TRexBio has raised about $116.7 million in a Nasdaq initial public offering, pricing 8,333,334 shares at $14.00 — the bottom of its advertised $14 to $16 range — and beginning to trade on 9 October 2026 under the ticker TRXB. The South San Francisco biotech's largest shareholder, Eli Lilly, is set to hold roughly 16.8% of the company after the offering, and the proceeds are earmarked chiefly to fund Phase 2 testing of TRB-061, an experimental drug designed to activate the body's own regulatory T cells against atopic dermatitis.
TRexBio's IPO in four figures
Figures from TRexBio's SEC prospectus and 8–9 October 2026 IPO coverage.
Priced at the bottom, backed by Lilly
TRexBio sold all 8,333,334 shares in its own offering at $14.00, the floor of the $14–$16 range it had marketed, for gross proceeds of about $116.7 million. J.P. Morgan, Evercore ISI, Cantor and Stifel led the book-running, with Wedbush PacGrow also a book-runner; underwriters hold a 30-day option on up to 1,250,000 additional shares. Trading opened on the Nasdaq Global Select Market on 9 October 2026 under TRXB, with the offering expected to close 13 October.
Eli Lilly's position is the deal's throughline. Lilly held about 24% of TRexBio's shares before the IPO and is expected to hold roughly 16.8% afterward, making it the company's largest shareholder through the listing. The relationship runs deeper than an investment: Lilly also co-developed TRB-051, a separate program from TRexBio's Treg platform that Lilly has advanced into a Phase 2a trial for lupus.
“Tissue Tregs are not merely passive suppressors of inflammation, but active orchestrators of tissue immune homeostasis and repair.” TRexBio, company description of its scientific thesis, 2026 financing and IPO materials
A fusion protein built to switch on Tregs, not add more of them
TRB-061 is a TNFR2 agonist Fc-fusion protein, not a cell therapy. Rather than manufacturing and infusing regulatory T cells the way some competitors do, it is designed to selectively agonize TNFR2, a receptor concentrated on the most tissue-protective Tregs already present in skin and gut, switching on cells the patient's immune system already has. The Phase 1a single ascending-dose portion in healthy volunteers is complete; the ongoing Phase 1b multiple ascending-dose portion is enrolling patients with moderate-to-severe atopic dermatitis, with topline data expected in mid-2027.
Three things that separate TRB-061's bet
Activates Tregs in place
TRB-061 agonizes TNFR2 on tissue-resident Tregs rather than manufacturing and infusing cells, avoiding the cell-therapy manufacturing and dosing complexity some Treg competitors carry.
An Fc-fusion, not an antibody cocktail
The molecule mimics the natural TNF ligand in a single fusion protein, a simpler construct than multi-antibody approaches targeting the same pathway.
Lilly as both investor and partner
Lilly's roughly 16.8% post-IPO stake sits alongside a separate co-development deal on TRB-051, giving TRexBio a committed partner with its own Phase 2a asset validating the underlying Treg biology.
A market nobody has priced yet because nothing is approved
No Treg-targeted therapy has reached approval in autoimmune or inflammatory disease, which is exactly why market researchers' forecasts for the category vary so widely — they are pricing a drug class, not a track record. What is not in dispute is the capital flowing toward the thesis: competitors pursuing tissue Tregs by other routes have raised far larger rounds than TRexBio's IPO, which suggests investors are placing several different bets on how to switch these cells on rather than converging on one approach.
Treg therapeutics, before a single approval
No approved drug yet
Published estimates for regulatory T cell (Treg) therapeutics vary widely by publisher and methodology, reflecting a market still defined by clinical-stage programs rather than sales.
Sources: BioSpace, Sonoma Biotherapeutics Series B financing · Future Market Insights, Treg Therapy Market
Regulatory News outlook
We read the roughly $630 million raised across TRexBio, Sonoma, GentiBio and Abata's disclosed rounds as the market's real current price on tissue-Treg biology, not any published total-addressable-market figure; the first Treg therapy to reach a Phase 2 readout, not a market report, will reset that price.
How we got here: We summed the four companies' most recently disclosed financing rounds (TRexBio $116.7M, Sonoma $265M, GentiBio $157M, Abata $95M) as a proxy for invested conviction in the approach, since no Treg-targeted therapy has generated sales to forecast from.
TRB-061 against the other ways to switch on a Treg
| Program | Approach | Lead indication | Stage |
|---|---|---|---|
| TRexBio TRB-061 | TNFR2 agonist Fc-fusion protein, activates existing tissue Tregs | Atopic dermatitis | Phase 1a/1b |
| Sonoma Biotherapeutics | Engineered Treg cell therapy | Type 1 diabetes and other autoimmune disease | Preclinical/early clinical |
| GentiBio | Engineered Treg cell therapy | Type 1 diabetes | Preclinical/early clinical |
| Abata Therapeutics | Engineered Treg cell therapy | Multiple sclerosis, type 1 diabetes, inclusion body myositis | Early clinical |
From each company’s own disclosures and financing announcements; not a clinical comparison.
From a Series B extension to a Nasdaq ticker
TRexBio’s road to TRXB
- 2024
TRB-061 enters Phase 1
First dosing in the Phase 1a/1b trial of TRB-061, TRexBio’s lead TNFR2 agonist program.
- January 2026
$50M financing extension
Series B extension to fund a growing clinical-stage immunology pipeline of tissue-targeted Treg therapeutics.
- 18 September 2026
S-1 filed
TRexBio files its initial Form S-1 with the SEC to go public.
- 8 October 2026
IPO priced
8,333,334 shares priced at $14.00, the bottom of the $14–$16 range, for about $116.7 million.
- 9 October 2026
TRXB begins trading
Shares begin trading on the Nasdaq Global Select Market.
- Mid-2027
Phase 1b topline data targeted
Topline results expected from the atopic dermatitis portion of the ongoing trial.
What the IPO money still has to answer
Going public raises the stakes on data TRexBio has not yet produced. The Phase 1a portion showed TRB-061 was generally well tolerated with consistent pharmacokinetics in healthy volunteers — a safety readout, not evidence the drug works. Whether activating tissue Tregs with a single fusion protein actually clears atopic dermatitis lesions, and at what dose, is exactly what the Phase 1b portion now underway, and the Phase 2 program the IPO proceeds are meant to fund, will have to show.
- No efficacy data yet: Phase 1a confirmed tolerability and pharmacokinetics in healthy volunteers, not that TRB-061 treats atopic dermatitis.
- Phase 1b timing: topline data from the atopic dermatitis cohort is targeted for mid-2027, after the $90 million earmarked for Phase 2 would already need to be committed.
- Underwriter option: underwriters can still purchase up to 1,250,000 additional shares within 30 days of the offering, which would raise further gross proceeds if exercised.
Sources & further reading
- TRex Bio, Inc., Form 424B4 (final prospectus), U.S. Securities and Exchange Commission, 9 October 2026. sec.gov
- Fierce Biotech, “Lilly-backed TRex rakes in $117M IPO, while hypertension biotech Retension reveals $45M listing,” 2026. fiercebiotech.com
- MedCity News, coverage of the TRexBio and Retension Pharmaceuticals IPO pricings, October 2026. medcitynews.com
- IPO Scoop, “The IPO Buzz: TRex Bio (TRXB) Prices IPO at $14 — Low End — to Raise $116.62 Million.” iposcoop.com
- Latham & Watkins, “Latham Advises on TRexBio Initial Public Offering,” October 2026. lw.com
- TRexBio, pipeline page (TRB-061, TRB-071, TRB-051). trex.bio
- ClinicalTrials.gov, Phase 1a/1b study of TRB-061, NCT06934252. clinicaltrials.gov
Regulatory News reports on public regulatory documents. It is not legal advice, and the primary sources above govern. If we have made an error, we will say so in public: see corrections.
Frequently asked questions
How much did TRexBio raise in its IPO?
About $116.7 million gross, selling 8,333,334 shares at $14.00 each — the bottom of its advertised $14–$16 range — which priced on 8 October 2026 with trading beginning on the Nasdaq Global Select Market on 9 October under the ticker TRXB.
What is Eli Lilly's role?
Lilly is TRexBio's largest shareholder, holding roughly 24% of shares pre-IPO and about 16.8% after the offering, and is also a discovery partner on a separate program (TRB-051) now in a Phase 2a lupus trial.
What will the IPO proceeds fund?
Company disclosures describe roughly $90 million earmarked for Phase 2 trials of TRB-061 in atopic dermatitis, plus work extending the Treg-activation platform into other autoimmune and inflammatory diseases, including alopecia areata.
Is TRB-061 an approved drug?
No. It is an investigational TNFR2 agonist Fc-fusion protein in a Phase 1a/1b trial (NCT06934252); the single ascending-dose portion is complete and multiple ascending-dose testing in patients with moderate-to-severe atopic dermatitis is underway, with topline Phase 1b data expected in mid-2027.
