Cullinan Therapeutics, Inc. 8-K

What Happened

• Cullinan Therapeutics (CGEM) filed an 8-K on May 18, 2026 and issued a press release announcing initial clinical data from its Phase 1 OUTRACE Program for CLN‑978 in patients with treatment‑refractory rheumatoid arthritis (RA) and treatment‑refractory moderate to severe systemic lupus erythematosus (SLE). The data reported reflect a January 14, 2026 cut‑off. The company will present updated data, including additional patients, at the EULAR European Congress of Rheumatology in June 2026.

Key Details

• Total dosed as of Jan 14, 2026: 14 patients (RA cohorts 1–3: n=5; SLE cohorts 1–3: n=9).
• Dosing regimen: day 1 step‑up doses = 10 mcg; day 8 target doses = 20 mcg (cohort 2) or 30 mcg (cohort 3).
• Pharmacodynamics: after 10 mcg, 9 of 11 patients had >75% B‑cell depletion vs baseline. After 20 mcg, 3 of 6 patients had B‑cell levels below the level of quantification; the other three showed 98.5%, 77%, and 64% reductions.
• Clinical activity (patients with ≥4 weeks follow‑up): 4 of 5 RA patients had decreased DAS28‑ESR scores (all 4 with baseline high disease activity >5.1 fell to moderate activity [3 patients] or remission [1 patient]); 5 of 6 SLE patients had SLEDAI decreases >4 points. Ultrasound synovitis scores fell in 3 of 4 RA patients.
• Safety: CLN‑978 was reported as well tolerated with a favorable safety profile; transient peripheral T‑cell decreases were observed, consistent with T‑cell engager activity. Dose escalation is ongoing.

Why It Matters

• These are early, interim Phase 1 results from a small group of heavily treatment‑refractory patients. The data show strong pharmacodynamic activity (robust B‑cell depletion) and initial signals of clinical benefit in both RA and SLE, which, if confirmed in larger cohorts, could support further development of CLN‑978.
• Risks remain: the trials are ongoing, the sample size is small, follow‑up is limited, and the company warns outcomes may change as more data accrue. The near‑term catalyst is the EULAR presentation in June 2026, where Cullinan will present updated data.