Cultured red blood cells:
a window into the future of transfusions and therapeutics
A team of researchers at the Bristol BioDesign Institute (BBI) have been culturing lab-grown red blood cells since 2009. Through collaboration and ingenuity, the team are increasing yields, conducting testing and manipulating the lab-grown cells towards tangible real-world impacts. Professor Ash Toye, Professor Jan Frayne and broader teams (originally led by Professor David Anstee at NHS Blood and Transplant (NHSBT)) — supported by funding from NIHR for the formation of a Blood and Transplant Research Unit in Red Cell products and NHS Blood and Transplant — are doing this work to try to fulfil a crucial clinical need for people with rare blood types or sickle cell disease.
Lab-culturing cells
Bone marrow is a site of remarkable biological transformation. Every single day, a tiny contingent of bone marrow stem cells creates billions of vital circulatory cells, including platelets, bacteria-destroying macrophages, and red and other white blood cells.
The research team at the Bristol BioDesign Institute has sought to better understand the organic processes through which these cells are produced in the body. In doing so, they have mimicked production by culturing cells in the lab, explored blood-based pathologies, and set about several divergent studies of disease.
The fundamental intention of the research team is to understand how we can use stem cells to make blood cells to order. The immediate goal is to produce mini quantities of lab-grown blood cells and robustly manufacture these under good manufacturing practice for early, pre-clinical assessment. Longer-term, the work could help to shape the production of new medicines and treatments — the team are striving to cost-effectively grow large enough volumes of red blood cells for use in adult transfusions, and as a novel platform for therapeutic delivery of treatments.
Replicating red blood cell production
Back in 2009 — whilst observing researchers in his lab at the time — Professor Ash Toye’s imagination was captured by the sight of small red blood cell pellets that had been grown in culture. Ever since, his teams and collaborators have been on an exciting, ever-expanding mission to engineer and grow these unique cells. The research is as much about scaling up as it is about innovating, with the team recognising the potential to address gaps in current clinical practice.
The important first step was to dive into the biological nature of erythropoiesis — the process by which red blood cells (erythrocytes) are produced from progenitor, or ‘parent’ stem cells, in the bone marrow. To replicate erythropoiesis in the lab, the scientists can grow the cells in media or use a synthetic scaffold as the growth environment to mimic the bone marrow. The scaffold used is called polyHIPE, a 5mm cube of polystyrene that mimics the structure of bone marrow. Within media or on the polyHIPE scaffold, the research team encourage stem cells to become progenitor cells with the capacity to further divide into more daughter cells. These daughter cells expand further and then become erythroblasts. The researchers then push and prompt each erythroblast to differentiate, during which they divide further into more daughter cells and then become a newly made red blood cell called a reticulocyte.
Early on, the project secured funding from the BBI’s Synthetic Biology Research Centre — BrisSynBio — which maintained research efforts to manipulate and refine the cells during development. For example, in their preliminary stages, Toye’s team collaborated with Frayne and Anstee to generate and characterise an immortalised erythroblast line through the introduction of viral proteins. This produces an erythroblast cells that can grow continually and then differentiate into fresh red blood cells. They showed that they could genetically engineer the immortalised line to remove problematic blood groups, dramatically increasing the potential compatibility of the line for more patients and making a new tool to study malaria parasite invasion. This form of erythroblast modification isn’t ready for use in the clinic, but it provides a blueprint for producing blood cells more sustainably.
Confronting challenges and driving change
The team has reached the stage where small doses of cells can be routinely made in specialist NHSBT labs; these lab grown red blood cells are now undergoing a clinical trial. A focal point for the research going forwards is scalability — the amount of red blood cells produced in the research labs initially crept up from 2ml to 5ml to 10ml. More recently, the yield has increased nearly threefold after filtration.
The goal is to continue to scale up processes through use of automation and bioreactors, whilst further reducing the costs of reagents by producing some of them with the BBI labs. Ultimately, the research team is aiming to get to the point of producing volumes of blood that are relevant for therapeutic use in adults, which would place the project in a unique global position to drive clinical use and also be a novel platform for therapeutic applications.
One obstacle to the future of the research lies in the fact that the BBI, Professor Toye and other blood cell researchers across the world are reliant on the evolution and adoption of specific biotechnology infrastructure, which is needed to increase red blood cell yields at scale and demonstrate reliability in testing. There is a shift required from blood culture in large-volume flasks to high-capacity, industrial style bioreactors. The latter can feasibly produce blood at a scale for clinical use, but are expensive, and their take-up throughout the blood cell culture community would require significant upfront investment. However, Professor Toye is clear that bioreactors would allow for increased automation and control, making them a more cost-effective vehicle for cost efficient blood production long-term.
Clinical practice — and blood transfusions specifically — are currently reliant on a network of altruistic donors. Naturally, there is variability in yields from donor to donor. The issue of yield is similarly present in culturing work, where filtration technology (a leukofilter) is used to extract red cells from whole blood. Though a pivotal process, filtration can cost researchers as much as half of what they produce as the filters used are designed for red blood cells not reticlocytes. The BBI researchers hope to access and adopt more proficient, controlled technologies for this filtration; ensuring consistent, reliable yields will bolster the potential of cultured blood to address clinical shortfalls.
Tapping into clinical application
With over £4M of funding from the National Institute for Health Research, NHSBT, BBI, the team and collaborators will continue to refine the culturing process, contributing vital further breakthroughs to the Blood and Transplant Research Unit.
For Professor Toye, his vision is to channel the bioengineered red blood cells towards commercial therapeutics application to help reach the culturing scale needed for transfusion. In the near term, the volumes of red blood cells already produced, if engineered to carry a therapeutic payload, have the potential to treat blood enzyme deficiencies or metabolic disorders. For transfusion, a recent paper, for example, focused on how these methodologies can be improved further and could assist in the treatment of patients with inherited anaemia or sickle cell disease by introducing a source of much needed compatible red blood cells for those with rare blood types. A futuristic vision of the therapeutic potential, with robust scaling in the coming years, could conceivably comprise culturing ‘factories’, growing blood for use in therapeutics and eventually transfusions.
This goal is grand, but the team believe it is achievable; what’s more, there is a clear view of how to get there, and feet on the ground to make it happen. Key to the next phases of the research will be spinning out the manufacturing and culturing process, working alongside companies with expertise in the area, and securing long-term investment. Clear direction is matched by a sense of emboldened ambition among blood cell researchers — this serves as a microcosm of BBI’s pioneering, entrepreneurial culture, which is taking us towards a future of true promise: that of reliable, safe and universally applicable blood based therapeutics for patients.
It takes a team…
The University of Bristol’s culturing efforts are now led by Professors Ash Toye and Jan Frayne. Further to the BBI space, Professor Toye also has a Research & Development lab working on the translation of red blood cell production in NHSBT Filton. Across the two sites in Bristol, around 30 scientists and PhD students are focused on the study.
The team also collaborated with Professor David Anstee, Director of the Bristol Institute for Transfusion Sciences, who had over 50 years of erythrocyte biology experience, focusing especially on patients with very rare blood groups and poor representation in the donor database. Professor Anstee passed away in 2021, leaving a legacy of high-impact work and forward-thinking research expertise.
Understanding, culturing and manipulating red blood cells is a major focus of many research groups. As the BBI work has evolved, Professors Toye and Frayne have worked with like-minded academics and labs with synergistic research goals across the UK and EU. Professor Toye’s lab is part of an EU International Training network, with around 15 labs conducting red blood cell research. The collaborations are highly productive, but there’s always a healthy dose of competition across — and specialism within — each lab.
The researchers have also collaborated with artists to help the public visualise and contribute to discussions about how blood cells are cultured in the lab.
At SynBioExpo, work by Claudia Stoker explored the research techniques used in gene-editing blood cells, whilst long-term collaborator Katy Connor (a Bristol-based artist and creative producer) has exposed the revolutionary work to broader audiences through new media.
Left: Synthetic Dwelling
A scaled-up version of a polyHIPE synthetic bone marrow scaffold, displayed next to the scaffold itself on the right. Credit: Katy Connor
Right: Synthetic Blood
Produced in partnership as part of SynBioExpo, a SciArt exhibition co-hosted by the BBI. Credit: Claudia Stocker
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