Cullinan Therapeutics said early clinical data from its CLN-978 program showed signs of activity in both systemic lupus erythematosus and rheumatoid arthritis after a single target dose, with deeper B-cell depletion at higher doses and only one high-grade cytokine release syndrome event.
The company said the data set included 29 patients evaluated as of May 15, 2026, across its OuTrace SLE and OuTrace RA phase 1 studies. In SLE, 18 patients were evaluated for safety, 17 for pharmacodynamics and 14 for efficacy. In RA, the counts were 11, 7 and 7, respectively.
In the SLE trial, among 14 patients with at least four weeks of follow-up, 10 patients, or 71%, had a reduction of at least four points in the HSLEDAI score. Five of those patients reached DORIS remission. All lab markers of disease activity cited by the company — anti-dsDNA, UPCR, C3 and C4 — improved in patients who had clinically significant abnormalities at baseline.
The company said peripheral B-cell counts in SLE fell by more than 80% from baseline in 14 of 17 patients, or 82%, after a single target dose. B-cell depletion below the limit of quantification was reached in 7 of 14 patients, or 50%, at target doses of at least 20 micrograms.
In RA, 6 of 7 patients, or 86%, had high baseline disease activity. Disease activity improved in 5 of 7 patients, or 71%, including one DAS28-ESR remission in a patient who received a single 30-microgram target dose. The company said CLN-978 reduced RA autoantibody levels without affecting protective vaccine titers.
Peripheral blood B-cell depletion below the limit of quantification was achieved in 4 of 6 RA patients, or 67%, at target doses of at least 20 micrograms. The company also said dose-dependent B-cell depletion was seen in lymph node and synovial tissue.
On safety, Cullinan said CLN-978 was well tolerated across the 10-, 20* and 30-microgram target dose cohorts, including in patients who received three administrations of the 20-microgram dose in a multi-dose regimen. Most cytokine release syndrome events were grade 1 and occurred after the first 10-microgram dose. One grade 3 cytokine release syndrome event occurred after the 45-microgram dose, and enrollment in that cohort was stopped. No immune effector cell-associated neurotoxicity syndrome was observed.
The company also said it will present new data from the first RA multi-dose regimen cohort and initial data for Velinotamig at its immunology day on June 10. Today the company's shares have moved -2.0% to a price of $13.24. Check out the company's full 8-K submission here.
