title: CD200 in CNS tumor-induced immunosuppression: the role for CD200 pathway blockade in targeted immunotherapy.
abstract: BACKGROUND
  Immunological quiescence in the central nervous system (CNS) is a potential barrier to immune mediated anti-tumor response. One suppressive mechanism results from the interaction of parenchyma-derived CD200 and its receptor on myeloid cells. We suggest that CD200/CD200R interactions on myeloid cells expand the myeloid-derived suppressor cell (MDSC) population and that blocking tumor-derived CD200 will enhance the efficacy of immunotherapy.
  
  
  METHODS
  CD200 mRNA expression levels in human brain tumor tissue samples were measured by microarray. The amount of circulating CD200 protein in the sera of patients with brain tumors was determined by ELISA and, when corresponding peripheral blood samples were available, was correlated quantitatively with MDSCs. CD200-derived peptides were used as competitive inhibitors in a mouse model of glioblastoma immunotherapy.
  
  
  RESULTS
  CD200 mRNA levels were measured in human brain tumors, with different expression levels being noted among the sub groups of glioblastoma, medulloblastoma and ependymoma. Serum CD200 concentrations were highest in patients with glioblastoma and correlated significantly with MDSC expansion. Similarly, in vitro studies determined that GL261 cells significantly expanded a MDSC population. Interestingly, a CD200R antagonist inhibited the expansion of murine MDSCs in vitro and in vivo. Moreover, inclusion of CD200R antagonist peptide in glioma tumor lysate-derived vaccines slowed tumor growth and significantly enhanced survival.
  
  
  CONCLUSIONS
  These data suggest that CNS-derived tumors can evade immune surveillance by engaging CD200. Because of the homology between mouse and human CD200, our data also suggest that blockade of CD200 binding to its receptor will enhance the efficacy of immune mediated anti-tumor strategies for brain tumors.
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Moertel
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA ; Department of Neurosurgery, Hospital Number 1 of China Medical University, Shenyang, China.
authors.forename: Junzhe
authors.initials: J
authors.lastname: Xia
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: LaRue
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Nate N
authors.initials: NN
authors.lastname: Waldron
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Andersen
authors.affiliation: Department of Neurosurgery, UCLA Medical Center, Los Angeles, CA 90095 USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Prins
authors.affiliation: Department of Neurosurgery, University of California San Francisco, San Francisco, CA 94158 USA.
authors.forename: Hideho
authors.initials: H
authors.lastname: Okada
authors.affiliation: Department of Pediatrics, University of Colorado, Denver Anschutz Medical Center, Aurora, CO 80045 USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Donson
authors.affiliation: Department of Pediatrics, University of Colorado, Denver Anschutz Medical Center, Aurora, CO 80045 USA.
authors.forename: Nicholas K
authors.initials: NK
authors.lastname: Foreman
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Hunt
authors.affiliation: University of Minnesota, Lab Medicine and Pathology, Minneapolis, MN 55455 USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Pennell
authors.affiliation: Department of Pediatrics, hematology/oncology, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Olin
keywords: Brain tumors; Checkpoint inhibitors; Immune suppression; Immunotherapy