Background/Purpose: A Phase IIb randomized controlled study (NCT01753193) was conducted with anifrolumab, a fully human, anti-interferon (IFN)–α receptor (IFNAR1) specific antibody in adults with moderate to severe systemic lupus erythematosus (SLE). Anifrolumab binds to subunit 1 of the IFNAR and inhibits the activity of all type I IFN. A complete blood count (CBC) analysis demonstrated that anifrolumab reversed leukopenia. However, the types of peripheral immune cells affected following treatment have not been reported. To better understand how changes in the immune cell repertoire may be associated with SLE severity, the type I IFN test status (IFN high vs. IFN low), and treatment with anifrolumab, we performed flow cytometry to assess several peripheral blood cell types: dendritic cells (myeloid and plasmacytoid), B cells (naïve, memory, and plasma cells), neutrophils, and T cells (CD4, CD8, naïve, memory, central memory, and effector).

Methods: Patients were randomized to anifrolumab at 300, 1,000 mg, or placebo (PBO) every 4 weeks for 48 weeks. Peripheral blood was collected from a subset of patients (91 total) on days 1 (prior to first dose), 85, 141, 169, 253, 337, and 365. Patients were approximately evenly distributed between the treatment and PBO groups. Baseline absolute immune cell numbers were compared over treatment course in the context of SLEDAI scores, the type I IFN test, and response to therapy. Statistics were calculated using the Student’s t-test, and p-values ≤ 0.05 were considered significant.

Results: At baseline, several blood cell types were lower for patients with SLEDAI ≥10 including naïve B cells, and memory T and B cells. In IFN-high patients, neutrophils, memory T cells, and plasmacytoid dendritic cells (pDCs) were significantly decreased. Anifrolumab led to significant increases in absolute numbers of T-cell subsets in the blood of IFN-high patients. In contrast, no significant changes were observed for IFN-low patients. Observed increases were within normal reference ranges. The alterations did not appear to be secondary to tapering of oral corticosteroids, as these cell types were not significantly different in PBO groups, regardless of tapering. Patients with ≥6-point SLEDAI reductions following anifrolumab demonstrated significant increases in total CD4 and CD8 T cells, and decreases in memory B cells Significant increases in pDCs were also evident. Anifrolumab did not cause significant differences in the other cell types measured.

Conclusion: Memory T cells numbers, among other cell types, were significantly reduced in patients with SLEDAI ≥10 and those classified as IFN-high at baseline suggesting that, for patients with more severe disease, type I IFN may be involved in cell migration into the peripheral tissues from the blood. Consistent with this, we found that neutralization of type I IFN with anifrolumab promoted immigration and/or prevented emigration of potentially pathologic immune cells between the tissues and the blood. These data suggest that some of the effects observed following anifrolumab treatment might be a result of altering the migration patterns of T and other immune cells, which may partially explain its biological activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effects-of-type-i-interferon-inhibition-on-blood-leukocyte-subsets-in-patients-treated-in-a-phase-iib-clinical-study-of-anifrolumab-in-sle/