Immunological and virological characterization of improved construction of recombinant vaccinia virus expressing rinderpest virus hemagglutinin

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

LC16m8: an attenuated smallpox vaccine

The frequency of moderate to severe adverse reactions associated with smallpox vaccines currently stockpiled in the US, and the continued threat of bioterrorism have prompted the development of effective vaccines with improved safety profiles. LC16m8, an attenuated, replicating smallpox vaccine derived from the Lister strain of vaccinia, is currently licensed in Japan where it was safely used in over 50,000 children in the 1970s. It has been shown to have markedly less neurotoxicity than unattenuated vaccines in nonclinical studies. LC16m8 is immunogenic after a single dose, and recent studies in two different animal models have demonstrated protective efficacy equivalent to that of the only FDA-licensed smallpox vaccine. This article reviews the history and available scientific literature regarding LC16m8 and provides comparisons to other smallpox vaccines.

Cytotoxic T cell epitope in cattle from the attachment glycoproteins of rinderpest and peste des petits ruminants viruses

The surface glycoproteins of rinderpest virus (RPV) confer protective immunity in cattle. We demonstrated that cattle immunized with a recombinant extracellular baculovirus expressing the hemagglutinin (H) protein of RPV (rECV-H) generate virus neutralizing antibody responses, bovine leukocyte antigen (BoLA) class II restricted helper T cell responses and BoLA class I restricted cytotoxic T cell (CTL) responses against RPV-H and hemagglutinin-neuraminidase (HN) glycoprotein of closely related Peste des petits ruminants virus (PPRV). In this study, employing autologous skin fibroblasts transiently expressing truncations of H and HN in a BoLA class I restricted lymphoproliferation assay, we have mapped a highly homologous domain (amino acids 400-423) on these proteins harboring a CTL epitope. Subsequently, based on sequence comparison with available BoLA class I binding motifs, we have identified a BoLA-A11 binding motif (amino acids 408-416) in the stimulatory domain. Autologous cells pulsed with a synthetic peptide corresponding to this sequence stimulated CTLs from rECV-H immunized as well as tissue culture attenuated RPV vaccinated cattle of different breeds and parentage. This is the first epitope identified in cattle on the attachment glycoproteins of RPV and PPRV.

Recombinant hemagglutinin protein of rinderpest virus expressed in insect cells induces cytotoxic T-cell responses in cattle

Rinderpest virus (RPV), a member of the genus Morbillivirus within the Paramyxoviridae family, causes a highly contagious and often fatal disease known as rinderpest in wild and domestic ruminants. The envelope of the virus contains two surface glycoproteins, namely the hemagglutinin (H) and the fusion (F) proteins, both of which have been shown to confer protective immunity in animals. In this paper, we demonstrate that single administration of low doses of recombinant H protein of RPV expressed in insect cells in the form of extracellular virus induces long lasting bovine leukocyte antigen class I restricted cytotoxic T-cell (CTL) responses in cattle in the absence of adjuvant. This is the first report of CTL responses in cattle against one of the protective antigens of RPV.

Mapping of T-helper epitopes of Rinderpest virus hemagglutinin protein

Rinderpest virus (RPV) is a highly contagious and often fatal disease of domestic and wild ruminants, caused by rinderpest virus of the genus Morbillivirus under the family Paramyxoviridae. Hemagglutinin (H) and fusion (F) proteins of this enveloped virus confer protective immunity against experimental challenge with virulent rinderpest virus. We have earlier demonstrated that immunization with a single dose of recombinant extracellular baculovirus expressing H protein elicits H-specific humoral and lymphoproliferative responses in cattle. The lymphoproliferative responses are predominantly BoLA class II restricted. In this work, we have analyzed lymphoproliferative responses of peripheral lymphocytes from immunized cattle to truncated H protein fragments expressed in E. coli for locating domains harboring Th epitopes. One region (aa 113-182) recognized by immune T cells is conserved in the H protein of measles virus, which was earlier shown to contain a dominant Th epitope in mouse. Synthetic peptides within this region of measles virus H protein were used to identify a Th epitope conserved in the H protein of RPV virus (aa 123-137) in cattle. A second Th epitope located at the C-terminus of RPV-H was mapped to the region corresponding to aa 512-609 using truncated protein fragments expressed in E. coli. The C-terminal epitope (aa 575-583) was mapped using synthetic peptides corresponding to measles virus H as well as RPV-H protein.

Recombinant hemagglutinin protein of rinderpest virus expressed in insect cells induces humoral and cell mediated immune responses in cattle

Rinderpest virus causes a highly contagious and often fatal disease in domestic and wild ruminants. The surface glycoproteins, hemagglutinin (H) and fusion (F) proteins of this enveloped virus are known to confer protective immunity in cattle. We have reported the generation of a recombinant baculovirus expressing H protein and studied its protective properties in cattle. In this report, we demonstrate that the recombinant baculovirus encoded H protein expressed in insect cells gets incorporated into extracellular baculovirus. Single administration of low doses of purified recombinant extracellular virus with or without adjuvant induces virus neutralizing antibody responses and bovine leukocyte antigen (BoLA) class II restricted helper T cell responses in cattle.

Long-term protective immunity to rinderpest in cattle following a single vaccination with a recombinant vaccinia virus expressing the virus haemagglutinin protein

A recombinant vaccine, produced by using a highly attenuated smallpox vaccine (LC16mO) as a vector and which expresses the rinderpest virus (RPV) haemagglutinin protein, has been developed. The properties of this vaccine, including its heat stability, efficacy in short-term trials, safety and genetic stability, have been confirmed in an earlier report. In the present study, the duration of the protective immunity generated by the vaccine in cattle was examined for up to 3 years following the administration of a single vaccination dose of 10(8) p.f.u. The vaccinated cattle were kept for 2 (group I) or 3 years (group II) and then challenged with a highly virulent strain of RPV. Four of five vaccinated cattle in group I and all six cattle in group II survived the challenge, some showing solid immunity without any clinical signs of rinderpest. Neutralizing antibodies were maintained at a significant level for up to 3 years and they increased rapidly following challenge. Lymphocyte proliferative responses to RPV were examined in group II cattle and were observed in four of the six vaccinated cattle in this group. The long-lasting protective immunity, in addition to the other properties confirmed previously, indicate the practical usefulness of this vaccine for field use.

Immunogenic and protective properties of haemagglutinin protein (H) of rinderpest virus expressed by a recombinant baculovirus

The hemagglutinin (H) protein of Rinderpest virus expressed by a recombinant baculovirus used as a vaccine produced high titres of neutralizing antibody to Rinderpest virus in the vaccinated cattle, comparable to the levels produced by live attenuated vaccine. The immunized cattle were protected against a vaccine-virus challenge, as demonstrated by the failure of development of antibodies to N protein of the vaccine virus. The lack of replication of vaccine virus in the immunized cattle indicated that they are capable of showing a protective response if challenged with a virulent virus.

Potency testing of tissue culture rinderpest vaccine in rabbits

Rinderpest (RP) vaccine potency testing requires virulent bovine rinderpest virus (RPV). Use of virulent RPV is a biosafety hazard. In this study we had vaccinated rabbits with tissue culture RP vaccine at different doses and thereafter challenged with lapinized virus. No thermal reaction in vaccinated rabbits was observed. Serum neutralizing antibody response to vaccine was dose dependent until the second week post-vaccination but by the fourth week post-vaccination all the rabbits had similar neutralizing antibody titres. Vaccinated rabbits exhibited mild clinical signs as compared to unvaccinated controls after challenge. All the vaccinated rabbits survived challenge while only 40% unvaccinated rabbits survived challenge with virulent lapinized RPV. A strong anamnestic response in all the vaccinated rabbits was observed after challenge with lapinized virus. This study shows that rabbits could be used for potency testing of RP vaccine virus.

Characterization of membrane-bound and membrane anchor-less forms of hemagglutinin glycoprotein of Rinderpest virus expressed by baculovirus recombinants

The Rinderpest virus (RPV) hemagglutinin (H) is a class 2 glycoprotein by means of which the virus attaches to the host cell receptor. A full length cDNA coding for H protein was used to construct a recombinant baculovirus expressing the H protein, recH(M), on the surface of insect cells. The small N terminal cytoplasmic domain was deleted and the transmembrane domain which extends from amino acids 35 to 59 was replaced with a signal peptide derived from the ecdysteroid UDP glycosyl transferase (egt) gene of the baculovirus, AcNPV. The protein recH(sec) expressed by the recombinant baculovirus carrying this engineered gene was secreted into the medium. Both forms of recombinant H protein retained reactivity with conformation-dependent monoclonal antibodies. The recH(M) was recognized by antibodies made in cattle either as the result of vaccination or natural infection. The soluble form of H is a valuable tool for studying the structure and function of the RPV H glycoprotein.

Characteristics of an attenuated vaccinia virus strain, LC16m0, and its recombinant virus vaccines

This article reviews studies concerning the characteristics of a vaccinia virus strain, LC16m0, and its recombinant virus vaccines. The LC16m0 strain is one of several temperature-sensitive and further attenuated variants derived from the Lister (Elstree) strain of vaccinia virus, which has a proven safety record in human populations. Several types of recombinant vaccinia viruses expressing a foreign antigen gene from a pathogenic virus have been constructed using the LC16m0 strain as a vector, and their immunological and virological characteristics have been investigated extensively. These studies indicate that the LC16m0 strain has potential as a vector in a live recombinant vaccine. The advantages, disadvantages and future prospects of vector are discussed.

Expression in baculovirus vector system of the nucleocapsid protein gene of rinderpest virus

The rinderpest (RV) nucleocapsid (NP) gene segment was inserted into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) adjacent to the polyhedrin promoter. The expression of NP protein in Sf9 cells was confirmed by indirect immunofluorescence and by Western blotting analysis with monoclonal antibodies. Recombinant RV-NP protein was purified by ultracentrifugation on a sucrose density gradient, and used as an antigen for an enzyme linked immunosorbent assay to detect anti RV-NP antibody. Both IgM and IgG antibodies against RV-NP were detected in the sera of rabbits infected with the L strain of RV. The pattern of development of IgG anti RV-NP antibody closely correlated with that of virus neutralizing antibody. In rabbits inoculated with recombinant vaccinia virus expressing RV-H gene (RRV-H), anti RV-NP was not detected. The results indicated that the baculovirus vector system can be used for the preparation of the diagnostic antigen of rinderpest as well as to distinguish between natural infection and vaccination with RRV-H.