Pre-emptive targeting of the epitope spreading cascade with genetically modified regulatory T cells during autoimmune demyelinating disease

Regulatory T-cell vaccination independent of auto-antigen

To date, efforts to treat autoimmune diseases have primarily focused on the disease symptoms rather than on the cause of the disease. In large part, this is attributed to not knowing the responsible auto-antigens (auto-Ags) for driving the self-reactivity coupled with the poor success of treating autoimmune diseases using oral tolerance methods. Nonetheless, if tolerogenic approaches or methods that stimulate regulatory T (T_reg) cells can be devised, these could subdue autoimmune diseases. To forward such efforts, our approach with colonization factor antigen I (CFA/I) fimbriae is to establish bystander immunity to ultimately drive the development of auto-Ag-specific T_reg cells. Using an attenuated Salmonella vaccine expressing CFA/I fimbriae, fimbriae-specific T_reg cells were induced without compromising the vaccine's capacity to protect against travelers' diarrhea or salmonellosis. By adapting the vaccine's anti-inflammatory properties, it was found that it could also dampen experimental inflammatory diseases resembling multiple sclerosis (MS) and rheumatoid arthritis. Because of this bystander effect, disease-specific T_reg cells are eventually induced to resolve disease. Interestingly, this same vaccine could elicit the required T_reg cell subset for each disease. For MS-like disease, conventional CD25⁺ T_reg cells are stimulated, but for arthritis CD39⁺ T_reg cells are induced instead. This review article will examine the potential of treating autoimmune diseases without having previous knowledge of the auto-Ag using an innocuous antigen to stimulate T_reg cells via the production of transforming growth factor-β and interleukin-10.

Th17 and Th1 responses directed against the immunizing epitope, as opposed to secondary epitopes, dominate the autoimmune repertoire during relapses of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease with similarities to multiple sclerosis (MS). It has been suggested that relapses of EAE and MS may be associated with, and even driven by, T cells specific for novel epitopes that are primed during the course of tissue destruction in the target organ or in secondary lymphoid tissues. We show, however, that IFNgamma and IL-17 responses against the immunizing epitope remain dominant through out the course of multiphasic EAE. Furthermore, induction of tolerance against a putative secondary epitope did not prevent clinical relapses.

Association between parasite infection and immune responses in multiple sclerosis

OBJECTIVE

To assess whether parasite infection is correlated with a reduced number of exacerbations and altered immune reactivity in multiple sclerosis (MS).

METHODS

A prospective, double-cohort study was performed to assess the clinical course and radiological findings in 12 MS patients presenting associated eosinophilia. All patients presented parasitic infections with positive stool specimens. In all parasite-infected MS patients, the eosinophilia was not present during the 2 previous years. Eosinophil counts were monitored at 3- to 6-month intervals. When counts became elevated, patients were enrolled in the study. Interleukin (IL)-4, IL-10, IL-12, transforming growth factor (TGF)-beta, and interferon-gamma production by myelin basic protein-specific peripheral blood mononuclear cells were studied using enzyme-linked immunospot (ELISPOT). FoxP3 and Smad7 expression were studied by reverse-transcriptase polymerase chain reaction.

RESULTS

During a 4.6-year follow-up period, parasite-infected MS patients showed a significantly lower number of exacerbations, minimal variation in disability scores, as well as fewer magnetic resonance imaging changes when compared with uninfected MS patients. Furthermore, myelin basic protein-specific responses in peripheral blood showed a significant increase in IL-10 and TGF-beta and a decrease in IL-12 and interferon-gamma-secreting cells in infected MS patients compared with noninfected patients. Myelin basic protein-specific T cells cloned from infected subjects were characterized by the absence of IL-2 and IL-4 production, but high IL-10 and/or TGF-beta secretion, showing a cytokine profile similar to the T-cell subsets Tr1 and Th3. Moreover, cloning frequency of CD4+CD25+ FoxP3+ T cells was substantially increased in infected patients compared with uninfected MS subjects. Finally, Smad7 messenger RNA was not detected in T cells from infected MS patients secreting TGF-beta.

INTERPRETATION

Increased production of IL-10 and TGF-beta, together with induction of CD25+CD4+ FoxP3+ T cells, suggests that regulatory T cells induced during parasite infections can alter the course of MS.

Cell-based gene therapy experiments in murine experimental autoimmune encephalomyelitis

With the ultimate goal of developing a novel treatment for multiple sclerosis (MS), we have developed a cell-based gene therapy protocol for the treatment of murine experimental autoimmune encephalomyelitis (EAE), a powerful animal model for MS. We have determined that transduced fibroblasts secreting encephalogenic epitopes, when injected into mice with EAE, cause a striking abrogation of disease. Both myelin basic protein (MBP) and proteolipid protein mini-gene constructs expressed in syngeneic fibroblast cells were capable of ameliorating ongoing EAE induced by MBP protein. These experiments are crucial since they suggest that not all encephalogenic epitopes need be secreted for the control of disease. We also demonstrate the success of this protocol when transduced syngeneic, and most importantly, allogeneic cells are sequestered within an implantable chamber. Furthermore, we find that through modifying antigen expression by changing the signal sequence of the mini-gene construct, we were able to significantly reduce the dose of cells required for treatment. These improvements to the mini-gene delivery system are critical for the eventual translation of our protocol to the clinic.

Elimination of an immunodominant CD4+ T cell epitope in human IFN-beta does not result in an in vivo response directed at the subdominant epitope

The BALB/cByJ mouse strain displays an immunodominant T cell response directed at the same CD4(+) T cell epitope peptide region in human IFN-beta, as detected in a human population-based assay. BALB/cByJ mice also recognize a second region of the protein with a lesser magnitude proliferative response. Critical residue testing of the immunodominant peptide showed that both BALB/cByJ mice and the human population response were dependent on an isoleucine residue at position 129. A variant IFN-beta molecule was constructed containing the single amino acid modification, I129V, in the immunodominant epitope. The variant displayed 100% of control antiproliferation activity. Mice immunized with unmodified IFN-beta responded weakly in vitro to the I129V variant. However, BALB/cByJ mice immunized with the I129V variant were unable to respond to either the I129V variant or the unmodified IFN-beta molecule by either T cell proliferation or Ag-specific IgG1 Ab production. This demonstrates that a single amino acid change in an immunodominant epitope can eliminate an immune response to an otherwise intact therapeutic protein. The elimination of the immunodominant epitope response also eliminated the response to the subdominant epitope in the protein. Modifying functionally immunodominant T cell epitopes within proteins may obviate the need for additional subdominant epitope modifications.

Human population-based identification of CD4(+) T-cell peptide epitope determinants

A human cell-based method to identify functional CD4(+) T-cell epitopes in any protein has been developed. Proteins are tested as synthetic 15-mer peptides offset by three amino acids. Percent responses within a large donor population are tabulated for each peptide in the set. Peptide epitope regions are designated by difference in response frequency from the overall background response rate for the compiled dataset. Epitope peptide responses are reproducible, with a median coefficient of variance of 21% when tested on multiple random-donor sets. The overall average response rate within the dataset increases with increasing putative human population antigenic exposure to a given protein. The background rate was high for HPV16 E6, and was low for human-derived cytokine proteins. The assay identified recall epitope regions within the donor population for the protein staphylokinase. For an industrial protease with minimal presumed population exposure, immunodominant epitope peptides were identified that were found to bind promiscuously to many HLA class II molecules in vitro. The peptide epitope regions identified in presumably unexposed donors represent a subset of the total recall epitopes. Finally, as a negative control, the assay found no peptide epitope regions in human beta2-microglobulin. This method identifies functional CD4(+) T-cell epitopes in any protein without pre-selection for HLA class II, suggests whether a donor population is pre-exposed to a protein of interest, and does not require sensitized donors for in vitro testing.

Epitope spreading is not required for relapses in experimental autoimmune encephalomyelitis

The sequential emergence of specific T lymphocyte-mediated immune reactivity directed against multiple distinct myelin epitopes (epitope spreading) has been associated with clinical relapses in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Based on this association, an appealing and plausible model for immune-mediated progression of the advancing clinical course in MS and EAE has been proposed in which epitope spreading is the cause of clinical relapses in T cell-mediated CNS inflammatory diseases. However, the observed association between epitope spreading and disease progression is not universal, and absolute requirements for epitope spreading in progressive EAE have not been tested in the absence of multiple T cell specificities, because most prior studies have been conducted in immunocompetent mouse strains that possessed broad TCR repertoires. Consequently, the precise nature of a causal relationship between epitope spreading and disease progression remains uncertain. To determine whether relapsing or progressive EAE can occur in the absence of epitope spreading, we evaluated the course of disease in mice which possessed only a single myelin-specific TCR. These mice (transgenic/SCID +/+) exhibited a progressive and sometimes remitting/relapsing disease course in the absence of immune reactivity to multiple, spreading myelin epitopes. The results provide direct experimental evidence relevant to discussions on the mechanisms of disease progression in MS and EAE.

Gene therapy in experimental autoimmune encephalomyelitis

Gene therapy traditionally has been associated with "gene replacement." where exogenous recombinant DNA is introduced ex vivo into somatic cells that are then introduced back into the patient as a way to correct an inherited genetic defect. However, several novel gene therapy strategies for treating autoimmune diseases recently have emerged. Strategies involving the use of several types of DNA vaccines, the application of various viral vectors, and the use of diverse cellular vectors have shown promise in inhibiting autoimmune-mediated inflammation and repairing tissue damaged as a result of autoimmune attack. In the current review, we examine and discuss the development and proposed use of emerging gene therapy strategies for the treatment of autoimmune disease with specific emphasis on experimental autoimmune encephalomyelitis (EAE), an animal model widely used in multiple sclerosis (MS) research.