TNFRSF14 (HVEM) is a novel immune checkpoint blockade that can be targeted by a monoclonal antibody to improve anti-tumor response in humanized mice

Abstract Background The TNFRSF14 (herpes virus entry mediator (HVEM)) delivers a negative signal to T cells through the B and T Lymphocyte Attenuator (BTLA) molecule and has been associated to a worse prognosis in various malignancies. Here, we investigated whether HVEM might represent a novel target for cancer immunotherapy. Methods To establish that HVEM represents a novel immune checkpoint, we compared the growth of a prostate cancer cell line expressing or rendered deficient for HVEM by CRISPR/Cas9 genetic editing in PBMC-humanized NOD.SCID.gamma.c-null (NSG) mice. A murine monoclonal antibody to human HVEM was then used to assess the impact of inhibiting the HVEM/BTLA immune checkpoint on tumor growth. We also investigated the mode of action of the antibody by monitoring in vitro its impact on tumor growth and cell viability. We used non parametric t-tests, linear and non linear regression modeling to assess statistical significance of our results. Results We show that deleting HVEM or blocking HVEM/BTLA with a mAb has a profound impact on tumor growth in mice reconstituted with human T cells. This was associated with an increase in the proliferation and number of TIL. However, the therapeutic effect of the mAb was lost with the tumor deficient for HVEM, showing that HVEM expression by the tumor was necessary for the therapeutic effect. Accordingly, no agonist activity of the mAb was detected on human T cells in vivo. Surprisingly, we observe a similar albeit milder effect of the antibody on tumor growth in non-humanized NSG mice that is also lost with the HVEM-deficient cell line. However, in vitro analyses show that the antibody alone has no significant impact on tumor survival per se. In contrast, addition of peritoneal macrophages from NSG mice to the culture results in higher mortality of the tumor, suggesting that myeloid cells of NSG mice might participate in tumor control in vivo. Finally, we reproduce the in vivo antitumor effect of the antibody with an HVEM-positive human melanoma cell line, but not with an HVEM-negative human breast cancer cell line, suggesting that the therapy could be applied to various HVEM-positive cancers, independently of their tissue origin. Conclusion Our results show that HVEM/BTLA is a novel immune checkpoint and that a mAb targeting HVEM might be a promising strategy for cancer immunotherapy.