In 2007 Timothy Ray Brown (the “Berlin patient”) became the first person to be cured of HIV. This came about through the use of a stem cell transplant as a means of treating acute myeloid leukemia. The doctors involved, while searching for a stem cell match for Brown, found a donor with a mutation in their CCR5 protein (CCR5D32). CCR5 is a protein on CD4 cells that functions as a gate keeper for HIV entry into cells. By replacing Brown’s leukemia-ridden hematopoietic cells that expressed the CCR5 protein with healthy donor cells that lack CCR5, the HIV virus could no longer infect T-cells. It is currently unknown exactly how Brown was functionally cured from HIV but there are many hypotheses. Three main factors are suspected: firstly, the conditioning regiment administered pre-transplant, next the infusion of allogeneic donor cells and finally the use of CCR5D32 mutated cells. Likely, all three contributed, leading to the HIV free outcome, however it is believed that the introduction of CCR5D32 mutated cells played a major role. CCR5D32 donor cells are rare and allogeneic transplantation is still risky. In a previous study, members of the Kiem laboratory and colleagues showed that transplantation with CCR5 gene-edited hematopoietic stem/ progenitor cells (HSPCs) was safe, feasible and led to long term engraftment of the cells. In the follow up study published in the journal PLOS Pathogens, researchers from the Kiem lab (Clinical Research and Vaccine and Infectious Diseases Divisions), sought to evaluate the feasibility and effectiveness of transplantation of CCR5 gene-edited cells in SHIV (simian HIV) infected non-human primates (NHP) in various stages of cART (combination antiviral therapy) treatment and viral latency (figure 1).
Cohorts of four to seven NHPs in four groups were followed for this study. Conditions for each group can be seen in figure 2. After transplantation of HSPCs, animals were tested for stable engraftment and the presence of edited cells in blood and tissue. The team found that all animals regardless of SHIV status had similar levels of uptake and persistence, thus supporting the feasibility of this approach in infected individuals. Tissue samples showed similar finding, with DCCR5 cells trafficking to and persisting in lymphoid tissue sites of virus persistence. When looking at viral load, there was no significant difference in the blood of animals between groups. However, the time to viral rebound after transplantation was slower in the DCCR5 group compared to the WT and no transfer groups. The WT cells group had a rebound magnitude (max load) higher than the other two groups as well as plateau at a higher value after transfer compared to transplantation of DCCR5 cells and no cells. This suggests that the DCCR5 transplantation may have a positive effect on time to viral rebound.
When looking at CD4 T cells (the target cells of SHIV) the group found an increased percentage of DCCR5 cells in tissue known to harbor SHIV during latency. This lead them to the finding that gut associated CD4 central memory T cells promptly recover in DCCR5 groups compared to controls. Further results indicated that DCCR5 derived CD4 T cells are under virally-dependent positive selection, however at the numbers seen in this study (~4% peripheral blood cells), it was not enough to impact the size of the latent peripheral SHIV reservoir. DCCR5 transplant did however affect the amount of SHIV in the tissue of transplanted animals compared to controls. This finding suggests that transplantation of DCCR5 cells suppressed virus, predominantly in tissue, which could be linked to the increase in viral dependent CD4 T cells. In response to why the cells are targeted to the tissues and why the viral load is most affected in tissue, author Dr. Peterson said, “Our hypothesis is that tissues are the primary sites of latent infection, whereas latently infected cells in the blood, which are particularly rare, are “spillover” from tissue sites. We are therefore focusing on the trafficking of hematopoietic stem cells and their progeny to candidate tissues that are likely to be primary sites of HIV latency, including lymph nodes, the gastrointestinal tract, and the brain.” Taken together these data suggest that increased efficacy of gene-edited CCR5 could be part of the puzzle for treating and curing HIV infection. In regards to the other pieces of the puzzle, first author Dr. Peterson said, “It’s important to note that what we describe in this paper is a purely “defensive” approach, i.e. gene edited cells are protected against infection. We are moving beyond simply protecting cells, to also enhance their ability to identify and destroy infected cells. We have several projects that approach this from multiple angles, including use of vaccines, chimeric antigen receptors, and broadly neutralizing antibodies.”
Peterson CW, Wang J, Deleage C, Reddy S, Kaur J, Polacino P, Reik A, Huang M-L, Jerome KR, Hu S-L, Holmes MC, Estes JD, Kiem H-P. 2018. Differential impact of transplantation on peripheral and tissue-associated viral reservoirs: Implications for HIV gene therapy. PLoS Pathogens, 14(4).
This work was supported by the National Institutes of Health.
Fred Hutch/UW Cancer Consortium faculty members Shiu-Lok Hu, Keith Jerome, and Hans-Peter Kiem contributed to this research.
Basic Sciences Division
Human Biology Division
Maggie Burhans, Ph.D.
Public Health Sciences Division
Vaccine and Infectious Disease Division
Clinical Research Division
Julian Simon, Ph.D.
Clinical Research Division
and Human Biology Division
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