Strengthening of antitumor effects in breast cancer from a novel B7-H4- and CD3-targeting bispecific antibody by an oncolytic virus

Background: For programmed cell death protein 1/programmed death-ligand 1 (PD-L1)-positive triple-negative breast cancer (TNBC), the addition of immune checkpoint inhibitors (ICIs) to chemotherapy has been shown to increase the objective response rate (ORR) by only 13.4-16.3%. Thus, examining converting tumor immunogenicity and targeting novel pathways may be needed to improve response to immunotherapy. B7-H4 is an emerging target for breast cancer immunotherapy. However, the antitumor effect of B7-H4 is unstable during cell generation and further research is necessary to strengthen the antitumor efficacy of B7-H4.

Methods: To explore the potential of B7-H4-targeted immunotherapy of breast cancer, current study generated four monoclonal antibodies (mAbs) against B7-H4 through immunization of mice followed by phage display technology. T cell-engaged bispecific antibodies and immunotoxins were created based on these mAbs. To evaluate the anti-tumor activity of B7-H4-targeting bispecific antibody and immunotoxin, the anti-tumor efficacy test in vitro and in mice models in vivo were performed. Moreover, to boost the efficacy, oncolytic virus herpes simplex virus type 2 (HSV-2) was combined with the bispecific antibody and tested in mice models.

Results: Rigorous in vitro cytotoxicity assay showed that both B7-H4 bispecific antibodies and immunotoxins were toxic to B7-H4 positive cells, with the former being more potent. However, in vivo studies showed that immunotoxin was slightly more effective in suppressing tumor growth. Further, bispecific antibody combined with oncolytic virus HSV-2 revealed a synergistic effect in suppressing tumor growth without causing obvious adverse effects.

Conclusions: Collectively, our findings uncover a novel strategy of combining oncolytic virus HSV-2 with bispecific antibody reinforce antitumor immune response, which warranted further translational investigation.