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Clinical Experience in Regenerative Medicine and Tissue Engineering: The Next Wave of Advanced Therapies

How do we move therapies from commercialization to industrialization, with tissue engineering being slightly less mature than cell and gene therapy?

Chair

Julie Allickson (Director, Regenerative Medicine Clinical Center, Wake Forest Institute for Regenerative Medicine, Winston-Salem, North Carolina, USA)

Speakers

Petter Björquist (CEO at VERIGRAFT, Gothenburg, Sweden)
Laura Niklason (Yale University, New Haven, Connecticut, USA and Humacyte Inc., Durham, North Carolina, USA)

Julie Allickson – Clinical Translation of Tissue Engineering in an Academic Facility

To begin this session, Julie Allickson sought to introduce the Wake Forest Institute for Regenerative Medicine (WFIRM) and begin to answer an important question: how do we take a research idea through clinical trials and toward the industrial scale.

The challenges to this process abound: a viable supply chain can be complicated due to the temperature-sensitive nature of many of the associated products; manufacturing remains a difficult task with regard to the level of automation required; intellectual property can be hard to deal with, the maintenance of investment and market opportunities can be problematic when intellectual property challenges exist; and finally, regulatory concerns are always a significant hurdle. Overall, controlling every variable that affects manufacturing represents a considerable challenge, especially when we are seeking to create sufficient donor organs to meet current demand.

While there are a large number of regenerative medicine companies, there remain considerations in biomaterials and tissue engineering with regard to receiving adequate grade products without needing to qualify each component in-house. However, the global landscape of clinical trials shows that 5% of the total are in tissue engineering, with a considerable number of these in phase II, showing the maturing state of the field.

Julie Allickson highlighted the WFIRM as a solution to many of the problems associated with this growing field. Simply put, is an under-one-roof solution the way forward?

The WFIRM covers a wide range of aspects regarding regenerative medicine. While the main focus lies on tissue engineering, other facets, such as cell therapy, biomaterials, devices, and small molecules, remain important. In this manner, the WFIRM works with a regenerative medicine “generator” concept in mind; this brings together aspects such as a technology incubator with accelerators (private partnerships and venture) to foment the generation of companies with a product as a means to accelerate commercialization of a tissue-engineered product, which includes possible fast tracks through regulation.

The WFIRM is organized for innovation and translation, bringing together multidisciplinary and cross-functional core programs to move toward preclinical testing, FDA-approved manufacturing, while integrating translational and commercialization services to commercialization. Their tissue engineering approach is mainly autologous, involving patient-derived cells and biomaterials/scaffolds for transplantation into patients. Scaffolds include decellularized tissues/organs, bioprinted products, or natural/synthetic biomaterials that combine with devices such as bioprinters, organ 3D printers, and skin printers, which are directed by imaging and modeling technologies.

The success stories of the WFIRM concept include a tissue-engineered biomaterial-mediated urethra (phase I FDA-approved) and tissue-engineered corpora that uses a decellularized scaffold to treat battlefield-associated injuries.

In summary, clinical translation begins with the end in mind, and the FDA/EU agencies will provide support to accelerate clinical translation if scientific evidence exists; however, multidisciplinary teams are required to move regenerative medicine from the bench to the bedside.

Petter Björquist – Personalized Tissue-Engineered Organs That Will Revolutionize Future Medicine

Petter Björquist sought to describe his company (Verigraft, meaning “true graft”), a classic university spin-off company, and their efforts toward personalizing organs to revolutionize regenerative medicine. Their main product is a blood vessel graft that combines tissue engineering and personalization, the two key terms in this highly entertaining presentation.

While we may hope to bioprint hearts and complex organs in the near future, we are not quite at that stage in the here and now, and we are limited to the generation of small patches of tissues. Verigraft does not aim to make new organs; instead, they aim to personalize organs and make them clinically useful. In brief, they take cadaveric donor blood vessels, which cannot be directly transplanted without creating immune problems, and remove their identity by removing cells and DNA. This leaves behind an extracellular matrix scaffold that can be safely stored in the long term. The next process in the Verigraft procedure is to use whole patient blood to recellularize the scaffold to generate a personalized organ—the blood vessel with a “new” identity or a personalized tissue-engineered vein (P-TEV).

Initial large-animal studies in minipigs confirmed the safety and efficacy of P-TEV over one year, with longer-term GLP studies employing large white pigs. For these studies, a P-TEV manufactured from porcine vein allograft was personalized with porcine autologous blood and implanted in the inferior vena cava. The endpoints for this study included rejection, occlusion, mechanical failure, or infection, which are all important potential side effects of blood vessel transplantation; however, results established that P-TEV biologically integrated, remained patent, and there existed no signs of transplant rejection. Encouragingly, the P-TEV and native vena cava did not show any significant differences in the degree of cellularity or the expression of endothelial markers, suggesting rapid engraftment; furthermore, P-TEV grafts in the long-term minipig model did not produce thrombosis, rejection, infection, or mechanical failure in any animal.

The final aim is to market P-TEV for patients with chronic venous insufficiency (CVI); the severe and incurable stages of CVI currently affect at least 1.5 million patients in the European Union and North America alone, with approximately 300,000 new patients diagnosed every year. The disease significantly affects a patient´s quality of life and puts numerous patients out of work or into disability programs and is, therefore, a significant burden to patients, employers, and health care systems. The Verigraft approach takes cadaveric vein segments of 4 to 6 cm that contain one functional valve and generates the P-TEV construct that can be grafted by a simple end-to-end anastomosis.

Encouragingly, Verigraft is about to start a first-in-man clinical trial—a phase I/II clinical trial planned in Europe (Spain) to evaluate safety and efficacy. The trial aims to replace vein segments with an incompetent valve with a P-TEV graft with a functional valve in 15 severe CVI patients. Safety endpoints will be evaluated at 4 weeks, and safety and efficacy monitored through 3, 6, and 12 months in what will be the first clinical trial of its kind worldwide.

The expected success of P-TEV for patients with CVI will hopefully lead to further trials in Europe (a further 50 patients in phase II trials) toward achieving approval. With regard to the U.S., the pre-IND meeting with the FDA had been set for March 2020 (delayed due to the ongoing COVID-19 situation), with 100 patients needed for market approval. Meanwhile, Verigraft is seeking licensing agreements in Asia and the rest of the world. Subsequent process development for the large-scale application of tissue-engineered grafts now has to consider how to scale-up—a crucial aspect that remains difficult but not impossible. With regard to P-TEV, the large scale decellularization process is currently being scaled up, although the scaling-up of the recellularization steps remains to be fully developed.

Finally, Petter Björquist discussed the future of Verigraft technology by briefly mentioning P-TEA (personalized tissue-engineered arteries) and P-TEN (personalized tissue-engineered nerves). P-TEA appears to be safe and effective in large animals and aims to address those high medical needs where synthetic and semi-synthetic grafts work poorly, such as in peripheral and cardiac bypass grafting. Clinical trials of P-TEA will begin in 2023. Meanwhile, P-TEN is currently being evaluated in large-animal testing for peripheral nerve repair.

The take-home message from Petter Björquist is that Verigraft technology is close to clinical reality—tissue engineering without making new organs but instead personalizing donor organs for patients. The critical next steps are considerations relating to scaling-up, industrialization, and process development.

Laura Niklason – Will Engineered Tissues Transform Medicine?

Laura Niklason aimed to take us through a high-level view of the Humacyte approach to arterial engineering, and while some similarities were drawn, there were also significant departures from the previous presentation from Petter Björquist.

To begin, Laura Niklason discussed the evolution of cell therapies and regenerative medicine to provide some “color” and background, given that this concept is now approximately 40 years old. Indeed, the mechanical engineer Eugene Bell at MIT coined the phrase tissue engineering in 1982, and he invented one of the first engineered skin products in 1981 and the engineered blood vessels in 1986. The term regenerative medicine was coined around 2002 after the initial boom and bust of the first tissue-engineered products, and the original concept was to place cells on a synthetic biocompatible scaffold and then coax them into forming a functional tissues/organs. This historical description was directed more at the younger members of the online audience, as the speaker believed it imperative to understand that many projects are audacious and are not simple, and they require a mix of optimism and realism for all involved at all levels.

Next, Laura Niklason began to describe her work, “Engineered Arteries – Off the Shelf Human Tissues?”, which formed the basis for the founding of Humacyte around 15 years ago. The Humacyte approach begins with the isolation of smooth muscle cells from the aortas of deceased patients and their characterization via an extensive battery of wide-ranging tests that evaluate both function and safety. Banked cells can be expanded in vitro and then seeded onto tubular biodegradable polyglycolic acid scaffolds in a single-use bioreactor, where they grow according to the scaffold size (generally around 42 cm in length). These constructs are grown with adequate growth factors on the medium; however, they are also grown under conditions of mechanical pulsatile stretching, which mimics the stretching of the aorta with each human heartbeat, to induce functional maturation. Overall, this mechanical stimulus represents a vital means to accelerate cell growth, cell organization, and matrix deposition. After 8 weeks in culture, the polymer has generally dissipated, leaving the cells/cell progeny and the extracellular matrix components surrounding them. The Humacyte process then decellularizes this construct to generate an engineered human vascular tissue that is non-immunogenic, has a shelf life of 1 year, and maintains the mechanical characteristics of original tissues, given that the vascular mechanics derive from the matrix and not the cells.

The following section discussed how they could move this advance into patients by first assessing safety and efficacy in animal models. This step employed baboons as a good model for humans with regard to size and immune toleration. Arterial venous grafts in a dozen baboons were conducted and analyzed in-depth to form the data required for the FDA submission (the “agony,” as Laura Niklason jokingly put it). From here, Humacyte moved to start phase I/II clinical trials in patients requiring hemodialysis access conduits. A total of 60 dialysis patients (end-stage renal failure) underwent implantation in Poland in 2012 and in the U.S. in June 2013, with safety and efficacy the primary objectives. From here, they determined patency rates of the bioengineered vessels at 6 months, although followed to 24 months (and then 10 years in some patients!). The engineered vessels allowed for efficient hemodialysis, and even though the vessels were regularly punctured with needles, some patients are still using them now, many years later. Interestingly, biopsies have shown that needle puncture sites appear to heal after repopulation with patient blood-derived monocytic CD68-expressing cells, which may contribute to smooth muscle formation.

More specifically, the 60 patients were implanted, and there was a mean follow-up of 36 months; this provided evidence of safety and functionality (for dialysis) with up to three punctures a week. The functional patency observed (90% of patients with functional vessels after 1 year, warranted further study in phase III. Indeed, the functional patency compares well with synthetic artery venous graft (e.g., Teflon has functional patency of 65% to 70%), which gave the FDA reason to allow two phase III trials, which are currently ongoing. The first phase III clinical study (NCT02644941) is perhaps the first prospective phase III randomized trial of an engineered tissue ever and uses 365 patients from six countries and 38 sites and a head-to-head comparison of the engineered vessel versus polytetrafluoroethylene. The trial has a primary follow-up of 2 years, with the primary endpoint secondary patency at 18 months and secondary endpoints infection and intervention rates and primary patency. While the trial data has yet to be published, the other trial is currently enrolling.

For the development of these phase III trials, they had to develop manufacturing systems that created ten engineered vessels per batch. In other words, they had to look at vessel production at an industrial scale—a vitally important feat that entailed significant difficulty and a considerable time/labor input from a range of people with different skills. With regard to the Humacyte approach, the cell banks helped the scale-up efforts; cells that can grow over many population doublings can permit the generation of thousands of vessels from a single donor, thereby fostering reproducibility and uniformity of final product. The generation of industrial-scale numbers of vessels also needs to take into consideration testing; small numbers are destructively tested while others are non-destructively imaged for the presence of defects before the remaining vessels are shipped to trial sites. In the hope of getting FDA approval, Humacyte has begun to look at an automated commercial system that can make up to 200 engineered vessels from a batch of cells from a single donor. This has entailed a substantial amount of design and engineering with a significant level of automation; however, there still exist manual aspects. The critical and interesting question is to ask which parts to automate. The answer here is that generally one should look to automate the highly repetitive steps, while allowing the steps performed once per batch to be manual.

Discussion

Petter Björquist first discussed the choice of the porcine model for preclinical safety; reasons included the similarity of the vascular system to humans and the accessibility of the abdominal cavity for surgery. Laura Niklason noted that before baboons, they had studied vessel implantation into dogs; however, they observed a robust immune response, and this risked the FDA asking for immunosuppressors to be given in the phase I trial, which is precisely what the strategy they use aimed to avoid. Encouragingly, the primate results were excellent and mirrored the human situation, thus making the problematic experiments worth the effort as they had a predictive model. Furthermore, analysis of the baboon model also provided evidence for the gradual and homogenous endothelization of the artificial vessels, suggesting that this is also the case in humans.

The next question arising related to access to cadaveric cells/tissues. Petter Björquist described this as a challenge, requiring the building of relationships with hospitals and donation associations; however, this is becoming easier with time, as the idea of donation is becoming normalized. Laura Niklason agreed that it could take years to gain and nurture partnerships with associations, although, in the case of Humacyte, their cell bank will allow them to produce vessels for many years at this point.

Petter Björquist then talked about the need for automation and lot release and testing for Verigraft products. While P-TEV has not yet passed into large scale automation, this will need to be developed. He notes that as projects such as these are multifactorial and need lots of people with various expertise, collaboration and the efficiency that derives from it are the key going forward. Lot release and testing for Verigraft products differ due to their personalization, which makes each batch a single unit in size; the “simple” solution to this problem is wide-ranging and exhaustive nondestructive testing and monitoring.

Laura Niklason then discussed the additional application of the Humacyte engineered vessels beyond hemodialysis, highlighting smaller clinical programs (phase I/II) ongoing in peripheral arterial disease with 35 patients in follow up. This uses the same vessel but in a different location (the legs), and the speaker notes that the data is very encouraging. Another foreseen application is vascular trauma; can we repair injured arteries? The ability to use artificial vessels as an off-the-shelf repair material may represent a real advantage for those suffering from severe acute injuries on several levels.

The next question dealt with industrialization across the globe. Laura Niklason described the flux of European guidelines and the difficulty of getting guidelines for the specifics of a graft that is, on one level, unclassifiable. However, ongoing communication seems to be the most crucial factor moving forward, and this may need to occur on a country-to-country basis. Petter Björquist broadly agreed, noting the probable need to make country-to-country agreements when a pan-European strategy would be better.

The final questions dealt with reimbursement: what will this look like; what is the strategy? Petter Björquist highlighted the importance of analyzing your market and making a careful health economic analysis; what does it cost to society? While costs will be high to start with small quantities of output, scaling will allow a lower price to address a larger market. In the case of P-TEV, they have a viable reimbursement model that prices the product at 3 to 10 times the production and material costs. Laura Niklason noted that the expenses with Humacyte are high due to a long time in cell culture; however, automation and scaling up have provided some savings, and they are now looking to technological advancements to save on medium and growth factors. As the Humacyte and related products will reach a larger market, as the diseases implicated are not rare, the reimbursement fees will not reach that observed for CAR-T therapies, so this must be taken into consideration.

More from the Speakers

Julie Allickson

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Laura Niklason

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