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P049. Investigation into the binding affinity of certolizumab pegol to FcRn and functional consequences for FcRn-mediated transcytosis: comparison to infliximab, adalimumab and etanercept

T. Baker, L. Kevorkian, A. Nesbitt, UCB Pharma, Slough, United Kingdom

Background

Certolizumab pegol (CZP) is an anti-TNF that lacks the monoclonal antibody Fc portion. In contrast, anti-TNF antibodies infliximab (IFX) and adalimumab (ADA) and receptor fusion protein etanercept (ETA) all possess an IgG1 Fc. It has been reported that lower levels of CZP, compared to ADA/IFX, are transferred from treated mothers to the neonate. This transfer differential may be due to the one-way active transport of antibodies across the placenta thought to be mediated by the neonatal Fc receptor (FcRn). The objective was to quantify binding of CZP, IFX, ADA and ETA to FcRn and to measure FcRn-mediated transcytosis of these agents.

Methods

A Biacore™ assay was used to determine the binding of CZP, ADA and IFX to human FcRn. Anti-TNFs were passed over an FcRn-coated chip for 5min at a range of concentrations from 21–670nM to determine the on-binding rate; a buffer at pH 6.0 was used to allow optimum binding. The off-rate was followed for a further 5min by running buffer alone over the chip. MDCK II cells transfected with human FcRn were used to measure FcRn-mediated transcytosis using a pH 5.9 buffer on the apical side and pH 7.2 on the basolateral side. The anti-TNFs and the control antibody (P146), which possessed an Fc modified to prevent binding to FcRn, were biotinylated to allow visualization. The amount of each anti-TNF transcytosed across the cell layer over 4hrs was measured by MSD assay.

Results

IFX (132nM) and ADA (225nM) had relatively high binding affinity to FcRn while the binding affinity of ETA to FcRn was approximately 5 to 10-fold lower (1500nM). In contrast, CZP did not bind to the FcRn with any measurable affinity. The mean levels of transcytosis seen with IFX and ADA were 249.6 ng/mL and 159.5 ng/mL, respectively (n = 3). Transcytosis of ETA (81.3 ng/mL) was lower than that of ADA and IFX. In contrast, the level of CZP transcytosis (3.2 ng/mL) was significantly lower than that observed with the other anti-TNFs tested. The control antibody P146 also showed low transfer (5.9 ng/mL). Since neither the control antibody nor CZP bind to FcRn, the levels detected are probably due to low level non-specific leakage across the cell layer.

Conclusion

CZP does not have an Fc and thus did not bind FcRn. Moreover, no FcRn-mediated CZP transcytosis was detected. In contrast, ADA and IFX had relatively high binding affinity to FcRn and were actively transcytosed. ETA showed lower binding affinity to FcRn and subsequent transcytosis, compared to IFX/ADA, but FcRn-mediated ETA transport could still be measured. These results explain previously observed active transport of anti-TNFs across the placenta seen in patients treated with IFX and ADA, whereas only low levels were observed with CZP.