Rapid Inflammasome Activation following Mucosal SIV Infection of Rhesus Monkeys.

The earliest events following mucosal HIV-1 infection, prior to measurable viremia, remain poorly understood. Here, by detailed necropsy studies, we show that the virus can rapidly disseminate following mucosal SIV infection of rhesus monkeys and trigger components of the inflammasome, both at the site of inoculation and at early sites of distal virus spread. By 24 hr following inoculation, a proinflammatory signature that lacked antiviral restriction factors was observed in viral RNA-positive tissues. The early innate response included expression of NLRX1, which inhibits antiviral responses, and activation of the TGF-ß pathway, which negatively regulates adaptive immune responses. These data suggest a model in which the virus triggers specific host mechanisms that suppress the generation of antiviral innate and adaptive immune responses in the first few days of infection, thus facilitating its own replication. These findings have important implications for the development of vaccines and other strategies to prevent infection.

Early antiretroviral therapy in SIV-infected rhesus macaques reveals a multiphasic, saturable dynamic accumulation of the rebound competent viral reservoir.

The rebound competent viral reservoir (RCVR)-virus that persists during antiretroviral treatment (ART) and can reignite systemic infection when treatment is stopped-is the primary barrier to eradicating HIV. We used time to initiation of ART during primary infection of rhesus macaques (RMs) after intravenous challenge with barcoded SIVmac239 as a means to elucidate the dynamics of RCVR establishment in groups of RMs by creating a multi-log range of pre-ART viral loads and then assessed viral time-to-rebound and reactivation rates resulting from the discontinuation of ART after one year. RMs started on ART on days 3, 4, 5, 6, 7, 9 or 12 post-infection showed a nearly 10-fold difference in pre-ART viral measurements for successive ART-initiation timepoints. Only 1 of 8 RMs initiating ART on days 3 and 4 rebounded after ART interruption despite measurable pre-ART plasma viremia. Rebounding plasma from the 1 rebounding RM contained only a single barcode lineage detected at day 50 post-ART. All RMs starting ART on days 5 and 6 rebounded between 14- and 50-days post-ART with 1-2 rebounding variants each. RMs starting ART on days 7, 9, and 12 had similar time-to-measurable plasma rebound kinetics despite multiple log differences in pre-ART plasma viral load (pVL), with all RMs rebounding between 7- and 16-days post-ART with 3-28 rebounding lineages. Calculated reactivation rates per pre-ART pVL were highest for RMs starting ART on days 5, 6, and 7 after which the rate of accumulation of the RCVR markedly decreased for RMs treated on days 9 and 12, consistent with multiphasic establishment and near saturation of the RCVR within 2 weeks post infection. Taken together, these data highlight the heterogeneity of the RCVR between RMs, the stochastic establishment of the very early RCVR, and the saturability of the RCVR prior to peak viral infection.

Impact of alemtuzumab-mediated lymphocyte depletion on SIV reservoir establishment and persistence.

Persistence of the rebound-competent viral reservoir (RCVR) within the CD4+ T cell compartment of people living with HIV remains a major barrier to HIV cure. Here, we determined the effects of the pan-lymphocyte-depleting monoclonal antibody (mAb) alemtuzumab on the RCVR in SIVmac239-infected rhesus macaques (RM) receiving antiretroviral therapy (ART). Alemtuzumab administered during chronic ART or at the time of ART initiation induced >95% depletion of circulating CD4+ T cells in peripheral blood and substantial CD4+ T cell depletion in lymph nodes. However, treatment was followed by proliferation and reconstitution of CD4+ T cells in blood, and despite ongoing ART, levels of cell-associated SIV DNA in blood and lymphoid tissues were not substantially different between alemtuzumab-treated and control RM after immune cell reconstitution, irrespective of the time of alemtuzumab treatment. Upon ART cessation, 19 of 22 alemtuzumab-treated RM and 13 of 13 controls rebounded in <28 days with no difference in the time to rebound between treatment groups. Time to rebound and reactivation rate was associated with plasma viral loads (pVLs) at time of ART initiation, suggesting lymphocyte depletion had no durable impact on the RCVR. However, 3 alemtuzumab-treated RM that had lowest levels of pre-ART viremia, failed to rebound after ART withdrawal, in contrast to controls with similar levels of SIV replication. These observations suggest that alemtuzumab therapy has little to no ability to reduce well-established RCVRs but may facilitate RCVR destabilization when pre-ART virus levels are particularly low.

Interleukin-15 response signature predicts RhCMV/SIV vaccine efficacy.

Simian immunodeficiency virus (SIV) challenge of rhesus macaques (RMs) vaccinated with strain 68-1 Rhesus Cytomegalovirus (RhCMV) vectors expressing SIV proteins (RhCMV/SIV) results in a binary outcome: stringent control and subsequent clearance of highly pathogenic SIV in ~55% of vaccinated RMs with no protection in the remaining 45%. Although previous work indicates that unconventionally restricted, SIV-specific, effector-memory (EM)-biased CD8+ T cell responses are necessary for efficacy, the magnitude of these responses does not predict efficacy, and the basis of protection vs. non-protection in 68-1 RhCMV/SIV vector-vaccinated RMs has not been elucidated. Here, we report that 68-1 RhCMV/SIV vector administration strikingly alters the whole blood transcriptome of vaccinated RMs, with the sustained induction of specific immune-related pathways, including immune cell, toll-like receptor (TLR), inflammasome/cell death, and interleukin-15 (IL-15) signaling, significantly correlating with subsequent vaccine efficacy. Treatment of a separate RM cohort with IL-15 confirmed the central involvement of this cytokine in the protection signature, linking the major innate and adaptive immune gene expression networks that correlate with RhCMV/SIV vaccine efficacy. This change-from-baseline IL-15 response signature was also demonstrated to significantly correlate with vaccine efficacy in an independent validation cohort of vaccinated and challenged RMs. The differential IL-15 gene set response to vaccination strongly correlated with the pre-vaccination activity of this pathway, with reduced baseline expression of IL-15 response genes significantly correlating with higher vaccine-induced induction of IL-15 signaling and subsequent vaccine protection, suggesting that a robust de novo vaccine-induced IL-15 signaling response is needed to program vaccine efficacy. Thus, the RhCMV/SIV vaccine imparts a coordinated and persistent induction of innate and adaptive immune pathways featuring IL-15, a known regulator of CD8+ T cell function, that support the ability of vaccine-elicited unconventionally restricted CD8+ T cells to mediate protection against SIV challenge.

Liver macrophage-associated inflammation correlates with SIV burden and is substantially reduced following cART.

Liver disease is a leading contributor to morbidity and mortality during HIV infection, despite the use of combination antiretroviral therapy (cART). The precise mechanisms of liver disease during HIV infection are poorly understood partially due to the difficulty in obtaining human liver samples as well as the presence of confounding factors (e.g. hepatitis co-infection, alcohol use). Utilizing the simian immunodeficiency virus (SIV) macaque model, a controlled study was conducted to evaluate the factors associated with liver inflammation and the impact of cART. We observed an increase in hepatic macrophages during untreated SIV infection that was associated with a number of inflammatory and fibrosis mediators (TNFα, CCL3, TGFß). Moreover, an upregulation in the macrophage chemoattractant factor CCL2 was detected in the livers of SIV-infected macaques that coincided with an increase in the number of activated CD16+ monocyte/macrophages and T cells expressing the cognate receptor CCR2. Expression of Mac387 on monocyte/macrophages further indicated that these cells recently migrated to the liver. The hepatic macrophage and T cell levels strongly correlated with liver SIV DNA levels, and were not associated with the levels of 16S bacterial DNA. Utilizing in situ hybridization, SIV-infected cells were found primarily within portal triads, and were identified as T cells. Microarray analysis identified a strong antiviral transcriptomic signature in the liver during SIV infection. In contrast, macaques treated with cART exhibited lower levels of liver macrophages and had a substantial, but not complete, reduction in their inflammatory profile. In addition, residual SIV DNA and bacteria 16S DNA were detected in the livers during cART, implicating the liver as a site on-going immune activation during antiretroviral therapy. These findings provide mechanistic insights regarding how SIV infection promotes liver inflammation through macrophage recruitment, with implications for in HIV-infected individuals.

Genetically-barcoded SIV facilitates enumeration of rebound variants and estimation of reactivation rates in nonhuman primates following interruption of suppressive antiretroviral therapy.

HIV and SIV infection dynamics are commonly investigated by measuring plasma viral loads. However, this total viral load value represents the sum of many individual infection events, which are difficult to independently track using conventional sequencing approaches. To overcome this challenge, we generated a genetically tagged virus stock (SIVmac239M) with a 34-base genetic barcode inserted between the vpx and vpr accessory genes of the infectious molecular clone SIVmac239. Next-generation sequencing of the virus stock identified at least 9,336 individual barcodes, or clonotypes, with an average genetic distance of 7 bases between any two barcodes. In vitro infection of rhesus CD4+ T cells and in vivo infection of rhesus macaques revealed levels of viral replication of SIVmac239M comparable to parental SIVmac239. After intravenous inoculation of 2.2x105 infectious units of SIVmac239M, an average of 1,247 barcodes were identified during acute infection in 26 infected rhesus macaques. Of the barcodes identified in the stock, at least 85.6% actively replicated in at least one animal, and on average each barcode was found in 5 monkeys. Four infected animals were treated with combination antiretroviral therapy (cART) for 82 days starting on day 6 post-infection (study 1). Plasma viremia was reduced from >106 to <15 vRNA copies/mL by the time treatment was interrupted. Virus rapidly rebounded following treatment interruption and between 87 and 136 distinct clonotypes were detected in plasma at peak rebound viremia. This study confirmed that SIVmac239M viremia could be successfully curtailed with cART, and that upon cART discontinuation, rebounding viral variants could be identified and quantified. An additional 6 animals infected with SIVmac239M were treated with cART beginning on day 4 post-infection for 305, 374, or 482 days (study 2). Upon treatment interruption, between 4 and 8 distinct viral clonotypes were detected in each animal at peak rebound viremia. The relative proportions of the rebounding viral clonotypes, spanning a range of 5 logs, were largely preserved over time for each animal. The viral growth rate during recrudescence and the relative abundance of each rebounding clonotype were used to estimate the average frequency of reactivation per animal. Using these parameters, reactivation frequencies were calculated and ranged from 0.33-0.70 events per day, likely representing reactivation from long-lived latently infected cells. The use of SIVmac239M therefore provides a powerful tool to investigate SIV latency and the frequency of viral reactivation after treatment interruption.

The ability of TNPO3-depleted cells to inhibit HIV-1 infection requires CPSF6.

BACKGROUND: Expression of the cellular karyopherin TNPO3/transportin-SR2/Tnp3 is necessary for HIV-1 infection. Depletion of TNPO3 expression in mammalian cells inhibits HIV-1 infection after reverse transcription but prior to integration. RESULTS: This work explores the role of cleavage and polyadenylation specificity factor subunit 6 (CPSF6) in the ability of TNPO3-depleted cells to inhibit HIV-1 infection. Our findings showed that depletion of TNPO3 expression inhibits HIV-1 infection, while the simultaneous depletion of TNPO3 and CPSF6 expression rescues HIV-1 infection. Several experiments to understand the rescue of infectivity by CPSF6 were performed. Our experiments revealed that the HIV-1 capsid binding ability of the endogenously expressed CPSF6 from TNPO3-depleted cells does not change when compared to CPSF6 from wild type cells. In agreement with our previous results, depletion of TNPO3 did not change the nuclear localization of CPSF6. Studies on the formation of 2-LRT circles during HIV-1 infection revealed that TNPO3-depleted cells are impaired in the integration process or exhibit a defect in the formation of 2-LTR circles. To understand whether the cytosolic fraction of CPSF6 is responsible for the inhibition of HIV-1 in TNPO3-depleted cells, we tested the ability of a cytosolic full-length CPSF6 to block HIV-1 infection. These results demonstrated that overexpression of a cytosolic full-length CPSF6 blocks HIV-1 infection at the nuclear import step. Fate of the capsid assays revealed that cytosolic expression of CPSF6 enhances stability of the HIV-1 core during infection. CONCLUSIONS: These results suggested that inhibition of HIV-1 by TNPO3-depleted cells requires CPSF6.

Myeloid cell tropism enables MHC-E-restricted CD8+ T cell priming and vaccine efficacy by the RhCMV/SIV vaccine.

The strain 68-1 rhesus cytomegalovirus (RhCMV)-based vaccine for simian immunodeficiency virus (SIV) can stringently protect rhesus macaques (RMs) from SIV challenge by arresting viral replication early in primary infection. This vaccine elicits unconventional SIV-specific CD8+ T cells that recognize epitopes presented by major histocompatibility complex (MHC)-II and MHC-E instead of MHC-Ia. Although RhCMV/SIV vaccines based on strains that only elicit MHC-II- and/or MHC-Ia-restricted CD8+ T cells do not protect against SIV, it remains unclear whether MHC-E-restricted T cells are directly responsible for protection and whether these responses can be separated from the MHC-II-restricted component. Using host microRNA (miR)-mediated vector tropism restriction, we show that the priming of MHC-II and MHC-E epitope-targeted responses depended on vector infection of different nonoverlapping cell types in RMs. Selective inhibition of RhCMV infection in myeloid cells with miR-142-mediated tropism restriction eliminated MHC-E epitope-targeted CD8+ T cell priming, yielding an exclusively MHC-II epitope-targeted response. Inhibition with the endothelial cell-selective miR-126 eliminated MHC-II epitope-targeted CD8+ T cell priming, yielding an exclusively MHC-E epitope-targeted response. Dual miR-142 + miR-126-mediated tropism restriction reverted CD8+ T cell responses back to conventional MHC-Ia epitope targeting. Although the magnitude and differentiation state of these CD8+ T cell responses were generally similar, only the vectors programmed to elicit MHC-E-restricted CD8+ T cell responses provided protection against SIV challenge, directly demonstrating the essential role of these responses in RhCMV/SIV vaccine efficacy.

Cytomegaloviral determinants of CD8+ T cell programming and RhCMV/SIV vaccine efficacy.

Simian immunodeficiency virus (SIV) insert-expressing, 68-1 rhesus cytomegalovirus (RhCMV/SIV) vectors elicit major histocompatibility complex E (MHC-E)- and MHC-II-restricted, SIV-specific CD8+ T cell responses, but the basis of these unconventional responses and their contribution to demonstrated vaccine efficacy against SIV challenge in the rhesus monkeys (RMs) have not been characterized. We show that these unconventional responses resulted from a chance genetic rearrangement in 68-1 RhCMV that abrogated the function of eight distinct immunomodulatory gene products encoded in two RhCMV genomic regions (Rh157.5/Rh157.4 and Rh158-161), revealing three patterns of unconventional response inhibition. Differential repair of these genes with either RhCMV-derived or orthologous human CMV (HCMV)-derived sequences (UL128/UL130; UL146/UL147) leads to either of two distinct CD8+ T cell response types-MHC-Ia-restricted only or a mix of MHC-II- and MHC-Ia-restricted CD8+ T cells. Response magnitude and functional differentiation are similar to RhCMV 68-1, but neither alternative response type mediated protection against SIV challenge. These findings implicate MHC-E-restricted CD8+ T cell responses as mediators of anti-SIV efficacy and indicate that translation of RhCMV/SIV vector efficacy to humans will likely require deletion of all genes that inhibit these responses from the HCMV/HIV vector.

Modulation of MHC-E transport by viral decoy ligands is required for RhCMV/SIV vaccine efficacy.

Strain 68-1 rhesus cytomegalovirus (RhCMV) vectors expressing simian immunodeficiency virus (SIV) antigens elicit CD8+ T cells recognizing epitopes presented by major histocompatibility complex II (MHC-II) and MHC-E but not MHC-Ia. These immune responses mediate replication arrest of SIV in 50 to 60% of monkeys. We show that the peptide VMAPRTLLL (VL9) embedded within the RhCMV protein Rh67 promotes intracellular MHC-E transport and recognition of RhCMV-infected fibroblasts by MHC-E-restricted CD8+ T cells. Deletion or mutation of viral VL9 abrogated MHC-E-restricted CD8+ T cell priming, resulting in CD8+ T cell responses exclusively targeting MHC-II-restricted epitopes. These responses were comparable in magnitude and differentiation to responses elicited by 68-1 vectors but did not protect against SIV. Thus, Rh67-enabled direct priming of MHC-E-restricted T cells is crucial for RhCMV/SIV vaccine efficacy.

Antibody-mediated depletion of viral reservoirs is limited in SIV-infected macaques treated early with antiretroviral therapy.

The effectiveness of virus-specific strategies, including administered HIV-specific mAbs, to target cells that persistently harbor latent, rebound-competent HIV genomes during combination antiretroviral therapy (cART) has been limited by inefficient induction of viral protein expression. To examine antibody-mediated viral reservoir targeting without a need for viral induction, we used an anti-CD4 mAb to deplete both infected and uninfected CD4+ T cells. Ten rhesus macaques infected with barcoded SIVmac239M received cART for 93 weeks starting 4 days after infection. During cART, 5 animals received 5 to 6 anti-CD4 antibody administrations and CD4+ T cell populations were then allowed 1 year on cART to recover. Despite profound CD4+ T cell depletion in blood and lymph nodes, time to viral rebound following cART cessation was not significantly delayed in anti-CD4-treated animals compared with controls. Viral reactivation rates, determined based on rebounding SIVmac239M clonotype proportions, also were not significantly different in CD4-depleted animals. Notably, antibody-mediated depletion was limited in rectal tissue and negligible in lymphoid follicles. These results suggest that, even if robust viral reactivation can be achieved, antibody-mediated viral reservoir depletion may be limited in key tissue sites.

Mutations in human immunodeficiency virus type 1 nucleocapsid protein zinc fingers cause premature reverse transcription.

Human immunodeficiency virus type 1 (HIV-1) requires that its genome be reverse transcribed into double-stranded DNA for productive infection of cells. This process requires not only reverse transcriptase but also the nucleocapsid protein (NC), which functions as a nucleic acid chaperone. Reverse transcription generally begins once the core of the virion enters the cytoplasm of a newly infected cell. However, some groups have reported the presence of low levels of viral DNA (vDNA) within particles prior to infection, the significance and function of which is controversial. We report here that several HIV-1 NC mutants, which we previously identified as being replication defective, contain abnormally high levels of intravirion DNA. These findings were further reinforced by the inability of these NC mutants to perform endogenous reverse transcription (ERT), in contrast to the readily measurable ERT activity in wild-type HIV-1. When either of the NC mutations is combined with a mutation that inactivates the viral protease, we observed a significant reduction in the amount of intravirion DNA. Interestingly, we also observed high levels of intravirion DNA in the context of wild-type NC when we delayed budding by means of a PTAP((-)) (Pro-Thr-Ala-Pro) mutation. Premature reverse transcription is most probably occurring before these mutant virions bud from producer cells, but we fail to see any evidence that the NC mutations alter the timing of Pr55(Gag) processing. Critically, our results also suggest that the presence of intravirion vDNA could serve as a diagnostic for identifying replication-defective HIV-1.

TLR7 agonist administration to SIV-infected macaques receiving early initiated cART does not induce plasma viremia.

Reduction/elimination of HIV-1 reservoirs that persist despite combination antiretroviral therapy (cART) will likely require induction of viral expression by residual infected cells and enhanced clearance of these cells. TLR7 agonists have potential to mediate these activities. We evaluated immunologic and virologic effects of repeated doses of the TLR7 agonist GS-9620 in SIV-infected rhesus macaques receiving cART, which was initiated at 13 days after infection and was continued for 75 weeks prior to GS-9620 administration. During cART, GS-9620 induced transient upregulation of IFN-stimulated genes in blood and tissues, increases in plasma cytokines, and changes in immune cell population activation and phenotypes but did not result in measurable increases in plasma viremia or viral RNA-to-viral DNA ratio in PBMCs or tissues nor decreases in viral DNA in PBMC or tissues. SIV-specific CD8+ T cell responses, negligible prior to GS-9620 treatment, were not measurably boosted by treatment; a second course of GS-9620 administration overlapping with later cART discontinuation was associated with increased CD8+ T cell responses during viral recrudescence. These results confirm and extend evidence for GS-9620-mediated enhancement of antiviral immune responses in SIV-infected macaques but suggest that GS-9620-mediated viral induction may depend critically on the timing of initiation and duration of cART and resulting characteristics of viral reservoirs.

A live-attenuated RhCMV/SIV vaccine shows long-term efficacy against heterologous SIV challenge.

Previous studies have established that strain 68-1-derived rhesus cytomegalovirus (RhCMV) vectors expressing simian immunodeficiency virus (SIV) proteins (RhCMV/SIV) are able to elicit and maintain cellular immune responses that provide protection against mucosal challenge of highly pathogenic SIV in rhesus monkeys (RMs). However, these efficacious RhCMV/SIV vectors were replication and spread competent and therefore have the potential to cause disease in immunocompromised subjects. To develop a safer CMV-based vaccine for clinical use, we attenuated 68-1 RhCMV/SIV vectors by deletion of the Rh110 gene encoding the pp71 tegument protein (ΔRh110), allowing for suppression of lytic gene expression. ΔRh110 RhCMV/SIV vectors are highly spread deficient in vivo (~1000-fold compared to the parent vector) yet are still able to superinfect RhCMV+ RMs and generate high-frequency effector-memory-biased T cell responses. Here, we demonstrate that ΔRh110 68-1 RhCMV/SIV-expressing homologous or heterologous SIV antigens are highly efficacious against intravaginal (IVag) SIVmac239 challenge, providing control and progressive clearance of SIV infection in 59% of vaccinated RMs. Moreover, among 12 ΔRh110 RhCMV/SIV-vaccinated RMs that controlled and progressively cleared an initial SIV challenge, 9 were able to stringently control a second SIV challenge ~3 years after last vaccination, demonstrating the durability of this vaccine. Thus, ΔRh110 RhCMV/SIV vectors have a safety and efficacy profile that warrants adaptation and clinical evaluation of corresponding HCMV vectors as a prophylactic HIV/AIDS vaccine.

Early antiretroviral therapy limits SIV reservoir establishment to delay or prevent post-treatment viral rebound.

Prophylactic vaccination of rhesus macaques with rhesus cytomegalovirus (RhCMV) vectors expressing simian immunodeficiency virus (SIV) antigens (RhCMV/SIV) elicits immune responses that stringently control highly pathogenic SIV infection, with subsequent apparent clearance of the infection, in ~50% of vaccinees. In contrast, here, we show that therapeutic RhCMV/SIV vaccination of rhesus macaques previously infected with SIV and given continuous combination antiretroviral therapy (cART) beginning 4-9 d post-SIV infection does not mediate measurable SIV reservoir clearance during over 600 d of follow-up on cART relative to RhCMV/control vaccination. However, none of the six animals started on cART on day four or five, across both RhCMV/SIV- and RhCMV/control-vaccinated groups, those rhesus macaques with SIV reservoirs most closely resembling those of prophylactically RhCMV/SIV-vaccinated and protected animals early in their course, showed post-cART viral rebound with up to nine months of follow-up. Moreover, at necropsy, these rhesus macaques showed little to no evidence of replication-competent SIV. These results suggest that the early SIV reservoir is limited in durability and that effective blockade of viral replication and spread in this critical time window by either pharmacologic or immunologic suppression may result in reduction, and potentially loss, of rebound-competent virus over a period of ~two years.

Antibody-mediated protection against SHIV challenge includes systemic clearance of distal virus.

HIV-1-specific broadly neutralizing antibodies (bNAbs) can protect rhesus monkeys against simian-human immunodeficiency virus (SHIV) challenge. However, the site of antibody interception of virus and the mechanism of antibody-mediated protection remain unclear. We administered a fully protective dose of the bNAb PGT121 to rhesus monkeys and challenged them intravaginally with SHIV-SF162P3. In PGT121-treated animals, we detected low levels of viral RNA and viral DNA in distal tissues for seven days following challenge. Viral RNA-positive tissues showed transcriptomic changes indicative of innate immune activation, and cells from these tissues initiated infection after adoptive transfer into naïve hosts. These data demonstrate that bNAb-mediated protection against a mucosal virus challenge can involve clearance of infectious virus in distal tissues.

Characterization of human immunodeficiency virus type 1 (HIV-1) containing mutations in the nucleocapsid protein at a putative HIV-1 protease cleavage site.

The HIV-1 nucleocapsid protein (NC) has been hypothesized to be cleaved by the viral protease (PR) during early infection. Characterization of viruses, with amino-acid substitutions that modulate PR cleavage of NC in vitro, was performed in cell culture. Two of the NC mutants, NCN17F and NCN17G, had decreased infectivity and exhibited severe H9 replication defects. Examination of viral DNA after infections revealed defects in reverse transcription and integration, although integration defects were cell-type dependent. However, while the defects in reverse transcription and integration correlate with lowered infectivity in a single-round of infection, they did not approach the magnitude of the replication defect measured in H9 cells over multiple rounds. Importantly, we fail to see evidence that H9 cells are re-infected with the NCN17G and NCN17F viruses 24 h after the initial infection, which suggests that the principal defect caused by these NC mutations occurs during late events of viral replication.

Human immunodeficiency virus type 1 nucleocapsid zinc-finger mutations cause defects in reverse transcription and integration.

The nucleocapsid (NC) protein from HIV-1 contains two zinc-fingers, both of which are necessary for virus replication. This is the first in-depth study that presents the effects of nucleocapsid zinc-finger substitutions on the kinetics of reverse transcription and integration. Over a 72-h time-course of infection, the quantities of viral DNA (vDNA) observed with viruses containing either the nucleocapsid His23Cys or His44Cys mutations were significantly lower than those observed in infections with virus containing wild-type NC. In addition, the kinetics of vDNA formation and loss were significantly different from wild-type. The kinetic profiles observed indicated reduced vDNA stability, as well as defects in reverse transcription and integration. Overall, the defect in integration was much more pronounced than the reverse transcription defects. This suggests that the principal reason for the replication defectiveness of these mutant viruses is impairment of integration, and thus demonstrates the critical importance of NC in HIV-1 infection.

Human immunodeficiency virus type 1 nucleocapsid zn(2+) fingers are required for efficient reverse transcription, initial integration processes, and protection of newly synthesized viral DNA.

Human immunodeficiency virus type 1 (HIV-1) containing mutations in the nucleocapsid (NC) Zn(2+) finger domains have greatly reduced infectivity, even though genome packaging is largely unaffected in certain cases. To examine replication defects, viral DNA (vDNA) was isolated from cells infected with viruses containing His-to-Cys changes in their Zn(2+) fingers (NC(H23C) and NC(H44C)), an integrase mutant (IN(D116N)), a double mutant (NC(H23C)/IN(D116N)), or wild-type HIV-1. In vitro assays have established potential roles for NC in reverse transcription and integration. In vivo results for these processes were obtained by quantitative PCR, cloning of PCR products, and comparison of the quantity and composition of vDNA generated at discrete points during reverse transcription. Quantitative analysis of the reverse transcription intermediates for these species strongly suggests decreased stability of the DNA produced. Both Zn(2+) finger mutants appear to be defective in DNA synthesis, with the minus- and plus-strand transfer processes being affected while interior portions of the vDNA remain more intact. Sequences obtained from PCR amplification and cloning of 2-LTR circle junction fragments revealed that the NC mutants had a phenotype similar to the IN mutant; removal of the terminal CA dinucleotides necessary for integration of the vDNA is disabled by the NC mutations. Thus, the loss of infectivity in these NC mutants in vivo appears to result from defective reverse transcription and integration processes stemming from decreased protection of the full-length vDNA. Finally, these results indicate that the chaperone activity of NC extends from the management of viral RNA through to the full-length vDNA.

Human cellular nucleic acid-binding protein Zn2+ fingers support replication of human immunodeficiency virus type 1 when they are substituted in the nucleocapsid protein.

A family of cellular nucleic acid binding proteins (CNBPs) contains seven Zn(2+) fingers that have many of the structural characteristics found in retroviral nucleocapsid (NC) Zn(2+) fingers. The sequence of the NH(2)-terminal NC Zn(2+) finger of the pNL4-3 clone of human immunodeficiency virus type 1 (HIV-1) was replaced individually with sequences from each of the seven fingers from human CNBP. Six of the mutants were normal with respect to protein composition and processing, full-length genomic RNA content, and infectivity. One of the mutants, containing the fifth CNBP Zn(2+) finger (CNBP-5) packaged reduced levels of genomic RNA and was defective in infectivity. There appear to be defects in reverse transcription in the CNBP-5 infections. Models of Zn(2+) fingers were constructed by using computational methods based on available structural data, and atom-atom interactions were determined by the hydropathic orthogonal dynamic analysis of the protein method. Defects in the CNBP-5 mutant could possibly be explained, in part, by restrictions of a set of required atom-atom interactions in the CNBP-5 Zn(2+) finger compared to mutant and wild-type Zn(2+) fingers in NC that support replication. The present study shows that six of seven of the Zn(2+) fingers from the CNBP protein can be used as substitutes for the Zn(2+) finger in the NH(2)-terminal position of HIV-1 NC. This has obvious implications in antiviral therapeutics and DNA vaccines employing NC Zn(2+) finger mutants.