Activity Transcript

David P. Lillicrap, MD: Hello, and welcome to this Medscape production on "Integrated Interprofessional Pathway for Gene Therapy: A Model to Optimize Care in Hemophilia." I'm David Lillicrap. I'm a professor in the Department of Pathology at Queens University in Kingston, Canada.

And today I'm joined by Jennifer Donkin, who's a pediatric nurse practitioner at the Cancer and Blood Disease Institute at Children's Hospital in Los Angeles, and Dr Ulrike M. Reiss, who's the director of the Hemophilia Treatment Center at St Jude Children's Hospital in Memphis, Tennessee.

The purpose of today's presentation is about providing you initially with some background on gene therapies for hemophilia. For the next few slides, I'm going to set the background of the subsequent discussion about introducing gene therapies in your treatment centers.

As all of you are aware, over the past several decades, we've gone through an incredible revolution of the treatment of hemophilia, from replacement therapies, on-demand, and prophylaxis using standard half-life and, more recently, extended half-life products. And then, in the past few years -- probably the last 5 or 6 years -- we've seen the introduction of nonreplacement therapies, particularly factor VIII mimetic therapies and antagonists to the anticoagulant pathways to produce hemostatic rebalancing benefits to hemophilia. So, the treatment landscape is competitive, increasing efficacy and safety for our patients. And today, we're going to talk about now the potential of gene therapy, particularly gene addition therapy in the hemophilia population.

The goals of gene therapy in hemophilia are to increase clotting factor levels. This ultimately will reduce annualized bleed rates, reduce the use of exogenous clotting factor concentrate usage, improve the quality of life of patients, and produce psychological benefits, and ultimately reduce the treatment burden. So, there are multiple facets as to why we believe that in the long term, gene therapy will be a benefit to hemophilia patients.

This next slide summarizes very briefly how we think gene therapy works. Current gene therapy uses adeno-associated viral vectors, or AAV vectors, which are transfused through peripheral venous infusion. The vectors enter the bloodstream; they circulate around. And the current vectors are aimed particularly at getting into liver cells, or hepatocytes.

The vectors shown on the right-hand side of this slide bind to receptors on the hepatocyte surface. They get internalized into hepatocytes, into endosomes. The endosomes traffic across the cytoplasm. They deliver their nucleic acid cargo into the nucleus of the cells.

A second DNA strand is made at that point, and then the vectors persist predominantly as extrachromosomal entities, or episomes, but a small percentage, a very small percentage, will actually get integrated into the host genome. The DNA from the vectors is then converted into mRNA and protein, and that therapeutic protein -- factor VIII or factor IX -- is then secreted from these cells into the bloodstream. So, that in a nutshell is the way that gene therapy currently works with these AAV vectors.

On the next two slides, we're showing selected gene therapies: first of all for hemophilia A, and on the next slide, hemophilia B. Currently, there are approximately 16 gene therapy studies ongoing for hemophilia. This changes actually quite a lot from month to month. Nine of those studies are hemophilia A studies, and you're looking at 3 of those hemophilia A studies on this slide. One of them is a phase 3 study, the one at the top of this table, which involves 132 individuals. And then, there are two phase 1/2 studies at the bottom of the slide. I'm not going to have time to discuss the information on the right-hand side, but you can see that in all of these studies, there's been a significant reduction in the annualized bleed rates (ABRs); factor usage is dramatically reduced; and there have been overall benefits in terms of quality of life. And the top one of these studies involving the valoctocogene gene therapy study has produced a European Medicines Agency conditional approval in August of last year.

Moving on now to the hemophilia B gene therapy summary, again, we've just focused here on 3 of those studies. I think there are now 7 gene therapy studies looking at hemophilia B. And again, these all involve AAV vectors. There's one phase 3 study here which involved 54 patients. Again, you can see that the ABRs are significantly reduced with all of these studies. And most importantly, the top one of these, etranacogene, the EtranaDez phase 3 study, has now resulted in FDA approval of this product in November of 2022. This study now can result in clinical usage of this product, this hemophilia B product, which involves the gain-of-function factor IX Padua variant in the United States of America.

So, durability of factor IX expression of the gene therapy for hemophilia. I'm now moving on to two slides which compare and contrast, first of all, on this slide factor VIII expression. This is looking at the results in 17 of the individuals in the phase 3 study with valoctocogene, showing that factor levels of factor VIII peak at around about 6 months. And then, at that time, there are around about 50%. The levels gradually decline from about 1 year out to 2 years, where the mean and median levels of factor VIII are now around about 20% to 30%. Some of these patients are now out to 5 years showing persistent expression, but at lower levels than was seen at 1 year. Those levels now are somewhere around about 10% to 20%.

And on this next slide, talking about greater stability of responses to factor IX gene therapy with the etranacogene study, you can see that the profiles of factor IX expression going out in these 50 individuals out to 18 months is different to what we see with factor VIII. The levels are at 1 year around about 40%, and they remain relatively persistent at around about 40% out to 18 months. So, there are differences between the factor IX studies and the factor VIII study that I showed on the previous slide.

I'm now going to hand it over to Ulrike to discuss the safety concerns in gene therapies for hemophilia.

Ulrike M. Reiss, MD: Thank you, David. Hello, everybody. We have divided in this slide the safety concerns in a couple of categories which have been found in the different clinical trials. There are 4 which are potential safety concerns for all the gene therapies, the AAV-mediated gene therapies, in development for hemophilia. And these include liver toxicity, which in almost all cases is transient transaminitis that occurs in up to 80% of the participants in the clinical trials. I will talk a little bit more in detail later. The second category is impaired immunity. This relates to the use of immunosuppressive therapy if needed for transient transaminitis, for the liver toxicity mentioned above. And third, a risk of thrombosis. There were a total of 2 cases of thrombosis in factor VIII or factor IX clinical gene therapy trials. One was an AV fistula thrombosis in a patient who had greater than 200% factor levels, and the other one was venous thrombosis, also in a patient with very high factor levels greater than 200%. So, all in all, very rare and indicated that it's really related to if very high factor expression occurs during the initial period of the follow-up. And last, there is a risk or a potential risk of oncogenesis, which has not been proven but will require long-term follow-up.

A little bit more details on number 1 and 4 in the next slide. Liver toxicity is something which has been observed in every clinical trial using AAV-mediated gene transfer for hemophilia. We have observed a manifestation of an increase in alanine aminotransferase (ALT) in the first 4 to 12 weeks after the vector infusion. Almost always this is transient, then coincides with a reduction in factor level, meaning that there is an immune response, attacking transduced liver cells causing destruction and therefore elimination of the gene, the presence of the gene and, therefore, the factor expression.

The possible mechanism has been shown to be a cytotoxic T-cell response. Other potential responses could be hepatocyte apoptosis to potentially higher factor expression or endoplasmic reticulum (ER) stress or any other direct effect of the vector particle load, which none of this is really proven and there's a lot of work going on towards that.

As I said, it's a variable number of patients who can have this liver response, depending on which type of product it is, as well. If it occurs, the typical approach was to use immunosuppression to suppress the immune attack, the cytotoxic T-cell response, using corticosteroids by mouth. And these have been used for a length of 2 to 3 months in general. Some products have used prophylactic immunosuppression in the clinical trials, so there will be some difference between different products potentially, but none of this treatment is required or will be continued long term.

Looking at the fourth category of potential oncogenesis, we have the real data of 4 cases of cancer or malignancy appearance in hemophilia patients having undergone AAV-mediated gene transfer. And these are listed here. They concern 3 different products as you can see, either for hemophilia B or for hemophilia A. And there were different cancers. All of the cancers have been determined to not deemed related to the study treatment as per evaluations which have been done, particularly a hepatocellular carcinoma (HCC) here listed in the first line, in a patient who had multiple risk factors such as higher age, greater than 65 years, history of active hepatitis C and B in the past, and evidence of nonalcoholic fatty liver disease. In addition, there were several gene mutations found in the tumor tissue which have been related to HCC in the past. So, overall, at this point, we do not think, or the data do not show that AAV-mediated gene transfer is clearly oncogenic at some point. But of course, some of these occurrences might take a long time to develop, and long-term follow-up is absolutely necessary for these patients.

Dr Lillicrap: We're now going to go on to the institutional gene therapy journey. We're going to touch on these 5 areas: education and institutional training, eligibility of patients, insurance authorization and support, procurement and administration of the vectors, and then patient monitoring and follow-up.

We're going to begin with the education and institutional training session. And I'd like to ask Jennifer if she'd like to comment on these 3 areas: the basics, possible benefits of gene therapy, and the possible risks.

Jennifer N. Donkin, DNP, FNP-C, PNP, RN: Hi, everybody. I'm here to address what patients and institution colleagues need to know before gene therapy is instituted at the various different institutions.

What we're going to need to provide for both the staff as well as patients and families is the basics of gene therapy and how it works, and the education materials that we can present to families, as well as developing standard procedures. Also, we're going to have to include the treatment and the administration practices, what does that mean to staff and what does it mean to the patients and families. And the level of follow-up is going to be very important to highlight to our patients and families as they and we, as the comprehensive care team, enter into shared decision-making.

We're going to have to help to assist families in understanding that there might be some variability of results. And as David mentioned earlier that these levels of results may also decline over time.

And one gray area that nursing, the comprehensive care team, will also be going over with patients and families and also educating the staff that are responsible for the care is the short-term effects such as liver toxicity, possible infusion reactions. And then, one of the big concerns, and one of the things that we're going to have to emphasize in our education is the long-term risks and follow-up. It will, I believe, take a whole comprehensive care approach and shared decision-making with the families.

Dr Lillicrap: Jennifer, thank you. We're now going to move on to the next stage of the gene therapy journey that is eligibility, and maybe I'll ask Ulrike if you'd like to summarize your thoughts on this.

Dr Reiss: Thank you, David. Yes. The first thing to look at for patient and clinician is the eligibility criteria: is a patient even in the right situation to receive such a product? The criteria or conditions will vary a little bit between different products. Overall in the clinical trials, the inclusion criteria were men who are 18 years or older with established severe hemophilia. The factor level cutoffs were at 1% for factor VIII deficiency and 2% for factor IX deficiency. The patients in whom the products have been tested in the clinical trials had to have between 50 and 150 exposure days, meaning these were patients who had a very low risk of inhibitor. Of course, they had to be negative for inhibitor and had not had any inhibitor in the past, and were asked to give numbers of their bleeding episodes and treatment necessities or if they were on prophylaxis.

Exclusion criteria have been children, women, patients with positive neutralizing antibodies against the AAV capsid of the vector, patients with significant liver dysfunction by lab values or by imaging methods, patients with active hepatitis B or active hepatitis C. And for HIV or history of HIV, there were different criteria applied in the different studies.

Dr Lillicrap: So, Jennifer, who are the potential good, and not such good candidates for gene therapy for hemophilia?

Ms Donkin: Yes, thanks, David. There's going to be a shared decision-making process that we will need to really highlight with the patients and families. But some of the potential candidates that might benefit could be patients that are perhaps very, very active in sports and they want to reduce the demands of prophylaxis. Maybe there are patients that have poor venous access, and patients that have had increased bleeding over time and are experiencing ongoing issues with pain management. They might be good candidates.

Some of the potential patients that you really might want to take a long look at are those with liver disease. I know factor VIII inhibitors are being studied in gene therapy at the current moment. So, we might have more information as we move forward with that. And then, the presence of antibodies in screening. We also have to look at is a potential challenge in these potential candidates that perhaps they have a history of alcohol abuse, what are their psychosocial supports. What is their transportation? What other family supports do they have? And will they be able to really continue with the ongoing follow-up?

Dr Lillicrap: Jennifer, thank you. We're now going to move on to the next stage of the journey that is insurance authorization and support. Dr Reiss and I are going to summarize on three slides where we are with this important area.

Dr Reiss: Cost and cost-effectiveness of the gene therapy for hemophilia: it's complicated and complex. Cost in general, you imagine it is based on what it actually costs to develop, to do the research, to develop the products, to go through the clinical trials, but also then develop the manufacturing, develop the scale-up of the manufacturing, and then the actual manufacturing of the product, as well as all the quality assurance testing which needs to be done on top of how do you get it out into the market and to the patient. So, the prices are expected to be very high, and as you see listed here, something between 2.5 to 3.5 million for a single dose. But as you have heard, the single dose may have an effect for a long time potentially for several decades or even lifelong. So, using the data from the clinical trials, a cost-effectiveness analysis is underlying the price predictions which looks at, is it still effective compared to what we're doing now with factor on-demand treatment or prophylaxis treatment? This will not pan out if the gene therapy only lasts for 4 to 5 years, but beyond 8 to 10 years, it's very likely cost-effective, meaning that high upfront cost for a gene therapy product will be cheaper than keeping going with prophylaxis over the lifetime. So, the prediction model suggests that gene therapy will be lower cost, lower bleed rate, and higher quality of life for the patients.

Dr Lillicrap: On this next slide, you see the results for an investigation carried out by the Institute for Clinical and Economic Review, or ICER, where at the top left of the slide, comparing factor VIII gene therapy with emicizumab, for example, there's a low certainty of net health benefit based upon the current ICER rating. I think it's important to keep in mind that these are very early studies and there are predictions which have a certain amount of uncertainty for all of these outcomes. The second bullet refers to factor VIII prophylaxis, where there's a rating of C++. You can see on the right-hand side the ICER rating matrix where all these results were derived, suggesting that there's a moderate certainty of comparable small or substantial health benefit with high certainty of at least a comparable net health benefit of gene therapy vs factor VIII prophylaxis. And then, at the bottom of the slide, there's a similar analysis that's been carried out for factor IX gene therapy. And you can see the results were rated B+, a moderate certainty of small substantial health benefits of gene therapy with factor IX vs factor IX prophylaxis.

So, really, payer reimbursement policies and practices are not yet known for gene therapy for hemophilia because of the very recent introduction of this gene therapy paradigm. Insurance authorization policies, will be complicated, and they'll be lengthy due to the high upfront costs. These are expensive therapies. And so, as you consider this for your different centers, this will alter and be different for different types of payers, specific insurers, and health plans. It will be variable between countries, states and regions and between individual health treatment centers.

So, now on to procurement and administration of gene therapy.

Ms Donkin: Different institutions are going to have to come up with their standard operating procedures and really develop plans of how they're going to initiate gene therapies. A key element to this is going to be education of the staff of how to deliver education with our patients and the families that is very interactive, and also on a level that they can understand, because it's very complex and it's a new understanding for most patients. And it will take some time and a process to go through this.

We're also going to have to really look at the administration, staff, the infrastructure of how we're going to procure it, the gene therapy, and also how are we going to deliver that as far as screening before the infusion. So, there's a lot of complex pieces that are in place that we are going to need to address and come up with protocols.

Dr Reiss: The day of infusion takes some planning and preparation to go smoothly. The coordination of the product receipt, which at that point hopefully is in the freezer or in the pharmacy at least depending on what temperature is required for it. The product needs to be present. There needs to be a time plan for the reconstitution such as thawing or just mixing up in the actual infusion solution. And then, the patient needs to be present, needs to be healthy, has had whatever prescreening labs are required, and has a location where the infusion can be done. The infusion should be done under a situation where allergic reactions can be treated. These were not frequent but possible and seen in some of the participants of the clinical trials.

All the staff involved need to know what has to be done first and second when the product gets infused and what the postinfusion monitoring involves. Typically, it's an observation time of several hours, most times in an outpatient setting. And then, there have to be patient instructions for the follow-up thereafter, such as potentially weekly or twice-weekly follow-up during the first several months. These plans and schedules need to be discussed thoroughly and well-known to the patient, as well as to the relevant staff. It might be good to have a very dedicated team trained for vector infusion and patient monitoring.

Postinfusion monitoring requires frequent lab tests, specifically looking at liver transaminase and at the factor levels during the first 3 to 4 months or 3 to 6 months, depending on the product. Patients and clinicians need to know about the necessity of immunomodulation, such as with corticosteroids potentially and when this should be used and how long and what dosing, et cetera. One other thing, what is really important is to have a communication plan. Who is the direct contact for the patient, and when and how often will be communicated about appointments, about lab values, about medications such as the steroids, and the future follow-ups? Very close, tight little team is very important.

And last but not least on this slide, you can see data collection plan and data sharing plan. It's very important that we collect safety and efficacy data on all patients who receive product, especially through commercial availability now.

Dr Lillicrap: So, in this last stage of the journey: patient monitoring and follow-up.

I think as Ulrike has just said, an interaction, communication between the dosing center and the follow-up center is critical. So, there will be lab measurements before gene therapy, including things like looking for preexisting immunity to AAV, and then the traveling between the dosing and management centers, and regular laboratory measurements following the administration of the vector.

The key questions as noted at the bottom of this slide are, when do you stop regular factor replacement therapy? AAV therapy usually kicks in at about 4 to 6 weeks following vector infusion. How to ensure early detection of liver damage with ALT measurements? This is a critical element of the postvector infusion follow-up. And then a plan in place for potential immunosuppressive therapy if you see elevations of the ALT.

The monitoring considerations -- and we've really been through most of this -- thinking about preexisting immunity, liver health and toxicity assessment, screening before infusion and then postinfusion looking for ALT elevations, and this communication and coordination between the centralized and local laboratories. And then, of course, considering bleed and factor infusion diaries, as we do currently with hemophilia patients.

And then, on the penultimate slide here: the American Thrombosis and Hemostasis Network (ATHN) registry and then the World Federation of Hemophilia (WFH) registry.

Dr Reiss: We have 2 registries which are very well developed, and I think both are approved at this point within the United States. ATHN Transcends is a protocol run through the ATHN group, American Thrombosis and Hemostasis Network, which collects data on all hemophilia patients and has a specific arm for gene therapy patients and will collect data on their enrollment, on their follow-up at 3, 6, 12, 18, and 24 months after infusion and then annually thereafter. And specifically focuses on safety assessments and efficacy outcomes assessments. It also has multicentral laboratory to confirm factor levels and genetic testing as required. Data from this will to a part be fit into the global gene therapy registry, which has been set up by the World Federation of Hemophilia in order to really capture information of all patients around the globe, which is an amazing project. It again looks at durability, reliability, variability, safety, and vector activity data and hopefully can give us this long-term information, which we don't have right now.

Dr Lillicrap: The take-home message is, I think from what we've been discussing in the last 30 minutes, is that hemophilia gene therapy has arrived, after 3 decades or more of preclinical investigation, and this really could revolutionize hemophilia care. Patients and treaters need to be well informed about what this involves, the multidisciplinary teams that are present within the hemophilia treatment centers (HTCs). Guidance is available on how HTCs can prepare. So, the National Hemophilia Foundation (NHF) Medical and Scientific Advisory Council (MASAC) is preparing documents which will be available to help you get ready to do this and offer this therapeutic possibility to your patients. And then, remember, long-term follow-up in national and international registries will make sure that these patients continue to do well on this revolutionary, new form of therapy.

With that, I'd like to thank Ulrike and Jennifer for their contributions to this discussion, and thank you for participating in this activity.

This transcript has not been copyedited.