The RV144 HIV vaccine trial, the first trial to demonstrate that vaccination could confer HIV protection, reported a modest 31% efficacy. gp120, a major component of the RV144 trial, was produced in Chinese Hamster Ovary (CHO) cells and lacked N-linked glycosylation sites critical for binding of anti-HIV broadly neutralizing antibodies (bN-mAbs). Researchers believe, at least in part, that the lack of N-linked glycosylation may play a role in the poor efficacy.
Many epitopes bound by bN-mAbs contain oligomannose terminal glycans — early intermediates in the N-linked glycosylation pathway.1 Dr. Berman’s group at University of California Santa Cruz demonstrated using MaxCyte electroporation that recombinant gp120 (rgp120) production using a HEK 293 cell line deficient in the N-acetylglucosaminyltransferase I enzyme (GnTI- 293; ATCC CRL-3022) resulted in HIV epitopes containing mainly mannose-5 terminal glycans.2 The presence of these glycan moieties improved binding of three major bN-mAb families suggesting use of these rgp120 during vaccination may result in improved efficacy. GnTI- 293 cells, however, are not suitable for large, clinical-scale bioproduction hindering migration to in vivo efficacy studies.
CHO cells continue to be the gold standard for biotherapeutic development, however, the complexity and heterogeneity of protein glycosylation can pose manufacturing and/or immunogenicity challenges. Creation of a CHO cell line deficient in alpha-1,3-mannosyl-glycoprotein 2-beta-N- acetylglucosaminyltransferase (MGAT1) would produce proteins primarily containing oligomannose glycans and could greatly improve HIV gp120 production, purification and potentially vaccine efficacy.