Microcytotoxicity assay of immune responses to non-mammary tumor virus-induced, preneoplastic, and neoplastic mammary lesions in BALB/c mice.

Using a microcytotoxicity assay we have studied the immune responses to the preneoplastic, hyperplastic alveolar nodule (HAN) lines D1 and D2 and to the mammary tumors arising spontaneously from them in BALB/c mice. Lymph node cells (LNC) from mice bearing HAN implants, or from mice whose implants had been removed greater than 1 week prior to testing, failed significantly to inhibit survival of HAN cells in culture. Specific inhibition of HAN cells was found, however, in 9 of 28 experiments with LNC from mice whose implants had been removed within the week of testing, and not with LNC from sham-operated controls. On the other hand, increased survival of HAN cells was also seen with LNC from sensitized, as opposed to normal, mice. This was more frequent for tests with D1 than with D2 HAN cells (38 versus 9%) and when the LNC donors were still bearing HAN IMPLANTs (60% of tests versus 27% when implants removed). Following sensitization by implantation and subsequent removal of D1 or D2 tumors, LNC-mediated inhibition of tumor cell survival, specific for each tumor, was found in about 25% of the tests. Increased survival of tumor cells, however, was seen in 30 to 40% of the tests. This increased survival cross-reacted between D1 and D2 tumors and between D1-D2 and mammary tumor virus-induced tumors, but not between D1-D2 and chemically induced mammary tumors or fibrosarcomas. Increased survival could be blocked by sera from sensitized mice. In contrast to mammary tumor virus-induced mammary lesions, the immune responses to D1 and D2 HAN lines and tumors are "weak" and indeed perhaps stimulate hyperplastic and neoplastic cell survival.