RLI mediates an antitumor effect against a B-cell lymphoma, A20. BALB/c (H2^d) recipient mice were conditioned with anti-CD4– and anti-CD8–depleting mAbs intraperitoneally 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. The indicated groups received 3 × 10⁷ recipient spleen cells (RLI) intravenously on day +49 after BMT and/or 5 × 10⁵ A20 BALB/c B lymphoma cells intravenously on day +56 after BMT. (A) Mean (± SEM) of B-cell chimerism at various times in mice receiving conditioning and BMT, including chimeras with spontaneous loss of chimerism between 6 and 10 weeks after BMT, without RLI (•; n = 12); chimeras with persistent chimerism at 10 weeks (no RLI) (⋄; n = 11); and chimeras receiving RLI on day 49 (▵; n = 13). Results of 2 similar experiments are combined. (B) Survival of the A20 tumor groups receiving conditioning alone (○; n = 13), conditioning and RLI without BMT (♦; n = 13), conditioning and BMT without RLI with spontaneous loss of chimerism by week 10 (•;n = 12), conditioning and BMT without RLI with persistent chimerism at Week 10 (⋄; n = 11), and conditioning, BMT and RLI (▿; n = 13). Results of 2 similar experiments are combined.