Alterations in sensitivity to nonspecific cell-mediated lysis associated with tumor progression: characterization of activated macrophage- and natural killer cell-resistant tumor variants.

Certain "membrane-mutant," lectin-resistant (Lecr) variants derived from the highly metastatic and poorly immunogenic DBA/2 mouse tumor MDAY-D2 previously were found to differ substantially in their ability to grow and to metastasize. In the present study, the parental MDAY-D2 tumor and several wheat germ agglutinin-resistant (WGAr) variants were examined for alterations in sensitivity to activated macrophage (M phi)- and natural killer cell (NK)-mediated lysis. The results indicated that selection in WGA after mutagenic treatment of a metastatic parental tumor cell line (MDAY-D2), which was M phi-sensitive (M phi S) and NK-resistant (NKR), can result in the isolation of a significantly M phi-resistant (M phi R) and NK-sensitive (NKS) tumor variant, MDW4. The in vivo hybridization of the M phi R, NKS, Lecr MDW4 variant with a normal host-derived cell within a primary subcutaneous tumor, previously demonstrated to result in the progressive and selective outgrowth and metastasis of hybrid products, was found to be associated directly with reversion to the M phi S, NKR phenotype of the metastatic parental MDAY-D2 cell line. DMA/2 mice given iv injections of 10(5) M phi R, NKS cells (MDW4 or MDW4-110c1, a cloned line isolated from a subcutaneous primary tumor of an MDW4-injected animal) survived for a significantly prolonged period as compared to animals given injections of either the parental tumor or M phi S, NKR hybrid products isolated from a MDW4 subcutaneous primary tumor (MDW4-110c2) or visceral metastases (MDW4-24a, MDW4-24b, and MDW4-24c). The results clearly indicate an inverse relationship among the tumor variants in their ability to be lysed by either M phi or NK and suggest a central role for NK rather than M phi surveillance in this tumor system.