ECP-treated splenocytes reduce allogeneic T-cell responses and increase Foxp3 expression in vitro. (A,B) B6-Ly5.2 responder T cells were incubated at a 10:1 ratio with syngeneic B6 (□) or allogeneic B6D2F1 (■) stimulator DCs for 60 hours in the presence of untreated (▨) or ECP-treated (▩) B6→B6D2F1 splenocytes at a 1:1 ratio with responders. (A) Numbers of responder CD8⁺IFN-γ⁺ cells per well (left) and proliferation of bulk responder cells (right); ▩ versus ■ or ▨, *P < .05. (B) Percentage of CD4⁺Foxp3⁺ cells; ▩ versus ■ or ▨, *P < .05. (C) Proliferation of fresh MLR cultures containing 10 B6-Ly5.2 responder T cells per B6D2F1 stimulator DC after cells harvested from panels A-B were added at a 1:1 ratio with responders. − indicates nothing added; +, cells added from primary cultures as colored in panels A,B; ▩ versus ■ or ▨, *P < .05. Syngeneic control groups had low background proliferation (< 2.0 × 10³ cpm) that was unaffected by addition of cells from panel A,B (data not shown). Data are means (± SD) pooled from at least 2 independent experiments (n = 6-9 wells per group).