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Key challenges posed to autologous and allogeneic treatments could be resolved by in-vivo CAR-T gene therapies.
There is no doubt that chimeric antigen receptor (CAR) T-cell therapies have had a tremendous positive impact on patients that have received them; however, autologous cell therapies produced in centralized manufacturing facilities have inherent limitations that inhibit widespread availability and access. Allogeneic, or off-the-shelf versions, are one potential solution, but developers of these therapies must overcome different challenges, such as graft-versus-host disease, the potential for introduction of chromosomal abnormalities, ensuring successful gene editing of all donor cells, and problems with T-cell exhaustion (1).
Another option is to produce autologous therapies at the point of care (POC) (2). Companies such as Miltenyi Biotech, Lonza, SQZ Biotech, Orgenesis, and Ori Biotech have developed or are commercializing closed, automated cell- and gene-therapy production platforms with small footprints that can be installed at hospitals and institutions for good manufacturing practice (GMP) production of CAR T-cell therapies onsite. There are various university hospitals around the world exploring the potential of these systems. Orgenesis and aCGT Vector are establishing networks of POC sites leveraging their own production technologies.
A third approach being explored by several companies eliminates the need for gene editing of immune cells outside the body altogether. These solutions involve in vivo generation of CAR cells. This approach also has its challenges, but offers the potential to combine some of the benefits of both autologous and allogeneic cell therapies.
Autologous cell therapies today require collection of immune cells from the patient that are then shipped to a central manufacturing facility. Most patients are extremely ill and have endured multiple previous therapies, leading to variability in the starting material and the potential for manufacturing failures. Production slots are also limited, often creating delays that such ill patients cannot generally afford. Facilities that offer cell therapy are limited as well, and as a result, patients must travel to them, adding to the burden placed on them and their families. Furthermore, the cost of gene-modified cell therapies is high.
An IQVIA survey (3), notes Gregory Frost, chairman and CEO of EXUMA Biotech, revealed that the patient’s health status, cost to patient, and geographic distance for the patient to travel were the top three reasons why community oncologists do not refer patients for CAR-T therapy.
Allogenic cell therapies offer compelling benefits relative to autologous CAR T-cell treatments for certain indications. As off-the-shelf products, they are available immediately, eliminating the logistics complexities that add time and cost to autologous therapies. They also do not suffer from the variability associated with patient-derived cells.
Avoiding the natural immune response to foreign CAR-T cells has, however, proven much more challenging than past industry hurdles such as the advancement from mouse antibodies to human antibodies, according to Frost. “Although many different strategies are being explored, the only clinically validated solutions to this challenge to date has been sustained immunosuppressive treatment regimens to eliminate the body’s T and NK cell function, thereby increasing the risk of opportunistic infections without transplant-ward-level care,” he says. Generally as a result, the time that must be spent in the specialized care setting is often extended and introduces additional burdens for patients and their families that do not live near one of these specialized facilities.
In vivo CAR therapies have the potential to offer the benefits of both autologous and allogeneic therapies. “The most apparent advantage that in vivo CAR therapy could provide over autologous or allogeneic cellular therapy is to capture the durability benefits of autologous cell therapy with the reduced cost and complexity of an off-the-shelf product,” contends Frost.
If other safety parameters can be maintained clinically, Frost explains a CAR therapy that delivers a cost-of-goods-per-patient-treated on par with biologics may change the efficacy bar from 30–50% durable complete responses to a 30+% improvement in progression-free survival or overall survival, a particularly relevant goal for indications in solid tumors. “Moreover,” he adds, “lymphodepletion may not be necessary for in vivo therapies, thereby potentially expanding the setting of care beyond tertiary care centers with intensive-care units and extending CAR therapy into indications not previously addressed (e.g., autoimmune disease) due to an unfavorable benefit-to-risk ratio.” Furthermore, as a true off-the-shelf option, in vivo CAR therapy products are unburdened by the complex logistics for cryopreservation of a cellular drug product.
Overall, in vivo CAR therapy “may address the significant concerns associated with autologous and allogenic gene-modified cell therapies and thus function to expand patient access to CAR therapy by making it safer, potentially more efficacious, less financially toxic, and available in settings more convenient to patients and their families,” Frost comments.
It is also worth noting that in addition to the reduced cost and complexity of therapy and the potential to expand to a wider array of care settings, in vivo CAR/T-cell receptor (TCR) therapies reduce the complexity of cell processing validation, according to Frost. “While the product is the process,” he observes, “the in vivo approach does not require the associated costs and time to develop an optimized and validated manufacturing cell process, which can introduce new challenges in comparability assessment with subsequent process changes.”
Frost also points out that enhancements and minor modifications to the transduction program encoded in the vector can easily be made, allowing for iterative evaluation preclinically and potentially clinically. “The versatility of the technology is anticipated to extend the technology broadly into academia and small and large biotechnology companies, which could result in the accelerated discovery and development of transformative therapies at substantially reduced costs,” he concludes.
Of course, in vivo gene-modified cell therapies face their own set of technical challenges. A key issue, according to Frost, is the inability to perform preparative lymphodepletion of the patient prior to the infusion of the engineered cells. This procedure removes other immune cells that would otherwise compete with the CAR cells for growth factors and other nutrients, reducing their chances to survive, expand, and exhibit antitumor function. “Lymphodepletion is not a viable option for in vivo CAR therapy since it would kill off the very cells targeted for in vivo engineering. As such, any in vivo approach will need a means for ensuring robust proliferation and survival in an environment that is rife with competition for the same nutrients,” Frost says.
It is also essential that the vehicle delivering the genetic material for reengineering of the target immune cells is highly selective for the right cells. “Whether the vehicle is a viral vector or lipid nanoparticle (LNP), it must target delivery to the specific cell type to be re-engineered (e.g., T cell, natural killer cell) in order to prevent any unintended gene modification,” comments Frost.
Viral vectors and lipid nanoparticles represent two different approaches being explored for in vivo engineering. Nonviral approaches typically involve LNPs encapsulating nucleic acids, while viral approaches are generally based on the same retroviral vectors used in current ex vivo cellular therapies.
Non-viral approaches, notes Frost, have the possible advantage of a more defined regulatory pathway based on the recent approvals of the COVID-19 vaccines. Non-integrating approaches may, however, not provide a sustained clinical response given that CAR transcripts become diluted (and eventually lost) as the cells divide, he observes.
Such therapies would likely require persistent retreatment in the absence of a clinical response, especially for the treatment of solid tumors, which require a prolonged T-cell response. “Integrating vectors, such as lentiviral (LV) vectors, may offer the benefit of stably
integrating into the host-cell genome to allow for a sustained response with a single dose,” says Frost. As such, he anticipates further investigations into the tropism of viral approaches to reduce the risks of adverse events associated with non-target cell integration.
The level of investment in in vivo gene-modified cell therapies suggests that this new approach truly does have real potential. Several startups have been established in the past few years with strong financial backing.
EXUMA Biotech’s in vivo CAR/TCR therapy platform, GCAR, comprises a lentivector with a CD3- targeting/activation element on its surface to target T cells and provide them with their initial proliferation stimulus. The genetic payload within the LV encodes for either a CAR or TCR, as well as EXUMA’s intracellular “DRIVER” signaling domain. Once integrated and expressed by T cells, DRIVER signaling and initial CD3 activation causes robust in vivo proliferation with persistence and antitumor activity in a lymphoreplete environment occurring from continued antigen engagement, according to Frost.
“Our proprietary LV design elements address the challenges faced by in vivo CAR therapy, as the DRIVER allows for proliferation and persistence in the midst of competing cells, and the CD3-targeting moiety directs the lentivector to T cells,” Frost states. In preclinical animal models, EXUMA has confirmed enhanced tropism to T cells, circulating CAR-positive cells, and a potent, dose-dependent elimination of target cells upon in vivo lentivector administration.
Umoja Biopharma has developed its VivoVec surface-engineered LV vector-based off-the-shelf viral-vector particles for the generation of CAR-T cells in vivo (4). The particles include rapamycin-activated cytokine receptors (RACRs) designed to selectively provide costimulatory molecules to CAR-T cells in the presence of rapamycin. Preclinical study results indicate the particle design demonstrates enhanced T-cell binding and activation both in vitro and in vivo, as well as generation of large numbers of CAR-T cells, thus enabling enhanced antitumor activity at lower doses.
Vector BioPharma’s Shielded, Retargeted Adenovirus (SHREAD) platform uses engineered adenoviral vectors combined with exogenous, high-avidity adapter proteins (in the form of virus-like particles) to achieve delivery to defined biomarkers on specific cells or tissues of DNA encoding various genes and regulators, allowing local production of potent drugs with reduced risk of systemic toxicities (5,6). The company was established in August 2022 to commercialize technology developed in the laboratory of Andreas Plückthun, PhD at the University of Zürich (7).
Ensoma, launched in February 2021, is also leveraging adenoviral vectors (8). Ensoma’s Engenious vectors are devoid of any viral genome, thus minimizing the chance of an immune response and freeing up to 35 kilobases of DNA packaging capacity to deliver a diverse range of genome modification technologies. The vectors can be used in vivo to engineer hematopoietic stem cells as well as erythroid, lymphoid (e.g., T cells, B cells), and myeloid (e.g., macrophages, microglia) cell types with precision. The company has entered into a strategic collaboration with Takeda Pharmaceutical Company (9).
Capstan Therapeutics, which was co-founded by Carl June, one of the original innovators in the autologous CAR T-cell-therapy space, and launched in September 2022 (10), is using mRNA technology to generate CAR-T cells in vivo. In one example, they injected CD-5 targeted mRNA-LNPs to reduce fibrosis and restore cardiac function in a mouse model of heart disease (11).
Interius BioTherapeutics is commercializing technology developed by Saar Gill at the University of Pennsylvania (12). The company is initially focused on treating hematologic malignancies using an in vivo CAR treatment, but hopes to expand to applications beyond immuno-oncology that address diseases not amenable to current gene-therapy modalities. It has provided minimal information about the specific technology involved.
Sana Biotechnology has several in vivo gene-modified cell therapies at the preclinical development stage. SG295 is an in vivo CAR T with CD8-targeted fusogen delivery of a CD19-targeted CAR for treatment of patients with B cell malignancies and for which the company expects to file an investigational new drug application (IND) in 2023 (13). SG418 is a hematopoietic stem cell-targeted fusosome with the ability to deliver gene-editing material in vivo to repair genetic abnormalities such as those that cause sickle cell disease and beta-thalassemia. Sana hopes to demonstrate preclinical proof of concept in 2023.
Although in vivo gene-modified cell therapies constitute a novel drug class, they are related to direct gene therapies, several of which have received regulatory approval in the United States, European Union, and other countries around the world. These gene-therapy approvals, according to Frost, provide a helpful roadmap for regulatory evaluation of in vivo CAR therapies. “While each product and platform has its own unique considerations that must be addressed for a specific indication, the FDA has also published numerous guidance documents regarding gene therapy that are helpful to sponsors developing in vivo gene therapies,” he says.
As is the case with recent regulatory reviews of retroviral gene vectors in cells other than T lymphocytes, Frost expects that regulators will expect developers of in vivo therapies based on retroviral vectors to demonstrate that those vectors are indeed transducing the target cell type (e.g., T cells) and not other cell types, such as hematopoietic stem cells or gametes. In this context, he notes that significant consideration must be given to the tropism of the delivery vehicle, whether viral or non-viral.
Given the growing number of companies developing in vivo CAR therapies using many different approaches, Frost anticipates candidates entering clinical trials within the next several years. The data gathered during those trials will serve to better refine the science. “With the advances that will be achieved and the growing body of evidence that will be generated as a result of these studies, it can be expected that the overall industry will become more comfortable with in vivo gene therapy, ultimately facilitating the progression of other products to the clinic and eventually the market. The widespread use and breadth of enhancements to monoclonal antibodies, which were first discovered in 1975 and first approved in 1986, is suggestive of the potential for in vivo CAR therapy. With today’s technology and know-how, the innovation cycle for this technology is expected to be dramatically accelerated,” he concludes.
Cynthia A. Challener, PhD has been a freelance technical writer for over 20 years, leveraging her education from Stanford University (BS) and University of Chicago (PhD) and 10+ years of industry experience. She currently focuses on pharma/biopharma topics, writing technical articles, white papers, blogs, and other content for a variety of clients in addition to contributing regularly to BioPharm International and Pharmaceutical Technology.