A biotech firm focused on immune system regulation has secured $116.7 million in its initial public offering, illustrating a new direction in autoimmune disease research. TRexBio, headquartered in South San Francisco, specializes in restoring immune balance by activating regulatory T cells (Tregs) already present in patients, rather than creating or sourcing new cells from external sources.
The company priced 8.33 million shares at $14 each, the lowest point in its preliminary range, and began trading on Nasdaq on Friday under the ticker TRXB. Unlike other Treg-based therapies that demand harvesting and modifying a patient’s own cells—or shipping blood samples to external labs—TRexBio’s method uses fusion proteins to selectively expand Tregs directly in inflamed tissues. The company claims this approach removes logistical and cost barriers that have restricted the broader use of cell-based treatments.
TRexBio’s lead program, TRB-061, targets tumor necrosis factor receptor 2 (TNFR2) to activate Tregs. Phase 1a results from August demonstrated the drug expanded Tregs in healthy volunteers without serious side effects. The company intends to move it into a Phase 1b trial for moderate-to-severe atopic dermatitis, with preliminary findings expected in mid-2027. Alopecia areata remains a key focus, given evidence linking Tregs to hair follicle cycles.
A second candidate, TRB-071, targets the CD30 protein to boost tissue Tregs and block inflammatory signals. TRexBio cites genetic studies connecting CD30 to inflammatory bowel disease and plans to initiate Phase 1 testing in early 2025. The company’s pipeline also includes TRB-051, developed with Eli Lilly, which is set to enter Phase 2a testing for lupus with skin involvement.
The IPO proceeds follow years of private funding, including a $55 million upfront payment from Lilly in 2023 and a $15 million milestone payment last year. Lilly remains TRexBio’s largest shareholder with a 16.8% stake, though it has indicated interest in purchasing additional shares, up to 19.9%, without a formal commitment.
Before the IPO, TRexBio had $90.9 million in cash reserves. The company plans to spend about $90 million to bring TRB-061 through the readout of topline Phase 2 data in atopic dermatitis and alopecia areata and $10 million for the start and completion of TRB-071’s Phase 1 test in healthy volunteers.
Unlike cell-based therapies that require complex manufacturing, such as Orca Bio’s FDA-approved Treg treatment, which ships patient blood to external facilities, TRexBio’s approach eliminates those requirements. The company’s platform relies on analyzing diseased and healthy tissue samples to identify molecules capable of restoring immune balance without triggering broader inflammation.
TRexBio was founded in 2018, and Lilly participated in its Series A financing in 2021. A prior collaboration with a Johnson & Johnson affiliate concluded last year, though JJDC retains a 4.6% stake post-IPO. The company had raised about $220 million in private funding before going public, including a $50 million financing early this year.
Lilly’s collaboration has generated $70 million in upfront and milestone payments, with up to $577.5 million more possible under the agreement.
