Interspecies Lewis lung carcinoma x Chinese hamster ovary hybrids as protective agents against Lewis lung carcinoma tumor growth.

Interspecies somatic cell hybrids formed between a clone of Lewis lung carcinoma (LLC/9) and Chinese hamster ovary cells were assessed for tumorigenicity in C57BL/6 mice and capacity to protect mice against a challenge with LLC/9 cells. LLC/9 cells were fused with ouabain-resistant-Chinese hamster ovary cells deficient in hypoxanthine guanine phosphoribosyl transferase. Hybrids were selected in medium supplemented with hypoxanthine: aminopterin: thymidine and 5 mM ouabain. Hybrids were shown to contain chromosomes and surface antigens of both parents. At doses up to 10(7) cells, uncloned hybrids and hybrid clones obtained by limiting dilution were nontumorigenic in C57BL/6 mice, while 10(4) LLC/9 cells were tumorigenic in 80% of mice. In protection experiments, hybrid cells were injected i.p., followed by foot pad challenge with 10(6) LLC/9 cells. Three injections of live uncloned hybrids produced complete protection, while one or two injections gave partial protection. Individual live hybrid clones conferred no or partial but never complete protection. Administration of hybrids or LLC cells killed by freezing and thawing or arrested in division by treatment with mitomycin C failed to confer protection against subsequent challenge with LLC/9 cells. These LLC/9 X CHO hybrid cells will be useful for studying therapy of primary LLC tumors and their pulmonary metastases.