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The AHC Foundation is pleased to share resources to help our community understand the complexities of the AAV Project and Genetic engineering projects now underway. As we continue with the project, additional resources will be shared to further our knowledge of this complicated therapy.

Below is a Glossary of terms used regarding gene therapy. The material is provided by the American Society of Gene & Cell Therapy and can be found at

Adeno Associated Virus
AAV are small DNA viruses that do not cause human disease. The nine distinct serotypes of AAV preferentially go to different tissues. AAV have been engineered to carry genes into dividing and non-dividing cells of the body.

Adenosine Deaminase Deficiency
ADA is a life threatening disease. The lack of the enzyme adenosine deaminase in T lymphocytes inhibits their ability to fight infection. Without treatment, ADA usually leads to death within the first few months of life. ADA is a type of immunodeficiency disease.

A group of DNA containing viruses. Some types cause respiratory disease, including one form of the common cold. Adenoviruses can be genetically modified and used in gene therapy to treat cancer and potentially other diseases.

A cell specialized in storing and making fat for energy, regulation of body temperature, and cushioning.

Adult stem cells
Stem cells isolated from an adult person or animal. They can self-renew and can mature into one or more types of specialized cells from organs such as liver cells, heart cells, muscle cells, neuron cells, blood cells, or bone cells.

Allogeneic Transplantation
The transfer of tissue or cells from one person to a distinct member of the same species. For example, a sister may donate bone marrow to a brother of the same family (bone marrow transplant). Another example is a car crash victim may donate his kidney which is surgically transferred to an unrelated person or recipient (kidney transplant).

Proteins that help fight infections and toxins and are found in the blood. They are made by B lymphocytes. Each antibody binds to a specific part of a protein or antigen. Recently, many biological drugs are comprised of huge quantities of exact copies of one antibody which binds to a specific disease target.

A part of a protein or other molecule that causes an immune response. Antigens are found in toxins, bacteria, molds, and viruses. They are also found on infected cells, proteins found on foreign blood cells (such as AB blood groups in transfusions), and, in some instances, proteins on the cells of transplanted organs. Antigens can induce the production of antibodies (immunoglobulins) and/or induce T lymphocytes to kill cells or suppress the immune response.

Programmed cell death, the body’s normal method of disposing of damaged, unwanted, or unneeded cells.

Autologous Transplantation
Removal of tissue or cells from one person and then returning the cells back to the same person. For example, a patient may donate her own bone marrow cells which were frozen and stored, then undergo chemotherapy which destroys her bone marrow, and subsequently the patient’s bone marrow is replenished with her own frozen bone marrow cells.

A classification of products derived from living sources, such as humans, animals, bacteria and viruses. Vaccines, immune globulin, antibodies with a specific target (such as anti-TNF), gene therapy vectors, cell therapy, stem cell therapy, and anti-toxins are biologics.

A very early embryo stage containing approximately 150 cells in a spherical mass. It has a fluid filled cavity, an inner cell mass that begets the embryonic stem cells, and the outer cell layer (trophoblast) that develops into the placenta.

Bone Marrow Stromal Cells
A subpopulation of cells from bone marrow containing several types of cells which are also called mesenchymal stem cells. They do not develop into blood cells, but can differentiate into bone, cartilage and fat cells among other types.

Specialized muscle cells in the heart that play key roles in maintaining the heart’s continuous beat in a rhythmical manner.

Cell Line
Cells isolated from an animal or human and grown in tissue culture for more than 3 passages or doublings. They are usually well characterized. Some cell lines are normal cells that grow in vitro under defined conditions. Some cell lines are derived from tumors, are called cancer cell lines, and are used to study cancer.

Cell Therapy
Cell therapy is the transfer of cells into a patient with the goal of improving a disease.

A chondrocyte is a specialized cell that produces cartilage for its neighboring structures. Cartilage is found in the ear canals, joints, trachea, and disks between the vertebrae and the ribs.

Long strings of genetic material made up of DNA and accessory proteins. The DNA contains approximately 30,000 to 100,000 genes that make up the human genome. Human cells contain 23 pairs of chromosomes (46 total), with the mother and the father each contributing one chromosome to each pair in their children.

Clinical Trial
A clinical trial is a research study in human volunteers and is designed to answer specific questions about a disease, new therapies, or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work in people.

Trials are in four phases:

  1. Phase I tests a new drug or treatment in a small group to evaluate safety and toxicity. Some Phase I trials solely examine characteristics of a disease and provide needed background information for developing novel therapies.
  2. Phase II expands the study and begins to assess efficacy.
  3. Phase III expands the study to an even larger group of people and often compares the agent to a standard of care treatment.
  4. Phase IV takes place after the drug or treatment has been licensed and marketed.

A multi-step process of maturation whereby a stem cell can generate daughter cells which then become the specialized cells within our body. The differentiated cell expresses some different genes and can perform specialized functions, such as contraction of muscle cells, or secretion of insulin from islet cells located in the pancreas.

DNA (deoxyribonucleic acid)
Genes are composed of segments of DNA, a very long molecule that carries a cell’s genetic information. DNA is made up of two antiparallel strands that are held together by weak chemical bonds between base pairs of nucleotides. DNA is comprised of the four nucleotides based on these four bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

DNA Oligonucleotides
DNA oligonucleotides are short strands of DNA designed to be complementary to target mRNA, which triggers RNAseH mediated degradation of the mRNA.

Embryonic Stem Cell
These cells, which are abbreviated as ES, can develop into all the types of cells in the body (pluripotent) and can replicate itself. Embryonic stem cells are derived from the inner cell mass of blastocysts.

Eugenic Genetic Engineering
The use of gene engineering technology to alter human traits (ex. height or intelligence) in contrast to gene therapy which uses the technology to treat human disease.

Ex Vivo Gene Therapy
Patient cells are harvested, cultivated in the laboratory, and 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.

A type of cell found in the connective tissues and most organs. In each tissue, fibroblasts lay down distinct combinations of proteins on a supportive network or matrix which helps instruct and maintain the specialized functions of the tissue’s cells.

A segment of DNA found on a chromosome that codes for a particular protein. Humans have tens of thousands of genes that act as a blueprint for making specific enzymes or other proteins for virtually every biomedical reaction and structure in the body.

The sum of all genes that code for a particular organism and found in the chromosomes.

The study of all of the nucleotide sequences, including structural genes, regulatory sequences, and non-coding DNA segments, in the chromosome of an organism.

Gene Therapy
Gene therapy is the introduction, removal, or change in the content of a person’s genetic code with the goal of treating or curing a disease.

Genetic Engineering
A way of directly manipulating genetic material in a cell or organism to produce desired traits.

Germ Layers
During growth of the fertilized egg to an embryo, three layers of cells called germ layers, develop within the first 2 weeks of growth in the human. These germ layers are called the endoderm, mesoderm, and ectoderm.

Germline Therapy
Gene therapy of the reproductive or germline cells (egg and sperm). Unlike somatic gene therapy, germ line gene therapy will change the genetic make-up of the patient and can be passed onto offspring of the patient. Currently, the ethical issues surrounding human germline gene therapy have not been resolved and there are no approved clinical applications of this form of gene therapy.

Hematopoietic Stem Cells
A specialized type of stem cell that can replenish itself and produce cells that develop into a variety of mature blood cells, including red blood cells, macrophages, basophils, eosinophils, neutophils, lymphocytes, and platelets. The greatest number of these cells are found in the bone marrow, but can also be found in the peripheral blood, umbilical cord blood, and the fetal liver.

Hematopoietic Cells
The various cell types that comprise blood. The blood contains red blood cells, platelets, macrophages, basophils, eosinophils, neutrophils, B lymphocytes, T lymphocytes.

Hematopoietic Cell Transplantation
The transfer of hematopoietic stem cells into an individual so they can home to the bone marrow, self-renew, and produce all the cell types of the blood including red blood cells, platelets, and white blood cells.

A specialized liver cell. It makes proteins for the blood plasma, synthesizes enzymes that breakdown toxins and pharmaceutical drugs, destroys old red blood cells, and recycles their parts.

Similar but not uniform. A heterologous stem cell population is a mixed cell population.

Same or uniform. Here, it is most often used to describe two stretches of gene that are identical. Homologous alleles of genes means the same allele (e.g. both blue eye genes).

Homologous Recombination
The joining of two separate pieces of DNA (recombination) that are identical (homologous).

Human Embryonic Stem Cell
An unspecialized cell that can replenish itself and can develop into any type of tissue or cell.

Human Genome Project
An international effort that has sequenced the approximately 30,000 to 100,000 individual genes that constitute a human being.

One or more defects in the immune system that leads to an increased risk of infections. Severe immunodeficiency’s can lead to early death due to repeated or serious infections. Some immunodeficiency’s are due to genetic mutations. Certain viruses, including HIV, can also cause immune deficiencies.

Islet Cell
A specialized cell residing in the pancreas. It produces insulin, gastrin, glucagon, and somatostatin.

In Situ Gene Therapy
The direct administration of a vector carrying the therapeutic genetic material to the affected tissue, such as injection into a tumor nodule or organ.

In Vivo Gene Therapy
The administration 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 various organs by other physical means of administration (hypodermic injection, aerosol, intrathecal, etc.).

Represents a class of animal and human viruses. Human Immunodeficiency Virus (HIV), the virus that causes AIDS, is a type of lentivirus. Modifications of these viruses for vectors involve removal of the viral genes that cause disease and replacing the viral genes with therapeutic genetic material. In this way the lentivirus is engineered to insert the new DNA into the genome of the target cells which can then be used to treat disease.

Mesenchymal Stem Cell
Rare cells found in the bone marrow and are also called bone marrow stromal cells. They self-renew and can mature into a large number of tissues and cell types including connective tissue which is located between organs and structures in the body, fat tissue, bones, and cartilage located in joints, ears, and nose.

Messenger RNA (mRNA)
mRNA is a single molecule of RNA that works as a chemical map for a protein product

Multipotent Stem Cells
Stem cells that can replicate themselves and produce cells of specific lineages, but not all types of cells of the body. For example, hematopoietic stem cells can undergo differentiation to produce the different types of cells found in the blood.

A change in the sequence of DNA which alters gene function. Sometimes the mutation changes the gene so that the protein encoded by the gene is abnormal. In other cases the protein may be normal but the mutation causes the cell to make too little or too much of the protein.

A specialized muscle cell. It can contract and lengthen.

Neural Stem Cell
A stem cell residing in the brain. It can self-renew and can mature into cells found in the brain, including neurons, and glial cells.

A specialized cell in the brain that conducts impulses. It is essential for thinking and regulating the processes of the body such as breathing, digesting, pumping blood, seeing, hearing, and regulating body temperature.

Non-Viral Gene Therapy
While some gene therapy approaches utilize engineered viruses to deliver genetic material, there are a number of other methods available and have been referred to as non-viral gene therapy. More recently, these methods have been called synthetic gene therapy.

Oligo-potent Progenitor Cells
Cells can differentiate into several types of cells. They cannot self-renew.

A gene that is associated with cancer. When a gene that regulates growth under normal conditions develops mutations that contribute to a cell becoming cancerous, the mutated gene is called an oncogene. Certain viruses can also carry oncogenes. Oncogenes play a key role in the transformation of normal cells into cancer cells.

A specialized cell found in bone that lays down new bone matrix and bone cells.

A specialized cell found in bone that removes old bone cells and matrix. In order for bone to be repaired, the osteoclast must remove the diseased or weak part of bones.

The observable traits or characteristics of an organism, such as weight, wrinkles, or the presence or absence of a disease. Phenotypic traits usually involve genetic characteristics influenced by the environmental or nutritional factors.

An inherent characteristic of a multipotent stem cell or pluripotent stem cell. Plasticity refers to the ability of stem cells to develop into two or more distinct types of specialized cells such as new blood cells and hepatocytes cells of the liver.

A circular, double-stranded unit of DNA that replicates within bacteria independently of the chromosomal DNA. Plasmids have been engineered to deliver genetic material to animal and human cells and are important tools for genetic engineering and non-viral gene therapy.

Pluripotent Stem Cells
Stem cells that can give rise to all the types of cells in the implanted embryo, fetus, or developed organism. They cannot give rise to embryonic cells found in the trophoblast or placenta.

Preclinical Studies
Refers to the testing of experimental drugs or therapies in the test tube or in animals. The testing occurs before trials in humans may be carried out.

Progenitor Cell
A cell that can differentiate or mature into a specialized cell. As cells undergo differentiation, the progenitor cell is between a stem cell and a specialized cell. Progenitor cells may produce cells of different types but cannot self-renew (i.e. have a limited lifespan). In contrast, a stem cell can self-renew and maintain a pool of stem cells for as long as the animal is alive.

Recombinant DNA
A novel DNA sequence formed by the joining DNA from different regions of the genome or from different organisms. Scientists often use special enzymes to cut and rejoin the DNA.

Regenerative Medicine
This branch of medicine aims to repair damaged tissue. It usually focuses on stem cells to repair the diseased or aging organs.

A type of virus that contains RNA as its genetic material. The RNA of the virus is translated into DNA, which inserts itself into an infected cell’s own DNA. Lentiviruses are a type of retrovirus.

RNA (ribonucleic acid)
RNA is a molecule which is chemically similar to DNA and carries a matching code. RNA is the intermediary molecule that cells use to translate the information found in genes into the corresponding protein the genes encode.

RNA Interference (RNAi)
RNAi is a cellular mechanism for the control of gene expression of messenger RNA (mRNA) translation

The ability of stem cells to make more of themselves.

A group of closely related microorganisms distinguished by a characteristic set of antigens and detected by an antibody.

Short Hairpin RNAs (shRNAs)
shRNAs are expressed by transcription and processed into siRNAs

Small Interfering RNAs (siRNAs)
siRNAs are short duplexes of RNA from 19 to 30 base pairs that serve as triggers for RNAi

Somatic Cells
Cells contain the normal number of chromosomes and comprise the vast majority of cells in the body and embryo. In contrast, the reproductive or germline cells (eggs and sperm) have half the number of chromosomes and are not somatic cells.

Somatic Gene Therapy
A therapy that changes gene expression in cells that will be corrective to the patient, but not inherited by the next generation. This therapy usually manipulates a small percentage of one type of somatic cells. It does not affect the reproductive cells (eggs, sperm) in the human body.

Stem Cells
Stem cells can self-renew and at any given time, some of these stem cells differentiate or mature into more specialized cells.

Suicide Gene
A strategy for introducing a self-destruct signal into cells using a special genetic sequence. The self-destruct signal is activated by a specific drug. In certain cases, the vector delivering the suicide gene is only effective in tumor cells; this approach is being explored as a novel cancer therapy. Suicide genes are also being used to engineer cells used in transplantation so that if the transplanted cells developed an unanticipated problem, the cells can be destroyed.

Syngeneic Transplantation
The transfer of tissue or cells from one individual to another individual with the same genetic make-up. For example, one identical twin donates a kidney to its other identical twin. Many mouse species have been bred to have identical genetic material and can serve as syngeneic donors and recipients.

Synthetic Gene Therapy
The use of non-viral vectors such as liposomes, polymers, polyplexes, and nanoparticles for targeting the delivery of the gene and its expression to the relevant cells.

Transplantation is the transfer of cells or tissues. Transplantation can be performed between identical twins (syngeneic transplantation), cells from self (autologous transplantation), between 2 non-identical members of the same species such as brother and sister (allogeneic transplantation) or between different species such as mouse into rat (xenogeneic transplantation).

Transplantation Biology
The field of science that studies the transfer of solid organs or cells from one person or animal to another person or animal. It also studies the immune response of the recipient to the donor and aims to develop methods to train the body to accept the new tissue.

The ability of a vector to bind to and enter a specific cell type. Certain vectors have been designed that have restricted tropism in an attempt to direct vector binding to cells of a specific species, organ or cell type.

Umbilical Cord Blood Stem Cells
Fetal hematopoietic stem cells can be found at high concentration in the blood at the time of birth. Blood collected from the umbilical cord at the time of delivery often contains sufficient cells for hematopoietic stem cell transplantation.

Gene therapy delivery vehicles, or carriers, encapsulate therapeutic genes for delivery to cells. They include both genetically disabled viruses such as adenovirus or AAV, and non-viral vectors such as liposomes.

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