Transitioning Therapeutics from Cells to the Clinic
Michael Burel
Regenerative Medicine: Transitioning Therapeutics from Cells to the Clinic
Organizers: Jane S. Lebkowski (Asterias Biotherapeutics), George Zavoico (JonesTrading Institutional Services), Sonya Dougal (The New York Academy of Sciences), and Caitlin McOmish (The New York Academy of Sciences)
Presented by the Biochemical Pharmacology Discussion Group
Academy eBriefing | Posted April 26, 2016
The New York Academy of Sciences
Overview
The field of regenerative medicine is burgeoning with cell-based therapies that aim to enhance or correct cell function. Preclinical and early-stage clinical trials have demonstrated that these therapies can provide local and systemic benefits by driving the production and secretion of biologically active mediators such as cytokines and growth factors to reverse disease progression and promote healing. Cell-based therapies are commercially available for cartilage and severe burn injuries, and clinical trials have shown promising results in diabetes, kidney disease, heart disease, stroke, cancer, spinal cord injury, neurodegeneration, graft-versus-host disease, and other areas. On February 22, 2016, representatives from academia and industry met at the Academy for a Biochemical Pharmacology Discussion Group symposium titled HYPERLINK "http://www.nyas.org/Events/Detail.aspx?cid=ae4dac0d-c719-4eba-a76f-6cdc8bd5e6e1" Regenerative Medicine: Transitioning Therapeutics from Cells to the Clinic. The symposium focused on efforts to make these new therapies routinely available in the clinic—requiring scaled manufacturing and formulation to meet distribution demands and regulatory guidelines, as well as adaptive clinical trial strategies, including novel outcome endpoints.
Mahendra Rao of Wake Forest University School of Medicine and Q Therapeutics opened the morning session by outlining the hurdles for bringing induced pluripotent stem cells (iPSCs) from bench to bedside. To meet clinical compliance standards, his group produced iPSC-derived therapies from already-compliant patient blood samples previously collected for clinical use. The team generated iPSC lines under good manufacturing practice (GMP) conditions, and then automated the process to lower cost and to be able to work with smaller samples. Host rejection is a major concern for iPSC-based therapies, and Rao suggested that countries should establish haplobanks of iPSC lines from "super donors" matching the common haplotypes of that region's population. He noted that the regions investigated so far, including ethnically diverse California, would require only around 200 lines.
After establishing iPSC lines in the lab, Rao's group tested the cells' differentiation capacity by generating dopaminergic neurons (DNs) as a potential treatment for Parkinson's disease. The group now has a 4-stage, GMP-compliant protocol for generating neural stem cells, a midpoint between iPSCs and terminally differentiated DNs. These cells are easy to culture, freeze, and transport. In animal model studies in rats injected with iPSC-derived DNs, the cells transplanted, survived, and integrated into host tissue. Working with collaborators at the University of California, San Francisco, Rao's group built a rotatable catheter to inject and uniformly distribute DNs in large animal models. Rao concluded by describing the successful generation of retinal pigment epithelium from GMP-compliant iPSC lines. This technique is undergoing clinical trial design for testing, safety, and efficacy.
Edward O. Lanphier from Sangamo BioSciences discussed the use of zinc-finger nucleases (ZFNs) as a means to genetically edit autologous diseased cells ex vivo before re-transplantation into patients. ZFNs are customizable genetic scissors that cut at precise loci; after DNA is snipped, it repairs itself via error-prone mechanisms to generate genetic knockouts. The method can also be used to insert genes into the genome. Lanphier described the ZFN approach in two disease contexts: HIV/AIDS and hemoglobinopathies. He began by noting the famous case of the "Berlin patient," a man with acute HIV/AIDS who in 2007 received a bone marrow transplant from a donor harboring a homozygous mutation in the CCR5 gene (CCR5Δ32), the functional form of which is a major co-receptor required for HIV to infect CD4+ T cells. After the transplant, the patient, Timothy Ray Brown, has remained HIV-free without medication and is considered cured. Lanphier's group generated ZFNs to mutate CCR5 in patient-obtained CD4+ T cells as a potential treatment for HIV/AIDS. Early data from a phase I/II trial demonstrated that viral load decreased in patients who received CCR5-mutated T-cells. Sangamo is enrolling additional cohorts for another phase I study. Next, Lanphier described his work on hemoglobinopathies (sickle cell disease and β-thalassemia), this time using ZFNs to target the BCL11A gene in bone marrow-derived CD34+ stem cells. BCL11A enables the switch from fetal (γ) to adult (β) globin during development. β-Globin is dysfunctional in patients with sickle cell disease and β-thalassemia. Lanphier's group is currently filing investigational new drug (IND) applications to test whether ZFNs that knock out BCL11A allow blood stem cells to revert to using functional γ-globin, bypassing the need for the defective β-globin gene and reversing disease symptoms.
Jonathan D. Glass of Emory University School of Medicine seeks to repair neurodegenerative diseases using stem cell therapies. His focus is on amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig's disease, a fatal disease affecting neurons that control voluntary muscle movement. Because neural stem cells (NSCs) can differentiate into neurons, oligodendrocytes, and astrocytes, Glass partnered with neurosurgeon Nick Boulis to build a device that injects NSCs directly into the spinal cord for ALS treatment. After animal validation studies, Glass began human trials in patients with severe ALS to evaluate the safety of NSC delivery via lumbar injections. Using MRI to determine the exact location of administration—which is "like hitting the size of Roosevelt's chin on a dime"—Glass injected NSCs under direct visualization in up to 20 different locations on each side of the spinal cord. The prognosis of ALS is notoriously difficult to predict, making it hard to determine the effectiveness of the therapy. Statistically, however, there was no difference in safety for the group receiving NSC injection compared to the placebo group. Autopsies later revealed donor DNA from the NSCs in every patient, suggesting that the cells successfully engrafted. Immunostaining showed that NSCs differentiated into neuronal and oligodendrocyte—but not astrocyte—lineages and retained stemness through Sox2 expression. Glass reported that the phase II trial is complete and the procedure is considered safe. The trial may move to phase III after its design is refined. Glass also aims to achieve intrathecal (spinal canal) administration of NSCs as a less invasive approach.
Using a method akin to Lanphier's ex vivo treatment of autologous cells, John F. DiPersio from Washington University School of Medicine developed a telomerase-based dendritic cell (DC) vaccine for acute myeloid leukemia (AML) called AST-VAC1. Researchers first obtained immature DCs from cancer patients via leukapheresis harvesting, then introduced messenger RNA (mRNA) encoding the human telomerase protein linked to a lysosomal targeting signal (LAMP) and cultured the modified DCs to maturity before vaccinating patients intradermally. DCs are well-studied antigen-presenting cells of the innate immune system, and telomere elongation via telomerase is both vital to cancer immortality and highly cancer specific. Attaching LAMP to the telomerase mRNA enhanced DC antigen processing. In a phase I safety and efficacy study, 95% of prostate cancer patients had an immune response to telomerase, and many showed reduced prostate cancer growth and had circulating immune complexes. In a phase II trial in AML patients, researchers successfully produced AST-VAC1 for 73% of enrolled patients, and the vaccine was well tolerated. Remarkably, more than 50% of patients were relapse-free after 52 months (compared to a historical average of 20%–40%) and all patients in second complete remission were relapse-free after 50 months (compared to a median survival of 3 months with standard treatments). DiPersio and colleagues are planning an AST-VAC1 registration program for a phase III trial.
A primary focus of regenerative medicine is to repair tissue damage from injuries such as severed spinal cord. Jane S. Lebkowski of Asterias Biotherapeutics described her work using cells called AST-OPC1s (human embryonic stem cell–derived oligodendrocyte progenitor cells) as a therapeutic approach for spinal cord injuries. OPCs remyelinate axons and secrete neurotrophic factors facilitating axonal repair and elongation. Lebkowski demonstrated that AST-OPC1s could remyelinate myelin-deficient shiverer mice and could stimulate new vascularization in injury-model rats. In fact, AST-OPC1s enabled spinal cord regeneration in rats, with myelinated fibers traversing the injury site. In human trials in subacute patients treated 7–14 days post-injury, AST-OPC1s were well tolerated; none of the phase I patients exhibited an immune response against the cells, perhaps because they received a 60-day course of immunosuppressants after the transplant. A year after treatment, patients had no significant adverse effects or ectopic growths and MRI imaging suggested that new tissue had formed in the injury cavities, but it was still too early to determine whether de novo regeneration had occurred. There were no changes in neurological function in the low-dose phase I trial, but in the phase I/IIa continuation trial the team tested an escalating dose of 2–20 million cells; as of October 2015, early results had demonstrated modest neurological improvement in the first patient. Lebkowski stressed the importance of this finding: recovering even two levels on a standardized scale of motor function considerably improves quality of life and patient autonomy. Her group has filed an IND application to use AST-OPC1s in cervical injuries.
Racheli Ofir of Pluristem in Israel described her team's work on post-birth placental cell–derived products to be administered locally for systemic effect. Placental cells resemble mesenchymal stem cells with a few key differences, including low immunogenicity and limited differentiation. But placental cells shine in their ability to secrete paracrine and endocrine factors that enable regeneration. Ofir discussed two products. First her group investigated angiogenic cells (PLX-PAD) from the maternal side of the placenta for their ability to recruit new vasculature to injury sites. Using a rat model and femoral artery dissection with blood flow as a functional readout, the researchers showed that transplanting PLX-PAD cells near the site of injury restored blood flow to 75% of normal levels within 28 days. Injecting PLX-PAD cells into the non-injured, contralateral limb also restored blood flow at the injury site—a striking result suggesting that the therapy has endocrine-based regenerative properties. In a phase I safety study, 85% of patients treated with PLX-PAD cells had amputation-free survival after critical limb ischemia, a 59% risk reduction compared to historical data. In patients receiving a total hip replacement, PLX-PAD treatment enabled muscle regeneration, muscle force recovery, and muscle volume growth. Next, the group investigated placental-derived hematological cells from the fetal side (PLX-R18), which have a different secretion profile from that of PLX-PAD cells and mediate haematopoietic colony formation and bone marrow migration in vitro. In mouse models of acute radiation syndrome, 96% of PLX-R18-treated mice survived compared to 30% of mice in the placebo group and all blood lineages were reconstituted. Ofir emphasized that local injection of this treatment had elicited a systemic effect and improved overall survival. PLX-R18 was approved recently for phase I testing in humans.
Describing another application of embryonic stem cells' regenerative potential, Thomas Schulz of ViaCyte gave an overview of the company's program to replace depleted pancreatic β cells in patients with type 1 diabetes. Current methods of β-cell replacement, including transplantation from cadavers, come with notable pitfalls, including low availability and rejection risk. ViaCyte has developed GMP-compliant culture conditions to differentiate pancreatic endoderm cells—precursors to insulin-producing islet β cells—from human embryonic stem cells. These early pancreatic cells are transplanted into the body using a semipermeable removable device the company designed, called Encaptra, which has pores small enough to allow nutrient exchange while preventing infiltration of the host's immune system. In mouse models, pancreatic precursors take 3 months to transition to islet cells in vivo, and within 6 months after implantation, treated mice successfully respond to glucose challenges. In hyperglycemic mouse models, blood glucose was gradually regulated to normal levels, and hyperglycemia returned upon device removal. Over time, vasculature grows around the perimeter of the device, and analysis of the cells inside showed that implanted pancreatic progenitors differentiated into islet-like endocrine cells. ViaCyte successfully filed for an IND in 2014, and a phase I/II open label, dose-escalating trial is underway to determine treatment safety and efficacy.
John D. Sinden of ReNeuron is developing an NSC treatment for stroke disability. Stroke is a single focal brain injury that is usually followed by some neural regeneration, and NSC therapies could augment that recovery and improve functional outcomes. However, stroke trials are difficult. Controlled studies in rats do not adequately capture stroke's heterogeneous presentation and outcomes in humans, which along with comorbidities in elderly patients, complicate trial designs that require large cohorts of similar patients. Using a GMP-compliant protocol, ReNeuron developed a conditionally-immortalized human NSC line, CTX, from a single fetal tissue sample. A phase I study demonstrated safety with doses up to 20 million cells, and the manufacturing process is being scaled up, with the goal of reaching an automated system with higher yields. The company also developed a method to store frozen cells for 6 months for efficient delivery to the clinic. In animal studies, rats recovered motor control at high doses and the NSCs generated motor neurons at the lesion site, promoted angiogenesis and neurogenesis, and abrogated the immune response. Sinden noted that only cells administered near the injury site had an effect. One outstanding question is when NSCs should be administered. Early therapy, which may be neuroprotective, requires quick administration of allogeneic cells, and it is often difficult to assess at this stage how severe the long-term effects of injury might be. Later, at chronic injury stages, NSCs may help with regeneration and rehabilitation from disability, and autologous cell products could be produced. ReNeuron is pursuing phase II testing of CTX cells to define endpoints, assessment tools, effect size, biological targets, and biomarkers.
Katherine Tsokas of Janssen Research & Development closed the meeting with a review of regulatory requirements for cell therapies in the U.S., Europe, and other markets. She explained the differing terminologies, manufacturing standards, and clinical trial requirements for approval. Tsokas described cell therapies as emerging products, and explained that regulatory and clinical development standards are therefore still being refined. As cell-therapy products are developed, consideration should be given to varying global regulatory requirements, to the risks and benefits of the specific product, and to the path to market, including coverage by insurance companies and other payers. She pointed to the need for flexibility on the part of companies and regulators, particularly taking into account the unique risks and benefits of therapeutic strategies that may not fit traditional clinical trial protocols.
The New York Academy of Sciences. Regenerative Medicine: Transitioning Therapeutics from Cells to the Clinic. Academy eBriefings. 2016. Available at: www.nyas.org/RegMed-eB
© 2016 The New York Academy of Sciences. All rights reserved.
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