June 15, 2016 (Vol. 36, No. 12)
Stem Cell Technology Is Shifting From Subsistence to Surplus
Clinical stem cell applications are the fruit of research efforts that have deep roots—years of research at the design and manufacturing level. It is from this ground that production processes for therapeutic stem cells are emerging like so many tender shoots. Ultimately, these processes will be scaled up and deployed widely, yielding a bumper crop of stem cell therapies.
From tissue engineering and immunotherapy to cell reprogramming and regenerative medicine, advances in stem cell technologies are being developed across diverse clinical indications and scientific disciplines. Dedicated researchers have navigated scientific and regulatory hurdles. Although they have few approved applications to their credit, these researchers are finding that their persistence is beginning to pay off. Several stem cell-based therapies are now in the clinical phase of investigation.
Getting to this point took a lot of spadework, recalls Kevin D’Amour, Ph.D., vice president of research and CSO of ViaCyte. “Everyone saw the great potential of using stem cells for therapy,” he says. “But the bottleneck there was that the cells themselves are not therapeutic.”
For decades, adds Dr. D’Amour, ViaCyte and other pioneers focused on learning “to isolate and grow embryonic stem cells and to harness, efficiently and at high purity, their differentiation potential.” Now, however, this technology is being exploited to pursue clinical therapies, the implications of which are beginning to emerge.
A particularly promising approach is genome editing. “The whole area of genome editing in stem cells is enormously broad and potentially curative in many diseases,” notes Edward Lanphier, president and CEO of Sangamo Biosciences. This shift to the “potentially curative” is significant. Perspectives in the field are broadening, and developers are embracing far-sighted plans.
Protein Factories
Human neural stem cells are at the forefront of therapeutic technologies for diseases of the central nervous system (CNS). Researchers at StemCells have had both preclinical and clinical success with their banks of human neural stem cells (HuCNS-SC®), which are isolated from fetal brain tissue, purified, expanded, and cryopreserved for use in direct transplantation.
The company pioneered this technology in 1999 and completing its first clinical trial in 2009. Initially, progress was slow because of extensive, albeit warranted, emphasis on safety. For example, the company’s researchers were cautious because there is no possibility of removing stem cells after they have been transplanted into patients. “We basically had to treat one patient at a time in the early days,” says Ian Massey, Ph.D., the company’s president and CEO.
Now, however, the company’s vigilance and perseverance seem to be paying off. “With the extensive safety data that we have, we are able to use this technology almost as a biological,” states Dr. Massey.
Proof of concept for HuCNS-SC therapy was established through years of rigorous preclinical research, and long-term, multi-year safety has been demonstrated in early-phase clinical studies. Now, researchers at StemCells are beginning to see evidence of efficacy—including self-renewal, engraftment, migration, and differentiation—when the stem cells are injected directly into patients.
Prospective applications for this technology, notes Dr. Massey, include “treating a number of CNS disorders through endogenous delivery of neurotrophic factors, by virtue of the fact that the cells are able to produce new neurons, oligodendocytes, and astrocytes.” Moreover, the potential exists to “gene modify these neural stem cells such that they become protein factories.”
“We have a very good opportunity to bring forward what will be a truly breakthrough therapy,” declares Dr. Massey. “It has the potential for opening up a broader series of indications for diseases where there are currently no real effective therapies.”
StemCells’ HuCNS-SC™ neurosphere is a cluster of purified human neural stem cells. The cells in this image, which was generated using a Leica SP2 confocal microscope, retain the ability to self-renew and differentiate into different cell types of the central nervous system.
Encapsulated Delivery
Delivery of stem cells is another challenge that researchers are addressing with innovation. VC-01™ islet replacement therapy, developed by ViaCyte for treatment of type 1 diabetes, consists of two components: a population of pancreatic precursors derived in vitro from pluripotent stem cells, and a macroencapsulation delivery device. This device, called Encaptra®, harbors the therapeutic precursors. It is implanted subcutaneously into patients where differentiation into islet cell types occurs in vivo.
Ultimately, the clinical goal is to functionally “cure” type 1 diabetes. “We put ‘cure’ in quotes because this product doesn’t change the underlying autoimmune etiology of diabetes,” explains Dr. D’Amour. “But the product helps patients cope with the disease, removing the need for the patient to constantly monitor blood sugar and inject insulin.”
Currently being tested in a Phase I/II study, VC-01 therapy is showing “encouraging amounts of cell survival, vascularization by the host, and differentiation into bona fide beta cells” at 12 weeks post-implantation, Dr. D’Amour affirms. These data validate the “ability of our encapsulation strategy to protect allografted cells in an autoimmune setting.”
As for the broader implications of this combination therapy, Dr. D’Amour expounds: “VC-01 for diabetes may become one of the first successful therapies to be developed from stem cells, and importantly from pluripotent stem cells. That, as a proof of concept, would have a huge impact on the field of regenerative medicine.” Moreover, “encapsulation would potentially have application for any cell therapy that aimed to replace a hormone-producing cell.”
Automation and scaled manufacturing will become indispensable for many stem cell technologies as projected approvals become reality. Dr. D’Amour gives this perspective: “The attractiveness of cell replacement therapy for type 1 diabetes is immense, but when you consider that each patient will need 300–500 million cells and that you have 1 million or more patients, you realize that you need to count in the trillions and not the billions.” ViaCyte has kept that need for scalability in mind as it has developed its manufacturing methods.
The cells in this image are ViaCyte PEC-01 pancreatic progenitor cells encapsulated within the ViaCyte Encaptra delivery system. Once implanted, the cells can mature into hormone-producing pancreatic cell types including those making insulin, glucagon, and somatostatin.
Body-on-A-Chip Systems
The generation of miniature organs, derived from human stem cells and grown on chips in the laboratory, is another exciting technology emerging from the field. The mini-model is monitored noninvasively and is more amenable to functional read-out than experimenting in a traditional clinical setting.
One researcher making good use of mini-models is James Hickman, Ph.D., professor, NanoScience Technology Center, University of Central Florida, and chief scientist, Hesperos. “Instead of measuring 20 biomarkers to see if a muscle will contract,” he says, “we just measure the contraction force.” Gene markers can still be evaluated, but the advantage is that a direct functional readout is obtainable in the same system. “It’s a real phenotypic model system,” he adds.
Notably, this technology allows for evaluation of different model organs in communication with one another. For example, a drug that treats heart disease might lead to toxicity upon being metabolized by the liver, so looking at the interaction between those systems is essential for evaluating the drug. Researchers demonstrated this capability in a chip that included both cardiac and liver cells.
“We showed that toxicity from metabolites was reversible,” Dr. Hickman explains. “When we took the liver out of the system, we showed that the cardiac cells were fine, but when we put the liver back into the system, we showed cardiac toxicity.”
This interconnecting aspect of the “body on a chip” system will be invaluable for achieving the ultimate goal—personalized medicine. “We can take your stem cells, derive the various tissues from whatever disease you have, and then show that one treatment versus another is better for you and use that personalized information to guide your treatment,” asserts Dr. Hickman.
Furthermore, the technology holds the potential for more efficient and cost-effective modeling of human disease. “We are trying to replace animals preclinically,” says Dr. Hickman. “But we are also trying to reduce the number of human subjects in clinical trials.” The researchers anticipate implementing the models for cancer research, diabetes, muscle wasting, and genetic diseases, among others. “We can build all of those different disease models on a chip,” concludes Dr. Hickman.
Hesperos, a human- on-a-chip company, has developed a system that models liver, heart, skeletal muscle, and neuron function. The system can assess cell activity and function via biochemical assays, micro- fabricated cantilevers, and patterned microelectrode arrays.
One-and-Done Outcomes
Genome editing of stem cells is also a huge focus in the field right now. For example, at Sangamo Biosciences, Edward Lanphier’s group is conducting research aimed, he says, at “engineering zinc finger nucleases (ZFNs) to target specific sequences of clinical relevance in stem cells and then re-engrafting the cells so they can have the intended benefit.” At Sangamo, ZFNs are the core technology, but other gene-editing strategies such as CRISPR/Cas9 or TALEN can also be employed.
Lanphier’s group uses ZFNs to disrupt the CCR5 gene in hematopoietic progenitors as therapy for patients infected with human immunodeficiency virus (HIV). The goal is to leave the immune system incapable of being infected by the virus but capable of mounting an antiviral response.
“Essentially, this could potentially be a curative outcome for HIV,” says Lanphier. The researchers are also using this technique to disrupt Bcl11a, a regulator of gamma globin and beta globin, in a way that shuts off the disease-related beta globin and turns back on the putatively curative gamma globin in the stem cells of patients with beta-thalassemia, a genetic blood disorder that reduces the production of hemoglobin.
Lanphier envisions a “one and done” outcome, where treatment with the modified stem cells results in HIV patients who no longer need chronic antiretroviral therapy, and in patients with beta-thalassemia who no longer depend on transfusions.
Democratization of Gene Therapy
Researchers at Calimmune are also “armoring cells against HIV” using stem cell–based techniques. In this case, the investigators are using a cell-delivered gene therapy approach that is in part built upon a natural mutation of the CCR5 receptor that occurs in about 1% of the population.
“In the homozygous condition, individuals are protected from HIV,” explains Geoff Symonds, Ph.D., head of scientific affairs and collaborations. “In the heterozygous context, there is a delay in onset and progression of HIV.” The company, he continues, aims to stop the binding of HIV with the cell surface and the “consequent fusion of the virus with the cell membrane.”
This is achieved by introducing genes in stem cells through the use of a self-inactivating lentiviral vector. In this case, the vector is based on HIV. “We use the patient’s own stem cells isolated from the blood, modify these outside the body by introducing the protective genes, and then reintroduce those cells back into the same patient,” details Dr. Symonds. This approach has the benefit of eliminating the need for immunosuppression as the cells are not modified in any way that will make them rejected by the body.
Researchers at Calimmune have taken the lentiviral vector approach further by developing Cytegrity™, a cell-based vector manufacturing process. As described in a recent press release from the company, Cytegrity is a “scalable manufacturing technology for the production of lentiviral vectors, which are used as a delivery mechanism for gene therapy.”
The idea behind the technology is to avoid the tedious, relatively small-scale manufacturing processes that usually accompany lentiviral production and to increase quality and efficiency of the therapy. The goal, Dr. Symonds insists, is to lower costs and increase accessibility of these types of vital therapies, essentially “democratizing gene therapy.”
