FLOW CYTOMETRY CROSSMATCH: FCXM VS. FLOWDSA-XM

Clinical impact of preformed HLA donor specific antibodies(DSA) ranges from an acceptable risk to an absolute contra-indication for kidney transplantation, according to the technique used to detect them (CDC vs. flow cytometry/solid phase). The new FlowDSA-XM technique combinessensitivity of the classical FCXM with specificity of the sin-gle antigen bead assay, allowing a better correlationbetween crossmatch result and patients' HLA class I and IIsensitization detected by solid phase assay. We performed acomparative analysis between FCXM and FlowDSA-XMresults by testing 46 sera (9 PRA=0%, 14 HLA class I posi-tive, seven HLA class II positive and 16 HLA class I&IIpositive) with five different lymphocytes population (typedfor all HLA class I&II loci by high resolution PCR-SSP/SSO techniques).The standard FCXM technique alloweddetection of IgG-antibodies specific for T and B lympho-cytes. The FlowDSA-XM consisted of an incubation oflymphocytes and serum was performed. Then, three differ-ent Capture Beads (HLA I A, B, C beads, HLA IIa DQbeads and HLA IIb DR, DQ, DP beads) were added. Lastly,a Lysis/Stain buffer was used to solubilize the HLA mole-cules and to label the antibodies bound to them. FlowDSA-XM and FCXM showed strong concordance in the ninePRA negative sera and in the 14 anti-HLA class I positivesera; FlowDSA-XM was partially discordant in one ofseven anti-HLA class II positive sera because of FCXM Bcells showed a very weak positivity while FlowDSA-XMHLA IIb showed a result near cut-off. Moreover, theFlowDSA-XM was more sensitive than the FCXM showinghigher values of positivity, especially in the presence ofanti-HLA class I DSA and gave "specific" results discrimi-nating between HLA class I and/or II DSA. On the contrarythe FCXM gave B positive results for the presence of bothHLA class I and class II DSA. In conclusion the FlowDSA-XM, allowing a better interpretation of the crossmatchresult, could represent the crossmatch of the newmillennium.