Differences in MHC-class I presented minor histocompatibility antigens extracted from normal and graft-versus-host disease (GVHD) mice

Autophagy differentially regulates tissue tolerance of distinct target organs in graft-versus-host disease models

Tissue-intrinsic mechanisms that regulate severity of systemic pathogenic immune-mediated diseases, such as acute graft-versus-host disease (GVHD), remain poorly understood. Following allogeneic hematopoietic stem cell transplantation, autophagy, a cellular stress protective response, is induced in host nonhematopoietic cells. To systematically address the role of autophagy in various host nonhematopoietic tissues, both specific classical target organs of acute GVHD (intestines, liver, and skin) and organs conventionally not known to be targets of GVHD (kidneys and heart), we generated mice with organ-specific knockout of autophagy related 5 (ATG5) to specifically and exclusively inhibit autophagy in the specific organs. When compared with wild-type recipients, animals that lacked ATG5 in the gastrointestinal tract or liver showed significantly greater tissue injury and mortality, while autophagy deficiency in the skin, kidneys, or heart did not affect mortality. Treatment with the systemic autophagy inducer sirolimus only partially mitigated GVHD mortality in intestine-specific autophagy-deficient hosts. Deficiency of autophagy increased MHC class I on the target intestinal epithelial cells, resulting in greater susceptibility to damage by alloreactive T cells. Thus, autophagy is a critical cell-intrinsic protective response that promotes tissue tolerance and regulates GVHD severity.

Inter-strain tissue-infiltrating T cell responses to minor histocompatibility antigens involved in graft-versus-host disease as determined by Vbeta spectratype analysis

Lethal graft-vs-host disease (GVHD) can be induced between MHC-matched murine strains expressing multiple minor histocompatibility Ag differences. In the B6->BALB.B model, both CD4(+) and CD8(+) donor T cells can mediate lethal GVHD, whereas in the B6->CXB-2 model, only CD8(+) T cells are lethal. TCR Vbeta CDR3-size spectratyping was previously used to analyze CD8(+) and CD4(+) T cell responses in lethally irradiated BALB.B and CXB-2 recipients, which showed significant overlap in the reacting repertoires. However, CD4(+) T cells exhibited unique skewing of the Vbeta2 and 11 families in only BALB.B recipients. These Vbeta family reactivities were confirmed by immunohistochemical staining of lingual epithelial infiltrates, and by positive and negative selection Vbeta family transfer experiments for GVHD induction in BALB.B recipients. We have now extended these studies to examine the T cell repertoire responses involved in target tissue damage. Infiltrating B6 host-presensitized CD8(+) and CD4(+) T cells were isolated 8-10 days post-transplant from the spleens, intestines and livers of CXB-2 and BALB.B transplant recipients. For both T cell subsets, the results indicated overlapping tissue skewings between the recipients, also between the tissues sampled within the respective recipients as well as tissue specific responses unique to both the BALB.B and CXB-2 infiltrates. Most notably, the CD4(+) Vbeta 11(+) family was skewed in the intestines of BALB.B but not CXB-2 recipients. Taken together, these data suggest that there are likely to be target tissue-related anti-multiple minor histocompatibility Ag-specific responses in each of the strain recipients, which may also differ from those found in peripheral lymphoid organs.

T cell immunity and graft-versus-host disease (GVHD)

Graft-versus-host disease (GVHD), induced by the reaction of donor T cells to recipient histoincompatible antigens, is a serious complication of allogeneic bone marrow transplantation (BMT), resulting in considerable morbidity and mortality. In MHC-disparate BMT, donor T cells directly react with major histocompatibility complex (MHC) antigens, while in MHC-matched BMT, T cells react with minor histocompatibility antigens (miHA) presented by shared MHC molecules. Clinically, acute and chronic GVHD can be distinguished on the basis of the time of onset, clinical manifestations and distinct pathobiological mechanisms. Acute GVHD usually occurs within 2 to 6 weeks following allogeneic BMT and primarily affects the skin, liver and the gastrointestinal tract with T cell infiltration of the epithelia of the skin, mucous membranes, bile ducts and gut. In addition, hair follicle cells, airways, bone marrow, and a variety of other tissue systems can be involved. Acute GVHD occurs in up to 50% of allogeneic HLA-matched and 70% of HLA-disparate BMT recipients despite prophylactic immunosuppressive drugs. Chronic GVHD involves a wider range of organs and clinical manifestations include scleroderma, liver failure, immune complex disease, glomerulonephritis, and autoantibody formation.