Stephan received his Ph.D. in the laboratory of Jan-Henning Klusmann at Hannover Medical School, where he investigated non-coding RNA regulation in pediatric acute myeloid leukemia. His doctoral work deciphered the role of miR-99/100~125 polycistronic microRNA clusters in the onset and progression of megakaryoblastic leukemia. During his first postdoctoral phase in the same environment, he generated a non-coding RNA expression atlas of healthy and leukemic human hematopoiesis, linking RNA regulation to blood cell differentiation and leukemia-initiating cell maintenance.

Supported by an HFSP fellowship, Stephan then joined the laboratories of Vera Gorbunova and Andrei Seluanov at the University of Rochester to investigate the hematopoietic system of the naked mole-rat, a long-lived mammalian model of longevity. There, he pioneered live stem cell sorting and transplantation approaches in naked mole-rats and mapped their blood and immune system, identifying distinctive features including increased quiescence in primitive stem and progenitor populations, splenic erythropoiesis, ectopic thymi, and absence of adult thymic involution.

For his third postdoctoral project, Stephan joined the Vannini Lab at the University of Lausanne through a collaboration with ImmuneAge Bio. As Director of Immunology, he developed and conducted a small-molecule screen to improve aged HSPC function, followed by metabolic, colony-forming, and in vivo transplantation validation.

His current appointment integrates leukemia modeling, stem cell aging, scalable co-culture systems and bioinformatics to identify interventions that preserve or restore blood stem cell function and interrogate pediatric AML biology.