Citations

ABSTRACT Hepatitis C virus (HCV) infection remains a serious public health problem worldwide. Treatments are limited, and no preventive vaccine is available. Toward developing an HCV vaccine, we engineered two recombinant measles viruses (MVs) expressing structural proteins from the prototypic HCV subtype 1a strain H77. One virus directs the synthesis of the HCV capsid (C) protein and envelope glycoproteins (E1 and E2), which fold properly and form a heterodimer. The other virus expresses the E1 and E2 glycoproteins separately, with each one fused to the cytoplasmic tail of the MV fusion protein. Although these hybrid glycoproteins were transported to the plasma membrane, they were not incorporated into MV particles. Immunization of MV-susceptible, genetically modified mice with either vector induced neutralizing antibodies to MV and HCV. A boost with soluble E2 protein enhanced titers of neutralizing antibody against the homologous HCV envelope. In animals primed with MV expressing properly folded HCV C-E1-E2, boosting also induced cross-neutralizating antibodies against two heterologous HCV strains. These results show that recombinant MVs retain the ability to induce MV-specific humoral immunity while also eliciting HCV neutralizing antibodies, and that anti-HCV immunity can be boosted with a single dose of purified E2 protein. The use of MV vectors could have advantages for pediatric HCV vaccination.

ABSTRACT Measles remains a leading cause of death worldwide among children because it suppresses immune function. The measles virus (MV) P gene encodes three proteins (P, V, and C) that interfere with innate immunity, controlling STAT1, STAT2, mda5, and perhaps other key regulators of immune function. We identified here three residues in the shared domain of the P and V proteins—tyrosine 110, valine 112, and histidine 115—that function to retain STAT1 in the cytoplasm and inhibit interferon transcription. This information was used to generate a recombinant measles virus unable to antagonize STAT1 function (STAT1-blind MV) differing only in these three residues from a wild-type strain of well-defined virulence. This virus was used to assess the relevance of P and V interactions with STAT1 for virulence in primates. When a group of six rhesus monkeys ( Macaca mulatta ) was inoculated intranasally with STAT1-blind MV, viremia was short-lived, and the skin rash and other clinical signs observed with wild-type MV were absent. The STAT1-blind virus less efficiently controlled the inflammatory response, as measured by enhanced transcription of interleukin-6 and tumor necrosis factor alpha in peripheral blood mononuclear cells from infected hosts. Importantly, neutralizing antibody titers and MV-specific T-cell responses were equivalent in hosts infected with either virus. These findings indicate that efficient MV interactions with STAT1 are required to sustain virulence in a natural host by controlling the inflammatory response against the virus. They also suggest that selectively STAT1-blind MV may have utility as vectors for targeted oncolysis and vaccination.

ABSTRACTThe signaling lymphocytic activation molecule (SLAM; CD150) is the immune cell receptor for measles virus (MV). To assess the importance of the SLAM-MV interactions for virus spread and pathogenesis, we generated a wild-type IC-B MV selectively unable to recognize human SLAM (SLAM-blind). This virus differs from the fully virulent wild-type IC-B strain by a single arginine-to-alanine substitution at amino acid 533 of the attachment protein hemagglutinin and infects cells through SLAM about 40 times less efficiently than the isogenic wild-type strain.Ex vivo, this virus infects primary lymphocytes at low levels regardless of SLAM expression. When a group of six rhesus monkeys (Macaca mulatta) was inoculated intranasally with the SLAM-blind virus, no clinical symptoms were documented. Only one monkey had low-level viremia early after infection, whereas all the hosts in the control group had high viremia levels. Despite minimal, if any, viremia, all six hosts generated neutralizing antibody titers close to those of the control monkeys while MV-directed cellular immunity reached levels at least as high as in wild-type-infected monkeys. These findings prove formally that efficient SLAM recognition is necessary for MV virulence and pathogenesis. They also suggest that the selectively SLAM-blind wild-type MV can be developed into a vaccine vector.

ABSTRACT The widely used hepatitis B virus (HBV) vaccine is based on three doses of hepatitis B surface antigen (HBsAg) protein. We previously showed that vectored measles viruses (MV) expressing HBsAg retain measles vaccine function in monkeys but do not induce a protective anti-HBs response in all animals. We show here that a single dose of HBsAg protein following a three-dose vaccination regimen with an optimized HBsAg-expressing MV elicits protective anti-HBs responses in all four vaccinated Rhesus monkeys. Vaccination strategies coupling the effective, long-term immunity elicited by the high-coverage MV vaccine to prophylactic HBV immunity are discussed.

ABSTRACT Hepatitis B virus (HBV) acute and chronic infections remain a major worldwide health problem. Towards developing an anti-HBV vaccine with single-dose scheme potential, we engineered infectious measles virus (MV) genomic cDNAs with a vaccine strain background and expression vector properties. Hepatitis B surface antigen (HBsAg) expression cassettes were inserted into this cDNA and three MVs expressing HBsAg at different levels generated. All vectored MVs, which secrete HBsAg as subviral particles, elicited humoral responses in MV-susceptible genetically modified mice. However, small differences in HBsAg expression elicited vastly different HBsAg antibody levels. The two vectors inducing the highest HBsAg antibody levels were inoculated into rhesus monkeys ( Macaca mulatta ). After challenge with a pathogenic MV strain (Davis 87 ), control naive monkeys showed a classic measles rash and high viral loads. In contrast, all monkeys immunized with vaccine or a control nonvectored recombinant vaccine or HBsAg-expressing vectored MV remained healthy, with low or undetectable viral loads. After a single vaccine dose, only the vector expressing HBsAg at the highest levels elicited protective levels of HBsAg antibodies in two of four animals. These observations reveal an expression threshold for efficient induction of HBsAg humoral immune responses. This threshold is lower in mice than in macaques. Implications for the development of divalent vaccines based on live attenuated viruses are discussed.