Validation of High-sensitivity Flow Cytometry for Reliable Immune Cell Analysis in Real-world Laboratory Settings

The adoption of high-sensitivity flow cytometry (HSFC) in routine laboratory settings has been slow owing to concerns regarding the reliability and reproducibility of results. Validation is an essential prerequisite for conducting assays, and implementing the CLSI guidelines has been confusing, primarily because many aspects are not yet established. We aimed to validate an HSFC protocol for detecting follicular helper T (Tfh) cells in a real-world laboratory environment. The analytical validity of the Tfh cell panel was ensured through rigorous testing, including evaluations of precision, stability, carryover, and sensitivity, following the CLSI H62 guidelines. We found that Tfh cells, present in very small numbers in the blood, could be sufficiently detected through HSFC, and concerns about the reliability and reproducibility of the results in real-world laboratories could be solved through systematic validation. Establishing the lower limit of quantification (LLOQ) is a critical step in HSFC evaluations. By selecting an appropriate sample, for example, collecting residual cells from CD4 isolation in our experiment and using them as low-level samples, the LLOQ could be accurately established. The strategic validation of flow cytometry panels can facilitate the adoption of HSFC in clinical laboratories, even with limited resources.

Development of a novel, highly sensitive assay for quantification of minimal residual B cells in autoimmune disease and comparison to traditional methods across B-cell-depleting agents

Targeted B-cell depletion is a useful therapy for many diseases, including autoimmune disorders and certain cancers. We developed a sensitive blood B-cell depletion assay, MRB 1.1, compared its performance with the T-cell/B-cell/NK-cell (TBNK) assay, and assessed B-cell depletion with different therapies. The empirically defined lower limit of quantification (LLOQ) for CD19+ cells in the TBNK assay was 10 cells/μL, and 0.441 cells/μL for the MRB 1.1 assay. The TBNK LLOQ was used to compare differences between B-cell depletion in similar lupus nephritis patient populations who received rituximab (LUNAR), ocrelizumab (BELONG), or obinutuzumab (NOBILITY). After 4 weeks, 10% of patients treated with rituximab retained detectable B cells vs 1.8% with ocrelizumab and 1.7% for obinutuzumab; at 24 weeks 93% of patients who received obinutuzumab remained below LLOQ vs 63% for rituximab. More-sensitive measurements of B cells may reveal differences in potency among anti-CD20 agents, which may associate with clinical outcomes.