Background/Purpose: The strategy of inhibiting toll-like receptors (TLR) 7 and 8 is being evaluated in clinical trials in systemic lupus erythematosus (SLE) to assess its glucocorticoid (GC)-sparing potential. To gain understanding of the mechanisms involved in the potential GC-sparing effect of TLR7/8 inhibition (TLR7/8i) in the SLE context, we studied the anti-inflammatory action of compound 2 (CMPD2), a well-characterised dual inhibitor of TLR7/8, using primary cells from SLE patients with low or high type I interferon (IFN) signatures. In parallel, we investigated whether the effects of GCs and TLR7/8i were synergistic.

Methods: Peripheral blood mononuclear cells (PBMCs) from healthy donors and SLE patients were treated with dexamethasone (Dex), CMPD2, or both. Cytokine concentrations and mRNA levels of IFN-stimulated genes (ISGs) and GC signature genes were subsequently measured in TLR7/8-activated PBMCs. The Loewe additivity model was employed to assess whether interactions between GC and TLR7/8i were synergistic. To investigate the effect of CMPD2 on B cell behaviour, we isolated and cultured murine B cells under a range of conditions. 

Results: TLR7/8 stimulation of SLE patient PBMC with resiquimod induced interleukin (IL)-6, IL-12p40 and IL-1beta, and ISG expression, and this was not inhibited by Dex alone. In contrast, CMPD2 significantly reduced cytokine and IFN expression, restored GC sensitivity of these outputs, and increased CD163 (GC signature gene) expression. Loewe analysis demonstrated that this effect was synergistic. CMPD2 had similar effects on healthy PBMC. In SLE samples, IFN status affected these results, with IFN hi patients requiring a higher dose of both TLR7/8 inhibitor and GC to achieve synergistic suppression of inflammation. A synergistic effect of combined TLR7/8i plus GC was also observed in PBMC from SLE patients stimulated with immune complexes, mimicking the activation of these cells in patients. In addition, CMPD2 powerfully inhibited TLR7/8-activation of mouse B cells by 5-fold, and restored GC sensitivity of B cells stimulated with TLR7/8 activation plus T cell co-stimulation and B cell receptor ligation.

Conclusion: TLR7/8i was highly effective in restraining resiquimod or immune complex-triggered inflammatory activation in SLE patient PBMC, and had synergistic effects with GC on cytokines and ISG expression. Endogenous IFN signature status in SLE patients may impact the synergy between GC and TLR7/8i to dampen inflammatory responses. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/in-vitroevidence-for-the-restoration-of-glucocorticoid-sensitivity-by-toll-like-receptor-7-and-8-inhibition-in-systemic-lupus-erythematosus/