Foreskin

Stem cells, fibroblasts.

https://journals.sagepub.com/doi/10.1177/2051415818761526

https://www.discovermagazine.com/the-sciences/why-human-foreskin-is-a-hot-commodity-in-science

Immune System

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5735067/

http://www.cirp.org/library/disease/STD/fleiss3/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2596734/

https://www.urotoday.com/conference-highlights/aua-2017/aua-2017-sexual-function/95986-aua-2017-nhanes-nearly-half-of-us-men-test-positive-for-hpv-yet-vaccination-rates-lag-and-recommendations-demur.html