7 - 8 weeks
||Human Homo sapiens
||Haynes BF, Markert ML, Sempowski GD, Patel DD, Hale LP. The role of the thymus in immune reconstitution in aging, bone marrow transplantation, and HIV-1 infection. Annu Rev Immunol. 2000 18: 529-60. DOI: 10.1146/annurev.immunol.18.1.529 p.529 bottom paragraphPubMed ID10837068
||Haynes BF, Heinly CS. 1995. Early human T cell development: analysis of the human thymus at the time of initial entry of hematopoietic stem cells into the fetal thymic microenvironment.J. Exp. Med.181: 1445–58PubMed ID7699329
||p.529 bottom paragraph:"The thymus is essential for the initial establishment of the peripheral T cell pool in animals and humans (refs 1–3). In humans, children born without a thymus (complete DiGeorge syndrome) lack functional peripheral T cells (ref 3). The normal human thymus develops early on in fetal development, and is colonized by stem cells at 7 to 8 weeks of gestational age (primary source)."