The current paradigm in HIV cure research is that virus production must be reactivated in latently infected cells prior to clearance (shock and kill). Since depletion of CD8+ lymphocytes in SIV-infected ART-treated rhesus macaques (RM) results in increased plasma viremia, we propose that CD8 depletion may act synergistically with latency reversing agents (LRA) in reactivating virus production. To test this hypothesis we used the IL-15 superagonist N-803, an agent that shows LRA activity in vitro and may also boost antiviral cellular immune responses.
35 SIV-infected RM started ART 8 weeks post-infection. After 1 year, 7 RM received four weekly doses of N-803 (100 µg/kg), 14 received 50 mg/kg of the CD8α-depleting Ab MT-807R1, and 14 RM received both treatments. All animals underwent ART interruption 3 weeks after the last N-803 dose and/or CD8 reconstitution. SIV reactivation was monitored by plasma viremia and RNAscope analysis in lymph node samples. The size of the viral reservoir was assessed by total cell-associated SIV DNA. Immunological changes were studied by flow cytometry and RNA sequencing. Diversity of the virus emerging after N-803 and/or CD8 depletion was assessed via single genome amplification.
In ART-treated RM, N-803 alone did not reactivate virus production; however, its administration in CD8-depleted RM resulted in loss of virus suppression (>60 copies/ml) in 14/14 animals (100%) in 41/56 samples (73.2%) collected 1 week after each dose. In addition, viremia >1,000 copies/ml was observed in 6/14 animals (42.9%) and 13/56 (23.2%) time points, with a maximum of 21,000 SIVgag copies/mL. Preliminary virus sequence analysis indicated a diverse range of circulating virus after CD8 depletion and N-803 treatment. Despite this very robust level of virus reactivation, all groups of RM showed stable levels of cell-associated SIV DNA in CD4+ T cells following treatment and a rapid rebound of viremia after ART interruption.
N-803 administration in CD8-depleted, ART-treated SIV-infected RM induces the most robust and persistent reversal of latency observed to date in humans or nonhuman primates. In absence of a clearance intervention, we did not observe a significant reduction of the reservoir size. Combining N-803 and CD8 depletion with an immune-clearing component (i.e. neutralizing antibodies, CD4 mimetics or immunotoxins) may be a powerful shock and kill strategy that profoundly affects reservoir size and stability in ART-treated HIV/SIV infections.