Recovery of the ability to induce immune resistance against L1210 lymphatic leukemia in semisyngeneic CD2F₁ mice after lethal irradiation and reconstitution with bone marrow purged of leukemia with mafosfamide (ASTA Z 7654)

Balb/c x DBA/2 F₁ (CD2F₁) mice were lethally irradiated (TBI) and reconstituted with syngeneic bone marrow cells (SBMT) untreated or treated with mafosfamide (ASTA Z 7654) for ex vivo purging of semisyngeneic L1210 leukemia (TBI+SBMT or TBI+SBMT-Maf mice, respectively). At various times after irradiation and reconstitution mice were injected intraperitoneally four times at weekly intervals with 10⁶ immunogenic L1210-Maf cells (L1210 cells treated in vitro with mafosfamide for inhibition of their growth in vivo). As positive controls we immunized normal (non-irradiated) CD2F₂ mice. Full resistance against L1210 leukemia (as compared to normal immunized mice) could be obtained in TBI+SBMT and TBI+SBMT-Maf mice when the immunization procedure was started from day +28 or day +56 after translplantation, respectively. Earlier immunization of TBI+SBMT mice (from day +14) or TBI+SBMT-Maf mice (from day +14 or +28) caused only partial resistance against the leukemia.