3D cell culture compares with 2D cell culture

Flat 2D cell cultures are widely used to study cellular and disease mechanisms. Recently, the researchers suggested that 3D culture system, compared to the 2D culture system, represents more accurately the origin microenvironment where cells presence in tissues. It has been demonstrated that cell responses in 3D culture is more like in vivo behavior than 2D culture, so the 3D cultures would provide more physiologically relevant information and better represent in vivo tests ^[1]. 

In the last decade, 3D culture has been used as a model system in drug screening platform, cancer cell biology, stem cell study, implantation of engineered functional tissues and other cell-based research. 3D culture can be a potential in vitro model and observe cellular responses in mimic situation in vivo environment ^[2].

The strategy to establish 3D cell culture is diverse. The 3D cell culture method can be divided into three groups: scaffold-free, scaffold base, and hybrids. In scaffold-free systems, cells aggregate as occurs in natural processes of organogenesis. Scaffold-based systems use structures that mimic the extracellular matrix. Hybrids use a matrix or a scaffold to support scaffold-free systems.

Application of 3D culture in SARS-CoV-2

As a new virus outbreak, it is crucial to elucidate the infection mechanism quickly and reliably. The 3D cell culture microenvironment simulation offers a good model for the study of virus–host cell interaction, the viral infective cycle, oncogenic viruses, new anti-viral drugs, and behavior used to study pathogens. The 3D cell culture pathophysiological models could be preliminary approaches or replace tests of animal models which are expensive and time-consuming to accelerate the research in drug/vaccine development for newly emerging viruses ^[3].

Several cells have been used in 3D cultures for SARS-CoV-2 virus studies, while the most widely used models are stem cell-based. The 3D organoids models can be divided into pulmonary or airway models, and extrapulmonary models such as intestine, heart, and brain.

A 3D culture models of the proximal-distal axis reveals the infection process of SARS-CoV-2 on proximal airway cells. The infection process was rapid and targets both ciliates and goblet cells. In the distal axis model, activated HAT2 cells induced a series of pro-inflammatory transcripts, such as interferon 1 (IFN-β1) and interferon 3 (IFN-3). Several drugs were evaluated, such as beta interferon (IFN-β1), hydroxychloroquine, and remdesivir. The results shown that, unlike hydroxychloroquine, remdesivir inhibited viral replication at a greater rate than IFN-β1 independently of the origin of epithelium ^[4]. 3D culture model showed that immune cells play an important role in dysfunction of alveolar barrier due to the disruption by viral infection-induced expression of interleukin 6 (IL-6) and interleukin 8 (IL-8), which damaged the alveolar barrier. Through these observations, correlations with findings in the postmortem lung tissues of patients severely affected by COVID-19, pointing out that the possible relationship with clinical manifestations such as severe tissue damage, thromboembolism, and excessive inflammation ^[5].

Extrapulmonary infection models provide the possibility to study another viral entry point and provide insights into the damage caused by SARS-CoV-2 virus to various tissues and organs. Through an extrapulmonary 3D culture model, SARS-CoV-2 virus was found to induce microclot formation within the vasculature of surrounding tissues and central neural system (CNS) ^[6].
Infects cardiomyocytes via the endolysosomal, pathway particularly using the cathepsin-L protease, disrupts metabolite transport, absorption, hamper hormonal secretion, and affects local immune defense of gastrointestinal tissues ^[7].