F-star Therapeutics, Inc. announced that the first patient has been dosed in its Phase 1 trial evaluating FS222, a potentially best-in-class bispecific antibody targeting CD137 and PD-L1. This multicenter, open-label, first-in-human trial will evaluate the safety, tolerability, and clinical activity of FS222 in adult patients diagnosed with advanced malignancies. The adaptive study design will allow for the early exploration of clinical activity of FS222 in a range of selected solid tumor types that will guide further targeted future clinical development. FS222 targets critical tumoral immune-suppressing pathways via PD-L1 checkpoint blockade and has exhibited in preclinical studies important costimulatory effects through potent clustering and activation of CD137, which in turn, synergistically promote T cell activation and enhance cytotoxic T cell responses. In preclinical models, engagement of PD-L1 and CD137 by FS222 induced T cell proliferation and cytokine production associated with significant tumor regression, significantly better than that observed with a combination of CD137 and PD-L1 targeting antibodies.