Pb2444: impact of lymphocytosis on long-term clinical outcomes after allogenic stem cell transplantation

Topic: 22. Stem cell transplantation - Clinical Background: Sustained lymphocytosis can occur as a result of constant antigenic stimulation in various situations such as allogenic stem cell transplantation (allo-SCT) and chronic CMV or VZV infections. Aims: Our aim was to assess the impact of lymphocytosis on transplant-related outcomes. Methods: We retrospectively examined the occurrence of sustained lymphocytosis after allo-SCT, performed in our center, between January 2012 and December 2016 for hematological malignancies. Patients that had survived beyond day 100 were included. Lymphocytosis was defined as a sustained elevation in the absolute lymphocyte count above 4 x 109/L, observed in at least 3 consecutive determinations over a time frame of 3 months. Results: Our study was conducted on 138 consecutive patients. The median age was 32 years (5-56) with a sex ratio of 1.5. The main underlying diseases were acute myeloblastic leukemia (n=62), acute lymphoblastic leukemia (n=48) and lymphoma (n=15). After a median follow-up of 5 years (3 months-11 years), 23 patients (16.6%) developed lymphocytosis during their post-transplant course. The median onset of lymphocytosis was of 9 months (1 month- 5 years) with a median duration of 3 years (9 months-7 years) and a median lymphocyte count of 5.1x109/L (4.1-10.3). The cumulative incidence of lymphocytosis at 1, 2 and 5 years was 10.3%, 12.5% and 13%. Patients with lymphocytosis showed an OS advantage at 5 years (78.3% vs 53.5%, p=0.02). Although not statistically significant, there was a trend towards lower non-relapse mortality (18.6% vs 31%, p=0.075) and lower relapse incidence (26.6% vs 42%, p=0.2). Factors classically associated with the development of lymphocytosis were studied but our results were not statistically significant: chronic GVHD (56% vs 43%, p=0.26), CMV reactivation (43% vs 35%, p=0.48). Conclusion: In our cohort, post-allo-SCT lymphocytosis seems to be associated with favorable outcomes, in accordance with many published reports. A better characterization of this lymphocytosis is necessary by morphological and immunophenotypical study. Keywords: Allogeneic hematopoietic stem cell transplant, Graft-versus-host disease (GVHD), CMV infection, Absolute lymphocyte count