Circulating Cytokines and Cytokine Receptors in Infliximab Treatment Failure Due to TNF-α Independent Crohn Disease

The inflammatory response at infliximab (IFX) treatment failure due to tumor necrosis factor (TNF)-α-independent Crohn disease activity is unknown. This is an exploratory, hypothesis-generating study based on samples collected in a clinical trial among patients failing conventional IFX dosages and treated with an intensified IFX regimen for 12 weeks. Patients with clinical response at week 12, as defined by a reduction of Crohn disease activity index by ≥70, were considered to suffer from nonimmune pharmacokinetic (PK) treatment failure (n = 18), and nonresponders had a presumed pharmacodynamic (PD) failure due to non-TNF-driven disease (n = 8). Patients failing IFX due to functional anti-IFX antibodies (n = 2) were excluded. The study population also comprised a group of 12 patients in long-term remission on IFX. A functional cell-based reporter gene assay was applied to measure IFX and anti-IFX antibodies. Circulating cytokines and cytokine receptors were assessed by enzyme-linked immunosorbent assay: granulocyte-macrophage colony-stimulating factor, interferon-γ, interleukin (IL)-1α, IL-1β, IL-1Ra, IL-6, IL-10, IL-12p70, soluble TNF receptor (sTNF-R) 1, sTNF-R2, IL-17A, and monocyte chemotactic protein 1. The IFX levels were similar between patients with IFX failure caused by nonimmune PK or PD at treatment failure (median 1.4 vs 2.4 μg/mL; P = 0.52), during treatment intensification (8.1 vs 5.6; P = 0.85), and after 12 weeks (8.8 vs 7.7; P = 0.93), congruent with nonresponders failing IFX due to predominantly TNF-α-independent signaling pathways in their disease. Cytokine and cytokine receptor levels were comparable between patients with nonimmune PK failure and PD failure at time of manifestation of IFX failure, but with higher IL-6 and sTNF-R2 levels among IFX treatment failures as compared with patients in remission (IL-6 median 3.6 vs <3.1 pg/mL; P = 0.03; sTNF-R2 3207 vs 2547 pg/mL; P = 0.01). IL-6 and sTNF-R2 were lower after 12 weeks in nonimmune PK failures than in PD failures (<3.1 vs 4.0; P = 0.02; 3209 vs 4740; P = 0.04, respectively), and were measured at levels comparable with patients in remission. Further, trends of decreased IL-6 and sTNF-R2 levels among nonimmune PK failures during IFX intensification (P < 0.05 and P = 0.12) were observed. These observations indicate that IL-6 and sTNF-R2 are of potential relevance in driving the inflammatory response in IFX refractory Crohn disease caused by TNF-α-independent disease activity.