Itolizumab regulates activating and inhibitory signals on effector cells, improving their cytotoxicity against CD318+ tumor cell lines.

Introduction: The CD6-CD318 axis has emerged as a potential target for immuno-oncology. Recent work has shown that blocking the CD6-CD318 interaction with a murine anti-human CD6 antibody increases lymphocyte cytotoxicity. However, several studies have demonstrated the drawbacks associated with the clinical use of murine antibodies and the variability among anti-CD6 antibodies. Therefore, evidence that the first-in-class humanized anti-human CD6 antibody itolizumab could be used for cancer immunotherapy may be a breakthrough in developing an antitumor clinical approach. Methods: Phenotypic and functional characterization of peripheral blood mononuclear cells (PBMCs) from healthy donors after challenge with CD318+ cell lines was performed by flow cytometry. In addition, IFNγ was determined by ELISA in culture supernatants. Immunohistochemical analyses of breast tumor samples were also performed. Results and Discussion: Here, we provide evidence supporting the rationale for itolizumab in cancer immunotherapy. The blockade of the CD6-CD318 interaction by itolizumab increases the cytotoxic capacity of CD8 T and NK cells over CD318+ tumor lines, reverses the NKG2A/NKG2D ratio, and increases granzyme B and IFNγ production. Itolizumab also regulates immune responses by downregulating CD5 expression and upregulating PD-1 and CTLA-4 inhibitory receptors on lymphocytes, which contribute to reducing exacerbated responses and additively enhancing CD318+ tumor cell cytotoxicity when combined with other immunocheckpoint inhibitors. In addition, we report that CD6-CD318 interaction inhibits lymphocyte proliferation and survival while downregulating CD6 expression on lymphocytes