Heteroconjugated antibodies enhance lymphocyte-mediated tumour cell lysis in vitro and in vivo

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 beta-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 beta-glucan plus BsAb. Fresh splenocytes, lymph-node cells and tumor-infiltrating lymphocytes (TIL) were tested for their proliferative response using incorporation of 3H-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 beta-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 beta-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 beta-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 beta-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 beta-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.

Pulmonary metastases neutralization and tumor rejection by in vivo administration of beta glucan and bispecific antibody

Bispecific antibody (BsAb) with specificity for tumor cell surface antigen and the CD3 molecule on T cells can redirect activated T cells to lyse tumor cells. Since the ex vivo expansion and activation of T cells is impractical and ineffective for treating established tumors, we tested whether the immune stimulant beta glucan could in situ-activate T cells, which could secondarily be retargeted with BsAbs to lyse tumor cells. To test for tumor neutralization, C3H/HeN mice were injected i.v. with Cl-62 melanoma cells and immediately treated with i.p. beta glucan and/or anti-CD3 (500A2) x anti-p97 (96.5) F(ab')2 BsAb i.v. Pulmonary metastases were counted 14 days later. To test for tumor rejection and survival in a solid tumor model, mice were injected s.c. and i.p. with Cl-62 cells and 7 days later administered beta glucan i.p. and/or F(ab')2 BsAb i.v. In the neutralization model, there was a significant reduction in the number of metastases in the beta glucan + BsAb group, as compared with controls, and with beta glucan alone. In the established tumor model, beta glucan + BsAb reduced the incidence of s.c. tumors as compared with control, with BsAb alone and with beta glucan alone. It also prolonged survival of tumor-bearing mice compared with control, BsAb alone and beta glucan alone. We conclude that T cells can be activated in vivo by beta glucan and retargeted with F(ab')2 BsAb.

The bispecific antibody 500A2 x 96.5 targets T-lymphocytes activated in vivo with staphylococcal enterotoxin B (SEB) against CL62 melanoma cells in vitro

Bispecific antibodies (BAb) direct T-lymphocytes to lyse selected tumour targets, both in vitro and in vivo. Significant tumour cell lysis with BAb requires pre-expansion of T-lymphocytes, which may be achieved in vitro by the addition of anti-CD3 monoclonal antibody plus interleukin-2 (IL-2), but anti-CD3 may cause immunosuppression. We investigated an alternative agent for in vivo immunostimulation, staphyloccal enterotoxin B (SEB), which selectively activates certain T-cell subsets and may result in less immunosuppression than with anti-CD3. We activated T-lymphocytes in vivo with SEB, expanded them in vitro with IL-2, and directed them against a tumour target with the BAb 500A2 x 96.5, specific for the murine CD3 antigen and the melanoma p97 antigen expressed by the CL62 tumour. C3H mice received SEB 50 micrograms intraperitoneally (i.p.). After 18 h mice were sacrificed and splenocytes extracted and either passed over a nylon wool column to isolate T-lymphocytes, or cultured in vitro for 3 to 7 days with 100 U ml-1 of IL-2. A 4-h chromium-release assay was used to assess the ability of T-lymphocytes to lyse the tumour target CL 62 in the presence or absence of the bispecific antibody 500A2 x 96.5. The addition of BAb significantly enhanced tumour lysis by SEB activated cells after a period of in vitro culture with IL-2. In vivo SEB results in the activation of T-lymphocytes which may be directed by bispecific antibodies to increase the lysis of selected tumour targets in vitro.