HIV, or human immunodeficiency virus, infects cells of the immune system and prevents the body from fighting disease. Unlike other more benign viruses, our immune system cannot get rid of HIV entirely. Eventually, the infection can weaken the immune system so much that HIV proceeds to AIDS (acquired immune deficiency syndrome). This renders the individual susceptible to further infections, cancer, and other insidious symptoms, eventually causing death. The CDC estimated that in 2010, more than 1.148 million people in the U.S. were infected with HIV.  There is also a significant global burden of this disease. In 2014, over 37 million people were infected with HIV worldwide. 
Stem cell approaches to treating people with HIV primarily involve reprogramming the HIV-infected immune system to be HIV-resistant. Hopes that this approach could work were boosted in late 2010 when scientists reported that Timothy Ray Brown, also known as the “Berlin Patient,” had effectively been “cured” of HIV.
Timothy Brown is a 40-year old HIV positive man who was diagnosed with acute myeloid leukemia. In order to treat his deadly cancer, he received a bone marrow transplant from a healthy donor, but with a game-changing twist. The donor was chosen from a small fraction of people who carry a rare genetic mutation in the CCR5 gene known as CCR5-delta32. The CCR5 gene is present in two copies called alleles, one from each parent. The delta32 mutation is present in one of the two CCR5 alleles in 5-10% of Northern Europeans. In approximately 1% of these persons, there is an occurrence of two mutant alleles; this results in the absence of the CCR5 protein and partial protection from the most common type of HIV. 
HIV is a virus that infects cells of a person’s immune system, killing them. Because their immune system is compromised, the person is prone to dangerous infections, which lead to the development of AIDS. All of the immune cells infected by the HIV virus come from the body’s blood-forming stem cells. Timothy Brown’s infected blood cells were removed and replaced with new blood stem cells immune to HIV. Eventually, Timothy’s entire immune system rebooted and became HIV-resistant, thereby curing his HIV.
Unfortunately, not every HIV positive person is as lucky as Timothy Brown. In fact, these treatments can be very dangerous, so blood stem cell transplants are reserved for cancers that are unresponsive to treatment. In addition, for the transplant to be successful, the donor and patient must be as closely matched as possible. Finding the right bone marrow donor that also has the rare genetic mutation that triggers HIV immunity is very difficult.
However, there is hope. Timothy Brown’s story taught us that it is possible to cure HIV, by replacing a patient’s damaged and HIV-infected immune system cells with HIV-resistant ones that come from HIV-resistant blood stem cells.
With the support of California’s stem cell agency, the California Institute for Regenerative Medicine (CIRM), scientists have begun to ask: what if, instead of waiting for the perfect donor to cure someone’s HIV, we figured out a way to make the patient’s own immune system HIV-resistant by making their own blood stem cells HIV-resistant?
A number of research groups are working on this question in novel and exciting ways. Thanks to funding from California’s Proposition 71, 3 groups are making significant contributions. A team led by Dr. John Zaia at City of Hope, in collaboration with the University of Southern California and Sangamo Biosciences, has developed a method to take blood stem cells from an HIV-positive patient, use gene therapy to make those cells HIV-resistant, and then return the modified blood stem cells to the patient. Another group, led by Dr. Joseph Anderson at University of California Davis, is taking a similar approach: they are isolating blood stem cells from an HIV-positive person, modifying the cells to become resistant to HIV by blocking the ability of HIV to infect cells at several stages, and then re-introducing only the engineered stem cells after a purification step. A study sponsored by Calimmune Inc. is genetically modifying both immune cells and stem cells to be HIV-resistant and transplanting them back into the patient.
Once the patient receives those modified, HIV-resistant blood stem cells, they could begin to rebuild an entirely new immune system that would have the potential to block HIV infection, thereby offering an approach to both cure and prevent HIV.
The City of Hope, Calimmune Inc, and UC Davis teams have been able to make animals’ immune systems resistant to HIV infection. Human clinical trials are underway to test this therapy in HIV-positive people. Importantly, if this approach can work in AIDS, it can also be applied to certain immune disorders, cancers, and more. Only with continued support for biomedical research can we realize the full potential of stem cell research.
There is another crucial part of the story. These tremendous milestones of progress would not have been possible without the hard work, advocacy and support of the HIV/AIDS patient advocate community. HIV advocates have been driving policy in support of medical research for over 20 years, and continue to be an incredibly strong force today.
As scientists and patient advocates build on the progress that Proposition 71 funding has enabled, it is critical that momentum continues, with the understanding that there is still much work to be done. Some human trials will celebrate successes; but, barriers will surface, along with complications, challenges and failures, so patience and understanding of the scientific discovery process are essential.
Selected disease and research progress information provided by the California’s stem cell research funding agency, the California Institute for Regenerative Medicine (CIRM). Visit www.cirm.ca.gov for more updates.
 Martinson JJ, Chapman NH, Rees DC, Liu YT, Clegg JB. Global distribution of the CCR5 gene 32-basepair deletion. Nat Genet. 1997;16(1):100-3.