Inhibitor formation is a serious complication of factor VIII (FVIII) replacement therapy for the X-linked bleeding disorder haemophilia A and occurs in 20%-30% of patients. No prophylactic tolerance protocol currently exists. Although we reported oral tolerance induction using FVIII domains expressed in tobacco chloroplasts， significant challenges in clinical advancement include expression of the full-length CTB-FVIII sequence to cover the entire patient population， regardless of individual CD4 T-cell epitope responses. Codon optimization of FVIII heavy chain (HC) and light chain (LC) increased expression 15- to 42-fold higher than the native human genes. Homoplasmic lettuce lines expressed CTB fusion proteins of FVIII-HC (99.3?kDa)， LC (91.8?kDa)， C2 (31?kDa) or single chain (SC， 178.2?kDa) up to 3622， 263， 3321 and 852?μg/g in lyophilized plant cells， when grown in a cGMP hydroponic facility (Fraunhofer). CTB-FVIII-SC is the largest foreign protein expressed in chloroplasts; despite a large pentamer size (891?kDa)， assembly， folding and disulphide bonds were maintained upon lyophilization and long-term storage as revealed by GM1-ganglioside receptor binding assays. Repeated oral gavages (twice/week for 2?months) of CTB-FVIII-HC/CTB-FVIII-LC reduced inhibitor titres ~10-fold (average 44?BU/mL to 4.7?BU/mL) in haemophilia A mice. Most importantly， increase in the frequency of circulating LAP-expressing CD4 CD25 FoxP3 Treg in tolerized mice could be used as an important cellular biomarker in human clinical trials for plant-based oral tolerance induction. In conclusion， this study reports the first clinical candidate for oral tolerance induction that is urgently needed to protect haemophilia A patients receiving FVIII injections.