SM03, an anti-human CD22 monoclonal antibody, for active rheumatoid arthritis: a phase II, randomized, double-blind, placebo-controlled study

SM03, a novel chimaeric mAb specific to B cell-restricted antigen CD22, has been developed to treat RA and other B-cell-related diseases. This 24-week phase II randomized, double-blind, multi-dose, placebo-controlled study aimed to evaluate the efficacy and safety of SM03 in moderately-to-severely active RA patients in China.One hundred and fifty-six patients on background MTX were randomized in a 1:1:1 ratio to receive a cumulative dose of 3600 mg (high dose, 600 mg × 6 infusions at weeks 0, 2, 4, 12, 14 and 16) or 2400 mg SM03 (low dose, 600 mg × 4 infusions at weeks 0, 2, 12 and 14) or the placebo. The primary outcome was the 24-week ACR 20% improvement criteria (ACR20) response rate. Safety was also assessed.The 24-week ACR20 response rate was significantly higher with high- (65.3%, P = 0.002) and low-dose SM03 (56.9%, P = 0.024) than with placebo (34.0%), but comparable between the high- and low-dose group. The rate of adverse events was not statistically different among the high-dose group (35.3%), the low-dose group (51.9%) and the placebo group (34.6%). Thirteen (12.6%) patients receiving SM03 reported treatment-emergent infections, including 3.9% patients in the high-dose group. No patients reported severe treatment-emergent infections or malignancies.In active RA Chinese patients receiving background MTX, SM03 at a cumulative dose of both 2400 mg and 3600 mg is efficacious and well-tolerated throughout the 24 weeks of treatment. Moreover, SM03 has demonstrated a good safety profile.ClinicalTrials.gov, https://clinicaltrials.gov, NCT04192617.