Whilst the original ideas to treat diseases at the genetic level must have seemed like science fiction when first posited three decades ago, the technique of gene therapy has now become a realistic option for the treatment of many disorders. In its simplest form, gene therapy is an experimental technique in which diseases caused by mutations in genes can be treated with the addition of a ‘working’ copy, and in doing so restore normal function to the cells of our bodies. It holds promise to treat diseases ranging from rare inherited disorders affecting the immune system (primary immunodeficiencies), blood disorders such as haemophilia, sickle cell disease and beta-thalassaemia, to cancer, viral infections, neurological and cardiovascular diseases, and hereditary diseases of the eye. This treatment addresses the underlying cause of a disease with the possibility of a one-time treatment option, avoiding the otherwise lengthy medical treatment during a patient’s lifetime. What’s more, it offers the opportunity to treat disorders with unmet medical needs, and where other treatment regimes have been ineffective or are associated with significant side effects.
The potential of gene therapy, along with cell therapy that uses cells as therapeutic agents, cannot be overstated, and significant progress has been made on their path to the clinic as medicinal products. The first commercial gene therapy, Gendicine (Shenzhen SiBiono GeneTech), was approved in China in 2003 for the treatment of certain cancers, and in 2011, uniQure’s Glybera was approved in the EU for an inherited condition affecting the normal breakdown of fats in the body. GSK’s Strimvelis (now acquired by Orchard Therapeutics within the gene therapy for rare diseases portfolio) was approved in 2016 for the treatment of a primary immunodeficiency, adenosine deaminase-severe combined immunodeficiency (ADA-SCID). This was the first autologous (using a patient’s own cells) ex vivo gene therapy to be developed – in which cells are first modified outside of the body and transplanted back again. This was followed in 2017 by Novartis’s Kymriah and Yescarta from Kite Pharma (now acquired by Gilead). These products consist of T-cells which have been modified to help their recognition and fight against certain types of cancer, known as chimeric antigen receptor-T (CAR-T) cell products. Spark Therapeutic's Luxturna for the treatment of a rare inherited retinal disease was released in the same year. These clinical approvals have paved the way for other therapies on their way to the clinic, and towards the end of 2017 almost 2600 gene therapy clinical trials were completed, in progress or approved worldwide.
Despite the great advances in this field, significant challenges remain for the delivery of both gene and cell therapy products to the clinic. In contrast to conventional pharmaceutical medicinal drugs or the more recent protein therapeutics, the manufacture of gene and cell therapy products is met with additional complexity and challenges to overcome. In the case of gene therapy, whilst good progress has been made in designing safer viral vectors, the cost of manufacturing high quality good manufacturing practice- (GMP-) compliant viral vectors at high yield is substantial. Gene therapies that have recently come to the market have in some cases had total healthcare costs exceeding $1 million. Indeed, uniQure’s Glybera has been withdrawn from the market with costs exceeding this per patient. In the case of autologous ex vivo gene therapy using a patient’s own blood stem cells, such as Strimvelis, a great challenge remains in correcting a sufficient number of stem cells, whilst maintaining their ability to re-establish themselves in the patient and give rise to all their blood cells during their lifetime. Similarly, for CAR-T cell therapies, the total number of modified T-cells of the correct type that are received by the patient is critically important for a successful outcome. Improved methods for the modification of blood stem cells, T-cells and other cell types used for immune-oncology, promoting their expansion whilst maintaining their function, are highly desirable. In the case of cell therapy, the nature of using live cell products brings with it additional complexity, and challenges arise in manufacturing a consistent, reliable, robust, cost effective and safe product.
Plasticell has developed a technology platform CombiCult that can help to address these and other critical challenges in gene and cell therapy. This includes the initial development of a product, as well as offering a unique combinatorial screening method for manufacturing process development and optimization. CombiCult has been highly successful in its application to the development and optimization of cell differentiation methods, from human embryonic stem cells, induced pluripotent stem cells (iPSCs), foetal and adult stem cells (e.g. neural and mesenchymal stem cells) to a range of terminally differentiated cell types (neural, cardiac, liver, muscle, brown fat, bone, cartilage, platelets, red blood cells), in which combinatorial cell culture allows tens of thousands of protocols to be screened in a single experiment. This approach has also been applied to developing methods for the expansion of umbilical cord blood (UCB) haematopoietic stem cells (HSCs); this improved HSC expansion protocol differentiates itself from other methods of expansion by a relatively rapid rise in the proportion of cells with properties of long-term engrafting potential. Recently, Plasticell established a collaboration with Professor Adrian Thrasher’s team at University College of London (UCL) Great Ormond Street Institute of Child Health (ICH) to develop advanced technologies for the manufacturing of autologous ex vivo gene therapies. This consortium, led by Plasticell, is partly funded by a competitive grant from Innovate UK as part of its ‘Innovation in Health and Life Sciences’ competition. In this project, Plasticell’s method of expanding HSCs is being used to: (i) increase the number of HSCs obtained from peripheral blood for ex vivo modification; (ii) CombiCult technology is being used to develop protocols and formulations that increase the efficiency of gene delivery into HSCs using clinical grade lentiviral vector; and (iii) that maintain the multipotency of HSCs carrying the therapeutic transgene up to the point of re-introduction into patients. This will lead to an increase in the efficiency and reliability of hematopoietic gene therapy. Professor Thrasher is a renowned expert in the clinical development of gene therapies for primary immune deficiencies, and these rare inherited disorders of the immune system are the initial focus of the study.
Going forward, Plasticell envisions broader application of CombiCult to gene and cell therapy development. Whilst our current focus is on the delivery of lentivirus to HSCs, this approach can be applied to the use of different viral vectors (as well as non-viral vectors) and delivery to different cell types, which differ in their mechanisms of action and receptivity. Increasing the efficiency of delivery, whilst expanding or maintaining cells with the correct phenotype, will allow a reduction in the cost of goods. CombiCult could also be advantageous in the application and advancement of gene editing technologies. For example, in the case of the recently identified CRISPR-Cas9 approach, appropriate conditions to promote homology-directed repair over non-homologous end joining could be developed. Next generation ‘off-the-shelf’ allogeneic therapies, from iPSCs or UCB, would also benefit from CombiCult, in which highly efficient GMP-compliant culture protocols can be readily developed. Where gene editing is applied, for example in disrupting HLA expression within donor cells to avoid graft-vs-host disease, optimal conditions for this process could be applied.