To generate industrially applicable new host cell lines for antibody production with optimizing antibody-dependent cellular cytotoxicity (ADCC) we disrupted both FUT8 alleles in a Chinese hamster ovary (CHO)/DG44 cell line by sequential homologous recombination. FUT8 encodes an alpha-1,6-fucosyltransferase that catalyzes the transfer of fucose from GDP-fucose to N-acetylglucosamine (GlcNAc) in an alpha-1,6 linkage. FUT8(-/-) cell lines have morphology and growth kinetics similar to those of the parent, and produce completely defucosylated recombinant antibodies. FUT8(-/-)-produced chimeric anti-CD20 IgG1 shows the same level of antigen-binding activity and complement-dependent cytotoxicity (CDC) as the FUT8(+/+)-produced, comparable antibody, Rituxan. In contrast, FUT8(-/-)-produced anti-CD20 IgG1 strongly binds to human Fcgamma-receptor IIIa (FcgammaRIIIa) and dramatically enhances ADCC to approximately 100-fold that of Rituxan. Our results demonstrate that FUT8(-/-) cells are ideal host cell lines to stably produce completely defucosylated high-ADCC antibodies with fixed quality and efficacy for therapeutic use.

No abstract

No abstract

Purpose: Recent studies have revealed that fucosylated therapeutic IgG1s need high concentrations to compensate for FcgRIIIa-competitive inhibition of antibody-dependent cellular cytotoxicity (ADCC) by endogenous human plasma IgG. Here, we investigated whether ADCC of nonfucosylated therapeutic IgG1 is also influenced by plasma IgG in the same way as fucosylated IgG1s. Experimental Design: Ex vivo ADCC upon CD20 + human B cells was induced by incubation of human whole blood with nonfucosylated and/or fucosylated anti-CD20 IgG1s rituximab, and quantified by measuring the remaining CD19 + human B cells using flow cytometry. Results: Nonfucosylated anti-CD20 showed markedly higher (over 100-fold based on EC 50 ) ex vivo B-cell depletion activity than its fucosylated counterpart in the presence of plasma IgG. The efficacy of fucosylated anti-CD20 was greatly diminished in plasma, resulting in the need for a high concentration (over 1.0 Ag/mL) to achieve saturated efficacy. In contrast, nonfucosylated anti-CD20 reached saturated ADCC at lower concentrations (0.01-0.1 Ag/mL) with much higher efficacy than fucosylated anti-CD20 in all nine donors through improved FcgRIIIa binding. Noteworthy, the high efficacy of nonfucosylated anti-CD20 was inhibited by addition of fucosylated anti-CD20. Thus, the efficacy of a 1:9 mixture (10 Ag/mL) of nonfucosylated and fucosylated anti-CD20s was inferior to that of a 1,000-fold dilution (0.01 Ag/mL) of nonfucosylated anti-CD20 alone. Conclusions: Our data showed that nonfucosylated IgG1, not including fucosylated counterparts, can evade the inhibitory effect of plasma IgG on ADCC through its high FcgRIIIa binding. Hence, nonfucosylated IgG1exhibits strong therapeutic potential through dramatically enhanced ADCC at low doses in humans in vivo.