Navigating complexity in oncology cell and gene therapy clinical trials

The development of chimeric antigen receptor T cell (CAR-T cell) therapies—such as Kymriah (tisagenlecleucel) and Yescarta (axicabtagene ciloleucel)—and their success in combating hematological malignancies, has paved the way for a surge in investment in CGT, especially adoptive cellular transfer (ACT), in oncology. While in the beginning, we were somewhat limited to CAR-T monotherapies anchored in single antigen targets for CD19-expressing lymphomas and leukemias, research has grown to include expanded and multi-targeting modalities, including additional adoptive cell therapy immune cell vehicles (e.g. NK cells, macrophages, dendritic cells, CD 4+ T cells, etc.). Therefore, it is likely CAR-T cells may be used as both monotherapy, or in combination with novel agents. Estimates as of February 2020 suggest there are more than 1,000 CGT trials globally, with nearly 600 of those in oncology. What’s more, recent market intelligence projects the global CGT market will continue to rise at a compound annual growth rate of 36.25 percent between 2019 and 2025. The investment in oncology emphasizes the importance of developing innovative and accelerated ways to deliver CGT trials and address the challenges of scaling to commercialization. As such, the demand for understanding how to solve these challenges will continue to increase over the next decade

Harnessing the power of diagnostic assays

CGT clinical trials will require more complex testing, with multiple biomarkers. Challenges in this process include the selection of target antigens, the management of toxicity, and the regulation of the immunosuppressive tumor microenvironment. Using an “omics” approach to characterize the drug product pre-infusion and for follow-up of patients post treatment will be needed to help identify key attributes to correlate phenotypes and outcomes. Gold standards include immuno histochemistry (IHC) and PCR-based testing. Other approaches may include flow cytometry or liquid biopsies of circulating tumor cells or circulating tumor DNA. Below we discuss some applications and benefits of these assays. The use of next generation sequencing (NGS) offers distinct data for treatment decisions. NGS can be used for evaluating tumor mutation burdens and microsatellite instability (MSI), which are measures used to identify tumors and treatment targets. NGS data can enable highly accurate detection of MSI, even from limited or degraded samples, offering advantages over existing PCR-based methods.

Further, health authorities in the U.S. and Europe require long-term, follow-up studies of CGT that use viral vectors and must be tested for replication-competent lentiviral (RCL) or replication competent retroviral (RCR) prior to treatment of the patient. Cellbased assays are typically used. However, many novel cellular therapies require the infusion of fresh cells, which does not allow completion of a full cell-based RCL/RCR assay prior to infusion. Quantitative PCR-based (qPCR) assays can provide an alternative for assessing RCL/RCR in products intended for infusion. In addition, as patient selection and monitoring is critical at all stages of the drug development and approval process, the ideal biomarker test accurately matches drugs with patients who will benefit from them. A number of targetable biomarkers have emerged since the first CD19 biomarker target, including B-cell maturation antigen (BCMA), Her2 (human epidermal growth factor receptor 2), MUC1 (Mucin 1), and EpCam (epithelial cell adhesion molecule). IHC or quantitative reverse transcription PCR (RT-qPCR) can be used to identify tumors that express the molecule that is being targeted by the CAR-T or TCR, providing a novel genomics-oriented approach to patient selection. Patients expressing the target of interest, such as BCMA, can then be enrolled in that specific clinical trial. Following infusion, patients will need to be monitored for persistence of recombinant T cells and drug/dose response. Droplet digital PCR- or qPCR-based assays are frequently used to quantify the vector copy number (VCN) of the endogenous target sequences. The VCN assays are used for pharmacokinetic (PK) measurements, a novel DNA-based assay to monitor drug levels as opposed to typical PK testing performed via highperformance liquid chromatography or mass spectrometry-based measurements of a small molecule drug.

The success of CGT has transformed the delivery of clinical trial services, requiring the design of new workflows, processes, and tools to address the nuances and complexities of how CGT trials are executed compared to traditional trials. As the industry evolves, the next generation of adoptive cellular transfer products will move closer to becoming a front-line treatment, as opposed to being limited to relapsed or refractory patients, and will have improved safety and durability of response. Developing improved investigational products requires the use of laboratory services to better identify targets and biomarkers, such as advancing polymerase chain reaction (PCR) and liquid biopsy techniques. Here, we outline the challenges in designing and executing oncology CGT clinical trials and potential solutions to those complexities.

Challenges in designing and executing CGT clinical trials

Cell therapies are “living medicines,” with many being autologous,requiring each patient sample to have its own process. This personalization creates a more complex development cycle than other biologic drugs. One of the main challenges in this approach is developing well-defined characteristics or attributes (i.e., cell phenotype of functional measurements) that are well correlated with outcomes for these investigational products, as there are many causes of variability. For example, there may be differences in cells from donor to donor, which can make it difficultto determine which factors drive efficacy and safety. Notably, with CAR-T therapies, significant side effects include cytokine release syndrome (caused by the production of a large number ofinflammatory molecules by CAR-T cells) and neurotoxicity, both ofwhich are related to therapeutic efficacy. New characteristic safetyprofiles could emerge, which need specific considerations on howto manage patients. Moreover, as biotech companies start to move toward solid tumor targets, the treatment of patients with advanced solid tumors has become more dependent on tissue biomarkers to help guide management decisions. As a result, the ability to obtain tissue for the production or expansion of cell therapies adds another burden. Further, targeted therapies are associated with superior clinical outcomes, but to obtain updated biomarkers and targets, large biopsy specimens are often needed. This is not always feasible, either because lesions are not safely accessible to a surgeon or an interventional radiologist, or because the patient declines further invasive procedures. Allogeneic therapies, or those using cells from healthy donors, may avoid some complexities of modifying a patient’s own cells. For example, Gracell Biotechnologies recently presented preliminary results of a first-in-human, universal CAR-T therapy, GC027—which targets CD7 on malignant T cells—for treating adult patients with relapsed/refractory T-cell acute lymphoblastic leukemia. The ability to produce hundreds of viable cells for multiple infusions can overcome issues related to the time it takes to manufacture T-cells, costs to generate a product for each patient, failures in the ability to generate a product from a patient’s immune cells, and the heterogeneity of T-cell products. However, allogeneic approaches will need to circumnavigate challenges in tissue-matching, which means that human leukocyte antigen typing becomes important in many cases, possibly limiting the target population. Gene editing and other engineered products, such as T-cell receptor (TCR)-engineered T cells, to treat cancer, are entering into safety and feasibility trials. For example, the first clinical trial using CRISPR-Cas 9 editing to engineer T cells in patients with refractory cancer launched in the fall of 2019. These experimental technologies will raise similar challenges as they move forward through early phase clinical trials.

Conclusion

Over the next 10 years, we will continue to witness significant advances and excitement as CGT saves the lives of patients. First, the industry will conquer the challenges created by the tumor microenvironment, opening opportunities to successfully tackle a broader range of solid tumors. Second, new strategies will emerge to improve the manufacturing and delivery of autologous and allogeneic therapies, improving cost-efficiency. These future advances will be assisted by enhanced diagnostic assays and other tests to improve our understanding of targeting and treating cancer.