The production of cells for cell therapy applications will reach industrial scale only after we expand our conception of bioprocessing. Historically, bioprocessing has been understood as the harnessing of cells—the use of cells as means, not ends. That is, cells have been used to churn out useful chemicals. Cells, however, may do more than toil on biotechnology’s assembly line. They may serve as therapeutic products themselves, provided they get out of the factory and enter the showroom.
One day, we may hear dealers of therapeutic cells ask, “What can I do to get this cell into your patient today?” At present, however, we’re still waiting for cell therapy’s Henry Ford to come along and show us the way to mass production. Fortunately, several would-be cell therapy industrialists are already vying for that role.
For example, the engineers and bioprocessing experts at Fibrocell Science put a lot of effort into their own version of a Model T cell, the azficel-T. In early road tests, this cell therapy vehicle showed itself to be underpowered, but it benefitted from know-how that remains in place and is growing in depth and breadth.
Fibrocell’s manufacturing process begins with the collection of skin biopsies from patients. Fibroblasts are extracted from skin samples, cultured through minimal passages, harvested, and then cryogenically stored. When a dose is requested, the cells are thawed, washed, and formulated to the target cell concentrations. Cells are kept at 2–8°C while they are shipped overnight to the administration site.
For genetically modified product candidates, Fibrocell scientists transduce the cells during an early passage, using lentivirus to deliver target genes locally for treatment of rare skin and connective tissue diseases.
“Our process requires high cell purity and viability,” says John Maslowski, Fibrocell’s CEO. Potency tests developed in-house confirm biological activity before administration. “We followed a lengthy CMC path with FDA to ensure that azficel-T meets cGMP standards,” he points out, “and we are applying this knowledge to our genetically modified programs as well.”
Fibrocell’s cell therapy program focuses on treating skin and connective diseases with the patient’s own fibroblasts. “We create localized gene therapies that are compatible with the unique biology of each patient and have the potential to address the underlying cause of disease,” informs Maslowski.
Fibroblasts are the most common cells in the body. They are present in all skin and connective tissue and are easily harvested, expanded, and processed. They are also readily modified genetically. It is said that fibroblasts are “functionally critical” because they are responsible for synthesizing the structural framework of tissue.
In early 2017, Fibrocell received FDA Fast Track designation for FCX-007, the company’s clinical-stage candidate for the treating recessive dystrophic epidermolysis bullosa, a rare genetic skin disease with no current treatment. Fibrocell’s commercial partner for FCX-007 is synthetic biology firm Intrexon.
Precursors to Production
BioTime, a clinical-stage biotechnology company focused on developing and commercializing pluripotent stem cell-based technologies, recently opened an 8,600-square-foot cGMP manufacturing center in Jerusalem, in association with Hadassah University Hospital. The new facility will help the company apply its stem cell-based knowledge to advance the treatment of degenerative diseases.
BioTime’s PureStem® cells are clonally pure, embryonic progenitor cells capable of undergoing scalable cultures to produce therapeutic cells free of potentially hazardous pluripotent stem cells. HyStem® Hydrogels are based on a unique hyaluronan chemical cross-linking. The resulting biomaterial mimics natural extracellular matrix.
The company recently indicated that it plans to present new findings about its OpRegen® cell-based therapeutic for age-related macular degeneration. The findings, from an ongoing Phase I/IIa trial, will be described in an abstract posted at a meeting to be held May 7–11 by the Association for Research in Vision and Ophthalmology.
PureStem cells derive from a library of clonally derived lines originating from pluripotent cells. Production consists of using growth factors to induce partial differentiation of embryonic pluripotent cells toward various tissue lineages, and isolating clones with high growth potential.
“We have various purified cell lines that represent the progenitor or precursor state of almost all tissue types in the human body,” says François Binette, Ph.D., BioTime’s head of global development. “If we need to repair bone we simply query the library for bone progenitors. If we need to repair blood vessels, we query the library for blood vessel cells, etc.”
The advantage of progenitor over pluripotent cells is their behavior and phenotypic fate are far more predictable for having lost their embryonic characteristics. They cannot form teratomas, for example, and have high proliferative capacities for commercial-scale expansion. “This is a characteristic that many adult cells or mesenchymal cells don’t have,” Dr. Binette explains.
PureStem lines grow very much like adherent adult cells but have far greater capacity to proliferate to commercial scale without reaching senescence. They may be expanded on various substrates such as flasks, bags, microcarriers, and various bioreactors using beads or hollow fibers.
In February, Cellectis received an Investigational New Drug (IND) approval from the FDA for a Phase I trial with UCART123, an allogenic gene-edited cell therapy, in patients with acute myeloid leukemia (AML) and blastic plasmacytoid dendritic cell neoplasm (BPDCN). UCART123 targets CD123, an antigen expressed at the surface of affected cells in AML and BPDCN.
According to the company, UCART123 is the first product of its kind to receive approval for such products. Human testing will begin in a few months.
Cellectis harvests primary T cells from patients for autologous therapy, or from donors for allogeneic products. Unlike immortalized protein-producing cell lines, cells for therapy are often primary cells for which phenotype and homogeneity are critical.
“Growing such cells in culture exerts pressure on their phenotype and, if maintained for long periods, may lead to emergence of subpopulations with potential genetic or epigenetic variations,” says David Sourdive, Ph.D., Cellectis’ executive vice president for technical operations. Moreover, these cells constantly renew their molecular composition and are physically fragile by nature. “They require,” Dr. Sourdive adds, “minimal manipulation and specific equipment, mostly for harvesting and general manipulation.”
Harvesting and purifying cells for therapy differs fundamentally from downstream processing for, say, CHO cells. “Fill and finish as well as quality control steps require completely different techniques and use specific measurements,” Dr. Sourdive explains. Terminal sterilization, which is common for protein preps, kills therapy cells. “In addition,” Dr. Sourdive comments, “maintaining stability—including genetic stability—and homogeneity of therapeutic cells is a concern throughout the process.”
As an allogenic therapy modality, UCART123 has the potential to trigger “non-self” immunogenic reactions in the recipient, a result of antigens and potential immunogens on their surface. Unlike proteins, cells may also trigger cell-mediated immune reactions, which is why so many cell therapies have been autologous or derived from compatible donors.
“This strong immunogenicity specific to cells has, de facto, confined a lot of cell therapies to the world of grafts, that is, autologous therapies or personalized products within stringent compatibility constraints,” Dr. Sourdive points out.
PCT, a contract development and manufacturing organization for cell therapies, is a relative old-timer in the cell-therapy marketplace. Since its founding in 2000, the company has acquired experience with more than 25 therapeutic cell and tissue types. This experience covers cell culture, expansion, and engineering plus cell product formulation. Late last year, PCT scientist Thomas R.J. Heathman, Ph.D., co-authored a review article on bioreactors for cell therapy with experts from GE Healthcare Life Sciences, Lonza, and Cellgene.
PCT specializes in autologous cell therapies. Just 14 cell therapies are marketed in the U.S. Most are based on cord blood, which is used to treat genetic diseases as an autologous therapy or through allogenic transplantation for siblings. The good news is that more than 500 cell therapy clinical trials are underway, with about half for oncology indications and about 10% in cardiovascular indications.
PCT is experienced with many of the approaches that are currently being evaluated. These approaches include therapies based on T cells (such as those incorporating transgenic T-cell receptors and chimeric antigen receptors), dendritic cells, CD34 cells, and mesenchymal cells.
Barriers to Industrialization
Whereas scaleup of production cell cultures encounters issues of feeding, mass transfer, and cell viability, the “industrialization” of autologous therapies runs into issues of its own. Many of these issues are related to cost.
“Many new technologies are emerging in process automation, closed systems, media formulation, cold chain transport, and rapid analytical testing that can improve the ability to commercialize these products,” says Maslowski. “The impact of these technologies depends various factors, including the nature of the therapy, number of cells needed to dose, growth substrates, media requirements, shipping configurations, shelf life, and analytical testing requirements.”
Sanjin Zvonic, Ph.D., business leader, clinical manufacturing, PCT, notes some of the shortcomings of today’s cell therapy production methods. “Cell therapies are based on highly manual, often open processes, which pose a significant issue as they move closer to commercialization. Cell-therapy developers need to look closely at the drivers for product commercial viability, with an eye to establishing processes that deliver high-quality, robust products that can scale to meet demand over the commercial life of the product, and importantly do so with a reimbursable cost of goods.”
Analogously to the manufacture of therapeutic proteins, cell-therapy business models must avoid the burdens imposed by unabsorbed overhead associated with idle capacity. “These models,” Dr. Zvonic insists, “must engage in mid- to long-term strategic planning to drive phase-appropriate process improvements and automation as products progress through clinical testing and approach/enter into commercial distribution.”
Dr. Zvonic predicts a strong future for both allogeneic and autologous cell-based treatments. Off-the-shelf cell therapies, where matching specific donors to a patients is unnecessary, have the potential for significantly reduced costs of goods and greater scalability compared to patient-specific cell therapies.
“This will lower the hurdle of the transformative value proposition often called for by the higher cost of goods of personalized cell treatments,” he explains. “The future success of off-the-shelf cell therapies must be established on a case-by-case basis, however, as these therapies reach pivotal trials.”
Industrializing cell therapies will require competencies that are relatively unfamiliar to biotech companies. To succeed, developers must recapitulate what was successfully achieved with therapeutic proteins decades ago; that is, developers must successfully transition from patient-bespoke autologous products to off-the-shelf products suitable for many patients.
The industry must also find a way to break the donor-recipient compatibility barrier. Otherwise, every treatment will be personalized and horrendously expensive.
“Manufacture of primary cells must be successfully scaled up, which is going to be more challenging than with immortalized cell lines,” says Dr. Sourdive. “Manufacturers need to establish robust quality controls and standards for cellular products, some of which may be comprised of complex composition. These standards need to be widely adopted throughout the industry and in all geographies.”
“Cost is probably the overriding issue in expanding therapy cells consistently and reproducibly,” Dr. Binette adds. “Growing batches for one or a few patients followed by production, testing, and all the other costs and logistics become a major issue.”
Having “almost immortal” cells with predictable behavior simplifies many process-development steps, again by analogy to production cell culture.
Other production issues, for example, transporting and storing live cells, can be solved in the near term but will require novel logistics. Developers must also consider addressing regulation of multiple jurisdictions, which according to Dr. Binette will “involve a learning curve where cell therapies are new and regulators are still in the process of developing guidelines.”
Industrialization holds implications for all therapeutic areas served by primary cells, including veterinary medicine. Vet-Stem BioPharma, which pioneered autologous cell therapy in animals to treat degenerative conditions such as arthritis, enjoyed a robust business but recognized allogenic treatments were more attractive.
Vet-Stem uses adipose-derived regenerative cells which are accessible in large quantities and differentiate into multiple lineages for bone, cartilage, and cardiac repair. Adipose-derived preparations contain a heterogeneous mixture of regenerative cells.
Vet-Stem subsequently developed an allogenic version of its therapy, which allows the manufacture of multiple batches for many patients from a single donor or pooled donor batch.
Steven St. Peter, CEO of Aratana Therapeutics, which has licensed the Vet-Stem allogenic technology, distinguishes between patient-specific and off-the-shelf cell-based therapies: “The advantages of a product-based stem cell-therapy versus the current service-based model include the potential for lower overall treatment costs for osteoarthritis and higher market penetration, facilitating scheduled campaign manufacturing and benefitting patients.”
Angelo DePalma Ph.D. is a writer for GEN.