Scarlet Therapeutics closed a $4 million seed round to move manufactured red blood cells into the clinic. The company says its RBCs behave in vivo like native cells and can be used as drug-delivery vehicles, with an early clinical plan focused on rare metabolic diseases using RBCs loaded with therapeutic proteins. The seed round supports development of the first application and further engineering work to validate that manufactured cells can reliably circulate, maintain function, and deliver payloads in a controlled way. If the concept translates clinically, manufactured RBC platforms could reshape logistics for protein therapies and potentially reduce reliance on conventional transfusions for certain indications. The financing also reflects a broader push toward cell-based delivery systems that aim to extend therapeutic exposure while leveraging the biology of well-tolerated circulating cell formats.