Engineering a broader bio-delivery system for gene therapy

The first gene therapies approved in the U.S. have undeniably transformed lives. Families describe the results with genuine wonder: Children who had been going blind can now see the moon for the first time, thanks to Spark Therapeutics’s Luxturna. Babies who would otherwise be paralyzed are crawling, rolling, and even learning to walk after treatment with Novartis’s Zolgensma.

These are truly accomplishments to celebrate, and they’re just the beginning. The accelerating pace of technological breakthroughs is dramatically increasing the number and kinds of diseases that are amenable to gene therapy. There’s a revolution afoot.

Luxturna and Zolgensma are both designed to deliver healthy genes to just a single location in each patient’s body: the eye (for patients with an inherited retinal disease) or motor neurons (for very small children with spinal muscular atrophy). The treatments are made using a highly modified adeno-associated virus (AAV) as a vector.

The challenge? Many diseases will not respond to a treatment delivered only to the eye, the liver, or one of the few other tissues that AAV vectors can target. For these diseases, we need a delivery system that can transport the transgene coding the therapeutic protein throughout the body – ideally even reaching hard-to-access areas, such as the brain and muscle.

“There’s a revolution afoot.”

In recent years, we have seen compelling evidence that such a delivery system can be engineered.

The approach is called ex vivo gene therapy, meaning that the transgene incorporation takes place in the lab, rather than in the patient’s body. The process starts with the collection of the patient’s hematopoietic stem cells. Back in the lab, a highly effective vector, based on a significantly modified lentivirus, is used to transduce those cells with a transgene that encodes for a functional version of the enzyme that the patient lacks. Those engineered cells are then infused back into the patient.

This is an elegant solution for several reasons.

First, lentiviral vectors are excellent at working undercover. An AAV vector can effectively introduce transgenes into cells, as we’ve seen, but their genetic message (DNA) will remain floating in the nucleus — an outsider, not integrated into the patient’s chromosomes. The lentiviral vector, on the other hand, seamlessly inserts its genetic message right into the patient’s DNA. That integration ensures durability: When the cell divides, each of the daughter cells will also carry the transgene.

As convenient as this sounds, there is a catch: For the treatment to take hold for the long-term, the engineered stem cells can’t just drift at random through the patient’s body — they have to “engraft” in the bone marrow. In other words, they have to move in and take up residence.

Once installed, these engineered stem cells can mature into all the elements needed for healthy circulatory and immune systems: red blood cells, platelets, T cells, macrophages and more. The nucleated descendants of the engrafted modified stem cells become delivery trucks for the therapeutic protein by manufacturing, delivering and secreting it throughout the body, thereby providing deficient cells with a 24/7 supply of functional protein.

Even more exciting, there’s evidence that one kind of descendant, the macrophages, recognize and flock toward organs that have been damaged by the patient’s disease. If the heart needs extra help, the macrophages swarm to the cardiac tissue. If the kidneys are in trouble, they congregate there, producing the functional enzyme where it’s needed most.

Perhaps the best news of all is that cells carrying the transgene also engraft in the brain.

“The key question… Does it work? Data from a number of biopharma leaders and academic institutions suggest it does.”

That is quite a feat considering that the human brain is protected by an intricate barrier of protective tissue. Known as the blood-brain barrier, it selectively moves key nutrients and selected proteins from the blood into the brain while blocking unwanted proteins, harmful toxins and immune cells that can interfere with brain function. This is a crucial protection in normal circumstances, but it makes it extremely difficult to get desperately needed protein-based therapies into the brain.

That’s why it’s so remarkable that the modified stem cells delivered via ex vivo lentiviral vector therapy have been shown to engraft not only in the bone marrow, but also to enable the sustainable repopulation of the microglia cell population in the brain. These new generations of modified microglia traffic throughout the brain, delivering functional enzyme directly to neural tissues.

The one tissue our ‘delivery trucks’ have a hard time reaching is muscle. That’s a common challenge for both gene therapy vectors as well as the enzyme replacement therapies (ERTs) typically used to treat lysosomal storage disorders, such as Pompe disease.

We at AVROBIO have developed innovative technology that we believe can overcome that limitation. In our preclinical development work for a potential Pompe therapy, we engineer the transgene to produce and secrete not just the functional protein the patient needs, but also to incorporate what’s known as a “GILT tag,” attached to the protein with a short linker. That GILT tag is designed to dock onto a receptor found on the surface of muscle cells in order to gain entry. Upon entry, the therapeutic protein does its essential work: it is designed to enable lysosomes in the cells to function properly, breaking down the toxic substrate that would otherwise accumulate and harm the patient’s health.

Thanks to the efficacy of this miniature manufacturing and trucking system, we believe that patients who receive lentiviral gene therapy treatment, if approved, can expect to have many billions of engineered cells in circulation for years – potentially decades – after treatment, their transgenes working around the clock to help produce the active enzymes the patients need to stay healthy.

This is the kind of delivery service we need to tackle more genetic diseases! It’s global, responsive – and a different way of thinking about gene therapy.

The key question, of course: Does it work?

Data from a number of biopharma leaders and academic institutions suggest it does.

Last spring, for instance, bluebird bio published strong interim data from two distinct ex vivo β-thalassemia programs in the New England Journal of Medicine. Fifteen of 22 patients followed for at least two years after treatment stopped needing regular red blood cell transfusions. The need for transfusions was significantly reduced in the majority of other patients.

Patients in these bluebird bio trials underwent “conditioning” before treatment with a drug called busulfan. This drug works by creating space in both the bone marrow and CNS compartments for the billions of infused stem cells that will soon be delivered. It’s an essential part of the process; the new cells need that space to engraft.

In another strong sign for this cutting-edge delivery system, Orchard Therapeutics this spring reported positive data from a trial evaluating a gene therapy for treatment of metachromatic leukodystrophy, or MLD, a life-threatening metabolic disease. Like the therapies mentioned above, this is an ex vivo, autologous, hematopoietic stem cell-based gene therapy. Children treated with the therapy scored substantially higher in gross motor function than children of the same age who were not treated; importantly, they also maintained cognitive performance scores within the normal range.

“We look forward to the day when the world will hear a new round of heartfelt stories from patients and families who have had their lives transformed by gene therapy.”

Both bluebird bio and Orchard Therapeutics found evidence that the gene-corrected cells they delivered via their therapy had engrafted into the patients’ bone marrow. In other words, they had settled in, as intended. That suggests these gene therapies could prove durable, with new generations of the engineered cells continuing to circulate and secrete active proteins for many years to come.

If those two data points weren’t enough, here at AVROBIO, we recently announced interim data from ongoing trials of our investigational gene therapy for Fabry disease. Patients living with Fabry have a genetic mutation that interferes with the function of a crucial enzyme. When that enzyme does not work properly, substrates and toxic metabolites, including Gb3, a fatty substrate, build up in the patient’s cells. Initially the patients often experience pain and burning sensations, especially in the hands and feet, followed by an array of other symptoms. Our interim data included a kidney biopsy performed on the first patient in our Phase 2 study a year after his treatment with our gene therapy. It found an 87% reduction in Gb3 substrate. We also saw substantial and stable reductions in Gb3 in plasma in the first four patients in our Phase 1 trial.

You can see why we’re excited.

To be sure, we still have considerable work to do. Like our peers, we’re working hard to improve our lentiviral vectors, to streamline our manufacturing process and to fine-tune our conditioning regimen so patients can get maximum benefit with minimal side effects. We’re also continuing to advance our clinical trials, with the help of courageous patients and a terrifically dedicated group of physician investigators.

We firmly believe that we – and others in the industry – will be able to demonstrate the efficacy and durability of ex vivo lentiviral gene therapy built around transducing hematopoietic stem cells with transgenes encoding functional proteins. This delivery system, we believe, will prove a vital tool for expanding the reach of gene therapy to many more indications and many more patients in need.

We look forward to the day when the world will hear a new round of heartfelt stories from patients and families who have had their lives transformed by gene therapy.

Geoff MacKay is President and Chief Executive Officer of AVROBIO, Inc.  AVROBIO is currently conducting clinical trials to evaluate the safety and efficacy of its investigational ex vivo lentiviral gene therapies.  None of these investigational gene therapies have been approved by the U.S. Food and Drug Administration or any other regulatory agency.  For more information, go to

Scaling up gene therapy to address global commercialization challenges

With clinical success, all eyes turn to gene therapy manufacturing and commercialization challenges

Cell and gene therapies are here to stay as a new class of life-changing medicines. They recently headlined the fiscal year report issued by the FDA’s Center for Biologics Evaluation and Research (CBER), in which CBER Director Peter Marks prominently noted, “FY 2018 was particularly exciting because of the pace of progress in cellular and gene therapies. CBER received more than 150 INDs for gene therapy products, bringing the total number of active INDs up to nearly 800 applications.1

Dr. Marks has been outspoken about what’s needed for the next stage of gene therapy. He has written, “For gene therapy, the quantum leap that I would expect in the next five years or so is solving the issue of manufacturing. This is needed to continue advancement of the field and to allow it to reach a broader range of patients.”2

I couldn’t agree more.  In fact, from the very first moment we formed AVROBIO in 2015, our raison d’être was to take ex vivo lentiviral gene therapy mainstream, first line, to industrialize it. We set our sights well into the future. I believe this longer-term vision is necessary for any gene therapy company that wants to create meaningful, sustainable value.

Like other gene therapy biotechs, our technologies and programs had their roots in academia. As AVRO has grown, we have focused on optimizing our vector and manufacturing systems with the expectation that they may become a commercial stage platform that can support the potential development of treatments for multiple diseases.  We call this platform plato™.

Beginning-to-End Integration

The plato platform has focused our attention on refining, and locking in, a set of process changes that seek to optimize the potential potency, efficacy and durability of our investigational gene therapies and solving the downstream operational bottlenecks.  For any gene therapy process, we believe the rigor of evaluating and integrating every step in the product commercialization process is required for mainstream market success.  We view this as beginning-to-end integration.

Putting Strategy into Practice

It’s a well-known fact that there are bottlenecks and barriers to manufacturing and commercializing gene therapies. It’s a big step to take something that’s really bench science – petri dish science – that can enable a lab procedure to treat one patient and turn it into a process for creating medicines for thousands of patients.  This transition to industrializing gene therapy is what Dr Marks suggests is needed now.

How is it possible to tease apart all the elements and complexities of commercializing gene therapy to build a beginning-to-end process?

The 3 Major Challenges

As a case in point, let me describe our approach building plato over the past three and a half years.  Essentially, we identified three historic bottlenecks or hurdles in developing gene therapies. Then, we steadily built plato to include proprietary or industry-leading solutions to enable optimization, integration, and scale with the goal that AVRO becomes a multi-product gene therapy leader. We build one platform that’s designed to be applied across our portfolio:

Challenge 1:  Developing a high-performance vector that’s a product engine

For every gene therapy developer, the vector is fundamental because it defines many performance characteristics.  It’s important to invest in vector design as early as possible.  For AVRO, plato includes our proprietary,  state-of-the-art, four-plasmid lentiviral vector system, called LV2, that is designed to be produced in a commercial-scale process.

At the outset of developing LV2, we envisioned a common vector that could be used throughout our portfolio of investigational gene therapies for a class of rare diseases, called lysosomal storage disorders. We integrate proven, best-in-class components into LV2, meaning the components have been previously successful in the clinic. Technical improvements include potentially enhanced safety by moving from a three- to four-plasmid system, streamlining the four plasmids to increase titer, and enhancing transgene transcription and translation, to increase in vivo enzyme production for a given promoter. All of the upgrades are designed with the goal to enhance safety while increasing efficacy and “manufacturability.”

With plato, our lentiviral vector design is standard and flexible in that it can accept different genes in order to meet the requirements for different diseases. In this way, it is a true producer engine for multiple investigational lentiviral gene therapies.  For example, the proven features of our first gene therapy for Fabry disease is designed to be quickly and easily leveraged for the next gene therapies in our pipeline for other lysosomal storage disorders, including Gaucher disease, cystinosis and Pompe disease.

With a common vector for our products, we believe there are some clear and compelling benefits, and I’ll note a few:

  • rapid expansion to new pipeline ideas;
  • low technical risk and higher probability of success for new product candidates;
  • leverage safety profile of a known, “regulatory compatible” vector backbone;
  • operational synergies across CMC functions.

Challenge 2:  Supply chain excellence to secure availability of critical raw materials and seamless patient experience

Managing all the steps in a complex supply chain is critical, especially for ex vivo lentiviral gene therapy which uses each individual patient’s cells.  In building plato, a central premise was to be streamlined and efficient throughout the entire process: from the initial point of gene therapy production, which in our case is collecting a patient’s cells, to delivering the final gene therapy product at the point of administering the medicine to the patient. The goal is to make the patient experience seamless and convenient, and securing the availability of critical raw materials so that the gene therapy is delivered to the patient reliably every time.

One of the first supply chain challenges that we addressed with plato was to produce vector at scale. We recognized that we needed to be able to do what the field of monoclonal antibodies did decades ago, which was to scale up a complex new medicine in large bioreactors. For us and any gene therapy company, producing vector at scale is essential in order to accommodate multiple clinical trials, as well as ultimately to supply commercial product. The ability to manufacture vectors at scale converts the vector into what it should always be: a long-lead time, critical raw material, but nothing more.  In our case with plato, our vector is produced in a 200-liter serum-free suspension bioreactor, producing high-titer vector.

There are other aspects of rigorous supply chain management which the plato platform addresses.  One important technical feature is optimizing the cryopreservation process to enable longer shelf life and convenient scheduling for patients, while still maintaining viability post-thaw. The fastidious attention to the supply chain is something that we consider to be an essential component of plato, and a critical competency for our potential future commercialization. 

Challenge 3: Commercial-scale manufacturing that’s ‘closed and compact,’ instead of ‘bricks and mortar’

In the early days of ramping up of gene therapy, the predominant manufacturing strategy has been to invest in “bricks and mortar” involving the building of large, centralized facilities.  These manufacturing facilities cost tens or hundreds of millions of dollars to build and require the highest levels of clean room standards.  They were justified because of the shortage of bioprocessing capacity and the huge fear of capacity shortages leading to major delays.  Worse than the upfront costs have been the ongoing operational drain of sustaining quality teams while demand is low and/or inconsistent.

With plato, AVRO has taken a markedly different approach to redefining gene therapy manufacturing. Rather than focusing on the bricks and mortar, we focus on the critical cell bioprocessing steps.  In lieu of “bricks and mortar,” we utilize a “closed and compact” automated manufacturing system with a 3-day process. This allows us to quickly and reliably open up manufacturing in multiple locations across the world.  Our vision for commercialization is to have three manufacturing facilities that service worldwide demand, one in the US, one in the EU and one in Asia Pacific. We are already active in each of these regions and prepping for anticipated eventual commercial demand.

Rather than large factories and high-grade cleanrooms, our approach addresses gene therapy manufacturing with technology innovation.  We believe that this approach is ideally suited to the manufacturing needs for ex vivo lentiviral gene therapies, where the supply chain involves the cells of individual patients.

To our knowledge, plato represents the first clinical-stage, automated, closed manufacturing system for CD34+ gene therapies.   In future blogs I will highlight various performance features in greater detail:

  • Automation of manufacturing units is flexible across geographies around the world. plato enables manufacturing at scale in closed, automated devices that can operate in any geography around the world. This gives us flexibility and portability, so we can meet anticipated demand in the continent or country where patients live.
  • Proprietary AVRO algorithms are optimized. With plato, we have programmed our proprietary algorithms into the devices, optimized so that manufacturing procedures are consistent from patient to patient and between CMOs.
  • Standardized units can yield high GMP quality and consistency, eliminating inter-operable variability. The automation of plato’s manufacturing system is designed to greatly reduce the need for skilled technicians and avoid human error and inconsistency.
  • Industrializing helps create cost efficiencies. An automated, standardized manufacturing system helps to deliver product with a well-defined fixed and variable cost.

Overall, plato’s automated, closed cell manufacturing system is key to our ability to commercialize our gene therapies worldwide for multiple products.

Taking the quantum leap

Entering 2019, AVRO’s highest priority was to secure regulatory clearances enabling the use of plato in multiple trials in multiple countries, including Australia, Canada and the U.S. Those regulatory clearances have now been achieved. We anticipate this will allow us to begin integrating plato into our clinical trials in the second half of 2019.

Like many of our cell and gene therapy peers, we are intensely focused on manufacturing scale-up and commercialization. plato represents our quantum leap and the realization of our vision to be world-class at designing, developing and commercializing ex vivo lentiviral gene therapy products.  It’s taken our team’s tremendous resolve and commitment from day one to get to the point where we can now say with confidence that AVRO is “powered by plato.”


  1. S. FDA, Center for Biologics Evaluation and Research (CBER) FY2018 Report from the Director, April 19, 2019.
  2. McKinsey & Company, Helping to accelerate cures: Regulating the rapidly evolving field of cell and gene therapies, Interview with Peter Marks of FDA, January 2019.



This blog contains forward-looking statements, including statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, without limitation, statements regarding AVROBIO’s business strategy, prospective products and goals, the therapeutic potential of our product candidates, and anticipated benefits of our gene therapy platform including potential impact on our commercialization. Any such statements in this blog that are not statements of historical fact may be deemed to be forward-looking statements based on current expectations, estimates and projections and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking statements. For a discussion of these and other risks and uncertainties, see the section entitled “Risk Factors” in AVROBIO’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018, as well as discussions of potential risks, uncertainties and other important factors in AVROBIO’s subsequent filings with the Securities and Exchange Commission.

Levers to get gene therapy to cruising altitude

I’m writing a series of blogs with insights from inside the gene therapy world. Starting with the analogy of the airplane industry, I highlighted how decades of sustained innovation can translate big ideas impacting everyday life. This theme was kicked off several weeks ago here.

In the case of ex vivo gene therapy, ensuring proper “take off” and then reaching a stable “cruising altitude” can be achieved via optimization of the following four levers:

  1. Vector copy number (VCN)
  2. Transduction efficiency
  3. Cell dose and
  4. Conditioning

These levers enable gene therapy developers to tune the gene therapy to sustainably deliver the amount of potency required to durably impact various diseases.

Successful flights navigated from the gene therapy cockpit

The path has been blazed by pioneers like The San Raffaele Telethon Institute for Gene Therapy (SR-Tiget) funded latterly by GSK, as well as University College London with Orchard Therapeutics, and bluebird bio. Each of these leaders made refinements to their gene therapy platforms to enable them to be adapted to specific diseases.

Let’s consider how bluebird bio was successful with this. According to publicly available information, bluebird bio upgraded their vector design, improved transduction efficiency and protein expression levels, and modified the dose of busulfan – a drug that is given to condition, or make space in, the bone marrow. By the time the company presented early data from the sickle cell program at ASH in 2017, bluebird bio’s CMO was able to state that “changes made to the HGB-206 protocol and to our manufacturing process are having a favorable impact on engraftment of the gene-modified stem cells.”

So let’s look some more at these complementary levers. A gene therapy cockpit might look something like this:

VCN and Transduction Efficiency

In this analogy, “power” equates to potency. Increasing the number of stem-cell daughter cells with a normal copy of the gene(s) increases the power of gene therapies.

For the drug product, two levers increase potency. Transduction efficiency is the percentage of the patient’s CD34+ stem cells that contain at least one integrated transgene, and VCN is the average number of copies of the transgene integrated into a patient’s cells.

Cell dose and Conditioning

“Lift” equates to a critical mass of modified cells engrafting.  The conditioning regimen exposes a patient’s bone marrow to a chemotherapeutic agent.  The more space made in the bone marrow and the appropriate duration of its existence, the greater the potential engraftment of the modified cells.  The goal of this engraftment is to enable lifelong expression of a protein, such as an enzyme.

We anticipate that even more innovative conditioning regimens will be available in the future. They could include using antibody-drug conjugates that recognize and selectively remove bone marrow stem cells. These targeted conditioning agents may help broaden the use of ex vivo gene therapies to an even wider range of disease indications.

Finally, vector design will continue to evolve. Those elements range from codon optimization, to insulators, promoters, tags and signal peptide sequencing. For example, tag technology involves genetically engineering the transgene to produce a fusion protein with a tag that enables increased secretion from CD34+ nucleated daughter cells and uptake into target cells. Because the efficiency of protein secretion is strongly determined by its signal peptide, we are exploring a number of signal peptide sequences.

Forging ahead on our journey 

AVROBIO expects to transition to our optimized platform in 2019 with enhancements across many of the levers discussed above. As excited as we are to elevate our game with the goal of advancing our optimized platform into the clinic, we doubt very much that the early aviation engineers rested on their laurels. Similarly, we are committed to continued R&D and process development work as we advance. Some of these are minor process changes while others represent more meaningful leaps forward. Collectively, they push us towards delivering on our mission of “Curing Rare Disease in a Single Dose”.

P.S. I’ll retire the aviation analogy soon. When it runs out of … runway.

TAKING FLIGHT: Gene Therapy Ascending

The gene therapy field is ready to soar into a new era. This is a pivotal moment and there is clearly a tail wind at our back. Our sights are set on developing gene therapies to deliver dramatic impact, and even cures, for patients.

Our name, AVROBIO, is inspired by cutting edge aeronautical innovation from the 1950’s, the avant-garde Canadian fighter jet AVRO Arrow. It truly represented technology ahead of its time.  In some ways, there’s a similarity between what’s happening in our industry now and the early days of the aviation industry.

While the Wright brothers were the first to make a sustained, controlled, powered, heavier-than-air manned flight in 1903, it took decades of consistent, incremental innovation for air travel to become economical, routinely safe, and mainstream. In the 1950s, often referred to as the “golden age” of air travel, commercial airlines emerged with regularly-scheduled flights and routes, so that airline travel began to reach the masses. By 2018, decades of advances in design, manufacturing, and safety features have brought the benefits of air travel to a mass market—with commercial airlines carrying four billion passengers worldwide each year.

It seems that we are approaching the “golden age” of gene therapy. Currently, there are more than 300 gene therapy clinical trials ongoing.  The fact that the number of gene therapy clinical candidates is estimated to exceed the number of monoclonal antibodies in clinical development is an astounding statistic.1, 2 The pace of innovation is accelerating as drug developers concurrently optimize potency and safety while beginning to take on the challenge of industrialization.

Pushing New Boundaries, Disease by Disease

In the quest to revolutionize travel, the aviation industry needed to push boundaries and focus on innovations across a multitude of fronts. That analogy holds true in our industry, as a number of academic labs and biotech companies work to chip away at key parameters in order to design gene therapies specifically tuned to the biology of targeted diseases.

While the early initiatives in gene therapy arose during the 1990s, it took until 2017—nearly three decades—for the first gene therapy to evolve from initial clinical trials to a full-fledged FDA approved product.

Advances continue to be driven by leading therapeutic companies like Bluebird, Novartis and Spark to name a few – coupled with enablers such as Miltenyi, GE, CCRM and Vineti. The experiences of these leaders are establishing a path and giving us a field of vision for optimizing gene therapy technology. Collectively, development and refinement of a host of new enabling tools, techniques and insights are solving historic bottlenecks.

Those of us developing gene therapies are both leveraging and adding to this collective wisdom as we apply know-how to specific diseases.  At AVROBIO, we are currently focusing on gene therapies for a class of rare diseases called lysosomal storage disorders. Others target oncology, ophthalmology, inherited blood disorders, primary immunodeficiencies, and several additional diseases. Boundaries are being pushed simply by opening up the big book of medicine and identifying genetic diseases with high unmet need which would benefit from the unique advantages of a potential single-dose, curative gene therapy.

Incremental Steps Toward the Mainstream

Let me offer examples of a few parameters that have opened up gene therapy, and set us on a course towards bringing breakthrough science into the mainstream:

  • Safety first. The first therapeutic gene transfer occurred in 1990, with a retroviral gene therapy administered to a four-year old girl with the severe immune deficiency ADA-SCID, in a landmark clinical trial directed by Dr. French Anderson at the NIH Clinical Center. So, you could say that this event nearly 30 years ago was almost a ‘Wright brothers moment’ for gene therapy. In spite of that initial milestone, the technology wasn’t yet ready to take off.  Retroviral gene therapy is in the same family as lentiviral (LV) gene therapy, with similar modes of action e.g. integrating therapeutic genes into the patient’s genome.  During the 1990s, the early developers of LV gene therapy addressed the primary safety challenges with the removal of HIV pathogenic genes. The LV vector systems evolved, and the third-generation LV vector – a four plasmid system and self-inactivated (SIN) approach – first reported in 1998 and reduced the risk of producing replication competent lentivirus.Potential safety hurdles were encountered by AAV gene therapy as well. Due to their design, the first AAV vectors were inherently contaminated with wild-type AAV. This hurdle was overcome with a major redesign of the AAV two plasmid system during the early 1990s. Achieving improved levels of assurances for the safety of gene therapy was a primary hurdle which needed to be overcome to trigger both investment and energy units to be applied towards creation of an industry.
  • Therapeutic functionality for different diseases. Beyond safety, gene therapy technologies required flexibility to be adapted to different diseases. For lentiviral gene therapies, pseudotyping with VSV-g became a game changer in the mid-1990s. VSV-g enabled switching out the HIV vector envelope to enable transduction of multiple cell types and not just CD4 cells. Since AAV does not have an envelope, the equivalent to pseudotyping for AAV is naturally-occurring AAV serotypes and AAV engineered with optimized capsids. Both enable targeting of specific tissues and can also identify novel AAV variants with reduced sensitivities to neutralizing antibodies.These advances in gene therapy vectors and delivery technology are akin to the engineering feats for airplanes which enabled sustained flight and high altitudes. Sir George Cayley is called the father of the airplane based on his pivotal innovations in the mid-1800s. His rigorous study of the physics of flight and aerodynamics led to the underpinnings for the Kitty Hawk flight in 1903. His insights enhanced lift from curving the wing surface, and defined the modern airplane’s configuration of fixed wing, fuselage and tail assembly.I could speculate that our industry’s version of Sir George may be Dr. Inder Verma at the Salk Institute, one of the pioneers of the lentiviral vector who established the foundation for gene delivery and harnessing viruses for the technology. Interviewed in 2005, Verma predicted that gene therapy “will affect everything, any disease. Every disease has a genetic component…It’s just a matter of learning the technology. Therefore, I think finding and looking for vectors and ways to do it is highly justified because there is no other technology in the world for every aspect of human health.” 3
  • Making the journey through manufacturing. For lentiviral gene therapy, innovation with VSV-g also propelled the field by enabling lentiviral vectors to be adequately robust for manufacturing, while enabling the essential increase in infectious titer by greater than two orders of magnitude. Gene therapy is a highly complex technology, and creating standardized manufacturing is a key factor for rolling out consistent and high quality product for both clinical grade and commercial uses.Today, I believe fully automated, closed system, cryo-preserved cell bioprocessing is the next revolutionary step in manufacturing for the leading lentiviral gene therapy companies. This should elevate quality while driving down costs and increasing global supply chain flexibility.As more gene therapies are developed, manufacturing remains an area ripe for innovation. It’s not uncommon for manufacturing strides to trail technology innovation. With airplanes, it took until the 1960s for key manufacturing achievements, such as the first small jet aircraft, the Learjet, to enter mass production in 1963 – selling 100 planes in two years – and the first wide-body turbofan-powered commercial airliner, the 747, produced by Boeing in 1969.

A Medical Revolution is in Flight

Ongoing incremental innovations are required to truly deliver on our mission to take gene therapy mainstream and impact the millions of deserving patients. What has changed, is that it no longer takes a visionary to see where this field is headed. Proof-of-concept is established – we have taken flight.

At Kitty Hawk, it wasn’t clear how airplanes would make a transatlantic flight or be mass produced, and yet industrialization happened because the ingenuity of an entire industry of dedicated engineers who mobilized to continually enhance outcomes.

We are now building the gene therapy industry on the shoulders of giants. Early achievements are important building blocks to refine new gene therapies. As these early brilliant scientists pass the baton to multiple developers of medicine, the expanded goal is to push gene therapy into the mainstream. That is our goal at AVROBIO, to develop first-line therapies with broad utility reaching tens of thousands of patients with lysosomal storage disorders, and eventually addressing other diseases.

In future blogs, I will outline some thoughts within our AVROBIO team on key parameters we focus on to take gene therapy mainstream. With our industry clearly in breakthrough mode, we have a responsibility to our patient community to collaborate and share collective wisdom as we are on the cusp of transforming medicine.


1 Alliance for Regenerative Medicine, Q2 Quarterly Data Report, Aug. 2018,

2 MTS Report on Gene Therapy, Nov. 2017,

3 Jacoby J. Interview with Dr. Verma. Gene Therapy (2005) 12, 950-953,