The mammalian target of rapamycin (mTOR) is a key regulatory kinase that controls glucose metabolism and cell growth. Inhibition of mTOR has been linked with several immune regulatory functions that may limit HIV persistence, including: 1) reducing CCR5 expression, 2) limiting CD4+ T cell homeostatic proliferation, 3) reducing PD-1 expression and 4) increasing anti-viral CD8+ effector T cell responses. Here we evaluated the impact of long-term mTOR inhibition on SIV DNA and RNA in blood and tissues of SIV-infected rhesus macaques (RM) on combination antiretroviral therapy (cART). We also evaluated whether potent T cell activation can induce latent SIV reactivation in the presence of rapamycin.
A total of 14 adult male RM were intravenously infected with SIVmac239 followed by cART (tenofovir, emtricitabine and dolutegravir) 12 days later. After 219 days of cART, RM were randomized into 2 groups that received twice daily IM injections of rapamycin at 0.02mg/kg (n=7) or vehicle control for 312 days. After 464 days of cART, RM on rapamycin received 2 doses of a non-depleting anti-CD3LALA monoclonal antibody at 0.5mg/kg IV at 21-day intervals. Plasma viral loads and cell-associated SIV RNA and DNA were quantified by qRT-PCR and qPCR, respectively. Lymphocyte populations were evaluated by flow cytometry.
After 24 weeks, there were significant decreases in the frequencies of Ki67+ (p = 0.0006), HLA-DR+ (p = 0.0262) and PD-1+ (p = 0.04) CD4+ memory T cells in blood of rapamycin-treated RM versus controls. In addition, surface expression of CCR5 (p=0.007) and the glucose transporter Glut1 (p=0.007) were also significantly reduced in rapamycin-treated RM. Despite these perturbations in CD4+ T cell homeostasis, cell-associated SIV DNA and RNA in blood and peripheral lymph nodes remained stable over time with no significant difference observed between treatment groups. However, 4 of 7 rapamycin-treated RM had blips in plasma viral loads >2 logs above threshold (1 RNA copy/ml) in response to anti-CD3LALA, suggesting T cell activation in the presence of rapamycin can induce SIV reactivation in vivo.
Despite profound changes in markers of immune activation, proliferation and T cell exhaustion, rapamycin had minimal effect the stability of the SIV reservoir. However, these data indicate that rapamycin used in synergy with potent T cell activation may be an effective strategy to induce viral reactivation while inhibiting global immune activation and T cell proliferation.