Transfection of Transforming Growth Factor-β Producing Tumor EMT6 with Interleukin-2 Elicits Tumor Rejection and Tumor Reactive Cytotoxic T-Lymphocytes

Abstract

One mechanism by which potentially immunogenic tumors evade the immune response is production of immunosuppressive factors. The murine mammary sarcoma EMT6 has previously been demonstrated to inhibit the proliferation of B-cells, suggesting that this tumor produces immunosuppressive factors. Here, we show that supernatant from EMT6 inhibits the development of cytotoxic T-lymphocytes (CTLs) and that this inhibition can be reversed by addition of recombinant interleukin (IL)-2. Furthermore, we show that EMT6 produces high levels of the immunosuppressant factor transforming growth factor (TGF)-beta. To determine if the T-cell growth factor IL-2 within the tumor microenvironment could reverse the immunosuppressive effect of EMT6, we transfected EMT6 with an expression vector containing the cDNA for murine IL-2 under the control of the beta-actin promoter. These transfectants produce significant levels of IL-2 (26 U/ml). EMT6/IL-2 is rejected by mice at 100-fold higher challenge than are parental cells or control transfectants (neomycin resistance only). Thy-1-expressing cells purified from EMT6/IL-2 tumors show greater cytotoxicity against the parental EMT6 cells than do those from the control transfectant. Thus, IL-2 can reverse the effects of TGF-beta on development and/or proliferation of CTL reactive with EMT6, allowing the establishment of mature effectors in vivo. This has significant implications for the development of CTL and immunotherapy for immunosuppressive tumors.