Title PageName of Journal: Clinical Case ReportsManuscript Type: Case ReportTitle: Passenger Lymphocyte Syndrome Treated with Recipient-Matched Transfusions – A Case ReportAuthors: Hyun Lee, Zahra S Hamedi, Asit Kr PaulFirst Author Information : Hyun Lee, MD, Fellow, Division of Hematology, Oncology, & Palliative Care, Department of Internal Medicine, Virginia Commonwealth University, Richmond, Virginia, 23219, USA. hyun.Lee@vcuhealth.org. ORCID ID: 0000-0003-0954-9174Co-Author Information : Zahra Hamedi, MD, Fellow, Division of Hematology, Oncology, & Palliative Care, Department of Internal Medicine, Virginia Commonwealth University, Richmond, Virginia, 23219, USA. zahraSadat.Hamedi@vcuhealth.org. ORCID ID: 0000-0002-7527-8782Corresponding Author Information : Asit Kr Paul, MD Ph.D, Associate Professor of Medicine, Division of Hematology, Oncology, & Palliative Care, Department of Internal Medicine, Virginia Commonwealth University, Richmond, Virginia, 23219, USA. asit.paul@vcuhealth.org. ORCID ID: 0000-0002-3517-4196Author contributions: Hyun Lee and Zahra S Hamedi contributed to manuscript writing and editing; Asit Kr Paul contributed to conceptualization and supervision; all authors have read and approved the final manuscript.Statements : None of the authors received any funding or have any conflict of interest regarding this manuscript. Written patient consent has been obtained for publication of this manuscript. The patient has provided written consent for manuscript writing and publication.Abstract:Passenger lymphocytes syndrome (PLS) is a rare form of immune hemolytic anemia caused by organ transplantation with red blood cell (RBC) antigen incompatibility. Donor lymphocytes may travel with the graft and produce alloantibody against recipient RBCs to cause post-operative hemolysis. We present a case of PLS that presented with acute hemolysis on post-operative day 8 following a deceased donor liver transplant from O+ donor to A- recipient and rapid tapering of post-operative steroid therapy. Although high-dose steroids and donor-matched transfusion are the typical supportive measures, our patient was treated with steroids and recipient-matched transfusions with each of the transfusion attaining adequate response. The reported case suggests that recipient-matched transfusion may be an acceptable alternative PLS treatment when donor-matched transfusion is not available.Key Words : Passenger Lymphocyte Syndrome, Alloimmune Hemolysis, Autoimmune Hemolysis Anemia, Liver Transplantation, ABO-mismatch Transplantation, Case ReportIntroduction :Post-transplant anemia is a common complication with estimated incidence of 4-28% following liver transplants.1 Among its broad differential is PLS, which is a form of graft-versus-host disease that can be seen after a transplant with RBC antigen incompatibility. ABO-mismatch is the most common type of such incompatibility, whereas Rh-mismatch is seen with lower incidence, and other mismatches of minor RBC antigens are rarely seen. Pathophysiology is centered on donor B-lymphocytes transferring with donor graft then producing antibodies against recipient RBC to cause hemolysis.2Unlike stem cell transplant, solid organ transplant does not have renewable source of the pathogenic B-lymphocyte population, hence the disease is typically self-limited.4 Severe cases nonetheless require treatments to temporize until pathogenic lymphocytes are cleared. Donor RBC matched transfusion and steroids have become the widely accepted PLS treatments based on case reports and series.2 However, PLS’s rarity and variable clinical course remain a hindrance to better understanding the disease and evaluating treatment efficacy. Here, we report a patient who was diagnosed with PLS shortly after the liver transplant and a course of post-operative steroids. Experience from this case will contribute to questioning the relationship between PLS’s variable clinical presentations and nonuniform post liver transplant steroid regimens as well as assessing the viability of recipient-matched transfusion as an alternative management option.