A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Novel mRNA-based vaccines have been proven powerful tools to combat the global pandemic caused by SARS-CoV2 with BNT162b2 (trade name: Comirnaty) efficiently protecting individuals from COVID-19 across a broad age range. Still, it remains largely unknown how renal insufficiency and immunosuppressive medication affect development of vaccine induced immunity. We therefore comprehensively analyzed humoral and cellular responses in kidney transplant recipients after the standard second vaccination dose. As opposed to all healthy vaccinees and the majority of hemodialysis patients, only 4/39 and 1/39 transplanted individuals showed IgA and IgG seroconversion at day 8±1 after booster immunization with minor changes until day 23±5, respectively. Although most transplanted patients mounted spike-specific T helper cell responses, frequencies were significantly reduced compared to controls and dialysis patients, accompanied by a broad impairment in effector cytokine production, memory differentiation and activation-related signatures. Spike-specific CD8 + T cell responses were less abundant than their CD4 + counterparts in healthy controls and hemodialysis patients and almost undetectable in transplant patients. Promotion of anti-HLA antibodies or acute rejection was not detected after vaccination. In summary, our data strongly suggest revised vaccination approaches in immunosuppressed patients, including individual immune monitoring for protection of this vulnerable group at risk to develop severe COVID-19.

We confirmed that HLAab produced even late after transplantation are detrimental to graft outcome. DSA were proven to have a strong adverse impact on graft survival. The results indicate that a posttransplant HLAab monitoring routine could be appropriate to improve long-term results.