Background/Purpose: Rheumatoid arthritis (RA)
is an autoimmune disease driven by chronic inflammation, upheld by sustained
recruitment and infiltration of leucocytes, especially macrophages. Mavrilimumab
is a fully human monoclonal antibody targeting the granulocyte-macrophage
colony-stimulating factor receptor-α. Mavrilimumab suppresses
the effect of granulocytes and monocytes/macrophages, in RA. Serologic
biomarkers can also be used to assess efficacy. The serum neo-epitope
biomarker, citrullinated and MMP-degraded vimentin (VICM), is a marker of
inflammation. We investigated whether the biomarker VICM is biomarker of
activated macrophages, and whether mavrilimumab modulates serum concentrations
of VICM in RA patients.

Methods:
In-
vitro experiments
were carried out on peripheral mononuclear cells (PBMCs). Isolated monocytes
were differentiated by incubating with M-CSF for 5 days prior to any treatment,
and were cultured as a monolayer on plastic. Cells were treated either with lipopolysaccharide
(LPS), LPS + calcium chloride (CaCl), or only CaCl as control. Treatment of LPS
was 100ng/ml, and CaCl was 0.22µg/mL. Conditioned medium were collected at Days
1, 5, and 8, and stored for ELISA analysis. The in-vitro studies was
repeated 4 times and analyzed by Kruskal-Wallis analysis. Serum samples were from
the Phase IIb RCT (NCT01706926) of RA patients (n=140) receiving either placebo
or 150-mg every-other-week dosages of mavri, in combination with methotrexate,
for 169 days. VICM was measured at Days 0 and 169. Spearman’s correlations were
carried out to investigate the association between disease activity (DAS28 and
mTSS) and serum concentrations of VICM, and changes in VICM concentrations after
mavrilimumab treatment compared to placebo.

Results:
The in-vitro
data indicated that the release of VICM was significantly greater in
supernatants from activated macrophages (LPS+CaCl treated) at Days 5
and 8 (p<0.01), compared with controls (Fig. 1A), indicating that VICM is a
biomarker of activated macrophages. Mavrilimumab significantly inhibited VICM
serum concentrations (30%) in patients receiving 150 mg every other week compared
with placebo at Day 169 (p<0.05) (Fig. 1B), as well as suppressed the
presence of CD14 positives cells by approximately 12%. In addition, VICM
correlated significantly with DAS28 (r=0.13, p<0.05), mTSS (r=0.15, p<0.01)
and CRP (r=0.26, p<0.01) at baseline. Patients with mTSS>23.5 had
significantly elevated VICM serum concentrations compared with patients with
mTSS<23.5 at baseline (p<0.01).

Conclusion:
The data indicate
that VICM is biomarker of activated macrophages by revealing i) the direct
release of VICM from activated macrophages in vitro, and ii) a
significant suppression upon treatment with the mavrilimumab. These data support
further development of mavrilimumab and other drugs
targeting macrophages in RA.