Safety and Pharmacokinetics of Intravaginal Rings Delivering Tenofovir in Pig-Tailed Macaques

ABSTRACTAntiretroviral-based microbicides applied topically to the vagina may play an important role in protecting women from HIV infection. Incorporation of the nucleoside reverse transcriptase inhibitor tenofovir (TFV) into intravaginal rings (IVRs) for sustained mucosal delivery may lead to increased microbicide product adherence and efficacy compared with those of conventional vaginal formulations. Formulations of a novel “pod IVR” platform spanning a range of IVR drug loadings and daily release rates of TFV were evaluated in a pig-tailed macaque model. The rings were safe and exhibited sustained release at controlled rates over 28 days. Vaginal secretion TFV levels were independent of IVR drug loading and were able to be varied over 1.5 log units by changing the ring configuration. Mean TFV levels in vaginal secretions were 72.4 ± 109 μg ml−1(slow releasing) and 1.84 ± 1.97 mg ml−1(fast releasing). The mean TFV vaginal tissue concentration from the slow-releasing IVRs was 76.4 ± 54.8 μg g−1and remained at steady state 7 days after IVR removal, consistent with the long intracellular half-life of TFV. Intracellular tenofovir diphosphate (TFV-DP), the active moiety in defining efficacy, was measured in vaginal lymphocytes collected in the study using the fast-releasing IVR formulation. Mean intracellular TFV-DP levels of 446 ± 150 fmol/106cells fall within a range that may be protective of simian-human immunodeficiency virus strain SF162p3 (SHIVSF162p3) infection in nonhuman primates. These data suggest that TFV-releasing IVRs based on the pod design have potential for the prevention of transmission of human immunodeficiency virus type 1 (HIV-1) and merit further clinical investigation.

Acute-phase CD4+ T-cell proliferation and CD152 upregulation predict set-point virus replication in vaccinated simian–human immunodeficiency virus strain 89.6p-infected macaques

Human immunodeficiency virus (HIV) infection in humans and simian immunodeficiency virus (SIV) infection in macaques are accompanied by a combined early loss of CCR5 (CD195)-expressing CD4+ memory T cells, loss of T-helper function and T-cell hyperactivation, which have all been associated with development of high virus load and disease progression. Here, a cohort of vaccinated simian–human immunodeficiency virus strain 89.6p (SHIV89.6p)-infected rhesus macaques, where preferential depletion of these memory T-cell subsets does not take place and CD4+ T cells are relatively well maintained, was used to study the role of hyperactivation as an independent factor in the establishment of set-point virus load. In the acute phase of the infection, a transient loss of CD4+ T cells, as well as strong increases in expression of proliferation and activation markers on CD4+ and CD8+ T cells, together with CD152 expression on CD4+ T cells, were observed. Peak expression levels of these markers on CD4+ T cells, but not on CD8+ T cells, were correlated with high virus replication in the chronic phase of the infection. In addition, the peak expression level of these markers was correlated inversely with acute-phase, but not chronic-phase, HIV/SIV-specific gamma interferon responses. These data highlight a central role for an acute but transient CD4 decrease, as well as CD4+ T-cell activation, as independent factors for prediction of set-point levels of virus replication.

Selection of a Simian-Human Immunodeficiency Virus Strain Resistant to a Vaginal Microbicide in Macaques

ABSTRACT PSC-RANTES binds to CCR5, inhibits human immunodeficiency virus type 1 (HIV-1) entry, and has been shown as a vaginal microbicide to protect rhesus macaques from a simian-human immunodeficiency virus chimera (SHIVSF162-p3) infection in a dose-dependent manner. In this study, env gene sequences from SHIVSF162-p3-infected rhesus macaques treated with PSC-RANTES were analyzed for possible drug escape variants. Two specific mutations located in the V3 region of gp120 (K315R) and C-helical domain of gp41 (N640D) were identified in a macaque (m584) pretreated with a 100 μM dose of PSC-RANTES. These two env mutations were found throughout infection (through week 77) but were found at only low frequencies in the inoculating SHIVSF162-p3 stock and in the other SHIVSF162-p3-infected macaques. HIV-1 env genes from macaque m584 (env m584) and from inoculating SHIVSF162-p3 (env p3) were cloned into an HIV-1 backbone. Increases in 50% inhibitory concentrations to PSC-RANTES with env m584 were modest (sevenfold) and most pronounced in cells expressing rhesus macaque CCR5 as compared to human CCR5. Nonetheless, virus harboring env m584, unlike inoculating virus env p3, could replicate even at the highest tissue culture PSC-RANTES concentrations (100 nM). Dual-virus competitions revealed a dramatic increase in fitness of chimeric virus containing env m584 (K315R/N640D) over that containing env p3, but again, only in rhesus CCR5-expressing cells. This study is the first to describe the immediate selection and infection of a drug-resistant SHIV variant in the face of a protective vaginal microbicide, PSC-RANTES. This rhesus CCR5-specific/PSC- RANTES resistance selection is particularly alarming given the relative homogeneity of the SHIVSF162-p3 stock compared to the potential exposure to a heterogeneous HIV-1 population in human transmission.

Human Immunodeficiency Virus Type 1 Reverse Transcriptase Mutation Selection during In Vitro Exposure to Tenofovir Alone or Combined with Abacavir or Lamivudine

ABSTRACT Mutations selected or deselected during passage of human immunodeficiency virus strain HXB2 or resistant variants with tenofovir (TFV), abacavir (ABC), and lamivudine (3TC) differed depending on the drug combination and virus genotype. In the wild-type virus, TFV-ABC and TFV-3TC selected K65R (with reduced susceptibility to all three inhibitors) and then Y115F. TFV-containing regimens might increase K65R selection, which confers multiple nucleoside reverse transcriptase inhibitor resistance.

Qualitative T-Helper Responses to Multiple Viral Antigens Correlate with Vaccine-Induced Immunity to Simian/Human Immunodeficiency Virus Infection

ABSTRACT Evidence is accumulating that CD4+ T-helper (Th) responses play a critical role in facilitating effector responses which are capable of controlling and even preventing human immunodeficiency virus (HIV) infection. The present work was undertaken to determine whether immunization with multiple antigens influenced individual Th responses and increased protection relative to a single antigen. Rhesus macaques were primed with DNA and boosted (immune-stimulating complex-formulated protein) with a combination of regulatory and structural antigens (Tat-Env-Gag) or with Tat alone. Immunization with combined antigens reduced the magnitude of the responses to Tat compared to the single-antigen immunization. Interestingly, the Th immune responses to the individual antigens were noticeably different. To determine whether the qualitative differences in vaccine-induced Th responses correlated with vaccine efficacy, animals were challenged intravenously with simian/human immunodeficiency virus (strain SHIV89.6p) 2 months following the final immunization. Animals that developed combined Th1- and Th2-like responses to Gag and Th2 dominant Env-specific responses were protected from disease progression. Interestingly, one animal that was completely protected from infection had the strongest IFN-γ and interleukin-2 (IL-2) responses prior to challenge, in addition to very strong IL-4 responses to Gag and Env. In contrast, animals with only a marked vaccine-induced Tat-specific Th2 response (no IFN-γ) were not protected from infection or disease. These data support the rationale that effective HIV vaccine-induced immunity requires a combination of potent Th1- and Th2-like responses best directed to multiple antigens.

Coreceptor Phenotype of Natural Human Immunodeficiency Virus with Nef Deleted Evolves In Vivo, Leading to Increased Virulence

ABSTRACT The Sydney Blood Bank Cohort is a group of patients with slowly progressive infection by a human immunodeficiency virus strain containing spontaneous deletions within the nef long terminal repeat region. In 1999, 18 years after the initial infection, one of the members (D36) developed AIDS. In this work, we used an ex vivo human lymphoid cell culture system to analyze two viral isolates obtained from this patient, one prior to the onset of AIDS in 1995 and one after disease progression in 1999. Both D36 isolates were less potent in depleting CD4+ T cells than a reference dualtropic, nef-bearing viral isolate. However, the 1999 isolate was measurably more cytotoxic to CD4+ T cells than the 1995 isolate. Interestingly, although both isolates were nearly equally potent in depleting CCR5+ CD4+ T cells, the cytotoxic effect of the 1999 isolate toward CCR5− CD4+ T cells was significantly higher. Furthermore, GHOST cell infection assays and blocking experiments with the CXCR4 inhibitor AMD3100 showed that the later D36 1999 isolate could infect both CCR5+ and CCR5− CXCR4+ cells efficiently, while infection by the 1995 isolate was nearly completely restricted to CCR5+ cells. Sequence analysis of the V1/V2 and V3 regions of the viral envelope protein gp120 revealed that the more efficient CXCR4 usage of the later isolate might be caused by an additional potential N-glycosylation site in the V1/V2 loop. In conclusion, these data show that an in vivo evolution of the tropism of this nef-deleted strain toward an X4 phenotype was associated with a higher cytopathic potential and progression to AIDS.

Molecular Evolution of Human Immunodeficiency Virus env in Humans and Monkeys: Similar Patterns Occur during Natural Disease Progression or Rapid Virus Passage

ABSTRACT Neonatal rhesus macaque 95-3 was inoculated with nonpassaged simian-human immunodeficiency virus strain SHIV-vpu+, which encodes env of the laboratory-adapted human immunodeficiency virus (HIV) strain IIIB and is considered nonpathogenic. CD4+ T-cell counts dropped to <200 cells/μl within 4.6 years, and monkey 95-3 died with opportunistic infections 5.9 years postinoculation. Transfer of blood from 95-3 to two naive adult macaques resulted in high peak viral loads and rapid, persistent T-cell depletion. Progeny virus evolved in 95-3 despite high SHIV-vpu+ neutralizing antibody titers and still used CXCR4 but, in contrast to parental SHIV-vpu+, productively infected macrophages and resisted neutralization. Sequence analysis revealed three new potential glycosylation sites in gp120; another two were lost. Strikingly similar mutations were detected in a laboratory worker who progressed to AIDS after accidental HIV-IIIB infection (T. Beaumont et al., J. Virol. 75:2246-2252, 2001), thus supporting the SHIV-vpu+/rhesus macaque system as a relevant model. Similar mutations were also described after rapid passage of chimeric viruses encoding IIIB env in rhesus and pig-tailed macaques (M. Cayabyab et al., J. Virol. 73:976-984, 1999; Z. Q. Liu et al., Virology 260:295-307, 1999; S. V. Narayan et al., Virology 256:54-63, 1999; R. Raghavan et al., Brain Pathol. 7:851-861, 1997; E. B. Stephens et al., Virology 231:313-321, 1997). Thus, HIV-IIIB env evolved similarly in three different species; this selection occurred in chronically infected individuals during disease progression as well as after rapid virus passage. We postulate that evolutionary pressure led to the outgrowth of more aggressive viral variants in all three species.

Outcome of Simian-Human Immunodeficiency Virus Strain 89.6p Challenge following Vaccination of Rhesus Macaques with Human Immunodeficiency Virus Tat Protein

ABSTRACT The regulatory proteins Nef, Rev, and Tat of human immunodeficiency virus type 1 (HIV-1) are attractive targets for vaccine development, since induction of effective immune responses targeting these early proteins may best control virus replication. Here we investigated whether vaccination with biologically active Tat or inactive Tat toxoid derived from HIV-1IIIB and simian-human immunodeficiency virus (SHIV) strain 89.6p would induce protective immunity in rhesus macaques. Vaccination induced high titers of anti-Tat immunoglobulin G in all immunized animals by week 7, but titers were somewhat lower in the 89.6p Tat group. Dominant B-cell epitopes mapped to the amino terminus, the basic domain, and the carboxy-terminal region. Tat-specific T-helper responses were detected in 50% of immunized animals. T-cell epitopes appeared to map within amino acids (aa) 1 to 24 and aa 37 to 66. In addition, Tat-specific gamma interferon responses were detected in CD4+ and/or CD8+ T lymphocytes in 11 of 16 immunized animals on the day of challenge. However, all animals became infected upon intravenous challenge with 30 50% minimal infective doses of SHIV 89.6p, and there were no significant differences in viral loads or CD4+ T-cell counts between immunized and control animals. Thus, vaccination with HIV-1IIIB or SHIV 89.6p Tat or with Tat toxoid preparations failed to confer protection against SHIV 89.6p infection despite robust Tat-specific humoral and cellular immune responses in some animals. Given its apparent immunogenicity, Tat may be more effective as a component of a cocktail vaccine in combination with other regulatory and/or structural proteins of HIV-1.

Polyvalent Envelope Glycoprotein Vaccine Elicits a Broader Neutralizing Antibody Response but Is Unable To Provide Sterilizing Protection against Heterologous Simian/Human Immunodeficiency Virus Infection in Pigtailed Macaques

ABSTRACT The great difficulty in eliciting broadly cross-reactive neutralizing antibodies (NAbs) against human immunodeficiency virus type 1 (HIV-1) isolates has been attributed to several intrinsic properties of their viral envelope glycoprotein, including its complex quaternary structure, extensive glycosylation, and marked genetic variability. Most previously evaluated vaccine candidates have utilized envelope glycoprotein from a single virus isolate. Here we compare the breadth of NAb and protective immune response following vaccination of pigtailed macaques with envelope protein(s) derived from either single or multiple viral isolates. Animals were challenged with Simian/human immunodeficiency virus strain DH12 (SHIVDH12) following priming with recombinant vaccinia virus(es) expressing gp160(s) and boosting with gp120 protein(s) from (i) LAI, RF, 89.6, AD8, and Bal (Polyvalent); (ii) LAI, RF, 89.6, AD8, Bal, and DH12 (Polyvalent-DH12); (iii) 89.6 (Monovalent-89.6); and (iv) DH12 (Monovalent-DH12). Animals in the two polyvalent vaccine groups developed NAbs against more HIV-1 isolates than those in the two monovalent vaccine groups (P = 0.0054). However, the increased breadth of response was directed almost entirely against the vaccine strains. Resistance to SHIVDH12 strongly correlated with the level of NAbs directed against the virus on the day of challenge (P = 0.0008). Accordingly, the animals in the Monovalent-DH12 and Polyvalent-DH12 vaccine groups were more resistant to the SHIVDH12 challenge than the macaques immunized with preparations lacking a DH12 component (viz. Polyvalent and Monovalent-89.6) (P = 0.039). Despite the absence of any detectable NAb, animals in the Polyvalent vaccine group, but not those immunized with Monovalent-89.6, exhibited markedly lower levels of plasma virus than those in the control group, suggesting a superior cell-mediated immune response induced by the polyvalent vaccine.