Immunoglobulin G (IgG) is transcytosed across intestinal epithelial cells of suckling mammals by the neonatal Fc receptor (FcRn); however, the contribution of FcRn vs. FcRn-independent uptake to serum IgG levels had not been determined in either rat pups or human (h)FcRn-expressing mice (Tg276 and Tg32). In isoflurane-anesthetized rodents, serum levels were determined after regional intestinal delivery of human monoclonal antibodies (hIgG) with either wild-type (WT) Fc sequences or variants engineered for different FcRn binding affinities. Detection of full-length hIgG was by immunoassay; intestinal hFcRn and hIgG localization was by immunocytochemistry. High (μg/ml) serum levels of hIgG were detected after proximal intestinal delivery (0.1-10 mg/kg) in 2-wk-old rats. Human FcRn was visualized in epithelial cells of Tg276 mice, but low serum hIgG levels (<10 ng/ml) were obtained. In rat pups, intraintestinal hIgG1 WT administration resulted in dose-related and saturable uptake, whereas uptake of a low FcRn-binding affinity variant was nonsaturable. There were no differences in hIgG levels from systemic and hepatic portal vein serum samples, and intense hIgG immunostaining was noted in villi enterocytes and within lymphatic lacteal-like vessels. This study demonstrated that FcRn-mediated uptake in rat pups accounted for ~80% of serum hIgG levels and that IgG enters the circulation via the lymph and not the hepatic portal vein. The remaining uptake though the immature intestine is nonreceptor mediated. Intestinal epithelial cell hFcRn expression occurred in Tg276 mice, but receptor-mediated transport of IgG was not observed. The suckling rat pup intestine is a mechanistic model of FcRn-IgG-mediated transcytosis.
Although much speculation has surrounded intestinally expressed FcRn as a means for systemic uptake of orally administered immunoglobulin G (IgG), this has not been validated in translational models beyond neonates or in FcRn‐expressing cells in vitro. Recently, IgG1 intestinal infusion acutely in anesthetized cynomolgus resulted in detectable serum monoclonal antibody (mAb) levels. In this study, we show that IgG2 has greater protease resistance to intestinal enzymes in vitro and mice in vivo, due to protease resistance in the hinge region. An IgG2 mAb engineered for FcRn binding, was optimally formulated, lyophilized, and loaded into enteric‐coated capsules for oral dosing in cynomolgus. Small intestinal pH 7.5 was selected for enteric delivery based on gastrointestinal pH profiling of cynomolgus by operator‐assisted IntelliCap System®. Milling of the lyophilized IgG2 M428L FcRn‐binding variant after formulation in 10 mmol/L histidine, pH 5.7, 8.5% sucrose, 0.04% PS80 did not alter the physicochemical properties nor the molecular integrity compared to the batch released in PBS. Size 3 hard gel capsules (23.2 mg IgG2 M428L ~3 mg/kg) were coated with hydroxypropyl methylcellulose acetate succinate for rapid dissolution at pH 7.5 in small intestine and FcRn binding of encapsulated mAb confirmed. Initial capsule dosing by endoscopic delivery into the small intestine achieved 0.2 + 0.1 ng/mL (n = 5) peak at 24 h. Weekly oral capsule dosing for 6 weeks achieved levels of 0.4 + 0.2 ng/mL and, despite increasing the dose and frequency, remained below 1 ng/mL. In conclusion, lyophilized milled mAb retains FcRn binding and molecular integrity for small intestinal delivery. The low systemic exposure has demonstrated the limitations of intestinal FcRn in non‐human primates and the unfeasibility of employing this for therapeutic levels of mAb. Local mAb delivery with limited systemic exposure may be sufficient as a therapeutic for intestinal diseases.
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