Published online 26 January 2008
Haematologica, Vol 93, Issue 2, 240-247 doi:10.3324/haematol.11708
Copyright © 2008 by Ferrata Storti Foundation
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Stem Cell Transplantation

Evidence for neo-generation of T cells by the thymus after non-myeloablative conditioning

Emilie Castermans1,2,*, Frédéric Baron1,2,*,, Evelyne Willems1,2, Nicole Schaaf-Lafontaine3, Nathalie Meuris1,2, André Gothot2,3, Jean-François Vanbellighen4, Christian Herens4, Laurence Seidel5, Vincent Geenen6, Remi Cheynier7, Yves Beguin1,2

1 Department of Medicine, Division of Hematology, University of Liège, Liège, Belgium;
2 GIGA Research, University of Liège, Liège, Belgium; Department of Laboratory Medicine, Division of Laboratory Hematology and
3 Immuno-Hematology, University of Liège, Liège, Belgium;
4 Department of Genetics, University of Liège, Liège, Belgium;
5 Department of statistics, University of Liège, Liège, Belgium;
6 Center of Immunology, University of Liège, Liège, Belgium;
7 Department of Virology, Institut Pasteur, Paris, France

Correspondence: Frédéric Baron, MD, PhD, University of Liège, Department of Hematology, CHU Sart-Tilman, 4000 Liège. Belgium, E-mail: f.baron{at}ulg.ac.be

Background: Background and objective. We investigated immune recovery in 50 patients given either unmanipulated or CD8-depleted allogeneic peripheral blood stem cells after non-myeloablative conditioning.

Design and Methods: Fifty patients were randomized to receive either CD8-depleted (n=22) or non-manipulated (n=28) peripheral blood stem cells. The median patients age was 57 (range 36–69) years. The conditioning regimen consisted of 2 Gy total body irradiation with or without added fludarabine. Twenty patients received grafts from related donors, 14 from 10/10 HLA-allele matched unrelated donors, and 16 from HLA-mismatched unrelated donors. Graft-versus-host disease pro-phylaxis consisted of mycophenolate mofetil and cyclosporine. Immune recovery during the first year after hematopoietic cell transplantation was assessed by flow cytometry phenotyping, analyses of the diversity of the TCRBV repertoire, and quantification of signal-joint T-cell receptor excision circles (sjTREC).

Results: CD8-depletion of the graft reduced the recovery of CD8+ T-cell counts in the first 6 months following transplantation (p<0.0001) but had no significant impact on the restoration of other T-cell subsets. Both sjTREC concentration and CD3+ T-cell counts increased significantly between day 100 and 365 (p=0.010 and p=0.0488, respectively) demonstrating neo-production of T cells by the thymus. Factors associated with high sjTREC concentration 1 year after transplantation included an HLA-matched unrelated donor (p=0.029), a high content of T cells in the graft (p=0.002), and the absence of chronic graft-versus-host disease (p<0.0001).

Conclusions: Our data suggest that while immune recovery is mainly driven by peripheral expansion of the graft-contained mature T cells during the first months after non-myeloablative transplantation, T-cell neo-generation by the thymus plays an important role in long term immune reconstitution in transplanted patients.

Key words: hematopoietic cell transplantation, non-myeloablative, T-cell depletion, GVHD, immunity, thymus.