Background: Acute humoral rejection, or rejection associated with de novo production of anti-HLA donor-specific antibodies (DSA) after kidney transplantation (KTx), is a clinicopathologic entity that is not completely understood. Recent studies have proposed criteria for its diagnosis, including: (1) steroid-resistant acute dysfunction; (2) positive post-Tx donor-specific crossmatch (XM); and (3) widespread C4d deposits in peritubular capillaries (PTC) upon renal biopsy.
Methods: During 2002, prospective screening for AHR was established at our unit, seeking DSA post-KTx in selected cases of steroid-resistant acute rejection or acute dysfunction in high-risk sensitized or re-Tx patients. Frozen donor lymphocytes were used for post-Tx flow cytometry (FC) XM and high-definition flow PRA for patients with no frozen donor cells. We treated patients diagnosed with DSA using plasma exchange and polyclonal immunoglobulin.
Results: Post-Tx DSA studies were performed in 9 of 94 patients transplanted during 2002. We detected DSA post-Tx in 3 of 9 recipients: 2 by FCXM and 1 using high-definition flow PRA. Two were highly sensitized pre-Tx, but the third patient was a 70-year-old woman receiving a first Tx (PRA=0%). All 3 recipients presented with severe steroid-resistant acute renal dysfunction during the first 2 weeks post-Tx. Biopsies showed some features of AHR (neutrophils in PTC); 1 case showed no signs of concomitant cellular rejection. All rejection episodes were treated successfully (XM became negative and renal function recovered) by combining plasma exchange and polyclonal immunoglobulin.
Conclusions: The use of specific tools, like the crossmatch, in cases of acute, steroid-resistant renal graft dysfunction is important to identify and treat otherwise undetected humoral mechanisms of rejection.