Scarlet Therapeutics closed a $4 million seed round to advance manufactured red blood cells (RBCs) into a first clinical application. The company said its RBCs function in vivo like natural cells and can serve as delivery vehicles for therapeutic proteins, with the longer-term goal of replacing conventional transfusions for certain patients. Scarlet’s stated initial focus is loading RBCs with therapeutic proteins aimed at rare metabolic diseases. The round provides early capital for GMP readiness and clinical translation of a cell-based delivery concept that may differentiate from conventional biologic carriers. The fundraising underscores continued investor interest in engineered blood components as platform assets for both therapeutics and supportive care.