Clinical response to interferon-β-1a may be linked to low baseline circulating BDCA1 myeloid dendritic cells

Many variables with association with better response to interferon-β-1a (IFNβ-1a) have been described, but none has yet been shown to be predictive of clinical response. In this real-life observational 1-year longitudinal study of 23 relapsing-remitting multiple sclerosis (RRMS) patients treated with subcutaneous IFNβ-1a, we have shown a lower proportion of circulating myeloid dendritic cells (mDCs) than in healthy controls at baseline. Both univariate (Kaplan-Meier) and multivariate (Cox regression) analyses were conducted to determine which variables (age, sex, baseline EDSS, MS relapse rates 1 year and 2 years before initiating IFNβ-1a, mDCs and plasmacytoid (pDCs) subsets, activated and regulatory CD4+ T-cells (TReg)) were associated with clinical response to IFNβ-1a. During 1 year of treatment, we observed a shift towards lower proportions of CD123+ pDCs expression and higher numbers and function of the TReg. Univariate analysis disclosed that MS activity was significantly associated with baseline BDCA1+ mDCs below ≤ 0.4% (p < 0.0025). Cox model analysis revealed that baseline BDCA1+ mDCs was the most closely associated factor with MS activity on IFN treatment during the 1-year follow-up (p < 0.01). A better understanding of the rules that govern the TReg-DC relationship will enable scientists to better manage the immune response in MS patients.