At data cut-off (April 2022), 100 pts had been treated with modakafusp; 56 pts in dose escalation and 44 pts in expansion cohorts. During dose escalation, dose-limiting toxicities were reported with QW and Q2W dosing schedules. In the Q4W dosing schedule, the maximum tolerated dose (MTD) of modakafusp was exceeded at 6 mg/kg due to a grade (G) 3 infusion-related reaction (IRR) in 1 pt and a prolonged thrombocytopenia and neutropenia in 1 pt; the MTD was therefore determined as 3 mg/kg Q4W. During dose escalation, PRs were reported with 0.1 mg/kg and 0.4 mg/kg QW (n=1 each), an unconfirmed VGPR was observed with 0.4 mg/kg Q3W, and PRs (n=3) and a CR (n=1) were reported with 1.5–6 mg/kg Q4W.

During expansion, of 8 pts receiving modakafusp 0.4 mg/kg Q3W, 5 had SD and 3 had PD. Of 3 pts in the 0.4 mg/kg Q3W + dex cohort, 2 had SD and 1 had PD.

Among 30 pts treated with modakafusp 1.5 mg/kg Q4W (5 in dose escalation and 25 in expansion), the ORR was 43% (Table), median time to response was 1.2 months, and median duration of response was not reached (range 1.0–18.9 months). Median progression-free survival was 5.7 months (95% confidence interval 1.2–15.9). At 1.5 mg/kg Q4W, G≥3 treatment-emergent adverse events (TEAEs) occurred in 26 (87%) pts, including neutropenia (n=19, 63% [G4 n=9, 30%]), thrombocytopenia (n=14, 47% [G4 n=6, 20%]), and lymphopenia (n=11, 37% [G4 n=7, 23%]); 3 (10%) pts had G3 infections, and 1 (3%) pt had a G3 bleeding event. Except for 1 report of G4 hyperuricemia, there were no G4 non-hematological TEAEs; IRRs occurred in 11 pts (37% [G3 n=1, 3%]).

Of 8 pts treated with modakafusp 1.5 mg/kg Q4W + dex, 1 pt had a VGPR and 1 pt had SD (1 pt was not evaluable and 5 pts had no post-baseline response assessment). At 1.5 mg/kg Q4W + dex, G≥3 TEAEs occurred in 7 (88%) pts, including thrombocytopenia (n=4, 50% [G4 n=1, 13%]), anemia (n=2, 25%), lymphopenia (n=2, 25% [G4 n=1, 13%]), pneumonia (n=2, 25%), and neutropenia (n=1, 13%). IRRs occurred in 2 pts (25%, none G≥3).

Of 4 pts treated at 1.5 mg/kg Q4W with MRD samples collected at screening and suspected CR, 1 pt was MRD– at 10-5. Preliminary analysis showed no correlation between CD38 receptor density on peripheral blood immune cells and clinical response. Further evaluation to explore the association between clinical response and CD38 receptor density on MM cells within BMAs is underway.

As of Oct 2021, 30 pts had received modakafusp alfa 1.5 mg/kg Q4W. The median number of prior lines was 7 (range 3–16); 90% of pts were refractory to an anti-CD38 monoclonal antibody (mAb), while 37% were exposed to an anti-B-cell maturation agent (BCMA). Grade (G) 3–4 treatment-emergent adverse events (TEAEs) were reported in 25 pts (83%); the most frequent G3–4 TEAEs were neutropenia in 19 (63%), thrombocytopenia in 13 (43%), leukopenia in 12 (40%), anemia in 9 (30%), and decreased lymphocyte count in 9 (30%) pts. As reported previously, 1 pt in the 1.5 mg/kg Q4W cohort had a G3 bleeding event, while 3 pts had G3 infections. Among all pts, the ORR was 40% (complete response, 7%; very good partial response, 20%; partial response, 13%); among anti-CD38 mAb-refractory and anti BMCA-exposed pts, the ORR was 37% and 27%, respectively. Median progression-free survival was 6 mos and median duration of response had not been reached (Kaplan-Meier estimate, 91% at 6 mos). Based on pooled available data for the Q3W and Q4W cohorts (all doses) within the escalation and expansion phases, there was a strong trend for a dose-exposure-response relationship for ORR, with the apparent inflection point at 1.5 mg/kg Q4W dosing. No apparent relationship between dose-exposure-response and G3/4 thrombocytopenia or neutropenia was observed across all doses, whereas a correlation between dose-exposure-response and incidence of infusion-related reactions across the 0.4–6 mg/kg Q3W and Q4W dosing cohorts was found. There was an apparent non-linear (more than dose proportional) increase in exposure in the dose range of 0.1–3 mg/kg with a geometric mean terminal half-life of 13 hours in serum for modakafusp alfa 1.5 mg/kg. Based on the available data, 14% and 60% of pts were ADA positive at baseline and post-treatment, respectively.

As of May 2021, 83 pts had been treated across all planned dosing schedules. With Q4W dosing, the MTD was exceeded at the 6 mg/kg dose due to DLTs: a grade 3 infusion reaction and prolonged thrombocytopenia and neutropenia, which delayed the start of cycle 2 by >14 days. In total, 24 pts were treated with 1.5 mg/kg modakafusp alfa Q4W (5 pts during dose escalation and 19 pts in an expansion cohort). Analyses include data from all 24 pts. The median number of prior lines of therapy received was 6 (range 4–16); 21 pts (88%) were refractory to an anti-CD38 mAb, and 20 (83%) were triple class-refractory (to a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 mAb). Grade 3 or higher treatment-emergent adverse events (TEAEs) were reported in 18 pts (75%). The most frequent grade 3–4 TEAEs were neutropenia in 12 pts (50%; grade 4 in 6 [25%]), leukopenia in 9 (38%), decreased lymphocyte count in 9 (38%), anemia in 8 (33%), and thrombocytopenia in 8 (33%; grade 4 in 3 [13%]). One pt (4%) had a grade 3 bleeding event and continues on study treatment; 3 pts (13%) had infections (grade 3 in 2 [8%]); and 8 (33%) had infusion reactions (grade 3 in 1 [4%]). The overall response rate (ORR, ≥partial response [PR]) was 42% (complete response [CR], n=2; very good partial response [VGPR], n=5; PR, n=3), and the clinical benefit rate (ORR + minimal response [MR]) was 54% (MR, n=3). Median progression-free survival was 5.7 months (95% confidence interval [CI], 1.9–not reached [NR]), median time to response was 1.9 months (95% CI, 0.95–NR), and median duration of response was 7.4 months (95% CI, 2.3–NR). Among the 21 anti-CD38 mAb-refractory pts, the ORR was 43%, while among the 4 pts who received an anti-CD38 mAb in their most recent line of therapy prior to enrollment, the ORR was 75% (CR, n=1; VGPR, n=2). Correlative studies show evidence of T-cell and natural killer-cell activation, as well as activation of IFN signaling in CD38+ cells, including upregulation of CD38 expression.