Effect of sublethal total body irradiation on acute graft-versus-host disease and graft-versus-leukemia effect in SCID mice.

SCID mice were transplanted with H-2-incompatible C3H/He splenocytes with or without previous TBI with 2Gy to evaluate the influence of sublethal TBI on GVHD and on the graft-versus-leukemia (GVL) effect. Transplantation immediately after TBI induced lethal GVHD, but delayed donor leukocyte infusion (DLI) 5 days after TBI reduced the severity of the GVHD. SCID mice inoculated with L1210 cells after TBI received a DLI 5 days after TBI to induce the GVL effect. Survival of these mice was longer than that of control nonirradiated mice. Serum levels of tumor necrosis factor-alpha, IL-1alpha, IL-6, IL-2 and IFN-gamma were significantly elevated, and they reached maximum levels at 5 days post-transplantation. Except for IFN-gamma, all cytokine levels were higher in irradiated mice than those in nonconditioned mice. Cytotoxicity against L1210 cells mediated by splenocytes from irradiated recipients was greater than that mediated by effector cells from nonirradiated mice. All the irradiated mice survived more than 120 days after L1210 rechallenge, while all nonirradiated mice died of leukemia within 5 weeks. In conclusion, compared with control mice infused with donor splenocytes without previous TBI, SCID mice which received sublethal TBI and DLI showed superior cytotoxicity against L1210 cells and survived longer without severe GVHD.