Clonal T Cell Large Granular Lymphocyte Leukaemia of Recipient Origin after Related Mismatched Allogeneic Haematopoietic Stem Cell Transplantation for Acute Myeloid Leukaemia as a Possible Consequence of Anti-Thymocyte Globulin in Conditioning Regimen
Authors: Fouillard Loïc , Marzac Christophe , Lagrange Monique , Huguet-Jacquot Stéphanie , Fabiani Betina , Davi Frederic , Mazurier Christelle , Soreau Elisabeth , Laporte jean-Philippe , Isnard Francoise , Gorin norbert-Claude , Bories Dominique 
Published: April 2020

Abstract
Polyclonal or oligoclonal expansion of T cell large granular lymphocyte (T-LGL) after allogeneic haematopoietic stem cell transplantation (HSCT) has been described. A few cases of clonal T-LGL leukaemia of donor origin has been reported as a post transplantation lymphoproliferative disorder (PTLD) and described after allogeneic HSCT (Chang, Am J Clin Pathol, 2005). We report here a patient with a clonal T-LGL of recipient origin occurring after allogeneic HSCT for acute myeloid leukaemia (AML). A 56 year old male patient with an AML received an HLA mismatched (disparity on locus A) related HSCT from his sister in first complete remission. Conditioning regimen was myeloablative and combined Busilvex (12.8 mg/kg) and Cyclophosphomide (120 mg/kg) (BuCy2). Anti-Thymocyte Globulin (ATG Sangstat) was added because of the HLA disparity between donor and recipient at a dose of 15 mg/kg. Prophylaxis of Graft versus Host Disease (GVHD) combined cyclosporine and methotrexate. Complete engraftment was observed with full haematopoietic recovery and 100% donor type chimerism detected by real time quantitative PCR (RQ-PCR). A grade II acute GVHD resolved under steroid and CMV infection was treated with valganciclovir. Ten months post HSCT while all immunosuppressive treatment was discontinued, a severe neutropenia (poly morpho nuclear &lt;0.2 × 109/l) and an hyperlymphocytosis up to 10×109/l occurred with a thrombocytopenia of 100×109/l. Relapse of AML and viral infection (CMV, HHV6, EBV, HCV, HBV, HIV, HTLV1, parvovirus B19) were eliminated. Seach for autoantibodies was negative. No chronic GVHD was diagnosed. The predominant cells in blood films were typical LGLs. Flow cytometric analysis showed a population CD3+/CD8+/CD57+/CD56− consistent with T-LGL. Bone marrow biopsy confirmed agranulocytosis and T-LGL infiltration CD3+/CD8+/CD57+/CD56−. Secondarily agranulocytosis and thrombocytopenia spontaneously resolved within one month, but hyperlymphocytosis persisted with the same T-LGL profile. Chimerism by RQ-PCR on CD3+ and CD3− peripheral blood mononuclear cells (PBMNC) population at time of profound agranulocytosis revealed that donor cells were only 8.2 % and 1.2% on CD3+ and CD3− fractions respectively. Chimerism done when cytopenia resolved became mixed with 47% and 39% donor markers on CD3+ and CD3− fractions respectively. Chimerism was then performed on selected subpopulations; donor markers were 98% on CD14+/15+ myeloid cells, 100% on CD56+ natural killer (NK) cells and 78 % on CD19+ B cells. Cell sorting isolated two T-LGL subpopulations according to CD57 expression: CD57+bright and CD57+weak. Donor markers were 0.02% on CD3+/CD8+/CD57+bright T-LGL cells and 1.2% on CD3+/CD8+/CD57+weak T-LGL cells. These results were in favor of a recipient origin of the T-LGL population without loss of the graft. The diagnosis of clonal T-LGL population was confirmed by TCRg gene rearrangement performed on the selected CD3+/CD8+/CD57+bright and CD3+/CD8+/CD57+weak population. In addition a polyclonal background was observed only in the CD3+/CD8+/CD57+weak population. These data show that T-LGL leukaemia of recipient origin can occur after allogeneic HSCT for AML and can be included as a PTLD. The role of ATG as an intensive immunosuppressive treatment cannot be excluded in the occurrence of this PTLD. In this patient no treatment of T-LGL leukaemia and a wait and watch attitude were undertaken. Eighteen months post HSCT the patient is alive and well with the same stable PTLD profile and no relapse of AML The cytolytic activity of the recipient T-LGL clone could explained the absence of AML relapse and a transient toxicity against donor haematopoiesis. In vitro cytolytic assay will be done to confirm the cytotoxic activity of T-LGL against leukaemic cells and haematopoietic stem cells.