B-cell imaging with zirconium-89 labelled rituximab PET-CT at baseline is associated with therapeutic response 24 weeks after initiation of rituximab treatment in rheumatoid arthritis patients

BACKGROUND B cells are key players in the pathogenesis of rheumatoid arthritis (RA). Although successful in 50-60% of patients with RA, anti-B-cell therapy given as rituximab could be more efficient by identifying potential responders prior to treatment. Positron emission tomography (PET) using radiolabeled rituximab for B-cell imaging might provide the means to fulfil this unmet clinical need. The objective of this study was to investigate the association between biodistribution of zirconium-89 (89Zr)-rituximab on PET-computed tomography (CT) and clinical response in patients with RA. METHODS We included 20 patients with RA who were starting rituximab treatment. At the first intravenous (i.v.) therapeutic dose, patients were also injected with 89Zr-rituximab, followed by PET-CT. European League Against Rheumatism (EULAR) response criteria were applied to determine response at week 24. PET-CT was analyzed visually and quantitatively. Lymph node (LN) biopsies were performed at 0 and 4 weeks to correlate B-cell counts with imaging data. RESULTS PET-positive hand joints (range 1-20) were observed in 18/20 patients. Responders had significantly higher 89Zr-rituximab uptake in PET-positive hand joints than non-responders (median target-to-background (T/B)) ratios (IQR) were 6.2 (4.0-8.8) vs. 3.1 (2.2-3.9), p = 0.02). At T/B ≥4.0, positive and negative predictive values for clinical response were respectively 90% and 75%. Quantitative 89Zr-rituximab hand joint uptake on PET correlated inversely with CD22+ B-cell count in LN tissue at 4 weeks of treatment (r = 0.6, p = 0.05). In addition, the CD22+ B-cell count in LN correlated positively with quantitative LN PET data at baseline, supporting the specificity of B-cell imaging on PET. CONCLUSIONS Non-invasive B-cell imaging by 89Zr-rituximab PET-CT has promising clinical value to select RA responders to rituximab at baseline. 89Zr-rituximab PET-CT may also hold promise for monitoring anti-B-cell therapies in other B-cell driven autoimmune diseases, such as systemic lupus erythematosus and Sjögren's disease.