Counts of TREC-containing CD4 T cells (but not counts of TREC-containing CD8 T cells) were low in patients who received transplants at the age of 18 years or older but not in transplant recipients younger than 18 years.

The patients (n = 17 for the younger patients, n = 15 for the older patients) were compared with their sibling marrow donors (n = 7 for the younger patients, n = 9 for the older patients) as well as to unrelated age-matched controls (n = 17 for the younger patients and n = 15 for the older patients). The median ages of the younger group at the time of the blood draw were 37 years for the patients, 37 years for the marrow donors, and 36 years for the unrelated controls (not significantly different by Mann-Whitney test). The median ages of the older group at the time of the blood draw were 44 years for the patients, 46 years for the marrow donors, and 45 years for the unrelated controls (not significantly different by Mann-Whitney test). The squares denote medians and the error bars denote 10th to 90th percentiles. A black star denotes significant difference (P < .05) by paired (Wilcoxon) signed-rank test. A gray star denotes significant difference (P < .05) by Mann-Whitney rank sum test (nonpaired).