ALTERATIONS IN SIGNAL TRANSDUCTION MOLECULES IN LYMPHOCYTES-T FROM TUMOR-BEARING MICE

Impaired immune responses occur frequently in cancer patients or in tumor-bearing mice, but the mechanisms of the tumor-induced immune defects remain poorly understood. In an in vivo murine colon carcinoma model (MCA-38), animals bearing a tumor longer than 26 days develop CD8+ T cells with impaired cytotoxic function, decreased expression of the tumor necrosis factor-alpha and granzyme B genes, and decreased ability to mediate an antitumor response in vivo. T lymphocytes from tumor-bearing mice expressed T cell antigen receptors that contained low amounts of CD3gamma and completely lacked CD3zeta, which was replaced by the Fc(epsilon) gamma-chain. Expression of the tyrosine kinases p56lck and p59fyn was also reduced. These changes could be the basis of immune defects in tumor-bearing hosts.