Immune reconstitution of human cytomegalovirus-specific T lymphocytes after allogeneic hematopoietic stem cell transplantation and their predictive role in reactivation

Human cytomegalovirus (HCMV) is the most common virus to affect the recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT). HCMV reactivation increases the risk of secondary fungal and bacterial infections, as well as that of non-relapse mortality after allo-HSCT. This study investigates the post-transplantation reconstitution of HCMV-specific T cells and their role in the regulation of HCMV infections. Peripheral blood samples from CMV-seropositive allo-HSCT recipients (R+) and CMV-seropositive donors (D+) were collected from October 2019 to June 2021. Continuous quantification and function monitoring of CMV-specific CD4+/CD8+T lymphocytes were performed by flow cytometry after stimulation in an HCMV-pp65 pool in vitro and intracellular cytokine staining was performed. Plasma CMV-DNA was quantitatively detected by qPCR. The median age of patients (n = 131) was 34 (23-45) years. Post-transplantation HCMV reactivation occurred in 88 (67.2%) patients. HCMV-responsive CD4+T cells in non-HCMV reactivation patients was significantly higher than that in HCMV reactivation patients 30 days after transplantation (0.21 cells/mu L vs 0.10 cells/mu L; P = 0.005). Kaplan-Meier analysis showed that the incidence of HCMV reactivation in patients with low levels of HCMV-responsive CD4+T cells (<0.14 cells/mu L) was significantly higher than that in patients with high levels of HCMV-responsive CD4+T cells (>0.14 cells/mu L) (83.9% vs 54.7%; P < 0.001). Patients lacking HCMV-responsive CD8+T cells (<2 cells/mu L) 60 days after allo-HSCT had a significantly higher risk of HCMV reactivation 100 days after transplantation (HR 9.932; P = 0.005). Patient age and the mononuclear cell-infusion level were correlated with the reconstructive levels of HCMV-responsive CD8+T cells 60 days after transplantation. Poor recovery of HCMV-responsive CD4+T cells 30 days post-transplantation is closely related to the risk of HCMV reactivation. The level of HCMV-responsive CD8+T cells 60 days post-transplantation is a good predictor for late-onset HCMV reactivation, which is particularly important for outpatient monitoring and management of patients with allo-HSCT, and facilitates individualized risk stratification for HCMV reactivation.