Inhibitory effect of a revertant cell on in vivo growth of its parental transformed cell line.

A revertant cell line, KSR-4111, cloned from a sarcoma virus transformed non-virus producing murine 3T3 cell line, K-BALB-23, was found to inhibit in vivo growth in newborn syngeneic mice of the transformed cells when grafted to the same locus, but not when grafted separately from the grafted tumor cells. No inhibition of outgrowth of the transformed K-BALB-23 cells was obtained with another revertant, KSR-12121, also cloned from the transformed K-BALB-23 cell, nor with the normal 3T3 cell. Furthermore, grafting of two syngeneic mammary tumors was unaffected by the presence of the protective revertant cells. The protective revertant KSR-4111 was furthermore characterized by inducing cytoxic non-theta-antigen-bearing spleen lymphocytes in grafted syngeneic recipients.