Definition of a novel binding site on CD8 cells for a conserved region of the MHC class Ib molecule Qa-1 that regulates IFN-gamma expression

Amelioration of arthritis through mobilization of peptide-specific CD8+ regulatory T cells

Current therapies to treat autoimmune disease focus mainly on downstream targets of autoimmune responses, including effector cells and cytokines. A potentially more effective approach would entail targeting autoreactive T cells that initiate the disease cascade and break self tolerance. The murine MHC class Ib molecule Qa-1b (HLA-E in humans) exhibits limited polymorphisms and binds to 2 dominant self peptides: Hsp60(p216) and Qdm. We found that peptide-induced expansion of tetramer-binding CD8(+) Tregs that recognize Qa-1-Hsp60(p216) but not Qa-1-Qdm strongly inhibited collagen-induced arthritis, an animal model of human rheumatoid arthritis. Perforin-dependent elimination of autoreactive follicular Th (T(FH)) and Th17 cells by CD8(+) Tregs inhibited disease development. Infusion of in vitro-expanded CD8(+) Tregs increased the efficacy of methotrexate treatment and halted disease progression after clinical onset, suggesting an alternative approach to this first-line treatment. Moreover, infusion of small numbers of Qa-1-Hsp60(p216)-specific CD8(+) Tregs resulted in robust inhibition of autoimmune arthritis, confirming the inhibitory effects of Hsp60(p216) peptide immunization. These results suggest that strategies designed to expand Qa-1-restricted (HLA-E-restricted), peptide-specific CD8(+) Tregs represent a promising therapeutic approach to autoimmune disorders.

Regulation of CD8+ regulatory T cells: Interruption of the NKG2A-Qa-1 interaction allows robust suppressive activity and resolution of autoimmune disease

Regulation of autoreactive CD4 T cells is essential to maintain self-tolerance and prevent autoimmune disease. Although CD8 T regulatory (Treg) cells that recognize self-peptides restricted by Qa-1 (HLA-E in humans) inhibit autoreactive CD4 cells and attenuate experimental autoimmune encephalomyelitis (EAE), the mechanism of this interaction is unclear. We generated Qa-1 mutant knock-in mice that impair Qa-1 binding to the T cell receptor (TCR) and CD94/NKG2A receptors. Analysis of these mice showed that TCR-dependent recognition of Qa-1-peptide complexes on target CD4 cells is essential for suppression by CD8 Treg cells. Further analysis revealed that genetic disruption of the Qa-1-CD94/NKG2A interaction unleashes robust CD8 Treg cell activity that completely abolishes development of EAE.

Induction of mucosal tolerance in SLE: a sniff or a sip away from ameliorating lupus?

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by aberrant immune responses against intracellularly derived self antigens. Treatment for SLE relies on the use of aggressive immunosuppressants and steroids that are nonspecific and can cause serious adverse effects. The observation that a systemic immune tolerance to self antigens or generation of regulatory T cells may follow mucosal (nasal or oral) exposure to self proteins or monoclonal antibody against CD3 respectively suggests that induction of mucosal tolerance offers the basis of a side effect-free therapy that could re-establish the ability to distinguish self from non-self and restore peripheral tolerance in individuals susceptible to developing autoimmune diseases. Here I review studies on mucosal tolerance in autoimmune diseases and discuss the therapeutic potential of inducing tolerance for the treatment of SLE.

Implication for the CD94/NKG2A-Qa-1 system in the generation and function of ocular-induced splenic CD8+ regulatory T cells

The injection of antigen into the anterior chamber (AC) induces the production of antigen-specific splenic CD8+ regulatory T cells (Tregs) /suppressor T cells that perform the local suppression of delayed-type hypersensitivity (DTH) responses. Because CD94/NKG2A-Qa-1-dependent interactions have been implicated in CD8+ Treg-mediated immune suppression and DBA/2J mice are deficient in CD94/NKG2R, we have utilized these mice to test the hypothesis that the CD94/NKG2A-Qa-1 system is essential to the induction and immunosuppressive function of CD8+ Tregs in anterior chamber-associated immune deviation (ACAID). We show that: (i) neither ACAID-mediated suppression of DTH to ovalbumin nor splenic Tregs/suppressor T cells was induced in DBA/2J mice that received an injection of antigen into the AC; (ii) splenic CD8+ Tregs from ACAID-induced DBA/2NCr mice suppressed the initiation of DTH when transferred to DBA/2J mice; (iii) following injection of antigen into the AC, intravenous administration of splenocytes or Peripheral Blood Mononuclear Cells (PBMC) isolated from DBA/2NCr but not from DBA/2J mice transferred suppression of DTH to DBA/2NCr mice; (iv) antibodies to CD94/NKG2A reduced the ACAID CD8+ T cell-mediated suppression of DTH and (v) The deficiency of such immune regulation in DBA/2J mice also correlated with a decreased number of Qa-1(b+) B cells, F4/80+ cells, a deficient number of CD94/NKG2AR and Qa-1 tetramer binding by CD8+ T cells. These results demonstrate that defective ACAID in DBA/2J mice involves multiple regulatory lesions resulting in a lack of induction of a CD8+ Treg response and possibly defective CD94/NKG2A-dependent suppression of peripheral cell-mediated immunity.

The immunoregulatory effects of Qa-1

The immune system is not only well equipped to control infections but also tightly controlled to prevent autoimmune disease. Despite the negative selection of T-cell clones in the thymus, mature T cells capable of recognizing self-antigens are present in every individual. Several types of specialized regulatory cells maintain homeostasis and prevent expansion of autoreactive T cells. In this issue of Immunological Reviews, the role of CD4+ regulatory T cells is extensively discussed. Suppression of T-cell responses by CD8+ T cells has received less attention. Here, we review research on Qa-1-restricted CD8+ regulatory T cells. We focus on the role of this class Ib major histocompatibility complex (MHC) molecule in both CD8+ regulatory T-cell activity and protection of activated T cells.

Suppression of autoimmune disease after vaccination with autoreactive T cells that express Qa-1 peptide complexes

The ability of autoreactive T cells to provoke autoimmune disease is well documented. The finding that immunization with attenuated autoreactive T cells (T cell vaccination, or TCV) can induce T cell-dependent inhibition of autoimmune responses has opened the possibility that regulatory T cells may be harnessed to inhibit autoimmune disease. Progress in the clinical application of TCV, however, has been slow, in part because the underlying mechanism has remained clouded in uncertainty. We have investigated the molecular basis of TCV-induced disease resistance in two murine models of autoimmunity: herpes simplex virus-1 (KOS strain)-induced herpes stromal keratitis and murine autoimmune diabetes in non-obese diabetic (NOD) mice. We find that the therapeutic effects of TCV depend on activation of suppressive CD8 cells that specifically recognize Qa-1-bound peptides expressed by autoreactive CD4 cells. We clarify the molecular interaction between Qa-1 and self peptides that generates biologically active ligands capable of both inducing suppressive CD8 cells and targeting them to autoreactive CD4 cells. These studies suggest that vaccination with peptide-pulsed cells bearing the human equivalent of murine Qa-1 (HLA-E) may represent a convenient and effective clinical approach to cellular therapy of autoimmune disease.

Regulatory CD8+ T cells fine-tune the myelin basic protein-reactive T cell receptor V beta repertoire during experimental autoimmune encephalomyelitis

A significant number of self-reactive T cell clones escape thymic negative selection and are released into the periphery, where some are potentially pathogenic. The clonal expansion of self-reactive T cells is known to be limited during initial antigen encounter by apoptotic or anergic mechanisms, regulatory CD4+ T cells, and cytokines. Here we report that superimposed on these mechanisms, during the evolution of autoimmunity in experimental autoimmune encephalomyelitis (EAE), CD8+ T cells are induced, which fine-tune the peripheral self-reactive T cell receptor (TCR) repertoire. We assayed the myelin basic protein-reactive TCR repertoire in naive, EAE-recovered mice as well as EAE-recovered mice depleted of CD8+ T cells by TCRV beta surface expression, complementarity-determining region 3 length distribution, and complementarity-determining region 3 sequencing analysis. In EAE-recovered mice, certain myelin basic protein-reactive CD4+V beta 8.2+ clones are significantly decreased and this decrease is not observed if CD8+ T cells were depleted from these mice. The clones that persist in CD8+ T cell-intact mice are highly diverse in contrast to the clones expanded in CD8+ T cell-depleted mice, which are dominated by the significant outgrowth of a few clones. Importantly, the T cell clones that expand in the absence of CD8+ T cell control are enriched in potentially pathogenic self-reactive T cell clones capable of inducing EAE in vivo.

The binding of thymus leukemia (TL) antigen tetramers to normal intestinal intraepithelial lymphocytes and thymocytes

Thymus leukemia (TL) Ags belong to the family of nonclassical MHC class I Ags and can be recognized by both TCRalphabeta and TCRgammadelta CTL with TL, but not H-2 restriction. We previously reported that the CTL epitope is TAP independent, but the antigenic molecule(s) presented by TL has yet to be determined. In the present study, TL tetramers were prepared with T3(b)-TL and murine beta(2)-microglobulin, not including antigenic peptides, and binding specificity was studied. CTL clones against TL Ags were stained with the T3(b)-TL tetramer, and the binding shown to be CD3 and CD8 dependent. Normal lymphocytes from various origins were also studied. Surprisingly, most CD8(+) intraepithelial lymphocytes derived from the small intestines (iIEL), as well as CD8(+) and CD4(+)CD8(+) thymocytes, were stained, while only very minor populations of CD8(+) cells derived from other peripheral lymphoid tissues, such as spleen and lymph nodes, were positive. The binding of T3(b)-TL tetramers to CD8(+) iIEL and thymocytes was CD8 dependent, but CD3 independent, in contrast to that to TL-restricted CTL. These results altogether showed that TL-restricted CTL can be monitored by CD3-dependent binding of T3(b)-TL tetramers. In addition, CD3-independent T3(b)-TL tetramer binding to iIEL and thymocytes may imply that TL expressed on intestinal epithelium and cortical thymocytes has a physiological function interacting with these tetramer(+)CD8(+) T lymphocytes.