January 17, 2013
Calimmune, a small biotechnology company, has been given the go-ahead by the U.S. Food and Drug Administration to start enrolling HIV-infected people in a first-of-its-kind gene therapy study that will modify two HIV attachment sites in CD4+ cells.
This early phase study will be looking at whether an experimental gene transfer, called LVsh5/C46 (also known as Cal-1), is safe and if it can protect the immune system from the effects of HIV without the use of antiretroviral drugs.
Cal-1 is an experimental gene transfer agent designed to inhibit HIV infection through two active parts:
CCR5 receptors, and those involved in virus-cell fusion (ruled by C46), are among the different receptors that HIV uses to infect cells. Modifying stem cells that have mutations to multiple sites has never been studied in people living with HIV. Single-receptor gene modification studies have been done recently with promising data (see "Other Players" below).
Participants in one arm of the study will only get modified stem cells, and the other two will get a single or double dose of the chemotherapy agent (busulfan) before the stem cell infusion. Cancer study data show that providing "conditioning" with a chemotherapy agent before a stem cell transplant may improve the body's "uptake" of the new cells that can then reproduce in the body.
The study is enrolling only for HIV-infected people who have an R5-tropic virus [a strain of HIV that enters and infects CD4+ cells by binding to the CCR5 receptor on the cell's membrane], as well as detectable levels of the virus, and have not taken HIV medications due to their own choice (side effects and other reasons) for at least six weeks. A CD4+ count over 500 is required. So, essentially, only "healthy" HIV-infected people are allowed.
[SIDE NOTE: In my opinion, heavily pretreated patients with multidrug resistance and non-R5-tropic virus are slowly getting left behind in HIV cure research studies like this one. Even though these patients have typically been the cornerstone of HIV drug approval and may be exposed to a better risk-to-benefit ratio, healthier patients can probably better respond to these early cure studies. Hopefully, we will see study teams in the future that will encourage advanced patient participation in future studies, although I doubt this will happen without community activism.]
Like any innovative trial, this study raised a lot of questions:
We all know of Timothy Brown, the "Berlin Patient," who has been cured of HIV after high-dose conditioning and infusion of bone marrow from a donor born with double CCR5 mutations in his cells. However, it is still not clear that Timothy's apparent cure resulted solely from HIV-resistant cell transplant. His standard conditioning protocol used for his lymphoma, containing chemotherapy, immunosuppressants and other drugs could have had an additive effect, especially on HIV reservoirs, before the CCR5-mutated donor immune cells populated his body.
Luckily, some more questions will be answered when study results are made public about other patients who have been exposed to procedures similar to Timothy's. These proof-of-concept studies in patients with malignancies pave the way for other studies that use simpler and less risky approaches in HIV-infected patients who may be doing well on HIV treatment.
The answer to a more practical and potentially safer cure approach would require determining what degree of "conditioning" and modified cell uptake/persistence are required to have complete eradication or control of HIV.
However, patients who stopped HIV medications in another sub-study using the same approach lost their gained modified cells with time and had viral rebound. Due to the length of the treatment interruption, we did not learn if such rebound reached a viral load set point lower than what patients had before starting HIV medications. Only one patient's immune system seemed to later control HIV. That patient was found to have been born with one mutation in his CCR5 receptor. Sangamo is now doing a study looking at this minority of people.
These are exciting times that present a lot of hope; but we should also be careful about false hope that may induce some people to join these studies that may offer more risks than benefits. I advise all potential participants to be informed and make educated decisions before enrolling in any clinical study. I am involved in a group of activists whose goal is to inform the community about studies so that they can make educated decisions about enrollment.
I am excited to see so many meetings where people are sharing ideas and data to work on the cure together!
The cure for HIV depends on patient altruism, community advocacy involvement, sufficient funding, and collaboration among groups racing toward being the first to get to the cure.