Effects of Anti-transforming Growth Factor-β Antibody and Interleukin-2 in Tumor-bearing Mice

Abstract

In previous studies we found that the immunosuppression seen in mice bearing Herpes virus type 2-transformed (H238) fibrosarcoma was likely to be due to tumor-derived transforming growth factor-β (TGF-β). In vitro experiments showed that interleukin-2 (IL-2) and antibodies against TGF-β could significantly counteract TGF-β-induced depression in lymphocytes. The present study was performed to determine if the administration of polyclonal anti-TGF-β antibody and recombinant IL-2, alone or in combination, could inhibit H238 tumor progression in vivo and to investigate possible mechanisms of action. The tumor cells were injected s.c. at 1 x 10⁶ cells/mouse and treatments were given 1-10 days post-injection. In phase I, a total of 25,000 units of IL-2 (5,000 units/injection) and/or 900 ng of anti-TGF-β (100 ng/injection) were administered i.p. per animal. Phase II was conducted similarly, except that each mouse received a total of 127,500 units of IL-2, either with or without the same amount of antibody. No treatment-related toxicity was noted. Tumor volumes were monitored for 16-18 days after tumor implantation. The H238 tumors in treated mice from both both phases grew as rapidly as, or significantly faster than, in untreated controls. Significant enhancement of tumor growth was found in the groups given IL-2 as a single agent, regardless of total dose. The combination of the higher IL-2 dose with anti-TGF-β resulted in more rapid tumor progression than in animals given the antibody alone. Relative spleen weights, peripheral blood leukocyte counts, and the chemiluminescent oxidative burst of phagocytes were significantly elevated in all tumor-bearing mice, whereas T cell response to mitogenic stimulation was depressed. However, the oxidative burst capacity of spleen (but not blood) cells and natural killer cell cytotoxicity were markedly lower in the treated groups compared to nontreated tumor-bearing controls. In contrast, plasma levels of tumor necrosis factor-α and IL-2 were substantially higher in the group given both modalities (phase II) compared to the other treated groups. These findings show that anti-TGF-β antibody, both with and without low-dose IL-2 regimens, can be safely administered in vivo. However, tumor growth was not delayed by the treatment protocols used. The induction of hyporesponsiveness in certain cell types may account, at least partly, for the enhancement seen in tumor progression.