Correlação dos níveis de anticorpos ANTI-HLA de classe I e II doador específicos detectados por ensaio de fase sólida com os resultados das provas cruzadas no pré-transplante renal

Abstract

Introduction: There has been a continuous search for safe tests that can predict antibody-mediated rejection in organ transplants, and the positive complement dependent cytotoxic crossmatch, developed in the 1960’s, was until recently considered the gold standard and the main test for prediction of rejection. The new methods for assessing humoral immunity, notably flow cytometric crossmatching and the Luminex® technology significantly increased the sensitivity of these assessments, but also the complexity in the interpretation of these results, as well as in the correlation of different methodologies. Despite the sensitivity of these methods, not any donor-specific antibody detected by solid phase assay results in positive or negative crossmatch. Information obtained with the specificities (such as fluorescence intensity) of anti-HLA antibodies may define the immunological risk for the patient, assisting in the selection of the ideal donor, as well as in the immunosuppressive regimen, for prophylactic and therapeutic uses. Objectives: The present study aimed to establish a cut-off point at the fluorescence intensity of antibodies detected by the panel Single Antigen Beads of class I and II that correlates to positive flow cytometric crossmatching (FCXM). It also aimed to assess whether there are differences between the use of DSAs with higher MFI alone and the sum of all the DSAs of a given patient. Methodology: A cross-sectional study of two databases of results of panels (Luminex®) and flow cytometric crossmatching of patients on a waiting list for kidney transplantation registered at the Laboratório de Imunologia de Transplantes da Santa Casa de Misericórdia, in Porto Alegre. Database 1 was composed of 1,316 crossmatches against deceased donors and panels of anti-HLA antibodies for loci A, B and DRB1 performed in 2010. Database 2 was composed of 2,288 crossmatches against deceased donors and panels of anti-HLA antibodies for loci C and DQB1 performed between July 2013 and July 2014. As an inclusion criterion for both databases, only samples with results available in the Panel on the same date of the serum tested in flow cytometry crossmatches were used resulting in 834 samples in database 1. Besides, for database 2 only samples with donor-specific antibody (DSA) for loci C and or DQB1, resulting in 348 crossmatches. Results and Conclusions: we demonstrated that 97.6% of the patients with DSAs anti-HLA- ABDRB1 with MFI ≥ 5000 resulted in positive FCXM. These were the optimal MFI cut-off values for donor selection when we assessed sensitivity and specificity for correlation with positive flow cytometric crossmatching. For DSAs HLA-DQB1, fluorescence intensities above 15,000 MFI offer high specificity (97.8%). Anti-HLA-C sensitization is less frequent (n=40). Only 5 patients showed MFI≥5000. Of these, the crossmatch was positive in only one patient (20%). Virtual crossmatch is a resource that can assist in making pre-kidney transplantation decisions.