ATMPs are innovative and complex live biological medicines, classified into three main types:

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• Gene therapy medicines: these contain genes that lead to a therapeutic, prophylactic or diagnostic effect. They work by inserting 'recombinant' genes into the body, usually to treat a variety of diseases, including genetic disorders, cancer or long-term diseases. A recombinant gene is a stretch of DNA that is created in the laboratory, bringing together DNA from different sources.

• Somatic-cell therapy medicines: made by cells or tissues that have been manipulated to change their biological characteristics or cells or tissues not intended to be used for the same essential functions in the body. They can be used to cure, diagnose or prevent diseases.

• Tissue-engineered medicines: containing cells or tissues that have been modified so they can be used to repair, regenerate or replace human tissue.

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Tissue engineering overarching goal is to assemble functional constructs that restore, maintain, or improve damaged tissues or whole organs. This involves the assembly of two types of components: cells, the building blocks of tissues and scaffolds, where cells will be “glued” in a specific 3D structure. An adequate environment for promoting cell growth, differentiation, and integration with the existing tissue is a critical factor for the survival of the engineered tissue. 

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Scaffolds are materials that have been engineered to cause desirable cellular interactions to contribute to the formation of new functional tissues for medical purposes. Cells are often 'seeded' into these structures capable of supporting three-dimensional tissue formation. Scaffolds mimic the extracellular matrix of the native tissue, recapitulating the in vivo milieu and allowing cells to influence their own microenvironments.