Beth A. Pulaski

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

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)-β. 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 β-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 (neo-mycin 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-β 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.

Interleukin-3 inhibits the generation of nonspecific killers by interleukin-2

Interleukin (IL)-3 has effects on a wide variety of cell types, including immature cells of the immune system, as well as mature cells such as granulocytes. We have investigated the effects of IL-3 on generation of cytolytic cells that can kill tumor cells. Previously, we have shown that IL-3 can enhance the development of cytolytic T cells (CTL) reactive with the line 1 tumor in a CD4-dependent manner. It is of interest that we found the development of CTL in response to IL-3 was not accompanied by increased development of nonspecific killer cells. This was in contrast to IL-2, which enhanced development of both CTL and nonspecific cells. To determine if IL-3 could inhibit the development of nonspecific killers, we added IL-3 to cultures of fresh spleen cells stimulated with high levels of IL-2. In this assay, IL-3 showed very potent inhibitory activity against the generation of nonspecific killers. To determine if IL-3 could inhibit the IL-2-driven generation of non-specific killers in vivo, we injected a mixture of IL-2- and IL-3-producing line 1 cells. Each cytokine-producing transfectant was also injected alone. The cytotoxicity of tumor-infiltrating lymphocytes (TIL) from these tumors confirmed that the presence of IL-3 inhibits the generation of nonspecific killer cells in vivo.