April 19, 2018

expert reaction to study looking at genome editing of stem cells for HIV in non-human primates

A new study, published in PLOS Pathogens, investigates the genome editing of bone-morrow stem cells in pigtail macaques as a potential treatment for simian/human immunodeficiency virus (SHIV).

Dr Andrew Freedman, Reader in Infectious Diseases and Honorary Consultant Physician, Cardiff University, said:

“HIV is now a chronic condition with a near normal life expectancy for those diagnosed early and treated with lifelong combination antiretroviral therapy (cART).  Only one patient has ever been cured of HIV – the ‘Berlin patient’.  This involved a bone marrow transplant, which he underwent as part of treatment for leukaemia, using a donor with a rare genetic mutation rendering their cells resistant to HIV.  This study is aimed at trying to reproduce this in a macaque animal model using the technique of gene editing to recreate the same mutation.

Although the transplanted stem cells were able to survive and multiply in the macaques, the efficiency was not sufficient to clear HIV and cART had to be continued.  Nevertheless, this approach offers promise in the search for an eventual cure for HIV, probably in combination with other interventions such as vaccines.  However, until this is achieved, the emphasis needs to be on early diagnosis of HIV infection and prompt initiation of lifelong cART treatment, as well as continued efforts to prevent new infections.”

Dr Helen O’Neill, Lecturer in Reproductive and Molecular Genetics and Programme Director, Reproductive Science and Women’s Health, University College London, said:

“Treatment for HIV currently relies on drugs which target the viruses cell-cycle to slow HIV replication (and the progression to AIDS) (called antiretroviral therapy (ART). This lifelong therapy can be expensive, with risks of the HIV becoming resistant.

“CCR5 has long been a target of research for HIV therapy. The CCR5 receptor is used by the virus (HIV) to get into T-cells and infect an individual. Around 1:100 HIV patients, however, are protected by a mutation that prevents them from producing CCR5.

“An alternative to lifelong antiretroviral therapy is gene therapy that targets or mutates the CCR5 co-receptor in order to disrupt HIV’s ability to interact with it. Patients own cells are removed, edited and re-transfused in order to create a pool of genetically altered host cells that are less susceptible to viral infection.

“This paper uses a method of genome editing called ZFN’s to create this mutation in the cells of non-human primates. While they successfully edited these cells, the monkeys still needed ART therapy to suppress infections as the percentage of CCR5-edited cells was too low to induce remission. It is likely that with more modern genome editing tools, a higher percentage of cells would be edited and lead to better results.”

Dr Kate Bishop, Senior Group Leader, Retroviral Replication Laboratory, The Francis Crick Institute, said:

“Curing HIV is a big challenge. Only one person has ever been cured, to our knowledge, and that is Timothy Brown. In this study, Peterson and colleagues have tried to recapitulate aspects of Brown’s treatment using gene editing and autologous stem cell transplant. Unfortunately, the number of edited stem cells persisting in the monkeys was too low to make definitive statements as to whether this approach will ultimately be successful.

“There are positive signs that the edited cells do end up in tissues that harbour infected white blood cells carrying dormant viruses, known as reservoirs, which is where they would be most useful. But at the moment, the monkeys still need antiviral drugs to suppress their infections. The authors hope to improve the percentage of edited cells present in monkeys in the future, but it is not clear from this study what percentage of the body’s white blood cells would need to be edited to stop virus replicating in the absence of drugs, and whether other interventions would also be needed in parallel.

“In any event, this kind of personalised medicine would be difficult to roll out across Africa, where they have the greatest burden of HIV, so other strategies will also be needed to achieve a global cure.”

*‘Differential impact of transplantation on peripheral and tissue-associated viral reservoirs: Implications for HIV gene therapy’ by Hans-Peter Kiem et al. published in PLOS Pathogens on Thursday 19^th April.

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/tag/genome-editing/

Declared interests

Dr Andrew Freedman: “I have no conflicts of interest to declare.”

Dr Kate Bishop: “I have no conflicts of interest to declare regarding this study”.

Dr Helen O’Neill: “I have no conflicts of interest.”