KT501

**KT501** is a novel IgG-like trispecific T cell engager (TriTE) antibody developed by Kali Therapeutics for the treatment of autoimmune diseases. It simultaneously binds **CD19**, **BCMA**, and **CD3** with high affinity, enabling targeted T-cell mediated cytotoxicity against a broad spectrum of B cells, including long-lived plasma cells, to achieve rapid and deep B-cell depletion. Featuring a unique CD3 masking platform, KT501 demonstrates potent B-cell killing with minimized cytokine release in preclinical studies, including in vitro assays and non-human primates, where single subcutaneous or intravenous doses led to profound depletion in blood, bone marrow, spleen, and lymph nodes, alongside reductions in serum immunoglobulin levels (IgA, IgG, IgM). It is well-tolerated in repeated-dose cynomolgus monkey toxicology studies across a wide dose range (0.01-10 mg/kg SC), with transient cytokine elevations resolving within 24 hours and no fever or clinical signs. A Phase 1 first-in-human trial (NCT07234773) in rheumatoid arthritis patients is recruiting, evaluating safety, tolerability, PK/PD via single subcutaneous ascending doses, with B-cell follow-up up to 6 months.[1][3][5]