Molecular Templates Inc. has received IND clearance from the FDA for its novel MT-8421 engineered toxin bodies (ETB) program targeting cytotoxic T-lymphocyte protein 4 (CTLA-4) in patients with relapsed/refractory solid tumors previously exposed to checkpoint inhibitors. MT-8421 is designed to eliminate CTLA-4-expressing regulatory T cells (Tregs) in the tumor microenvironment (TME) through a direct cell-kill mechanism independent of the effector cell presence that antibodies rely upon while not affecting Tregs in the periphery.