Impact of low-dose anti-thymocyte globulin on immune reconstitution after allogeneic hematopoietic cell transplantation.

How low-dose anti-thymocyte globulin (ATG) for prophylaxis of graft-versus-host disease (GVHD) influences immune reconstitution after allogeneic hematopoietic stem cell transplantation (allo-HCT) remains incompletely understood. We prospectively enrolled 41 consecutive adult patients and conducted cytometry-based immunophenotyping for 12 months after allo-HCT. Rabbit ATG (Thymoglobulin) was administered at a median total dose of 1.75 mg/kg in 16 of the 41 patients. Compared with patients who did not receive ATG, those who did had a significantly smaller number of naïve T cells (especially CD4+ ) within three months after allo-HCT. No significant difference was observed between the two groups in the reconstitution of other T cells (effector, memory, Th1, Th2, Th17, Treg, and Tfh), B cells (transitional, naïve, memory, and plasmablast), NK cells (regulatory and cytolytic), or dendritic cells (myeloid and plasmacytoid). Patients with fewer CD4+ naïve T cells than the median count (7.60 cells/µL) at two months after allo-HCT developed chronic GVHD less frequently than those with CD4+ naïve T cells above the median count (2-year cumulative incidences were 0.31 and 0.53, respectively; p = 0.133). This pilot study suggests low-dose Thymoglobulin suppresses the recovery of naïve T cells after allo-HCT, which may contribute to a lower incidence of chronic GVHD.