The companies didn't provide details, which will be presented at a medical meeting next year. Still, they said the drug's effects were consistent across subgroups and rates of treatment-related side effects were similar between both study groups. The partners intend to start late-stage development, pending discussions with regulators.

While the results are from a short Phase 2 trial, Sanofi and Teva's findings suggest duvakitug could be the most potent drug among a handful of closely watched antibody therapies for inflammatory bowel disease, or IBD, wrote Jefferies analyst Peter Welford.

These drugs are aimed at a protein called TL1A, which regulates inflammation and fibrosis. They've caught the attention of pharmaceutical companies because of their potential to drive hard-to-treat cases of IBD into remission more powerfully and durably than existing treatments.

Merck & Co. spent nearly $11 billion on Prometheus Biosciences in April 2023 largely to get a hold of a TL1A blocker that had shown promise in Phase 2 testing for instance. Roche followed with a $7 billion purchase of Televant months later and, earlier this year, AbbVie joined the chase, too.

Duvakitug trails Merck's and Roche's prospects; Merck has already initiated Phase 3 testing. But Teva's executives have long argued the drug could prove superior and, in Oct. 2023, Sanofi bought in, paying Teva $500 million to collaborate on development. The drug has since become more important to both companies, giving Teva -- known for its generics -- a chance at a branded blockbuster medicine, and Sanofi an opportunity to build investor confidence in its pipeline.

While cross-trial comparisons can mislead, duvakitug's performance in Phase 2 testing appears strong. Merck's drug led to a placebo-adjusted remission rate of 25% in a Phase 2 trial in ulcerative colitis. Roche's therapy was associated with an 18 to 23 percentage-point difference versus placebo in a similar trial, depending on the dose.

Duvakitug's roughly 27% delta, and higher rates of disease improvement in Crohn's disease, suggest the drug's different design versus its peers "could perhaps translate to better efficacy," wrote Jefferies analyst Welford.

"If the magnitude of effect persists in the Phase 3 program, we believe we will have a differentiated medicine for IBD," said Sanofi R&D chief Houman Ashrafian, in the companies' statement.

Teva shares surged nearly 20% in early Tuesday trading, while Sanofi's climbed by almost 5%.

The program's advancement into Phase 3 will trigger a $600 million milestone payment from Sanofi to Teva.