Anthony C. Allison

RS-61443 : A NEW, POTENT IMMUNOSUPPRESSIVE AGENT

The immunosuppressive activity of RS-61443, a semisynthetic derivative of mycophenolic acid, was examined in 33 canine renal allografts. Initial studies established that triple therapy consisting of 20 mg/kg RS-61443 in combination with 5 mg/kg cyclosporine and 0.1 mg/kg methylprednisolone was the optimal combination to prevent graft rejection. The median survival time was 8.1 +/- 1.2 days in dogs without treatment (n = 5), 8.5 +/- 1.7 days in the treatment control group (CsA 5 mg/kg, MP 0.1 mg/kg; n = 6), 36.0 +/- 9.6 days with RS-61443 monotherapy (40 mg/kg; n = 6); and 122.4 +/- 38.75 days with triple therapy (n = 16). Graft prolongation was statistically significant when compared with controls (P less than 0.05 and 0.002, respectively). Six recipients in the triple therapy group survived over 150 days without major adverse effects. Long-term administration of RS-61443 (20 mg/kg/day) did not cause nephrotoxicity, hematotoxicity, or hepatotoxicity, with the exception of a slight elevation of the alkaline phosphatase levels. Gastrointestinal symptoms including gastritis, diarrhea, and anorexia were common, especially under 40 mg/kg RS-61443 monotherapy, and appeared to be dose-related. Despite its immunosuppressive activity, an increased susceptibility to bacterial or viral infections was not observed. Histological studies of the kidney grafts revealed slight interstitial cell infiltration without vascular or glomerular damage.

Mycophenolate mofetil (RS-61443): Mechanisms of action and effects in transplantation

W hereas cyclosporine and glucocorticoids have had a major impact in transplantation, their side effects are well known. Cyclosporine efficiently suppresses T-cell-mediated immune responses and acute rejection of allografts. Nevertheless, many human organ graft recipients who have been given combination therapy with cyclosporine and steroids, with or without azathioprine, have episodes of rejection. Often these are controlled by high-dose bolus steroid and/or OKT3 therapy. However, such treatments may increase susceptibility to infections and the eventual development of lymphomas. The first requirement is for a drug that can be used in combination therapy with well-tolerated doses of cyclosporine to decrease the incidence of rejection episodes in allograft recipients. The second is for a drug that can reverse ongoing rejection without increasing susceptibility to infections or causing other limiting side effects. Now that grafts have better survival rates, other problems are emerging. The problem of chronic rejection and its effects on the ~asculature of grafted organs is becoming recognized as a major limitation of long-term graft survival. A third and major requirement in transplantation is for a drug that can prevent chronic rejection when used over long periods. With these considerations in mind, we and other investigators in the laboratories at Syntex and the University of Wisconsin developed a novel immunosuppressive drug, demonstrated efficacy in experimental animal models of transplantation, and conducted the first human trials in allograft recipients. Our strategy was to define a biochemical pathway that is especially important for proliferation of human T and B lymphocytes and, by inhibiting that pathway, to suppress the proliferation of clones of lymphocytes responding to antigenic stimulation.

IL‐6 Is the Principal Factor Produced by Synovia of Patients with Rheumatoid Arthritis That Induces B‐Lymphocytes to Secrete Immunoglobulins

First, IL-6 is produced by synovial tissue of patients with rheumatoid arthritis (RA) and is the principal mediator produced by that tissue inducing differentiation of B-lymphocytes into antibody-forming cells. The Leu-1+ subset of B-lymphocytes is induced by IL-6 to secrete rheumatoid factor (IgM with anti-Fc gamma specificity). Second, the main cell types producing IL-6 in cells dissociated from RA synovial tissue are mononuclear leukocytes. Connective tissue type cells (synoviocytes) cultured from RA synovial tissue produce IL-6 in response to IL-1 beta, and IL-6 formation is increased by TGF-beta. Glucocorticoids strongly inhibit and PGE2 slightly inhibits IL-1-induced IL-6 mRNA expression in synoviocytes. Production of IL-6 increases when undissociated RA synovial tissue is maintained in culture, thus suggesting release from inhibition by a factor or factors not yet identified. Third, the major known local effect of IL-6 in RA synovial tissue is the augmentation of antibody formation and the major known systemic effect is the induction of the synthesis by the liver of acute-phase proteins, especially C-reactive protein. Levels of circulating C-reactive protein are reported to decrease in RA patients receiving long-acting antirheumatic drugs, which would be consistent with the interpretation that immature monocyte-derived macrophages are major producers of IL-6 in these patients.

Facilitation of specific tolerance induction in adult mice by RS-61443.

RS-61443 is an immunosuppressive agent that facilitates pancreatic islet allograft acceptance in two mouse strain combinations (BALB/c----CBA and C57Bl/6J----BALB/c). A remarkable feature of this agent is its ability to facilitate long-term graft acceptance after a short (30 days) period of treatment; following withdrawal of the agent 40-70% of islet allografts are maintained for an indefinite period. This long-term graft acceptance has been shown to result from specific tolerance induction in the recipient animal. The state of specific tolerance is an active rather than a passive form of tolerance, such as clonal deletion or anergy. Active tolerance induction is cyclosporine-sensitive, although cyclosporine enhances graft acceptance when used in combination therapy with RS-61443, this agent inhibits tolerance development under the influence of RS-61443.

Cytokines Mediating the Proliferation and Differentiation of B‐1 Lymphocytes and Their Role in Ontogeny and Phylogeny

The B-1 (CDS) subset of lymphocytes is expanded in late fetal life, but newborn mice and humans have very low levels of the characteristic product of El cells, IgG in newborns is largely of maternal origin. The low level of IgM formation in the fetus suggests that the conditions and factors required for proliferation of B-1 lymphocytes are present in the fetal omentum and liver, but not those required for their differentiation into antibody-forming cells. If the fetus is infected (and in normal postnatal development), IgM antibodies are formed. The host response to infection provides an additional factor or factors required for differentiation of B-1 cells into antibody-forming cells. Many antibodies produced by B-1 cells have rather broad specificities and low affinities for antigensqd Nevertheless they may constitute an adaptive system of immunity effective against a wide range of organisms of relatively low pathogenicity.6 Indeed, B-1 cells have properties resembling those of B lymphocytes in fish, and a case can be made that this system preceded the conventional B-lymphocyte system in phylogeny. Cross-reactions of antibodies produced by B-1 cells can explain the origin of several heterophile antibodies associated with infections. The broad specificity of antibodies produced by B1 cells includes reactions with autoantigens. Indeed, engagement of surface-membrane Ig receptors on B-1 cells by autoantigens may provide one signal for their proliferation in late fetal life, whereas a cytokine (e.g. IL-3) provides the second obligatory signal. Autoantibodies produced by B-1 cells may play a role in the pathogenesis of autoimmune and other diseases. For all these reasons definition of the range or specificities of antibodies produced by B-1 cells, as well as the factors required for their proliferation and differentiation, are of general interest.

NATURAL CELL-MEDIATED IMMUNITY AND INTERFERON IN MALARIA AND BABESIA INFECTIONS

Publisher Summary This chapter examines natural cell-mediated immunity and interferon in malaria and Babesia infections. The investigation described in the chapter began with an analysis of the susceptibility of different mouse strains to Plasmodium chabaudi (P. chabaudi) and Babesia microti (B. microti). It was found that strain A/He mice are highly susceptible to both infections; in this strain, P. chabaudi is nearly always lethal and the mice do not recover from B. microti infections. Investigations of congenic strains suggested that susceptibility does not correlate with H-2 haplotype. The F-1 offspring of susceptible A and resistant BIO.A mice are resistant. The observations in the study also suggest that sensitized T-cells, reacting with parasite antigens, recruit and activate macrophages and natural killer (NK) cells. These effector cells may, in turn, liberate factors that can inhibit the replication of parasites in circulating erythrocytes, leading to degenerate crisis forms. Effector cells appear to be NK cells and/or macrophages. The chapter discusses the possibility of these cell types being of the same lineage. It also highlights the role that they may play in immunity and immunopathology in these infections.

Prolongation of murine thyroid allografts by interleukin 2 (DAB486)-toxin and RS-61443.

We evaluated the efficacy of interleukin 2 (DAB486)-toxin (IL-2-diphtheria toxin fusion protein; IL-2-toxin) in combination with RS-61443 to prolong murine thyroid allograft survival. B10.BR thyroid allografts were transplanted beneath the renal subcapsule in recipient (C57BL/10 mice and graft survival determined 21 days later. Treatment with IL-2-toxin (25 microg/day for 14 days) was unable to prolong graft survival significantly. RS-61443 treatment (21 days) achieved significant graft prolongation only at doses of 300 mg/kg daily or greater. When both drugs were used in combination (IL-2-toxin, 25 microg/day for 14 days RS-61443 200 mg/kg daily for 21 days), statistically significant (P < 0.0001) graft prolongation was obtained. Our results suggest that IL-2-toxin in combination with subtherapeutic RS-61443 levels significantly prolongs murine thyroid allograft survival. IL-2-toxin and RS-61443, because of their unique and complementary mechanisms, hold promise for more selective immunosuppression.