Glossary of terms

The immune response occurs when an foreign (immunogenic) substance, such as a virus or bacteria, is introduced into the body. The immune system identifies it as non-self and initiates a defence mechanism aiming at neutralising or destroying the foreign substance. The immune response typically involves the activation of the body's immune system, including the production of antibodies, T cells, and other components of the immune system, in response to the presence of the immunogenic substance.

When developing new therapies or transplantation techniques, researchers must consider how to deal with the immune response. Otherwise, the immune system may treat the therapy or transplanted tissue as non-self and attack it. This may involve suppressing the immune system (leaving the patient at risk in the event of an infection). Researchers are also investigating means of preventing therapeutic or transplanted material as being recognised as non-self by the immune system.

Immunodeficiency means that the body's defense system, the immune system, weakens and is unable to respond and protect the body from harmful invaders such as bacteria and viruses. This makes the individual more susceptible to  infection and disease.

Immunogenicity refers to the ability of a substance, such as a foreign molecule or a therapeutic product, to provoke an immune response within an organism.

In situ ('in place') gene therapy refers to the direct administration of a therapeutic gene into a selected tissue of the patient, resulting in the correction of the affected cells at a genetic level.

In vitro (in Latin for "in glass") refers to experiments or processes that take place outside a living organism in a controlled environment. In vitro research typically involves working with cells or tissues in the laboratory, such as culturing cells in a petri dish or testing the efficacy of gene therapy vectors on different cells. For example, in vitro systems can be used to study the fundamental mechanism of biological processes in a simplified enviroment or to evaluate the toxicity of drug candidates without the use of living organism. The benefits of in vitro research systems include increased control and reproducability of the research experiments, as well as simplified study models. However, these models often lack physiological relevance and fail to capture the important biological interactions.

In vivo is a Latin term that refers to experiments, studies, or processes that occur within a living organism such as animals and humans. For example, scientists can study disease development or impact of a drug treatment in a whole organism by using in vivo models such as mice as model organisms. In vivo models are essential for undertanding biological processes and to capture the complexity of interactions in various biological levels. These range from interactions between different cell types to systemic responses affecting the whole organism.

The use of in vivo models must always be ethically approved. This is evaluated by comparing the potential harm to the living organism against benefit that is gained by the use of the model. Additionally, research with in vivo models requires highly trained research personnel and specialised facilities.

Induced Pluripotent Stem Cells (iPSCs) are a type of pluripotent stem cell created in the laboratory. They are derived from adult somatic cells that have been genetically or epigenetically reprogrammed to an embryonic stem (ES) cell-like state. This reprogramming is typically achieved through the forced expression of specific genes and transcription factors (the proteins involved in carrying out the 'instructions' of a gene.) These are collectively known as Yamanaka factors, which include Oct4, Sox2, c-Myc, and Klf4.

iPSCs share many characteristics with ES cells, such as the ability to differentiate into any cell type in the body. They represent a significant advancement in regenerative medicine. Unlike ES cells, which are derived from embryonic stem cells and involve the destruction of pre-implantation embryos, iPSCs can be generated from an adult donor, without the ethical and moral considerations associated with embryonic stem cell research. This technology has opened up new possibilities for cell replacement therapy and disease modeling. It offers a nearly identical match to the cell donor, which is crucial for patient-specific treatments.

See Genetic disease.

Insertion is a form of change in the DNA sequence which involves the addition of a piece of DNA into the genome. This can be a whole gene, or a shorter segment of DNA.

Insertion can be achieved by methods including lentiviral or transposon-based delivery or the CRISPR-Cas9 system.