title: Depletion of donor-reactive cells as a new concept for improvement of mismatched bone marrow engraftment using reduced-intensity conditioning.
abstract: OBJECTIVE
  New nonmyeloablative strategies to improve acceptance of mismatched bone marrow (BM) may compensate for the inadequate supply of compatible grafts. Recently we proposed to facilitate engraftment of mismatched BM by selective depletion of activated donor-reactive host cells with cyclophosphamide (CY). Here we have compared engraftment of allogeneic BM after depletion of antigen-activated host lymphocytes by CY, with BM engraftment following general immunosuppression by the same CY dose.
  
  
  METHODS
  Naive or mildly irradiated BALB/c mice were primed with C57BL/6 BM cells (day 0), treated with CY in order to deplete activated T cells (day 1), and transplanted with a second C57BL/6 BM inoculum (day 2) in order to achieve BM engraftment. Alternatively, mice received an equal dose of donor BM cells in a single injection one day after the same CY dose. Treated animals were repeatedly tested for persistence of donor cells in the blood.
  
  
  RESULTS
  Depletion of alloantigen-primed lymphocytes by 200 mg/kg CY provided stable GVHD-free engraftment of allogeneic BM in nonirradiated mice, while immunosuppressive treatment with the same CY dose alone resulted in BM rejection. Low-dose irradiation before priming with donor BM allowed the tolerance-inducing CY dose to be reduced to 100 mg/kg. Alloantigen-primed lymphocyte depletion (APLD) by a reduced CY dose resulted in engraftment of donor BM after a significantly lower irradiation dose than treatment with irradiation and CY alone.
  
  
  CONCLUSIONS
  Our results demonstrate that conditioning that focuses on APLD has a definite advantage over general immunosuppression with CY and radiation therapy.
authors.affiliation: Department of Bone Marrow Transplantation and Cancer Immunotherapy, Hadassah University Hospital, Jerusalem, Israel.
authors.forename: Tatyana B
authors.initials: TB
authors.lastname: Prigozhina
authors.forename: Gregory
authors.initials: G
authors.lastname: Elkin
authors.forename: Sofia
authors.initials: S
authors.lastname: Khitrin
authors.forename: Shimon
authors.initials: S
authors.lastname: Slavin
mesh_terms: D000818:Animals; D016026:Bone Marrow Transplantation / Q000276:immunology*; D003520:Cyclophosphamide / Q000008:administration & dosage / Q000494:pharmacology; D006085:Graft Survival; D006086:Graft vs Host Disease / Q000517:prevention & control; D006648:Histocompatibility; D007165:Immunosuppression Therapy; D008213:Lymphocyte Activation; D008212:Lymphocyte Depletion / Q000379:methods*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018714:Radiotherapy, Adjuvant; D019172:Transplantation Conditioning / Q000379:methods*
chemical_list: D003520:Cyclophosphamide