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

Abstract 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.

Patent protection of adalimumab is approaching its expiration date, which will allow biosimilars to be marketed and made available to patients. Biosimilars are defined as biological products that are highly similar to, and have no clinically meaningful differences

from, the existing US Food and Drug Administration-and European
Medicines Agency-approved reference products (RPs). 3 FKB327 (adalimumab) was developed as a biosimilar product of adalimumab. In a randomized, double-blind (DB) study conducted to compare the pharmacokinetics (PK), safety, tolerability, and immunogenicity of FKB327 with both European Union-approved and USlicensed RP in healthy adult subjects, FKB327 demonstrated similar PK, safety, tolerability, and immunogenicity to EU-and US-RP, following a single subcutaneous dose of FKB327 or the RP. 4 Biologic therapies have unique structures that can induce immune responses, which may lead to the development of therapy-limiting adverse events (AEs). 5 Antidrug antibodies (ADAs) have been implicated as contributors to increased risk for AEs and treatment failure in patients who are treated with biologics. 6 Data suggest that most patients treated with natalizumab and adalimumab develop ADAs, with the majority developing within the first 6 months of treatment. 7 Notably, the presence of ADAs alone does not guarantee an impaired clinical response. Therapeutic levels of active drug may still be present as long as the ADA levels are not sufficient to bind all therapeutic antibodies, as has been demonstrated in patients treated with natalizumab who exhibit an ADA response. 8 The long-term safety and immunogenicity of FKB327 following repeated dosing in patients with moderate-to-severe RA are currently unknown.
To begin answering these questions, a DB phase 3 study and a long-term open-label extension (OLE) study were designed to compare the safety, efficacy, and immunogenicity of FKB327 with the US-approved RP in patients with RA. Preliminary results through 54 weeks of treatment have been previously published. 9 Therefore, the aim of the current study was to compare the long-term immunogenicity and safety of FKB327 with the RP in patients with RA out to 104 weeks, including patients who single-and double-switched treatments between FKB327 and the RP. The immunogenicity of the RP and FKB327 was examined across the DB and long-term OLE studies. Additional objectives included the following: (a) comparing the proportion of patients developing ADAs with long-term treatment; (b) comparing the PK of long-term treatment; and (c) evaluating changes in PK and immunogenicity in patients who were single-or double-switched between the RP and FKB327.

| Study design
The initial part of the study design of the DB and the OLE has been previously described. 9 The FKB327-002 DB study (National or the RP from week 0 to 30 (Period 2; week 24 to 54 from start of the DB study), with two-thirds of patients remaining on the same treatment as in the DB study and one-third of patients switching to the alternate treatment ( Figure 1)

| Patients
Inclusion and exclusion criteria have been previously described. 9 Briefly, patients were aged ≥18 years with moderate-to-severe, inactive, inadequately controlled RA despite MTX management for ≥3 months. At baseline screening for Period 1, patients had ≥6 tender joint count and ≥6 swollen joint count at screening and baseline, and C-reactive protein ≥10 mg/L. Patients received MTX (10-

| Safety evaluations
Safety was assessed via documentation of AEs, which were evaluated for severity and relationship to study drug. Treatment-emergent AEs

| Statistical analyses
Summary statistics, including the number of patients, mean, standard deviation, median, minimum and maximum, were presented for all continuous variables. For categorical variables, per category, the absolute counts (n) and percentages of patients with data, and if appropriate, the number of patients with missing data, were presented.
In general, missing data were not imputed.
The primary PK analysis was comprised of 2 mixed models for repeated measures fitted to the log-transformed serum concentrations at weeks 12, 24, and 30 (during the randomized treatment period), with patients included as a random effect and the following as fixed effects: (a) week, treatment group, and week × treatment group; and (b) week, treatment sequence, and week × treatment sequence.
Due to the potential formation of ADAs, the primary analysis was repeated for the overall treatment period with ADA titer results at the last sampling time point included as an additional covariate, along with an ADA titer × treatment sequence interaction term to test for differences in the effect of ADA activity on the PK data.
All analysis datasets and output were produced by the Biostatistics Department of Quanticate UK Limited, using the SAS ® system Version 9.3 (Unicode Support).

| Baseline demographics
In the DB study (Period 1), 730 patients were initially enrolled; however, 2 patients dropped out of the study prior to randomization and receipt of study drug. Therefore, 366 patients were randomized to FKB327 and

| Immunogenicity comparison between FKB327 and RP
At the beginning of the OLE study (week 0; Period 2), the propor-

| Safety
Overall, 208 patients (32.2%) experienced a TEAE that was considered to be related to the study drug ( whereas the incidence of treatment-emergent serious AEs (TESAEs) was the same for both groups (0.091 events per patient-year).

| The impact of switching on safety
A similar incidence of TEAEs was reported in the RP-RP vs the RP-F sequence (54.9% vs 54.6%) but a lower incidence of TEAEs was re-  (Table 3).
By contrast, fewer patients in the F-RP-F (5.0%) and RP-RP-F (4.7%) sequences reported TEAEs that resulted in treatment interruption. Note: Percentages are based on the number of patients in the Safety Analysis Set. N for FKB327 includes patients who were randomized to FKB327 in Period 1 and patients who were randomized to the RP and then switched to FKB327 after week 30. Exposure-adjusted IRs are calculated by dividing the number of events within a given PT or SOC for each treatment by the total number of patient-years for each treatment. TEAEs are defined as AEs that started or increased in severity after the first study medication administration. Each patient is counted only once within each SOC and PT under the "n (%)" columns but will be counted more than once in the "Events (IR)" columns if more than 1 event within a given SOC or PT occurs. TEAEs were coded using MedDRA Version 17.1.

| The impact of switching on pharmacokinetics
Mean serum trough drug concentrations at week 0 (week 24 overall; start of Period 2) were higher among patients receiving FKB327 in Period 1 (F-F, 6500 ng/mL; F-RP, 6000 ng/mL; RP-F, 5170 ng/mL; RP-RP, 5720 ng/mL). In all treatment sequences, the interindividual variability was high; however, the mean serum trough drug concen-  Note: Percentages are based on the number of patients in the Safety Analysis Set who entered Period 3. Death was defined as the fatal outcome of an (S)AE. SAEs were defined as AEs that were fatal, life-threatening, or required or prolonged inpatient treatment; resulted in persistent or significant disability or incapacity; were a congenital anomaly or birth defect; or were medically important events that may have jeopardized the patient. TEAEs were defined as AEs that started or increased in severity after the first study medication administration. Severe TEAEs were defined as SAEs occurring or increasing in severity after the first dose of study medication was taken. Related TEAEs were defined as TEAEs for which the relationship to study medication was recorded as "Related," "Possibly related," or missing. AEs were counted under the treatment arm and period in which the event started. quartile), and high (≥upper quartile; 17 600) ADA titer from week 4 through week 104 of the entire study ( Figure 3).
To evaluate PK in patients who switched treatments, ratios of geometric least squares means at all time points in Period 2 were estimated. Patients who received the RP in Period 1 but switched to FKB327 were estimated to have up to 11% higher drug exposure than those who continued receiving the RP during Period 2.
Patients who received FKB327 in Period 1 but switched to the RP were estimated to have a 20%-29% lower drug exposure than those who continued receiving the RP during Period 2 ( Figure 3).

| D ISCUSS I ON
This was the final analysis of the 2-year, combined DB and OLE studies designed to compare the safety, efficacy, and immunogenicity of FKB327 with the RP in patients with moderate-to-severe RA, for which the preliminary analysis of data through 54 weeks has been previously published. 9 The current analysis focused on immunogenicity over longterm use (out to 2 years) to support the biosimilarity of FKB327 to the RP and to assess the impact of switching on safety and PK. Assessing immunogenicity is important, because biologic therapies have unique structures that can induce immune responses, which may lead to the development of therapy-limiting AEs. 5 Furthermore, ADAs have been implicated as contributors to increased risk for AEs and treatment failure in patients who are treated with biologics. 6 ADA formation can lead to diminished treatment efficacy via different mechanisms. 6 Neutralizing ADAs can block the binding of the therapeutic agent to its target, which reduces treatment efficacy. In addition, both neutralizing and non-neutralizing ADAs can bind to the therapeutic agent, which can result in the formation of immune complexes that are subsequently cleared from the circulation, resulting in reduced drug half-life. In a study evaluating adalimumab-specific ADAs, at least 98% had neutralizing capabilities. 10 Dimer-sized immune complexes between ADAs and adalimumab have been detected in patients 2 weeks postinjection, suggesting that these immune complexes are not cleared rapidly from the circulation.
Not all patients will respond favorably to biological treatment; some do not exhibit any response, whereas others initially exhibit a response but demonstrate a loss of response over time despite administration of higher doses of the drug and/or more frequent drug administration. 11 ADA formation contributes to this observed loss of response through decreased serum levels of biologicals via increased clearance and inactivation, which ultimately contributes to premature therapy termination. 12 Therefore, some patients exhibit subtherapeutic levels of drugs, which decreases efficacy. By identifying these patients via monitoring of ADA formation and drug serum trough levels, appropriate treatment guidance can be provided. The ADA assay used in the current study includes an acid dissociation step to improve drug tolerance for multiple-dosing studies.
In the validation study, we confirmed an assay sensitivity of 9. Regarding the decrease in the proportion of patients testing positive for ADAs throughout the study, it has been shown that patients treated with natalizumab or adalimumab exhibited decreasing ADA levels over time, which was suggestive of immune tolerance induction. 7 One study reported approximately one-third of adalimumab-treated patients became tolerant over the treatment period. 6 The current results support findings from a review of 53 switching studies, which demonstrated no unexpected safety findings post-switch. 19 The current results also extend the findings of the preliminary analysis, which included data through the first 54 weeks, 9 with no demonstrated effect of switching between FKB327 and RP in terms of safety or immunogenicity. This is supported by findings from the current, final analysis, which extended to 2 years of treat-  23 These findings support our current data, improving our knowledge on long-term safety and immunogenicity of the adalimumab biosimilar FKB327, demonstrating similar safety and immunogenicity compared with the RP, with a 6-month switching interval and 2 years of follow-up.
By filling the information gap related to long-term immunogenicity, safety, and PK, these data will help inform clinician decision making regarding switching from the RP to FKB327, and may result in increased patient access to adalimumab treatment.

ACK N OWLED G M ENTS
We would like to thank the patients who participated in the clinical studies.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.