Antiretroviral drug therapy (ART) effectively suppresses replication of both the immunodeficiency viruses, human (HIV) and simian (SIV); however, virus rebounds soon after ART is withdrawn. SIV-infected monkeys were treated with a 90-day course of ART initiated at 5 weeks post infection followed at 9 weeks post infection by infusions of a primatized monoclonal antibody against the α4β7 integrin administered every 3 weeks until week 32. These animals subsequently maintained low to undetectable viral loads and normal CD4+ T cell counts in plasma and gastrointestinal tissues for more than 9 months, even after all treatment was withdrawn. This combination therapy allows macaques to effectively control viremia and reconstitute their immune systems without a need for further therapy.

HIV/SIV infections induce chronic immune activation with remodeling of lymphoid architecture and hypergammaglobulinemia, although the mechanisms leading to such symptoms remain to be fully elucidated. Moreover, lymph nodes have been highlighted as a predilection site for SIV escape in vivo. Following 20 rhesus macaques infected with SIVmac239, as they progress from pre to acute and chronic infection, we document for the first time the local dynamics T follicular helper (TFH) cells and B cells in situ. Progression of SIV infection was accompanied with increased numbers of well delineated follicles containing germinal centers (GCs) and TFH cells with a progressive increase in the density of PD-1 expression in lymph nodes. The rise in PD-1+ TFH cells was followed by a substantial accumulation of Ki67+ B cells within GCs. However, unlike in blood, major increases in the frequency of CD27+ memory B cells were observed in lymph nodes, indicating increased turnover of these cells, correlated with increases in total and SIV specific antibody levels. Of importance, compared to T cell zones, GCs seemed to exclude CD8+ T cells while harboring increasing numbers of CD4+ T cells, many of which are positive for SIVgag, providing an environment particularly beneficial for virus replication and reservoirs. Our data highlight for the first time important spatial interactions of GC cell subsets during SIV infection, the capacity of lymphoid tissues to maintain stable relative levels of circulating B cell subsets and a potential mechanism for viral reservoirs within GCs during SIV infection.

The detection of viral dynamics and localization in the context of controlled HIV infection remains a challenge and is limited to blood and biopsies. We developed a method to capture total-body simian immunodeficiency virus (SIV) replication using immunoPET (antibody-targeted positron emission tomography). The administration of a poly(ethylene glycol)-modified, 64Cu-labeled SIV Gp120–specifc antibody led to readily detectable signals in the gastrointestinal and respiratory tract, lymphoid tissues and reproductive organs of viremic monkeys. Viral signals were reduced in aviremic antiretroviral-treated monkeys but detectable in colon, select lymph nodes, small bowel, nasal turbinates, the genital tract and lung. In elite controllers, virus was detected primarily in foci in the small bowel, select lymphoid areas and the male reproductive tract, as confirmed by quantitative reverse-transcription PCR (qRT-PCR) and immunohistochemistry. This real-time, in vivo viral imaging method has broad applications to the study of immunodeficiency virus pathogenesis, drug and vaccine development, and the potential for clinical translation.

Human immunodeficiency virus (HIV)-infected and viremic individuals exhibit elevated levels of plasma cytokines. Here we show that most cytokines are not in free form but appear associated with exosomes that are distinct from virions. Purified exosomes were analyzed to determine the levels of 21 cytokines and chemokines and compared with exosome-depleted plasma. Most cytokines were markedly enriched in exosomes from HIV-positive individuals relative to negative controls and to plasma. Moreover, exposure of naive peripheral blood mononuclear cells to exosomes purified from HIV-positive patients induced CD38 expression on naive and central memory CD4(+) and CD8(+) T cells, probably contributing to inflammation and viral propagation via bystander cell activation.

PD-1 expression is generally associated with exhaustion of T cells during chronic viral infections based on the finding that PD-1 expressing cells respond poorly to antigen activation and blockade of PD-1/PD-ligand interaction restores such antigen specific responses in vitro. We tested this hypothesis by examining PD-1 expression on virus-specific CD8 T cells and total T cells in vivo to determine whether PD-1 expression constitutes a reliable marker of immune exhaustion during SIV infection. The expression of PD-1 and Ki67 was monitored longitudinally on T cell subsets in peripheral blood, bone marrow, lymph node and rectal biopsy specimens from rhesus macaques prior to and post infection with pathogenic SIVmac239. During the course of infection, a progressive negative correlation was noted between PD-1 density and Ki67 expression in p11CM+ CD8+ T cells, as seen in other studies. However, for total and memory CD4 and CD8 T cells, a positive correlation was observed between PD-1 and Ki67 expression. Thus, while the levels of non-proliferating PD-1+ p11CM+ CD8 T cells were markedly elevated with progressing infection, such an increase was not seen on total T cells. In addition, total memory PD1+ T cells exhibited higher levels of CCR5 than PD-1− T cells. Interestingly, few PD-1+ CD8+ T cells expressed CCR7 compared to PD-1+ CD4 T cells and PD-1− T cells. In conclusion, overall PD1+ T cells likely represent a particular differentiation stage or trafficking ability rather than exhaustion and in the context of chronic SIV infection, the level of PD-1 expression by T cells does not by itself serve as a reliable marker for immune exhaustion.