Reconstitution of lymphocyte subpopulations after paediatric bone marrow transplantation

We prospectively studied the reconstitution of lymphocyte subpopulations in a group of 22 children, who survived disease-free at least 6 months after allogeneic BMT for a haematological malignancy. Absolute counts of total ly mphocytes, B lymphocytes, T lymphocytes, and CD4(+) helper T lymphocytes re ached the 5th percentile (p(5)) Of age-matched reference values within 6 mo nths after BMT in 15, 17, 7 and 2 patients, respectively. In particular, CD 4(+) helper T lymphocyte reconstitution was very slow. Unexpectedly, CMV re activation had a profound positive influence upon the number of CD4(+) help er T lymphocytes in the children. In five patients, absolute B lymphocyte c ounts above the 95th percentile were reached from 6 months after BMT onward s, mimicking normal ontogeny, Unlike normal ontogeny, the percentages of he lper T lymphocytes expressing the 'naive' CD45RA isoform were low and those expressing the 'memory' CD45RO isoform were high in the first 3 months aft er BMT, as described before. Thereafter, the CD45RA:CD45RO ratio slowly nor malised, Also, CD7 expression was absent on up to 90% of T lymphocytes in t he first months after BMT, and on a steadily decreasing percentage thereaft er, as recently described in adults. However, the absolute counts of CD45RO (+)/CD4(+) and CD7(-)/CD4(+) helper T lymphocytes did not change significan tly. So, we found no evidence of peripheral expansion of previously primed donor-derived 'memory' T lymphocytes during the follow-up period which span ned 1-18 months after BMT, The absolute counts of 'naive' CD45RA(+) helper T lymphocytes did not show a faster increase after BMT than in adults, desp ite the presumed presence of a non-involuted thymus in children.