CROI 2015 Program and Abstracts

Abstract Listing

Poster Abstracts

Results: We have previously shown that HIV-1 evades cell-intrinsic restrictions in DCs by exploiting CD169 for enhanced transfer to CD4 + T lymphocytes. Interestingly, there was a 3-fold reduction in capture of HIV-2 compared to HIV-1 by THP1/CD169 cells. Similar reduction in CD169 specific capture is seen with mature DCs, though both HIV-1 and HIV-2 virions were localized following capture within a CD81 + compartment. Though HIV-1 and HIV-2 are equally infectious for CD4 + T cells, there was a 7-fold decrease in mature DC- mediated HIV-2 trans infection of CD4 + T cells compared to HIV-1 suggesting that HIV-2 might interact with additional receptors on the mature DC surface, which inhibit access to the trans-infection pathway. Conclusions: We conclude that a reduced interaction of HIV-2 with CD169 inhibits access of HIV-2 to the DC-mediated trans infection pathway and might result in attenuated dissemination in vivo. 223 Identification of the First Nonhuman Primate CD4 Receptor for T/F HIV-1 Isolates Nicholas Meyerson 2 ; Amit Sharma 1 ; GregoryWilkerson 3 ; Julie M. Overbaugh 1 ; Sara Sawyer 2 1 Fred Hutchinson Cancer Research Center, Seattle, WA, US; 2 The University of Texas at Austin, Austin, TX, US; 3 University of Texas, MD Anderson Cancer Center, Bastrop, TX, US Background: Nonhuman primate species are resistant to HIV-1 infection, in most cases due to the inability of their CD4 to function as HIV-1 receptor for viral entry and/or species- specific host factors that restrict HIV-1 replication. Envelopes (Envs) from lab-adapted and some chronic-stage isolates of HIV-1 use the CD4 receptor encoded by multiple primate species, including macaque CD4. However, only the human CD4 receptor can mediate entry of Envs from HIV-1 variants representing transmitted/founder (T/F) viruses, which are most relevant to the HIV-1 pandemic. CCR5 presents an additional barrier to entry in many other primate species. These factors have limited the development of animal models to study viral pathogenesis of these more clinically relevant, T/F HIV-1 strains. Methods: In this study we analyzed the CD4 sequence of multiple individuals from 11 different nonhuman primate species, including two Old World macaque species and five different species of NewWorld monkeys. We also utilized human SNP databases and previous reports on CD4 diversity in chimpanzees and three different species of Old World monkeys. We cloned selected CD4 and CCR5 alleles from primate species that were polymorphic at sites identified in previous studies as critical for HIV-1 envelope binding and/ or entry. We tested these CD4 and CCR5 alleles for their ability to function as HIV-1 receptor and coreceptor, respectively, by generating cells expressing different combinations of these receptors. Results: Multiple CD4 alleles were identified in one NewWorld monkey species, the Spix’s owl monkey ( Aotus vociferans ), which encode CD4s that support entry mediated by circulating Envs from all of the major clades of HIV-1 group M. The Spix’s Owl monkey CD4 receptor facilitated entry at levels similar to the human receptor in combination with human CCR5 and pig-tailed macaque CCR5. Interestingly, CCR5 from Spix’s owl monkey was not a functional coreceptor when combined with their permissible CD4. Conclusions: We demonstrate that CD4 is polymorphic in primate species at sites critical for HIV-1 entry. We have identified the first nonhuman primate CD4 compatible with entry of transmitted, circulating HIV-1 Envs. These findings support efforts to use novel strategies, including genetic screening, for developing better HIV-1 animal models. 224LB Vpr Increases Env Spikes on Virions to Enhance HIV-1 Replication in Nondividing Myeloid Cells Tao Zhou 1 ; Xianfeng Zhang 2 ; Yonghui Zheng 1 1 Michigan State University, East Lansing, MI, US; 2 Harbin Veterinary Research Institute, Harbin, China Background: Vpr plays an important role in maintenance of high viral load and disease progression in vivo through unknown mechanisms. Vpr has a very important function in vitro , enhancing viral replication in non-dividing myeloid cells, but the mechanism is likewise unknown. Because these cells are primary targets for HIV-1 infection and contribute to viral persistence, understanding how Vpr enhances HIV-1 replication in vitro is critically important to understanding the functional role of Vpr in vivo . Notably, Vpr is packaged into HIV-1 particles at large numbers via a specific interaction with Gag, and Vpr activates the oxidative stress pathway in mammalian cells and fission yeast. However, it is still unknown how these Vpr activities contribute to the enhancement of viral replication. Methods: Previously, we identified a human T cell line CEM.NKR (NKR), where we reported that Vpr is absolutely required for HIV-1 replication. We also reported that Env is misfolded and rapidly degraded via the ER-associated protein degradation (ERAD) pathway in these cells. We then investigated HIV-1 replication, Env expression, and Env incorporation in NKR cells, monocyte-derived macrophages (MDM), and monocyte-derived dendritic cells, after creating a panel of Vpr mutations in HIV-1 proviral constructs. We also compared how Env was degraded in the presence or absence of Vpr by activating the oxidative stress pathway and/or inhibiting the ERAD pathway. Results: It was found that when Vpr was not expressed, Env was more aggressively degraded via the ERAD pathway. Vpr could strongly block this degradation, resulting in significant increase of Env expression. A single A30L mutation within the 1 st α -helix of Vpr could disrupt this activity, suggesting that the N-terminal region of Vpr plays a critical role in Env expression. Interestingly, although Env could be expressed, it was not efficiently incorporated into virions unless Vpr was expressed. However, Vpr was not required for Env trafficking to the cell surface. Using Vpr packaging deficient mutants, it was further uncovered that the Env incorporation was dependent on the Vpr incorporation. Importantly, Vpr was found to interact with both Gag and Env, resulting in increase of Env incorporation. Conclusions: We concluded that Vpr increases Env expression likely by promoting Env folding via the oxidative stress pathway, and it also increases Env incorporation via bridging Env with Gag, resulting in increase of Env spikes on virions and enhancement of HIV-1 replication.

Poster Abstracts

THURSDAY, FEBRUARY 26, 2015 Session P-A6 Poster Session

Poster Hall

2:30 pm– 4:00 pm Nef Functions 225 Env and Nef Cooperatively Contribute to HIV-1 – Induced pDC Activation via CD4-Dependent Mechanisms Natalia J. Reszka-Blanco 1 ;Vijay Sivaraman 1 ; Liguo Zhang 2 ; Lishan Su 1 1 University of North Carolina, Chapel Hill, NC, US; 2 Key Lab of Infection and Immunity, Insitute of Biophysics, Chinese Academy of Science, Beijing, China

Background: HIV-1 infection induces high levels of type I IFN (IFN-I). The function of IFN-I in HIV-1 infection is not entirely defined, with results showing either its beneficial effect in anti-vial therapy or contribution to the HIV-1 related immune activation and CD4 T cell loss. Moreover, HIV-1 early isolates are resistant to IFN-I control and can succeed in establishing systemic infection despite the high level of IFN-I. Plasmacytoid dendritic cells (pDC) are the major source of IFN-I and play a critical role in the response to HIV-1. pDC are rapidly activated by HIV-1 infection and are implicated in both early reduction of viral load and HIV-1 induced pathogenesis. Interestingly cell-free virions of most HIV-1 isolates

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CROI 2015