Cellular Engineering Strategies for Improvement of Mammalian Cell Phenotypes in Commercial Applications (Paperback)

Biopharmaceuticals is a $48 billion dollar industry with a 19% annual growth rate. The vast majority of such proteins are produced in mammalian cells, which offers high level production of proteins with human-like characteristics. Yet, mammalian cells production systems are limited by the density and longevity of the cells in culture, since a number of bioreactor stresses (such as nutrient deprivation, byproduct accumulation, and elevated pH) can cause cells to die through programmed cell death, or apoptosis. To prevent apoptosis, we have investigated the use of three different anti-apoptosis proteins in mammalian cell culture. In the first study, we applied the anti-apoptotic molecule Bcl-xL to a CHO cell transient gene expression system for production of recombinant protein and found that Bcl-xL-engineered cells exhibit increased protein production, higher viability, and decreased apoptosis. A second study investigated the use of the anti-apoptotic Bcl-2 protein, Mcl-1, to prevent apoptosis in mammalian cell culture. Expression of wild-type Mcl-1 or a non-degradable mutant of Mcl-1 led to high culture viabilities and increased production of an antibody in stable mammalian cell lines. The final anti-apoptosis engineering project involved the expression of MDM2, an inhibitor of the master cell cycle and apoptosis regulator p53, in HEK 293 and CHO cell lines. HEK 293 and CHO cells expressing MDM2 showed higher viabilities and decreased apoptosis when exposed to extended culture conditions. To enhance the cell density of mammalian cell cultures, this work describes a research study to enhance the mammalian cell cycle for improved growth phenotype of CHO cells. The method used was to express the cell cycle transcription factor E2F-1. CHO cells expressing E2F-1 grew for an extra day in batch culture and attained higher peak cell densities than control cells. This enhancement was seen without increased production of an antibody or significant changes in viability, apoptosis induction, or cell cycle distribution. Finally, this work reviews the emerging directed evolution technologies that can be applied to mammalian cell engineering or whole mammalian cell evolution for creating novel phenotypes. Such technologies combined with cell engineering strategies will help increase mammalian recombinant production to new levels in the future.