Tissue myeloid cells in SIV-infected primates acquire viral DNA through phagocytosis of infected T cells.

The viral accessory protein Vpx, expressed by certain simian and human immunodeficiency viruses (SIVs and HIVs), is thought to improve viral infectivity of myeloid cells. We infected 35 Asian macaques and African green monkeys with viruses that do or do not express Vpx and examined viral targeting of cells in vivo. While lack of Vpx expression affected viral dynamics in vivo, with decreased viral loads and infection of CD4⁺ T cells, Vpx expression had no detectable effect on infectivity of myeloid cells. Moreover, viral DNA was observed only within myeloid cells in tissues not massively depleted of CD4⁺ T cells. Myeloid cells containing viral DNA also showed evidence of T cell phagocytosis in vivo, suggesting that their viral DNA may be attributed to phagocytosis of SIV-infected T cells. These data suggest that myeloid cells are not a major source of SIV in vivo, irrespective of Vpx expression.

Cytotoxic T Cell Functions Accumulate When CD4 Is Downregulated by CD4+ T Cells in African Green Monkeys.

African green monkeys (AGMs) are a natural host of SIV that do not develop simian AIDS. Adult AGMs naturally have low numbers of CD4+ T cells and a large population of MHC class II-restricted CD8αα T cells that are generated through CD4 downregulation in CD4+ T cells. In this article, we study the functional profiles and SIV infection status in vivo of CD4+ T cells, CD8αα T cells, and CD8αß T cells in lymph nodes, peripheral blood, and bronchoalveolar lavage fluid of AGMs and rhesus macaques (in which CD4 downregulation is not observed). We show that, although CD8αα T cells in AGMs maintain functions associated with CD4+ T cells (including Th follicular functionality in lymphoid tissues and Th2 responses in bronchoalveolar lavage fluid), they also accumulate functions normally attributed to canonical CD8+ T cells. These hyperfunctional CD8αα T cells are found to circulate peripherally, as well as reside within the lymphoid tissue. Due to their unique combination of CD4 and CD8 T cell effector functions, these CD4- CD8αα T cells are likely able to serve as an immunophenotype capable of Th1, follicular Th, and CTL functionalities, yet they are unable to be infected by SIV. These data demonstrate the ambiguity of CD4/CD8 expression in dictating the functional capacities of T cells and suggest that accumulation of hyperfunctional CD8αα T cells in AGMs may lead to tissue-specific antiviral immune responses in lymphoid follicles that limit SIV replication in this particular anatomical niche.

Homeostatic cytokines induce CD4 downregulation in African green monkeys independently of antigen exposure to generate simian immunodeficiency virus-resistant CD8αα T cells.

UNLABELLED: African green monkeys (AGMs; genus Chlorocebus) are a natural host of simian immunodeficiency virus (SIVAGM). As they do not develop simian AIDS, there is great interest in understanding how this species has evolved to avoid immunodeficiency. Adult African green monkeys naturally have low numbers of CD4 T cells and a large population of major histocompatibility complex class II-restricted CD8α(dim) T cells that are generated through CD4 downregulation in CD4(+) T cells. Mechanisms that drive this process of CD4 downregulation are unknown. Here, we show that juvenile AGMs accelerate CD4-to-CD8αα conversion upon SIV infection and avoid progression to AIDS. The CD4 downregulation induced by SIV infection is not limited to SIV-specific T cells, and vaccination of an adult AGM who had a negligible number of CD4 T cells demonstrated that CD4 downregulation can occur without antigenic exposure. Finally, we show that the T cell homeostatic cytokines interleukin-2 (IL-2), IL-7, and IL-15 can induce CD4 downregulation in vitro. These data identify a mechanism that allows AGMs to generate a large, diverse population of T cells that perform CD4 T cell functions but are resistant to SIV infection. A better understanding of this mechanism may allow the development of treatments to induce protective CD4 downregulation in humans. IMPORTANCE: Many African primate species are naturally infected with SIV. African green monkeys, one natural host species, avoid simian AIDS by creating a population of T cells that lack CD4, the human immunodeficiency virus/SIV receptor; therefore, they are resistant to infection. However, these T cells maintain properties of CD4(+) T cells even after receptor downregulation and preserve immune function. Here, we show that juvenile AGMs, who have not undergone extensive CD4 downregulation, accelerate this process upon SIV infection. Furthermore, we show that in vivo, CD4 downregulation does not occur exclusively in antigen-experienced T cells. Finally, we show that the cytokines IL-2, IL-7, and IL-15, which induce homeostatic T cell proliferation, lead to CD4 downregulation in vitro; therefore, they can provide signals that lead to antigen-independent CD4 downregulation. These results suggest that if a similar process of CD4 downregulation could be induced in humans, it could provide a cure for AIDS.

mTOR Overcomes Multiple Metabolic Restrictions to Enable HIV-1 Reverse Transcription and Intracellular Transport.

Cellular metabolism governs the susceptibility of CD4 T cells to HIV-1 infection. Multiple early post-fusion steps of HIV-1 replication are restricted in resting peripheral blood CD4 T cells; however, molecular mechanisms that underlie metabolic control of these steps remain undefined. Here, we show that mTOR activity following T cell stimulatory signals overcomes metabolic restrictions in these cells by enabling the expansion of dNTPs to fuel HIV-1 reverse transcription (RT), as well as increasing acetyl-CoA to stabilize microtubules that transport RT products. We find that catalytic mTOR inhibition diminishes the expansion of pools of both of these metabolites by limiting glucose and glutamine utilization in several pathways, thereby suppressing HIV-1 infection. We demonstrate how mTOR-coordinated biosyntheses enable the early steps of HIV-1 replication, add metabolic mechanisms by which mTOR inhibitors block HIV-1, and identify some metabolic modules downstream of mTOR as druggable targets for HIV-1 inhibition.

mTOR signaling mediates effects of common gamma-chain cytokines on T cell proliferation and exhaustion: implications for HIV-1 persistence and cure research.

: Chronic elevation of plasma cytokines is a key feature of HIV infection. The physiological consequences of this response to infection and its role in HIV persistence are not fully understood. Here, we show that common gamma chain (γc)-cytokines induce both proliferation and expression of T cell exhaustion markers in a mammalian target of rapamycin (mTOR)-dependent fashion, suggesting a possible therapeutic target that, if inhibited, could diminish HIV reservoir expansion, persistence, and resistance to immune surveillance.

Probiotics Reduce Inflammation in Antiretroviral Treated, HIV-Infected Individuals: Results of the "Probio-HIV" Clinical Trial.

BACKGROUND: HIV infection results in damage to the gastrointestinal (GI) tract, microbial translocation and immune activation. These are not completely normalized with combined antiretroviral therapy (cART). Moreover, increate morbidity and mortality of cART-treated HIV-infected individuals is associated with inflammation. METHODS: In order to enhance GI tract immunity, we recruited and treated 20 HIV-infected humans with cART supplemented with probiotics and followed inflammation and immunological parameters (clinical trial number NCT02164344). 11 HIV seronegative subjects were included as control group. The enumeration of CD4+, CD8+, CD38+ and HLA-DR+ lymphocytes were evaluated on peripheral blood; HIV-RNA levels, sCD14, d-dimer, C-reactive protein (CRP) high sensitivity C-reactive protein (hsCRP), IL-6 and Lipopolysaccharide Binding Protein (LBP) were assayed on plasma. RESULTS: We observe that cART does not normalize the levels of immune activation in HIV positive patients anyway inflammation and markers of microbial translocation were significantly reduced with probiotic supplementation. Patients show a clear and statistically significant reduction in the levels of immune activation on CD4 T-lymphocytes, for both markers CD38 and HLA-DR and their simultaneous expression, LBP and hsCRP plasma levels after probiotic diet supplementation settling to values comparable to controls. CONCLUSIONS: Supplementing cART with probiotics in HIV-infected individuals may improve GI tract immunity and there by mitigate inflammatory sequelae, ultimately improving prognosis. TRIAL REGISTRATION: ClinicalTrials.gov NCT02164344.