title: Multipotent adult germ-line stem cells, like other pluripotent stem cells, can be killed by cytotoxic T lymphocytes despite low expression of major histocompatibility complex class I molecules.
abstract: BACKGROUND
  Multipotent adult germ-line stem cells (maGSCs) represent a new pluripotent cell type that can be derived without genetic manipulation from spermatogonial stem cells (SSCs) present in adult testis. Similarly to induced pluripotent stem cells (iPSCs), they could provide a source of cellular grafts for new transplantation therapies of a broad variety of diseases. To test whether these stem cells can be rejected by the recipients, we have analyzed whether maGSCs and iPSCs can become targets for cytotoxic T lymphocytes (CTL) or whether they are protected, as previously proposed for embryonic stem cells (ESCs).
  
  
  RESULTS
  We have observed that maGSCs can be maintained in prolonged culture with or without leukemia inhibitory factor and/or feeder cells and still retain the capacity to form teratomas in immunodeficient recipients. They were, however, rejected in immunocompetent allogeneic recipients, and the immune response controlled teratoma growth. We analyzed the susceptibility of three maGSC lines to CTL in comparison to ESCs, iPSCs, and F9 teratocarcinoma cells. Major histocompatibility complex (MHC) class I molecules were not detectable by flow cytometry on these stem cell lines, apart from low levels on one maGSC line (maGSC Stra8 SSC5). However, using a quantitative real time PCR analysis H2K and B2m transcripts were detected in all pluripotent stem cell lines. All pluripotent stem cell lines were killed in a peptide-dependent manner by activated CTLs derived from T cell receptor transgenic OT-I mice after pulsing of the targets with the SIINFEKL peptide.
  
  
  CONCLUSIONS
  Pluripotent stem cells, including maGSCs, ESCs, and iPSCs can become targets for CTLs, even if the expression level of MHC class I molecules is below the detection limit of flow cytometry. Thus they are not protected against CTL-mediated cytotoxicity. Therefore, pluripotent cells might be rejected after transplantation by this mechanism if specific antigens are presented and if specific activated CTLs are present. Our results show that the adaptive immune system has in principle the capacity to kill pluripotent and teratoma forming stem cells. This finding might help to develop new strategies to increase the safety of future transplantations of in vitro differentiated cells by exploiting a selective immune response against contaminating undifferentiated cells.
  
  
  METHODS
  This article was reviewed by Bhagirath Singh, Etienne Joly and Lutz Walter.
authors.affiliation: Department of Cellular and Molecular Immunology, University of Göttingen, Heinrich-Düker-Weg 12, 37073 Göttingen, Germany. rdresse@gwdg.de
authors.forename: Ralf
authors.initials: R
authors.lastname: Dressel
authors.forename: Kaomei
authors.initials: K
authors.lastname: Guan
authors.forename: Jessica
authors.initials: J
authors.lastname: Nolte
authors.forename: Leslie
authors.initials: L
authors.lastname: Elsner
authors.forename: Sebastian
authors.initials: S
authors.lastname: Monecke
authors.forename: Karim
authors.initials: K
authors.lastname: Nayernia
authors.forename: Gerd
authors.initials: G
authors.lastname: Hasenfuss
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Engel
mesh_terms: D000375:Aging / Q000276:immunology*; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic; D053595:Embryonic Stem Cells / Q000166:cytology / Q000276:immunology; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D007267:Injections; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016513:Mice, SCID; D039902:Multipotent Stem Cells / Q000166:cytology / Q000276:immunology*; D010455:Peptides / Q000276:immunology; D039904:Pluripotent Stem Cells / Q000166:cytology / Q000276:immunology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000378:metabolism; D015843:Serpins / Q000378:metabolism; D013094:Spermatozoa / Q000166:cytology*; D013602:T-Lymphocytes, Cytotoxic / Q000166:cytology / Q000276:immunology*; D013696:Temperature; D013724:Teratoma / Q000473:pathology
chemical_list: D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D010455:Peptides; D015843:Serpins; D012697:Serine Endopeptidases; C106610:Serpinb9 protein, mouse