Bystander DCs induce memory T cell proliferation and promote naïve CD4 cells towards T_reg phenotype that inhibit proliferation of anti-HAdV T cells.

A) Bystander DCs, generated via IC-HAdV stimulation of direct DCs or mock-treated DCs, were incubated with CFSE-labeled PBMCs and proliferation was quantified by flow cytometry. CD3+/CFSElow cells were screened for memory T cell profile (CD45RO vs. CD45RA). Bystander DCs, generated using the media from DCs challenged with IgG, HAdV5, and IC-HAdV5, were incubated with 105 naive CD4+ T (ratio of 10:1 PBMC/ bystander DC) cells isolated from the same donors. The percentage of Tregs (CD25+/FoxP3high/CD127dim/CD4+ cells) varies between 1 to 5% of CD4+ cells in peripheral blood. The number of Tregs in the CD4+ cell population, ± bystander DCs, was quantified by analyzing 50,000 cells by flow cytometry. The results are presented as percentage of increase of mock-treated cells at day 3 (B) or day 7 (C). D) Tregs generated by bystander DCs reduce the proliferation of memory anti-HAdV CD4 T cells. Experiments were carried out in ≥7 donors with similar results. * p 0.05 vs. mock, HAdV5 and IgG.