Assessment of Immune Reconstitution After Hematopoietic Cell Transplantation in Pediatric Patients with Inborn Errors of Immunity

Introduction Hematopoietic cell transplantation (HCT) offers a curative treatment for many inborn errors of immunity. Immune reconstitution (IR) of different cellular subsets occurs at variable time points (days, D) and may differ in completeness and functional capacity. We aim to summarize laboratory findings in patients post-HCT. Methods Retrospective analysis of laboratory data collected of 21 post-HCT patients (p) diagnosed with Wiskott–Aldrich syndrome (7p), chronic granulomatous disease (8p), severe combined inmunodefiency (2p), CD40L (3p), and XIAP (1p) deficiency. We evaluated lymphocyte subsets, T/B cell compartments, immunoglobulin levels, and proliferative assay. Spearman correlation was performed. Results 21p (20 male), median age at HCT 3 years [0.5-11]. 1 died before D+90 post-HCT. By D+360, immune monitoring showed the following median values across lymphocyte subsets: CD3+CD4+ (23%), CD3+CD8+ (39%), CD16+CD56+ (8.5%), and CD19+ (19%) with a persisted inverted CD4/CD8 ratio. CD4+ lymphocytes (mm3) gradually increased by D+180, D+360, D+540, and D+720 (median [mm3]: 378, 618, 809, and 1,211). 13/17p achieved adequate T cell IR, defined as CD4+ naive T cell >20% (median: 35%) and good proliferative response to PHA after D+360. Furthermore, CD4+ naive count correlated inversely with HLA-DR expression (r:0,4926 p:0.022), suggesting reduced T cell activation as IR progressed. According to humoral reconstitution at different points (D+60, D+120, D+180, D+360, D+720), median levels of IgA (mg/dl) (8, 47, 76, 90, 161) and IgM (mg/dl) (33, 38, 73, 75, 94) display an increase over time. 5/13p showed a normal B cell subset after D+540. Conclusion As reported in the literature, T cell reconstitution occurs first, while B cell compartment reconstitution tends to take much longer. Standardizing immune monitoring post-HCT could improve the assessment of immune recovery and optimize patient management.