Early renal graft function deterioration in recipients with preformed anti-MICA antibodies: partial contribution of complement-dependent cytotoxicity.

Background: We previously reported that preformed anti-MHC class I-related chain A (MICA) antibodies increase the risk for renal graft rejection and enhance the deleterious effect of PRA(+) status early after transplantation.

Methods: We studied 727 kidney recipients. Days to reach optimal serum creatinine level, estimated glomerular filtration rate (eGFR) at Month 3 and chronic kidney disease (CKD) stages were recorded. Anti-MICA specificities and C1q binding were tested by solid-phase assay. Complement-dependent cytotoxicity (CDC) and flow cytometry (FC) cross-matches with HeLa and PMA/CD28-T-blasts were performed.

Results: PRA(+)MICA(+) recipients exhibited longer time to reach optimal serum creatinine level after transplantation (P = 0.005) and had the lowest eGFR at Month 3 (P = 0.006). PRA(+)MICA(+) status independently increased the risk for CKDT stage 5 at Month 3 [hazard ratio (HR) 4.92, P = 0.030]. Pre-transplant anti-MICA antibodies were polyspecific and showed stronger reactions when coexisting with anti-HLA antibodies (mean standard fluorescent intensity 112 157 ± 44 426 in HLA(+)MICA(+) sera versus 49 680 ± 33 116 in HLA(-)MICA(+) sera, P = 0.0006). Anti-AYVE supereplet reactivity was significantly higher in HLA(+)MICA(+) versus HLA(-)MICA(+) patients (P < 0.001) and significantly superior than anti-CMGWS supereplet within HLA(+)MICA(+) patients (P = 0.001). Three of 13 anti-MICA(+) pre-transplant sera were positive for the C1q binding assay; one of them (serum 3) exclusively recognized AYVE supereplet with a strong reactivity against MICA*027 antigen (same as MICA*008). Anti-MICA antibodies in anti-HLA-absorbed serum 3 bound native MICA molecules in MICA*008(+) HeLa and PMA/CD28-T-blasts and mediated cell death by activating complement.

Conclusion: Preformed anti-MICA antibodies may occasionally be cytotoxic by fixing and activating complement. This way they might contribute to worse early kidney graft function.