Abstract
Eight children with neuroblastoma and five with Wilms' tumour, or osteogenic sarcoma, had serum taken at diagnosis (progressor sera) and again several weeks after the start of treatment (remission sera). Progressor sera, which specifically blocked in vitro, lymphocytotoxic immunity for autochthonous tumour cells, contained immune complexes of tumour‐specific antigen and antibody. Blocking progressor sera from five patients contained both complexes and free antigen, while maximum blocking activity was found in three progressor sera which contained complexes but neither free antigen nor free antibody. Remission sera contained neuroblastoma‐specific antibody which specifically bound antigenic protein spontaneously released from autochthonous tumour‐cell membranes in vitro, and also bound soluble antigen in progressor serum. Neuroblastoma‐specific immune complexes, formed by titration of autochthonous remission serum and membrane‐turnover antigen, produced maximum blocking of autochthonous lymphocytotoxic immunity at antigen‐antibody equivalence. Complexes formed in antigen excess showed moderate blocking activity while complexes formed in antibody excess showed minimal blocking activity. The ability of a malignant tumour to generate local or systemic excess of membrane‐derived antigen may assist successful escape from specific cellular immune destruction.