Some AAV manufacturing processes use adherent cells grown in stacked trays. AGTC sees that model as a barrier to scaling, pointing to the inability to scale processes up by adding volume. Scaling of adherent cell processes requires additional surface area.
AGTC overcame that limitation by designing a process that makes use of bioreactors, enabling it to scale up from 50 L to 500 L and beyond without significantly increasing its footprint. AGTC enhanced the approach with changes it says improved yield by more than 10 fold.
“We adjusted the upstream process which uses two HSV helper viruses to increase AAV production in a number of ways, one of which was optimizing the ratio and amount of the two viruses. Further, we optimized the bioreactor conditions to increase cell density. Both of these changes led to substantial increases in volumetric productivity,” said AGTC CEO Sue Washer.
Adjusting the ratios and conditions of the process enabled AGTC to make more vectors and increase the percentage of them that are full. AGTC is now achieving finished product specifications that demonstrate nearly 90% full capsids.
Washer went on to say that AGTC also optimized the column chromatography purification process to more completely separate residuals from vectors. In doing so, AGTC was able to collect a higher quality product from the elution peak, according to Washer.
Using the process, AGTC estimates it could generate 2,000 ophthalmology gene therapy doses from a 50-L manufacturing run. That would enable AGTC to support its move into late-phase clinical trials using a relatively small manufacturing footprint.
From eyes to other organs
The improvements could prove particularly valuable to AGTC as it expands beyond diseases affecting the eye. The gene therapy doses needed to treat ocular diseases are far smaller than those required to address conditions affecting other organs, which typically need to be given systemically.
The industry-wide move from rare diseases treated via local delivery to more common conditions that require systemic administration is putting a strain on manufacturing capacity. If AGTC is right, its process will equip it to manage the manufacturing side of the shift in therapeutic focus better than some other gene therapy companies.
AGTC is now advancing programs that will enable it to start putting that hypothesis to the test. While AGTC’s clinical pipeline is focused on rare genetic eye diseases, the biotech is working to get gene therapies for central nervous system disorders into human testing. Washer is alert to the implications of AGTC’s manufacturing process.
“Improved yields makes use of gene therapy for larger patient populations or systemic diseases much more achievable,” said Washer.
AGTC is working to further improve the system. Ongoing areas of activity relate to purification, where Washer sees opportunities to eliminate all process residuals, and the improvement of yields and the percentage of full capsids.
The nature of the process means manufacturing runs could become more productive even in the absence of further technological advances. Simply running the same process at a larger scale should confer some benefits.
“Continuing to scale to larger bioreactors could continue to increase the number of doses from a single run and drive down costs as bioreactor scale-up does not put a burden on factory space or FTE needed like the use of plastic ‘flat-stock’ does,” said Washer.