Applications of light scatter to separation of stem cells.

A case is presented for light scatter as a potentially important discrimination parameter for electronic sorting of hemopoietic stem cells. Examples are presented of application of light scatter to sorting of primitive hemopoietic cells from bone marrow, thymus, and fetal yolk sac, using simple empirical approaches and a cell sorter equipped with a standard fixed-angle detector. Cells sorted in this way were ultrastructurally indistinguishable from stem cells observed in whole tissue sections or unfractionated suspensions and remained viable under culture conditions. Cells were further sorted into proliferative and nonproliferative stages whose morphologies were those expected for primitive and mature cells, respectively. Light scatter was a more specific marker for primitive thymocytes than binding of peanut agglutinin. Cells sorted from fetal yolk sac suspensions were ultrastructurally similar to candidate pluripotential stem cells of bone marrow. Therefore, where sorting rather than positive identification is the primary objective of flow analysis and histochemical correlations can be established after sorting, viable stem cells can be sorted from the simple hemopoietic tissues in high and verifiable purity. Sorting of pure stem cells from marrow will require an additional parameter for which an additional angle of light scatter may suffice.