Rabies Virus Vaccine Research Articles

Protective Vaccine-Induced CD4+T Cell-Independent B Cell Responses against Rabies Infection

A major goal in rabies virus (RV) research is to develop a single-dose postexposure prophylaxis (PEP) that would simplify vaccination protocols, reduce costs associated with rabies prevention in humans, and save lives. Live replication-deficient RV-based vaccines are emerging as promising single-dose vaccines to replace currently licensed inactivated RV-based vaccines. Nonetheless, little is known about how effective B cells develop in response to live RV-based vaccination. Understanding this fundamental property of rabies immunology may help in developing a single-dose RV vaccine. Typically, vaccines induce B cells secreting high-affinity, class-switched antibodies during germinal center (GC) reactions; however, there is a lag time between vaccination and the generation of GC B cells. In this report, we show that RV-specific antibodies are detected in mice immunized with live but not inactivated RV-based vaccines before B cells displaying a GC B cell phenotype (B220(+)GL7(hi)CD95(hi)) are formed, indicating a potential role for T cell-independent and early extrafollicular T cell-dependent antibody responses in the protection against RV infection. Using two mouse models of CD4(+) T cell deficiency, we show that B cells secreting virus-neutralizing antibodies (VNAs) are induced via T cell-independent mechanisms within 4 days postimmunization with a replication-deficient RV-based vaccine. Importantly, mice that are completely devoid of T cells (B6.129P2-Tcrβ(tm1Mom) Tcrδ(tm1Mom)/J) show protection against pathogenic challenge shortly after immunization with a live replication-deficient RV-based vaccine. We show that vaccines that can exploit early pathways of B cell activation and development may hold the key for the development of a single-dose RV vaccine wherein the rapid induction of VNA is critical.

A replication-deficient rabies virus vaccine expressing Ebola virus glycoprotein is highly attenuated for neurovirulence

We are developing inactivated and live-attenuated rabies virus (RABV) vaccines expressing Ebola virus (EBOV) glycoprotein for use in humans and endangered wildlife, respectively. Here, we further characterize the pathogenesis of the live-attenuated RABV/EBOV vaccine candidates in mice in an effort to define their growth properties and potential for safety. RABV vaccines expressing GP (RV-GP) or a replication-deficient derivative with a deletion of the RABV G gene (RVΔG-GP) are both avirulent after intracerebral inoculation of adult mice. Furthermore, RVΔG-GP is completely avirulent upon intracerebral inoculation of suckling mice unlike parental RABV vaccine or RV-GP. Analysis of RVΔG-GP in the brain by quantitative PCR, determination of virus titer, and immunohistochemistry indicated greatly restricted virus replication. In summary, our findings indicate that RV-GP retains the attenuation phenotype of the live-attenuated RABV vaccine, and RVΔG-GP would appear to be an even safer alternative for use in wildlife or consideration for human use.

Further characterization of the immune response in mice to inactivated and live rabies vaccines expressing Ebola virus glycoprotein

We have previously developed (a) replication-competent, (b) replication-deficient, and (c) chemically inactivated rabies virus (RABV) vaccines expressing Ebola virus (EBOV) glycoprotein (GP) that induce humoral immunity against each virus and confer protection from both lethal RABV and mouse-adapted EBOV challenge in mice. Here, we expand our investigation of the immunogenic properties of these bivalent vaccines in mice. Both live and killed vaccines induced primary EBOV GP-specific T-cells and a robust recall response as measured by interferon-γ ELISPOT assay. In addition to cellular immunity, an effective filovirus vaccine will likely require a multivalent humoral immune response against multiple virus species. As a proof-of-principle experiment, we demonstrated that inactivated RV-GP could be formulated with another inactivated RABV vaccine expressing the nontoxic fragment of botulinum neurotoxin A heavy chain (HC50) without a reduction in immunity to each component. Finally, we demonstrated that humoral immunity to GP could be induced by immunization of mice with inactivated RV-GP in the presence of pre-existing immunity to RABV. The ability of these novel vaccines to induce strong humoral and cellular immunity indicates that they should be further evaluated in additional animal models of infection.

Preparation and identification of anti-rabies virus monoclonal antibodies.

To provide a foundation for the development of rapid and specific methods for the diagnosis of rabies virus infection, anti-rabies virus monoclonal antibodies were prepared and rabies virus nucleoprotein and human rabies virus vaccine strain (PV strain) were used as immunogens to immunize 6–8 week old female BALB/c mice. Spleen cells and SP2/0 myeloma cells were fused according to conventional methods: the monoclonal cell strains obtained were selected using the indirect immunofluorescence test; this was followed by preparation of monoclonal antibody ascitic fluid; and finally, systematic identification of subclass, specificity and sensitivity was carried out. Two high potency and specific monoclonal antibodies against rabies virus were obtained and named 3B12 and 4A12, with ascitic fluid titers of 1:8000 and 1:10000, respectively. Both belonged to the IgG2a subclass. These strains secrete potent, stable and specific anti-rabies virus monoclonal antibodies, which makes them well suited for the development of rabies diagnosis reagents.

Analysis of the genetic differences in the nucleoprotein between rabies virus and its vaccine strains in Guizhou province from year 2005 to 2010

This study was to explore the differences in the nucleoprotein gene between rabies virus (RABV) and its vaccine strains in Guizhou province from year 2005 to 2010. Samples from 4 rabies patients and cerebral tissue samples of 28 rabies infected dogs were collected from different districts in Guizhou province between year 2005 and 2010. Direct Immunofluorescence Assay (DFA) and RT-nested PCR assay were applied to detect the overall length of N gene sequence. Meanwhile, based on the comparison between the homology and phylogenetic tree, the differences in N gene sequence between the prevalent RABV and the RABV vaccine strains collected from NCBI database in these years. According to DFA and RT-nested PCR assay, the antigen and nucleic acid of the 21 dogs and 4 human samples were both confirmed positive; whose full length of N gene sequences were both 1353 bp. The homological analysis showed that the 25 strains of RABV virus and the RABV type I virus stored by GenBank database shared a high homology in N gene nucleotide and amino acid sequences, which were 89%-100% and 98%-100%, respectively. Besides, the homology between the 25 strains of RABV virus and its vaccines in nucleotide and amino acid sequences were separately 86%-95% and 96%-100%. The N gene of vaccines for livestock shared the highest homology with HEP-Flury strain in the nucleotide and amino acid, which were 88%-89% and 98%-99%, respectively. The vaccines for human use showed its greatest homology with the CTN strain in nucleotide (86%-100%) and amino acid (96%-100%). The phylogenetic tree analysis indicated that the 25 strains of RABV virus, RABV type I virus and the CTN vaccine strains constituted one individual cluster, which was least different from the CTN vaccine for human use. The prevalent RABV virus, the vaccine HEP-Flury for livestock and the vaccine CTN for human use were found to be highly similar in N gene expression in Guizhou province from 2005 to 2010.

Assessment of inactivated human rabies vaccines: Biochemical characterization and genetic identification of virus strains

The World Health Organization (WHO) recommends the periodic evaluation of the purity of the cell lines used in the production of rabies vaccines, as well as the antigenic identity of the virus strains. Here, we analyzed seventeen marketed inactivated human rabies virus vaccines for viral and non-viral proteins by SDS-PAGE and Coomassie/silver staining. Mass spectrometric analysis of an abundant 60–70kDa signal indicated that in most vaccines serum albumin of human origin (HSA) was the major component. Quantification of HSA in the vaccines revealed a mean concentration of 22mg HSA/dose in all tested PVRV (purified vero cell rabies vaccine), HDCV (human diploid cell rabies vaccine) and PHK (primary hamster kidney) vaccines. In contrast, 1000-fold lower HSA levels and no HSA were detected in PCECV (purified chick embryo cell-culture vaccine) and PDEV (duck embryo rabies vaccine), respectively. Western blot analyses further confirmed a high bias in the HSA content, whereas the virus protein levels were rather similar in all tested vaccines. In addition, the vaccine viruses were sequenced within the N- and G-genes to identify the strain. In the majority of sequenced vaccines, the declared vaccine strain was confirmed. However, some discrepancies in the genetic identification were observed, supporting WHO's recommendation for the molecular characterization of vaccine seed strains. This research highlights the variation in purity found between different human rabies virus vaccines, and suggests that further research is needed to establish the impact non-active components have on the potency of such vaccines.

Postexposure Treatment with the Live-Attenuated Rabies Virus (RV) Vaccine TriGAS Triggers the Clearance of Wild-Type RV from the Central Nervous System (CNS) through the Rapid Induction of Genes Relevant to Adaptive Immunity in CNS Tissues

Postexposure treatment (PET) of wild-type rabies virus (RV)-infected mice with a live-attenuated triple-glycoprotein RV variant (TriGAS) promotes survival but does not prevent the pathogenic RV from invading and replicating in the brain. Successful PET is associated with the induction of a robust virus-neutralizing antibody response and clearance of the wild-type RV from brain tissues. Comparison of the transcriptomes of normal mouse brain with those of wild-type-RV-infected mice that had received either mock or TriGAS PET treatment revealed that many of the host genes activated in the mock-treated mice represent type I interferon (IFN) response genes. This indicates that RV infection induces an early type I IFN response that is unable to control the infection. In contrast, most of the activated genes in the brain of the RV-infected, TriGAS-treated mouse play a role in adaptive immunity, including the regulation of T cell activation, T cell differentiation, and the regulation of lymphocyte and mononuclear cell proliferation. These findings were confirmed by quantitative PCR (qPCR) array studies, which showed that 3 genes in particular, encoding chemokine ligand 3 (Ccl3), natural killer cell activator 2 (interleukin 12B [IL-12B]), and granzyme A (GzmA), were activated earlier and to a greater extent in the brains of RV-infected mice treated with TriGAS than in the brains of mock-treated mice. The activation of these genes, known to play key roles in the regulation of lymphocyte and mononuclear cell proliferation, is likely an important part of the mechanism by which TriGAS mediates its PET activity.

Molecular characterization of China rabies virus vaccine strain

BackgroundRabies virus (RV), the agent of rabies, can cause a severe encephalomyelitis in several species of mammals, including humans. As a human rabies vaccine strain employed in China, the genetic knowledge of the aG strain has not been fully studied. The main goal of the present study is to amplify the whole genome of aG strain, and genetic relationships between other vaccine strains and wild strains were analyzed.ResultsThe entire genome of human rabies virus vaccine strain aG employed in China was sequenced; this is the second rabies virus vaccine strain from China to be fully characterized. The overall organization and the length of the genome were similar to that of other lyssaviruses. The length of aG strain was 11925nt, comprising a leader sequence of 58nt, nucleoprotein (N) gene of 1353nt, phosphoprotein (P) gene of 894 nt, matrix protein (M) gene of 609nt, glycoprotein (G) gene of 1575nt, RNA-dependent RNA polymerase (RdRp,L) gene of 6384nt, and a trailer region of 70 nt. There was TGAAAAAAA (TGA7) consensus sequence in the end of each gene, except AGA7 at the end of G gene. There was AACAYYYCT consensus start signal at the beginning of each gene.ConclusionsIn this report, we analyzed the full genome of China human rabies vaccine strain aG. Our studies indicated that the genome of aG retained the basic characteristics of RV. At gene level, N was the most conserved among the five coding genes, indicating this gene is the most appropriate for quantitative genotype definition. The phylogenetic analysis of the N indicated the aG strain clustered most closely with Japanese and Russian rabies vaccine strains, suggesting that they may share the same ancestor; also, the aG strain did not share high homology with wild strains isolated from China, making it may not be the best vaccine strain, more research is needed to elucidate the genetic relationship among the RV circulating in China.

Oral immunisation of mice with a recombinant rabies virus vaccine incorporating the heat-labile enterotoxin B subunit of Escherichia coli in an attenuated Salmonella strain

To investigate effective new rabies vaccines, a fusion protein consisting of the rabies virus (RV) glycoprotein and the heat-labile enterotoxin B subunit of Escherichia coli (LTB) was successfully constructed and delivered in a live attenuated Salmonella strain LH430. Mice were immunised with LH430 carrying pVAX1-G, pVAX1-G-LTB or pVAX1-ori-G-LTB. The antibody titres of mice immunised with oral LH430 carrying pVAX1-G-LTB or pVAX1-ori-G-LTB were significantly higher than those of pVAX1-G-immunised mice. The results of the challenge with the rabies virus standard strain (CVS-11) showed that the LH430 strain carrying the G-LTB gene induced immunity and elevated IL-2 levels in immunised mice (∗∗P<0.01), whereas LH430 carrying pVAX1-G did not contribute to protection. These results show that LH430 carrying recombinant G-LTB could provide overall immunity against challenge with CVS-11 and should be considered to be a potential rabies vaccine.

Generation of a recombinant rabies Flury LEP virus carrying an additional G gene creates an improved seed virus for inactivated vaccine production.

The rabies Flury Low Egg Passage virus (LEP) has been widely used as a seed virus to generate inactive vaccine. Here, we established a reverse genetic system for LEP and generated a recombinant LEP virus (rLEP-G) that carries two identical G genes. This recombinant virus showed similar properties to those of LEP with respect to in vitro growth, neurotropism index, and virulence in mice. rLEP-G produced 4.3-fold more G protein than did LEP in BHK-21 cells. The inactivated vaccine generated from rLEP-G induced significantly higher virus neutralization titers in mice and dogs than those produced in response to LEP-derived vaccine. Our results suggest that rLEP-G is an improved seed virus candidate for inactivated rabies virus vaccine manufacture.

Inactivated or Live-Attenuated Bivalent Vaccines That Confer Protection against Rabies and Ebola Viruses

The search for a safe and efficacious vaccine for Ebola virus continues, as no current vaccine candidate is nearing licensure. We have developed (i) replication-competent, (ii) replication-deficient, and (iii) chemically inactivated rabies virus (RABV) vaccines expressing Zaire Ebola virus (ZEBOV) glycoprotein (GP) by a reverse genetics system based on the SAD B19 RABV wildlife vaccine. ZEBOV GP is efficiently expressed by these vaccine candidates and is incorporated into virions. The vaccine candidates were avirulent after inoculation of adult mice, and viruses with a deletion in the RABV glycoprotein had greatly reduced neurovirulence after intracerebral inoculation in suckling mice. Immunization with live or inactivated RABV vaccines expressing ZEBOV GP induced humoral immunity against each virus and conferred protection from both lethal RABV and EBOV challenge in mice. The bivalent RABV/ZEBOV vaccines described here have several distinct advantages that may speed the development of inactivated vaccines for use in humans and potentially live or inactivated vaccines for use in nonhuman primates at risk of EBOV infection in endemic areas.

Immunogenicity Studies in Carnivores Using a Rabies Virus Construct with a Site-Directed Deletion in the Phosphoprotein

Different approaches have been applied to develop highly attenuated rabies virus vaccines for oral vaccination of mesocarnivores. One prototype vaccine construct is SAD dIND1, which contains a deletion in the P-gene severely limiting the inhibition of type-1 interferon induction. Immunogenicity studies in foxes and skunks were undertaken to investigate whether this highly attenuated vaccine would be more immunogenic than the parental SAD B19 vaccine strain. In foxes, it was demonstrated that SAD dIND1 protected the animals against a rabies infection after a single oral dose, although virus neutralizing antibody titres were lower than in foxes orally vaccinated with the SAD B19 virus as observed in previous experiments. In contrast, skunks receiving 107.5 FFU SAD dIND1 did not develop virus neutralizing antibodies and were not protected against a subsequent rabies infection.

Rabies Virus Expressing Dendritic Cell-Activating Molecules Enhances the Innate and Adaptive Immune Response to Vaccination

Our previous studies indicated that recruitment and/or activation of dendritic cells (DCs) is important in enhancing the protective immune responses against rabies virus (RABV) (L. Zhao, H. Toriumi, H. Wang, Y. Kuang, X. Guo, K. Morimoto, and Z. F. Fu, J. Virol. 84:9642-9648). To address the importance of DC activation for RABV vaccine efficacy, the genes for several DC recruitment and/or activation molecules, e.g., granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage-derived chemokine (MDC), and macrophage inflammatory protein 1α (MIP-1α), were individually cloned into RABV. The ability of these recombinant viruses to activate DCs was determined in vitro and in vivo. Infection of mouse bone marrow-derived DCs with each of the recombinant viruses resulted in DC activation, as shown by increased surface expression of CD11c and CD86 as well as an increased level of alpha interferon (IFN-α) production compared to levels observed after infection with the parent virus. Intramuscular infection of mice with each of the viruses recruited and/or activated more DCs and B cells in the periphery than infection with the parent virus, leading to the production of higher levels of virus-neutralizing antibodies. Furthermore, a single immunization with recombinant RABV expressing GM-CSF or MDC protected significantly more mice against intracerebral challenge with virulent RABV than did immunization with the parental virus. Yet, these viruses did not show more virulence than the parent virus, since direct intracerebral inoculation with each virus at up to 1 × 10(7) fluorescent focus units each did not induce any overt clinic symptom, such as abnormal behavior, or any neurological signs. Together, these data indicate that recombinant RABVs expressing these molecules activate/recruit DCs and enhance protective immune responses.

Experimental rabies vaccines for humans

Rabies remains a global public health threat that kills more than 55,000 people per year. Rabies disproportionately affects children and, therefore, is ranked the seventh most important infectious disease due to years lost. Prevention of human rabies is accomplished by controlling rabies in domestic and wild animals, including the use of vaccination programs. The usefulness of human rabies vaccines is hampered by high cost, complicated vaccination regimens and lack of compliance, especially in areas of Africa and Asia where human rabies infections are endemic. A single-dose vaccine would greatly benefit efforts to combat this global health threat. However, a single-dose vaccine based on current inactivated vaccines does not appear feasible and other approaches are needed. Technology has advanced since modern human rabies vaccines were developed over 40 years ago. In addition, our understanding of immunological principles that influence the outcome of vaccination has increased. This article describes the current status of inactivated rabies virus vaccines and recent developments arising from the use of reverse genetics technologies designed to develop replication-deficient or single-cycle live rabies virus-based vectors for use as a single-dose rabies vaccine for humans.

Dendritic cells infected by recombinant rabies virus vaccine vector expressing HIV-1 Gag are immunogenic even in the presence of vector-specific immunity

Dendritic cells (DC) are the most potent antigen presenting cells whose ability to interact with T cells, B cells and NK cells has led to their extensive use in vaccine design. Here, we designed a DC-based HIV-1 vaccine using an attenuated rabies virus vector expressing HIV-1 Gag (RIDC-Gag). To test this, BALB/c mice were immunized with RIDC-Gag, and the primary, secondary as well as humoral immune responses were monitored. Our results indicate that RIDC-Gag stimulated HIV-1 Gag-specific immune responses in mice. When challenged with vaccinia virus (VV) expressing HIV-1 Gag, they elicited a potent Gag-specific recall response characterized by CD8+ T cells expressing multiple cytokines that were capable of specifically lysing Gag-pulsed target cells. Moreover, RIDC-Gag also enhanced CD8+ T cell responses via a homologous prime-boost regimen. These results show that a DC-based vaccine using live RV is immunogenic and a potential candidate for a therapeutic HIV-1 vaccine.

Molecular characterization of a Chinese variant of the Flury-LEP strain

The entire genome of rabies virus vaccine strain Flury-LEP-C, a Chinese variant of the rabies virus vaccine strain Flury-LEP, was sequenced. The overall length of the genome of Flury-LEP-C strain was 11 924 nucleotides (nt), comprising a leader sequence of 58 nt, nucleoprotein (N) gene of 1353 nt, phosphoprotein (P) gene of 894 nt, matrix protein (M) gene of 609 nt, glycoprotein (G) gene of 1575 nt, RNA-dependent RNA polymerase (RdRp, L) gene of 6384 nt, and a trailer region of 70 nt. There was TGAAAAAAA (TGA7) consensus sequence in the end of each gene in Flury-LEP-C genome, except G gene which had a GAGAAAAAAA sequence in the end of the non-coding G-L region. There were AACAYYYCT consensus start signal close to the TGA7. Flury-LEP-C has 310 nucleotides more than HEP-Flury in G-L intergenic region. The analysis showed that the residue at 333 of the mature G protein was Arg, which was reported to be related to pathogenicity. Compared with FluryLEP, there were 19 different amino acids (AAs) in five proteins of Flury-LEP-C, including 15 AAs which were identical with corresponding residues of Hep-Flury, and 4 AAs which were neither identical with the residues of FluryLEP nor with the residues of Hep-Flury. The results showed the topology of the phylogenetic trees generated by two protein sequences were similar. It was demonstrated that HN10, BD06, FJ009, FJ008, D02, D01, F04, F02 have a close relationship to CTN-1 and CTN181, and MRV was closely related to Flury-LEP, HEP-Flury and Flury-LEP-C.

Safety and Immunogenicity of an AMA1 Malaria Vaccine in Malian Children: Results of a Phase 1 Randomized Controlled Trial

BackgroundThe objective was to evaluate the safety and immunogenicity of the AMA1-based malaria vaccine FMP2.1/AS02A in children exposed to seasonal falciparum malaria.Methodology/Principal FindingsA Phase 1 double blind randomized controlled dose escalation trial was conducted in Bandiagara, Mali, West Africa, a rural town with intense seasonal transmission of Plasmodium falciparum malaria. The malaria vaccine FMP2.1/AS02A is a recombinant protein (FMP2.1) based on apical membrane antigen 1 (AMA1) from the 3D7 clone of P. falciparum, formulated in the Adjuvant System AS02A. The comparator vaccine was a cell-culture rabies virus vaccine (RabAvert®). One hundred healthy Malian children aged 1–6 years were recruited into 3 cohorts and randomized to receive either 10 µg FMP2.1 in 0.1 mL AS02A, or 25 µg FMP2.1 in 0.25 mL AS02A, or 50 µg FMP2.1 50 µg in 0.5 mL AS02A, or rabies vaccine. Three doses of vaccine were given at 0, 1 and 2 months, and children were followed for 1 year. Solicited symptoms were assessed for 7 days and unsolicited symptoms for 30 days after each vaccination. Serious adverse events were assessed throughout the study. Transient local pain and swelling were common and more frequent in all malaria vaccine dosage groups than in the comparator group, but were acceptable to parents of participants. Levels of anti-AMA1 antibodies measured by ELISA increased significantly (at least 100-fold compared to baseline) in all 3 malaria vaccine groups, and remained high during the year of follow up.Conclusion/SignificanceThe FMP2.1/AS02A vaccine had a good safety profile, was well-tolerated, and induced high and sustained antibody levels in malaria-exposed children. This malaria vaccine is being evaluated in a Phase 2 efficacy trial in children at this site.Trial RegistrationClinicalTrials.gov NCT00358332 [NCT00358332]

Development of a reverse genetics system for a human rabies virus vaccine strain employed in China

The CTN rabies virus was isolated from a human in China in 1953 and subsequently attenuated by multiple passaging to a vaccine strain now approved by the WHO. In this study, we describe the development of a reverse genetics system for the CTN rabies virus strain. The recombinant full-length genomic cDNA was flanked by a hammerhead ribozyme (HamRz) and the hepatitis delta virus ribozyme (HdvRz) while the non-coding G–L region was replaced with a green fluorescent protein (GFP) gene. A set of helper plasmids encoding nucleoprotein (N), phosphoprotein (P), and large protein (L) were constructed and co-transfected with recombinant full-length genome plasmid into BHK-21 cells. Recombinant virus was successfully recovered from cloned cDNA under control of the CMV promoter driven by RNA polymerase II. The recombinant virus, CTN–GFP, stably expressed GFP as detected by fluorescence microscopy. A group of 1-day-old suckling mice was challenged with the CTN–GFP strain by intracerebral inoculation, resulting in 100% morbidity and GFP expression was detected in brain tissues. The recombinant virus CTN–GFP strain recovered from cloned cDNA will be useful as a viral vector to express other foreign genes.

Characterization of a Single-Cycle Rabies Virus-Based Vaccine Vector

Recombinant rabies virus (RV)-based vectors have demonstrated their efficacy in generating long-term, antigen-specific immune responses in murine and monkey models. However, replication-competent viral vectors pose significant safety concerns due to vector pathogenicity. RV pathogenicity is largely attributed to its glycoprotein (RV-G), which facilitates the attachment and entry of RV into host cells. We have developed a live, single-cycle RV by deletion of the G gene from an RV vaccine vector expressing HIV-1 Gag (SPBN-DeltaG-Gag). Passage of SPBN-DeltaG-Gag on cells stably expressing RV-G allowed efficient propagation of the G-deleted RV. The in vivo immunogenicity data comparing single-cycle RV to a replication-competent control (BNSP-Gag) showed lower RV-specific antibodies; however, the overall isotype profiles (IgG2a/IgG1) were similar for the two vaccine vectors. Despite this difference, mice immunized with SPBN-DeltaG-Gag and BNSP-Gag mounted similar levels of Gag-specific CD8(+) T-cell responses as measured by major histocompatibility complex class I Gag-tetramer staining, gamma interferon-enzyme-linked immunospot assay, and cytotoxic T-cell assay. Moreover, these cellular responses were maintained equally at immunization titers as low as 10(3) focus-forming units for both RV vaccine vectors. CD8(+) T-cell responses were significantly enhanced by a boost with a single-cycle RV complemented with a heterologous vesicular stomatitis virus glycoprotein. These findings demonstrate that single-cycle RV is an effective alternative to replication-competent RV vectors for future development of vaccines for HIV-1 and other infectious diseases.

Response to Vaccination with a Commercial Inactivated Rabies Vaccine in a Captive Colony of Brazilian Free-Tailed Bats (Tadarida brasiliensis)

A captive colony of Brazilian free-tailed bats (Tadarida brasiliensis) was vaccinated with a commercial monovalent inactivated rabies virus (RABV) vaccine (RABVAC 1). Baseline rabies virus neutralizing antibodies (VNA) and the response to vaccination were measured in 50 bats. Rabies VNA was detected in the plasma of 64% (27/42) of bats that had been vaccinated 1 yr prior, but only 19% (8/42) had levels considered adequate. Rabies VNA was detected in the plasma of 63% (5/8) of bats with no record of previous vaccination, suggesting natural RABV exposure before captivity. All bats demonstrated a VNA response by 10 days postvaccination, and baseline titer significantly predicted humoral response to vaccination. No adverse reactions to vaccination or clinical signs of RABV infection were observed in the bats during a 6-mo observation period. Annual vaccination may maintain immunity against RABV infection in captive colonies of bats. Bat, rabies virus, Tadarida brasiliensis, vaccination, virus neutralizing antibodies.