Transient gene expression optimization and expression vector comparison to improve HIV-1 VLP production in HEK293 cell lines.

Transient gene expression (TGE) has been used at small and medium scale for the production of biologicals in sufficient quantities to perform pre-clinical and characterization studies. Polyethyleneimine (PEI)-mediated transfection offers a low toxicity and non-expensive method for cell transfection. DNA and PEI concentration for transient gene expression has been extensively optimized in order to increase product titers. However, the possibility to extrapolate the optimal concentrations found for a specific bioprocess when expression vectors or cell lines need to be changed has not been investigated.In this work, the combination of three different HEK293 cell lines with three different vectors was studied for the production of HIV-1 virus-like particles (VLPs). The concentration of DNA and PEI was optimized for the nine combinations. The obtained results were very similar in all cases (DNA = 2.34 ± 0.18 μg/mL and PEI = 5.81 ± 0.18 μg/mL), revealing that transfection efficiency is not dependent on the cell line or vector type, but on DNA and PEI quantities. Furthermore, two of the cell lines tested stably expressed a protein able to recognize specific origins of replication: HEK293T/SV40 and HEK293E/oriP. Origins of replication were included in the vector sequences in order to test their capacity to increase production titers. HEK293T/SV40 resulted in a decrease of cell density and productivity of 2.3-fold compared to a control plasmid. On the other hand, HEK293E/OriP platform enabled a threefold improvement in HIV-1 VLP production keeping the same cell densities and viabilities compared to a control plasmid.