The combination regimen of MGTA-145 plus plerixafor for same-day hematopoietic stem cell (HSC) mobilization for autologous transplant in multiple myeloma had 100% efficacy, according to research presented at the ASCO21 Virtual Scientific Program.

The phase 2, single-center study is evaluating HSC mobilization with MGTA-145 (GroβT), a CXCR2 agonist, plus plerixafor and same-day apheresis in patients with multiple myeloma. Investigators reported their interim analysis of 10 patients, including a safety cohort of the first 6 patients who completed the transplant.

Participants received plerixafor 0.24 mg/kg (0.16 mg/kg if renal dysfunction was present) subcutaneously, followed by 2 hours of MGTA-145 (0.03 mg/kg) IV for 3 to 10 minutes and apheresis within 30 minutes. Mobilization was repeated for a second day if the day 1 yield was <6 × 106 CD34+ cells/kg. The primary endpoint was collection of 2 × 106 CD34+ cells/kg.

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Participants’ median age was 63 years (range, 46-68), and 50% were female. Induction therapy was bortezomib, lenalidomide, and dexamethasone (VRD) in 7 patients and daratumumab plus VRD in 3 patients. The median induction duration was 4 months (range, 3-6 months) and the median lenalidomide exposure was 6 cycles.

The median total stem cell yield (CD34+ cells/kg × 106) was 7.1 (range, 3-16.2). The day 1 yield was 5.4 (range, 1.1-16.2) and the yield per apheresis session was 4 (range, 1.1-16.2).

The researchers found that 100% of patients met the primary endpoint of collecting adequate HSCs in <2 days of mobilization with apheresis to proceed to transplant (2 × 106 CD34+ cells/kg). The secondary endpoints of 4 and 6 × 106 CD34+ cells/kg in <2 days were met in 90% and 80% of participants, respectively.

MGTA-145 was well tolerated, according to the study authors. About 90% of patients had at least 1 adverse event (AE), 20% had grade 2 AEs, and 20% had grade 3 AEs, including worsening of baseline grade 3 anemia and hypocalcemia, all of which resolved.

The 6 patients in the safety cohort completed the transplant with melphalan 200 mg/m2. The patients had a median of 4.1 × 106 CD34+ cells/kg infused (range, 3.4-5.6 × 106 CD34+ cells/kg), and all engrafted timely, the researchers noted. The median time to neutrophil engraftment was 12 days, and the median time to platelet engraftment was 17 days.

Grafts with MGTA-145 with plerixafor demonstrated high enrichment for CD90+CD45RA in CD34+ cells, a CD34 subset of long-term engrafting HSCs (median 31% of CD34+ cells), according to the investigators. In addition, 67% of grafts were minimal residual disease–negative with next generation flow cytometry.

Disclosures: Some of the study authors declared affiliations with pharmaceutical companies. Please see the original reference for a full list of disclosures.

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Sidana S, Bankova A, Hosoya H, et al. Phase 2 study of MGTA-145 + plerixafor for rapid and reliable hematopoietic stem cell (HSC) mobilization for autologous transplant in multiple myelomaJ Clin Oncol. 2021;39(suppl 15; abstr 8023). doi:10.1200/JCO.2021.39.15_suppl.8023