In a groundbreaking case involving stem cell therapy, a patient who was positive for the human immunodeficiency virus, or HIV, showed signs of clearing the disease after receiving a bone marrow transplant (BMT) from a donor who was resistant to the virus. BMTs are a form of stem cell therapy that are used extensively in the field of cancer treatment.

The bone marrow is the soft tissue inside of our bones, and is responsible for up to 95% of blood formation. The cells that are made in the bone marrow are immature stem cells that will go on to develop into the various components of our blood, including white blood cells, which are important for immunity and for fighting infection (and include HIV’s target, T-cells); red blood cells, which deliver oxygen throughout the body; and platelets, which are necessary for clotting.

The patient in question was originally being treated for leukemia, a form of cancer that affects the blood. With leukemia, a person’s bone marrow has literally gone awry and is producing too many cells. A BMT is undertaken in order to replace the cancerous bone marrow with stem cells from a healthy donor that will then begin producing normal, healthy blood.

This particular case was complicated by the fact that the patient was also HIV-positive, and the idea to use bone marrow from an HIV-resistant donor was based on the mechanism of how the virus infects cells. HIV recognizes and targets a specific cell-type (T-cells, which are responsible for the body’s immune response) by way of certain receptors on the cell’s surface. These receptors, specifically CD4 and the co-receptor CCR5, are used by HIV to identify T-cells, enter them, and ultimately destroy them. The disease that ensues is acquired immune deficiency syndrome, or AIDS.

In a small segment of the population, however, (around 1%, primarily northern European), there is a mutation, or genetic alteration, in the protein structure of CCR5 that hinders and even blocks certain types of HIV from even getting in. By infusing bone marrow from a donor that carries this mutation, doctors were hoping that HIV-resistant stem cells would confer the same advantage to the patient receiving them.

And that appears to be exactly what happened. Two years after the HIV-resistant bone marrow was given, the doctors were unable to detect the virus in the patient, even after antiretroviral medications were discontinued.

While the results are extremely promising, it is important to clarify that even though the patient’s viral levels were undetectable, this does not necessarily mean that the disease has been completely cured, for HIV can escape detection while sequestering itself in other cells or tissue and re-enter the body at a later time. Furthermore, stem cell therapy has its own share of risks and difficulties, and should not be looked upon as a routine procedure for the treatment of HIV.

Nevertheless, it is still a significant milestone in the field of stem cell therapy, and is an important first step to maybe one day developing techniques to combat AIDS, and for that matter, many other diseases, as well.

This story was originally reported in the New England Journal of Medicine.