T cell reconstitution after bone marrow transplantation into adult patients does not resemble T cell development in early life.

Immune reconstitution after marrow transplantation has some characteristics of immune development in early life. Here we provide phenotypic data suggesting this may not be true for T cells (particularly CD4+ T cells) in the case of marrow transplantation into adults. T cells from 35 adult patients at 1 year after transplant, 14 normal neonates and 22 normal adults were studied by 3-color flow cytometry. Marked disparity between the phenotype of neonatal vs post-transplant T cells was found. Of the total CD4+ T cells, the neonates had supranormal percentages of CD45RAhigh, L-selectin+, CD29low/-, CD11alow/- and CD28+ cells whereas most patients at 1 year after transplant had subnormal percentages of these CD4+ T cell subpopulations. (sub/supra-normal denotes below/above normal adult values). Absolute blood counts of naive (CD45RAhigh, L-selectin+, CD29low/- and CD11alow/-) CD4+ T cells correlated inversely with patient age. Neonates had also supranormal percentages of CD45RAhigh, L-selectin+, CD29low/-, CD11alow/- and CD28+ CD8+ T cells whereas the patients (particularly those with chronic GVHD) tended to have subnormal percentages of these CD8+ T cell subpopulations. Contrary to the CD4+ T cells, there was no correlation between the absolute counts of CD45RAhigh, L-selectin+, CD29low/- or CD11alow/- CD8+ T cells and patient age. Whereas the vast majority of neonatal T cells were CD38high, most patient and normal adult T cells were CD38- or CD38intermediate (both CD4+ and CD8+ T cells). We conclude that, in contrast to early life, the production of naive CD4+ T cells is deficient in adult (and particularly elderly) transplant recipients.