Cutting Edge: T Regulatory Cell Depletion Reactivates Latent Simian Immunodeficiency Virus (SIV) in Controller Macaques While Boosting SIV-Specific T Lymphocytes.

T regulatory cells (Tregs) are critical in shaping the latent HIV/SIV reservoir, as they are preferentially infected, reverse CD4 ⁺ T cell activation status, and suppress CTL responses. To reactivate latent virus and boost cell-mediated immune responses, we performed in vivo Treg depletion with Ontak (denileukin diftitox) in two SIVsab-infected controller macaques. Ontak induced significant (>75%) Treg depletion and major CD4 ⁺ T cell activation, and only minimally depleted CD8 ⁺ T cells. The overall ability of Tregs to control immune responses was significantly impaired despite their incomplete depletion, resulting in both reactivation of latent virus (virus rebound to 10 ³ viral RNA copies/ml plasma in the absence of antiretroviral therapy) and a significant boost of SIV-specific CD8 ⁺ T cell frequency, with rapid clearance of reactivated virus. As none of the latency-reversing agents in development have such dual activity, our strategy holds great promise for cure research.
(Copyright © 2016 by The American Association of Immunologists, Inc.)