Viral immunity is preserved in the presence of Tregs. (A,B) Lethally irradiated Balb/c received FVB T cell–depleted BM alone (BM, ▴), with Tcons (●), or with Tcon + Treg (O). Shown are the weight change (A), a surrogate measure of graft-versus-host disease, and survival (B) following bone marrow transplantation (BMT) (Tcons vs Tcon + Treg, n = 20, P < .001). (C-E) Balb/c recipient mice transplanted with BM alone (▴), with Tcons (●) or Tcon + Treg (O) as described above are challenged with murine CMV on days 14 (C), 30 (D), or 63 (E). P value for Tcons vsersus Tcon + Treg: < .001, < .001, and = .08, respectively. P is NS for BM versus Tcon + Treg. Data combined from 3 separate experiments.