ASSAYS TO PREDICT ALLOGRAFT REJECTION

D. Fuerst¹, M. Sadeghi², I. Lahdou³, K. Recker¹, H. Schrezenmeier⁴, J. Mytilineos^5
1Department Of Transplantation Immunology, Institute for Clinical Transfusion Medicine and Immunogenetics, University Clinic Ulm, 89081/GERMANY, ²Department Of Transplantation-immunology, Institute of Immunology, University of Heidelberg, Heidelberg/GERMANY, ³Transplantation Immunology, IMMUNOLOGY AND SEROLOGY, Heidelberg/GERMANY, ⁴Transplantation Immunology, IKT, 89081/GERMANY, ⁵Department Of Transplantation Immunology, Institute for Clinical Transfusion Medicine and Immunogenetics, University Clinic Ulm, Ulm/GERMANY

Body: Introduction MICA (MHC class I polypeptide-related sequence A) genes are a highly polymorphic lineage of non classical HLA-genes. They act as ligand for the activating NKG2D-receptor on natural killer (NK) cells. MICA-antibodies and sMICA (soluble form of the MICA-antigen) have been implicated in immunological processes in the transplantation setting as well as in autoimmune diseases and cancer. Methods We developed a highly sensitive Luminex assay for detection of sMICA. Detection threshold was approximately 5pg/ml, although lower target values can be extrapolated by the system. Our method is 10 times more sensitive than conventional ELISA assays. We tested 25 post transplant serum samples of two groups of solid organ recipients. Group 1: recipients with stable graft function (n=16; serum samples deriving from post Tx days 2-745, median day 12); group 2: recipients with acute rejection (AR) or acute tubular necrosis (ATN) (n=9; serum samples deriving from post Tx days 3-610, median day 8). DNA-samples of 15 transplant recipients were available and in these samples MICA typing was performed by an in house Sequence Based Typing-method which included testing for exons 2-5. As a control the serum sMICA levels were detected in a group of 75 healthy blood donors. Student t test as well as Chi square test were used for statistical evaluation. Results Results are summarized in table 1. The absolute sMICA levels were significantly higher in the serum of patients with AR/ATN (group 2) as compared to patients with stable graft function (group 1) and healthy controls (p=0.036 and 0.026 respectively). When using a positivity cutoff of 10 pg/ml separation power was even higher (p=0.042 and p<0.001, respectively). Comparison of sMICA levels in group 1 with healthy controls did not reach statistical significance neither for absolute nor for positive/negative assignment (p=0.37 and 0.79 respectively). The recipients with the highest levels of sMICA in both groups were carriers of MICA*008 (A5.1), which is not only the most frequent MICA allele, but also characterized by a stop codon in exon 5 leading to a truncated protein with defective membrane anchorage. Conclusion We speculate that sMICA levels are influenced by two factors: Presence or absence of the A5.1 allele and presence or absence of disease activity (cell turnover). Larger studies are needed to assess the relationship between sMICA, MICA-genetics and rejection. As sMICA might have immunomodulatory effects due to the functional interactions with NK cells, assessment of sMICA levels may have implications for graft outcome prognosis as well as donor allocation.

Disclosure: All authors have declared no conflicts of interest.