UCLA researchers have discovered a type of cell that is the “missing link” between bone marrow stem cells and all the cells of the human immune system, a finding that will lead to a greater understanding of how a healthy immune system is produced and how disease can lead to poor immune function.

The studies were done using human bone marrow, which contains all the stem cells that produce blood during postnatal life.

“We felt it was especially important to do these studies using human bone marrow as most research into the development of the immune system has used mouse bone marrow,” said study senior author Dr. Gay Crooks, co-director of the Eli and Edythe Broad Center of Regenerative Medicine and a co-director of the Cancer and Stem Cell Biology program at UCLA’s Jonsson Comprehensive Cancer Center. “The few studies with human tissue have mostly used umbilical cord blood, which does not reflect the immune system of postnatal life.”

The research team was “intrigued to find this particular bone marrow cell because it opens up a lot of new possibilities in terms of understanding how human immunity is produced from stem cells throughout life,” said Crooks, a professor of pathology and pediatrics.

Understanding the process of normal blood formation in human adults is a crucial step in shedding light on what goes wrong during the process that results in leukemias, or cancers of the blood.

The study appears Sept. 2 in the early online edition of Nature Immunology.