Scarlet raises £3.2 million to advance lab-grown red blood cell therapies

Biotechs including Rubius Therapeutics, which raised hundreds of millions of dollars before liquidating in 2023, and Erytech have tried to develop medicines based on RBCs. Scarlet is differentiated by its use of immortalized cell lines to generate RBCs, which the biotech predicts will bypass the challenges faced by companies that rely on donor cells.

“If you’re using donor material, even if you’re generating from stem cells, you can only expand them a certain amount to get the red blood cells. So, you’ve got a scalability problem,” Scarlet CEO Alistair Irvine said in an interview with European Biotechnology Magazine. “Also, not everybody’s cells react the same to cell culture, so you’ve got an issue of reproducibility and, therefore, you’ve got an issue of product quality.”

Scarlet’s approach entails growing cells from a master cell bank. Because the cells are immortal, Scarlet can grow them to any scale, Irvine said, before differentiating and purifying them to create the RBC product. The goal is to make off-the-shelf products that are applicable to any patient using a scalable, biologic-like manufacturing process.

The British biotech is in the early stages of showing it can achieve that objective, with the latest evidence coming from preclinical assessments of the half-life of its RBCs. The lab-grown cells successfully matured and circulated in vivo, achieving a half-life comparable to normal donated RBCs. Red blood cells have an average lifespan of about 120 days.

Scarlet’s preclinical study is the first time it has shown its RBCs circulate for at least as long as donated cells. When someone gives blood, the material contains RBCs of varying ages. All Scarlet’s cells are new. As such, RBCs in donated blood die gradually because they reach the end of their lifespan at different times. Scarlet’s cells reach the end of their lifespan around the same time, resulting in a longer half-life.  

Boosted by the results, the biotech has raised a seed round led by new investor Eos Advisory. Two other new investors, Oshen Bio and Daft Capital, contributed to the round, as did the existing backer SCVC.

Spending the funding

Scarlet will use the money to generate animal data in three indications. The biotech’s target indications include hyperammonemia and hyperoxaluria, metabolic disorders driven by excessive levels of ammonia and oxalate, respectively. Scarlet has modified RBCs to convert the toxic molecules.

“The RBCs circulate within the patient, constantly converting any toxic metabolite they come across into something that’s non-toxic,” Irvine said. “We hope that patients will receive the RBCs once every quarter. For that whole quarter, there will effectively be red blood cells that are little biomachines circulating and detoxifying their blood.”

Scarlet will use data from the in vivo studies to inform the selection of its lead program. By performing initial process development and engaging with regulators in parallel, the biotech aims to get clarity on its path to the clinic to support talks with investors about its next financing round, Irvine said.