Several companies want to stretch IBD antibodies from a shot every few weeks to one every three months, or even six. Keeping the drug in the blood that long is the easy part. Whether the disease stays controlled right up to the next dose is the hard part, and the bet the newest programs are making.
“Long-acting” hides three claims: the drug stays in the blood (PK), keeps blocking its target (PD), and keeps the disease controlled (durability). Only the last proves a long interval works. Across 1,147 IBD trials, TL1A is the most crowded emerging target, with 7 antibodies, 6 sponsors and 36 trials, and 3 already in Phase 3. The leading long-acting candidates report 56–85 day half-lives, a 3–5× leap. But the trough, how much drug is left at the next dose, tells the real story: at the proposed quarterly and six-month intervals it sits at roughly 19–47% of peak, inside the range today’s biologics already tolerate. The PK was never the wall; durability is, and only XmAb942 is yet testing a long interval in patients.
Prometheus gave IBD its best shot at oncology-style patient selection: a companion diagnostic for its anti-TL1A drug, tulisokibart. Merck paid $10.8 billion, then built its Phase 3 trials to enroll everyone. The more crowded the anti-TL1A field gets, the stronger the case for a precision-medicine approach, even as the science has yet to deliver one.
Prometheus built a companion diagnostic to pick the ulcerative colitis patients its anti-TL1A antibody tulisokibart would help, and Merck bought the company for $10.8B. But when Merck launched the Phase 3 program in 2023 (soon after the acquisition), it chose to enroll everyone and demote the test to a secondary endpoint, a design choice fixed years before the trials read out. The now-positive Phase 3 confirms it, and the rest of the anti-TL1A class (Roche, Sanofi/Teva, Spyre, the newly-launched Bionyra) competes on potency and half-life, not patient selection. Yet the more crowded the field gets, the stronger the case for a precision-medicine approach, even as the science has yet to deliver it.
Every approved IBD drug fights inflammation. None of them touch fibrosis. TL1A does both.
30% of Crohn's disease patients will need surgery within ten years of diagnosis - not because their drugs failed to control inflammation, but because no approved drug stops the scar tissue that narrows their bowel. TL1A is the first target that could change that. Here is the biology behind the $18 billion bet.
