Anti-BDCA2 monoclonal antibody inhibits plasmacytoid dendritic cell activation through Fc-dependent and Fc-independent mechanisms.
Bottom Line: These effects were confirmed in vivo using a single injection of 24F4A in cynomolgus monkeys. 24F4A also inhibited pDC activation by SLE-associated immune complexes (IC).In addition to the inhibitory effect of 24F4A through engagement of BDCA2, the Fc region of 24F4A was critical for potent inhibition of IC-induced IFN-I production through internalization of CD32a.This study highlights the novel therapeutic potential of an effector-competent anti-BDCA2 mAb that demonstrates a dual mechanism to dampen pDC responses for enhanced clinical efficacy in SLE.
Affiliation: Immunology Research, Biogen Idec, Cambridge, MA, USA.Show MeSH
Related in: MedlinePlus
Mentions: Nine cynomolgus monkeys were divided into three groups that received a single intravenous (IV) injection of vehicle (sodium citrate buffer), 1 mg/kg 24F4A, or 10 mg/kg 24F4A. Animals were bled at various time points before and after 24F4A administration. First, we addressed whether administration of 24F4A leads to BDCA2 internalization in vivo, using flow cytometry. Because the 2D6 anti-BDCA2 clone does not cross-react with cynomolgus BDCA2 (Supplementary Table S1), a two-step approach was used to detect internalization of BDCA2 on cynomolgus monkey pDCs. Unoccupied surface BDCA2 was detected on pDCs in whole blood using fluorescently labeled 24F4A (direct method), while surface BDCA2 bound to 24F4A was detected using a fluorescently labeled anti-human IgG1 (indirect method). The lack of unoccupied BDCA2 (direct method) coupled with loss of detectable 24F4A (indirect method) indicated BDCA2 internalization. Results from a representative animal from both the vehicle-treated group and the 1 mg/kg 24F4A-treated group are shown in Fig3A and B. Prior to vehicle and 24F4A administration, the baseline surface expression of BDCA2 was assessed for each cynomolgus monkey using the direct method (Fig3A-i and B-i, dotted red line). In addition, maximal binding of BDCA2 to 24F4A was established prior to 24F4A administration by “spiking” whole blood with saturating amounts of 24F4A in vitro and measuring bound 24F4A by the indirect method (Fig3A-ii and B-ii, solid red line). Within 6 h of 24F4A administration at 1 mg/kg, BDCA2 expression on the surface of pDCs decreased to almost undetectable levels (Fig3B-iii, dotted red line) but not in the vehicle-treated group (Fig3A-iii, dotted red line). In addition, the levels of bound 24F4A (Fig3B-iv, solid black line) were indistinguishable from the vehicle-treated group (Fig3A-iv, solid black line). The lack of available BDCA2 receptor together with the lack of detectable 24F4A on the surface of pDCs indicated internalization of BDCA2. Over 95% of surface BDCA2 was internalized in all animals within 6 h of IV treatment (1 and 10 mg/kg) (Fig3C). Internalization of BDCA2 correlated with circulating levels of 24F4A, establishing a pharmacokinetic/pharmacodynamic (PK/PD) relationship in vivo. When 24F4A serum concentrations decreased to a range of 0.1–0.03 μg/ml, the level of BDCA2 recovered to > 70% of the baseline level (Fig3D-i–iii), establishing an EC50 of 0.133 μg/ml (Fig3D-iv).
Affiliation: Immunology Research, Biogen Idec, Cambridge, MA, USA.