Awakening Dormant Virus
amfAR grantee Dr. Ole Søgaard of Aarhus University Hospital in Denmark presented results of his team’s clinical study using the anti-cancer drug romidepsin, a histone deacetylase inhibitor (HDACi). In several of the six chronically infected patients, they showed that the drug successfully “awoke” the dormant virus. Infected cells began to manufacture and release new virus, potentially exposing them to recognition and destruction by the immune system. The Danish team will now build upon these exciting results by employing an immune-boosting therapy to see if they can facilitate this outcome.
News of the reappearance of virus in the Mississippi child after more than two virus-free years off treatment presents researchers with the task of figuring out how HIV disappeared for so long in the absence of both antiretroviral treatment and any detectable HIV-specific immune responses, explained amfAR grant recipient and principal investigator for this study Dr. Deborah Persaud. She and her colleagues will also attempt to identify the source of the re-emerging virus— the areas of the body and the specific types of cell—as well as any particular events that might have led to its reappearance.
Molecular “Bar Code”
Imaginative work from former amfAR fellow Brandon Keele, now working at the National Institutes of Health’s Frederick National Lab, might well make this task less daunting. Keele and his team have re-engineered the classic monkey version of HIV, SIVmac239, with a molecular tag they are likening to a “bar code.” After testing their stock of nearly 10,000 unique bar-coded viruses in live animals, they showed that it propagated just like the standard SIVmac239. Using these barcoded viruses, they will now be able to track back any breakthrough replication after successful treatment to the anatomical site it came from.
Measuring the Reservoir
Appearing to respond to such calls, amfAR grantee Dr. Nicolas Chomont shared with delegates a new blood test for quantifying the size of the latent HIV reservoir that, unlike previously available assays, requires only a small volume of blood—10ml—and is both reliable and inexpensive enough to be widely adapted by HIV cure research teams around the world. Named TILDA for “Tat/Rev Induced Limiting Dilution Assay,” Dr. Chomont claims the new test provides estimates of viral reservoir size more accurately than those produced by quantitative viral outgrowth assays (“Q-VOA”) and PCR measurements of HIV DNA.
A Three-Pronged Approach
Overall, there is a growing consensus that early antiretroviral therapy will be essential to reduce seeding of the viral reservoir and, in the words of Dr. Anthony Fauci, chief of the National Institute of Allergy and Infectious Diseases at NIH, to “stack the deck” in favor of viral eradication. During a conference wrap-up session, Zabrina Brumme of the British Columbia Centre for Excellence in HIV/AIDS, explained how in some cases “kick and kill” strategies are evolving to a three-pronged approach where, after waking up latent virus, gene therapy techniques would be employed to make immune system cells resistant to HIV infection. Immunotherapies would then tweak antibody and/or cellular immune responses to help them clear any remaining free virus and infected cells.
In a somewhat related report, amfAR grantee Dr. Nicolas Chomont shared with conference goers how he and his team at the Vaccine and Gene Therapy Institute in Port St. Lucie, FL, are beginning to appreciate the “extraordinary heterogeneity” of T-cell subsets in terms of their contribution to the viral reservoir, their persistence and their susceptibility to drug-induced reactivation—and how this differs between people treated during acute HIV infection and those treated during chronic infection.
Dr. Hiromi Imamichi, from the Clinical and Molecular Retrovirology Laboratory at NIAID, presented a worrisome scenario of what she is calling “zombie proviruses;” that is, proviral DNA that, although technically defective, continues to make RNA proteins and RNA transcripts. Imamichi suspects that this never-before-reported phenomenon could be what is driving the chronic inflammation seen in even well controlled HIV infection, as well as the continued presence of defective immune responses to the virus.
Also from NIAID, Dr. Richard Koup presented a possible solution to clearing virus that is protected inside what are called the “germinal centers” of lymph nodes, where it is inaccessible to the immune system’s normal immune surveillance. Koup and his NIAID team have engineered a bi-specific antibody, meaning that it can attach to T-cells’ CD3 receptor from one end and to an HIV envelope protein from the other. He demonstrated that this engineered antibody can specifically kill cells that harbor HIV.
“A Novel Immune Response”
Jonah Sacha and his team at Oregon Health and Science University, working to understand how their CMV vector vaccine resulted in viral eradication in immunized monkeys even though it failed to prevent infection, hailed their discovery of MHC-E-restricted CD8 T cell responses to HIV as “a novel immune response to retroviruses.” While reports of the ability of these “nonclassical” MHC class Ib molecules to stimulate T-cell responses against Epstein-Barr, hepatitis C and CMV viruses emerged in recent years, this is the first instance of their being observed with HIV. Sacha predicted that the discovery of their role in SIV neutralization could open the door for a one-size-fits-all immunotherapy.
Locking Down Latent Virus
Proposing something of an opposite alternative to “kick and kill” strategies, Dr. Eric Verdin of San Francisco’s Gladstone Institute of Virology and Immunology, proffered the idea of suppressing viral reactivation. After conducting a screen of thousands of RNAs to identify genes that may control HIV latency, Verdin and his colleagues identified both latency-promoting and latency-suppressing protein complexes and singled out suppression of the mTOR protein as the best therapeutic candidate. Inhibiting this mTOR pathway, he explained, would have the effect of “locking down” latent virus and preventing it from even “waking,” reproducing and causing harm. One possible downside to this lock-down approach would be that any mTOR inhibitor would likely have to be taken for life.