[1] He later worked at the Institute of Cancer of Villejuif under Charles Oberling and Wilhelm Bernhard, where he made pioneering observations of the structure of centrioles.

[5] He was subsequently hired by Memorial Sloan-Kettering Cancer Center, where he worked alongside Charlotte Friend and studied viruses, mostly in mice systems[6] and the causation and incidence of leukemia[7] and other malignant diseases related to those viruses.

[10] While at Sloan-Kettering, de Harven was part of a team which discovered "virus-like particles" in cells taken from patients with Hodgkin's disease.

[14] De Harven was a prominent skeptic of the scientific validity of the link between HIV and AIDS,[15] one of a group invited in 2000 to South Africa by president Thabo Mbeki to serve on a presidential panel on AIDS.

[16][17] He published a book in 2005 entitled Les Dix Plus Gros Mensonges sur le SIDA (Ten Lies About AIDS),[citation needed] in which he denies a connection between the HIV virus and AIDS, instead attributing the disease to lifestyle and environmental factors.