Background T and B cell-driven immunity is critically involved in immunopathology of pSS. Recently we demonstrated synergistic T and B-cell activation upon T cell triggering and TLR7/9-driven B cell activation in pSS patients, accompanied by synergistic induction of immunoglobulins and IFN-γ- and IL-17-producing T cells¹. In addition, TLR7/9-expressing activated pDCs associated with increased type I IFNs and IFN-inducible genes are increased pSS patients. Several studies have shown that the DMARDs leflunomide and hydroxycholoroquine inhibit immune activation in pSS but only show moderate efficacy. However, LEF and HCQ target different pathways with overlapping, but also potentially additive mechanisms, where LEF primarily targets T and B cells and HCQ TLR7/9-driven B cell and pDC activation.

Objectives To assess the additive effects of LEF and HCQ on CD4 T- and B-cell activation and production of interferons IFN-α and IFN-γ, Tfh-related cytokine CXCL13, as well as IgG and IgM in vitro employing SEB/TLR9-triggered PBMC.

Methods PBMCs of healthy individuals (n=9) and of pSS patients (n=8) were cultured with antigen (SEB), TLR9 and their combination, in presence or absence of LEF, HCQ and their combination in clinical relevant concentrations. Proliferation of T and B cells and release of IFN-α, IFN-γ, CXCL13, IgG and IgM were measured.

Results In line with robust T and B cell activation, IFN-γ, IFNα, CXCL13, IgG and IgM production was achieved by a combination of SEB and TLR9 (all at least p<0.001). LEF dose dependently inhibited B and T cell proliferation, Interferon, CXCL13 and immunoglobulin production. HCQ dose dependently inhibited B cell proliferation, IFN-α, CXCL13, and immunoglobulin production. T cell proliferation and IFN-γ production were inhibited by HCQ only at higher concentrations. At several suboptimal concentrations LEF and HCQ additively inhibited T cell proliferation both in healthy individuals and in pSS patients. (Figure 1). Significant additive effects were seen for all outcome measures except IFN-α. Since IFNa was already robustly inhibited by HCQ alone (eg.for pSS 90% at 3.3 μM, p<0.001), only trends towards additive effects were observed.

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Conclusions LEF and HCQ robustly inhibited proliferation of T and B cells, cytokine production and immunoglobulin production with clear additive efficacy in both healthy individuals as in pSS patients. These data support the potential surplus value of combination therapy with LEF and HCQ for patients with pSS.

References

1. Bikker et al. Interleukin-7 and Toll-Like Receptor 7 induce synergistic B cell and T cell activation. PLoS ONE 9(4): e94756.

References

Disclosure of Interest None declared