Multi-centre validation of a flow cytometry method to identify optimal responders to interferon-beta in multiple sclerosis

Background and objectives: Percentages of blood CD19 + CD5 + B cells and CD8 + perforin + T lymphocytes can predict response to Interferon (IFN)-beta treatment in relapsing-remitting multiple sclerosis (RRMS) patients. We aimed to standardize their detection in a multicenter study, prior to their implementation in clinical practice. Methods: Fourteen hospitals participated in the study. A reference centre was established for comparison studies. Peripheral blood cells of 105 untreated RRMS patients were studied. Every sample was analyzed in duplicate in the participating centre and in the reference one by flow cytometry. When needed, participating centres corrected fluorescence compensations and negative cut-off position following reference centre suggestions. Concordance between results obtained by participating centres and by reference one was evaluated by intraclass correlation coefficients (ICC) and Spearman correlation test. Centre performance was measured by using z-scores values. Results: After results review and corrective actions implementation, overall ICC was 0.86 (CI: 0.81-0.91) for CD19 + CD5 + B cell and 0.89 (CI: 0.85-0.93) for CD8 + perforin + T cell quantification; Spearman r was 0.92 (0.89-0.95; p < 0.0001) and 0.92 (0.88-0.95; p < 0.0001) respectively. All centres obtained z-scores 5 0.5 for both biomarkers. Conclusion: Homogenous percentages of CD19 + CD5 + B cells and CD8 perforin + T lymphocytes can be obtained if suitable compensation values and negative cut-off are pre-established.