Thymus

The thymus was the first tissue the Leningrad military-medical group worked on. Thymalin is a polypeptide extract of calf thymus. Thymogen (Glu-Trp) and Vilon (Lys-Glu) are short synthetic peptides that came out of that work.

This is the clearest place to hold the extract/synthetic line. Thymalin is an extract. Vilon is two amino acids made in a reactor. Outcomes reported for one do not transfer to the other.

Published work is largely Russian-language, much of it from the St. Petersburg Institute of Bioregulation and Gerontology. English-language coverage is thinner than the citation counts suggest.