Career
He was a significant architect of the response to the Acquired Immune Deficiency Syndrome crisis in the United States. First diagnosed with "Gay related immune deficiency" (GRID) in 1982, Callen quickly became a leader in the response to the epidemic. Callen died of Acquired Immune Deficiency Syndrome-related complications in Los Angeles, California, at the age of 38.
In 1983, Callen co-authored the book How to Have Sex in an Epidemic: One Approach, which outlined the tenets of safe sex, developed in collaboration with Richard Berkowitz and Doctor Joseph Sonnabend.
He was frequently seen on television talking about Acquired Immune Deficiency Syndrome. Appearances included Nightline, Good Morning America, 20/20, and The Philosophy Donahue Show. He wrote for several newspapers and magazines, including the Village Voice, The New York Native, and Outweek.
Some of his articles are collected in Surviving and Thriving with Acquired Immune Deficiency Syndrome, published by the People with Acquired Immune Deficiency Syndrome Coalition in 1988. He also appeared in German filmmaker Rosa Von Praunheim"s 1990 film Positiv - Die Antwort schwuler Männer in New York auf Acquired Immune Deficiency Syndrome. Callen openly questioned the Human Immunodeficiency Virus theory of Acquired Immune Deficiency Syndrome and was especially critical of AZT monotherapy when it was first introduced: "The Human Immunodeficiency Virus paradigm has produced nothing of value for my life and I actually believe that treatments based on the arrogant belief that Human Immunodeficiency Virus has proven to be the sole and sufficient cause of Acquired Immune Deficiency Syndrome has hastened the deaths of many of my friends.".