Discussion
Morbidity in patients with SLE results from the combined deleterious effects of disease activity and treatment. Most patients with SLE require combination treatment and many of the agents currently recommended have either multiple, or non-specific, mechanisms of action, making AEs both more likely and less predictable.22 The potential introduction of a new immune-targeting drug as an add-on therapy for SLE requires comprehensive assessment of safety for its risk–benefit, and therefore its place in the therapeutic armamentarium, to be determined. Anifrolumab, which specifically targets the common receptor for all type I IFN signalling proteins, has been shown to suppress IFN gene signatures and deliver efficacy in active SLE across three phase II and III trials.18–20 Although safety data for each of these studies have been reported separately, the integrated safety analysis reported here allows for assessment of the rate and severity of both common and less common AEs.
These analyses were focused on reporting of the safety in the anifrolumab 300 mg group because this is the recommended dose for anifrolumab. The anifrolumab 150 mg dose in TULIP-1 had suboptimal efficacy and pharmacokinetics, and the 1000 mg dose in MUSE was associated with a higher rate of HZ.18 19 These analyses of pooled data indicate that anifrolumab 300 mg was generally well tolerated by patients with SLE. The most commonly reported AEs were mild to moderate in severity and included nasopharyngitis, upper respiratory tract infection, urinary tract infection, bronchitis and infusion-related reactions. AEs leading to discontinuation of investigational product were infrequent and were balanced between the groups. During the three 52-week studies, there were three deaths among patients treated with anifrolumab (two with 300 mg and one with anifrolumab 1000 mg) and one death in a patient receiving placebo. There was a lower reported rate of SAEs in patients receiving anifrolumab versus placebo. Lupus affects multiple organs, and anifrolumab has demonstrated efficacy for disease activity and reduction of flares,18–20 which may explain the lower rate of SAEs in the anifrolumab group of these trials. Among SAEs, infections including pneumonia were most common and were similar between anifrolumab (4.8%) and placebo (5.6%) groups. The rate of worsening of SLE as an SAE was greater in patients receiving placebo (3.0% vs 1.5% with anifrolumab), concordant with the numerically lower flare rates observed with anifrolumab 300 mg versus placebo in all three studies.18–20
Compared with patients receiving placebo, more patients in the anifrolumab 300 mg group experienced an AE in the System Organ Class of infections and infestations (69.7% vs 55.4%). The percentages of infections in treatment and placebo groups in patients with SLE were each comparable with those reported in clinical trials of the monoclonal antibodies to B cell activating factor tabalumab and belimumab and for epratuzumab, a monoclonal antibody to CD22.23–25 Most infections in both anifrolumab and placebo groups were mild or moderate in intensity, were not classified as SAEs and did not result in discontinuation of investigational product. The difference in rates was driven by differences in the incidence rates of mild and moderate respiratory tract infections (excluding pneumonia) and by HZ. Overall, the rate of serious infections was low with anifrolumab and similar to that in the placebo group.
There was an increased risk of HZ with anifrolumab versus placebo (6.1% and 1.3%, respectively; EAIR risk difference 5.4). However, HZ event characteristics, including duration and severity, were similar between treatment groups. Most HZ events were mild or moderate, cutaneous and resolved with antiviral treatment and without treatment discontinuation. One patient had an SAE of transverse myelitis during the MUSE study.18 The patient had a positive PCR test for HZ in spinal fluid, there were no cutaneous manifestations of HZ, and they responded following treatment with both antivirals and glucocorticoids. We cannot determine whether the underlying cause was HZ or a manifestation of SLE. This transverse myelitis case was not considered by investigators to be related to treatment, and the patient made a full recovery with no observed long-term disability. This analysis did not reveal any patient or treatment characteristics predictive of HZ reactivation, although these were numerically more common in patients receiving immunosuppressants as part of SOC therapy. As patients with SLE are known to have an increased baseline risk of HZ reactivation, it may be valuable to evaluate strategies to vaccinate this patient population prior to receipt of immunosuppressive therapies in both the clinic and clinical trial setting.26 This strategy is supported by recently updated EULAR guidelines on vaccination in autoimmune inflammatory rheumatic diseases, which recommend considering HZ vaccination in patients considered high risk.27
Infusion-related reactions were uncommon, although the rate of AEs reported as hypersensitivity and infusion-related reactions was greater with anifrolumab-treated patients (2.6% and 9.4%, respectively) than placebo (0.6% and 7.1%, respectively); most occurred early and were mild or moderate in intensity. Hypersensitivity SAE was observed in one patient receiving anifrolumab 300 mg, and one patient receiving anifrolumab 150 mg had an anaphylactic reaction. The rates of hypersensitivity/infusion-related reactions are comparable with those reported in patients with SLE in 52-week phase III trials of tabalumab and belimumab.24 25
Exposure to anifrolumab, a fully humanised monoclonal antibody, administered as an intavenous infusion to patients with SLE was minimally immunogenic. Among patients in whom ADAs were detected, there was no clinically relevant impact on pharmacokinetics, pharmacodynamics or safety. The subgroups of patients positive for ADA were small; thus, these results should be interpreted with caution. The selection of low assay cut-points also made detection of false positive results possible. The number, temporal response, titre and all other categories of ADA assessments conducted never favoured anifrolumab (as compared with placebo) supporting the conclusion that anifrolumab is very poorly immunogenic when administered intravenously to patients with SLE.
In patients treated with anifrolumab, flares of SLE as AEs were less common, despite protocol-determined glucocorticoid tapering in all three studies. The harmful effects of glucocorticoids, both in general and in the setting of SLE, are well known and include increased risk of irreversible organ damage and susceptibility to infection.28 29 Furthermore, fewer patients had Cushingoid features at week 52 compared with baseline across all treatment groups, with notable decreases with anifrolumab versus placebo. Therefore, the sustained glucocorticoid reduction achieved with anifrolumab represents a potential safety benefit.
The safety profile in these trials of anifrolumab is broadly comparable with that reported in phase III programmes of other treatments for patients with SLE.23–25 The patient populations selected in the MUSE, TULIP-1 and TULIP-2 trials were intended to reflect the real-world population of patients with moderate to severe SLE despite SOC therapy; however, certain exclusion criteria were necessary to minimise confounding in safety evaluations. Therefore, the future reporting of real-world safety experience with anifrolumab treatment in patients with SLE will be important.
These analyses have several limitations, including a duration of only 1 year. However, 218 patients who completed MUSE were enrolled in a long-term extension study, 139 of who completed 3 years of treatment. This long-term observational study reported that the rate and patterns of SAEs and AEs of special interest over the 3 years were consistent with those reported for 1 year of treatment in the primary MUSE study.30 A further placebo-controlled long-term observational extension study of patients enrolled in the TULIP-1 and TULIP-2 trials is ongoing and will provide additional long-term safety data. Another limitation was that patients with severe renal lupus and neuropsychiatric disorders were excluded from the TULIP-1, TULIP-2 and MUSE trials, and therefore, the efficacy and safety of anifrolumab in these patient subgroups still needs to be studied. A phase II study of anifrolumab in patients with lupus nephritis is ongoing.
The decision to use any medication requires a patient-focused shared decision-making process balancing benefit and risk. The current analysis shows that anifrolumab 300 mg intravenous monthly had an acceptable safety profile during 52 weeks of treatment in adult patients who had moderate to severe SLE despite SOC therapy. Taken together with the previously reported efficacy based on global disease activity improvement, glucocorticoid dosage tapering and SLE flare reduction,18–20 anifrolumab has a positive benefit–risk profile and is a potential new treatment option for a disease with few therapeutic options.