Organ-like structure is a three-dimensional structure that can simulate the structure and function of organs in vivo. It is developed by stem cells under specific in vitro culture conditions, including many cell types.
The breakthrough of organ-like technology occurred in 2009, when Hans cleaves laboratory of Utrecht University Medical Center in the Netherlands first discovered that stem cells in adult small intestine can proliferate in vitro and organize themselves into organ-like structures [1].
Compared with traditional two-dimensional cell culture, organoid has many advantages. For example, organoid can show cell composition and physiological function close to physiological state, and many organoid can proliferate and pass through many times in the process of culture, and maintain the stability of genome. The model with these characteristics is especially suitable for biological sample bank and Qualcomm screening. Compared with the animal model, the organ-like model can reduce the complexity of the experiment and can apply real-time imaging technology. More importantly, it is difficult or impossible for animal models to accurately simulate human development and disease research, while organ-like models can do this.
The key of organ-like technology is to obtain adult stem cells, and then reconstruct the structure and function of the source tissue under suitable culture conditions. Organ-like culture system is the microenvironment needed to construct stem cells to develop into tissues with specific structures and functions.
Organ-like organs can be constructed from surgically excised solid samples or puncture samples. For solid tissues, the first step is to remove non-epithelial tissues such as muscle and fat as much as possible. Then the primary tissue was cut into small pieces with a scalpel, and then digested with enzyme, thus the tissue was dissociated into single cell suspension. Next, the single cell suspension is planted on 3D extracellular matrix hydrogel, such as basement membrane extract (BME), Matrigel or Geltrex. After planting, it is necessary to add a culture medium containing growth factors to trigger the regeneration reaction of stem cells. There are differences in the composition of culture medium needed in different tissues and organs.
After constructing the organ-like model, some methods are needed to compare the similarity between the constructed organ-like model and physiological tissue. For example, after constructing the mouse intestinal organ-like model, the author examined whether the organ-like model contains the common cell types in the intestinal crypt structure, such as intestinal epithelial cells, goblet cells, Paneth cell cells and intestinal endocrine cells by immunofluorescence staining, immunohistochemistry and electron microscope photos. Therefore, it can be explained that the constructed intestinal organ can reproduce the cell diversity contained in normal intestinal tissue.
To a great extent, organ-like system should be regarded as a rapidly developing model system, and this technology has shown great development potential in many fields. The following are some application fields where organ-like structures have emerged.
(1) Establish a biological sample database. For example, a recent study established a biological sample bank of gastric cancer. Gastric cancer is a heterogeneous disease, which is characterized by a variety of tissue and molecular subtypes, such as microsatellite instability (MSI), EB virus, intestinal chromosomal instability (CIN), diffuse type and so on. As a cell model in vitro, the biological sample bank of tumor-like organs can obtain genome characteristics very close to tumor cells in vivo through sequencing technology, and various tumor subtypes can be identified by combining genome sequencing data and histomorphology.
(2) Study the mechanism of diseases. For example, normal tissues, tissues in non-inflammatory and inflammatory areas of ulcerative colitis, and colitis-related tumor tissues were taken to construct organ-like models, and all exons of monoclonal organs were sequenced and targeted to reveal somatic mutations accumulated during the pathogenesis of ulcerative colitis.
(3) Predicting drug sensitivity. After constructing the organ-like model of tumor tissue obtained from patients, it can be predicted whether the tumor of a specific patient is sensitive to drugs by drug treatment. The response of organ-like model to drug treatment can guide clinical medication.
(4) Regenerative medicine and organ repair. The small intestine is the main organ that absorbs nutrients. Large-scale resection of small intestine can lead to short bowel syndrome (SBS), which is a serious malabsorption characterized by diarrhea, dehydration and weight loss. A recent study transplanted the constructed human ileoid organ into a rat model of short bowel syndrome. The transplanted ileoid organ can produce a highly vascularized functional small intestine and colon, which not only includes vascular system and innervation, villous structure and chylous duct, but also has the physiological function of absorbing cholesterol.