Christopher Bohl, Ph.D., ADME Product Technical Sales Specialist, BioIVT
Gene therapies using CRISPR or similar techniques utilize the body’s own DNA repair mechanisms, and gene sequence specificity, to edit individual genes, or even single nucleotides to repair a mutant protein or coding region within a targeted cell.
As gene therapies are intended to alter cell protein expression and change the target cell’s phenotype, often permanently, it is imperative that every effort is made to ensure each candidate drug is safe to use before it is employed in clinical trials.
To that end, many resourceful researchers are repurposing traditional ADME in vitro test systems to assess the potential for candidate gene therapy products to elicit off-target hepatotoxicity. Even if the gene therapy is not targeted at the liver, many gene editing delivery systems result in the product being dispersed systemically.
Plated primary hepatocytes in long-term micropatterned culture systems with fibroblasts or fibroblasts and Kupffer cells, such as HEPATOPAC® or HEPATOMUNE®, allow the acute and chronic effects of the candidate gene therapy product to be evaluated. As a result, potential safety issues may be identified early.
As patients have died during gene therapy clinical trials due to an unexpected immune response, the importance of conducting additional safety testing cannot be overstated.
Vanee Pho, Ph.D., Vice President Global Marketing, Mission Bio
The same complexity that enables genome editing therapies to treat previously intractable diseases brings a degree of risk. Regulators need a deep understanding of their safety.
In 2018, the National Institute of Standards and Technology (NIST) launched the Genome Editing Consortium to develop standard analytical approaches that would increase confidence in CRISPR and other gene editing therapies. We joined the public–private consortium to leverage our platform’s unique capability for single-cell DNA and multi-omics for rapid characterization of gene-edited drug products. MB’s results were in agreement between expected variant frequencies based on NIST ddPCR estimates yielding an accuracy regardless of variant frequency as low as 0.1%.
Characterizing allelic variants is fundamental to understanding the consequences of gene editing, especially when multiple edits are desired
By detecting on- and off-target editing, the zygosity of edits, and the co-editing of multiple targets in single cells, we have enabled developers to validate genome editing in clinical batches, so that developers can confidently assess and describe to regulators exactly what happens with their products.
Steve Becker, Chief Commercial Officer, Broken String Biosciences
Gene editing therapies have already made a tremendous public impact, most recently with the N-of-1 CRISPR-edited gene therapy that was developed, cleared for clinical use by FDA, and treated a patient in under 8 months. The speed was impressive, but about half of that time was tied to ensuring the therapy is safe.
Stakeholders are fully invested in ensuring these therapies are safe. FDA held one CRISPR clinical program for a year until its sponsor could characterize its unintended off-target edits to understand the drug’s risks. But during the delay, the company lost about $1 billion in market capitalization.
Until recently, companies have struggled to demonstrate safety, often spending months developing a bespoke informatics pipeline to ascertain even limited data on off-target gene edits. A gold standard is now emerging with technology that can accurately identify off-target editing through characterization of double stranded breaks in DNA — in depth and within days. Such tools will underpin the safe growth of gene editing therapies.
Jakob Reiser, Ph.D., Senior Director of Regulatory Affairs, Vector BioMed
Traditional gene therapy approaches utilize viral vectors, including lentiviral vectors, to stably deliver genetic sequences into cells ex vivo, including patient-derived immune cells and hematopoietic progenitor and stem cells. Lentiviral vectors have several safety features and are generally regarded as safe, and they have been tested in numerous clinical trials. There are several commercial gene therapy products available involving lentiviral vectors for the treatment of cancer (CAR-T cells for leukemia, lymphoma, and multiple myeloma) and for inherited diseases, such as sickle cell disease. Typically, the manufacture and release testing of lentiviral vectors is cumbersome and time-consuming, resulting in high production costs. Recent improvements in the manufacture of such vectors by Vector BioMed have increased the quality and yields of such vectors, resulting in lower production costs and a timelier release of such vectors for partners.
Current efforts focus on strategies aimed at using lentiviral vectors directly in patients (in vivo approach). This overall strategy is early and developing. Various companies, including Caring Cross and Vector BioMed, are pursuing this approach. It is anticipated that the direct in vivo approach will greatly lower patient costs in the future, granted that they are still safe and efficacious.
Gene editing, including CRISPR-based strategies, utilizes a novel modality involving lipid nanoparticles to deliver genetic sequences into cells and to introduce specific genetic changes. This approach is promising.