Some somatic hybrid cells prepared by cell fusion of MC-induced primary
tumor cells with
8-azaguanine resistant L cells were immunogenic in the induction of specific resistance in syngeneic normal mice to the challenge of parental
tumor cells. However, inoculations of immunogenic hybrid cells in
tumor-bearing hosts evoked enhancement of
tumor growth. In these mice with enhanced
tumors, the level of
immune complexes and antitumor
antibodies in sera was more markedly elevated than in sera of untreated
tumor-bearers, despite generation of effective cytotoxic T cells in the spleen. Enhancement was not observed by pretreatment with
cyclophosphamide (CY), followed by treatment with hybrid cells, but
tumor regression occurred. Complete
tumor regression was observed in about 70% of animals treated with CY (100 mg/kg) plus viable hybrid cells (10(6)) three times at weekly intervals starting 1 week after
tumor transplantation. Coincidental decreases of
immune complexes and antitumor
antibodies in sera were observed. The results suggest that suppression of the immunological escape mechanism is of primary importance in active
tumor-specific
immunotherapy.