Agrobacterium-mediated transformation of Chlamydomonas reinhardtii to produce recombinant human serum albumin

Human serum albumin (HSA) constitutes the most significant fraction of proteins in human blood plasma. It remains one of the most widely used therapeutic biomolecules in modern medicine, with global demand exceeding 500 t annually. Limitations in plasma-derived HSA (pHSA), including supply shortages and the risk of pathogen transmission, have accelerated the pursuit of recombinant production strategies. This study demonstrates the first successful expression of structurally and functionally validated rHSA in Chlamydomonas reinhardtii through Agrobacterium -mediated nuclear transformation, highlighting the platform's novelty. Molecular analyses validated stable integration and transcriptional activity of the transgene, while expression levels reached up to 0.5% of total soluble protein. Structural and functional assessments confirmed that algal-derived rHSA closely resembles native pHSA, and cytotoxicity assays (MTT) verified its safety in human cell cultures. Taken together, the results highlight C. reinhardtii as an economically viable and scalable platform for sustainable biomanufacturing of high-value therapeutic proteins, making it an attractive alternative to traditional production sources. • Recombinant human serum albumin (rHSA) was successfully expressed in Chlamydomonas reinhardtii . • Transformation was achieved via Agrobacterium -mediated nuclear integration of the HSA gene. • Molecular analyses confirmed stable transgene integration and transcriptional activity. • rHSA expression reached ~0.5% of total soluble protein in algal cells. • Purified rHSA exhibited structural and functional equivalence to plasma-derived HSA. • Demonstrates C. reinhardtii as a safe , cost-effective, and scalable platform for therapeutic protein production.