Blocking of Lymphocyte-mediated Cytotoxicity for Rat Hepatoma Cells by Tumour-specific Antigen-Antibody Complexes

Abstract

LYMPHOCYTES from tumour-bearing animals are often cytotoxic in vitro against cultured tumour cells from the same individual^1–4. It is possible that the serum of tumour-bearing hosts may contain circulating factors which interfere with the cell-mediated immune responses concerned in tumour rejection reactions⁵. Evidence has been provided by the demonstration that lymphocyte cytotoxicity against cultured tumour cells could be blocked by first exposing tumour cells to serum from tumour-bearing animals^2,3; similar effects have also been observed in cancer patients^6,7. The blocking factor in tumour-bearer serum has the characteristic properties of 7S immunoglobulins², suggesting the involvement of tumour-specific antibody. Serum blocking activity is rapidly lost, however, in animals rendered tumour free and the activity of tumour-bearer serum can be neutralized by the addition of serum from these animals^8,9. One explanation is that the blocking factor in tumour-bearer serum is antigen-antibody complex, and the objective of these studies, using a transplanted rat hepatoma (D23), was to test directly whether such complexes prepared from solubilized tumour-specific antigen and antiserum exhibit blocking activity.