HLA Sensitization in the Era of COVID-19: Single-Center Experience

Anti-HLA Immunization in Patients After Lung Transplantation: A Comparative Study Before and During the Pandemic

Anti-human leukocyte antigen (anti-HLA) sensitization in lung transplant recipients (LTRs) can significantly impact graft survival and patient outcomes. The global pandemic, induced by the SARS-CoV-2 virus, brought about numerous challenges in the medical sphere, including potential alterations in HLA immunization patterns among LTRs. A retrospective analysis of LTRs group transplanted from July 2018 to 1 March 2020 (pre-pandemic) was compared with patients transplanted from 1 March 2020 to December 2022 (during the pandemic). Totally 92 patients were controlled. Patients were also divided into 2 groups: vaccinated and non-vaccinated. The results of cytotoxic crossmatch, results of anti-HLA antibody testing, presence of DSA before and after transplantation, and early and late graft function were compared between groups. In the pandemic and vaccinated groups, an increase was observed in the number of positive crossmatch tests performed with a pool of B lymphocytes. However, the presence of dithiothreitol abolished the positive reaction in 90% of cases. We also observed an increased percentage of patients immunized based on the results of solid phase tests both in the pandemic group and in the group of patients who received vaccination against the SARS-CoV-2 virus. It might be that the pandemic/vaccination has influenced the prevalence of anti-HLA immunization in LTRs. Further studies are essential to establish causative factors and develop targeted interventions for this population of patients.

Impact of COVID-19 pandemic on transplant laboratories: How to mitigate?

A positive flow cytometry crossmatch (FCXM) due to donor specific antibodies (DSA) constitutes a risk for kidney transplantation; such a finding may indicates an unacceptable donor for this patient. However, positive FCXM in the absence of DSA is considered discordant and need further investigations. During COVID-19 pandemic, we observed 22% discordant results out of 445 FCXM performed during eight months period in our laboratory and another 7% were invalid due to high background negative control (NC). No study has addressed the impact of COVID-19 pandemic on FCXM and the overall pre-kidney transplant workups or described a solution to deal with these non-specific reactivities. Herein, we analyzed all FCXM results in SARS-CoV-2 seropositive patients and addressed how this pandemic affected significantly the pre-kidney transplant workups, highlighting both technical and financial implications. We also shared our modified FCXM procedures using dithiotheritol (DTT) sera treatment or blocking donor cells with negative control human serum (NCS) which we found to be successful to abrogate 98% of all discordant FCXM results and to validate all invalid results due to high background NC. In conclusion, COVID-19 pandemic has affected our HLA laboratory significantly by creating many false positive or invalid crossmatch results. Transplant laboratories must consider this before test interpretations and immune risk assessments. We recommend the use of DTT serum treatment to remove nonspecific bindings in the sera of kidney transplant candidates and the use of NCS-blocked donor cells to correct high background when performing FCXM in transplant candidates or donors with recent history of SARS-CoV-2 immunization respectively.

HLA Sensitization in Patients Bridged to Lung Transplantation With Extracorporeal Membrane Oxygenation

Lung transplantation is a definitive therapy for many end-stage lung pathologies. Extracorporeal membrane oxygenation (ECMO) is increasingly being used as a bridge to lung transplantation (BTT). HLA sensitization is a major barrier to lung transplantation. The development of HLA sensitization while undergoing ECMO support as a BTT has recently been reported in a 2-patient series.

Methods

We performed a retrospective analysis of patients undergoing ECMO as a BTT at a single large academic medical center from January 2016 to April 2022. The study was approved by the institutional review board. We selected patients who had undergone ECMO support for at least 7 d with either negative HLA before cannulation or initial negative HLA on ECMO (3 patients).

Results

We identified 27 patients bridged to lung transplantation with available HLA data. Of this group, 8 patients (29.6%) developed significant HLA sensitization (>10%). We did not identify any factors predisposing to sensitization, including infection episodes or blood product transfusion. Sensitized patients demonstrated a trend toward an increased primary graft dysfunction rate, a need for posttransplant ECMO support, and a decreased 1-y survival; however, these did not meet statistical significance.

Conclusions

Our study is the largest series today describing the association between HLA sensitization and ECMO therapy. We suggest that interaction between the immune system and ECMO circuit contributes to allosensitization pretransplant, similar to that occurring with ventricular assist device. Further work is needed to better characterize the incidence of HLA sensitization in a multicenter cohort and to identify potentially modifiable factors associated with HLA sensitization.