Coverage of some subjectively selected presentations from the recent CROI meeting in Atlanta, in addition to the prior post on the case report of a potentially functionally cured infant.
Gene Modification of Virus-Specific CD4 T Cells
Patrick Younan from the Fred Hutchinson Cancer Research Center delivered an interesting talk about transplantation of gene-modified stem cells in pigtailed macaques (abstract, webcast—third in session). The experiment used lentiviral vectors to deliver the gene for a virus entry inhibitor, C46 (also known as M87o, it has a similar mechanism of action to the approved antiretroviral Fuzeon), into stem cells along with a green fluorescent protein (GFP) marker to make the modified cells identifiable. Four macaques underwent stem cell transplantation, with two given C46-modified cells and two controls given cells with only the GFP marker. All were subsequently challenged with the dual-tropic SIV/HIV hybrid virus SHIV89.6P. The two controls displayed typical rapid CD4 T-cell loss, and one was euthanized at week 32 due to the onset of simian AIDS. In contrast, recipients of the modified cells recovered CD4 T-cell counts after an initial dip and showed significantly lower viral loads. Levels of gene-modified CD4 T cells peaked at around 90% during acute infection, but subsequently declined to pre-challenge levels (around 20% in one animal, 55% in the other) during follow-up. Despite the decline in modified CD4 T cells, levels of unmodified cells improved over time, suggesting a protective effect of the intervention on the overall CD4 T-cell pool.
Further studies revealed that superior SHIV-specific CD4 T-cell and antibody responses were associated with the salutary outcome. SHIV-specific CD4 T cells were not detectable in either of the controls. Younan found that a striking 85% of the SHIV-specific CD4 T cells in treated animals were gene-modified, suggesting that protection of these cells had allowed them to better perform their role of providing help to B cells and CD8 T cells. One potentially encouraging implication of this work is that gene therapy approaches might not have to protect all susceptible cells from HIV infection in order to offer benefit; if sufficient numbers of HIV-specific CD4 T cells can be protected, it is possible that these cells will do a better job of coordinating the immune response against HIV, leading to improved control of viral replication. This possibility is being investigated in ongoing trials of Sangamo BioSciences SB-728-T gene therapy, which aims to protect CD4 T cells by abrogating expression of the CCR5 coreceptor.
Engineering SIV to Spare the CD4 T-Cell Help
Adrienne Swanstrom from the University of Pennsylvania described a novel approach to defining the role of infection of CD4 T cells in SIV pathogenesis, using an engineered version of the highly pathogenic SIVmac239—named iMac-ΔD385—that does not bind the CD4 molecule (abstract, webcast—seventh in session). In a preliminary experiment involving just two macaques, Swanstrom found that the modified virus replicated to levels comparable to the wild-type SIVmac239 during acute infection and targeted a variety of non-CD4 cell types, but was then robustly controlled by the immune response. Strong neutralizing antibody responses were detected, which is unusual in pathogenic SIV infection, and ongoing work is now looking at CD8 T-cell responses. The findings, at least so far, suggest that sparing CD4 T-cell help led to more effective CD4 T cell–dependent immune responses and superior control of SIV replication.
CMV Vector Vaccination Leads to Apparent Clearance of SIV Infection
Louis Picker from the Vaccine and Gene Therapy Institute at Oregon Health & Science University gave an update on results obtained in macaques with a CMV-based vaccine against SIV (abstract, webcast—fourth in session). As Picker has shown in published work, the vaccine consistently facilitates strict control of a pathogenic SIVmac239 challenge in around 50% of immunized macaques. The remarkable news shared by Picker at CROI is that, over time, these protected animals appear to clear SIV infection. This claim is based on multiple criteria, including loss of detectable virus, waning of CD8 T-cell responses to viral antigens not included in the vaccine, and the failure to transmit infection to uninfected macaques despite transfer of over 50 million blood and/or tissue white blood cells (in contrast, similar transfers from elite controller animals or those on suppressive ART reliably transmitted infection). Picker noted that the CD8 T-cell responses in the vaccine recipients appear to “violate all the rules” in that they target very large numbers of different SIV epitopes and, in many cases, their ability to recognize the virus involves MHC class II molecules, which normally facilitate antigen recognition by CD4 T cells rather than CD8 T cells. Picker is now working to shed further light on these findings, as well as collaborating with the Vaccine and Gene Therapy Institute of Florida to try and develop a CMV vaccine vector that can safely be studied in humans.
Results from Multidose Vorinostat Trial
Sharon Lewin from Monash University in Melbourne debuted data from the first multidose trial of vorinostat (also known as SAHA) as a potential anti-HIV latency drug (abstract, webcast—ninth in session). Consistent with results published by David Margolis from a single-dose trial, expression of HIV RNA significantly increased among the twenty participants after 14 days of vorinostat. However, there was no evidence for reduction in the size of the latent HIV reservoir, suggesting that additional approaches will be needed to facilitate the elimination of the infected cells. As expected, vorinostat side effects were more prevalent as a result of the multiple dosing, particularly fatigue and lethargy.
Curing HIV Removes the Scars of the Past
One small but encouraging piece of news about the lone adult considered cured of HIV, Timothy Brown, was to be found in a presentation by Joyce Sanchez from the University of Minnesota (abstract, webcast—second in session). Sanchez’s study focused on lymphoid structure abnormalities in people with HIV, particularly fibrotic (scarring) damage to lymph tissue resulting from persistent HIV replication and associated immune activation. The extent of lymph tissue fibrosis can be quantified by measuring collagen deposition using imaging techniques. Sanchez showed that in gut lymph tissue, even HIV controllers (individuals with low viral loads in the absence of ART) have levels of collagen deposition that are higher than those of uninfected individuals (15.9% compared with 7%). However, samples from Timothy Brown showed levels of collagen deposition comparable to the uninfected study participants (6.8%), consistent with studies showing no HIV activity in his body (despite the occasional detection of viral genetic material that was reported last year).