Prime-boost vaccination with recombinant mumps virus and recombinant vesicular stomatitis virus vectors elicits an enhanced human immunodeficiency virus type 1 Gag-specific cellular immune response in rhesus macaques.

Intramuscular inoculation of rhesus macaques with one or more doses of recombinant vesicular stomatitis virus (rVSV) expressing human immunodeficiency virus type 1 (HIV-1) Gag (rVSVgag) typically elicits peak cellular immune responses of 500 to 1,000 gamma interferon (IFN-gamma) enzyme-linked immunospots (ELISPOTS)/10(6) peripheral blood lymphocytes (PBL). Here, we describe the generation of a novel recombinant mumps virus (rMuV) expressing HIV-1 Gag (rMuVgag) and measure the Gag-specific cellular immune responses detected in rhesus macaques following vaccination with a highly attenuated form of rVSV expressing HIV-1 Gag (rVSVN4CT1gag1) and rMuVgag in various prime-boost combinations. Notably, peak Gag-specific cellular immune responses of 3,000 to 3,500 ELISPOTS/10(6) PBL were detected in macaques that were primed with rMuVgag and boosted with rVSVN4CT1gag1. Lower peak cellular immune responses were detected in macaques that were primed with rVSVN4CT1gag1 and boosted with rMuVgag, although longer-term gag-specific responses appeared to remain higher in this group of macaques. These findings indicate that rMuVgag may significantly enhance Gag-specific cellular immune responses when administered with rVSVN4CT1gag1 in heterologous prime-boost regimens.

The potential for CYP2D6 inhibition screening using a novel scintillation proximity assay-based approach.

High throughput inhibition screens for human cytochrome P450s (CYPs) are being used in preclinical drug metabolism to support drug discovery programs. The versatility of scintillation proximity assay (SPA) technology has enabled the development of a homogeneous high throughput assay for cytochrome P450 2D6 (CYP2D6) inhibition screen using [O-methyl-(14)C]dextromethorphan as substrate. The basis of the assay was the trapping of the O-demethylation product, [(14)C]HCHO, on SPA beads. Enzyme kinetics parameters V(max) and apparent K(m), determined using pooled human liver microsomes and microsomes from baculovirus cells coexpressing human CYP2D6 and NADPH-cytochrome P450 reductase, were 245 pmol [(14)C]HCHO/min/mg protein and 11 microM, and 27 pmol [(14)C]HCHO/min/pmol and 1.6 microM, respectively. In incubations containing either pooled microsomes or recombinant CYP2D6, [(14)C]dextromethorphan O-demethylase activity was inhibited in the presence of quinidine (IC(50) = 1.0 microM and 20 nM, respectively). By comparison, inhibitors selective for other CYP isoforms were relatively weak (IC(50) > 25 microM). In agreement, a selective CYP2D6 inhibitory monoclonal antibody caused greater than 90% inhibition of [(14)C]dextromethorphan O-demethylase activity in human liver microsomes, whereas CYP2C9/19- and CYP3A4/5-selective antibodies elicited a minimal inhibitory effect. SPA-based [(14)C]dextromethorphan O-demethylase activity was also shown to correlate (r(2) = 0.6) with dextromethorphan O-demethylase measured by high-performance liquid chromatography in a bank of human liver microsomes (N = 15 different organ donors). In a series of known CYP2D6 inhibitors/substrates, the SPA-based assay resolved potent inhibitors (IC(50) < 2 microM) from weak inhibitors (IC(50) >or= 20 microM). It is concluded that the SPA-based assay described herein is suitable for CYP2D6 inhibition screening using either native human liver microsomes or cDNA-expressed CYP2D6.

A novel method for detection and ex vivo expansion of HIV type 1-specific cytolytic T lymphocytes.

Studies have shown that cytolytic T lymphocyte (CTL) responses may be critical to the clearance of the early viremia in acute HIV-1 infection. It is likely that these cells play an important role in prolonging the asymptomatic phase of the infection. Although HIV-1-specific CTL activity can be detected in direct assays of freshly isolated peripheral blood lymphocytes (PBL) from some infected individuals, this method fails to detect CTL that are present at low frequency and resting, memory CTL. For these reasons, direct CTL assays on PBL from seropositive individuals may underestimate the level of CTL immunity. As part of ongoing investigations of CTL activity in HIV-1-infected individuals, we developed a novel strategy for the detection and ex vivo expansion of HIV-1-specific CTL. This technique involves selective stimulation of PBL from seropositive individuals with autologous Epstein-Barr virus (EBV)-transformed, B-lymphoblastoid cell lines (B-LCL) infected with vaccinia vectors expressing various HIV-1 genes. Prior to their use for in vitro stimulation, B-LCL are treated with psoralen and UV light to inactivate vaccinia virus. After 1 week of stimulation, CTL activity in stimulated cultures is measured in a standard 51Cr release assay. This ex vivo expansion method can selectively increase the bulk culture CTL activity against env, gag and nef, even in some seropositive individuals with low CD4 counts and little evidence of HIV-1-specific CTL in assays of freshly isolated PBL. These expanded CTL are predominantly of the CD8+ phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Human immunodeficiency virus type 1 envelope protein endocytosis mediated by a highly conserved intrinsic internalization signal in the cytoplasmic domain of gp41 is suppressed in the presence of the Pr55gag precursor protein.

The mechanisms involved in the incorporation of viral glycoproteins into virions are incompletely understood. For retroviruses, incorporation may involve interactions between the Gag proteins of these viruses and the cytoplasmic domains of the relevant envelope (Env) glycoproteins. Recent studies have identified within the cytoplasmic tail of the human immunodeficiency virus type 1 (HIV-1) Env protein a tyrosine-containing internalization motif similar to those found in the cytoplasmic domains of certain cell surface proteins that undergo rapid constitutive endocytosis in clathrin-coated pits. Given that surface expression of the HIV-1 Env protein is essential for the production of infectious virus, the presence of this internalization motif is surprising. We show here that in contrast to the rapid rate of Env protein internalization observed in cells expressing the Env protein in the absence of other HIV-1 proteins, the rate of internalization of Env protein from the surfaces of HIV-1-infected cells is extremely slow. The presence of the Pr55gag precursor protein is necessary and sufficient for inhibition of Env protein internalization, while a mutant Pr55-gag that is incapable of mediating Env incorporation into virions is also unable to inhibit endocytosis of the Env protein. The failure of the Env protein to undergo endocytosis from the surface of an HIV-1-infected cell may reflect the fact that the proposed interaction of the matrix domain of the Gag protein with Env during assembly prevents the interaction of Env with host adaptin molecules that recruit plasma membrane molecules such as the transferrin receptor into clathrin-coated pits. When the normal ratio of Gag and Env proteins in the infected cells is altered by overexpression of Env protein, this mechanism allows removal of excess Env protein from the cell surface. Taken together, these results suggest that a highly conserved system to reduce surface levels of the Env protein functions to remove Env protein that is not associated with Gag and that is therefore not destined for incorporation into virions. This mechanism for the regulation of surface levels of Env protein may protect infected cells from Env-dependent cytopathic effects or Env-specific immune responses.

Altered metabolism in the ex vivo remnant kidney. I. Effects of time, substrate and perfusion pressure.

Oxygen consumption is increased in the rat remnant kidney (RK), but the basis of this enhanced metabolic activity has not been defined fully. To characterize the hypermetabolism further, isolated RK and normal kidneys (NK) were perfused using a range of perfusion pressures and substrates, and at varying times after 5/6 nephrectomy. Altered and increased RK metabolism was found as early as 1 week after 5/6 nephrectomy. The rate of net glucose consumption was higher in RK than NK (e.g., 0-30 min, 2.42 +/- 0.28 vs. 1.21 +/- 0.33 mumol.min-1 x g-1), a difference not explained by changes in oxygen delivery or glycosuria. Ammonia production was significantly greater early in perfusion in RK than NK. Calculated nephron oxygen consumption (QO2) was greater in RK than NK for all substrates tested (e.g., pyruvate 5 mM: 552.3 +/- 43.1 vs. 173.3 +/- 25.6 pmol.min-1, p < 0.001). When considered together, site I mitochondrial substrates supported QO2 and net sodium reabsorption (TNa+) better than site II substrates. In RK, QO2 did not change with increasing perfusion pressure, and TNa+ rose only slightly for pressures > or = 120 mm Hg. In summary, RK hypermetabolism is characterized by increased oxygen consumption, glycolysis and ammoniagenesis, is not substrate-specific and does not appear to be an artefact of the altered physiology of remnant perfusion.

The human immunodeficiency virus type 1 gag gene encodes an internal ribosome entry site.

Several retroviruses have recently been shown to promote translation of their gag gene products by internal ribosome entry. In this report, we show that mRNAs containing the human immunodeficiency virus type 1 (HIV-1) gag open reading frame (ORF) exhibit internal ribosome entry site (IRES) activity that can promote translational initiation of Pr55(gag). Remarkably, this IRES activity is driven by sequences within the gag ORF itself and is not dependent on the native gag 5'-untranslated region (UTR). This cap-independent mechanism for Pr55(gag) translation may help explain the high levels of translation of this protein in the face of major RNA structural barriers to scanning ribosomes found in the gag 5' UTR. The gag IRES activity described here also drives translation of a novel 40-kDa Gag isoform through translational initiation at an internal AUG codon found near the amino terminus of the Pr55(gag) capsid domain. Our findings suggest that this low-abundance Gag isoform may be important for wild-type replication of HIV-1 in cultured cells. The activities of the HIV-1 gag IRES may be an important feature of the HIV-1 life cycle and could serve as a novel target for antiretroviral therapeutic strategies.

Use of major histocompatibility complex class I/peptide/beta2M tetramers to quantitate CD8(+) cytotoxic T lymphocytes specific for dominant and nondominant viral epitopes in simian-human immunodeficiency virus-infected rhesus monkeys.

To evaluate the impact of the diversity of antigen recognition by T lymphocytes on disease pathogenesis, we must be able to identify and analyze simultaneously cytotoxic T-lymphocyte (CTL) responses specific for multiple viral epitopes. Many of the studies of the role of CD8(+) CTLs in AIDS pathogenesis have been done with simian immunodeficiency virus (SIV)- and simian-human immunodeficiency virus (SHIV)-infected rhesus monkeys. These studies have frequently made use of the well-defined SIV Gag CTL epitope p11C,C-M presented to CTL by the HLA-A homologue molecule Mamu-A*01. In the present study we identified and fine mapped two novel Mamu-A*01-restricted CTL epitopes: the SIVmac Pol-derived epitope p68A (STPPLVRLV) and the human immunodeficiency virus type 1 (HIV-1) Env-derived p41A epitope (YAPPISGQI). The frequency of CD8(+) CTLs specific for the p11C,C-M, p68A, and p41A epitopes was quantitated in the same animals with a panel of tetrameric Mamu-A*01/peptide/beta2m complexes. All SHIV-infected Mamu-A*01(+) rhesus monkeys tested had a high frequency of SIVmac Gag-specific CTLs to the p11C,C-M epitope. In contrast, only a fraction of the monkeys tested had detectable CTLs specific for the SIVmac Pol p68A and HIV-1 Env p41A epitopes, and these responses were detected at very low frequencies. Thus, the p11C,C-M-specific CD8(+) CTL response is dominant and the p41A- and p68A-specific CD8(+) CTL responses are nondominant. These results indicate that CD8(+) CTL responses to dominant CTL epitopes can be readily quantitated with the tetramer technology; however, CD8(+) CTL responses to nondominant epitopes, due to the low frequency of these epitope-specific cells, may be difficult to detect and quantitate by this approach.

Induction of human immunodeficiency virus type 1 (HIV-1)-specific cytolytic T lymphocyte responses in seronegative adults by a nonreplicating, host-range-restricted canarypox vector (ALVAC) carrying the HIV-1MN env gene.

CD8+ cytolytic T lymphocytes (CTL) are likely to be an important component of effective vaccines against human immunodeficiency virus type 1 (HIV-1). CTL can be induced most effectively with live virus vectors. However, because of concerns about the safety of such vectors, a nonreplicating canarypox vector (ALVAC) capable of expressing foreign genes in mammalian cells has been developed. This study evaluated the capacity of an ALVAC vector expressing the HIV-1MN envelope (env) glycoprotein to induce HIV-1-specific CTL in seronegative volunteers. Protocols were designed to determine whether immunization with ALVAC alone or in combination with subunit boosting could induce CTL in vaccinia-immune and -naive volunteers. A simple method for antigen-specific in vitro stimulation was used to detect CTL responses in HIV-1-seronegative vaccine recipients. The results indicate that low doses of a nonreplicating virus vector alone can elicit both CD4+ and CD8+ HIV-1-specific CTL in a subset of seronegative volunteers.

Simian immunodeficiency virus (SIV) gag DNA-vaccinated rhesus monkeys develop secondary cytotoxic T-lymphocyte responses and control viral replication after pathogenic SIV infection.

The potential contribution of a plasmid DNA construct to vaccine-elicited protective immunity was explored in the simian immunodeficiency virus (SIV)/macaque model of AIDS. Making use of soluble major histocompatibility class I/peptide tetramers and peptide-specific killing assays to monitor CD8(+) T-lymphocyte responses to a dominant SIV Gag epitope in genetically selected rhesus monkeys, a codon-optimized SIV gag DNA vaccine construct was shown to elicit a high-frequency SIV-specific cytotoxic T-lymphocyte (CTL) response. This CTL response was demonstrable in both peripheral blood and lymph node lymphocytes. Following an intravenous challenge with the highly pathogenic viral isolate SIVsm E660, these vaccinated monkeys developed a secondary CTL response that arose with more rapid kinetics and reached a higher frequency than did the postchallenge CTL response in control plasmid-vaccinated monkeys. While peak plasma SIV RNA levels were comparable in the experimentally and control-vaccinated monkeys during the period of primary infection, the gag plasmid DNA-vaccinated monkeys demonstrated better containment of viral replication by 50 days following SIV challenge. These findings indicate that a plasmid DNA vaccine can elicit SIV-specific CTL responses in rhesus monkeys, and this vaccine-elicited immunity can facilitate the generation of secondary CTL responses and control of viral replication following a pathogenic SIV challenge. These observations suggest that plasmid DNA may prove a useful component of a human immunodeficiency virus type 1 vaccine.

Interaction of diclofenac and quinidine in monkeys: stimulation of diclofenac metabolism.

The cytochrome P-450 (CYP)3A4-mediated metabolism of diclofenac is stimulated in vitro by quinidine. A similar effect is observed in incubations with monkey liver microsomes. We describe an in vivo interaction of diclofenac and quinidine that leads to enhanced clearance of diclofenac in monkeys. After a dose of diclofenac via portal vein infusion at 0.055 mg/kg/h, steady-state systemic plasma drug concentrations in three male rhesus monkeys were 87, 104, and 32 ng/ml, respectively (control). When diclofenac was coadministered with quinidine (0.25 mg/kg/h) via the same route, the corresponding plasma diclofenac concentrations were 50, 59, and 18 ng/ml, representing 57, 56, and 56% of control values, respectively. In contrast, steady-state systemic diclofenac concentrations in the same three monkeys were elevated 1.4 to 2.5 times when the monkeys were pretreated with L-754,394 (10 mg/kg i.v.), an inhibitor of CYP3A. Further investigation indicated that the plasma protein binding (>99%) and blood/plasma ratio (0.7) of diclofenac remained unchanged in the presence of quinidine. Therefore, the decreases in plasma concentrations of diclofenac after a combined dose of diclofenac and quinidine are taken to reflect increased hepatic clearance of the drug, presumably resulting from the stimulation of CYP3A-catalyzed oxidative metabolism. Consistent with this proposed mechanism, a 2-fold increase in the formation of 5-hydroxydiclofenac derivatives was observed in monkey hepatocyte suspensions containing diclofenac and quinidine. Stimulation of diclofenac metabolism by quinidine was diminished when monkey liver microsomes were pretreated with antibodies against CYP3A. Subsequent kinetic studies indicated that the K(m) value for the CYP-mediated conversion of diclofenac to its 5-hydroxy derivatives was little changed (75 versus 59 microM), whereas V(max) increased 2.5-fold in the presence of quinidine. These data suggest that the catalytic capacity of monkey hepatic CYP3A toward diclofenac metabolism is enhanced by quinidine.

Elicitation of high-frequency cytotoxic T-lymphocyte responses against both dominant and subdominant simian-human immunodeficiency virus epitopes by DNA vaccination of rhesus monkeys.

Increasing evidence suggests that the generation of cytotoxic T-lymphocyte (CTL) responses specific for a diversity of viral epitopes will be needed for an effective human immunodeficiency virus type 1 (HIV-1) vaccine. Here, we determine the frequencies of CTL responses specific for the simian immunodeficiency virus Gag p11C and HIV-1 Env p41A epitopes in simian-human immunodeficiency virus (SHIV)-infected and vaccinated rhesus monkeys. The p11C-specific CTL response was high frequency and dominant and the p41A-specific CTL response was low frequency and subdominant in both SHIV-infected monkeys and in monkeys vaccinated with recombinant modified vaccinia virus Ankara vectors expressing these viral antigens. Interestingly, we found that plasmid DNA vaccination led to high-frequency CTL responses specific for both of these epitopes. These data demonstrate that plasmid DNA may be useful in eliciting a broad CTL response against multiple epitopes.