Gene therapy: the trap of biomanufacturing
With the recent approval of Yescarta and Kymriah CAR-T therapies in the US market, several years after approval of Glybera and Strimvelis in Europe, the therapeutic proof of concept of gene therapy has been validated. The next, though highly challenging, step for gene therapy development will be to bypass current limitations of biomanufacturing technologies.
The principle of gene therapy is to bring functional DNA to a patient suffering genetic disease. The current trend, for both ex vivo and in vivo treatments, is the use of viruses for delivering the repaired DNA to patient cell. Manufacturing these vectors is a technical and financial bottleneck for current gene therapy development.
Ex vivo gene therapy is the first stage of innovative biomanufacturing
Yescarta (Gilead) and Kymriah (Novartis) have been approved in 2017 in the US1,2. Both treatments are intended to treat rare cancers and are based on CAR-T technology: a genetic modification of immune cells to make them attack the tumour of the patient. In Europe, Strimvelis (GSK) was approved at the end of 2016 for the treatment of Severe Combined Immunodeficiency due to Adenosine Deaminase deficiency (ADA-SCID) by modification of patient hematopoietic stem cells. All these treatments consist of an ex vivo modification of autologous (from the patient himself) cells to give their function back or provide a new function.
Manufacturing processes of these therapies have been validated but are long and complex: they require cell extraction and modification (with DNA loaded viruses) before reintroducing the cell to the patient. Thus, Strimvelis process is only carried out at MolMed and San Raffaele Hospital (Milan Italy), where it has been developed, and patients must travel there to get treated – cryopreservation of modified cells is not set yet.
Ex vivo therapies need smaller amount of viruses compared to in vivo therapies. This is one of the main reasons why they reached the market first.
Several other ex vivo treatments, developed by American firms, such as BlueBird Bio with Lenti-D (for the treatment of cerebral adrenoleukodystrophy) and LentiGlobin (for the treatment of transfusion-dependant B-Thalassemia) and European biotech, such as Orchard Therapeutics (OTL-101 for ADA-SCID) are expected to reach the market soon. Biomanufacturing is already prepared for these products; BlueBird Bio set a supply agreement with Lonza in the US and Apceth in Europe, whilst Orchard partnered with PharmaCell.
In vivo gene therapy faces the technical and financial challenges of targeting large organs
Glybera was the first in vivo gene therapy approved in Europe in 2012, for lipoprotein lipase deficiency. It was withdrawn for profitability reasons, with only one treatment sold since its approval in 2012. Uniqure sold Glybera for a fee in excess of 1m€. The price was high partly due to high R&D and manufacturing costs, driven by production of loaded viruses (dose around 1012 vg/kg).
In vivo gene therapy is mostly based on DNA loaded adeno associated viruses and requires higher doses of viruses because of the lower rate of transfection compared to ex vivo. Furthermore, viruses must reach the right tissue after in vivo injection. For these reasons, most of the approved-to-date gene therapies are ex vivo and most mature in vivo therapies are focussing on easy-to-reach small organs. Examples include Spark therapeutics’ Luxturna or Gensight’s GS010 product, which are both intended for ophthalmic disease.
Luxturna is in the process of approval in the US and Europe, and focusses on Leber congenital amaurosis and retinitis pigmentosa diseases. Its administration requires a dose around 1012vg/kg, to target eyes.
To target larger organs such as the liver, CNS or skeletal muscles, the required dose of viruses must be increased. AveXis, for Spinal Muscular atrophy, expects the clinical trial dosage to be around 1014vg/kg3, a hundred time higher than Glybera and Luxturna. AveXis took the strategic decision to control their manufacturing activity by having in-house capabilities and developing future marketable processes. In September, this process received FDA authorization for use in next trials.
On a technical prospective, most of the actual AAV production processes are based on sub-optimal transient transfection of mammalian cells, which requires expensive plasmids and transfection agents in large quantities. Other approaches are under development, such as stable cell lines and baculovirus-mediated production, to answer the demand of large volumes when reaching clinical or commercial stage4. Even if the recent move from adherence culture to suspension bioreactors was an improvement, each step of the product manufacturing needs to be optimized to improve yields, starting from the type of vector used.
Pharmaceutical companies and CMOs have increased interest for gene therapy biomanufacturing
Pharmaceutical industries have started investing in gene therapy manufacturing capacities. In 2016, Pfizer demonstrated strategic importance of gene therapy manufacturing technologies: they acquired Bamboo therapeutics, which had become famous for the discovery of a more yield-efficient mammalian cell line.
Owning biomanufacturing forces in US and Europe is essential to provide treatments to patients in both locations. The European pharmaceutical group Merck (EMD Serono) invested in gene therapy manufacturing plants in the UK and the US (BioReliance), strategically combining positions in North America and Europe for supplying therapies to patients on both continents.
Their plants, like many of the gene therapy manufacturing entities, offer CMO services. Gene therapy CMOs are not traditional manufacturers, as they also innovate production processes, to ascertain an easy-to-scale, affordable technique. Following the US, firms across Europe including Oxford BioMedica, YposKesi, Lonza, UniQure, Cell for Cure, etc… are developing and strengthening capabilities in gene therapy biomanufacturing. Europe will position as a competitive player in gene therapy.
Biomanufacturing will remain the challenge of gene therapy development in the next year, especially regarding viral production. Recent development of CRISPR-Cas9 editing therapy, may even enhance this trend, as virus may be the answer to treatment delivery.
1 – Press release – “Kite’s Yescarta becomes first CAR-T therapy approved by the FDA for the treatment of adult patients with relapsed or refractory large B-cell lymphoma after two or more lines of systemic therapy” – oct 2017
2 – Press release – “Novartis receives first ever FDA approval for a CAR-T cell therapy, Kymriah™ (CTL019), for children and young adults with B-cell ALL that is refractory or has relapsed at least twice” – aug 2017
3 – Press release – “AveXis announces plan to initiate pivotal trial of AVXS-101 in SMA type 1 using product from new GMP commercial process” – sept 2017
4 – Tony Hitchcock “manufacturing of AAV vectors for gene therapy” – jul 2017
