Mechanisms of "cytostasis" of tumours in vitro by syngeneic lymphoid cells of tumour bearers.

The cytostasis assay is an in vivo-in vitro radioactive technique which detects antitumour responses of the syngeneic tumour-bearing hosts. Examination and characterization of effector mechanisms at the cellular and humoral levels revealed that the cytostasis assay using Meth A (a 3-methylcholanthrene-induced) tumour was T cell independent. Furthermore, both B cells and macrophages were required. It was concluded that the mechanism involved complement-dependent antibody-mediated lysis of the tumour cells, with B cells producing antibody and macrophages producing the complement components during incubation. However, antibody-dependent cell-mediated cytotoxicity with or without complement could not be completely excluded. Although antibody was detected in vivo, specific antibody against Meth A tumour was produced in vitro by cultured lymphoid cells from the tumour-bearers. Antibody-coated Meth A cells caused regression of some tumours when inoculated into BALB/c mice. When these regressor mice were rechallenged with tumour, they were found to be permanently immune to the tumour. In the light of these findings, the role of antibody in the protection of tumours and its implications are discussed.