Siba El Hussein1, Andrew G. Evans1, John M. Fitzsimmons1, Nufatt Leong1, Meghan Buldo1, Jeremy P. Segal2, Audrey N. Jajosky1, Paul G. Rothberg1, Jane L. Liesveld3,4 and Zoltán N. Oltvai1 1Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA; 2Department of Pathology, University of Chicago Medicine, Chicago, Illinois 60637, USA; 3Department of Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA; 4The Wilmot Cancer Institute, University of Rochester Medical Center, Rochester, New York 14642, USA Corresponding authors: elhusseinsibagmail.com; zoltan_oltvaiurmc.rochester.edu Abstract

Autologous and allogeneic hematopoietic stem cell transplantation (HSCT) has revolutionized the therapy of hematolymphoid malignancies. Yet, how to best detect or predict the emergence of HSCT-related complications remain unresolved. Here, we describe a case of donor-derived, transient Alpha Beta (αβ) T-cell large granular clonal lymphocytosis and cytopenia that emerged post-HSCT in a patient with a history of gamma delta (γδ) T-cell large granular lymphocytic leukemia (T-LGLL). Clonal unrelatedness of post-transplant T-LGL lymphocytosis to the patient's pretransplant T-LGLL was first identified by T-cell receptor (TCR) PCR showing different sized fragments of rearranged gamma chains, in addition to shift from γδ to αβ TCR expression by flow cytometry analyses. Donor-derivation of the patient's post-transplant clonal lymphocytosis was confirmed by serial chimerism analyses of recipient's blood specimens demonstrating 100% donor DNA. Moreover, oncogenic DNMT3A and RUNX1 mutations were detected by next-generation sequencing (NGS) only in post-transplant specimens. Intriguingly, despite continued increase in DNMT3A and RUNX1 mutation load, the patient's clonal lymphocytosis and anemia eventually largely resolved; yet, the observed mutation profile with persistent thrombocytopenia indicated secondary clonal cytopenia of undetermined significance (CCUS) in the absence of overt morphologic evidence of myeloid neoplasm in the marrow. This case illustrates the utility of longitudinal chimerism analysis and NGS testing combined with flow cytometric immunophenotyping to evaluate emerging donor-derived hematolymphoid processes and to properly interpret partial functional engraftment. It may also support the notion that driver mutation-induced microenvironmental changes may paradoxically contribute to reestablishing tissue homeostasis.

Received August 12, 2022. Accepted March 9, 2023.