California-based Kali Therapeutics announced US FDA clearance of an investigational new drug (IND) application for KT501, a trispecific B-cell–depleting antibody licensed globally to Sanofi in a deal worth up to approximately USD 1.23 billion. The clearance allows Kali to expand development of the autoimmune candidate into the US after beginning first-in-human testing in rheumatoid arthritis in Australia.

KT501 is an IgG-like trispecific antibody that engages CD19, BCMA, and CD3, with the aim of depleting both mature B cells and plasma cells while recruiting T cells to drive cytotoxic activity. A masking design on the CD3-binding arm is intended to reduce cytokine release, although whether that translates into a wider therapeutic window in humans remains to be established.

The Phase Ia first-in-human trial (NCT07234773) in Australia is an open-label, dose-escalation study evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics of a single subcutaneous dose. Estimated completion is August 2027. The US clearance will allow expansion of clinical activity to American sites, with RA as the entry indication for a broader program targeting B cell–mediated autoimmune diseases.

The broader competitive context for multi-targeted B-cell depletion in autoimmune disease is evolving rapidly, driven in part by early signals from CD19-directed CAR-T therapies in conditions such as systemic lupus erythematosus and myositis. TCEs like KT501 represent an off-the-shelf alternative to cell-based approaches, without the manufacturing complexity or conditioning requirements associated with CAR-T. Whether the CD3 masking strategy can reliably separate potency from cytokine-related toxicity at therapeutic doses in humans remains to be demonstrated; the Australian Phase Ia data informing the IND submission have not been disclosed in detail. Kali said it intends to develop KT501 across a range of B cell–mediated autoimmune diseases beyond RA, with the RA study serving as the initial clinical proof-of-concept setting.

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