Thymic hyperplasia after chemotherapy in adults with mature B cell lymphoma and its influence on thymic output and CD4+ T cells repopulation

To investigate the thymic regenerative potential in adults accepting chemotherapy for lymphoma. The dynamics of thymic activity in 54 adults from baseline to 12 mo post-chemotherapy was analyzed by assessing thymic structural changes with serial computed tomography (CT) scans, and correlating these with measurements of thymic output by concurrent analysis of single-joint (sj) T-cell receptor excision circles (sjTREC) and CD31(+) recent thymic emigrants (RTE) in peripheral blood. Furthermore, the consequence of thymic renewal on peripheral CD4(+) T cell recovery after chemotherapy was evaluated. Time-dependent changes of thymic size and thymic output assessed by both sjTREC levels and CD31(+) RTE counts in peripheral blood were observed during and after chemotherapy. Enlargement of thymus over baseline following chemotherapy regarded as rebound thymic hyperplasia (TH) was identified in 20 patients aged 18-53 y (median 33 y). By general linear models repeated measure analysis, it was found that, patients with TH (n = 20) had a faster recovery of sjTREC levels and CD31(+) RTE counts after chemotherapy than patients with comparable age, gender, diagnosis, disease stage, thymic volume and output function at baseline but without TH (n = 18) (p = 0.035, 0.047); besides, patients with TH had a faster repopulation of both naïve CD4(+) T cell and natural regulatory CD4(+) T cell subsets than those without TH (p = 0.042, 0.038). These data suggested that adult thymus retains the capacity of regeneration after chemotherapy, especially in young adults. The presence of TH could contribute to the renewal of thymopoiesis and the replenishment of peripheral CD4(+) T cell pool following chemotherapy in adults.