title: Short-course rapamycin treatment enables engraftment of immunogenic gene-engineered bone marrow under low-dose irradiation to permit long-term immunological tolerance.
abstract: Application of genetically modified hematopoietic stem cells is increasingly mooted as a clinically relevant approach to protein replacement therapy, immune tolerance induction or conditions where both outcomes may be helpful. Hematopoietic stem and progenitor cell (HSPC)-mediated gene therapy often requires highly toxic pretransfer recipient conditioning to provide a 'niche' so that transferred HSPCs can engraft effectively and to prevent immune rejection of neoantigen-expressing engineered HSPCs. For widespread clinical application, reducing conditioning toxicity is an important requirement, but reduced conditioning can render neoantigen-expressing bone marrow (BM) and HSC susceptible to immune rejection if immunity is retained.
  
  
  
  BM or HSPC-expressing OVA ubiquitously (actin.OVA) or targeted to MHC II+ cells was transferred using low-dose (300 cGy) total body irradiation. Recipients were administered rapamycin, cyclosporine or vehicle for 3 weeks commencing at BM transfer. Engraftment was determined using CD45 congenic donors and recipients. Induction of T-cell tolerance was tested by immunising recipients and analysing in-vivo cytotoxic T-lymphocyte (CTL) activity. The effect of rapamycin on transient effector function during tolerance induction was tested using an established model of tolerance induction where antigen is targeted to dendritic cells.
  
  
  
  Immune rejection of neoantigen-expressing BM and HSPCs after low-dose irradiation was prevented by a short course of rapamycin, but not cyclosporine, treatment. Whereas transient T-cell tolerance developed in recipients of OVA-expressing BM administered vehicle, only when engraftment of neoantigen-expressing BM was facilitated with rapamycin treatment did stable, long-lasting T-cell tolerance develop. Rapamycin inhibited transient effector function development during tolerance induction and inhibited development of CTL activity in recipients of OVA-expressing BM.
  
  
  
  Rapamycin acts to suppress acquisition of transient T-cell effector function during peripheral tolerance induction elicited by HSPC-encoded antigen. By facilitating engraftment, short-course rapamycin permits development of long-term stable T-cell tolerance.
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: Kunal H
authors.initials: KH
authors.lastname: Bhatt
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Rudraraju
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: Jeremy F
authors.initials: JF
authors.lastname: Brooks
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Jung
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: Ryan
authors.initials: R
authors.lastname: Galea
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia.
authors.forename: James W
authors.initials: JW
authors.lastname: Wells
authors.affiliation: The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia. r.steptoe@uq.edu.au.
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Steptoe
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000276:immunology*; D016026:Bone Marrow Transplantation; D060846:Cell Engineering; D003713:Dendritic Cells / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects; D015316:Genetic Therapy; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000276:immunology* / Q000528:radiation effects; D006801:Humans; D007108:Immune Tolerance / Q000187:drug effects / Q000276:immunology* / Q000528:radiation effects; D051379:Mice; D011827:Radiation; D020123:Sirolimus / Q000008:administration & dosage; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects; D019172:Transplantation Conditioning
chemical_list: D020123:Sirolimus
keywords: Bone marrow transplant; Gene therapy; Immune tolerance