Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S532 -1.04–24.21). MicroRNA target analysis showed PTEN as a target of 3 miRNAs (hsa-miR-21-5p, hsa-miR-144-3p, and hsa-miR-23a3p). Other targets included APP, JMY, TGFBR3, and YOD1, several of which are involved in tumour suppression. Further assessment of EV surface markers, serum cytokines, and TCR diversity is ongoing. Summary: Preliminary analysis shows the potential for miRNA biomarkers as an indicator of ECP response, while also providing insight into the mechanisms of ECP action. Keywords: CT, extracorporeal photopheresis, extracellular vesicle, microRNA, Graft versus host disease CT-513 Pure Red Cell Aplasia in Major ABO‑Incompatible Allogenic Stem Cell Transplantation: Retrospective Analysis From a Single‑Center Experience David Alonso MD, Mónica Cabrero MD, Marta Fonseca MD, Elena Alejo MD, José María Navarro MD, Sandra Patricia Gómez MD, Carlos Puerta MD, Evelyn Zapata MD, Pablo García MD, Cristina Teresa Fuentes MD, Adolfo Fernández MD, Diego Clavo MD, Carmen Santos MD, Rafael José Malaver MD, Ana África Martín MD, Miriam Lopez MD, Maria Luisa Martín-Mateos MD, Estefanía Pérez-López MD, Borja Puertas MD, Alberto Hernadez MD, Mónica Baile MD, Almudena Cabero MD, Alejandro Avendaño MD, Cristina de Ramon MD, Ana García-Bacelar MD, Lourdes Vázquez MD, Fermin Sánchez-Guijo MD, Olga López-Villar MD, Lucía LópezCorral MD Hospital Universitario de Salamanca-IBSAL, Salamanca, Spain Context: Pure red cell aplasia (PRCA) is a complication of major ABO incompatibility (ABO-MM) allogeneic stem cell transplantation (alloHSCT). Evidence is lacking for PRCA incidence, optimal management, and prognosis. Objective: To describe the characteristics of PCRA in a homogeneous patient sample. Design: Retrospective review of patients receiving alloHSCT in our center between 2017 and 2021, selected for those with suspected PCRA. Patients: Inclusion criteria: anemia (hemoglobin [Hb] <10 g/dL) with neutrophil- and platelet recovery (>1500/μL; >50 000/μL); bone marrow (BM) erythroid progenitor aplasia or hypoplasia (<20%) at day +21, +56, and +100; and complete BM donor chimerism. Patients with other causes of anemia were excluded. Results: Among 454 alloHSCT patients, 92 had ABO-MM (20.2%). Of these, 13 met inclusion criteria, yielding a PRCA incidence of 14.1%. Five of these 13 patients were initially considered to have multifactorial anemia. Incidence of PRCA in ABO-MM was 9.1%, 5.5%, and 7% for haploidentical, unrelated, and matched-related donors. Patients with PCRA had a median Hb at day +21, +56, and +100 of 9.8 g/dL (range, 8.2–10.9 g/dL), 9.1 g/dL (range, 8–12.3 g/dL), and 9.6 g/dL (range, 7.2–12.1 g/dL). Patients received a median of 8 packets of red blood cells between days +21 and +100. In immunohematology studies at PRCA diagnosis (available for 11 patients), serologic and erythroid patient ABO type persisted in 9 individuals (81.1%). All but 1 patient received treatment (92.3%); treatment was based on erythropoietin (n=10), intravenous immunoglobulin (n=2), rituximab (n=3), and daratumumab (n=1). Three patients needed >1 line of therapy. All but 3 patients (76.9%) achieved complete response (Hb >10 g/dL without transfusion) after a median of 62 days (range, 6–119 days). One patient did not respond after 3 lines of therapy and is still under treatment; 2 patients died before resolution of PCRA from relapsed acute myeloid leukemia (n=1) and acute graft-vs-host disease (n=1). Conclusions: Our results are in line with previously published studies. Moreover, we demonstrate that PRCA can be underdiagnosed. Our most used treatment was erythropoietin; the majority of patients achieved a satisfactory response. Given the low incidence of this complication, multicenter studies are needed to better characterize PRCA. Keywords: cellular therapy, pure red cell aplasia, major ABO incompatibility, allogeneic HSCT CT-526 Updated Results From a Rapcabtagene Autoleucel (YTB323) Phase I Study Demonstrate Durable Efficacy and a Manageable Safety Profile in Patients With Relapsed or Refractory Diffuse Large B‑Cell Lymphoma (R/R DLBCL) Nirav N. Shah MD1, Ian Flinn MD, PhD2, Mi Kwon MD, PhD3, Ulrich Jäger MD4, Javier Briones PhD5, Emmanuel Bachy MD, PhD6, Didier Blaise MD7, Nicolas Boissel MD, PhD8, Koji Kato MD, PhD9, Peter A. Riedell MD10, Matthew J. Frigault MD11, Leyla O. Shune MD12, Takanori Teshima MD13, Fabio Ciceri MD, PhD14, Shaun A. Fleming MBBS, FRACP, FRCPA15, Silvia Ferrari MD16, David Pearson PhD, MBA17, Jeanne Whalen MSc18, Aiesha Zia MSc19, Jaclyn Davis MD20, Aisha Masood MD20, Michael Dickinson MD21, Pere Barba MD, PhD22 1Medical College of Wisconsin, Milwaukee, WI, USA. 2Sarah Cannon Research Institute and Tennessee Oncology, Nashville, TN, USA. 3Department of Hematology, Hospital General Universitario Gregorio Marañón, Institute of Health Research Gregorio Marañón, Madrid, Spain. 4Clinical Division of Hematology and Hemostaseology, Department of Medicine I, Vienna General Hospital – Medical University of Vienna, Vienna, Austria. 5Hematology Department, Hospital Santa Creu i Sant Pau, Barcelona, Spain. 6Hospices Civils de Lyon and Université Claude Bernard Lyon 1, Lyon, France. 7Département d’Hématologie, Programme de Transplantation et de Thérapie Cellulaire, Centre de Recherche en Cancérologie de Marseille, Aix-Marseille University, Institut Paoli Calmettes, Marseille, France. 8Hematology Adolescent and Young Adult Unit, Saint-Louis Hospital, Paris, France. 9Department of Hematology, Oncology, and Cardiovascular Medicine, Kyushu University Hospital, Fukuoka Prefecture, Japan. 10University of Chicago, Chicago, IL, USA. 11Massachusetts General Hospital, Boston, MA, USA. 12University of Kansas Medical Center, Kansas City, KS, USA. 13Department of Hematology, Hokkaido University Hospital, Sapporo, Japan. 14Department of Onco-Hematology, Università Vita-Salute San Raffaele and Istituto di Ricovero e Cura a Carattere Scientifico Ospedale San Raffaele, Milan, Italy. 15Department of Hematology,
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