In a previous post I mentioned that, in the case of leukaemia sufferers, scientists have discovered a new therapy which could remove the need for the risky, painful and expensive bone marrow transplant procedure. This would be done by harvesting T cells from the cancer patient, and genetically modifying them using disease-neutralised HIV cells. Well today, at the International AIDS Society Conference in Kuala Lumpur, it was announced that two men may have been cured of the HIV virus as a result of transplants for their leukaemia!
This is not the first time that a stem-cell transplant for a patient suffering from both HIV and leukaemia has effectively cured the patient of HIV. Timothy Brown, the famous “Berlin Patient”, was the first person to be cured of the disease in 2008[i]. But in Timothy’s case, the donor was one of the small proportion of the population which are immune to the virus. This immunity comes from the inherited genetic mutation which shortens the CCR5 gene. It is this gene that the HIV virus uses to enter the CD4+ T cells, and thus to infect the patient[ii].
In the cases of the two Boston Patients, both were recipients of stem-cells from CCR5+ (i.e. non-mutation) donors. This means that something else, rather than the HIV-1 resistant truncated CCR5 gene, was at work. It is possible that it is graft-versus-host disease - one of the very things that makes bone-marrow transplants so dangerous - that is the answer, as it could be responsible for wiping out the remaining HIV reservoir in the patients.[iii]
Currently, the two Boston Patients have stopped taking their antiretroviral drugs for 15 and 7 week respectively, and both currently show no sign of HIV in the blood[iv]. However, caution is being urged before stating that the men have been cured. It is unknown whether there is another reservoir of HIV in the body from which the virus could theoretically resurrect. It is possible that the brain, heart tissue or the gut could harbour latent HIV cells. In fact, it is known that it is through the proliferation of CCR5+ genes in the gut of newborn babies that HIV for a mother’s infected breast milk can facilitate the infection of the child[v].
Also, the bone-marrow transplant procedure itself is not without its dangers. It is also painful, and expensive. As a cure for HIV, it is not currently a viable option. But its importance lies in the fact that it has given scientists another piece of the puzzle in the fight to understand and cure this terrible disease. It has also given the world its possible third and fourth survivors of HIV[vi]. That at least is worth celebrating!
[i] “Stem-cell transplant seems to fend off HIV” 14 Nov 2008 Nature Blog.
[ii] “Long-Term Control of HIV by CCR5 Delta32/Delta32 Stem-Cell Transplantation” Gero Hütter, M.D., Daniel Nowak, M.D., Maximilian Mossner, B.S., Susanne Ganepola, M.D., Arne Müßig, M.D., Kristina Allers, Ph.D., Thomas Schneider, M.D., Ph.D., Jörg Hofmann, Ph.D., Claudia Kücherer, M.D., Olga Blau, M.D., Igor W. Blau, M.D., Wolf K. Hofmann, M.D., and Eckhard Thiel, M.D. N Engl J Med February 12, 2009; 360:692-698
[iii] “Stem-cell transplants may purge HIV” Erika Check Hayden, Nature News. 03 July 2013
[v] “Memory CD4+CCR5+ T cells are abundantly present in the gut of newborn infants to facilitate mother-to-child transmission of HIV-1” Madeleine J. Bunders, Chris M. van der Loos, Paul L. Klarenbeek, John L. van Hamme, Kees Boer, Jim C. H. Wilde, Niek de Vries, Rene A. W. van Lier, Neeltje Kootstra, Steven T. Pals3, and Taco W. Kuijpers. Blood. November 22, 2012 vol. 120 no. 22 4383-4390
[vi]The second being a baby in Mississippi born to a HIV positive mother, who started receiving antiretroviral treatment before she was 30 hours old. The treatment has so far removed all trace of the virus from her system. See: “Infant's vanquished HIV leaves doctors puzzled” Erika Check Hayden Nature. 05 March 2013