Background: Anti-human leukocyte antigen (HLA) antibody sensitisation represents a major barrier to cardiac transplantation. Patients with heart failure, supported by Ventricular Assist Devices (VAD), or those who have undergone surgical repair for congenital heart defects are at higher risk of developing anti-HLA antibodies, and thus limiting their compatibility with potential donors. Currently there is no consensus as to how, or when desensitisation should take place, and through what mechanism, meaning that sensitised patient must wait for a compatible donor for many months, if not years. For many this delay in finding a suitable organ results in increased risk of complications from VADs, with poorer waiting-list outcomes. We aimed to determine if it were possible to use immunoadsorption in an ex vivo laboratory setting to provide a potential, intraoperative desensitisation methodology.
Methods: Anti-HLA antibody-containing whole blood was obtained from NHS Blood and Transplant and quantified using a Luminex Single Antigen Bead assay. A Cardiopulmonary bypass (CPB) circuit was set up to mimic a 20kg patient undergoing cardiac transplantation, into which a plasma separator was placed. Anti-HLA antibody containing plasma was then diverted to a standalone, secondary immunoadsorption system, with antibody-depleted plasma return to the CPB circuit.

A total treatment volume of 3-fold the pseudo-patient’s plasma volume (4500ml at 75ml/kg) was treated. Samples for anti-HLA antibody quantification were taking at baseline, when combined with the CPB prime (on bypass), and then every 20 minutes for the duration of treatment (total 3 hours).
Results: All 3 experiments demonstrated a reduction in individual bead mean fluorescence intensity (MFI) to below clinically relevant levels (<1000 MFI), and in the majority of cases below the lower detection limit (<500 MFI), even in HLA specificities with a baseline MFI >4000. Reduction occurred in all cases within 120 minutes, demonstrating efficacy in a time period usual for cardiac transplantation.

Flow cytometric crossmatching of suitable pseudo-patients demonstrated a flipping from T cell and B cell positive channel shifts to negative, demonstrating a reduction in binding capacity.
Conclusions: Intraoperative immunoadsorption in an ex vivo­ setting demonstrates a clinically relevant reduction in anti-HLA antibodies within the normal timeframe for cardiac transplantation. This method represents a potential desensitisation technique that could enable sensitised children to accept a donor organ earlier, even in the presence of donor-specific anti-HLA antibodies.