Transgene expression levels and kinetics determine risk of humoral immune response modeled in factor IX knockout and missense mutant mice

Immune responses leading to antibody-mediated elimination of the transgenic protein are a concern in gene replacement for congenital protein deficiencies, for which hemophilia is an important model. Although most hemophilia B patients have circulating non-functional but immunologically crossreactive factor IX (FIX) protein (CRM+ phenotype), inciting factors for FIX neutralizing antibody (inhibitor) development have been studied in crossreactive material-negative (CRM-) animal models. For this study, determinants of FIX inhibitor development were compared in hemophilia B mice, in which circulating FIX protein is absent (CRM- factor IX knockout (FIXKO) model) or present (CRM+ missense R333Q-hFIX model) modeling multiple potential therapies. The investigations compare for the first time different serotypes of adeno-associated virus (AAV) vectors (AAV2 and AAV1), each at multiple doses, in the setting of two different FIX mutations. The comparisons demonstrate in the FIXKO background (CRM- phenotype) that neither vector serotype nor vector particle number independently determine the inhibitor trigger, which is influenced primarily by the level and kinetics of transgene expression. In the CRM+ missense background, inhibitor development was never stimulated by AAV gene therapy or protein therapy, despite the persistence of lymphocytes capable of responding to FIX with non-inhibitory antibodies. This genotype/phenotype is strongly protective against antibody formation in response to FIX therapy.

A retro-inverso peptide mimic of CD28 encompassing the MYPPPY motif adopts a polyproline type II helix and inhibits encephalitogenic T cells in vitro

Complete activation of T cells requires two signals: an Ag-specific signal delivered via the TCR by the peptide-MHC complex and a second costimulatory signal largely provided by B7:CD28/CTLA-4 interactions. Previous studies have shown that B7 blockade can either ameliorate experimental autoimmune encephalomyelitis by interfering with CD28 signaling or exacerbate the disease by concomitant blockade of CTLA-4 interaction. Therefore, we developed a functional CD28 mimic to selectively block B7:CD28 interactions. The design, synthesis, and structural and functional properties of the CD28 free peptide, the end group-blocked CD28 peptide, and its retro-inverso isomer are shown. The synthetic T cell-costimulatory receptor peptides fold into a polyproline type II helical structure commonly seen in regions of globular proteins involved in transient protein-protein interactions. The binding determinants of CD28 can be transferred onto a short peptide mimic of its ligand-binding region. The CD28 peptide mimics effectively block the expansion of encephalitogenic T cells in vitro suggesting the potential usefulness of the peptides for the treatment of autoimmune disease conditions requiring down-regulation of T cell responses.

Neuroendocrine modulation of chronic relapsing experimental autoimmune encephalomyelitis: a critical role for the hypothalamic-pituitary-adrenal axis

Murine relapsing EAE can be profoundly suppressed by restraint stress (RST) administered beginning prior to neuroantigen immunization. This study determined what hormone pathway(s) mediate disease suppression. Our results showed that nadolol (NAD), a beta2-adrenergic antagonist, did not reverse the RST-induced suppression of EAE. However, administration of either RU486 or aminoglutethimide, which block the action of peripheral glucocorticoids, resulted in a partial reversal of EAE suppression. Administration of exogenous corticosterone mimicked the effects of RST, in terms of suppression of EAE, decrease in lymphoid cell numbers and decrease in Thl cytokine production. Therefore, the HPA axis plays a more profound role in the RST-induced suppression of EAE than does the sympathetic nervous system.

Oral administration of myelin basic protein is superior to myelin in suppressing established relapsing experimental autoimmune encephalomyelitis

Oral administration of a myelin component, myelin basic protein (MBP), induces immunological unresponsiveness to CNS Ags and ameliorates murine relapsing experimental autoimmune encephalomyelitis (REAE). However, a recent clinical trial in which multiple sclerosis patients were treated with repeated doses of oral myelin was unsuccessful in reducing disease exacerbations. Therefore, we directly compared the tolerizing capacity of myelin vs MBP during REAE in B10.PL mice. Oral administration of high doses of myelin, either before disease induction or during REAE, did not provide protection from disease or decrease in vitro T cell responses. In contrast, repeated oral administration of high doses of MBP suppressed established disease and MBP-specific T cell proliferation and cytokine responses. The frequency of IL-2-, IFN-gamma-, and IL-5-secreting MBP-specific T cells declined with MBP feeding, implicating anergy and/or deletion as the mechanism(s) of oral tolerance after high Ag doses. We have previously shown that the dosage and timing of Ag administration are critical parameters in oral tolerance induction. Studies presented here demonstrate that Ag homogeneity is also important, i.e., homogeneous Ag (MBP) is more effective at inducing oral tolerance than heterogeneous Ag (myelin).

Oral tolerance in the treatment of inflammatory autoimmune diseases

Oral tolerance refers to the oral administration of protein antigens, which induces a state of systemic nonresponsiveness specific for the fed antigen. This method of inducing immune non-responsiveness has been applied to the prevention and treatment of experimental animal models of autoimmune disease. Extensive research in this area over the past ten years has led to the conclusion that two mechanisms are operative in the mediation of oral tolerance--active suppression and clonal anergy/deletion. A number of factors have been identified that determine which mechanism of tolerance is operative--antigen dose, antigen form, and the timing of antigen administration. Work from these animal models has recently been extended into human clinical trials of multiple sclerosis, rheumatoid arthritis, diabetes, uveitis, and allergy, with differing degrees of success. In this review, a discussion is provided of the animal model systems where oral tolerance has been applied and the clinical trials where an oral tolerization approach has been attempted. Moreover, recent mechanistic studies are reviewed and a model proposed for the induction of oral tolerance.