Therapeutic Controversies

Switching tumor necrosis factor inhibitors in the treatment of axial spondyloarthritis

OBJECTIVE

To assess the impact of switching tumor necrosis factor (TNF)-alpha inhibitors on patients with axial spondyloarthritis (axSpA).

METHODS

PubMed literature searches were conducted using combinations of search terms including ankylosing spondylitis, spondyloarthropathy, spondyloarthritis, switch/switching, drug survival, and TNF/tumor necrosis factor to identify published articles with data on outcomes related to switching biologic therapies in patients with axSpA.

RESULTS

Of the 134 studies screened, 21 were identified as reporting data on switching TNF inhibitors in patients carrying a diagnosis of axSpA or ankylosing spondylitis. The most common reasons for switching from the first TNF inhibitor were lack of efficacy (14-68%), loss of efficacy (13-61%), and adverse events/poor tolerability (13-57%). Switching TNF inhibitors was beneficial for a substantial proportion of patients with axSpA who failed to respond to initial or even second TNF inhibitor therapy and adverse effects were not enhanced. Drug survival rates were generally lower for the second (47-72% at 2 years) or third TNF inhibitor (49% at 2 years) than for the first TNF inhibitor (58-75% at 2 years). Predictors of responses in TNF-naïve patients included HLA-B27 positivity, absence of enthesitis, age ≤40 years, elevated C-reactive protein level, good functional status, and shorter disease duration. Predictors of drug survival included male sex and peripheral arthritis. Common characteristics of patients who switched TNF inhibitors included female sex, older age, more severe disease, greater symptom burden, higher erythrocyte sedimentation rate, complete ankyloses, and enthesitis.

CONCLUSION

When the first or even the second TNF inhibitor fails, switching to an alternate one is not an unreasonable clinical therapeutic decision.

HLA-B27 misfolding and ankylosing spondylitis

Understanding how HLA-B27 contributes to the pathogenesis of spondyloarthritis continues to be an important goal. Current efforts are aimed largely on three areas of investigation; peptide presentation to CD8T cells, abnormal forms of the HLA-B27 heavy chain and their recognition by leukocyte immunoglobulin-like receptors on immune effector cells, and HLA-B27 heavy chain misfolding and intrinsic biological effects on affected cells. In this chapter we review our current understanding of the causes and consequences of HLA-B27 misfolding, which can be defined biochemically as a propensity to oligomerize and form complexes in the endoplasmic reticulum (ER) with the chaperone BiP (HSPA5/GRP78). HLA-B27 misfolding is linked to an unusual combination of polymorphisms that identify this allele, and cause the heavy chain to fold and load peptides inefficiently. Misfolding can result in ER-associated degradation (ERAD) of heavy chains, which is mediated in part by the E3 ubiquitin ligase HRD1 (SYVN1), and the ubiquitin conjugating enzyme UBE2JL. Upregulation of HLA-B27 and accumulation of misfolded heavy chains can activate ER stress signaling pathways that orchestrate the unfolded protein response. In transgenic rats where HLA-B27 is overexpressed, UPR activation is prominent. However, it is specific for heavy chain misfolding, since overexpression of HLA-B7, an allele that does not misfold, fails to generate ER stress. UPR activation has been linked to cytokine dysregulation, promoting lL-23, IFNβ, and lL-1α production, and may activate the IL-23/IL-17 axis in these rats. IL-1α and IFNβ are pro- and anti-osteoclastogenic cytokines, respectively, that modulate osteoclast development in HLA-B27-expressing transgenic rat monocytes. Translational studies of patient derived cells expressing HLA-B27 at physiologic levels have provided evidence that ER stress and UPR activation can occur in peripheral blood, but this has not been reported to date in isolated macrophages. Inflamed gastrointestinal tissue reveals evidence for HLA-B27 misfolding, ERAD, and autophagy, without acute UPR activation. A more complete picture of conditions that impact HLA-B27 folding and misfolding, the full spectrum and time course of consequences of ER stress, and critical cell types involved is needed to understand the role of HLA-B27 misfolding in spondyloarthritis pathogenesis.