Assessment of the HIV-1 reservoir in CD4+ regulatory T cells by a Droplet Digital PCR based approach

•Droplet Digital PCR as readout for total HIV DNA and replication competent HIV reservoir in CD4+ T cell subsets.•No difference in total HIV DNA in Treg as compared with Tcm or Tem.•Quantification of replication competent reservoir in Treg for the first time.

The relative contribution of regulatory T cells (Treg) as reservoir of HIV-1 in patients on chronic antiretroviral therapy is unclear to date. The aim of the current study was to assess the total HIV DNA burden and replication competent viral reservoir in Treg in comparison to central and effector memory cells (Tcm and Tem). Peripheral blood mononuclear cells were obtained from 10 HIV patients treated with antiretroviral therapy. Droplet Digital PCR (ddPCR) was used to quantify total HIV DNA loads in FACS-sorted CD4+ Treg (CD25+CD127lo) as compared to Tcm (CD45RO+CCR7+) and Tem (CD45RO+CCR7-). In contrast to earlier reports, no significant difference was found in total HIV DNA burden associated with Treg when compared to Tem and Tcm cells. In a subset of patients, quantitative viral outgrowth assays were also performed, using novel ddPCR based readout to quantify frequencies of Treg harboring replication competent virus.