AIC-CCMB

CPHMS Newsletter July Edition

Editorial

“Humans are not 70 kg rats”

In 2009, Thomas Hartung (Director, John Hopkins Centre for Alternatives to Animals) made this deceptively simple statement that also captures the limitations and challenges of animal models. In the last few decades, science has made huge strides. We have sequenced the entire human genome, we can extract multidimensional omics data, create stem cells from mature skin cells, grow tissues in the lab, and many more such breakthrough discoveries. Yet, we continue to predominantly rely on animal models to provide insights into complex and heterogeneous human biology. 

This realization has led to a global reckoning to promote the development of human biology-based technologies, such as 3D organoids, organ-on-chips, etc. These methods along with powerful computational tools which can integrate vast amounts of existing information are being used to predict human biological responses. For example, the US Environmental Protection Agency passed a resolution in 2019 to phase out funding for mammalian models by 2035. 

The Centre for Predictive Human Model Systems, a science and policy centre, was established at Atal Incubation Centre in 2019 in collaboration with Humane Society India to propel the education, awareness, research, infrastructure, and regulation in these human-relevant emerging technologies in India and develop it as a key global player.

This newsletter aims to provide a snippet of the latest research, educational resources, opinion pieces on the current research and regulatory landscape of this field. We hope you enjoy reading it, and we look forward to your feedback!

Surat Parvatam
Senior Research Associate
Centre for Predictive Human Systems
Atal Incubation Centre-CCMB

Blog

Understanding the ocular route of COVID-19 infection via human-relevant models

DeepThink: Adoption of MPS models by industry

Lookback in to CPHMS monthly webinars: Delving into the brain using organoids

Excerpts from the JRC Virtual Summer School on ‘Non-animal approaches in science

Upcoming events:

  • 13th annual Advances in Cell and Tissue Culture conference (ACTC) 2021 |Date and time: Wed, 30 Jun 2021 | 13:30 & Wed, 3 Nov 2021, 23:30 IST | Location: Online event. Register here
  • OpenTox 2021 Virtual Conference. Register here
  • 10th Annual Meeting of the American Society of Cellular and Computational Toxicology | Overarching theme: “Practical applications of new tools in toxicology” | Dates of Meeting: October 12-14, 2021 (virtual) Register here
  • Survey to Assess Publication Bias in Animal Studies: Physicians Committee for Responsible Medicine (PCRM) and Humane Society International (HSI) are conducting a survey to understand and collect insights on when and why researchers are being asked to add animals to their studies. You can contribute to this global survey here
  • 11 TH World Congress on Alternatives and Animal Use in the Life Sciences. 23 August – 2nd September 2021. Virtual Congress. Register here

Understanding the ocular route of COVID-19 infection via human-relevant models

With the widespread impact of the SARS-CoV-2, understanding all possible routes of viral entry is essential to contain the transmission and spread of the virus. Currently, aerosol transmission via the nasal route is most widely studied and understood; however, the ocular route (via the eyes) has also been suggested as a vulnerable point of entry. In this paper, the researchers investigate the possibility of viral entry via the ocular route using two human-relevant model systems:

  1. Ex vivo culture: The researchers used ocular tissues of patients who had passed and were positive for SARS-CoV-2. They cultured various cell types from the eye tissues isolated from adult human cadaver donors, including cornea, limbus and sclera. These cell cultures were then investigated for the presence of ACE2 receptors and SARS-CoV2 infection permittivity.
  2. Whole-eye 3D organoids: They also used a pluripotent stem cell differentiation protocol that included the differentiation into retina, retinal pigment epithelium (RPE), ciliary margin, iris, lens, and cornea.

Figure 1: Ocular tissues and COVID-19 infection: The ocular tissues have the machinery (ACE2 and TMPRRS2 expression) for the COVID-19 infection and limbus tissue is most prone to SARS-CoV-2 viral replication.

The researchers used these systems to show that SARS-CoV-2 viral antigens are present in the ocular epithelium of COVID-19 infected patients. In addition, the eye organoids could get infected with the SARS-CoV-2 virus when challenged and also generate a NF-kB mediated immune response. Interestingly, they found that limbus tissue (the border of the cornea and the sclera) seems to be most at risk for viral entry because of higher expression of ACE2, TMPRSS2, and other SARS-CoV-2- associated genes. This tissue also has a higher infection propensity compared with other ocular cell types.

The current evidence surrounding COVID-19 infection via the eyes of patients is mixed. A recent meta-analysis of around 895 articles suggested that approximately one out of ten COVID-19 patients show at least one ocular symptom and around 1-5% of COVID-19 patients present the virus in tears. This study presents the evidence that the eye, and particularly the limbus tissue, has the machinery to get infected in an experimental setting.

However, one of the limitations of the study stated by the authors is that it may be difficult to distinguish if the ocular tissue derived from cadavers were directly infected by aerosol droplets or the infection was originally an airway infection which then systematically spread to the ocular surface.

None-the-less these model systems derived directly from human tissues present very powerful models to study SARS-CoV-2 infection dynamics and screen compounds for infection prevention.

Reference: Eriksen et al., SARS-CoV-2 infects human adult donor eyes and hESC-derived ocular epithelium, Cell Stem Cell (2021), https://doi.org/10.1016/j.stem.2021.04.028

DeepThink: Adoption of MPS models by industry

Organs-on-chips are 3D microfluidic devices that are lined with living human cells and aim to capture mechanics and physiological response of particular organ or a system of organs (watch our video in this newsletter on how lungs-on-a-chip are being for developing COVID-19 therapeutics). While these organ chips have gained tremendous traction in the past decade, there are certain challenges that still prevent the widespread adoption of these models in the industry for drug discovery, disease modelling and personalized medicine. 

A recent survey attempted to understand the broad challenges for translation and commercialization of this technology by the various stakeholders

Fig 1: Stakeholders included in the survey

Fig 2: Sources of variabilities hindering wide-spread adoption of organ-on-chip models in industry

The survey highlighted several parameters that need to be considered during the development and design of an organ-on-chip: design of the chip itself, material of the chip and 3D matrices, source of cells used in these devices, differentiation protocols when using induced pluripotent stem cells, type and density of media, the flow rates, and validation protocols.  

For example, different developers can employ different designs of organ chip device, use different substrates and biomaterials. Polydimethylsiloxane (PDMS) is one of the most widely used 3D matrix, due to its non-toxic and flexible nature. However, its propensity to absorb tracers, drugs, and toxicants is a significant drawback which is leading to developers exploring new matrices and substrates. The source of cells can also contribute to a huge amount of variability. Particularly, iPSCs often exhibit an immature phenotype and require validation of differentiation methods due to line-to-line variability, and complex differentiation protocols can further add to heterogeneity. 

Different developers can use different rates of perfusion of media which can lead to differences in nutrient consumption, waste production, shear flow stress, and diffusion kinetics across membranes. Validating these models in another area which is a point of hesitancy amongst the industry stakeholders. As these models are based on human cells and human biology, validating the results obtained from these models using animal models is a highly debatable idea. Whereas, the idea of validating these systems against human clinical samples and human-relevant data is gaining ground.

However, there are no guidelines or standardization protocols that are in place to address these points which bring about site-to-site and batch-to-batch variabilities. 

Many of the end-users felt that having detailed guidelines and standards for each of these parameters is necessary to ensure robustness and reproducibility in organ-on-chip. This in turn would increase trust in these systems, leading to wider adoption by industry and other end-users.

Reference: Allwardt, V. et al. Translational Roadmap for the Organs-on-a-Chip Industry toward Broad Adoption. Bioengineering 2020, 7, 112. https://doi.org/10.3390/bioengineering7030112