Surface membrane changes of T cells induced by syngeneic tumour cells. II. T-cell defects induced by small tumour cell inocula or tumour cell antigens.

Injection of a large number of tumour cells, like other strong immunogenic challenges, is followed within 6 h by the uptake of cytophilic Ig (probably complexes) by a subpopulation of T cells. This phenomenon, known as the "6-hour T-cell response" is abrogated when small tumour cell inocula (10(2)), or small amounts of a preparation from tumour cells, which contains tumour antigens, are injected prior to the immunogenic challenge Abrogation of the "6-hour T-cell response" resulted in a decrease in specific anti-tumour cell immunity as tested in vitro by measuring growth inhibition (cytostasis). It has also resulted in loss of the amplifying function on antibody formation against sheep erythrocytes, normally detected in a T-B cell co-operative system when T cells are used 6 h after priming with sheep erythrocytes. It is postulated that this T-cell defect may represent a mechanism by which tumour cells, in the early stages of their growth, interfere with inductive stages of the immune response for a sufficient period of time to allow the tumour to grow beyond immune control.