Clinical Experience in the Randomized Phase 3 Sierra Trial: Anti-CD45 Iodine (131I) Apamistamab [Iomab-B] Conditioning Enables Hematopoietic Cell Transplantation with Successful Engraftment and Acceptable Safety in Patients with Active, Relapsed/Refractory AML Not Responding to Targeted Therapies

• Published in: Blood 2021-11, Vol.138 (Supplement 1), p.1791-1791
• Main Authors: Gyurkocza, Boglarka, Nath, Rajneesh, Seropian, Stuart, Choe, Hannah, Litzow, Mark R., Koshy, Nebu V., Stiff, Patrick, Abboud, Camille, Tomlinson, Benjamin, Abhyankar, Sunil, Hari, Parameswaran, Al-Kadhimi, Zaid S., Chen, George L., Sabloff, Mitchell, Orozco, Johnnie J., Foran, James M., Kebriaei, Partow, Jamieson, Katarzyna Joanna, Magalhaes-Silverman, Margarida Magalhaes, van Besien, Koen, Schuster, Michael W., Law, Arjun, Levy, Moshe, Lazarus, Hillard M, Giralt, Sergio A, Berger, Mark S., Spross, Jennifer A, Desai, Avinash G, Reddy, Vijay, Pagel, John M.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2021-148497

Background: Several targeted therapies have been recently approved as treatment options for acute myeloid leukemia (AML), however, complete remissions (CR) in relapsed/refractory (R/R) patients remain low. Due to suboptimal responses to standard therapies, most of these patients do not receive an allogeneic hematopoietic cell transplant (HCT). In addition, AML patients ≥55 years have poor tolerance and high morbidity from a myeloablative HCT. The SIERRA trial (Study of Iomab-B in Elderly Relapsed or Refractory AML) has been investigating the use of Iomab-B, an 131I-labeled anti-CD45 monoclonal antibody, to reduce relapse in patients with active, R/R AML who receive HCT as compared to Conventional Care (CC) therapies. With the recent approval of various targeted therapies like BCL-2 inhibitors (e.g., venetoclax), FLT-3 inhibitors (e.g., midostaurin and gilteritinib) and IDH inhibitors (e.g., ivosidenib), the protocol was amended to include patients refractory to these therapies. We are reporting on the success rate of engraftment and tolerability of Iomab-B among the CC patients who cross-over to receive Iomab-B and HCT after failing these agents. Methods: Approximately 150 older patients with R/R AML are to be randomized (1:1) to receive Iomab-B followed by fludarabine, total body irradiation (2 Gy) and allogeneic HCT, or to conventional care (CC). CC patients receive physician's choice of therapy, including targeted therapies, and may proceed to standard of care allogeneic HCT if they achieve CR. CC patients not achieving CR may cross over to Iomab-B-based HCT. Results: Available data for 136 patients (>90% of target enrollment; median age 65) demonstrated they had a median of 3 (range: 1-7) prior lines of AML therapies. Median marrow blast at time of study entry was 25%. Prior to enrollment, 85 (63%) patients received targeted therapies, including BCL-2 inhibitors (62%), FLT-3 inhibitors (18%), IDH inhibitors (7%) and others (13%; e.g., gemtuzumab ozogamicin). Among the 50 evaluable patients in the Iomab-B group that received HCT, all successfully engrafted after a median radiation dose delivered to marrow of 14.7 Gy (range: 4.6 - 44.6) with a median time to neutrophil and platelet engraftment of 14.5 (range: 9-28) and 18 (range: 4-58) days, respectively. Of 63 patients randomized to the CC arm and with data available, 11 (17%) achieved CR and proceeded to standard of care HCT without Iomab-B while 52 (83%) did not respond to CC therapy. Twenty-seven of