Antigenic structure of human tumour necrosis factor: recognition of distinct regions of TNF alpha by different tumour cell receptors.

TNF alpha is a cytokine which causes cytolysis of tumour cell lines in vitro as well as haemorrhagic necrosis of many transplanted tumours in vivo. In association with these activities, the cytokine manifests a high degree of toxicity in vivo. The in vitro and in vivo effects of a panel of 13 monoclonal antibodies against human TNF alpha have been investigated. Of these MAbs, eight neutralized TNF alpha activity in the WEHI-164 cytotoxicity assay as well as in the binding of TNF alpha to receptors on these cells. The effects of this group of antibodies on TNF alpha-induced regression of WEHI tumours in vivo correlated with their in vitro neutralizing activities. One MAb which inhibited cytotoxicity, receptor interaction and tumour regression in the WEHI model (MAb 37) failed to inhibit TNF alpha-receptor binding and tumour regression in Meth A models. This observation indicates that different classes of receptor specificity may exist on different tumour cells. Together the antibodies define six non-overlapping epitopic domains on TNF alpha and within these regions there are at least nine overlapping epitopes. Inhibitory MAbs, when co-injected into tumour-bearing mice with radiolabelled TNF alpha, resulted in the diversion of TNF alpha away from both tumour and lung, which correspond to the sites of highest TNF alpha uptake in control MAb-TNF alpha treated mice. In contrast, uptake of TNF alpha by the liver was increased and overall, biodistribution studies showed that very little TNF alpha reached the target tumour but was rapidly and widely dispersed throughout the body. Preliminary studies with these MAbs show that segregation of TNF alpha activities and receptor binding may be possible.