TRexBio Secures $50M Funding Round in San Francisco

South San Francisco has seen plenty of biotech ambition, but TRexBio moves with a different weight. Founded in 2018, the company didn’t arrive selling buzzwords or miracle cures. It arrived with a harder question: why does the immune system lose control inside tissues, where disease actually lives, while most drugs keep treating blood like the whole story. That question became a platform, and that platform is now in the clinic.

This week, TRexBio closed a $50M Series B extension, announced January 26–27, 2026, bringing total capital raised to roughly $219M and extending the November 2024 Series B. New investors Janus Henderson Investors, Balyasny Asset Management, and Affinity Asset Advisors joined returning backers including Alexandria Venture Investments, Avego BioScience Capital, Delos Capital, Eli Lilly and Company, Johnson & Johnson Innovation JJDC, Pfizer Ventures, Polaris Partners, and SV Health Investors. In a cautious biotech market, this round filled up.

The science carries it. TRexBio decodes tissue immune biology with a focus on regulatory T cells, the immune system’s internal moderators. Most T cells live in tissue, not blood, and TRexBio built its Deep Biology Platform around that fact. The result: more than 20 therapeutic targets translating dense human tissue data into drugs designed to restore balance, not flatten immunity.

The lead program, TRB-061, has crossed real lines. First patient dosed June 2, 2025. Phase 1a complete. Phase 1b underway in moderate to severe atopic dermatitis. The molecule selectively activates TNFR2 on the most suppressive tissue-resident Tregs, expanding restraint without igniting the broader immune system. Precision where it matters.

Validation followed. Eli Lilly advanced the partnered TRB-051 program into Phase 1 in June 2024, triggering a double-digit million milestone and unlocking more than $1.1B in potential future payments. That’s not belief. That’s chips on the table.

Execution sits with a team built for this phase. CEO Johnston Erwin brings deep drug development and venture experience from Eli Lilly. CSO Ali Zarrin, PhD, turns immunology into medicines. CMO Ariella Kelman, MD, adds nearly two decades of inflammatory disease development. COO Laura Berner, JD, MBA, and CFO Brandon Hants, MBA, complete a leadership bench designed for clinical scale.

TRexBio may be named like a predator, but the strategy is restraint. Precision over brute force. Tissue over theory. With TRB-061 advancing, programs like TRB-071 and TRB-081 following, and capital in place, the question is no longer whether this approach works. It’s how far immune discipline can go once the data starts speaking louder than the funding.