By David Holzman
The research landscape for curing HIV has changed substantially since 2007. That was the year when Timothy Ray Brown, more commonly known as “the Berlin patient,” received his first transplant of stem cells comprising an HIV resistance gene. By 2011, he was generally considered cured.
The HIV of the still anonymous “London patient” was put into remission in early March of this year, 18 months after stopping antiretroviral therapy (ART). “A person with HIV seems to be free of the virus after receiving a stem-cell transplant that replaces their white blood cells with HIV-resistant versions,” the physicians wrote in Nature ([Epub Mar 5, 2019]. doi: 10.1038/d41586-019-00798-3).
Note the hedge: Many think 18 months was too soon to proclaim cure, and at CROI 2019, lead author Ravindra Gupta, PhD, MA, MPH, FRCP, FRCPath, used the term remission, rather than cure.
Despite the success of stem cell transplants, there are risks, and they would not be used to cure HIV without a cancer diagnosis that’s treatable with hematopoietic cell transplantation (HCT). During his procedure, Mr. Brown almost died from graft-versus-host disease. “There have been at least six other cases where the individuals died, either due to the underlying cancer or graft-versus-host disease induced by the stem cell transplant,” said Richard Jefferys, the project director of the Basic Science, Vaccines, and Cure Project for the Treatment Action Group, in New York City. “The mortality rate was actually so high that some researchers feared that the CCR5 [resistance] mutation might be negatively affecting the success of the stem cell transplant.”
Nonetheless, these two cases serve as proof of principle that HIV might be cured. Now the mechanism involved in these cures is driving some research.
During the last 10 years, clinical trials have been increasingly designed to cultivate knowledge that will further the quest for cure, testing combinations of measures seeing the biggest increase, Mr. Jefferys said. Currently, 96 interventional clinical trials and 37 observational trials that are listed in the clinical trial registry (clinicaltrials.gov) are seeking to advance the search for a cure for HIV, he said.
Cure Versus ART
When ART is so successful at getting viral loads down to undetectable levels, therefore preventing HIV transmission, one might wonder why anyone would seek a cure, but experts said there are several reasons to try to cure HIV.
“There are some people who don’t want to be reminded every day that they have HIV,” said Anthony Fauci, MD, the director of the National Institute of Allergy and Infectious Diseases. On the other hand, “if you are OK with taking a single pill a day, you may not want to go through the process of being cured.
“If you cure someone so they don’t need medication anymore, you save the expense of having somebody on ART the rest of their life,” Dr. Fauci said. Lifetime treatment for HIV could run up to $500,000.
Additionally, patient surveys have shown that a priority for patients is to make their HIV intransmissible, Mr. Jefferys said. In practice, ART can eliminate that risk, but many people don’t like to face the specter of spreading HIV should a rebound occur, he explained.
While an HIV-eradicating cure is the holy grail, experts expect that sustained remission will happen sooner. Sustained remission refers to treatments that would suppress the virus indefinitely without requiring daily medication, but won’t necessarily eradicate it.
“Certainly a sustained remission would be easier [to accomplish],” said Jeffrey Laurence, MD, pointing out that while “elite controllers” naturally suppress the virus, no patient has eradicated HIV. Dr. Laurence is a professor of medicine at Weill Cornell Medical College, in New York City, and senior scientist for programs at amfAR, the Foundation for AIDS Research. The second-largest investor in HIV cure research in the world in 2018—second only to the National Institutes of Health—amfAR supports both options.
“I think there will be continuous improvements in treatments that will lead to more and more sustained remissions, and maybe eventually a true cure,” said Dan Barouch, MD, PhD, a professor of medicine at Harvard Medical School and the director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, both in Boston.
“In achieving ART-free control, the key is which combination of products to deliver,” said Marcella Flores, MPH, PhD, an associate director of research at amfAR. “The amfAR institute is betting on a triple combination: vaccine, antibodies and an immune activator.”
But Leor Weinberger, PhD, is developing a form of “molecular parasite,” a singular intervention that uses up resources the virus needs, reducing the reservoirs of HIV to the point where transmission ceases, increasing the asymptomatic lifetimes of people living with HIV. Dr. Weinberger is the Bowes Distinguished Professor and Director of the Gladstone Center for Viral Circuitry at the University of California, San Francisco.
These “therapeutic interfering particles” (TIPs) are a minimalist HIV that lacks the structural and envelope genes required for self-replication, co-opting these from HIV. “Epidemiological models indicate TIPs could outperform vaccines and antiretroviral therapy campaigns (i.e., PrEP [pre-exposure prophylaxis] and TasP [treatment as prevention]) in sub-Saharan Africa,” he said. On the downside, since TIPs require HIV to replicate, they can never completely expunge it.
The transplanted stem cells that cured Mr. Brown, and likely the London patient, contained a mutant CCR5 gene. CCR5 codes for the protein that HIV uses to gain entry to CD4 T cells. For HIV, that mutant, CCR5delta32, is like a broken doorknob. An estimated 1% to 3% of Europeans carry CCR5delta32, as did the stem cells that Mr. Brown’s physician, Gero HÜtter, MD, and the London Patient’s Dr. Gupta, knowingly procured.
In theory, HIV could be cured by gene therapy to disable CCR5. However, HIV defies simple answers.
True, CD4 T cells with mutant CCR5 decrease the latent reservoir of HIV, said Benigno Rodriguez, MD, an associate professor of medicine in the Division of Infectious Diseases and HIV Medicine at Case Western Reserve University, in Cleveland, and a principal investigator in the AIDS Clinical Trials Unit.
However, the reservoir shrinkage could result from replacement of T cells with huge numbers of “fresh T cells that have been expanded in the laboratory,” rather than from mutant CCR5, Dr. Rodriguez said.
Dr. Rodriguez has begun a study to determine the mechanism. Thirty patients will be randomly assigned to receive either normal CD4 T cells or ones with damaged CCR5. He anticipates no cures. “Only about one out of five T cells at best can be expected to be modified,” he explained. Yet, the information that results will help fill in the cure map.
Another gene therapy involves using “molecular scissors” to excise HIV from CD4 T cells. Rather than removing said cells from the body for this procedure, as is often done, it would be far less expensive “to inject gene therapy tools into the body, like a vaccine,” Dr. Flores said.
As described in their paper in Nature Communications, published in early July, researchers led by Kamel Khalili, PhD, did just that. They cured nine of 23 humanized mice using CRISPR-Cas9, which functions as molecular scissors, to slice HIV from the mice’s CD4 T cells. The CRISPR-Cas9 was delivered to the CD4 cells by viral vector. CRISPR-Cas9’s cuts were confined to HIV removal: There was no “off-target editing.”
“We showed that AAV9 [the viral vector] gets to every cell and tissue, including bone marrow, spinal cord, liver, spleen and brain,” said Dr. Khalili, the director of the Center for Neurovirology and director of the Comprehensive NeuroAIDS Center at the Lewis Katz School of Medicine at Temple University, in Philadelphia.
Although he calls it a “promising approach,” Jonathan Z. Li, MD, MMSc, an assistant professor of medicine at Harvard Medical School and a faculty member in the Division of Infectious Diseases at Brigham and Women’s Hospital, in Boston, foresees a long road ahead. “The weakness lies in the diversity of HIV sequences in the average HIV-infected patient and the challenges of designing a CRISPR system that can account for that diversity without mediating undesirable off-target effects. I suspect that the level of HIV diversity is far lower than that seen in the typical HIV patient,” said, Dr. Li, who is also a member of the Infectious Disease Special Edition editorial advisory board.
With excitement over the two cured patients, the thousands of elite controllers have been eclipsed, said Bruce D. Walker, MD, the director of the Ragon Institute of MGH, MIT and Harvard, and a Harvard University Center for AIDS Research investigator in the Howard Hughes Medical Institute at Harvard Medical School. “Yet those are the people that offer the greatest promise to achieve a cure.”
A distinguishing factor among some of the exceptional elite controllers is that the T cells attack the most highly networked amino acids in HIV proteins, according to Dr. Walker. Just as removing a highly networked person in a small company could undermine that company’s effectiveness, taking out a highly networked amino acid—one that forms numerous connections within a protein—could ruin that protein’s functionality, disabling HIV.
Dr. Walker, who is assembling a cohort of elite controllers to better understand the phenomenon, said they are characterized by “decades of infection with a normal CD4 count, no ability to grow the virus, repeatedly undetectable viral load and no immune activation.” He concluded, “Nature has achieved a functional cure.”
Measuring The Reservoirs
Antiretroviral therapy (ART) doesn’t cure infection because it fails to eradicate latent reservoirs in CD4 T cells, even after ART suppresses the viral load to undetectable levels
To determine the success of any potential cure, reservoir shrinkage must be quantified. Before now, such efforts were highly inaccurate, as the assays have been unable to distinguish impotent, defective forms of HIV from those that can infect CD4 cells. These assays analyzed only one HIV gene, for example, out of nine, thus missing defects and overestimating the reservoirs’ size, according to Richard Jefferys, the project director of the Basic Science, Vaccines, and Cure Project for the Treatment Action Group, in New York City.
A research group at the Johns Hopkins University School of Medicine developed a new assay (Nature 2019;566(7742):120-125), which distinguishes intact from defective provirus in a sample of infected cells, quantifying each, and discounting the defectives. That’s because it “interrogates provirus at different places along the proviral sequence,” explained co-author Janet Siliciano, PhD, an associate professor of medicine in the Division of Infectious Diseases at the Johns Hopkins University, in Baltimore.
6 Ways Researchers Are Looking to Cure HIV
Shock and kill – a strategy that awakens HIV reservoirs and kills the activated cells.
Lock and block — traps HIV in its reservoir so that it cannot be reactivated
Hemopoetic stem cell transplants – destroying the patient’s immune system and introducing new stem cells
ART as a Cure – Often done with infants born of HIV-positive mothers; ART given early after exposure can reduce the reservoir and prevent HIV.
Drs. Fauci, Flores, Li, Rodriguez, Walker and Weinberger reported no relevant financial relationships. Mr. Jefferys reported no relevant financial relationships, but the organization that pays his salary receives some donations from industry. Dr. Khalili founded a company to raise money for clinical trials. Further remuneration would result from commercialization, if successful. Dr. Siliciano has financial relationships with Gilead and the U.S. Military HIV Research Program.