As of 16 May 2022, a total of 73 pts received SEA-BCMA. Patient baseline characteristics are summarized in Table 1.

The most common non-hematologic, treatment-emergent adverse events (TEAEs) in Parts B (n=15), C1 (n=12), and C2 (n=8) were fatigue (33%, 50%, and 25%), back pain (20%, 17%, and 25%), pneumonia (7%, 25%, and 25%), and cough (20%, 8%, and 25%). The most common hematologic TEAE was anemia (42% in Part C1). The most common ≥Grade 3 TEAEs were anemia (33% in Part C1) and pneumonia (7%, 25%, and 0% for Parts B, C1, and C2, respectively).

Both intensive SEA-BCMA dosing (Part B) and the addition of DEX (Part C1) showed increased ORRs relative to Q2W monotherapy (Part A; Table 2). In Part B (n=15), the ORR was 27% (95% CI: 7.8, 55.1); median duration of response (DOR) was 6.5 months (95% CI: 1.8, -); 3 pts remain on treatment, including 2 responders. In Part C1 (n=12), the ORR was 17% (95% CI: 2.1, 48.4); the median DOR was not yet reached; 1 responding pt remains on treatment.

For the combination of the intensive SEA-BCMA dosing schedule and the addition of DEX (Part C2), the ORR across both SEA-BCMA dose levels (800 mg [n=3] and 1600 mg [n=5]) was 38% (n=8; 95% CI: 8.5, 75.5); median DOR was not yet reached; 2 responding pts remain on treatment.

The combined ORRs of both intensive dosing cohorts (Parts B + C2) relative to both standard dosing (Q2W) cohorts (Parts A [1600 mg SEA-BCMA] + C1) were 30% versus 15%, respectively (Table 2).