Early lymphocyte recovery post-allogeneic hematopoietic stem cell transplantation is associated with significant graft-versus-leukemia effect without increase in graft-versus-host disease in pediatric acute lymphoblastic leukemia.

To study the effect of early lymphocyte recovery post-allogeneic hematopoietic stem cell transplantation (HSCT) on outcome in pediatric ALL, we reviewed 136 consecutive pediatric patients with ALL who received allogeneic HSCT between 1994 and 2005 at the Hospital for Sick Children, Toronto, Canada. Patients with an absolute lymphocyte count (ALC) <0.3 x 10(9) per liter at day 21 (n=104) had more than five times risk of relapse compared to those with ALC >0.3 x 10(9) per liter (n=32) (hazard ratio (HR) 5.3; P=0.002) and had inferior 3-year event-free survival, (EFS), 0.42 (95% confidence interval (CI) 0.32, 0.51) compared to 0.66 (95% CI 0.48, 0.82; P=0.02). Similarly, patients with an ALC <0.3 x 10(9) per liter (n=48) at day 30 were more than twice as likely to relapse compared to those with an ALC >0.3 x 10(9) per liter (n=88) (HR 2.2; P=0.01) and had an inferior 3-year EFS, 0.30 (95% CI 0.18, 0.45) compared to 0.57 (95% CI 0.46, 0.68; P=0.0001). Interestingly, increasing ALC at days 21 and 30 was not associated with increased incidence of acute or chronic GVHD or transplant-related mortality (TRM). Early lymphocyte recovery post-HSCT is associated with a significant GVL without increase in GVHD.