Direct evidence for new T-cell generation by patients after either T-cell–depleted or unmodified allogeneic hematopoietic stem cell transplantations: Presented in part in abstract form at the 42nd Annual Meeting of the American Society of Hematology, San Francisco, CA, December 2000.

Successful allogeneic hematopoietic stem cell transplantation (HSCT) requires reconstitution of normal T-cell immunity. Recipient thymic activity, biologic features of the allograft, and preparative regimens all contribute to immune reconstitution. We evaluated circulating T-cell phenotypes and T-cell receptor rearrangement excision circles (TRECs) in 331 blood samples from 158 patients who had undergone allogeneic HSCTs. All patients had received myeloablative conditioning regimens and were full donor chimeras in remission. Younger patients exhibited more rapid recovery and higher TRECs ( P  = .02). Recipients of T-cell–depleted allografts initially had lower TRECs than unmodified allograft recipients ( P P + T cells. Low TRECs also correlated strongly with extensive chronic graft-versus-host disease ( P