Beatriz Chamun Gil

Comparative analysis of two methods to detect donor-specific anti-HLA antibodies after kidney transplant

Preformed anti-human leukocyte antigen (HLA) antibodies may be present in the blood of kidney transplant candidates. The production of these antibodies may occur in the post-transplant period, with the possible development of donor-specific antibodies (DSA). Luminex-based tests, such as the single antigen (SA) assay and the Luminex crossmatch (Xm-DSA) assay are the most commonly used tools to detect anti-HLA antibodies, due to their high sensitivity and specificity. This cross-sectional study aimed to compare the findings of two methods for the detection of DSAs after kidney transplant: SA and Xm-DSA. A total of 122 patients who underwent deceased donor kidney transplant at Hospital de Clínicas de Porto Alegre were included. The SA assay detected anti-class I HLA DSAs in 17 patients (13.9%) and anti-class II HLA DSAs in 22 patients (19.6%), whereas the Xm-DSA detected DSAs in 18 patients (14.8%) both against class I and class II antigens. There was agreement between the two methods for class I (kappa = 0.66, p = 0.001) and class II (kappa = 0.54, p = 0.025) antigens. The incidence of DSAs as obtained by the SA assay was 15.57%, and the most prevalent DSAs were those against HLA-DR antigens. Patient survival at 3 years was 92%. The two techniques assessed in this study provide important information on the presence of DSAs and may help in the post-transplant patient monitoring and in immunosuppressive strategy.

Accuracy of the median channel shift in the flow cytometry for predicting complement dependent cytotoxicity crossmatching in kidney transplant candidates

Crossmatching either by complement-dependent cytotoxicity (CDC) and/or by flow cytometry (FCXM) are routinely used for assessing anti-HLA donor antibodies before kidney transplantation. FCXM has demonstrated greater sensitivity and many transplant centers have opted for its use without the concomitant CDC assay. The objective of this study was to evaluate the accuracy of the median channel shift (MCS) in the FCXM in predicting the CDC assay results. A total of 1516 T cell FCXM and 1408 B cell FCXM were studied in deceased donors lymphocytes between January/2016 and March/2017. The high detection rate of CDC+ results by FCXM+ resulted in 87% (FCXM-T) and 90% (FCXM-B) sensitivity, and 98% negative predictive value, for both. The low specificity of FCXM B (43%) is atributed to cases of CDC-/FCXMB+. FCXM T and B were able to detect 53% and 76% of cases with donor specific antibodies of classes I and II with intensity of fluorescence ≥5001. The MCS differentiated CDC+ (Md, P25 and P75) results: MCS-T 390 (245-469) and MCS-B 282 (180-350). Through ROC curve analysis (AUC), the MCS showed satisfactory performance in detecting CDC+: MCS-T 0.909 (0.886-0.933) and MCS-B 0.775 (0.724-0.826). Considering the accuracy and sensitivity evaluation, the MCS-T 245 and MCS-B 282 cutoffs showed a better prediction of CDC+. This study showed that it is possible to calibrate MCS based on CDC+ with accuracy >90%, however, that leads to a risk in terms of non-detection of low-titer anti-HLA antibodies.