Immune Reconstitution After Hematopoietic Stem Cell Transplantation: Cellular Dynamics, Clinical Determinants, and Emerging Therapeutic Strategies.

BACKGROUND

Immune reconstitution following HSCT is a complex process that strongly determines post-transplant outcomes. Delayed or impaired immune recovery increases susceptibility to opportunistic infections, viral reactivation, graft-versus-host disease, relapse, and transplant-related morbidity and mortality.

OBJECTIVE

This review summarizes current evidence on the kinetics, functional recovery, and clinical significance of innate and adaptive immune reconstitution after HSCT.

METHODS

A narrative review of recent literature was performed focusing on immune cell reconstitution dynamics and influencing clinical and biological factors.

RESULTS

Innate immunity (neutrophils, NK cells) recovers early, providing initial defense. Adaptive immunity is delayed, driven by thymic output and peripheral T- and B-cell expansion. Regulatory T cells and γδ T cells support tolerance and graft-versus-leukemia effects. Recovery is influenced by age, conditioning, graft source, GVHD, infections, and microbiome. Numerical recovery may not equal functional immune competence.

CONCLUSION

Advances in immune profiling, biomarkers, and systems immunology, along with adoptive cellular therapy and microbiome-based interventions, may enable personalized strategies to improve immune reconstitution and long-term outcomes.