title: Immunosuppressive and anticancer effect of a mammalian ribonuclease that targets high-affinity interleukin-2-receptors.
abstract: OBJECTIVE
  To target high-affinity interleukin (IL)-2 receptors involved in lymphocyte proliferation processes such as allograft rejection, autoimmune disorders, and certain haematological malignancies, using a minimally immunogenic mammalian-derived enzyme, bovine RNaseA, which becomes cytotoxic on entering cytoplasm.
  
  
  METHODS
  Laboratory study.
  
  
  METHODS
  Teaching hospital, Japan.
  
  
  METHODS
  Human lymphocytes isolated from healthy histoincompatible donors in mixed lymphocyte cultures or stimulated with phytohemagglutinin (PHA) to promote IL-2Ralpha expression. MJ, an HTLV-1-infected malignant T-cell line that overexpresses IL-2Ralpha, and the IL-2Ralpha-negative cell lines MOLT-4F and MT-1, were used as controls.
  
  
  METHODS
  Bovine RNaseA was chemically conjugated to 7G7B6, a monoclonal antibody to the alpha-chain of human IL-2 receptors, and several concentrations of the conjugates were added to the lymphocyte cultures.
  
  
  METHODS
  Inhibition of cell proliferation as a percentage of 3H-thymidine incorporation in 24 hours.
  
  
  RESULTS
  7G7B6-RNaseA dose-dependently inhibited cell proliferation in PHA-stimulated human lymphocytes at a 50% inhibitory concentration (IC50) of 2 x 10(-7) M. whereas RNase alone and RNase plus antibody had no inhibitory effect. 7G7B6-RNaseA also dose-dependently inhibited the human mixed lymphocyte reaction at an IC50 of 2 x 10(-6) M, whereas RNase alone did not. The conjugate also inhibited cell proliferation in MJ cells, a cell line that is infected with HTLV-I and overexpresses the high-affinity IL-2 receptor, at an IC50 of 5 x 10(-7) M. However the conjugate had no inhibitory effect on the IL-2 receptor non-expressing human T-cell lymphoblastic leukaemia cell lines MOLT-4F or MT-1.
  
  
  CONCLUSIONS
  7G7B6-RNaseA can inhibit cell proliferation in antigen- or mitogen-stimulated lymphocytes that overexpress high-affinity IL-2 receptors, and it may be safer than conventional chemotherapy or immunotoxins in the treatment of transplant rejection, certain lymphocytic malignancies, and other IL-2R-associated diseases, because it contains a mammalian cytotoxic enzyme.
authors.affiliation: Department of Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yamamura
authors.forename: Masakazu
authors.initials: M
authors.lastname: Ueda
authors.forename: Kyriakos
authors.initials: K
authors.lastname: Psarras
authors.forename: Tatsushi
authors.initials: T
authors.lastname: Suwa
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Watanaabe
authors.forename: Noriaki
authors.initials: N
authors.lastname: Kameyama
authors.forename: Minoru
authors.initials: M
authors.lastname: Tanabe
authors.forename: Hiroji
authors.initials: H
authors.lastname: Imamura
authors.forename: Masaki
authors.initials: M
authors.lastname: Kitajima
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007959:Lymphocyte Culture Test, Mixed; D008214:Lymphocytes / Q000187:drug effects; D051379:Mice; D015375:Receptors, Interleukin-2 / Q000187:drug effects*; D012259:Ribonuclease, Pancreatic / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D007166:Immunosuppressive Agents; D015375:Receptors, Interleukin-2; D012259:Ribonuclease, Pancreatic