Replication and Excretion of the Live Attenuated Tetravalent Dengue Vaccine CYD-TDV in a Flavivirus-Naive Adult Population: Assessment of Vaccine Viremia and Virus Shedding.

Background: We assessed replication and excretion of the live attenuated tetravalent dengue vaccine (CYD-TDV) into biological fluids following vaccination in dengue-naive adults in Australia. Methods: Vaccinal viremia/shedding was assessed in a subset of participants enrolled in a lot-to-lot consistency study; 95 participants received 3 subcutaneous doses of CYD-TDV from phase 2/3 lots of the vaccine, and 8 received placebo; doses were administered 6 months apart. Quantitative reverse-transcription polymerase chain reaction (qR-PCR) analysis was used to initially detect the yellow fever virus (YFV) core protein gene in the backbone of CYD-TDV in serum, saliva and urine, followed by serotype-specific qRT-PCR analysis of samples positive for YFV by qRT-PCR (lower limit of detection, 5.16 GEq/mL). Results: YFV viremia was detected by qRT-PCR in 69.5% of participants (66 of 95) who received CYD-TDV, mainly 6-14 days after injection 1. The serotypes detected were serotype 4 (in 68.2% of participants [45 of 95]), serotype 3 (in 19.7% [13 of 95]), and serotype 1 (in 12.1% [8 of 95]); serotype 2 was not detected. None of the placebo recipients had vaccinal viremia/shedding. No participants had detectable viral shedding into saliva at levels above the lower limit of quantitation. Two participants had low-level viral shedding (serotype 3) in urine (5.47 and 5.77 GEq/mL). None of the participants with viremia or shedding experienced concomitant fever. Conclusions: Low-level vaccinal viremia may occur following vaccination with CYD-TDV, but this is not associated with any symptom or adverse event. Clinical Trials Registration: NCT01134263.

Safety and immunogenicity of a recombinant tetravalent dengue vaccine in 9-16 year olds: a randomized, controlled, phase II trial in Latin America.

BACKGROUND: The dengue virus is a member of the Flavivirus (FV) genus, which also includes the yellow fever virus. Dengue disease is caused by any 1 of 4 dengue virus serotypes and is a serious public health concern in Latin America. This study evaluated the safety and immunogenicity of a candidate recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) in 9-16 year olds in Latin America. METHODS: In this randomized, blinded, controlled study, volunteers received either 3 doses of CYD-TDV (n = 401) or placebo as first and second injection and tetanus/diphtheria/acellular pertussis vaccine as third injection (n = 199) at 0, 6 and 12 months. Adverse events were documented. Plaque reduction neutralization test antibody titers against the 4 CYD-TDV parental strains were measured before and 28 days after each dose. Seropositivity was defined as antibody titers ≥10 1/dil. RESULTS: The number of adverse reactions decreased after each successive CYD-TDV dose. After each CYD-TDV dose, antibody titers against all 4 serotypes were higher than baseline and respective predose titers. After the third dose of CYD-TDV, 100%, 98.6% and 93.4% of participants were seropositive for at least 2, at least 3 or all 4 serotypes, respectively. Higher antibody titers were observed in participants in the CYD-TDV group who were FV-seropositive at baseline compared with those who were FV-seronegative. CONCLUSIONS: CYD-TDV had a favorable safety profile and elicited antibody responses against all 4 dengue virus serotypes in 9-16 year olds in Latin America. These findings support the continued development of CYD-TDV.

An unusual syncytia-inducing human immunodeficiency virus type 1 primary isolate from the central nervous system that is restricted to CXCR4, replicates efficiently in macrophages, and induces neuronal apoptosis.

Macrophage/microglia cells are the principal targets for human immunodeficiency virus type 1 (HIV-1) in the central nervous system (CNS). Prototype HIV-1 isolates from the CNS are macrophage (M)-tropic, non-syncytia-inducing (NSI), and use CCR5 for entry (R5 strains), but whether syncytia-inducing (SI) CXCR4-using X4 strains might play a role in macrophage/microglia infection and neuronal injury is unknown. To explore the range of features among HIV-1 primary isolates from the CNS, the authors analyzed an HIV-1 strain (TYBE) from cerebrospinal fluid of an individual with acquired immunodeficiency syndrome (AIDS) that was unusual because it was SI. Like other CNS isolates, HIV-1/TYBE replicated to high level in primary human macrophages, but, in contrast to CNS prototypes, TYBE used CXCR4 exclusively to infect macrophages. A functional TYBE env clone confirmed the X4 phenotype and displayed a highly charged V3 sequence typical of X4 strains. Supernatant from TYBE-infected primary human macrophages induced apoptosis of neurons. Thus, TYBE represents a novel type of CNS-derived HIV-1 isolate that is CXCR4-restricted yet replicates efficiently in macrophages and induce neuronal injury. These results demonstrate that HIV-1 variants in the CNS may possess a broader range of biological characteristics than generally appreciated, raise the possibility that X4 strains may participate in AIDS neuropathogenesis, and provide a prototype clade B HIV-1 strain that replicates efficiently in primary macrophages through the exclusive use of CXCR4 as a coreceptor.

HIV-1 entry and entry inhibitors as therapeutic agents.

Defining the mechanisms of HIV-1 entry has enabled the rational design of strategies aimed at interfering with the process. This article delineates what is currently understood about HIV-1 entry, as a window through which to understand what will likely be the next major group of antiretroviral therapeutics. These exciting new approaches offer the promise of adding viral entry to reverse transcription and protein processing as steps to block in the viral life cycle. Several principles learned with other antiretroviral drugs are sure to be valid for entry antagonists, whereas other considerations may be unique to this group of agents. There is no agent to which HIV-1 has not been able to acquire resistance and this is likely to remain the case. Multiple rounds of viral replication are required to generate the genetic diversity that forms the basis of resistance. Combination therapy in which replication is maximally suppressed will remain a cornerstone of treatment with entry inhibitors, as with other agents. Furthermore, the coreceptor specificity of some entry and fusion inhibitors argues that combinations will likely be needed to broaden the effective range of susceptible viral variants. Finally, the targeting of multiple steps within the entry process has the potential for synergy. The fusion inhibitor T20 and CXCR4 antagonist AMD3100 are synergistic in vitro at blocking infection of PBMC with clinical isolates [115] and T20 combined with the CD4 inhibitor PRO 542 have synergistic in vitro effects, with more than 10-fold greater inhibition of R5, X4, and R5X4 strains than either agent alone [116]. Entry antagonists raise other, unique issues. As discussed previously, the theoretic concern exists that blocking CCR5 could enhance the emergence of CXCR4-using variants and possibly accelerate disease. So far, in vitro selection for variants resistant to the CCR5 antagonist SCH-C in PBMC (which express both CCR5 and CXCR4) has resulted in mutants that were resistant to the blocker but still used CCR5. Alternatively, because many HIV-1 strains have the capacity to use several other chemokine or orphan receptors for entry, blocking both CCR5 and CXCR could lead to a variant that uses one of these other molecules in place of the principal coreceptors, although data in vitro so far suggest that this is unlikely [13,14]. This new class of antiviral drugs offers great promise but also novel concerns, and careful analysis of viruses that arise with their use in vivo is essential.