10 - 20 %
||Human Homo sapiens
||Krueger A, Ziętara N, Łyszkiewicz M. T Cell Development by the Numbers. Trends Immunol. 2017 Feb38(2):128-139. doi: 10.1016/j.it.2016.10.007 p.135 bottom paragraphPubMed ID27842955
|| I. den Braber, et al. Maintenance of peripheral naive T cells is sustained by thymus output in mice but not humans, Immunity, 36 (2012), pp. 288-297 doi: 10.1016/j.immuni.2012.02.006PubMed ID22365666
||Primary source  abstract: "By combining in vivo kinetic labeling using deuterated water, thymectomy experiments, analysis of T cell receptor excision circles and CD31 expression, and mathematical modeling, [investigators] have quantified the contribution of thymus output and peripheral naive T cell division to the maintenance of T cells in mice and men."
||P.135 bottom paragraph: "One groundbreaking study directly compared age-dependent thymic output in human and mouse using TCR [T cell receptor] excision circles as molecular timers and in vivo cell labeling with deuterated water [primary source]. This study suggested that whereas in mice thymic output contributes to the majority of naïve T cells generated throughout life, in adult humans only 10–20% of naïve T cell production is thymus derived with the remainder being generated through homeostatic proliferation in the periphery."