Organoids and Spheroids – The 3D Cell Culture Systems Advancing Science

With major advances in modern medicine, there has been a high demand for cell model systems that can accurately mimic the microenvironment and biological complexity. 2D cell cultures, however useful, have several limitations such as changes in cell morphology, disturbance of interactions between the cellular and extracellular environments, polarity, amongst others. These limitations have lead to the development of alternative cell culture methods that mimic in vivo conditions. One such method is three-dimensional “3D” cell culture. With the advent of 3D cell cultures, researchers can now establish in vivo-like models to study normal or pathophysiological processes and complex cellular responses to drug stimuli amongst others.

3D cell culture systems that have gained much attention in recent years include Organoids and Spheroids. These are cell aggregates that range from 300 µm to 5 mm in size. Both systems however differ from each other and offer various applications based on their cellular organisation and differences. This article aims to highlight the key differences between the two cell culture systems, in addition to their key applications in various fields of research.

Organoids are mini organs accurately mimicking the complexity and cellular organization of the parent organ as an in vitro study model. Simply put, an organoid is a mini version of a specific organ. They essentially grow from stem cells - either pluripotent (embryonic or induced) or adult stem cells from various organs. either embryonic (ESCs) or human-induced pluripotent (iPSCs) assemble themselves. There are several ways to generate stem cell-derived organoids, one of which is growing them in a given scaffold, such as Matrigel, Collagen, or Geltrex. This artificial scaffold provides the support required to undergo lineage-specific differentiation and develop the structure that closely resembles the natural process of organ development.

Lancaster et al., has developed two approaches to generating brain organoids, namely: Guided differentiation and Unguided differentiation methods. Guided methods (left) provided with patterning factors that have been employed in producing cerebral organoids. They enable the generation of region-specific brain organoids that look like discrete parts of a developing human brain, including the cerebellum, midbrain, and forebrain. Unguided methods (right) have been employed in producing cerebral organoids, which lead to the production of organoids that mimics the whole human brain. These brain organoids can be formed again with similar properties and can precisely serve as a great tool for studying human development and disease biology. In addition, this technology can be used to generate other organ types, including heart, lung, liver, stomach, kidney, retina, small and large intestines.

On the other hand, Spheroids are simple cell clusters that grow by sticking to each other, without the need for a scaffold. Although less advanced compared to organoids and cannot fully restate the genomic features, phenotypic complexity, and cellular organization of actual body systems, this 3D cell culture system still offers an opportunity for studying the tumour microenvironment outside the body. To date, spheroids have been utilized as a study model for tumour tissue, embryoid bodies, hepatocytes, nervous tissue, mammary glands and to predict drug efficacy in the field of personalised cancer therapy. ESCs or iPSC-derived spheroids can also be used to study underlying mechanisms of neurological or neurodevelopmental disorders.

Potential Applications of 3D Cell Culture Systems

Based on the ability to precisely mimic the in vivo cellular processes of the human body, organoids and spheroids can be used to study complex mechanisms of human development and disease states. Some applications include:

• Biomedical research: to examine tissue morphogenesis, disease modelling, drug discovery, and formation of complex tissues for transplantation.
• Regenerative medicine: to replicate complex body functions by applying bio fabrication strategies in organoid systems.
  
• Personalised medicine: using iPSC-derived organoids that can help in estimating drug response, toxicity and treatment plans that are being prescribed to the patient.
  
• Cancer research: using this system for modelling cancer development and treatments. Also, for studying the complex interactions of cancer cells within and outside the tumour mass and screening of potential chemotherapeutic agents in vitro.
  
• Disease Mechanisms: to examine the role of specific genes in disease mechanisms by using CRISPR/Cas9 editing technology in iPSCs.
  
• High-throughput platforms: for drug screening, pathologies development, tissue engineering, and bio fabrication, 3D bioprinting, and microfluidics.

Transporting 3D live cells across the globe

Several logistic companies are dedicated to transporting 3D live cell cultures around the globe. The list includes Cellbox Solutions, Celartia, Bionano Genomics, AllCells, Altogen, InvivoGen, Cell biologics, etc. Most of these companies ship live cultures overnight to the various locations without freezing them and maintaining growth conditions. Amongst these, Cellbox Solutions was the first to bring this innovative technology to the market. Moreover, recently, Singh et al. (2020) demonstrated a detailed protocol of live cell transport from one geographical location to another. They used Retinal organoid technology to enable the generation of 3D retinal tissue from iPSCs. Highlighting the challenges of this very promising approach, they stated that it requires specialised stem cell and grafting techniques to successfully derive the retinal tissue derivation followed by its transplantation. Therefore, experts from different locations around the globe work together for the successful development and transplantation of iPSC-derived organoids in the patient.

Organoid versus Spheroid – new trends in the market!

Recently, a detailed market analysis on organoids and spheroids was published by the Grand View Research agency. According to the report, the global market size of these 3D cell culture models was valued at USD 405.3 million in 2019, which is expected to grow at a CAGR of 22.5% by 2027. Since the organoid models have revealed important mechanisms associated with its entry and the interactions of SARS-CoV-2 with intestinal and alveolar tissues, this system has been signified as a promising approach for testing new drugs and medicines. Many biotechnology and pharmaceutical companies are bringing in new products in the market that could assist in utilizing these culture systems as an in vitro study model. Some prominent players in the organoids and spheroids market include:

• 3D Biomatrix.
• 3D Biotek LLC.
• AMS Biotechnology (Europe) Ltd.
• Cellesce Ltd.
• Lonza.

These companies are involved in active collaborations and are continuously involved in the launch of new, improved products utilizing organoid and spheroid technology. For instance, MatTek has commercialized bronchial airway (EpiAirway), skin (EpiDerm, EpiDermFT), vaginal (EpiVaginal), and ocular (EpiOcular) epithelium. In addition, Hubrecht Organoid Technology (HUB) collaborated with MIMETAS to commercialize Organoids-on-a-Chip technology.

Conclusion

Organoids are 3D cellular models that incredibly resemble small pieces of tissue and are frequently referred to as “mini-organs” while spheroids are non-uniform cell aggregates mimicking the in vivo cellular system of the human tissues. These 3D models have overcome the failures of the routine 2D cell-based models and successfully help researchers to understand the truly relevant biological complexity of corresponding disease and physiological conditions outside the body.

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