Immune reconstitution and outcome after unrelated cord blood transplantation: a single paediatric institution experience

We report the outcome of 12 children who underwent unrelated cord blood transplant (U-CBT) in a single institution between February 1997 and July 1998. The 1 year event-free survival was 67% (95% CI of 26%). Four children died with infectious complication as cause of death in three cases. Immune reconstitution was studied during first year post transplant by assaying total lymphocyte counts, B cells, NK cells and T cell subsets in the eight disease-free surviving patients. We observed a prompt recovery of CD19(+) cell number which was greater than 500/mu l at 9 months for all patients except the one with severe cGVHD, B cells constituted the predominant lymphocyte subset at 6 and 9 months post transplant with normal or elevated B cell numbers according to normal paediatric range. We noted normal serum immunoglobulin levels at 6 months post transplant for IgA and IgM and at 9 months for IgG, The CD3(+) cell count and particularly the CD3(+)CD8(+) T cell subset remained depressed until 12 months post transplant, Six months after unrelated CBT, seven out of eight patients had less than 100 CD3(+)CD8(+) cells/mu l. CD3(+)CD4(+) cell recovery was less impaired with all children achieving an absolute count of CD3(+)CD4(+) cells greater than 200/mu l during the first year in a median of 5 months. The percentage of NK cells was elevated during the first 6 months after CBT but their absolute count remained within the normal range.