Overlapping cytotoxic T-lymphocyte and B-cell antigenic sites on the influenza virus H5 hemagglutinin

Patterns of predicted T-cell epitopes associated with antigenic drift in influenza H3N2 hemagglutinin

Antigenic drift allowing escape from neutralizing antibodies is an important feature of transmission and survival of influenza viruses in host populations. Antigenic drift has been studied in particular detail for influenza A H3N2 and well defined antigenic clusters of this virus documented. We examine how host immunogenetics contributes to determination of the antibody spectrum, and hence the immune pressure bringing about antigenic drift. Using uTOPE™ bioinformatics analysis of predicted MHC binding, based on amino acid physical property principal components, we examined the binding affinity of all 9-mer and 15-mer peptides within the hemagglutinin 1 (HA1) of 447 H3N2 virus isolates to 35 MHC-I and 14 MHC-II alleles. We provide a comprehensive map of predicted MHC-I and MHC-II binding affinity for a broad array of HLA alleles for the H3N2 influenza HA1 protein. Each HLA allele exhibited a characteristic predicted binding pattern. Cluster analysis for each HLA allele shows that patterns based on predicted MHC binding mirror those described based on antibody binding. A single amino acid mutation or position displacement can result in a marked difference in MHC binding and hence potential T-helper function. We assessed the impact of individual amino acid changes in HA1 sequences between 10 virus isolates from 1968-2002, representative of antigenic clusters, to understand the changes in MHC binding over time. Gain and loss of predicted high affinity MHC-II binding sites with cluster transitions were documented. Predicted high affinity MHC-II binding sites were adjacent to antibody binding sites. We conclude that host MHC diversity may have a major determinant role in the antigenic drift of influenza A H3N2.

Protection of mice and poultry from lethal H5N1 avian influenza virus through adenovirus-based immunization

The recent emergence of highly pathogenic avian influenza virus (HPAI) strains in poultry and their subsequent transmission to humans in Southeast Asia have raised concerns about the potential pandemic spread of lethal disease. In this paper we describe the development and testing of an adenovirus-based influenza A virus vaccine directed against the hemagglutinin (HA) protein of the A/Vietnam/1203/2004 (H5N1) (VN/1203/04) strain isolated during the lethal human outbreak in Vietnam from 2003 to 2005. We expressed different portions of HA from a recombinant replication-incompetent adenoviral vector, achieving vaccine production within 36 days of acquiring the virus sequence. BALB/c mice were immunized with a prime-boost vaccine and exposed to a lethal intranasal dose of VN/1203/04 H5N1 virus 70 days later. Vaccination induced both HA-specific antibodies and cellular immunity likely to provide heterotypic immunity. Mice vaccinated with full-length HA were fully protected from challenge with VN/1203/04. We next evaluated the efficacy of adenovirus-based vaccination in domestic chickens, given the critical role of fowl species in the spread of HPAI worldwide. A single subcutaneous immunization completely protected chickens from an intranasal challenge 21 days later with VN/1203/04, which proved lethal to all control-vaccinated chickens within 2 days. These data indicate that the rapid production and subsequent administration of recombinant adenovirus-based vaccines to both birds and high-risk individuals in the face of an outbreak may serve to control the pandemic spread of lethal avian influenza.

Pathogenesis of and immunity to avian influenza A H5 viruses

In 1997 in Hong Kong, 18 human cases of respiratory illness were caused by an avian influenza A H5N1 virus. Although avian influenza viruses had not previously been known to cause respiratory illness in humans, the H5N1 viruses caused severe illness and death, primarily in individuals aged > 12 years. The introduction of H5N1 viruses into humans raised concerns about the potential of these viruses to cause a pandemic. We have used the BALB/c mouse to better understand the pathogenesis of and immunity to the H5N1 viruses in a mammalian model. Previously, we demonstrated that H5N1 viruses isolated from humans replicated efficiently in the lungs of mice without prior adaptation to this host. Two general phenotypes of pathogenicity of H5N1 viruses, based on high and low lethality for mice, were observed. We now demonstrate that in addition to a lethal outcome, H5N1 viruses with a high pathogenicity phenotype exhibit additional features that include rapid and uncontrolled replication in the lungs of infected mice, dissemination and replication of the virus in other organs, and depletion of peripheral blood leukocytes. The BALB/c mouse model was also used to better understand the parameters of protective immunity to the H5N1 viruses. Prior infection with H5N1 viruses of low pathogenicity or an antigenically related non-pathogenic H5N3 virus protected mice from death by infection with a highly pathogenic HK/483 virus. Serum hemagglutination-inhibition antibody titers of 40 or greater were associated with protection of mice from death. Immunization of mice with baculovirus-expressed recombinant H5 hemagglutinin protein or a previously defined HS-specific synthetic peptide induced MHC class II restricted CTL activity. Mice that had CTL activity but no serum hemagglutination-inhibition antibody were not protected from a lethal challenge with H5N1 virus. These results suggest that antibody is required for protection of mice against lethal challenge with H5N1 viruses of the high pathogenicity phenotype.

bcl-2 alters influenza virus yield, spread, and hemagglutinin glycosylation

We previously demonstrated that expression of bcl-2 in Madin-Darby canine kidney (MDCK) cells blocks influenza virus-induced apoptosis and DNA fragmentation. We show here that expression of bcl-2 also reduces the level of infectious virus production and the spread of virus in MDCK cell cultures infected at a low multiplicity of infection. This effect is associated with modified glycosylation of the hemagglutinin protein.

Analysis of overlapping T- and B-cell antigenic sites on rubella virus E1 envelope protein. Influence of HLA-DR4 polymorphism on T-cell clonal recognition

A CTL antigenic site located between residues 273 and 291 of the E1 envelope protein of RV was identified by 51Cr-release assays employing SPs. Two E1-specific CTL clones were examined for immune recognition of RV wild-type and attenuated vaccine strains and recombinant E1 protein. The exact sequence (273-284) recognized by both clones was delineated by using truncated and overlapping SPs covering these residues. The defined T-cell site overlapped almost completely with a virus neutralizing antibody-binding site previously identified with mouse monoclonal and human antibodies. A series of single aa-substituted SP analogues of E1(273-284) was used to define residues critical for T-cell recognition. Using EBV-BL displaying different HLA-DR haplotypes and -DR4 subtypes as targets to determine MHC class II restriction elements, immune recognition by both T-cell clones was shown to be associated with HLA-DR4. Three HLA-DR4 subtypes (DR4Dw13A, DR4Dw13B, and DR4KT2) sharing a common residue, glutamic acid at position 74 in their beta 1 chains, were able to present SP E1(273-284) to the T-cell clones.

Induction of syngeneic cytotoxic T lymphocytes against a B cell tumor. II. Characterization of anti-idiotypic CTL lines and clones

In an earlier communication we showed that idiotypic immunoglobulin (Id+ Ig) of a B cell hybrid, 2C3, can induce cytotoxic T lymphocytes (CTL) in the spleens of mice that are hyperimmunized with the irradiated tumor cells. To understand the extent of heterogeneity in the splenic CTL population, stable anti-idiotypic CTL lines and clones were established from 2C3-primed splenocytes. One representative CTL line A102 which exhibited the phenotype of CD3+, CD4-, and CD8+, has been maintained in long-term culture for more than 18 months. Cytotoxic specificity of A102 was determined by cold target inhibition assay using a panel of syngeneic and allogeneic B cell tumors. The CTL line A102 was highly cytotoxic to 2C3, only weakly to other syngeneic tumors, but not at all to allogeneic B cell tumor CH12. Furthermore, CTL-mediated cytolysis was significantly abrogated by blocking 2C3 cells with anti-idiotypic monoclonal and polyclonal antibodies. These results clearly show that 2C3 Id represents the immunodominant epitope(s) recognized by the CTL line A102. To isolate a highly Id-specific effector population, A102 was repeatedly subcloned by limiting dilution. One such clone 102.F5 exhibited considerable specificity toward Id+ 2C3 while another clone 102.E10 showed no such specificity in a competitive cytotoxicity assay. This was further confirmed by the inhibition studies with anti-Id mAb. Thus, hyperimmunization with irradiated 2C3 cells evokes a spectrum of anti-2C3 cytotoxic effector cells, of which a major population is reactive to the idiotypic determinants associated with 2C3 Ig.

Human immunodeficiency virus vectors for inducible expression of foreign genes

Tat-dependent expression of an endogenous lethal or deleterious foreign gene might be useful for abrogating the production of human immunodeficiency virus (HIV) from cells. This type of HIV-induced cellular killing, as well as other approaches to gene therapy for HIV infection, would be facilitated by simple HIV vectors that express introduced genes in a Tat-inducible manner. As part of studies to examine the feasibility of this concept, we constructed HIV-1 vectors that express the hygromycin B phosphotransferase gene (Hygr) in a Tat-dependent manner. Comparison of the efficiency of propagation of each vector indicates that sequences extending into the gag open reading frame are necessary in cis for efficient vector propagation. Southern blot analysis of genomic DNA isolated from vector-infected cells demonstrated that the vectors were capable of being propagated as expected without gross rearrangements or deletions. A fragment of the influenza A virus hemagglutinin (H5 HA) gene, capable of eliciting antibody and cytotoxic T-cell responses, was used as a marker for further characterization of the vector system. A Tat-dependent vector conferring the H5 HA+ phenotype was assayed by indirect immunofluorescence, and cells which contained but did not express the H5 HA gene were isolated. The activation of H5 HA expression following HIV infection of Tat- cells that stably contained but did not express the H5 HA construct was determined to be an efficient process.