Host resistance to tumor after cure of advanced LSA lymphoma by treatment with BCNU and chlorozotocin.

C57BL mice carrying the syngeneic advanced LSA ascites lymphoma initiated with a 10(6)-cell LSA inoculum were treated with four combinations of BCNU and/or chlorozotocin (CLZ) on Days 5 and 6 after tumor inoculation. The percentage of mice surviving greater than or equal to 60 days was greater than 80% for all four combinations. Surviving mice were then challenged with live LSA cells beginning with 100 cells and increasing the inoculum by factors of 10 every 3 weeks until a 10(7)-cell inoculum level was reached. The latter dose was repeated four times. A marked difference in resistance to tumor challenge was observed for the various groups. Surviving tumor-resistant mice at the end of the experiment, classified by original treatment, were as follows: BCNU-BCNU, 86.7%; CLZ-BCNU, 56.3%; BCNU-CLZ, 23.5% and CLZ-CLZ, 0. Various hypotheses are presented which might explain these differences.