James Till and Ernest McCulloch's landmark 1960s experiments at Ontario Cancer Institute demonstrated that haematopoietic bone marrow cells could self-renew and differentiate into multiple blood cell lineages—the first empirical evidence that stem cells existed. Their colony-forming unit spleen (CFU-S) assay provided a quantitative method to identify and measure stem cell activity, establishing a methodological framework that underpins stem cell biology to this day. Till and McCulloch's work proved that a single cell could generate diverse progeny and that stem cell behaviour could be analysed mathematically, legitimising stem cells as a biological category worthy of systematic study. Their discoveries laid groundwork for haematopoietic stem cell transplantation, now routine clinical practice for leukaemias, lymphomas, and inherited blood disorders, saving millions of lives over five decades. The conceptual framework they established—that tissues contain long-lived progenitors capable of self-renewal and multilineage differentiation—became the template for identifying and characterising stem cells in other tissues. Without Till and McCulloch's experimental validation and quantitative framework, the modern regenerative medicine field would lack its foundational concept. Their legacy is present in every stem cell clinic, research laboratory, and transplant centre worldwide.
Most clinical uses of stem cells remain investigational — check the evidence and approval status for your condition before acting on any clinic's claims.
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