Due to their clinical importance, the development of therapeutic proteins has accelerated immensely over the past years. However, the expression of highly glycosylated recombinant therapeutic proteins, as for example blood coagulation factors or serum proteins has remained a challenging task. Human cell lines, as HEK293 cells or our amniocyte-derived CAP cell line, appear to be efficient in producing and secreting these proteins, however glycosylation can be incomplete.
Although, we have found that CAP cells generate a more authentic human glycosylation pattern than HEK293, we have for some proteins, e.g. human C1 esterase inhibitor (hC1-Inh), also detected incomplete sialylation, resulting in reduced serum half-life of the recombinant protein.
C1 esterase Inhibitor (C1 Inh) belongs to the serpin superfamily. Its main function is the inhibition of the complement system to prevent spontaneous activation. The 500 aa protein is highly glycosylated with 7 predicted N-glycans and 8 predicted O-linked glycans. Plasma derived C1 Inhibitors (Berinert, CSL Behring and Cinryze, ViroPharma,) as well as recombinant C1 Inh derived from milk of transgenic rabbits (Ruconest, Pharming N.V.) are approved for the treatment of acute attacks in patients with hereditary angioedema (HAE). However, the recombinant product shows a dramatically reduced serum half-life in pharmacokinetic studies in comparison to the plasma derived counterparts.