Novel method for quantifying cells on carriers and its demonstration
during SARS-2 vaccine development
Abstract
The most effective way to prevent and control infectious disease
outbreak is through vaccines. The increasing use of vaccines has
elevated the need to establish new manufacturing strategies. One of the
major approaches is cell-based production, which creates a need for high
cell density to enable higher cell production levels. This has led to
development of the technology of cell carriers, including micro and
macro cell carriers. To follow the production process, quantifying the
number of cells on these carriers is required, as well as the tracking
of their viability and proliferation. However, owing to various
carriers’ unique structures, tracking the cell’s is challenging using
current traditional assays that were originally developed for monolayers
of adherent cells. The current “gold standard” method is counting cell
nuclei, separating cells from the carrier, staining with crystal violet
and visually counting under a microscope. This method is tedious and
counts both live and dead cells. A few other techniques were developed
but were specific to the carrier type and involved specialized
equipment. In this study, we describe a broadly ranging method for
counting cells on carriers that was developed and employed as part of
the production of a vaccine for use in the SARS-CoV-2 pandemic. The
method is based on the Alamar blue dye, a well-known, common marker for
cell activity, and was found to be successful in tracking cell
adsorption, cell growth and viability on carriers. No separation of the
cells from the carriers is needed, nor is any specialized equipment; the
method is simple and rapid, and provides comprehensive details necessary
for process control of viral vaccine production in cells. This method
can be easily implemented in any of a number of cell-based processes and
other unique platforms for measuring growth of encapsulated cells.