Sanofi licenses KT501 tri-specific T-cell engager from Kali Therapeutics in USD 1.23b deal

Sanofi has licensed exclusive worldwide rights to KT501, a tri-specific T-cell engager developed by Kali Therapeutics, for the treatment of B cell-mediated autoimmune diseases. Kali Therapeutics, a clinical-stage biotechnology company based in San Mateo, California, will receive upfront and near-term payments totaling USD 180 million under the agreement announced March 23, 2026. Paris-based Sanofi assumes full responsibility for development and commercialization of the asset globally.

Kali Therapeutics is also eligible for up to USD 1.05 billion in development and commercial milestone payments. The deal includes tiered royalties on net product sales ranging from high-single digits to double digits. The company did not disclose the breakdown between development and commercial milestones. No equity component was mentioned. The total potential deal value, excluding royalties, reaches approximately USD 1.23 billion.

Deal context

KT501 is an IgG-like tri-specific T-cell engager that simultaneously binds three targets: CD3 on T cells, and CD19 and BCMA on B-lineage cells. By engaging both CD19 and BCMA, the molecule is designed to deplete a broader range of B cell populations than agents targeting a single B cell marker. This includes long-lived plasma cells expressing BCMA, which may evade CD19- or CD20-directed therapies. The tri-specific format recruits T cells to kill the targeted B cells directly.

A central feature of KT501 is Kali Therapeutics' CD3 masking technology, which aims to decouple T-cell activation potency from cytokine release. In non-human primate studies, KT501 demonstrated B cell depletion in peripheral blood and tissues with reduced cytokine production relative to unmasked constructs, according to the company. No peer-reviewed preclinical data have been published.

KT501 is currently in a first-in-human Phase 1 trial evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics in adults with moderately to severely active rheumatoid arthritis who have had inadequate responses to disease-modifying antirheumatic drugs. The trial (NCT07234773) began enrolling in March 2026 with an anticipated 24 participants and an estimated completion date of August 2027. No clinical data have been reported.

The deal is structured as a full outright license with no option gates or co-development provisions. Sanofi obtains all operational control from signing. Kali Therapeutics retains no co-promotion or co-commercialization rights and participates only through milestone and royalty economics. The company retains its proprietary multi-specific antibody engineering platform, which was used to generate KT501 but is not part of this transaction.

For Sanofi, the deal adds a differentiated autoimmune asset to its immunology portfolio. The use of T-cell engagers for B cell depletion in autoimmune diseases has attracted multiple large pharma companies over the past two years. Sanofi's existing capabilities in immunology and biologics manufacturing position it to advance KT501 through later-stage development. For Kali Therapeutics, the USD 180 million in upfront and near-term payments provides capital while the company retains its platform for additional programs.

Several other companies are pursuing T-cell engagers for autoimmune indications with overlapping biology:

• CMG1A46 — GSK/Chimagen Biosciences — tri-specific T-cell engager targeting CD19 × CD20 × CD3 for systemic lupus erythematosus • LBL-051 — Oblenio Bio — CD19 × BCMA × CD3 engager for autoimmune diseases • REGN7257 — Regeneron — bispecific T-cell engager targeting CD20 × CD3 for autoimmune indications

The CD19 × BCMA × CD3 target combination used by KT501 is shared by Oblenio Bio's LBL-051, making that program the most directly comparable asset. The rationale for dual B cell targeting rests on the hypothesis that depleting both CD19-positive B cells and BCMA-positive plasma cells may produce deeper and more durable responses than single-target approaches in autoimmune diseases where pathogenic antibody-secreting cells persist.

KT501 holds no special regulatory designations from the US FDA. The Phase 1 trial remains in early recruitment, and no efficacy signals are yet available.

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