AVB-114

Avobis Bio's AVB-114 is an implantable cell-plus-device combination product for complex Crohn's perianal fistulas, a nasty complication where inflammation eats tunnels between the rectum and the perianal skin. Fat is harvested from the patient, stromal vascular fraction is isolated as the starting material, and culture-expanded pure mesenchymal stem cells (MSCs) are then seeded onto a bioabsorbable plug that fills the fistula tract [1][3]. STOMP-II (NCT04847739), a 48-patient randomized Phase 2 trial (1:1, 24 per arm) at 14 U.S. sites, hit its primary endpoint: 45.8% (11/24) combined remission on AVB-114 versus 8.3% (2/24) on standard-of-care at 9 months, p=0.0078 [1][2][8]. Those results were presented in a plenary session at the American College of Gastroenterology annual meeting and published by Schwartz, Dozois and Ehman in the American Journal of Gastroenterology [1][9]. FDA has granted both Fast Track (February 2025) and Regenerative Medicine Advanced Therapy (RMAT) designation (October 3, 2025), materially de-risking the regulatory path [10][11]. This matters because the only cell-therapy predicate in this indication, Takeda's Alofisel (darvadstrocel), was withdrawn from the European market after its confirmatory ADMIRE-CD II study failed, leaving a real gap for the substantial fraction of patients whose fistulas don't close on anti-TNF therapy plus repeated surgery [4][5].

AVB-114 is a novel investigational combination product (biologic plus device) that has not been approved anywhere. The lead study is STOMP-II (NCT04847739), a Phase 2 randomized trial in adults with complex Crohn's perianal fistulas whose disease has failed conventional and biologic therapy and who have quiescent rectal disease at the time of treatment [2]. Primary-analysis results were reported in 2025 and published by Schwartz et al. in the American Journal of Gastroenterology, with combined remission of 45.8% on AVB-114 versus 8.3% on standard-of-care at 9 months (p=0.0078) [1][8]. FDA has granted AVB-114 Fast Track designation (announced February 2025) and RMAT designation (October 3, 2025) [10][11]. RMAT is among the FDA's most substantial expedited-development programs for cell and regenerative therapies, providing intensive FDA guidance, senior-management engagement, potential rolling review, and design flexibility for the confirmatory trial. Avobis Bio is a small privately-held sponsor and no Series A or B financing round has been publicly announced as of the writeup date; the company appears to be leveraging the RMAT designation and STOMP-II readout as fundraising catalysts. A Phase 3 registration study in this indication will typically demand 200-plus patients with 52-week MRI-adjudicated follow-up, so the commercial path likely requires either a financing round or a partnering deal. Regulators are unlikely to accept STOMP-II as a stand-alone registration package given the Alofisel precedent, where an initially positive Phase 3 (ADMIRE-CD) failed to replicate in the mandated confirmatory study [5]. Watch for Phase 3 initiation announcements, financing or partnering news, and longer-term durability updates.

Crohn's perianal fistulas are abnormal tunnels that form when chronic inflammation from the rectum burns through tissue into the perianal skin. Even the best current medical therapy leaves many patients cycling through drainage procedures for years. Infliximab, the workhorse anti-TNF, closes only about a third of complex fistulas durably in trials like ACCENT II [6]. AVB-114 takes a different route: fill the tract and load it with immunomodulatory cells. Fat tissue is harvested from the patient (typically by liposuction), and the stromal vascular fraction (SVF) is isolated as the starting material. From that SVF, mesenchymal stem cells (MSCs) are then culture-expanded and purified to produce the actual drug substance seeded onto the plug. This step matters: the finished implant is not raw SVF but a defined, expanded MSC product, which affects potency consistency, regulatory classification (combination biologic-device product), and manufacturing scale-up complexity. The expanded MSCs secrete anti-inflammatory and pro-repair factors, recruit regulatory immune cells, and support tissue remodeling. The bioabsorbable plug provides physical scaffolding while the cells locally suppress inflammation and drive healing. Because the cells are autologous, there is no rejection risk and no HLA matching needed. The mechanism has partial external validation: allogeneic adipose-derived MSCs (darvadstrocel/Alofisel) showed benefit in ADMIRE-CD that supported European approval in 2018 [7], but failed the ADMIRE-CD II confirmatory study and were pulled from EU markets [5]. Plug-only devices have shown modest efficacy but poor durability. AVB-114's bet is that plug plus autologous expanded MSCs gives you both structural closure and lasting local immunomodulation, without the donor-to-donor potency variability that likely hurt the allogeneic product.

STOMP-II (NCT04847739) is a Phase 2 randomized study of AVB-114 in adults with complex Crohn's perianal fistulas who have failed prior therapy (typically anti-TNF plus surgical drainage) and who have quiescent rectal disease at the time of treatment [2]. Enrollment was 48 subjects randomized 1:1 (24 per arm) at 14 U.S. sites, with the comparator arm receiving standard-of-care seton drainage plus continued background medical therapy [1][8]. A seton is a surgical thread or drain placed through the fistula tract to keep it open, prevent abscess formation, and allow chronic drainage; it is the workhorse control condition for complex fistulas that have failed medical therapy, which is why placebo/SoC response rates in this indication are typically 30-40 percent even without an active investigational product. The primary endpoint mirrors the one used for Alofisel's Phase 3: combined remission, defined as clinical closure (no drainage on gentle finger compression across all treated openings) plus MRI-confirmed absence of collections larger than 2 cm in at least two of three dimensions, adjudicated by a blinded core lab [1][7]. The primary-analysis result was 45.8% (11/24) combined remission on AVB-114 versus 8.3% (2/24) on standard-of-care at 9 months, p=0.0078 [1][8]. Two design nuances worth flagging: (1) the primary endpoint was assessed at 9 months rather than the week 52 that Alofisel's confirmatory trial used, so regulators and investors will scrutinize longer-term durability data before accepting the effect as registrational, and (2) with only 24 patients per arm the trial is well-powered for the 37-point separation actually observed but leaves relatively wide confidence intervals around subgroup effects. The quiescent-rectal-disease inclusion criterion may also limit generalizability to real-world patients with active proctitis.

Our model estimates a 9% chance this drug is eventually approved. It starts from the historical base rate for Phase 2 drugs in this area (about 30%), then adjusts using ten facts about the trial and sponsor. What moves the number most: it is helped by more secondary endpoints than usual; it is held back by the sponsor's thin or weak approval record, weak or limited earlier-phase results, and a randomized design. The other facts land near average for this stage, so they leave the estimate roughly where the base rate put it.

Efficacy risk is the top concern. The closest predicate (Alofisel) hit its Phase 3 primary endpoint (ADMIRE-CD) and then failed the confirmatory ADMIRE-CD II study, which is why Takeda withdrew the product from Europe [5]. That failure tells you that statistically significant Phase 2 or even Phase 3 signals in this indication can evaporate under confirmatory conditions. Placebo/SoC response rates of 30-40 percent are typical in this space because controls also get seton drainage and continue background therapy; STOMP-II's SoC arm came in unusually low at 8.3%, which widens the observed effect size but should be regressed toward the mean when projecting the Phase 3 comparator. Durability past 9-12 months is where cell-therapy products in this space have historically weakened, and STOMP-II's 9-month primary endpoint is earlier than the week 52 that regulators typically want for confirmatory approval. Safety risk is comparatively manageable. Autologous MSCs avoid rejection and donor viral transmission. The plug component carries known device-related risks: local infection, plug extrusion, and (rarely) sepsis in immunocompromised patients. Theoretical tumorigenicity risk with any expanded-cell product exists but adipose-derived MSCs have a favorable safety history across cosmetic, reconstructive and IBD applications. Execution risk is high given sponsor size. A Phase 3 registration study will need 200-plus patients, likely 52-week follow-up with central MRI adjudication, and multi-center coordination. Avobis Bio has no publicly announced Series A or B round as of this writeup, and will need a partner, a large financing round, or both; the RMAT designation is a real fundraising asset here [11]. Commercial risk is real even with approval: payers will demand demonstrated benefit versus repeated surgery, and Alofisel priced in the €50-60k range struggled with European uptake before it was pulled. Autologous manufacturing is likely more expensive per patient than allogeneic, which will pressure pricing negotiations with payers who already view Crohn's fistulas as a surgical problem.

Worth watching, and materially more interesting than the pre-computed PoS suggests. The STOMP-II primary readout (45.8% vs 8.3% combined remission at 9 months, p=0.0078) is a clinically meaningful positive signal in an indication with substantial unmet need and no successful cell-therapy incumbent after Alofisel's withdrawal [1][5][8]. AVB-114 received RMAT designation from the FDA on October 3, 2025, building on Fast Track from February 2025, and that provides intensive FDA guidance, senior management engagement, and clinical trial design flexibility that materially de-risks the regulatory path to Phase 3 initiation [10][11]. Complex Crohn's perianal fistulas destroy quality of life, and current standard of care (anti-TNF plus repeated seton drainage and surgery) fails a substantial fraction of patients [6]. The specific signals to watch: (1) longer-term durability updates beyond 9 months and any 12-24 month follow-up from STOMP-II, since durability is the historical failure point in this space, (2) Phase 3 initiation announcements, including patient-population criteria (will they exclude active proctitis?), endpoint timing (52 weeks is the regulatory sweet spot), and comparator arm design, (3) financing or partnering news for Avobis Bio, since no Series A or B round has been publicly announced and this is the primary execution risk to monitor, and (4) any expanded RMAT-enabled interactions with FDA that clarify what will constitute a registrational package. Check back after the next major GI meeting (Digestive Disease Week or UEGW) for longer follow-up or Phase 3 design. Big-pharma GI franchises (AbbVie, Takeda, Johnson and Johnson, Bristol Myers Squibb) will be tracking this closely because it fits alongside their anti-TNF and anti-integrin franchises for fistulizing Crohn's. A Takeda in-licensing move would be ironic given Alofisel's history, but plausible if AVB-114's autologous expanded-MSC approach delivers the durability that the allogeneic product could not.