[3] His undergraduate studies at New York University began in 1934 but were interrupted by a case of tuberculosis, which required him to withdraw from school for a year; he later recalled this as a key event in his life inspiring him to focus on intellectual activities.
Eisen was one of the first recipients of a new form of National Institutes of Health fellowship for physician-scientists, which supported further work at NYU with Fred Karush studying antibodies.
[1][2][4] Eisen's first faculty position was at NYU in the then-new Department of Industrial Medicine, where he was funded to work part-time as a researcher and invest the remainder of his time in clinical practice.
Eisen officially retired in 1989, assuming professor emeritus status, but remained active in research and in mentoring younger scientists in the MIT community.
[4] Eisen remained an active research scientist for many years following his official retirement and was working on a manuscript related to antibody affinity the day he died in 2014.