Analysis of graft-versus-host disease (GVHD) and graft rejection using MHC class I-deficient mice

Successful tapering of immunosuppression to low-dose monotherapy steroids after living-related human leukocyte antigen-identical renal transplantation

BACKGROUND

Living-related (LR) human leukocyte antigen (HLA)-identical renal transplant (RTx) recipients often receive standard immunosuppression, despite the absence of mismatched major HLA-antigens and the known complications of long-term use of immunosuppression. No data are available on the need for immunosuppression for these specific patients. We wondered whether their immunosuppressive load could be radically reduced.

METHOD

Between November 1982 and November 2005, 83 LR HLA-identical RTx were performed in our center. Their unadjusted graft survival was 74% at 10 years. In 29 patients (median time after transplantation 5.6 [range 1.0-21.4] years) with stable uncompromised renal function, we tapered their immunosuppression from triple or dual therapy to prednisolone 5 mg/day. Follow up on prednisolone monotherapy was at least 24 months.

RESULTS

In 27 of 29 patients reduction of immunosuppression to prednisolone monotherapy was uneventful. One patient, using dual therapy, developed JC-virus nephropathy resulting in graft loss. One refused further discontinuation of his medication. Four (15%) of the 27 patients on monotherapy developed biopsy-proven recurrence of their original disease. Only one of them showed a transient decline in renal function. One additional patient developed minor proteinuria and a rise in serum creatinine level, as a result of chronic urinary tract infections. The remaining 23 of 27 patients (85%) had an uneventful follow up during 24 months prednisolone monotherapy.

CONCLUSION

We conclude that HLA-identical LR RTx recipients who are at least 1 year after transplantation might be treated with low-dose steroid monotherapy. Close surveillance of patients for recurrence of their original disease is recommended to allow for potential early therapeutic intervention.

T cell immunotherapeutic populations control viral infections in bone marrow transplant recipients

Immunotherapies designed to prevent infection serve as an increasingly important adjunct to bone marrow transplantation (BMT). T cell immunotherapies are particularly useful for the control of virus infections, provided that T cell populations are free of graft-vs-host (GVH) activity. In this review, we describe positive and negative selection methods with which donor T cell populations devoid of GVH activity can be prepared for transfer to the immunodeficient BMT recipient. The support of patients with T cell immunotherapies may ultimately revolutionize BMT, elevating the procedure from a salvage to a front-line treatment strategy for otherwise fatal disorders.

Rejection of grafts with no H-2 disparity in TAP1 mutant mice: CD4 T cells are important effector cells and self H-2b class I molecules are target

Our previous results showed that TAP1 mutant mice rejected heart and skin grafts from donors with no H-2 disparity that express normal density of MHC class I molecules at the cell surface. During rejection, CD4 cells were predominant and essentially, no CD8 cells were found infiltrating the grafts. We hypothesized that TAP1 mutant mice, which developed and matured in an MHC class I-deficient environment, may have selected a repertoire of T cells with distinct reactivity to self class I molecules. The rejection of grafts with no H-2 disparity could be mediated by CD4+ T cells reactive to wild type H-2b class I molecules, or derived peptides, in the context of self-APC. Accordingly, we observed that transplanted TAP1 mutant mice presented a significant amplification of the proliferative T cell response to H-2Kb peptides, indicating that the stimulus with the graft was sufficient to induce peripheral expansion of these T cell repertoires. Therefore, the response to H-2Kb molecules could be a relevant pathway of activating T cells and triggering rejection of grafts expressing normal levels of these class I molecules. To test our hypothesis, we investigate the effect of pre-transplantation H-2Kb peptide-immunization on TAP1 mutant, which were then transplanted with C57BL/6 skin grafts (H-2b). Mice were immunized with a pool of five peptides derived from the polymorphic region of Kb alpha chain, before tail skin grafting. To study the role of CD4+ T cells in the rejection of C57BL/6 skin grafts, mice were in vivo depleted with an anti-CD4 monoclonal antibody GK1.5, and transplant evolution was observed. Sensitization of TAP1 mutant mice with H-2Kb peptides accelerated the rejection of skin grafts. Immunized mice rejected grafts with a MST of 13 days, compared to 16 days for the non-immunized mice (P=0.0089). The significant acceleration of graft rejection, induced by immunization with H-2Kb peptides, indicates that these peptides are capable of mobilizing effector T-cells that participate in rejection. These results support our hypothesis that class I molecules may be a target in the rejection of grafts with no MHC disparity. Depletion of CD4 T-cells resulted in a significant delay in rejection compared with the untreated control group. The MST of skin grafts in the controls was 16 days, whereas CD4-depleted recipients rejected skin grafts with a MST of 41 days (P=0.025). Moreover, some animals did not show macroscopic signs of rejection up to > 100 days posttransplantation. The contribution of CD4+ T cells to skin graft rejection, in our model, may reflect the occurrence of the presentation of H-2b peptides during graft rejection, in the context of self-APC. In conclusion, our results demonstrate an important role for H-2b molecules and CD4 T cells in the rejection of C57BL/6 grafts by TAP1 mutant mice. The low expression of MHC-I molecules on TAP1-/- mice may be determinant in the selection of a T cell repertoire strongly reactive to self MHC class I molecules which probably escapes the control of peripheral regulatory mechanisms.

The DBY gene codes for an HLA-DQ5-restricted human male-specific minor histocompatibility antigen involved in graft-versus-host disease

Graft rejection or graft-versus-host (GVH) disease after HLA-identical stem cell transplantation is the result of recognition of minor histocompatibility antigens (mHags) by immunocompetent T lymphocytes from recipient or donor origin, respectively. Cytolytic T lymphocyte (CTL) clones can be isolated during graft rejection and GVH disease to identify mHags and their corresponding genes. Thus far, all human mHags identified appeared to be HLA class I-restricted. Here, we report the characterization of the first human HLA class II-restricted sex-linked mHag involved in GVH disease. Previously, we isolated an HLA-DQ5-restricted CD4(+) CTL clone from a male patient with chronic myeloid leukemia who developed acute GVH disease grade III-IV after transplantation of HLA genotypically identical female stem cells. Using a panel of female HLA-DQ5(+) EBV cells that we stably transfected with Y chromosome-specific genes, we determined that the HLA class II male-specific mHag (H-Y) was encoded by the Y chromosome-specific gene DBY. The H-Y epitope was localized in the DBY protein using female HLA-DQ5(+) peripheral blood mononuclear cells loaded with DBY protein fragments. The minimal peptide sequence leading to maximal recognition by the specific HLA-DQ5-restricted CTL clone was characterized as the 12-amino acid sequence HIENFSDIDMGE. Although the epitope differed by 3 amino acids from its X-homolog DBX, only 2 polymorphisms were shown to be essential for recognition by the CTL clone.