LOCID differs from classic CVID in its clinical and immunologic characteristics. Systematic T cell phenotype may help to discriminate such patients from those with CVID. Identification of this phenotype should result in a more fitted diagnostic and therapeutic approach of infections and could provide insights for genetic diagnosis.

Long-term T-cell reconstitution after hematopoietic stem cell transplantation (HSCT) is dependent on patient thymic function and affected by graft-versushost disease (GVHD). To assess the impact of acute GVHD (aGVHD) on thymic function, we followed a cohort of 93 patients who received HSCT from a human histocompatibility leukocyte antigenidentical sibling, mainly for hematologic malignancies. Thymic output was measured by signal-joint T-cell receptor excision circles (sjTREC) real-time polymerase chain reaction. Absolute sjTREC number was lower at 6 months in patients with aGVHD (P ‫؍‬ .014), associated with lower absolute counts of naive CD4 T cells at 6 and 12 months (P ‫؍‬ .04 and .02), and persistent abnormalities in T-cell repertoire diversity. Age and aGVHD affected thymic function independently in multivariate analysis. In patients less than 25 years of age, thymic function recovered almost totally at 1 year. As a marker of thymocyte proliferation, we quantified the ␤TREC generated during the T-cell receptor ␤-chain recombination, in a group of 20 age-matched patients. Mean ␤TREC level was reduced at 6 months in patients with aGVHD, indicating an impact on early thymic differentiation rather than on intrathymic proliferation. These data show that aGVHD or its treatment has a transient impact on thymic function in younger patients in the first months after HSCT. (Blood. 2009;113:6477-6484)