What challenges do hemophilia gene therapy need to overcome?

However, the 35-year journey to develop a cure for haemophilia is expected to come to an end after successful cloning genes that express coagulation factorviiis VIII (FVIII) and IX (FIX)BioMarin's gene therapy valoctocogenevre Roxaparvovec, developed by BioMarin, could be approved by the FDA this summer, becoming the first listed gene therapy to treat haemophilia AIt provides significant protection for some haemophiliacpatients and achieves functional healing effectsAs a new era of hemophilia treatment approaches, DrGlenn Pierce, vice president of the World Hemophilia Alliance (WFH), wrote in the journal Haemophilia, reviewing the history of the development of hemophilia gene therapy and explaining our attitude towards hemophilia gene therapysince being invited to speak to local media about the challenges hemophilia poses, DrPierce has been at the forefront of the fight against haemophilia at the age of 7, and has transformed his role over the past 60 years from a patient suffering from multiple joint bleeding in a wheelchair to being a key leader in the field of haematology in several multinational pharmaceutical companies, driving the birth of five innovative haemophilia therapiesTo make him even more unusual, his haemophilia was cured in 2008 after a liver transplantBut there is no denying that he remains an important member of the haemophiliac community and has played an absolutely critical role in the organization's humanitarian assistance to developing countries since joining WFH in 2018First wave of haemophilia gene therapy: Experienceand lessons DrTheodore Friedmann of the University of California, San Diego, and DrRichard Roblin of Massachusetts General Hospital wrote in the 1972 issue of Science that gene therapy could be a powerful tool for treating monogenetic diseases in humans in the futureAs genes encoding FXIII and FIX are cloned, the concept of replacing abnormal genes in the cells of haemophiliacs with normal genes is the first to see a realityEarly basic scientific studies using retroviruses would have expressed FXIII and FIX genetically modified into the body cells of animals and then infusion them into the animalsAlthough the results of these experiments have been limited, they are sufficient to support the continuation of research in this areaIn 1992, the National Instituteofd (NIH) held its first hemophilia gene therapy summitMolecular biologists and virologists who develop gene therapy, together with patient advocates and doctors at haemophilia treatment centers, are working together to explore gene therapies for haemophilia As of 2005, a total of five haemophilia gene therapies were in clinical trials These clinical trials provide valuable experience and lessons for the development of gene therapy for haemophilia In a clinical trial conducted at Children's Hospital of Philadelphia and Avigen, researchers injected the expression OF FIX with a genetically modified gene, using adeno-related viral vectors (AAV2) into a patient's liver cells This is an important precedent, using intravascular delivery to introduce genetically modified genes that express FIX into naturally produced FIX liver cells However, even with the highest dose of gene therapy, the patient's FIX activity reached a maximum of 12% of normal levels during the first 4 weeks of treatment and disappeared completely in the following weeks The disappearance of FIX activity was accompanied by a significant increase in liver transaminase levels, which returned to normal after FIX activity returned to the baseline This means that all liver cells that can produce FIX are wiped out by the immune system! Subsequent studies found cytotoxic T cells that targeted the specific amino acid sequence of viral shell protein in patients The findings led to the termination of the clinical trial and delayed the start of subsequent clinical trials Subsequent studies have found that the human immune response to AAV transfection is a very complex process, and the difference between the immune response to AAV by humans and animal models, including non-human primates, prevents animal models from effectively predicting the immune response that occurs in human clinical trials This is an important lesson learned from clinical trials Since many people have been infected with AAV, they already have immunity against AAV in their bodies This existing immunity includes not only neutralizing antibodies against AAV shell protein, but also memory T cells against AAV When AAV vectors carrying gene therapy enter the body, these existing immunitys can seriously affect the strength and quality of the immune response produced by the body In addition, the innate immune response that adhesion to AAV vectormay also promote the production of an immune response to indications Therefore, to overcome the human body's immune response to AAV vector needs to consider a number of problems such as serotype, tissue specificity, the quality of the carrier itself and the patient's unique innate immune response "Multi-pronged approach" to maintain coagulation factor levels Based on experience gained in early clinical trials, gene therapy for haemophilia has been improved both in terms of the selection of AAV virus vectors, the design of genetically modified organisms, and the treatment process after gene therapy administration Take valoctocogene roxaparvovec, which is expected to be approved this summer, using the AAV5 virus vector AAV5 is unique in that it has the highest homologous ity with goats, compared with 65% of the primate AAV shell protein Because human contact with goats is low, and the cross-reaction of neutralized antibodies to primate AAV and AAV5 is weak, this means that only a few people in the population carry antibodies that bind to AAV5 Valoctocogene roxaparvovec also uses hepatocellular-specific promoters, which means that gene therapy does not need to be fed into liver tissue through the liver artery, and only through peripheral venous infusions can still lead to specific expression of coagulation factors in liver tissue This can further reduce the potential tissue damage caused by gene therapy administration and the resulting immune response Genetically modified coders that express coagulation factors are also optimized to further improve the production of coagulation factors the genetically modified structure of BioMarin haemophilia A gene therapy (Photo: BioMarin)Professor Amit Nathwani, Professor Edward Tuddenham and their colleagues pioneered treatment soroktoas using corticosteroids to suppress cellular immune response and potentially affect the transfection process in clinical trials of gene therapy for hemophilia B This protocol was later applied in clinical trials to treat haemophilia A Based on these improvements, a number of current therapeutic therapies for haemophilia have been able to maintain treatment levels of FVIII and FIX in clinical trials over time BioMarin has just announced the results of a long-term follow-up to valoctocogene roxaparvovec at this year's World Hemophilia Union Congress After four years of gene therapy, the level of FVIII in patients still prevents them from receiving other preventive treatments In the treatment of haemophilia B, a mutant called FIX Padua increased the activity of natural FIX by six times due to a mutation in individual amino acids This means that the gene therapy dose, which could only express 5% normal level FIX, can increase FIX activity to 30% to 40% of normal levels in clinical trials Currently, Both Pfizer and uniQure are in clinical phase 3 trials for gene therapy for haemophilia B UniQure's etranacogene dezaparvovec is expected to obtain Phase 3 clinical trial results by the end of this year The company just agreed a $2 billion research and development partnership with CSL Behring earlier this month Realize the dream of a cure, but not all patients will benefit from the potential of approved gene therapy to provide long-term protection for bleeding and even functional cure for some patients However, gene therapy using AAV to deliver FVIII or FIX is not perfect, and many patients with the disease are not yet able to benefit from it For example, haemophilia children who are most likely to benefit from gene therapy are not suitable for gene therapy Because AAV's genomes exist in the nucleus in the form of extra-chromosomal free genes (episome), they are lost as the cells divide, leading to decreased levels of protein expression Among young children, the liver grows the fastest, reaching two-thirds the size of an adult by the age of 12 Researchers still need clinical trials to find out how old a patient is, and current gene therapy does not provide long-term protection The largest group of patients who cannot receive gene therapy is those who already carry antibodies to AAV Most of the AAV serotypes currently used in clinical trials are derived from primates or isolated strains of the virus in humans Their viral shell homogeneity is about 85% There is a cross-reaction between different AAV serotypes, which means that patients who have been infected with AAV2 may produce antibodies that cross-react with AAV1, AAV3, AAV6, AAV8, AAV9 and rhAAV10 If the cross-reaction produces significant antibody titer, the patient cannot accept gene therapy using these AAV serotype deliveries Currently, with the exception of AAV5, most non-primate AAV serotypes cannot effectively transfect human cells, so high levels of pre-existing immunity are an important obstacle to patients receiving gene therapy or re-administration of gene therapy One way to address this obstacle is to use different gene therapy delivery systems In this regard, the use of slow virus delivery FVIII and FIX GMO has been successful in animal models of non-human primates and dogs This technology platform has considerable potential because slow viruses can be integrated into the cellular genome and rarely produce existing immunity in humans However, the production of slow virus vectors is still facing challenges, and the production of a sufficient number of vectors for clinical trials is currently a problem that researchers need to solve Embrace the future of gene therapy Over the past 30 years, gene therapy has made significant progress in enabling haemophilia A and haemophilia Patients with near-normal or normal coagulation factor activity However, there are still many questions about its efficacy and safety that remain unanswered , Dr Pierce, says embracing gene therapy as a medical model for "cure" haemophilia means pursuing these answers with uncompromising spirit and perseverance while acknowledging the uncertainty surrounding gene therapy This will continue to be used in the first generation of haemophilia gene therapy in more patients Original title: What challenges do hemophilia gene therapy need to overcome to achieve the patient's dream of a cure?