What is stemness?
What is a stem cell? This is both a biological and a philosophical issue. As a philosopher, my aim is to describe the kind of property (or set of properties) that stemness is. On the basis of scientific literature analysis, interviews of stem cell and cancer stem cell specialists, and my own experience of wet lab experiments, I will address four successive questions:
(1) What kind of property is stemness? I will show that stemness can be four kinds of properties: categorical (stemness is an intrinsic property of stem cells), dispositional (stemness is an intrinsic property whose expression relies on extrinsic stimuli), relational (stemness is an extrinsic property induced by the microenvironment), or systemic (stemness is an extrinsic property that is maintained and controlled at the cell population level). Stemness is different in different types of stem cells (e.g. stemness is a dispositional property for the hematopoietic stem cells and a relational property for the germ line stem cells).
(2) Does it matter? I will show that clarifying the nature of stemness for each kind of stem cell is of major importance at least for oncology, as the efficiency of some therapeutic strategies (cancer stem cell-targeting therapies, niche-targeting therapies) directly relies on whether stemness is a categorical, a dispositional, a relational, or a systemic property.
(3) Is stemness stable? I will explore malignant hemopathies and show that some data suggest that while stemness is a dispositional property in the normal hematopoietic system, it might switch to a categorical, relational, or systemic property in leukemic stem cells, depending on genetic and epigenetic alterations.
(4) Is stem cell a unified biological category? If stem cells fall under four distinct categories then are we giving the same name to unrelated cell types? I will suggest that crossing phylogeny and philosophy of stem cells might shed light on the natural boundaries of the concept of stem cell.
Institut d'Histoire et de Philosophie des Sciences et des Techniques, Paris