Delayed T-cell recovery after hematopoietic cell transplantation is associated with decreased overall survival in adults

Allogeneic hematopoietic cell transplantation (allo-HCT) can provide curative treatment for hematologic malignancies but is associated with prolonged lymphopenia that may contribute to an increased risk of infection and relapse, resulting in decreased survival. We hypothesized that patients with rapid and robust CD4 T- and B-cell recovery have improved survival and decreased treatment-related mortality (TRM). A total of 2089 patients were included who underwent first allo-HCT for acute myeloid leukemia/acute lymphoblastic leukemia/myelodysplastic syndrome from 2008 to 2019 reported to the Center for International Blood and Marrow Transplant Research with available CD4 counts at days 100 and 180. Patients (median age, 51 years [range, 2-75]) were categorized into 4 groups based on graft-versus-host disease (GVHD) prophylaxis: ex vivo T-cell depletion (TCD/CD34), posttransplant cyclophosphamide, calcineurin inhibitor alone (CNI), or CNI with antithymocyte globulin. Based upon survival, we could identify optimal cutoff points for CD4⁺ T cells in pediatric (age of <20 years) patients: 248 × 10⁶/L and 420 × 10⁶/L at days 100 and 180, respectively; and in adult (age of >20 years) patients: 104 × 10⁶/L and 115 × 10⁶/L at days 100 and 180, respectively. In adults, day-100 CD4 count was associated with overall survival (OS), progression-free survival (PFS), and TRM but not relapse, incidence of infections, or chronic GVHD. Similarly, CD4 counts above the cutoff point at day 180 in adults were associated with improved OS, PFS, and TRM but no other outcomes. No clinical associations for CD4 counts were identifiable in pediatric patients. These findings underscore the importance of tailoring transplant strategies for adults to optimize immune recovery and improve patient outcomes.