Functional assessment in vitro of human-complement-dependent antibody-induced cytotoxicity of neoplastic cells

The complement system is one potential cytotoxic effector mechanism that might be effective in immunotherapy of cancer using monoclonal antibodies (mAb) directed against tumor antigens. In order to evaluate the treatment outcome from trials using mAb in cancer patients, assessment of complement-dependent cytotoxicity (CDC) may therefore be of interest. Here we describe the elaboration of a CDC assay in vitro using a rat hepatoma cell line, H4-II-E, as target cells sensitised with mAb F12, directed against the tumor-associated ganglioside antigen fucosyl-GMI. Sensitised cells were incubated with various concentrations of fresh serum as complement source for 48 h and cytotoxicity was then assessed by the tetrazolium bromide (MTT) test. A large variation in CDC efficacy was observed between individual serum donors. No differences in CDC could be seen between healthy donors and cancer patients. The CDC showed a strong correlation to the serum concentrations of complement factor C4, supporting the validity of the assay. Our results suggest that there may be significant variations in complement function within and between individuals that might influence the outcome of clinical mAb therapy. The H4/F12 CDC assay described here, together with measurement of individual complement factors. such as C4, should be further validated in cancer patients at various disease stages and phases of treatment.