Background Biomarkers that stratify rheumatoid arthritis (RA) patients according to responsiveness to existing and emerging therapeutics are urgently required. We previously showed the protein kinase PIM1 to be strikingly up-regulated in CD4⁺ T cells of untreated early RA (eRA) patients compared with disease controls at the RNA level.¹ PIM1 has a recognised role in T cell development and is implicated in the pathogenesis of inflammatory diseases including RA. We hypothesised that, amongst an identifiable subgroup of eRA patients, measurable PIM1 overexpression in CD4⁺ T cells is a targetable early event in pathogenesis.

Methods Peripheral blood (PB) was obtained from consenting, treatment-naïve eRA patients. Western blotting and immunofluorescence were used to determine relative expression and sub-cellular localization of PIM1 in PB CD4⁺ T cells isolated by positive selection, in order to validate our observations at a protein level. A PIM1-specific small molecule inhibitor (TCS PIM-1 1, Tocris) and flow cytometric analysis were used to assess its potential role in the activation and proliferation of CD4⁺ T cells following CD3/CD28-mediated stimulation.

Results Disease-specific PIM1 up-regulation at a protein level was confirmed, with detectable levels seen in the CD4⁺ T cells of eRA patients in contrast to healthy controls. We observed that circulating CD4⁺ T cells of eRA patients have an activated, hyper-proliferative phenotype (significantly higher CD25 and ki67 expression) compared to healthy controls. The use of a PIM1-specific small molecule inhibitor appeared to decrease both the activation (CD25 expression) and proliferation (CFSE dilution) of stimulated ex vivo CD4+ T cells. Preliminary data suggest that this effect may be more pronounced in cells derived from eRA patients compared with controls.

Conclusions Taken together, these data implicate PIM1 as prominent amongst genes whose induction ‘pre-programmes’ CD4⁺ T cells to function aberrantly in disease. The resultant activated and hyper-proliferative phenotype is reminiscent of that we have observed in eRA, and appears to reflect known roles of PIM1 in T cell biology. Future work will include PIM1 knock down in primary CD4⁺ T cells to further determine its biological role.

Reference

1. Pratt AGet al, Ann Rheum Dis71(8):1374–81.