Gene therapy and gene-mediated cell therapy (e.g. CAR-T cell therapy) approach hold great promise for treating debilitating diseases with unmet clinical needs. The drive to address the genetic cause of a disorder has brought about a gamut of innovative tools that can correct a cell’s function at the DNA level or engineer a cure via in vivo or ex vivo methodologies. Since 2021, the US Federal Drug and Food Administration (FDA), approved a record number of five gene- and chimeric antigen receptor (CAR)-T cell-therapy products. While there are thousands of clinical trials currently on the horizon, the progress of such therapies to the market is hampered by safety, efficacy, and reproducibility concerns. Market approval relies on consistently presenting robust and reliable data displaying the highest levels of purity, potency (i.e. intended biological activity and/or therapeutic effect), and, ultimately, the safety of the products throughout all phases of development. Harnessing the ability of specific techniques, and providing accurate and precise data on product characteristics, is key to extending product accessibility to more patients across a wider range of genetic disorders. This article discusses the fundamental principles of gene and gene-mediated-cell therapies, addresses the challenges associated with in vivo and ex vivo gene delivery approaches, and presents tools the industry can use to support product development.
Over the past two decades, advances in gene therapy and gene-mediated cell therapy have led to the development of versatile treatment strategies which fundamentally involve the delivery of nucleic acids into specific cells using gene delivery vectors. Using an in vivo approach, a gene therapy product is delivered directly to a patient, while ex vivo gene delivery combines a gene therapy product with allogeneic (patient-derived) or autologous (healthy donor-derived) cells, resulting in engineered cells which can be then transferred into the patient (Figure 1). Depending on the underlying cause of genetic disease, delivery of genetic material into a cell can result in gene augmentation, editing or suppression (Figure 2).
Currently, there are two FDA-approved gene therapy products (GTPs), both of which are examples of in vivo gene augmentation therapy using an adeno-associated virus (AAV) vector to deliver functional copies of a gene to alleviate symptoms caused by a dysfunctional protein.2 Luxturna (Spark Therapeutics), was approved in 2017 for the treatment of biallelic retinal pigment epithelium-specific 65 (RPE65) mutation-associated retinal dystrophy, which can result in blindness.3 Luxturna can restore normal retinal cell function by supplying an RPE65 transgene thus restoring protein function. Following Luxturna, Zolgensma (Novartis) received marker approval for the treatment of spinal muscular atrophy (SMA) in 2019. SMA is the leading inherited cause of infant death resulting primarily from biallelic loss-of-function of survival motor neuron 1 gene (SMN1). Zolgensma works by supplying a functional copy of the SMN gene from which a fully functional protein can be produced. Both clinical trials and post-approval studies assessing the long-term safety and efficacy of Zolgensma treatment demonstrated a significant increase in survival rates and quality of life in infants with the disease.4,5 Numerous pre-clinical and clinical trials are currently underway exploring how gene editing or suppression can alleviate symptoms of genetic conditions caused, for example, by toxic gain of function of proteins, such as in the case of Huntington’s disease. Protein overexpression can be treated by gene ‘silencing’ or by post-transcriptionally targeting a specific mRNA sequence.6 Gene editing is a powerful approach that can also be used to restore gene function. Pre-clinical and clinical trials are currently underway, assessing the efficacy of these tools, such as small interfering RNA (siRNA), CRISPR-Cas9 and zinc finger nucleases.7 During the process of generating CAR-T cells, an ex vivo gene therapy, a CAR is delivered into either autologous or allogeneic T cells via lenti- or retro-viral vectors.8 This type of gene-mediated cell therapy product (GMCTP) has revolutionised the field of Immuno-oncology. Four out of five CAR-T cell therapy products were granted FDA approval in 2022; most recently, Breyanzi (Bristol-Myers) was authorised for the treatment of patients with B-cell lymphoma and works by identifying and eradicating CD19-positive cells, i.e. B cells.2
