BALB/c-derived IFN-γ plays a critical role in the antitumor effect of RLI against A20 but is not required for loss of chimerism. BALB/c WT and BALB/c IFN-γ knock-out (KO) recipient mice were conditioned with anti-CD4– and anti-CD8–depleting mAbs on day –5, CTX 200 mg/kg intraperitoneally on day – 1, and 7 Gy thymic irradiation on day 0 prior to transplantation of 20 × 10⁶ B10.BR BMCs intravenously. Some groups received 3 × 10⁷ recipient spleen cells (RLI) from BALB/c WT or BALB/c IFN-γ KO mice intravenously on day +49 after BMT and/or 5 × 10⁵ A20 BALB/c B lymphoma cells intravenously on day +56 after BMT. (A) Levels of peripheral blood B-cell chimerism before and after RLI in BALB/c WT mice receiving conditioning, BMT and WT RLI. B-cell chimerism is representative of chimerism in all lineages. Each line represents an individual animal. (B) Levels of peripheral blood B-cell chimerism before and after RLI in BALB/c IFN-γ KO mice receiving conditioning, BMT, and IFN-γ KO RLI. B-cell chimerism is representative of chimerism in all lineages. Each line represents an individual animal. (C) Survival of A20 tumor recipients. BALB/c WT mice had been treated with conditioning alone (○; n = 4); conditioning and BMT without RLI (▵; n = 4); or conditioning, BMT, and WT RLI (⋄; n = 7). BALB/c IFN-γ KO mice received conditioning and BMT without RLI (•;n = 4) or conditioning, BMT, and IFN-γ KO RLI (♦;n = 7).