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More surprises about blood development — and a possible lead for making lymphocytes

blood development chart
Blood development in the embryo begins with cells that make myeloid and erythroid cells – but not lymphoid cells. Why? A partial answer is in today’s Nature.

Hematopoietic stem cells (HSCs) have long been regarded as the granddaddy of all blood cells. After we’re born, these multipotent cells give rise to all our cell lineages: lymphoid, myeloid and erythroid cells. Hematologists have long focused on capturing HSCs’ emergence in the embryo, hoping to recreate the process in the lab to provide a source of therapeutic blood cells.

But in the embryo, oddly enough, blood development unfolds differently. The first blood cells to show up are already partly differentiated. These so-called “committed progenitors” give rise only to erythroid and myeloid cells — not lymphoid cells like the immune system’s B and T lymphocytes.

Researchers in the lab of George Q. Daley, MD, PhD, part of Boston Children’s Hospital’s Stem Cell Research program, wanted to know why. Does nature deliberately suppress blood cell multipotency in early embryonic development? And could this offer clues about how to reinstate multipotency and more readily generate different blood cell types?

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