Helen Blau FRS is a cell biologist and stem cell researcher famous for her work on muscle diseases, regeneration and aging. She is the Donald E. and Delia B. Baxter Foundation Professor and the Director of the Baxter Laboratory for Stem Cell Biology at Stanford University. Blau is known for overturning the prevailing view that once a cell assumes a certain specialty in the body — or differentiated state —such as a skin or liver cell, it cannot be changed. Her research established that the fate of mammalian cells can be altered. Her finding that specialized cells can be triggered to turn on genetic programs characteristic of other differentiated states provided early evidence that mammalian cellular reprogramming was possible and opened the door to the use of reprogramming in stem cell biology.  Her work set the stage for the development of induced pluripotent stem cells and associated stem cell therapies.

Blau is also known internationally for her work on adult stem cells and how they maintain, repair and rejuvenate tissues, in particular muscle.  She revealed the role of the microenvironment of the niche, most notably tissue stiffness, in regulating stem cell function and showed how stem cell function declines in aging and hereditary muscle wasting diseases. She discovered ways to rejuvenate aged stem cell function.  Blau discovered a new class of aging-associated enzyme she termed a "gerozyme" and showed that pharmacological targeting of the gerozyme in aged muscle tissue can rejuvenate tissue structure and metabolism and increase strength.

Blau was born in London and is a dual citizen of the United States and Great Britain. She earned a B.A. from the University of York in England and an M.A. and Ph.D. in biology from Harvard University with Fotis C. Kafatos.

After a postdoctoral fellowship with Charles J. Epstein in the departments of Biochemistry and Biophysics and the Division of Medical Genetics at The University of California, San Francisco (UCSF), she joined the faculty at Stanford University in 1978. She was awarded an endowed chair in 1999 and named Director of the Baxter Laboratory for Stem Cell Biology in 2002.

It was long thought that the differentiated state is fixed and irreversible. In the 1980s, Blau challenged that idea using a cell fusion system she devised to join cells of two different species and differentiated states.  Her experiments showed that previously silent genes could be activated. Specifically, when human skin, connective tissue, or liver cells were fused with mouse muscle cells, the human cells began to make muscle-specific gene products. This body of work showed that the differentiated state requires continuous reinforcement, and that a shift in the balance of regulator proteins called transcription factors in the nucleus can reprogram the cell to become a different type of cell.  This discovery of an unexpected plasticity, or flexibility, in cell fate was foundational for the development of the field of stem cell biology and regenerative medicine.  It was featured as "Plasticity of the Differentiated State" on the cover of the Frontiers in Biology special issue of the journal Science in 1985.

Adult stem cells are found in tissues throughout the body. When they divide during development, or to repair damage after injury, one daughter cell remains a stem cell (it self-renews), while the other differentiates (it specializes) to become one of the cell types that make up that tissue.

In 2008, Blau published the first parameters for isolating muscle stem cells, also known as satellite cells, using flow cytometry. Her lab pioneered the use of bioluminescence imaging to monitor the dynamics of muscle stem cell engraftment in muscles in live mice and confirmed that the cells were true stem cells, capable of both self-renewal and differentiation. They also designed a bioengineered hydrogel with a stiffness that mimics healthy young muscle. Unlike rigid plastic tissue culture dishes, the elastic hydrogel preserves the stemness of the cells when grown in culture. This discovery provided the first functional link between substrate elasticity and the maintenance of stem cell self-renewal properties and established a paradigm with broad utility to enhance the regenerative capacity of tissue-specific stem cells grown in the laboratory.

In 2014 Blau's lab provided early evidence that stem cell function declines during aging due to internal defects, in addition to external factors. They identified a small molecule, SB202, that inhibits an enzyme associated with aging called p38-MAP kinase and showed that the regenerative properties of aged muscle stem cells could be rejuvenated through a combination of biophysical (growth on the bioengineered hydrogels Blau's lab designed) and biochemical (blocking p38MAPK) signals. More recently, Blau showed that muscle stem cells exhibit an age-dependent increase in CD47 levels, and that this increase is a hallmark of age-related muscle stem cell dysfunction. CD47 is a protein found on the surface of many cells in the body that protects them from attack by the body's immune system; an increase in the number of CD47 molecules on old or diseased cells can prevent the body from disposing of them properly. Overcoming this increase in CD47 levels led to a robust increase in muscle strength after injury. These approaches provide a paradigm for cell therapy strategies to treat muscle wasting.