The population of haematopoietic stem cells (HSCs) found in our bone marrow are responsible for repopulating the body with all blood and immune cells throughout our lives. As we age, our HSCs can collect DNA mutations, and this can result in many blood disorders like leukaemia. Methods of curing blood cancers require HSC’s for either the testing of drugs and treatments, or physically replacing faulty HSCs with those from someone else, known as a stem cell transplant (SCT, commonly called a bone marrow transplant).
Unfortunately, the availability of donor HSCs is limited because, out of the body, in 2D cultures they lose their ‘stemness’; the ability to become dormant (quiescent) for longevity and self-renew for population maintenance, and instead differentiate; this means that they cannot engraft and renew the blood supply in a cancer patient. Yet vast quantities are required in the development of a drug (multiple rounds of drug screening), and around 2 million are required per Kg of body mass for SCT.
Therefore, there is great need for in vitro methodologies that sustain this most primitive group and the project I am undertaking stems from this issue.
Firstly, I intend to form a 3D model of the most common place for HSCs to reside – the bone marrow (BM) microenvironment coined the ‘BM Niche’. The aim of any in vitro model is to replicate an environment in vivo. In the case of the bone marrow, it has been shown that marrow HSCs can be maintained by utilising a hydrogel scaffold* to mimic the physical features of the niche (stiffness), while biological additives such as extracellular matrix proteins and growth factors (structural and signalling proteins of the bone marrow), and cellular co-culture with marrow mesenchymal stromal cells (MSCs)** mimic the biochemical features that help support the HSCs.
Secondly, one type of signalling molecule secreted by MSCs to help support HSCs are bioactive metabolites*** which signal to HSCs and result in retained stemness. Using this niche model, I shall isolate these metabolites and add them artificially to a simplified niche models without any biological additives with the aim of ‘tricking’ the cells into thinking they are in an optimal environment and so that they retain their HSC characteristics for long enough to allow drug
screening.
This is where Atelerix come in, as their alginate hydrogels induce cell quiescence, enabling short-term storage of various cell types from days to weeks. We are looking to take advantage of this feature using their bead-ready kits, to enable the encapsulation, storage, and distribution of the core components of the simplified ‘niche’ model – HSCs, MSCs and metabolites. We are then left with a neat little package with the basic ‘niche’ components required for HSC maintenance that can be kept at room temperature and without media changes for long enough to be sent and delivered to labs around the world, who themselves are now able to grow their own population of stemness maintained HSCs or use the niches for drug testing directly without needing to thaw any cells.
To do this I am initially testing the viability of MSCs arranged into round clusters of cells, termed spheroids encapsulated in bead-ready kits. MSCs are being used initially as they retain primitive characteristics (especially when in spheroid formation and when encapsulated in a soft hydrogel) for much longer than HSCs when grown in 2D. The end product will consist of 96 ‘mini niches’ within a 96 well plate. To do this, we aim to use a bioprinter to print well-ready encapsulated cells and metabolites in a highly controlled and reproducible environment, ensuring batch-to-batch consistency not only between each niche, but between each 96 well plate of niches. This ensures the product is a viable option for drug testing as variance between niches and therefore testing conditions is minimised.
In summary, haematopoietic disorders lack in treatments due to the cost and poor availability of primary human HSCs. This project should yield a simplified niche model to grow human HSCs without loss of stemness, the core components of which shall be encapsulated and stored within Atelerix ‘bead-ready’ gels. This will improve the availability of HSCs and in turn should greatly enhance the development of treatments for blood disorders and reduce the cost of stem cell treatments.
*Hydrogels have high water content, collagen, one of the most abundant proteins in our body forms hydrogels and this gives structure to our soft tissues and is why hydration helps these tissues.
**Mesenchymal stromal cells are a stem cell containing population that help repair, bone, cartilage, ligament, and tendon. However, in the bone marrow, they spend most of their time looking after HSCs, telling the blood stem cells what to do.
***Metabolites are biological small molecules made by cells to and which drive metabolism
(respiration, energy supply, amino acid synthesis (amino acids are the building blocks of proteins and
so help in making of tissues).
