Bone Marrow Transplant. 2017 Jan 30. doi: 10.1038/bmt.2016.364. [Epub ahead of print]

Lymphocyte expansion after unrelated cord blood allogeneic stem cell transplantation in adults.

Le Bris Y¹, Guillaume T², Ménard A¹, Illiaquer M³, Martin J⁴, Malard S⁵, Duquesne A⁵, Peterlin P², Debord C¹, Robillard N¹, Eveillard M¹, Wuillème S¹, Delaunay J², Mohty M⁶, Garnier A², Moreau P², Béné MC¹, Chevallier P².

Limited information is available regarding the incidence and features of lymphocyte expansions after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Large granular lymphocytes (LGL) expansions have been reported after bone marrow or peripheral blood, but not after unrelated cord blood (UCB) allo-HSCT, associated with indolent clinical courses and favorable outcomes. Here, we considered 85 recipients of UCB allo-HSCT to more broadly define the impact of lymphocytosis, not limited to LGL. Sustained lymphocytosis was observed in 21 (25%) patients at a median onset of 12.6 months and with a median duration of 12 months. Immunophenotypic analysis showed predominantly CD8⁺ T and/or polyclonal B-cell expansions. Three patients only had monoclonal T-cell expansion. CMV reactivation was significantly more frequent in the group of patients with lymphocytosis (76% vs 28%, P=0.0001), but was not associated with survival. Conversely, 2-year disease-free survival and overall survival were significantly higher for lymphocytosis patients (85% vs 55%, P=0.01 and 85% vs 63%, P=0.03, respectively). In conclusion, expansion of T or B lymphocytes after UCB allo-HSCT in adults is not a rare event. Although occurring relatively late after transplant, this feature is predictive of a better outcome for the patients.Bone Marrow Transplantation advance online publication, 30 January 2017; doi:10.1038/bmt.2016.364.