The presence of donor specific HLA antibodies (DSA) has been shown to be detrimental to heart transplant (HTx) survival. Virtual crossmatching (VXM) offers a rapid assessment of the patient's anti-HLA antibodies (Ab) in lieu of a real time crossmatch. There is currently no standardized protocol to perform the virtual XM and each transplant center uses different anti-HLA Ab mean fluorescence intensity (MFI) cutoffs to identify a positive VXM.

To study this problem we evaluated 70 HTx transplant recipients comparing the presence of anti-HLA Abs, MFIs, crossmatch results (AHG, FCXM) and rejection episodes to determine whether an association/correlation exists between the various test results. Panel reactive antibody tests (PRAs) and HLA Ab specificities were performed using One Lambda, Inc. reagents per the manufacturer's instructions.

Thirty percent (21/70) of these patients experienced either a cellular or antibody mediated rejection post-HTx. Of the 21 rejecting patients, 71% (15/21) presented with HLA Abs compared to 49% of the non-rejecting recipients (p=NS). Of great interest was the fact that of 19/21 rejectors who had pre-Tx DSA evaluations, 47% (9/19) presented with pre-Tx DSA vs 11% (5/44) of non-rejectors, p<0.0003. Rejecting and non-rejecting patients had similar HLA Ab MFIs of 1375-5024 pre-transplant. However, these pre-Tx DSA positive rejectors presented with significant post-Tx MFI increases vs non-rejectors (p<0.05). Rejection was not associated with either real time (AHG, FCXM) or virtual XM results. We did not observe a correlation between rejection and the degree of HLA mismatch, gender or race of donor-recipient pairings.

These data suggest that post-Tx donor specific anti-HLA Ab monitoring remains a solid predictor of HTx rejection. Both the virtual and physical crossmatch can be negative; however, patients require anti-HLA antibody testing post-transplant. HTx usually follows negative real time and/or virtual crossmatching. Our data suggest the benefit of post-Tx anti-HLA Ab monitoring in lieu of waiting for clinical symptoms of rejection to arise.

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