Thymosin alpha-1 (thymalfasin, Tα1) is a heat-stable, highly acidic peptide of 28 amino acid residues. It was isolated from calf thymus as one of the polypeptides of thymosin fraction 5, and its sequence was reported in 1977. The material studied today is the synthetic peptide with an acetylated N-terminus. Research has centred on innate and adaptive immune signalling, particularly in dendritic cells, using mouse fungal and viral infection models, haematopoietic transplant models, and human and murine cell culture. A 2016 review summarises the preclinical and clinical literature.