Distinctive clinical characteristics and favorable outcomes in patients with large granular lymphocytosis after allo-HCT: 12-year follow-up data.

An increase in large granular lymphocytes (LGL) is frequently seen in patients following allogeneic hematopoietic cell transplantation (allo-HCT) and it has been associated with better outcomes in some reports. We assessed 826 consecutive patients at our institution with over 12 years of follow-up for the occurrence of LGL lymphocytosis after allo-HCT. The 3-year cumulative incidence of LGL lymphocytosis was 14.5% with a median duration of over 3.5 years. The development of LGL lymphocytosis was strongly correlated with CMV viremia and GVHD. The clinical course of patients with LGL lymphocytosis after allo-HCT was indolent, with the majority of these patients not displaying any clinical signs or symptoms related to the LGL proliferation. LGL lymphocytosis was associated with better outcomes, including higher overall survival (OS 86.6% vs 44.7% at 3 years), lower non-relapse mortality (NRM 5.5% vs 30.4% at 3 years), and lower risk of relapse (8.9% vs 22.9% at 3 years). A time-dependent multivariable analysis confirmed the favorable impact of LGL lymphocytosis on OS and NRM, but not on the risk of relapse. In multivariable analysis, a longer duration of LGL lymphocytosis was associated with better OS and NRM. Improved immunomodulatory properties of these cells, regulating GVHD and infections, may explain the observed favorable outcomes of patients who developed LGL lymphocytosis following allo-HCT.