Immunogenicity of an adalimumab biosimilar, FKB327, and its reference product in patients with rheumatoid arthritis

Aim This study, FKB327-003, is a phase 3, open-label extension (OLE) study comparing the long-term immunogenicity of an adalimumab biosimilar, FKB327 (F), with the reference product (RP). Methods In the OLE, patients completing 24 weeks of an initial randomized, double-blind (DB) study (Period 1) with clinical response and no safety concerns were rerandomized to F or RP, so that two-thirds of patients remained on the same treatment and one-third switched to the alternate treatment for weeks 24 through 54 (OLE weeks 0-30; Period 2), then all received F through week 100 (OLE week 76; Period 3). Treatment sequences were F-F-F (no switch), RP-F-F and RP-RP-F (single switch), and F-RP-F (double switch). Patients who entered the OLE study were evaluated for immunogenicity across switching sequences. Results The proportion of patients with positive antidrug antibody (ADA) status at the end of Period 1 was 61.7% and 60.0% for F and RP, respectively. The proportion of patients with positive ADA status did not increase throughout Period 1, and was similar for F and RP at all time points. At the end of Period 3, the proportion of patients with positive ADA status was lower in all treatment sequences, at 51.1%, 54.4%, 48.1%, and 42.5% for F-F-F, F-RP-F, RP-F-F, and RP-RP-F, respectively. Conclusion The RP and F showed comparable immunogenicity characteristics after long-term administration. Development of ADAs with the RP and F was similar, and was not impacted by switching and double switching between F and RP treatment.