Introduction: Adherence to quality control in multi-center longitudinal research is crucial for maintaining sample integrity and enhancing research impact. The ENDIA Study Quality Control (QC) Team identified four critical "P-points" to evaluate and improve practices, focusing on the vulnerability of peripheral blood mononuclear cells (PBMC) to external variation.
Methods: The "P-points" included:
- Processing: Auditing sample processing times from collection to -80°C storage, including during COVID-19.
- Proficiency: Establishing a QC program for PBMC at each lab, with a central evaluation of post-thaw viability and functional quality. Annual participation in the IBBL PBMC isolation proficiency testing program.
- Primary Outcome (islet-autoantibody testing): Monitoring assay performance using inter-assay CVs of controls and standards, with biannual participation in IASP workshops.
- PBMC: Developing linear mixed-effect models using data from 1520 thawed PBMC samples to evaluate post-thaw viability concerning time and storage conditions between blood collection and PBMC isolation, total viable cell number, cell storage volume, inter-laboratory shipping, and LN2 biobank storage duration.
Results:
- Processing: Significant differences in processing times were observed across sites (p<0.001) and between pre-, intra-, and post-COVID periods (p<0.001).
- Proficiency: QC samples' storage viability and total viable cell numbers exceeded international CHAVI standards, achieving "very satisfactory/satisfactory" levels in IBBL metrics. Differences were noted in post-thaw viability, recovery, and IFN-γ release assays between sites.
- Primary Outcome: Intra-assay CVs were <33% for all islet antibody tests, with ENDIA consistently ranking among the highest in IASP sensitivity and specificity.
- PBMC: Post-thaw viability was significantly reduced by delays between blood collection and PBMC isolation (-23%), room temperature storage (-11.6%), reduced cell storage volume (-21%), and biobanking over 100 days (-2.4%). Improvements included higher total cell number at storage (23.4%) and LN2 versus dry-ice shipping (37.1%).
Conclusions: ENDIA's practices meet acceptable standards, ensuring reliable outcomes. External validation is underway to develop a predictive tool to estimate post-thaw cell yield and viability, aiding experimental planning.