HIV Persistence, Reservoirs and Eradication Strategies Workshop: Day 3
The third day of the workshop, on December 8, 2011, addressed the issues of "Innate Immunity", "Immune Control of HIV Reservoirs" and "Acute HIV Infection". It was also the opportunity to listen to the late breaker abstracts that were selected a few weeks prior to the meeting.
The third day of the workshop began with a session on innate immunity.
Judy Lieberman explained how HIV evades an innate immune response and escale destection. Trex1is an exonuclease which mutation is linked in humans to some auto-immune and inflammatory diseases related to an increase in type I Interferons.
Trex1 digests cytosolic DNA. HIV does not normally induce type I IFNs but does in Trex1 KO cells. IFN induction requires reverse transcription but not integration.
Trex1 inhibits the IFN response to both simple retroviruses and lentiviruses.
HIV DNA accumulates in Trex1 KO cells. There is accumulation of cytosolic DNA, either from HIV or transfection, in the absence of Trex1. Only Trex1 rescues HIV infection. Trex1 knockdown in primary human macrophages increases HIV DNA in cytosol and IFN production but inhibits HIV replication.
One application of these findings is the possibility to induce INF in HIV-infected cells by targetting Trex1 and lower the risk of sexual transmission of HIV. Knocking down Trex1 in CD4+ cells in the genital tract of humanized mice indeed inhibits HIV sexual transmission.
The following talk given by Nicolas Manel dealed with the relations between innate immunity and establishment of HIV reservoirs. HIV replication is blocked at RT in DCs, but viral particles can be transfered to T cells. Vpx can alleviate the restriction to HIV replication in DCs. HIV-1sensing in DCs occurs after integration. DC requires Gag expression. CypA knock down abrogates HIV induces DC matuarion.
Nadine Laguette addressed the issue of viral restriction and SAMHD1. One main question is why HIV-1 did not evolve means of conteracting SAMHD1? Anti-HIV1 activity of SAMHD1 is evolutionary conserved accross primates. The selection pressures dictating SAMHD1 evolution began before the existence of lentiviruses.
Jeanne Sisk addressed the issue of microRNAs and the innate immune response to SIV infection. There may be more than 1000 total miRNAs which are predicted to target more than 50% of the genome. The authors studied 4 particular microRNAs that we able to reduce levels of SIV infection. These endogenous anti-SIV microRNAs are increased by Interferon beta. In primary macrophages, TNF alpha increases microRNA-9 levels.
The more general session on the immunology of HIV persistance took place after this session on innate immunity.
Una O'Doherty addressed the issue of measuring what is going on in Elite Controllers. Unintegrated DNA as a short half life although the half life of LTR circles is not clear and the half life of integrated DNA is life-long. Integrated DNA is strickingly lower in elite suppressors. The elite suppressors also had higher levels of 2-LTR circles. So, total DNA might not be a good surrogate for measuring the reservoir. In these elite suppressors the authors think that CTLs are able to restrict the reservoir. In vitro data show that CD8 T cells from elite suppressors are able to decrease expression of HIV proteins in resting CD4 T cells. The authors show that latently infected cells still produce HIV proteins, even if they do not produce full virions.
Steven Deeks addressed the role of chronic inflammation, or host response, as a barrier to eradication. Not only activation appears with HIV infection but remains detectable during effective ART. There is a weak association between T cell activation in blood and levels of plasma viremia with the SCA. The association with immune activation and viral load is stronger in the gut tissue. The degree of these lymphoid tissues fibrosis is indeed related to persistent activation and high viral load in these tissues.
Can chronic inflammation contribute to HIV persistence? A vicious circle may exist involving microbial translocation.
A number of biologics are considered to block this process of inflammation to build curative strategies. Inhibition of the PD1 system may both increase the expression of HIV and help the immune system clearing these cells.
Hatano is curently building an ACTG 5301 trial using an anti-PD1 antibody.
Other studies will use IDO inhibitors or ACE inhibitors to act of lymphoid fibrosis, methotrexate, MCSF inhibitors....to act on this inflammatoon side.
Nicolas Chomont showed evidence that the reservoir is maintained by immune mechanisms allowing to keep the memory of the immune response. At least in blood, CD4+ T cells constitute more than 95% of the reservoir. The CD4/CD8 ratio is highly negatively correlated with the reservoir size. The lower the CD4 count is, the higher the reservoir will be after CD4 have been increased by ART. Because, in fact, in multivariate analysis only the nadir of the CD4 count before ART is highly correlated with the size of the reservoir on ART.
Homeostatic and antigen driven proliferation of the reservoir to not expand the same cells. The authors consequently measured the stability/changes in the Vbeta repertoire during ART in different patients. They found repertoire/reservoir evolution in some of them and their data favor the fact that those with increase reservoir genetic evolution are expanding cells following antigentic stimulation, although those without evolution follow the effect of IL-7 homeostatic proliferation. Consequently, the reservoir is dynamic not because of viral replication but because of cells contraction and expansion.
Claire Vandergeeten talked about the impact of IL7 and IL15 on HIV persistence. Samples from patients included in the ACTG5214 trial with IL7 showed an increase in the absolute number of CD4+ T cells harbouring HIV DNA. In vitro, stimulation of cells from patients shows increased cell survival for both IL7 or IL15. But IL15 is far more efficient for reactivating latent HIV in these cells.
During the afternoon late breaker session Rafick Sekali presented new data on PD1 and HIV persistence. PD1 mediates its inhibitory efect by interfering with proximal TCR signaling.
CD4+ TM and CM, but not naive CD4+ proliferate in response to PD1 blockade. PD1 blockade leads to an increase in CD8+ specific anti SIV cells.
John Mellors discussed the factors involved in the cure of the Berlin patient. He consequently analyzed HIV patients receiving autologous hematopoietic stem cell transplantation for relapsing lymphomas. He collected 10 cases where the mean time to engraftment was 12 days. Six patients continued ART during the transplant and all we taking it after the transplant. Nine out of 10 patients were viremic after the transplant at a mean level of 2 copies/ml. John Mellors discussed the possible reasons for this failire: no intense conditioning regimen like for allogenic transplantation, no graft verus host disease, no CCR5 deletion.
During the acute HIV infection session Martin Markowitz presented the 96 weeks results of his study comparing 3 to 5 ARV drugs at this stage. The primary end point was the SCA. Infectious virus in resting CD4+ T cells measured at 96 weeks was a secondary end point.
At 96 weeks 10 patients remained in the 3 drugs arm and 18 in the 5 drugs arm. At 48 weeks 11/11 patients were suppressed in the 3 drug arm and 20/23 in the 5 drugs arm; at 96 weeks all patients still in the trial were suppressed.
Through 96 weeks the evolution of proviral DNA was not diffent between the 2 arms.
There is however a borderline (p=0.05) difference concerning cell-associated RNA.
Infectious virus in resting CD4 cells was measured in 21 patients at 96 weeks with no difference between arms. No difference was either found in terms of immunological gain.
When looking in the gut, the levels of CD4 were the same between the 2 arms with a persistent depletion compared to blood. No difference was also found in terms of CD8 activation or proliferation in gut between the 2 arms.
One problem in this study is that an important proportion of patients were early infection cases, not acute.
Jintanat Ananworanich updated her data on mega-ART at acute infection presented eralier this year at CROI. They enrolled 62 acutely HIV-infected patients with a mean time from testing and enrollment of 3 days. Then the delay of starting ART was also 3 days. 35 patients have reached 24 weeks of follow up, most if them at Fiebig I to III stages. Fiebig I patients had significantly lower proviral DNA levels than Fiebig III, and less CD4+CCR5+ loss in sigmoid colon. Twenty two patients had mega-ART for 6 months, then ART and 23 had ART since the start. In terms of plasma viremia, the results were the same for the 2 regimens. Fiebig III and IV subjects showed an increase in sigmoid CD4+CCR5+ cells. Total and integrated DNA declined significantly after mega-ART in sigmoid colon, but not after 3-drug ART. Total DNA in blood became undetectable in 40% of patients.
The next step of the group is to treat for 1 year a cohort of acutely infected patients, then give them a therapeutic vaccine.
Maria Buzon showed data of HIV reservoir size reduction after 10 years of ART initiated at acute infection. This concerned 9 patients who were compared to 10 treated at the chronic stage and 37 elite controllers. After a median of 3 years of therapy, total DNA remained stable, although integrated DNA decreased after 3 years. This was particularly true for patients treated at Fiebig III and IV stages compared to stage V. Integrated DNA levels were similar between acutely infected treated patients and elite controllers, and lower than chronically infected treated patients.
The last session of the day concerned anatomic reservoirs and will be the subject of a special report in the forthcoming weeks.
Key words: HIV cure, HIV eradication, HIV persistence, HIV reservoirs, acute HIV infection.