Using SSI Pools to Quickly Initiate Pandemic Molecule
Manufacturing Campaigns for Phase I Clinical Trial
Site-specific integration (SSI) technology has brought forward much
greater efficiency in inserting genes of interest (GOIs) into the host
cell genome than the classical random integration transfection methods.
While SSI has greatly improved the productivity of the stable cell
lines, the much higher efficiency of recombinant gene integration into
the genome of the host cells than the traditional random insertion has
even greater pragmatic value for the industry. While the traditional
method of plating and screening of stable cell pools can take up to 3
months from transfection to the fed-batch culture for a material
generation, the SSI stable pool takes as short as 3 weeks for the same
scale of production. This enabled us to conceive a more aggressive but
pragmatic CMC timeline for counter-pandemic projects like neutralizing
antibody productions. Since the transfections are performed under cGMP
conditions, the SSI transfectants can be directly expanded for the
production of toxicology materials and even one or two following batches
of GMP production (Gen1 GMP), depending on the calculated needs for the
initial clinical trials. From the perspective of CLD, which is
ultimately intended for the creation of a high-quality, monoclonal
production cell line, prioritizing the closest product quality proximity
to the Gen1 GMP materials will be necessary for the top clone selection
criteria, to control the product quality consistency between the Gen1
GMP batch materials and the following clonal GMP batch materials (Gen2
GMP). The MCB of the final clone (Gen2 GMP path) will eventually be used
to succeed the Gen1 GMP production for the subsequent supply of clinical
materials. The high-level flowchart for such a strategy is illustrated
in Fig. 1.
Our SSI pools have proven to be quite capable of productivity on several
toxicology or GMP productions with COVID-19 molecules (Fig. 2A). One
representative toxicology production, which was directly expanded after
transfection, yielded harvested titer as high as 4 g/L on day 14 with
good growth and metabolic profiles, such as viability, viable cell
density, glucose level, lactate level, and osmolality (Fig. 2B-F).
The comparability between toxicology and clinical materials is
undoubtedly critical, one of the key challenges to overcome if the
stable pools, instead of the monoclonal cell banks, should be used for
manufacturing. The application of the SSI technology to such material
generation strategy has an underlying prerequisite that the SSI pools
should display stable product quality profiles, which we have observed
with different seed train lengths for different batches of productions
(data not shown). As illustrated in Figure 3, the toxicology batch and
the following two GMP clinical batches of the same SSI pool (Molecule A)
with different seed-train lengths shared similar productivity and
product quality profiles to the smaller-scale bioreactor evaluations. In
this case, the required amount of the appropriate materials was
generated with satisfactory consistency, which also obviated the
necessity for the purification and qualification protocol alterations.