Tumor-infiltrating lymphocytes can be activated in situ by using in vivo activants plus F(ab')₂ bispecific antibodies

In vitro-activated T lymphocytes can be retargeted with anti-CD3 x anti-tumor bispecific antibodies (BsAb) to kill tumor cells in vitro and in vivo. The purpose of the present study was to examine the systemic and intra-tumor effects of in vivo T-cell activation with BsAb, staphylococcal enterotoxin B (SEB), and β-glucan in combination with BsAb as a retargeting agent. CL-62 melanoma cells were injected subcutaneously into C3H/HeN mice. Mice were subsequently treated with BsAb alone or with SEB or β-glucan plus BsAb. Fresh splenocytes, lymph-node cells and tumor-infiltrating lymphocytes (TIL) were tested for their proliferative response using incorporation of ²H-thymidine, and for their ability to lyse CL-62 cells in the presence or absence of BsAb in 4-hr ⁵¹Chromium release assays. Toxicity of treatments was assessed in a D-galactosamine model. BsAb, alone or combined with β- glucan, had essentially no effect on systemic T-cell cytotoxicity, and essentially no effect on systemic proliferation, unless exogenous IL-2 was provided. At the tumor site, BsAb alone, BsAb plus β-glucan, and SEB plus BsAb all significantly increased BsAb-mediated TIL cytotoxicity. In contrast to the TIL-limited effects of BsAb and of BsAb plus β-glucan, SEB plus BsAb markedly increased both systemic and intra-tumor T-lymphocyte activation. Toxicity correlated with measures of systemic activation, with limited effects from BsAb alone and from β-glucan plus BsAb, and with marked lethality from SEB plus BsAb. Overall, these results suggest moderate intra- tumor activation of TIL, but no measurable systemic activation after in vivo treatment with BsAb or β-glucan plus BsAb. SEB plus BsAb results in complete T-cell activation in both systemic and intra-tumor compartments, but at the expense of increased systemic toxicity. In conclusion, TIL can be activated in situ with different combinations of in vivo activants. In vivo- activated TIL can be retargeted with bispecific antibodies to lyse tumor cells, and may be an alternative to ex vivo T-cell activation and adoptive transfer therapy.