Anticitrullinated peptide antibody epitope expansion and the HLA DRB1 'shared epitope' are less common in seropositive checkpoint inhibitor-induced inflammatory arthritis than in longstanding rheumatoid arthritis.

BACKGROUND: Immune checkpoint inhibitors (ICI) can potentially cause ICI-inflammatory arthritis (ICI-IA), which often resembles rheumatoid arthritis (RA). In this study, we examined the degree of anticitrullinated peptide antibodies (ACPA) epitope expansion in CCP+ICI-IA and patients with RA. METHODS: We used clinical data and serum from ICI-IA and patients with RA with early disease as well as longstanding disease. A custom, bead-based antigen array was used to identify IgG ACPA reactivities to 18 putative RA-associated citrullinated proteins. Hierarchical clustering software was used to create a heatmap to identify ACPA levels. Additionally, HLA DRB1 typing was performed on ICI-IA patients as well as controls of patients treated with ICI that did not develop ICI-IA (ICI controls). RESULTS: Compared to patients with CCP+RA, patients with CCP+ICI-IA were older (p<0.001), less likely to have positive rheumatoid factor (p<0.001) and had a shorter duration of symptoms (p<0.001). There were less ACPA levels and a lower number of distinct ACPA epitopes in the serum of patients with ICI-IA compared with longstanding patients with RA (p<0.001). Among those tested for HLA DRB1, there were no differences in the frequency of the shared epitope between those with ICI-IA and ICI controls. CONCLUSION: Patients with ICI-IA had lower ACPA titres and targeted fewer ACPA epitopes than longstanding patients with RA, and there were no significant differences in the presence of the shared epitope between those that developed ICI-IA and ICI controls. It remains to be determined if ICI-IA represents an accelerated model of RA pathogenesis with ICI triggering a transition from preclinical to clinical disease.

Comparative safety and effectiveness of TNF inhibitors, IL6 inhibitors and methotrexate for the treatment of immune checkpoint inhibitor-associated arthritis.

OBJECTIVES: To compare the safety and effectiveness of biologic and conventional disease-modifying antirheumatic drugs (DMARDs) for immune checkpoint inhibitor-associated inflammatory arthritis (ICI-IA). METHODS: The retrospective multicentre observational study included patients with a diagnosis of ICI-IA treated with a tumour necrosis factor inhibitor (TNFi), interleukin-6 receptor inhibitor (IL6Ri) and/or methotrexate (MTX); patients with pre-existing autoimmune disease were excluded. The primary outcome was time to cancer progression from ICI initiation; the secondary outcome was time to arthritis control from DMARD initiation. Cox proportional hazard models were used to compare medication groups, adjusting for confounders. RESULTS: 147 patients were included (mean age 60.3 (SD 11.9) years, 66 (45%) women). ICI-IA treatment was TNFi in 33 (22%), IL6Ri 42 (29%) and MTX 72 (49%). After adjustment for time from ICI initiation to DMARD initiation, time to cancer progression was significantly shorter for TNFi compared with MTX (HR 3.27 (95% CI 1.21 to 8.84, p=0.019)) while the result for IL6Ri was HR 2.37 (95% CI 0.94 to 5.98, p=0.055). Time to arthritis control was faster for TNFi compared with MTX (HR 1.91 (95% CI 1.06 to 3.45, p=0.032)) while the result for IL6Ri was HR 1.66 (95% CI 0.93 to 2.97, p=0.089). A subset analysis in patients with melanoma gave similar results for both cancer progression and arthritis control. CONCLUSION: The treatment of ICI-IA with a biologic DMARD is associated with more rapid arthritis control than with MTX, but may be associated with a shorter time to cancer progression.