• umbilical cord blood transplantation;
  • immune reconstitution;
  • T-cell recovery;
  • B-cell recovery;
  • NK-cell recovery

Immune recovery after cord blood transplantation (CBT) is of concern owing to the low number of lymphocytes transferred with the graft and their immaturity. Risk factors influencing lymphocyte subset reconstitution related to disease, patient, donor and transplant were studied in 63 children (< 16 years), given either related (n = 14) or unrelated (n = 49) CBT for malignant (n = 33) or non-malignant diseases (n = 30). Only children with sustained myeloid engraftment were analysed. Absolute numbers of T (CD3+, CD4+, CD8+), B and natural killer (NK) cells were reported 2–3, 6, 9, 12 and 12–24 months after CBT. Median patient age was 4·0 years (0–15) and median follow-up was 23 months (1·7–61·0). Twenty-six patients received human leucocyte antigen (HLA)-matched CBT and 37 received HLA-mismatched CBT. The median number of nucleated cells (NCs) collected/recipient weight was 6·1 × 107/kg. In this selected population, the estimate 2 year survival was 85%. Lymphocyte reconstitution (defined as the median time to reach the normal value of age-matched healthy children) was 3, 6 and 8 months for NK, B and CD8+ cells, while it was 11·7 months for both CD3+ and CD4+ lymphocytes. In the multivariate analysis, factors favouring T-cell recovery were: related donor (P = 0·002); higher NCs/kg (P = 0·005) and recipient cytomegalovirus (CMV)-positive serology (P = 0·04). Presence of acute graft-versus-host disease (GVHD) delayed T-cell recovery (P = 0·04). To summarize, in children with sustained myeloid engraftment the concern that lymphocyte recovery after CBT could be delayed does not appear to be substantiated by our results.