Identifying biomarkers of immune reactivity to the graft is an emerging theme in the diagnosis of transplant rejection. Monitoring the immune response to the allograft permits early identification of patients at risk of rejection and graft loss, optimization of immunosuppressive drug regimens, surveillance of response to therapy, and guidance in developing new therapeutic strategies.
Patients who develop T-cell alloreactivity or anti-donor HLA antibodies are at higher risk of graft rejection. There is a growing recognition that if these changes can be detected in advance of clinical symptoms, appropriate immunosuppressive intervention can be administered to prevent rejection. Thus, monitoring changes such as anti-HLA antibody levels in the serum or increased perforin and granzyme B gene expression in cytotoxic T-cells released in the blood can provide useful data for the management of transplant recipients.
Post-transplant monitoring tests have been developed to detect various activation states that reflect a change in the immune status of the patient. The most informative approach to immune monitoring is to perform a sequential analysis using assays that measure distinct immune functions.
Organ transplant recipients who produce anti-HLA antibodies following transplantation are at higher risk of acute and chronic allograft rejection. Anti-HLA antibody tests provide accurate assessments of the recipient's sensitization to the allograft and often identify the HLA antigens that are specific targets of the antibodies. The development of antibodies to endothelial cell antigens such as MICA may also contribute to allograft rejection.
Application: Organ transplant recipients producing anti-HLA antibodies following transplantation are at higher risk of acute and chronic allograft rejection. Anti-HLA antibody testing provides an accurate assessment of the recipient's sensitization to the allograft and often identifies the HLA antigens that are specific targets of the antibodies.
** Reed EF, Hong B, Ho E, Harris PE, Weinberger J and Suciu-Foca N. Monitoring of soluble HLA alloantigens and anti-HLA antibodies identifies heart allograft recipients at risk of transplant associated coronary artery disease. Transplantation 1996; 61:1-7.
** Zhang Q, Liang LW, Gjertson DW, Lassman C, Wilkinson AI, Kendrick E, Pham TP, Danovitch G, Gritsch A, Reed EF. Development of post transplant anti-donor HLA antibodies is associated with acute humoral rejection and early graft dysfunction. Transplantation 2005; 79:591-8.
** Reed EF, Demetris AJ, Hammond E, et al. Acute antibody-mediated rejection of cardic transplants. J Heart Lung Transplant 2006; 25:153-9.
Antibodies to HLA-A, -B, -C or -DR, -DQ antigens can be accurately identified using purified HLA class I and/or class II antigens. The flow cytometry and luminex methods are very sensitive and can detect low levels of anti-HLA class I and/or class II antibodies present in the patient's serum. Results are reported as the percent PRA and anti-HLA-A, -B, -C and/or HLA-DR, -DQ antibody specificity. The use of purified MICA antigen coated beads permits the identification of anti-MICA IgG antibodies.
The frequency of T-cell precursors to donor alloantigens can be measured by a cytokine secretion flow cytometry assay. Responder cells are cultured with stimulator cells, soluble donor antigens or mismatched peptides and assayed for proliferation or Th1 vs Th2 type cytokine release. The degree of T-cell alloreactivity correlates with acute and chronic rejection. This test has the advantage of measuring the transplant recipient's immune response to the allograft using peripheral blood.
** Korin YD, Lee C, Gjertson DW, Wilkinson AH, PHam TP, Danovitch GM, Gritsch HA, Reed EF. A novel flow assay for the detection of cytokine secreting alloreactive T cells: application to immune monitoring. Hum Immunol 2005; 66:1110-24.
** Liu Z, Colovai AI, Tugulea S, Reed EF, et al. Indirect recognition of donor HLA-DR peptides in organ allograft rejection. J Clin Invest 1006; 98:1150-7.
The present of increased numbers of T-cells directed against graft HLA antigens identifies patients at risk of acute and chronic rejection. The results are reported as the frequency of proliferating or cytokine-producing T-cells.
Quantitation of global cell-mediated immunity by the Cylex Immuknow assay can be used to measure the potency of immunosuppressive therapy. This assay is also informative for monitoring immunosuppression compliance. T-cells are stimulated with mitogens, superantigens or protein antigens and the degree of activation is measured by the generation of ATP measured by luminometry or production of cytokines measured by flow cytometry. The degree of T-cell responsiveness to antigenic stimuli correlates with the patient's net immunosuppression. The results are reported in ng/ml ATP.
** Kowalski RJ, POst DR, Mannon RB, Sebastian A, Wright HI, Sigle G, Burdick J, Elmagd KA, Zeevi A, Lopex-Cepero M, Daller JA, Gritsch HA, Reed EF, Jonsson J, Hawkins D, Britz JA. Assessing relative risks of infection and rejection: A meta-analysis using an immune function assay. Transplantation 2006; 82:663-8.
Quantitative flow cytometry analysis of T-cells binding HLA tetramers detect antigens specific T-cells and monitor response to vaccines for tracking antigen specific T-cells in disease diagnosis and immune monitoring. Tests are reported in percent tetramer-positive cells.
Flow cytometry immunophenotyping is the analysis of cell surface markers using fluorochrome-conjugated monoclonal antibodies. Immunophenotyping of lymphocyte subsets can be used for assessing the immune status of the patient and monitor effectiveness of immunotherapies. Test results are reported as percent positive cells. Absolute cell counts are available.
|
