Lymphocyte recovery following allogeneic stem cell transplantation: New possibilities for improvement

Allogeneic stem cell transplantation (allo-SCT) has been established as an important treatment modality for patients with hematological malignancies, aplastic anemia, and inborn errors of hematopoietic progenitor cells. Treatment related mortality (TRM), however, has restricted the use of allo-SCT to younger patients, in particular those diagnosed with poor-risk underlying disease. TRM is mainly caused by severe opportunistic infections, due to impaired immune reconstitution following allo-SCT. While epithelial barriers and granulocytes are restored within weeks following transplantation, B lymphocytes and T lymphocytes may be deficient for a prolonged period of time. The extreme slow recovery of newly developed, donor stem cell derived, naive CD4T+ T-cells is currently considered to be the most important determinant of this impaired immune competence in the later time period after allo-SCT. Especially older patients, those receiving an unrelated or mismatched related donor graft, and patients receiving a T-cell depleted graft may show a CD4+ lymphopenia for more than 12 months after allo-SCT. Thus, in spite of better supportive care and prophylactic measures, the immunedeficiency of the later post-transplant period has remained a major problem. Here, we review the literature concerning B- and T-cell recovery following allo-SCT, discuss the role of GVHD and consider possibilities for improvement of lymphocyte recovery.

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