title: Evidence for neo-generation of T cells by the thymus after non-myeloablative conditioning.
abstract: 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.
  
  
  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.
authors.affiliation: Department of Medicine, Division of Hematology, University of Liège, Liège, Belgium.
authors.forename: Emilie
authors.initials: E
authors.lastname: Castermans
authors.forename: Frédéric
authors.initials: F
authors.lastname: Baron
authors.forename: Evelyne
authors.initials: E
authors.lastname: Willems
authors.forename: Nicole
authors.initials: N
authors.lastname: Schaaf-Lafontaine
authors.forename: Nathalie
authors.initials: N
authors.lastname: Meuris
authors.forename: André
authors.initials: A
authors.lastname: Gothot
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Vanbellighen
authors.forename: Christian
authors.initials: C
authors.lastname: Herens
authors.forename: Laurence
authors.initials: L
authors.lastname: Seidel
authors.forename: Vincent
authors.initials: V
authors.lastname: Geenen
authors.forename: Remi
authors.initials: R
authors.lastname: Cheynier
authors.forename: Yves
authors.initials: Y
authors.lastname: Beguin
mesh_terms: D000328:Adult; D000368:Aged; D000762:Anesthesia Recovery Period; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D016572:Cyclosporine / Q000008:administration & dosage; D005260:Female; D005434:Flow Cytometry; D006086:Graft vs Host Disease / Q000276:immunology / Q000517:prevention & control; D006650:Histocompatibility Testing; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage; D008212:Lymphocyte Depletion; D008297:Male; D008875:Middle Aged; D009173:Mycophenolic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives; D019653:Myeloablative Agonists / Q000008:administration & dosage; D009369:Neoplasms; D036102:Peripheral Blood Stem Cell Transplantation; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology; D013950:Thymus Gland / Q000276:immunology*; D013997:Time Factors; D014019:Tissue Donors; D019172:Transplantation Conditioning; D014184:Transplantation, Homologous; D014740:Vidarabine / Q000008:administration & dosage / Q000031:analogs & derivatives; D014916:Whole-Body Irradiation
chemical_list: D007166:Immunosuppressive Agents; D019653:Myeloablative Agonists; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016572:Cyclosporine; D014740:Vidarabine; D009173:Mycophenolic Acid; C024352:fludarabine