Background
HIV persistence within cellular and anatomical viral reservoirs remains the primary barrier to a cure for HIV, with virus rebounding upon ART interruption (ATI) in most people with HIV. As such, developing interventions aimed at improving immune responses is a key priority for HIV cure strategies. Here, we investigated the effects of a combined heterodimeric IL-15 (hetIL-15) and IL-21 treatment.
Methods
Eighteen rhesus macaques (RMs) infected with SIVmac239 started ART at six weeks post infection (p.i.). After 13 months on ART, ten RMs received two cycles of hetIL-15 (step-dose, 2-21 µg/kg, six subcutaneous [s.c.] injections every 3-4 days) and one cycle of IL-21-Fc (four weekly s.c. injections), after which two treatment groups were established. Six RMs discontinued ART during the second hetIL-15 cycle (arm 1) and four RMs discontinued ART 20 days after its completion (arm 2). Eight RMs remained on ART-only (arm 3). Plasma viral load was quantified by RT-qPCR, and intact proviral DNA by IPDA. Phenotypic and transcriptional profiles of T and NK cells in blood and lymph nodes (LN) were assessed by flow cytometry and single-cell RNA sequencing.
Results
HetIL-15/IL-21 treatment significantly increased the levels of effector memory (EM) CD8 T cells in the LNs, including those expressing Ki-67, HLA-DR+CD38+, and granzyme B, indicating enhanced proliferative capacity, activation, and cytolytic function, respectively. NK cell frequencies were also increased in LNs after the first hetIL-15 cycle when compared to controls, with notable expansion of CD16+CD56+ subsets and increased cytolytic capacity. Ki-67 upregulation was observed across all NK subsets, remaining elevated in RMs still receiving hetIL-15 following ART cessation (arm 1). A reduction in LN viral reservoir during ART and an enhanced post-ATI virological control was found in RMs completing the hetIL-15/IL-21 administration before ATI (arm 2), but not in those with treatment prolonged after ATI (arm 1). Notably, post-ATI controllers were distinguished by higher pre-ATI effector CD8 T cells and type-I interferon-driven transcriptional programs, whereas non-controllers exhibited elevated TGF-β signaling signatures.
Conclusions
These findings demonstrate that hetIL-15 and IL-21 co-administration potently enhances antiviral immunity in blood and lymphoid tissues, identify IFN-driven responses as critical for HIV control, and provide a mechanistic support for cytokine-based strategies toward durable HIV remission.