Tumor‐bound immunoglobulins. Evidence for the in vivo coating of tumor cells by potentially cytotoxic anti‐tumor antibodies

The experiments described herein were designed to determine whether part of the Ig coat of tumor cells consists of specific anti‐tumor antibodies. It was demonstrated that the inoculation of polyoma virus‐induced sarcoma cells (SEYF‐a) into syngeneic A.B Y mice stimulates the production of cytotoxic antibodies against the tumor‐cell population. The level of these antibodies, which was undetectable during the first week after transplantation, increased markedly during the second week, and remained high thereafter. Following the increase in cytotoxic antibodies in the serum, a cell‐bound potentially cytotoxic antibody was detected on the tumor cells by testing their sensitivity to rabbit complement. The increase in cell‐bound, potentially cytotoxic antibody followed the kinetics of the increase in serum antibody during the second week after transplantation and was inversely correlated to the amount of free antigens on the cell surface. These antigens, responsible for the sensitivity of the cells to a syngeneic hyperimmune cytotoxic antiserum, became non‐available for the cytotoxic antibodies during propagation of the tumor cells. Cells from a tumor propagated for 3 weeks could not compete for antitumor antibodies with cells propagated for 1 week. Yet it was possible to increases the antigenic capacity of cells from an old tumor by a treatment that would cause the release of tumor‐associated Ig. Cytotoxic anti‐SEYF‐a antibodies could be dissociated from tumor cells propagated in vivo by methods causing dissociation of antigen‐antibody complexes, and detected in tumor eluates.