PRE-TRANSPLANT HLA ANTIBODY SCREENING BY SOLID PHASE ASSAYS: INCIDENCE OF ANTI-HLA IGM ANTIBODIES IN KIDNEY TRANSPLANT CANDIDATES

A positive lymphocytotoxic crossmatch represents an absolute contraindication to kidney transplantation. This paradigm is widely accepted for IgG antibodies but few data on the clinical relevance of IgM antibodies are available and so their role is still controversial. Some studies report that they can be protective for transplant, while other suggest that IgM antibodies are harmful for the graft. Pre-transplant antibody screening by CDC technique does not allow to discriminate IgG and IgM isotype. Instead, serum treatment with DTT can indirectly highlight because is able to inactivate the IgM pentamer. Moreover, in both cases it is not possible to know if these antibodies are or not specific for HLA molecules. The new solid-phase techniques permit to evidence anti-HLA antibodies and to discriminate their isotype. Since September 2016, 189 kidney transplant candidates were analyzed to evaluate the incidence of IgM antibodies. The antibody characterization was performed using FlowPRA Screening Test to detected either anti-HLA IgM alone, otherwise unknown, or in combination with IgG antibodies and by Luminex Single Antigen Beads to identify antibody specificity. The incidence of anti-HLA IgM antibodies was 10% (19/189). Only IgM antibodies were detected in 10 (53%) patients, both IgM/IgG antibodies were presented in 9 (47%) patients. IgM positive-group showed in 6 cases only anti-HLA class I antibodies (2000>=MFI<=7000) and 4 cases only class II antibodies (4000>=MFI<=12000). The antibody characterization of IgM/IgG positive-group evidenced in 3 patients the same IgM and IgG specificity, while 6 patients showed additional IgM specificity respect to evidenced IgG antibody specificity. In conclusion, our study suggests to enlarge the antibody screening to anti-HLA IgM antibodies in transplant candidates. The strength and specificity of detected IgM antibodies highlighted the importance of an accurate characterization to understand their clinical significance and to improve graft survival.