What is the difference between in vivo (in the living organism) and ex vivo (outside the living organism)?

From the Guidelines

In vivo studies are preferred over ex vivo for assessing safety and therapeutic efficacy due to their ability to provide a more realistic biological context. When considering the differences between in vivo and ex vivo studies, it's essential to understand the advantages and disadvantages of each approach. In vivo studies, which are conducted within a living organism, offer the most realistic biological context, including all physiological systems working together 1. However, they can be complex to control and may raise ethical considerations.

Key differences between in vivo and ex vivo studies

• In vivo studies provide a complete physiological environment, allowing for the assessment of drug interactions and side effects in a realistic setting.
• Ex vivo studies, on the other hand, involve experiments performed on tissues or cells that have been removed from an organism but are still alive and functioning, offering better experimental control than in vivo while maintaining some of the biological complexity.
• Despite the advantages of ex vivo studies, such as being cheaper and less time-consuming, safety and therapeutic efficacy assessments are often severely limited in these studies 1.

Implications for research and clinical practice

• In vivo studies are crucial for validating the findings of ex vivo studies and providing a more accurate assessment of a drug's effects in a living organism.
• The use of in vivo studies can help to ensure that new treatments are safe and effective, ultimately improving patient outcomes and quality of life.
• As noted in a recent systematic review, ex vivo experimentation is commonly used as an initial proof of concept for drug delivery research, but in vivo studies are necessary for translating these findings into clinical practice 1.

From the Research

Definitions and Differences

• In vivo refers to experiments or procedures conducted within a living organism 2, 3, 4.
• Ex vivo refers to experiments or procedures conducted on living tissue outside its host environment, while striving to maintain conditions as close to the host surroundings as possible 3, 4, 5.
• In vitro refers to experiments or procedures conducted in a controlled environment, such as a test tube or petri dish, outside of a living organism 2, 5, 6.

Applications and Uses

• In vivo approaches are often used to edit cells in organs and are suitable for gene therapy and other treatments 3.
• Ex vivo approaches are mainly used to edit blood cells, improve cancer therapy, and treat infectious diseases 3.
• In vitro models are commonly used in biological fields, but have limitations such as the absence of biokinetics, which can lead to misinterpretation of data 2, 6.

Methodological Approaches

• In vitro, ex vivo, and in vivo methodological approaches are used to study therapeutic targets of various diseases, including osteoporosis and degenerative joint diseases 6.
• Biomarkers can assist in these methodological approaches by providing insights into the mechanisms driving disease progression and allowing for the quantification of pharmacodynamic effects 6.

Clarification of Terminology

• There is a need for clarity between in vitro and ex vivo terminology in the tissue engineering and regenerative medicine community, as the terms are often used interchangeably 5.
• Ex vivo experiments must meet certain criteria to be legitimately defined as such, including maintaining conditions close to the host surroundings 5.