help to B cells in vitro for production of IgG. These data demonstrate that chronic SIV infection promotes expansion of Th1-biased GC-Tfh cells, which are phenotypically and functionally distinct from conventional GC-Tfh cells and contribute to hypergammaglobulinemia and viral reservoirs.

OBJECTIVEMetreleptin has been efficacious in improving metabolic control in patients with lipodystrophy, but its efficacy has not been tested in obese patients with type 2 diabetes.RESEARCH DESIGN AND METHODSWe studied the role of leptin in regulating the endocrine adaptation to long-term caloric deprivation and weight loss in obese diabetic subjects over 16 weeks in the context of a double-blinded, placebo–controlled, randomized trial. We then performed detailed interventional and mechanistic signaling studies in humans in vivo, ex vivo, and in vitro.RESULTSIn obese patients with diabetes, metreleptin administration for 16 weeks did not alter body weight or circulating inflammatory markers but reduced HbA1c marginally (8.01 ± 0.93–7.96 ± 1.12, P = 0.03). Total leptin, leptin-binding protein, and antileptin antibody levels increased, limiting free leptin availability and resulting in circulating free leptin levels of ∼50 ng/mL. Consistent with clinical observations, all metreleptin signaling pathways studied in human adipose tissue and peripheral blood mononuclear cells were saturable at ∼50 ng/mL, with no major differences in timing or magnitude of leptin-activated STAT3 phosphorylation in tissues from male versus female or obese versus lean humans in vivo, ex vivo, or in vitro. We also observed for the first time that endoplasmic reticulum (ER) stress in human primary adipocytes inhibits leptin signaling.CONCLUSIONSIn obese patients with diabetes, metreleptin administration did not alter body weight or circulating inflammatory markers but reduced HbA1c marginally. ER stress and the saturable nature of leptin signaling pathways play a key role in the development of leptin tolerance in obese patients with diabetes.

Therapeutic strategies that augment antiviral immunity and reduce the viral reservoir are critical to achieving durable remission of HIV. The coinhibitory receptor programmed death-1 (PD-1) regulates CD8+ T cell dysfunction during chronic HIV and SIV infections. We previously demonstrated that in vivo blockade of PD-1 during chronic SIV infection improves the function of antiviral CD8+ T cells and B cells. Here, we tested the immunological and virological effects of PD-1 blockade combined with antiretroviral therapy (ART) in rhesus macaques. Administration of anti-PD-1 antibody 10 days prior to ART initiation rapidly enhanced antiviral CD8+ T cell function and diminished IFN-stimulated genes. This resulted in faster viral suppression in plasma and better Th17 cell reconstitution in the rectal mucosa following ART initiation. PD-1 blockade during ART resulted in lower levels of cell-associated replication-competent virus. Following ART interruption, PD-1 antibody-treated animals showed markedly higher expansion of proliferating CXCR5+perforin+granzyme B+ effector CD8+ T cells and lower regulatory T cells that resulted in better control of viremia. Our results show that PD-1 blockade can be administered safely with ART to augment antiviral CD8+ T cell function and reduce the viral reservoir, leading to improved control of viral rebound after ART interruption.