Application of IgG-derived natural Treg epitopes (IgG Tregitopes) to antigen-specific tolerance induction in a murine model of type 1 diabetes

HLA class II-restricted regulatory T cell (Treg) epitopes in IgG (also called "Tregitopes") have been reported to suppress immune responses to coadministered antigens by stimulating the expansion of natural Tregs (nTregs). Here we evaluate their impact on human immune responses to islet cell antigens ex vivo and on the modulation of type 1 diabetes (T1D) in a murine model in vivo. Co-administration of Tregitopes and T1D antigens delayed development of hyperglycemia and reduced the incidence of diabetes in NOD mice. Suppression of diabetes could be observed even following onset of disease. To measure the impact of Tregitope treatment on T cell responses, we evaluated the effect of Tregitope treatment in DO11.10 mice. Upregulation of FoxP3 in KJ1-26-stained OVA-specific CD4(+) T cells was observed following treatment of DO11.10 mice with Tregitopes, along with reductions in anti-OVA Ig and T effector responses. In ex vivo studies of human T cells, peripheral blood mononuclear cells' (PBMC) responses to GAD65 epitopes in the presence and absence of Tregitope were variable. Suppression of immune responses to GAD65 epitopes ex vivo by Tregitope appeared to be more effective in assays using PBMC from a newly diagnosed diabetic subject than for other more established diabetic subjects, and correlation of the degree of suppression with predicted HLA restriction of the Tregitopes was confirmed. Implementation of these defined regulatory T cell epitopes for therapy of T1D and other autoimmune diseases may lead to a paradigm shift in disease management.

Regulating immune responses to biologics: Epitope prediction and applications (58.23)

Immune responses directed against protein therapeutics can directly impact drug safety and efficacy. The ability to predict and reduce immunogenicity of a potential protein therapeutic presents tremendous benefits at every stage of drug development. While many factors contribute to protein immunogenicity, T cell-dependent responses play a critical role. We report two approaches to mitigate therapeutic protein immunogenicity, one involving epitope modification and the other inducing antigen-specific tolerance induction. Rational epitope modification applied to either Factor VIII or botulinum toxin demonstrates reduced immunogenicity when following a systematic process of in silico epitope mapping, in vitro and in vivo validation of computational predictions, iterative in silico modification of immunogenic epitopes and experimental validation of carefully selected modified sequences. Tolerance induction involves co-delivery, chemical or recombinant linkage of regulatory T cell epitopes (Tregitopes) to therapeutic proteins. We have demonstrated that Tregitope incorporation leads to lower immune responses against target epitopes identified in insulin, Factor VIII and botulinum toxin. The ability to analyze, predict, and modify the immunogenicity of a protein expands the available strategies for mitigating therapeutic protein immunogenicity, enables quality by design for drugs in development and improvement of licensed biologics to create biobetters.

Tregitope mechanism of action and applications for tolerance induction. (116.8)

Tregitopes are T cell epitopes naturally located in immunoglobulins that bind to multiple MHC Class II alleles and induce regulatory T cell (Treg) responses. Harnessing tolerogenic effects of Tregitopes provides a novel tool to suppress unwanted immune responses and maintain antigen-specific tolerance, thus changing treatment paradigms in autoimmunity. We have now demonstrated that APCs present Tregitopes to natural (n) Treg, engage feedback mechanisms promoting a tolerogenic APC phenotype, induce Treg expansion, and modulate antigen-specific effector T cell responses. Proportions of APC expressing MHC II, CD80, and CD86 are suppressed, consistent with reported effects of IVIG (Bayry et al. Blood, 2003, 101:758) and of the IgG-derived peptide hCDR1 (Sela et al. Immunology, 2009, 128:395). Moreover, we observed significant increases in proportions of IL-10-producing CD4+CD25+ FoxP3-expressing nTreg in the presence of Tregitopes. These studies are an exciting first step towards understanding the basic mechanism of Tregitope tolerance induction that we propose to be as follows: 1) APC present Tregitopes to nTreg, 2) nTreg are activated to proliferate and produce IL-10, 3) nTreg provide tolerogenic feedback signals to APC, modulating the APC phenotype, and 4) nTreg and tolerogenic APC together suppress antigen-specific T cell responses. These data suggest a role for Tregitopes in the mechanism of action for IVIG, and provide insight critical for future therapeutic applications.

Tregitope applications to tolerance induction in autoimmune diseases. (116.10)

Modulation of T cell responses may contribute to the design of new approaches for the treatment of autoimmune and inflammatory diseases. IVIG is one example of a therapy with this effect, and evidence is accumulating that Tregitopes (De Groot et al. Blood, 2008, 112:3303; natural T regulatory epitopes derived from IgG) provide beneficial immunomodulatory effects that parallel the effects of IVIG. In this presentation, we will provide evidence that Tregitope sequences derived from human IgG can reproduce immunomodulatory effects of IVIG in vitro and in vivo. In vitro, Tregitopes activate CD4+CD25+FoxP3+ natural regulatory T cells (nTreg). In vitro and in vivo, Tregitopes cause Tregs to produce IL-10, and to expand, and iTreg are induced. Induction and functions of nTregs have been examined in model systems such as D011.10 TCR transgenic mice, transplant of BM12 to C57BL/6, AAV-mediated gene transfer and EAE. Together, the data show that effector T cells, Th17, and Th9 cells are modified in the presence of Tregitopes. In OVA-induced allergic airway disease, we observed significant and reproducible expansion of Tregs in conjunction with decreased airway reactivity that was comparable to, if not greater than IVIG. We will provide additional unpublished evidence demonstrating the antigen specificity of tolerance induction using Tregitopes in conjunction with target antigens, and discuss the relevance of Tregitopes to the treatment of human immune-mediated diseases.

Coupling sensitive in vitro and in silico techniques to assess cross-reactive CD4(+) T cells against the swine-origin H1N1 influenza virus

The outbreak of the novel swine-origin H1N1 influenza in the spring of 2009 took epidemiologists, immunologists, and vaccinologists by surprise and galvanized a massive worldwide effort to produce millions of vaccine doses to protect against this single virus strain. Of particular concern was the apparent lack of pre-existing antibody capable of eliciting cross-protective immunity against this novel virus, which fueled fears this strain would trigger a particularly far-reaching and lethal pandemic. Given that disease caused by the swine-origin virus was far less severe than expected, we hypothesized cellular immunity to cross-conserved T cell epitopes might have played a significant role in protecting against the pandemic H1N1 in the absence of cross-reactive humoral immunity. In a published study, we used an immunoinformatics approach to predict a number of CD4(+) T cell epitopes are conserved between the 2008-2009 seasonal H1N1 vaccine strain and pandemic H1N1 (A/California/04/2009) hemagglutinin proteins. Here, we provide results from biological studies using PBMCs from human donors not exposed to the pandemic virus to demonstrate that pre-existing CD4(+) T cells can elicit cross-reactive effector responses against the pandemic H1N1 virus. As well, we show our computational tools were 80-90% accurate in predicting CD4(+) T cell epitopes and their HLA-DRB1-dependent response profiles in donors that were chosen at random for HLA haplotype. Combined, these results confirm the power of coupling immunoinformatics to define broadly reactive CD4(+) T cell epitopes with highly sensitive in vitro biological assays to verify these in silico predictions as a means to understand human cellular immunity, including cross-protective responses, and to define CD4(+) T cell epitopes for potential vaccination efforts against future influenza viruses and other pathogens.