title: T cells mediate resistance to genetically modified bone marrow in lethally irradiated recipients.
abstract: BACKGROUND
  In order for gene therapy to attain clinical relevance, efficient engraftment and long-term survival of cells that express transduced genes of interest must be achieved. In this study, we examined the extent to which host T cells affect engraftment of syngeneic bone marrow cells engineered to express a retrovirally transduced allogeneic major histocompatibility complex class-I gene.
  
  
  METHODS
  B10.AKM mice were preconditioned with lethal irradiation or lethal irradiation plus transient CD4 and CD8 T-cell depletion in addition to CD40-CD154 costimulatory blockade and were then reconstituted with syngeneic bone marrow cells transduced with retroviruses that carried the gene that encoded H-2K(b) (K(b)). Expression of K(b) on bone marrow-derived cells was then analyzed, and induction of tolerance to K was evaluated.
  
  
  RESULTS
  Mice conditioned using CD4 and CD8 T-cell depletion in addition to CD40-CD154 costimulatory blockade and lethal irradiation showed a significant increase in the frequency of bone marrow-derived cells that expressed K(b) when compared to animals that received lethal irradiation alone. Survival of allogeneic skin grafts that expressed K(b) was significantly prolonged in animals conditioned with anti-CD4, anti-CD8, and co-stimulatory blockade in addition to lethal irradiation (median survival time, 81 days) when compared to mice that received irradiation alone (mean survival time, 31 days; P=0.001).
  
  
  CONCLUSIONS
  Radioresistant host T cells significantly affect the ability to induce tolerance by gene therapy by affecting engraftment of transduced cells that expressed allogeneic major histocompatibility complex class-I genes in the absence of host T-cell depletion and costimulatory blockade, even after lethal irradiation. Thus, radioresistant host T cells are a significant barrier to engraftment of transduced bone marrow progenitors and to the induction of tolerance by gene therapy.
authors.affiliation: Transplantation Biology Research Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Jessamyn
authors.initials: J
authors.lastname: Bagley
authors.forename: Chaorui
authors.initials: C
authors.lastname: Tian
authors.forename: David H
authors.initials: DH
authors.lastname: Sachs
authors.forename: John
authors.initials: J
authors.lastname: Iacomini
mesh_terms: D000818:Animals; D016026:Bone Marrow Transplantation / Q000276:immunology*; D005260:Female; D005805:Genes, MHC Class I; D015316:Genetic Therapy / Q000379:methods*; D006183:H-2 Antigens / Q000235:genetics*; D007108:Immune Tolerance; D051379:Mice; D012190:Retroviridae / Q000235:genetics; D016038:Skin Transplantation / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D014161:Transduction, Genetic; D019172:Transplantation Conditioning; D014184:Transplantation, Homologous
chemical_list: D006183:H-2 Antigens; C032876:H-2Kb protein, mouse