Compass Therapeutics, Inc. announced that the first patient has been dosed in the Phase 1b study of CTX-471 in combination with KEYTRUDA®, Merck's anti-PD-1 therapy, in patients with advanced solid tumors. CTX-471 is supplied by Compass, which is also the sponsor of this study, and KEYTRUDA® will be supplied by Merck (known as MSD outside the United States and Canada) under a clinical collaboration and supply agreement between the companies. This study enrolls patients with metastatic or locally advanced non-small cell lung cancer, melanoma, small cell lung cancer, mesothelioma, and head and neck cancer that have progressed after treatment with a checkpoint inhibitor.

Patients enrolled in the study will be treated with CTX-471 in combination with KEYTRUDA® with the goal of restoring response. CTX-471 is a next generation, CD137 agonist, fully human, IgG4, with optimized affinity for an agonistic antibody. It binds to a unique, membrane proximal epitope of the CD137 receptor, leading to enhanced activation of T-Cells and NK Cells.

CTX-471 has completed a Phase 1 dose escalation and cohort expansion study, where it was shown to be well-tolerated. The Phase 1b monotherapy study is fully enrolled and ongoing. In this study, CTX-471 has been evaluated as a monotherapy treatment in patients with advanced solid tumors who received at least one checkpoint inhibitor post progression.

As of September 30, 2022, 4 partial responses (PRs) have been observed in the Phase 1b study and 3 of the 4 were confirmed by RECIST 1.1.