Summary. Immune reconstitution was studied prospectively in 66 children who underwent 77 haematopoietic cell transplantations (HCT): 46 autologous HCTs in 39 patients and 31 allogeneic HCTs in 27 patients. We studied the dynamic analysis of immune recovery with regard to potential factors affecting its speed, including age, type of HCT, diagnosis, graft-versus-host disease (GvHD) and cytomegalovirus (CMV) infection reactivation. Absolute counts of different lymphocyte subsets and immunoglobulin serum levels were determined in peripheral blood of patients on d )7 and +16, and then at various intervals up to 24 months post transplant. Common patterns of immune recovery after both allogeneic and autologous HCT were identified: (i) CD4 + CD45RO + peripheral T-cell expansion on d +16; (ii) inverted CD4 + :CD8 + ratio from d +30 onwards; (iii) rapid natural killer (NK) cell (CD16 ± CD56 + ) count normalization. We observed prolonged T-cell lymphopenia (CD3 + , CD3 + CD4 + , CD4 + CD45RA + ) until 24 months after autologous HCT, whereas in the allogeneic setting CD3 + CD4 + cells, including naive CD45RA + cells, returned to normal values at 9 months post transplant. Age > 10 years and coexistence of GvHD and CMV reactivation were associated with a substantial delay in T-(CD4 + , including CD45RA + ) and B-cell recovery after allogeneic HCT. Multidrug GvHD prophylaxis resulted in impaired T-(CD4 + , CD4 + CD45RA + ) and B-cell reconstitution only in the early phase after allogeneic HCT (up to 4 months). Our results demonstrated that T-cell recovery was severely impaired in children after autologous HCT. It should be emphasized that specific approaches to enhance immune reconstitution are necessary to control minimal residual disease and avoid the risk of infectious complications in the autologous setting. Thymic involution after allogeneic HCT seems to be associated with age and coexistence of GvHD and CMV reactivation.

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A total of 527 children with acute lymphoblastic leukaemia (ALL) from the most frequent risk groups: standard risk group (SRG) and intermediate risk group (IRG) were treated between 1987 and 1991 according to an intensified treatment program (based on the BFM protocol) including the use of an intermediate dose of methotrexate in the IRG. A comparison of the treatment results in this group from 513 children treated between 1981 and 1987 indicates that the chance for a 6 year event‐free survival has increased to 73% (previously 55%).

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