Evidence for host resistance in 1,3 bis(2-chloroethyl)-1-nitrosourea treatment induced in syngeneic LSA lymphoma.

The anticancer agent 1,3 Bis(2-chloroethyl)-1-Nitrosourea (BCNU) cures the advanced syngeneic LSA lymphoma of C57BL mice with high efficiency. The cured animals resist further tumor challenge by large numbers of viable syngeneic tumor cells. Growth assays of spleen proliferation of the intravenously inoculated tumor revealed a progressive-regressive pattern of spleen growth after LSA-tumor injection. Lymphoma colony forming units (LCFU) in the spleen initially increased then regressed. In vitro assays of serum showed a lack of cytotoxic activity in mice cured by BCNU. Added spleen, thymus, or bone-marrow cells were similarly ineffective. Spleen and bone-marrow cells from immune mice passively transferred to normal mice showed weak cytotoxic activity against the LSA tumor. BCNU-cured mouse cells were more effective in protection than those cured with Chlorozotocin (CLZ).