T Cells from Late Tumor - bearing Mice Express Normal Levels of p 56

Loss o f T cell-associated signal transduction molecules has recently been implicated in immune suppression in tumor-beat ing hosts. In the present study, we have examined this and related phenomenon extensively in a large number o f tumor-beat ing mice, analyzed individually. Splenic T cells from tumor-beat ing mice were isolated and characterized with respect to the following: (a) levels o f three tyrosine kinases, p56 tck, p59~", and ZAP-70; (b) expression of CD3-~; (c) alloreactive responses; and (d) antigen-specific responses. Contrary to recent reports, T cells from tumor-bearing mice were observed to express normal levels o f lck, fyn, ZAP-70, and CD3-~. Further, T cells showed healthy alloreactive and antigen-specific responses until ~3 wk after post tumor challenge, when the tumors constituted -20% of the body weight. Alterations with respect to some parameters were observed only in mice that had been beating larger tumors for a considerably longer period. As human tumors are unlikely to grow to such large sizes (e.g., >20% of the total body weight), the significance o f the alterations in T cell expression of Ick, fyn, ZAP-70, or C D 3 r in the immune status of cancer patients is unclear. Altogether, these results indicate that alterations in T cell signal transduction molecules do not account for the profound tumor-specific suppression observed during tumor growth.