Arnold Irving Caplan was a pioneering stem cell biologist and professor at Case Western Reserve University whose groundbreaking work transformed regenerative medicine. Born in Chicago on January 5, 1942, he earned his Bachelor of Science in Chemistry from the Illinois Institute of Technology before completing his Ph.D. in Biochemistry at Johns Hopkins University School of Medicine. He joined Case Western Reserve University as an assistant professor of biology in 1969 and steadily rose through the academic ranks, becoming a full professor in 1981. Caplan served as the founding director of the university's Skeletal Research Center and held secondary appointments at both the School of Engineering and School of Medicine, establishing himself as a multidisciplinary leader in biomedical science.
Caplan's most significant contribution came in the late 1980s when he isolated human mesenchymal stem cells (MSCs) from adult bone marrow, a discovery that revolutionized the field of regenerative medicine. He demonstrated MSCs' remarkable therapeutic properties including immune system modulation, inhibition of cell death and scar formation, stimulation of blood vessel formation, and promotion of tissue-specific stem cell growth. His visionary research led to the founding of Osiris Therapeutics in 1992, which developed the first stem-cell based drug to receive regulatory approval anywhere in the world. Caplan authored over 400 scientific papers and held more than 20 patents related to MSC technology, with his work directly impacting clinical treatments for multiple sclerosis, osteoarthritis, spinal cord injuries, cancer, and numerous other conditions.
Widely recognized as the Father of Mesenchymal Stem Cells, Caplan mentored over 150 graduate students, postdoctoral fellows, and researchers from around the world, creating a global network of scientists advancing stem cell therapies. His conceptual shift in understanding MSCs as Medicinal Signaling Cells better reflected their therapeutic functions and guided the development of numerous clinical applications across multiple medical specialties. Caplan's legacy continues through the countless patients who have benefited from MSC-based treatments and through the next generation of scientists he inspired during his fifty-four year career at Case Western Reserve University. His death on January 10, 2024, marked the end of an era in regenerative medicine, but his foundational contributions will continue to shape the field for decades to come.
