Zenas BioPharma and Royalty Pharma announced a strategic $300 million funding partnership that will accelerate development of obexelimab, an investigational bifunctional monoclonal antibody for autoimmune diseases. The agreement provides Zenas with immediate capital to advance its lead program through late-stage development and potential commercial launch while offering Royalty Pharma a 5.5% royalty on worldwide net sales.
Novel B Cell Modulation Approach
Obexelimab represents a differentiated approach to treating autoimmune diseases through its unique dual-targeting mechanism. The bifunctional monoclonal antibody is designed to bind both CD19 and FcγRIIb, which are broadly present across B cell lineage, to inhibit the activity of cells implicated in autoimmune diseases without depleting them.
"There is clear unmet need in IgG4-RD where obexelimab, with its exciting novel B cell modulating mechanism of action, has demonstrated compelling proof-of-concept," said Pablo Legorreta, founder and CEO of Royalty Pharma. "IgG4-RD represents a potential blockbuster opportunity for obexelimab."
The drug candidate has been evaluated in five completed clinical trials involving 198 subjects who received obexelimab either as intravenous infusion or subcutaneous injection. Across these trials, obexelimab was well tolerated and demonstrated pharmacologic activity, providing initial clinical proof of concept as a potent B cell inhibitor.
Comprehensive Development Program
Zenas is currently conducting multiple Phase 2 and Phase 3 trials of obexelimab across several autoimmune diseases. The company's lead indication is Immunoglobulin G4-Related Disease (IgG4-RD), where obexelimab is in Phase 3 development through the INDIGO trial. Additional Phase 2 programs are underway for Relapsing Multiple Sclerosis (RMS) and Systemic Lupus Erythematosus (SLE).
"We are committed to bringing obexelimab to as many patients living with autoimmune diseases as possible and look forward to our upcoming key milestones," said Lonnie Moulder, Founder and Chief Executive Officer of Zenas. These milestones include topline results from the pivotal Phase 3 trial in IgG4-RD expected around year-end, Phase 2 trial results in Relapsing Multiple Sclerosis expected early in the fourth quarter of 2025, and Phase 2 trial results in Systemic Lupus Erythematosus expected in mid-2026.
Transaction Structure and Timeline
Under the agreement, Zenas will receive funding through a structured milestone-based approach. The company receives an upfront payment of $75 million, with three additional $75 million payments contingent upon: achievement of defined success criteria in the Phase 3 INDIGO trial of obexelimab in IgG4-RD, U.S. FDA approval of obexelimab for IgG4-RD, and U.S. FDA approval of obexelimab for SLE.
The financing will support obexelimab development and a potential IgG4-RD commercial launch in the first half of 2027, subject to FDA approval. With the initial $75 million payment, Zenas expects to have sufficient cash to fund operations through the first quarter of 2027.
Strategic Rationale
The partnership reflects confidence in obexelimab's potential as a franchise molecule across multiple autoimmune indications. "This transaction underscores our conviction in the potential of obexelimab as a franchise molecule and provides us with financial flexibility to rapidly advance our clinical programs," Moulder noted.
For Royalty Pharma, the deal builds on what the company describes as a record year for announced value of synthetic royalty transactions. The agreement adds to Royalty Pharma's portfolio of royalties on more than 35 commercial products and 17 development-stage product candidates.
The unique mechanism of action and self-administered subcutaneous injection regimen may position obexelimab to broadly and effectively address the pathogenic role of B cell lineage in chronic autoimmune disease, potentially differentiating it from existing B cell-depleting therapies in the autoimmune space.
