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Learning Center

The content of this site is provided for educational purposes and is intended only for U.S. healthcare professionals.

Gene therapies for hemophilia are currently being studied to determine their safety and efficacy. No gene therapies for hemophilia have been approved for use.

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Welcome to the Hemophilia Gene Therapy Learning Center. Here you will find links to further resources to explore the topics on this website in more detail.

Resources include:


The Hemophilia Gene Therapy Webinar Series will explore the complex science underpinning hemophilia gene therapy. Hosted by an expert hematologist, joined by a specialist, each webinar will focus on providing a high-science review of key areas of interest in hemophilia gene therapy.


The journey of the DNA in hemophilia gene therapy


Gerry Dolan and Thierry VandenDriessche explore the complex processes involved in gene therapy, from transgene packaging to expression of the protein of interest.


The Hemophilia Gene Therapy Brochures are complementary to the webinar series. Each brochure delves deeper into the topic covered during the webinar episode. These can be viewed online or downloaded using the links below.

Hemophilia Gene Therapy: Key Principles

Explore and advance your understanding of the basic principles of hemophilia gene therapy.

Educational Videos

The following videos provide additional educational content around the key concepts important for understanding hemophilia gene therapy.

Stay Up-To-Date




3’ (3 prime)3' refers to the end of a single-stranded nucleic acid chain to which a hydroxyl group (-OH) is attached to the 3'-carbon atom of the nucleotide.1
5’ (5 prime)5' refers to the end of a single-stranded nucleic acid chain to which a phosphate is attached to the 5'-carbon atom of the nucleotide.1
CapsidThe capsid is the protein shell of a virus that protects the genetic material while interacting with the host environment.2 Capsid proteins determine cell-type specificity.3
ChromosomeA chromosome is an organized package of DNA found in the nucleus of a cell. Humans have 23 pairs of chromosomes–22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y.4
Codon A codon is a sequence of three nucleotides that codes a specific amino acid. For DNA, there are four different nucleotides (A, T, C, or G) from which a codon can be composed.5


A cellular process by which substances are brought into a cell. The substance is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material.6
EnhancerAn enhancer is an upstream regulatory DNA sequence that provides binding sites to regulatory proteins and can augment the activity of a promoter.7
EpisomeExogenous DNA that remains physically independent of the cell’s endogenous chromosome or complement of chromosomes.8
Ex vivo gene therapyHarvesting and cultivating of patient cells in the laboratory. Cells are incubated with vectors carrying a corrective or therapeutic gene. Cells with the new genetic information are then transplanted back into the patient from whom they were derived.9
Gene editingRemoval, disruption or correction of faulty elements of DNA within the gene.10
Gene transfer (gene addition)Addition of a functional copy of a missing gene or augmentation of a gene that is non-functional into target cells to produce more of a protein.10,11
ImmunogenicityThe ability of a substance, such as an antigen or epitope, to trigger an immune response in the host.12
IntronAn intron is a portion of DNA that does not code for an amino acid.13
Inverted terminal repeats (ITRs)ITRs are 145-bp sequences that frame the expression cassette.14
In vivoAdministration of a vector carrying the therapeutic genetic material to a live animal. The vector can be delivered by a variety of methods, including direct injection into the blood (intravenous injection) or by various organs by other physical means of administration (hypodermic injection, aerosol, intrathecal, etc.).9
Messenger RNA (mRNA)Single molecule of RNA that works as a chemical map for a protein product.9
NucleusMembrane-bound organelle that contains the cell's chromosomes. Pores in the nuclear membrane allow for the passage of molecules in and out of the nucleus.15
PlasmidAn extrachromosomal, self-replicating piece of DNA. Plasmids are usually circular and transferable between cells.16
PromoterSequence of DNA, typically at the 5’ region, where regulatory elements such as transcription factors bind and initiate transcription of the associated gene.17
ProteasomeA large protease complex which selectively degrades proteins by proteolysis. The proteasome works in collaboration with ubiquitin–polymerization of ubiquitin serves as a degradation signal that transports the target proteins to the proteasome for degradation.18


The proportions of individuals within a population with an antibody to a serotype. Seroprevalence is measured in blood serum.19
SerotypeGroup of closely related microorganisms distinguished by a characteristic set of antigens and detected by an antibody.9
Terminator sequence (Poly(A))The Poly(A) signal sequence acts as the transcription terminator, halting transcription once the transgene is fully transcribed.20
TransductionTransfer of genetic material into the nucleus of a cell, such that elements of the newly transferred DNA are then expressed. This can be accomplished naturally by a virus or other vector or experimentally by augmenting the receptivity of the cell membrane of the recipient cell with chemicals or electricity.21
Transfer RNA (tRNA)tRNAs act as adaptors between the mRNA and the amino acids during translation. The tRNA has an anticodon loop that binds to the complementary mRNA codon and also has a bound amino acid.22
TransgeneThe transgene is the nucleic acid sequence encoding an artificially added gene.23
TropismThe ability of a virus to infect a particular type of cell in the body.23
VectorA gene therapy delivery vehicle, which encapsulates a therapeutic gene and delivers it to target cells. Vectors can be either virus-derived or non-viral.9


1. Nature Scitable: Glossary (others). (Accessed April 2021). 2. Thomas CE, et al. Nat Rev Genet 2003;4:346–58. 3. George LA. Blood Adv 2017;1(26):2591–9. 4. National Institutes of Health: Genetics glossary (chromosome). (Accessed April 2021). 5. National Institutes of Health: Genetics glossary (codon). (Accessed April 2021). 6. Cooper GM. The Cell: A Molecular Approach. 2nd Edition. Sunderland (MA): Sinauer Associates, 2000. Endocytosis. (Accessed April 2021). 7. Nature Scitable: Glossary (gene expression). (Accessed April 2021). 8. NEJM Illustrated Glossary (episome): (Accessed April 2021). 9. American Society of Gene and Cell Therapy: Glossary. (Accessed April 2021). 10. American Society of Gene and Cell Therapy: Gene and Cell Therapy FAQs. (Accessed April 2021). 11. National Hemophilia Foundation: Future Therapies FAQs. (Accessed April 2021). 12. NEJM Illustrated Glossary (immunogenicity): (Accessed April 2021). 13. National Institutes of Health: Genetics glossary (intron). (Accessed April 2021). 14. Li C, Samulski RJ. Nat Rev Genet 2020;21(4):255–72. 15. National Institutes of Health: Genetics glossary (nucleus). (Accessed April 2021). 16. NEJM Illustrated Glossary (plasmid): (Accessed April 2021). 17. Ohmori T. Int J Hematol 2020;111:31–41. 18. Tanaka K. Proc Jpn Acad 2009;85:12–36. 19. Merriam-Webster Definition (seroprevalence). (Accessed April 2021). 20. Tran DP, et al. Mol Cell Biol 2001;21(21):7495–508. 21. NEJM Illustrated Glossary (transduction): (Accessed April 2021). 22. Cooper GM. The Cell: A Molecular Approach. 2nd Edition. Sunderland (MA): Sinauer Associates, 2000. Translation of mRNA. (Accessed April 2021). 23. Sidonio Jr, R. Blood Rev 2020;100759. doi: 10.1016/j.blre.2020.100759. Online ahead of print.

Date of preparation: April 2021