Based on the tolerogenic properties of IgG carriers and B cell Ag presentation, we developed a retrovirally mediated gene expression approach for treatment of autoimmune conditions. In this study, we show that the IgG-Ag retroviral constructs, expressing myelin basic protein (MBP) or glutamic acid decarboxylase in B cells, can be used for the treatment of murine models for multiple sclerosis and diabetes. Transduction of syngeneic B cells with MBP-IgG leads to the amelioration of ongoing experimental allergic encephalomyelitis induced by the transfer of primed cells from PL×SJL F1 mice with ongoing disease and could be effective even after symptoms appeared. This effect is specific and does not involve bystander suppression because treatment with MBP-IgG does not affect disease induced after immunization with proteolipid protein immunodominant peptide plus MBP. Interestingly, if donor B cells are derived from gld mice (Fas ligand-negative), then tolerance is not induced with a model Ag although there was no evidence for Fas ligand-mediated deletion of target T cells. In spontaneous diabetes in nonobese diabetic mice, we were able to stop the ongoing autoimmune process by treatment at 7–10 wk with glutamic acid decarboxylase-IgG retrovirally transduced B cells, or attenuate it with B cells transduced with an insulin B chain (B9–23) epitope IgG fusion protein. Furthermore, IgG fusion protein gene therapy can also protect primed recipients from Ag-induced anaphylactic shock, and thus does not cause immune deviation. These results demonstrate proof of principle for future efforts to develop this approach in a clinical setting.

A gene therapy model has been designed to induce tolerance to multiple epitopes expressed in-frame on a soluble IgG fusion protein scaffold. Tolerance to the λ repressor cI sequence p1-102 or its immunodominant epitopes (p12-26, p73-88) can be elicited when bone marrow (BM) or LPS blasts are transduced and injected into naive or even primed recipients. To explore the mechanism of tolerance, class II−/− (knockout, KO) BM cells were transduced with p1-102-IgG and transferred to irradiated recipients. These cells failed to induce tolerance to challenge with p1-102 epitopes, whereas transduced +/+ BM cells did. This supports the importance of class II MHC on the tolerogenic APC rather than secretion and representation in tolerogenesis. When BM cells from μMT KO mice were transfected with p12-26-IgG and injected into irradiated mice, these transduced BM cells also failed to induce tolerance to an immunodominant epitope. These results suggest the direct involvement of B cells in tolerance to p1-102 epitopes. IL-10 KO BM cells infected with a p12-26-IgG construct were still tolerogenic. Importantly, anti-CTLA-4 injections reversed tolerance in primed, but not in naive, recipients of transduced LPS blasts. These data emphasize the importance of MHC class II presentation, B cell involvement, and CTLA-4 engagement in induction and/or maintenance of tolerance.

IgG molecules can be highly tolerogenic carriers for associated antigens. Previously, we reported that recipients of bone marrow or lipopolysaccharide-stimulated B-cell blasts, both of which were retrovirally gene-transferred with an immunodominant peptide in-frame with the variable region of a murine IgG heavy chain, were rendered profoundly unresponsive to that epitope. To further investigate whether tolerance to larger molecules can be achieved via this approach and whether the IgG scaffold is important for induction and maintenance of immunological tolerance, we engineered two retroviral constructs encoding the cI repressor (MBAE-1-102 and MBAE-1-102-IgG) for gene transfer. Our results show that recipients of bone marrow or peripheral B cells, transduced with the MBAE-1-102-IgG recombinant, are hyporesponsive to p1-102. In addition, the self-IgG scaffold enhanced the induction and maintenance of such an immune hyporesponsiveness. Thus, our studies demonstrate that in vivo-expressed IgG heavy chain fusion protein can be processed and presented on the appropriate MHC class II, resulting in hyporesponsiveness to that antigen and offering an additional therapeutic approach to autoimmune diseases. Individuals normally develop tolerance to self-constituents during the development of the immune system. Tolerance induction, however, is a lifelong process and also must occur extrathymically (1). Moreover, the maintenance of this unresponsive state requires the persistence of antigen and continued induction in adults (2). The failure to discriminate between immunological self and nonself components leads to the clinical manifestations of autoimmunity. A number of experimental procedures have been proposed to induce tolerance to autoantigens and therefore to prevent and͞or reverse autoimmune diseases (3-5), although tolerance induction and maintenance in mature animals has proven difficult. Hence, novel methods need to be developed to promote tolerance induction in immunocompetent adults and to express the tolerogen in multipotential hematopoietic compartments for persistence of tolerogen and long-term maintenance of tolerance.Peptide fragments of multideterminant antigens can be divided into three main groups: dominant, subdominant, and cryptic epitopes (6-8). An immunodominant epitope is a peptide fragment specifically processed by antigen-presenting cells from a larger, multideterminant antigen and varies individually as a function of its MHC. Such an epitope is capable of binding to the MHC molecule, and this peptide͞MHC complex then is recognized by the T-cell repertoire (6, 7). Subdominant epitopes are the determinants that can stimulate native protein primed cells to proliferate, but less than dominant epitopes or the whole protein (7,8). In contrast, cryptic determinants are rarely revealed during antigen processing and therefore fail to activate T cells when the native antigen is used as immunogen (7,8). However, these hidden determinants might play a role in pathogenic autoimmune responses. One of the...