Immunosuppressive and anticancer effect of a mammalian ribonuclease that targets high-affinity interleukin-2-receptors.
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.
Yamamura
Tadashi
T
Department of Surgery, Keio University School of Medicine, Tokyo, Japan.
Ueda
Masakazu
M
Psarras
Kyriakos
K
Suwa
Tatsushi
T
Watanaabe
Yasuo
Y
Kameyama
Noriaki
N
Tanabe
Minoru
M
Imamura
Hiroji
H
Kitajima
Masaki
M
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*
D000970:Antineoplastic Agents; D007166:Immunosuppressive Agents; D015375:Receptors, Interleukin-2; D012259:Ribonuclease, Pancreatic