Generation of highly differentiated NK cells to act in synergy with broadly neutralizing antibodies to reduce the SIV reservoir and establish viral control in absence of ART

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PROJECT SUMMARY/ABSTRACT Lymph nodes and the gastrointestinal tract are major tissue viral reservoirs in people living with HIV and treated with antiretroviral treatment (ART). A distinguishing feature of SIV infection in African green monkeys (AGMs), a natural host species for SIV, is the absence of viral dissemination in the lymphoid B-cell follicle (BCF) and the presence of strong NKcell-mediated control of viral replication in the T-cell zone and BCF of secondary lymphoid tissues (SLT). In SIVagm-infected AGMs, we recently identified the expansion of NK cells with a terminally-differentiated phenotype expressing (i) high levels of CD16, an activating Fc receptor that mediates antibody-dependent cellular cytotoxicity (ADCC), and (ii) low levels of NKG2a, an inhibitory receptor, that modulates NK cell education via interactions with MHC-E. This terminally-differentiated NK cell (NKTD) subset (NKG2alowCD16+) exhibited adaptive-like properties and, due at least in part to reduced NKG2a expression, showed high cytolytic activity against target cells presenting SIV-Env peptides in the context of MHC-E. The formation of adaptive NKTD cells was blocked in SIVmac-infected rhesus macaques (RMs) in favor of a subset (NKG2ahiCD16+) with pro-inflammatory function, such as production of IFN, a cytokine also known for its capacity to increase MHC-E expression on target cells. Remarkably, in a separate cohort of SIVmac-infected, ART-treated RMs, we demonstrated that AGM-like profiles of adaptive NKTD cells are rescued via treatment with interleukin-21 (IL-21). In IL-21 treated RMs, the frequency and responsiveness of the adaptive NKTD cells to target cells presenting SIV peptides in the context of MHC-E strongly correlated with a reduction of SIV DNA in the gut, lower levels of replication competent virus in SLT, and a delay in viral rebound following ART interruption. In Aim 1 of this proposal we will define (I) the mechanisms driving the formation and activity of adaptive NKTD cells, such as cytokine environment and lymphoid inflammation; (II) their tissue distribution; and (III) ADCC capacity. In addition to NK cells, the impact of IL-21 will be investigated in T-cells and other immune cells that can respond to IL-21. In Aim 2, we will assess whether and to what extent the combination of IL-21-induced NKTD cells and a cocktail of anti-SIV broadly neutralizing antibodies (bNAbs) facilitates, through ADCC-mediated clearance of infected cells, a reduction of viral burden and control of viral rebound following ART interruption. Specifically, in SIVmac-infected, ART-treated RMs, the “differentiate, target, and kill” approach will allow differentiation of the NKTD cells with IL-21 followed by targeting of cells harboring reactivated virus with bNAbs. Using a model reproducing the complex virus-host interactions occurring in people living with HIV, we expect that the rescue of NK cell terminal differentiation will promote robust ADCC activity, which will synergize with the selective targeting of viral reservoirs that reactivate following ATI, thus leading to prolonged ART-free remission.