Tumor-induced suppression of antitumor reactivity and depression of TCRzeta expression in tumor-draining lymph node lymphocytes: possible relationship to the Th2 pathway.

Abstract

T lymphocytes from tumor-draining lymph nodes (TDLN), after activation and expansion in vitro, can mediate regression of metastatic tumor in animal models. We have shown that TDLNs are subject to tumor-induced suppression that is tumor specific, T-cell mediated, and dependent on the duration of tumor growth, but the mechanism of this suppression remains largely unknown. Recently, in other model systems, tumor-bearer T cells have been shown to have decreased expression of T-cell receptor-zeta (TCR zeta), a key component in antigen-driven activation pathways. We sought to investigate whether the suppression of TDLN reactivity that accompanies prolonged tumor growth was associated with decreased expression of TCR zeta in fresh and in vitro activated lymph node lymphocytes. Mice bearing subcutaneous tumor deposits of MCA 205 had TDLN cells harvested after various durations of tumor growth, then activated in vitro with anti-CD3 for 2 days (activation phase), followed by expansion with interleukin-2 (IL-2) (10 U/ml) for 3 days (expansion phase). Two-color flow cytometry was used to determine TCR zeta expression in fresh and activated TDLN cells. Antitumor reactivity was assessed by the ability of activated TDLN to mediate regression of lung metastases. There was a time-dependent suppression of the antitumor reactivity of the activated TDLN; activated TDLN from mice bearing tumors 14 days or less were able to mediate the regression of established lung metastases, whereas activated TDLN from animals bearing tumors 21 days or more were ineffective. In addition, TCR zeta expression on T lymphocytes from fresh and activated TDLN was also depressed in a time-dependent manner. Because tumor-induced immunosuppression in our model is known to be T cell mediated, we examined whether the Th2 cytokine IL-4, when added in vitro during activation or expansion, could suppress antitumor reactivity and lead to a depression in TCR zeta expression of TDLN cells in a fashion similar to prolonged tumor growth. The addition of 10 U/ml of IL-4 in vitro had a marked suppressive effect on the antitumor activity of day 14 TDLN; the effect was most pronounced when IL-4 was present during the expansion phase. Fluorescence-activated cell sorter analysis of day 14 TDLN exposed to IL-4 in vitro demonstrated a marked decrease in TCR zeta expression, comparable to that seen in late tumor-bearer TDLN. Thus, TDLN from late tumor-bearers show a consistent decrease in TCR zeta expression that is associated with suppressed antitumor reactivity, and exposure to IL-4 in vitro results in qualitatively and quantitatively similar changes. Our observations suggest a mechanism whereby Th2 cells could mediate immunosuppression by downregulating a critical component of the T-cell-receptor signal transduction machinery.