Further studies on antitumour responses induced by short-term pretreatment with syngeneic tumour cells.

The ability of s.c. injected tumour cells to specifically inhibit the growth of similar cells injected i.v. 2 days later has been confirmed. The capacity of tumour cells to elicit this effect varies form tumour to tumour. Furthermore, it is more readily achieved with cultured than with freshly excised tumour cells. The superior effect elicited by cultured tumour cells was not overcome by treating them with trypsin or pronase. The protection achieved was impaired in T-cell-depleted mice and mice which had been irradiated (400 rad) prior to pretreatment. In contrast, it was not affected by administration of silica, sodium aurothiomolate or cortisone acetate. The results imply that T-cell-dependent responses are involved in the protection conferred by pre-injecting tumour cells shortly before i.v. challenge.