A practical alternative to live cell-based assay for AQP4 and MOG antibody detection

BACKGROUND: Live cell-based assay (LCBA) is the gold standard for sensitive detection of aquaporin-4 (AQP4) and myelin oligodendrocyte glycoprotein (MOG) autoantibodies in neuromyelitis optica spectrum disorder (NMOSD) and MOG antibody-associated disorder (MOGAD). However, LCBA is less practical, standardisable and cost-effective than fixed cell-based assay (FCBA). METHODS: We developed a high-performance untransfected vector cells lysate, named AbFine, to process patients' sera to pre-bind and deplete interferents before FCBA, and examined its rationality. We then conducted a multicentre, double-blind, prospective discovery study to compare the diagnostic accuracy of conventional FCBA, FCBA-AbFine, and LCBA in detecting AQP4-IgG and MOG-IgG. A retrospective validation cohort was used to assess generalisability. Participants included patients with NMOSD, MOGAD, and seronegative inflammatory demyelination syndromes, and controls with other neurological disorders. FINDINGS: 818 participants were recruited, including 410 in the discovery and 408 in the validation cohorts with good consistency. Among 205 patients with NMOSD, AQP4-IgG was detected in 165, 185, and 178 by FCBA, FCBA-AbFine, and LCBA, yielding sensitivity of 80.5% (95% CI, 74.4-85.7), 90.2% (95% CI, 85.3-93.9), and 86.8% (95% CI, 81.4-91.1), respectively. Among 171 patients with MOGAD, MOG-IgG was found in 134, 155, and 158 by FCBA, FCBA-AbFine, and LCBA, with sensitivity of 78.4% (95% CI, 71.4-84.3), 90.6% (95% CI, 85.3-94.6), and 92.4% (95% CI, 87.4-95.9), respectively. All assays achieved specificity greater than 99.5%. The area under the curve for FCBA-AbFine was higher than that for FCBA for both AQP4-IgG (0.950 vs. 0.902; p < 0.0001) and MOG-IgG (0.935 vs. 0.888; p < 0.05), and was comparable to LCBA (AQP4-IgG 0.950 vs. 0.934; MOG-IgG 0.935 vs. 0.940; p > 0.05 for both). INTERPRETATION: AbFine enables the use of FCBA as an alternative to LCBA in AQP4-IgG and MOG-IgG detection with operationally practical and cost-efficient characteristics and could be extended to other fixed cellular assays. FUNDING: Beijing Precigen Biopharma Co., Ltd., Beijing, China.