title: Prostate tumor microenvironment alters immune cells and prevents long-term survival in an orthotopic mouse model following flt3-ligand/CD40-ligand immunotherapy.
abstract: A novel orthotopic metastatic model of mouse prostate cancer was developed using MHC-negative TRAMP-C1P3 (transgenic adenocarcinoma of mouse prostate) cells derived by serial passage of the parental TRAMP-C1 line in mouse prostate glands. TRAMP-C1P3 cells grew efficiently in mouse prostate glands and reproducibly metastasized to draining lymph nodes. Using this model, we show that Fms-like tyrosine kinase-3 ligand (flt3-L) dramatically inhibited growth of preexisting orthotopic TRAMP-C1P3 tumors and the development of metastatic disease. Mice remained in remission for several months following termination of flt3-L treatment but eventually relapsed and died of progressive disease. flt3-ligand treatment induced a pronounced mixed inflammatory cell infiltrate that consisted of CD8alpha-CD4- dendritic cells (CD11c+), macrophages, granulocytes (Gr-1+) and to a lesser extent T cells (CD4+ and CD8+). Dendritic cells isolated from TRAMP-C1P3 tumors were phenotypically immature (CD11c+ B7.2-I-A-CD40-), and this phenotype was also predominant in peripheral organs of mice treated with flt3-L alone or in combination with the DC maturation factor, CD40-L. Diminished expression of TCR-beta, CD3-epsilon, and CD3-zeta was also observed on intratumoral T cells, although these signaling proteins were reexpressed following in vitro culture with IL-2. The TCR/CD3 complex remained intact on peripheral T cells except in mice treated with flt3-L where CD3-zeta loss was observed. In contrast to alphabeta-T cells, tumor-infiltrating gammadelta-T cells maintained expression of their antigen receptors but not CD3epsilon. Thus, TRAMP-C1P3 tumors quickly establish a microenvironment that profoundly diminishes expression of molecules critical for normal dendritic cell and T cell function, thus limiting the efficacy of flt3-L and CD40-L immunotherapy. Overall, these data suggest that long-term cures of established MHC-negative tumors may not be achieved until therapeutic interventions are engineered to overcome this immunosuppressive microenvironment.
authors.affiliation: Departments of Microbiology and Molecular Cell Biology, Virginia Prostate Center, Eastern Virginia Medical School, Norfolk, Virginia 23501, USA. ciavarrp@ems.edu
authors.forename: Richard P
authors.initials: RP
authors.lastname: Ciavarra
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Holterman
authors.forename: Roy R
authors.initials: RR
authors.lastname: Brown
authors.forename: Patricia
authors.initials: P
authors.lastname: Mangiotti
authors.forename: Nazita
authors.initials: N
authors.lastname: Yousefieh
authors.forename: George L
authors.initials: GL
authors.lastname: Wright
authors.forename: Paul F
authors.initials: PF
authors.lastname: Schellhammer
authors.forename: W F
authors.initials: WF
authors.lastname: Glass
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Somers
mesh_terms: D000818:Animals; D023201:CD40 Ligand / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D003713:Dendritic Cells / Q000276:immunology; D004195:Disease Models, Animal; D018572:Disease-Free Survival; D007165:Immunosuppression Therapy; D007167:Immunotherapy; D008207:Lymphatic Metastasis; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology; D008297:Male; D008565:Membrane Proteins / Q000627:therapeutic use*; D051379:Mice; D008822:Mice, Transgenic; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; C084881:flt3 ligand protein; D023201:CD40 Ligand