Functional divergence of antigen-specific T-lymphocyte responses in syngeneic graft-versus-host disease

Anti-IL-23p19 therapy inhibits the adoptive transfer of syngeneic graft-versus-host disease

Syngeneic graft-versus-host disease (SGVHD), a chronic inflammatory disease, develops following irradiation, syngeneic bone marrow transplantation (BMT) and treatment with the immunosuppressive agent cyclosporine A (CsA). We have shown that TH1 and TH17 cytokine responses are increased during the development of SGVHD. The current study was designed to further investigate the involvement of TH17 immunity in SGVHD-associated colitis. IL-23 is a TH17 cytokine responsible for maintaining the effector functions of TH17 cells. The administration of anti-mouse IL-23p19 was shown to significantly reduce the clinical symptoms of primary and secondary SGVHD-associated colitis resulting in a significant reduction in both TH1 and TH17 associated cytokine expression. These results demonstrate that the TH17-associated cytokine, IL-23, may prove to be a beneficial therapeutic target in the treatment of chronic colon inflammation.

Equal opportunity targeting in chronic GVHD

In this issue of Blood, studies by Rangarajan et al comprehensively analyzing the clonotypic T-cell response provide evidence that the effector T cells that mediate chronic GVHD may have a unique specificity that includes recognition of self.1

Reconstitution of self-tolerance after hematopoietic stem cell transplantation

Graft-versus-host disease (GVHD) is a major complication of allogeneic bone marrow or hematopoietic stem cell transplantation. GVHD is thought to be primarily due to the response of mature T cells transferred along with the bone marrow graft to foreign histocompatibility antigens expressed on host tissues. Recent studies, however, have challenged this paradigm set forth in the 1960s and have suggested that self-MHC class II antigens can be recognized in GVHD. Many questions still remain unanswered particularly in regard to the role of immune reconstitution, the ability to recognize and discriminate self and the re-establishment of self-tolerance. In fact, the failure to re-establish tolerance to self can lead to systemic autoimmunity that may exacerbate or even mimic GVHD. The present review summarizes our studies in autologous GVHD characterizing the underlying immune mechanisms and their potential impact in allogeneic hematopoietic stem cell transplantation.

Modulation of graft-versus-host disease: role of regulatory T lymphocytes

Graft-versus-host (GVH) disease (GVHD) continues to be a major life-threatening complication after allogeneic bone marrow transplantation. Considerable progress has been made elucidating the pathophysiology of acute GVHD. Mature donor T cells transferred along with the marrow graft directly recognize antigenic differences on antigen-presenting cells of the host. Once activated, donor antihost-specific T cells can mediate tissue destruction. Interestingly, the failure to clonally delete autoreactive T cells in the thymus can also lead to an autoimmune syndrome mimicking the pathology of GVHD. Negative selection in the thymus may be compromised either by damage to the thymic epithelium (because of a direct attack by donor antihost alloreactive T cells) or by the use of immunosuppressive drugs that inhibit clonal deletion. An important component underlying GVHD mediated by either alloreactive or autoreactive T cells is the absence of a competent peripheral regulatory system. Studies in animal model systems clearly indicate that regulatory T cells play a vital role in down-regulating GVHD and are critically important for the establishment of active dominant tolerance to both allo- and self-major histocompatibility complex antigens. Although multiple populations of cells appear to participate in this process, CD4(+) regulatory T cells that innately express CD25(+) appear to orchestrate the regulatory control of the immune response. Evidence for regulatory T cells in clinical bone marrow transplantation, however, remains rudimentary. The recent identification that CD4(+)CD25(+) regulatory T cells preferentially express the Foxp3 nuclear transcription factor and the development of molecular reagents to isolate antigen-specific T cells have provided unique opportunities to explore immunoregulatory mechanisms after clinical marrow transplantation. Recent studies in recipients of clinical bone marrow transplantation suggest that antigen-specific CD4(+)CD25(+)Foxp3(+) T cells play a vital role in the regulatory control of GVH reactions mediated by both alloreactive and autoreactive lymphocytes. These regulatory T cells also appear to facilitate the establishment of donor antihost and donor antidonor (self) tolerance.

Immune Tolerance to Self-Major Histocompatability Complex Class II Antigens after Bone Marrow Transplantation: Role of Regulatory T Cells

The immune system undergoes rapid reconstitution after autologous or syngeneic bone marrow transplantation with the re-establishment of tolerance to self-antigens. Administration of drugs such as cyclosporine that inhibit thymic-dependent clonal deletion disrupts the reconstitution of the immune system. In the absence of a peripheral regulatory T cells eliminated by the preparative regimen, systemic autoimmunity with pathology similar to graft-versus-host disease often develops. Moreover, the resolution of autoaggression is dependent on the reconstitution of CD4+ regulatory T cells. This study examined the specificity and function of this regulatory population assessed ex vivo that plays a critical role in down-regulating the autoreactive T lymphocyte response in cyclosporine-induced syngeneic graft-versus-host disease. The results suggest that both the antigen-specific regulatory and pathogenic effector T cells recognize a common peptide antigen framework (CLIP, a peptide derived from the invariant chain) presented by major histocompatibility complex class II molecules. Analysis of the CD4+ T-cell compartment revealed two subsets of CLIP-reactive T cells that differentially require the N- and C-terminal flanking domain of this peptide. Regulatory function is associated with the cells that require the C-terminal flanking domain. This population expresses the Foxp3 nuclear transcription factor and plays a critical role in re-establishing tolerance to self-major histocompatibility complex class II antigens. In addition to suppressing the production of type 1 cytokines, these regulatory T cells can direct the apoptotic death of the pathogenic autoreactive lymphocytes. This study also suggests that the development of functional regulatory activity is an active response initiated by the presence of autoreactive lymphocytes that can present the target antigen (major histocompatibility complex class II CLIP) to the regulatory T cells. Moreover, this process can be mimicked by peptide antigen in the absence of the pathogenic effector lymphocytes leading to the development of functional regulatory T-cell activity.

Functionally divergent T lymphocyte responses induced by modification of a self-peptide from a tumor-associated antigen

The N- and C-terminal flanking domains of the invariant chain peptide, CLIP, have remarkable immunological properties. Addition of these flanking domains to a foreign peptide antigen increases its immunologic potency. The present studies evaluated whether altering a peptide ligand from the tumor-associated antigen c-neu with the flanking domains of CLIP could modify the systemic immune response. The results indicate that the immunogenicity of an MHC class II restricted peptide (NEU) derived from c-neu was significantly altered by addition of the flanking domains from CLIP. Interestingly, selective modification of the peptide with either the N- or the C-terminal flanking domains resulted in functionally divergent systemic immune responses. Immunization of normal F344 rats with the NEU peptide modified with the N-terminal domain of CLIP (N-NEU) resulted in an immune response primarily consisting of type 1 (IL-2, IFNgamma) cytokine producing T cells. On the other hand, type 2 (IL-4) cytokine responses were largely predominant following immunization with the self-peptide modified with the C-terminal flanking domain (NEU-C). The functionally divergent responses elicited by the modified self-peptides were accompanied by significant changes in the expression of the CD28/CTLA4/B7 family of co-stimulatory molecules. Immunization with the N-NEU peptide led to enhanced expression of CD28 in the antigen-specific, CD4+ T cell compartment while expression of B7.1 was dramatically reduced in antigen-specific CD8+ T cells. Comparatively, expression of CTLA4 was down-regulated in the antigen-specific CD4+ T cell compartment following immunization with NEU-C peptide. The N-NEU peptide also had a direct effect on dendritic cells leading to the up-regulation of B7.1 expression. Taken together, functionally divergent systemic immune responses can be elicited by strategically altering a self-peptide ligand with the N- and C-terminal flanking domains of CLIP. Moreover, changes in expression of co-stimulatory molecules that are required for T cell activation and T cell-T cell communication may account for the polarization of the immune response elicited by the chimeric peptides.

Antigen-specific T-lymphocyte responses in acute and chronic syngeneic graft-versus-host disease

Administration of cyclosporine (CyA) following autologous bone marrow transplantation elicits a T-lymphocyte autoaggression syndrome with remarkable similarity to acute and chronic graft-versus-host disease (GVHD). This syndrome termed syngeneic (S) GVHD is mediated by a restricted repertoire of autoreactive T cells that promiscuously recognize major histocompatibility complex (MHC) class II determinants in association with a peptide from the invariant chain (CLIP). The present studies evaluated and compared antigen-specific autoreactive T cells during acute and chronic SGVHD isolated ex vivo with a soluble MHC class II-immunoglobulin (sMHC class II-Ig) molecular construct. Two major subsets were detected that had overlapping specificity recognizing the MHC class II binding domain of CLIP but were differentially dependent on the N- and C-terminal flanking domains of this peptide. Both subsets were detected in acute and chronic SGVHD. Interestingly, the cytokine profiles of the CLIP-reactive T cells closely correlated with the onset and progression of disease. Levels of type 1 cytokines, particularly IFN-gamma mRNA production assessed by quantitative polymerase chain reaction (PCR), were dominant during acute SGVHD, whereas chronic SGVHD was associated with type 2 cytokine mRNA production. Although there was a dramatic polarization with respect to cytokine production, only subtle changes in antigen specificity were detected. Of additional interest, autoreactive T cells producing IL-10 mRNA were detected in both acute and chronic SGVHD, suggesting that this cytokine may play an important but perhaps paradoxical role in both the onset and progression of this experimental autoaggression syndrome.