Pim Kinases as Therapeutic Targets in Early Rheumatoid Arthritis

Objective As well as being an established oncoprotein and therapeutic target in cancer, proviral integration site for Moloney murine leukemia virus 1 (Pim‐1) is implicated in human autoimmunity. This study was undertaken to investigate Pim‐1 and its family members as potential therapeutic targets in early rheumatoid arthritis (RA). Methods A flow cytometry assay for PIM1 transcript measurement in peripheral blood mononuclear cells from patients with early arthritis was validated and applied as a biomarker of Pim‐1 activity at the cellular level. Synovial protein expression was similarly determined by multiplex immunofluorescence in tissue samples from untreated RA patients and non‐RA disease controls. Functional consequences of Pim kinase family manipulation in freshly isolated CD4+ T cells from these individuals were ascertained, along with the impact of Pim inhibition on mice with collagen‐induced arthritis (CIA). Results The percentage of circulating CD4+ T cells positive for PIM1 transcript by flow cytometry proved a faithful surrogate for gene expression and was significantly higher in patients with early RA than in those with other diseases. Pim‐1 protein levels were similarly up‐regulated in synovial CD4+ T cells from patients with early RA. Ex vivo, exposure of T cell receptor–stimulated early RA CD4+ T cells to Pim kinase inhibitors restrained their activation and proliferative capacity. Diminished production of proinflammatory cytokines (interferon‐γ and interleukin‐17) and an expanded CD25 high FoxP3+ Treg cell fraction were also observed in exposed versus unexposed cells. Finally, administration of Pim inhibitors robustly limited arthritis progression and cartilage destruction in CIA. Conclusion Our findings indicate that Pim kinases are plausible therapeutic targets in a readily identifiable subgroup of patients with early RA. Repurposing of Pim inhibitors for this disease should be considered.