Heterologous protection induced by the inner capsid proteins of rotavirus requires transcytosis of mucosal immunoglobulins

Protective immunization against rotavirus (RV) can be achieved with heterologous RV, i.e., virus isolated from another species, and with heterologous inner core VP2 and VP6 proteins assembled as virus-like particles (VLP). Although the antigenically conserved VP6 protein does not induce in vitro-neutralizing antibodies, it may, however, elicit immunoglobulins (Ig) involved in heterologous protection, as some IgA against VP6 prevent RV infection in a backpack mouse model. The protective role of Ig directed to the RV inner core proteins VP2 and VP6 was investigated in J-chain-deficient mice (J chain(-/-)), which have a defect in the polymeric Ig receptor (pIgR)-mediated transcytosis of IgA and IgM. J chain(-/-) mice and wild-type (WT) mice were intranasally vaccinated with bovine RV-derived VLP2/6 and then challenged with highly infectious murine ECw RV. Whereas WT mice were totally protected, immunized J chain(-/-) mice shed RV for several days. In addition, naïve J chain(-/-) mice exhibited a 2-day delay in clearing RV compared with WT mice. The immunized J chain(-/-) mice displayed unaltered VLP2/6-specific B-cell numbers in spleen and in mesenteric nodes and similar levels of serum anti-VLP2/6 Ig, confirming that the adaptive B-cell response is preserved in J chain(-/-) mice. These results indicate that J-chain-mediated transcytosis of Ig participates in the clearance of RV and that epithelial pIgR-mediated transport of Ig is involved in the heterologous protection induced by VLP2/6.

Preferential induction of IL-10 in APC correlates with a switch from Th1 to Th2 response following infection with a low pathogenic variant of Theiler's virus

Theiler's murine encephalomyelitis virus induces immune-mediated demyelination in susceptible mice after intracerebral inoculation. A naturally occurring, low pathogenic Theiler's murine encephalomyelitis virus variant showed a single amino acid change within a predominant Th epitope from lysine to arginine at position 244 of VP1. This substitution is the only one present in the entire viral capsid proteins. In this paper, we demonstrate that the majority of T cells specific for VP1(233-250) and VP2(74-86) from wild-type virus-infected mice are Th1 type and these VP1-specific cells poorly recognize the variant VP1 epitope (VP1(K244R)) containing the substituted arginine. In contrast, the Th2-type T cell population specific for these epitopes predominates in variant virus-infected mice. Immunization with UV-inactivated virus or VP1 epitope peptides could not duplicate the preferential Th1/Th2 responses following viral infection. Interestingly, the major APC populations, such as dendritic cells and macrophages, produce IL-12 on exposure to the pathogenic wild-type virus, whereas they preferentially produce IL-10 in response to the low pathogenic variant virus. Thus, such a spontaneous mutant virus may have a profoundly different capability to induce Th-type responses via selective production of cytokines involved in T cell differentiation and the consequent pathogenicity of virally induced immune-mediated inflammatory diseases.

CD4 T cells are the only lymphocytes needed to protect mice against rotavirus shedding after intranasal immunization with a chimeric VP6 protein and the adjuvant LT(R192G)

Intranasal immunization of mice with a chimeric VP6 protein and the mucosal adjuvant Escherichia coli heat labile toxin LT(R192G) induces nearly complete protection against murine rotavirus (strain EDIM [epizootic diarrhea of infant mice virus]) shedding for at least 1 year. The aim of this study was to identify the protective lymphocytes elicited by this new vaccine candidate. Immunization of mouse strains lacking one or more lymphocyte populations revealed that protection was dependent on alphabeta T cells but mice lacking gammadelta T cells and B cells remained fully protected. Furthermore, depletion of CD8 T cells in immunized B-cell-deficient mice before challenge resulted in no loss of protection, while depletion of CD4 T cells caused complete loss of protection. Therefore, alphabeta CD4 T cells appeared to be the only lymphocytes required for protection. As confirmation, purified splenic T cells from immunized mice were intraperitoneally injected into Rag-2 mice chronically infected with EDIM. Transfer of 2 x 10(6) CD8 T cells had no effect on shedding, while transfer of 2 x 10(5) CD4 T cells fully resolved shedding in 7 days. Interestingly, transfer of naive splenic CD4 T cells also resolved shedding but more time and cells were required. Together, these results establish CD4 T cells as effectors of protection against rotavirus after intranasal immunization of mice with VP6 and LT(R192G).

Adenovirus hexon protein is a potent adjuvant for activation of a cellular immune response

The capacity of recombinant adenoviruses (rAd) to induce immunization against their transgene products has been well documented. In the present study, we evaluated the vaccinal adjuvant role of rAd independently of its vector function. BALB/c mice received one subcutaneous injection of a mixture of six lipopeptides (LP6) used as a model immunogen, along with AdE1 degrees (10(9) particles), a first-generation rAd empty vector. Although coinjected with a suboptimal dose of lipopeptides, AdE1 degrees significantly improved the effectiveness of the vaccination, even in the absence of booster immunization. In contrast to mice that received LP6 alone or LP6 plus a mock adjuvant, mice injected with AdE1 degrees plus LP6 developed both a polyspecific T-helper type 1 response and an effector CD8 T-cell response specific to at least two class I-restricted epitopes. The helper response was still observed when immunization was performed using LP6 plus a mixture of soluble capsid components released from detergent-disrupted virions. When mice were immunized with LP6 and each individual capsid component, i.e., hexon, penton base, or fiber, the results obtained suggested that hexon protein was responsible for the adjuvant effect exerted by disrupted Ad particles on the helper response to the immunogen. Our results thus have some important implications not only in vaccinology but also for gene therapy using rAd vectors.

Preservation of motor function by inhibition of CD8+ virus peptide-specific T cells in Theiler's virus infection

Central nervous system-infiltrating CD8+ T cells are potential mediators of neuropathology in models of multiple sclerosis induced by Theiler's murine encephalomyelitis virus (TMEV) infection. C57BL/6 mice mount a vigorous cytotoxic T lymphocyte (CTL) response against the immunodominant virus peptide VP2121-130 and clear TMEV infection. Interferon-g (IFN-g)R-/- mice also mount a strong CTL response against the VP2121-130 epitope, but because of genetic deficiencies in critical IFN-g signaling pathways, they do not clear TMEV infection and develop prominent neurological deficits within 6 wk. This pronounced disease process, coupled with a defined CTL response, provides an ideal model for evaluating the importance of antiviral CTL activity in the development of severe demyelination and loss of motor neuron function. By administering the VP2121-130 peptide before and during TMEV infection, 99% of the VP2121-130-specific CD8+ T cell response was inhibited. No decrease in virus infection was observed. Peptide treatment did result in significantly less motor dysfunction, even when no differences in levels of demyelination were observed. Although most investigators focus on the role of CD4+ T cells in demyelinating disease, these studies are the first to demonstrate a clear contribution of antiviral CD8+ T cells in neurological injury in a chronic-progressive model of multiple sclerosis.

Delivery of herpes simplex virus vectors through liposome formulation

Viral vectors have been widely used as gene delivery vehicles for both experimental and clinical investigations. Although these vectors are capable of achieving high gene transduction efficiency in vitro, one of the major limitations facing the therapeutic viral vectors is that the preexisting host anti-vector immunity can substantially reduce their transduction efficiency in vivo. This is especially of concern when the therapeutic remedy requires repeated systemic administration. Here we report the delivery of herpes simplex virus (HSV) derived vectors through liposome formulation. In these studies, we have prepared HSV vectors in three different forms for liposome formulation: purified viral DNA (obtained from a bacterial artificial chromosome containing an infectious HSV genome), HSV capsids, and intact viral particles. All three forms of HSV were readily transfected into cultured cells and infectious virus was efficiently generated. Furthermore, introduction of HSV vectors as DNA/liposome complexes improved in vivo transduction efficiency, by effectively evading the host anti-HSV immunity during systemic administration. We conclude that viral vectors such as HSV can be systemically delivered through liposome formulation for safe and repeated administration for gene transduction or oncolytic purposes.

Enhancement of the immunity to foot-and-mouth disease virus by DNA priming and protein boosting immunization

Subunit vaccination is effective in eliciting humoral responses to a variety of viral antigens, however, it has not generated persistent protective immunity to foot-and-mouth disease virus (FMDV). In this study, we observed that priming mice with a DNA plasmid encoding VP1 of the FMDV O/Taiwan/97 capsid protein followed by boosting with a VP1 peptide conjugate (P29-KLH) resulted in production of not only high titers of antibodies but also antibodies with FMDV neutralizing activities. Moreover, the mice immunized in this manner cleared the virus from their sera in FMDV challenge experiments. Mice subjected to DNA plasmid priming and P29-KLH protein boosting had relatively higher ratio of IgG2a/IgG1 than those primed and boosted with P29-KLH conjugate. Addition of an oligodeoxynucleotide (ODN) containing immunostimulatory cytosine-phosphate-guanosine (CpG) motifs to P29-KLH conjugate also induced a higher ratio of IgG2a/IgG1 and significantly higher titer of neutralizing antibodies. These results indicate that treating animals with DNA plasmids priming and FMDV antigen(s) boosting may elicit immunity to FMD and this immune response may be augmented by CpG ODN.

Pre-clinical safety and efficacy of TA-CIN, a recombinant HPV16 L2E6E7 fusion protein vaccine, in homologous and heterologous prime-boost regimens

Human papillomavirus (HPV) E6 and E7 oncoproteins are attractive targets for T-cell-based immunotherapy of cervical intraepithelial neoplasia (CIN) and cancer. A newly designed vaccine, comprising the HPV16 L2, E6 and E7 as a single fusion protein (TA-CIN), was shown to elicit HPV16-specific CTL, T-helper cells and antibodies in a pre-clinical mouse model. These immune responses effectively prevented outgrowth of HPV16-positive tumour cells in a prophylactic setting as well as in a minimal residual disease setting. CTL immunity was optimally induced when TA-CIN was employed in heterologous prime-boost regimens in combination with TA-HPV, a clinical grade vaccinia-based vaccine. These data provide a scientific basis for the use of TA-CIN, alone or in combination with TA-HPV in future human trials.

Improvement of gene transfer to cervical cancer cell lines using non-viral agents

Virus-like particles (VLPs) composed of recombinant capsid protein L1 and L2 of human papillomavirus type 16 were conjugated with polylysine (PL) and gene transfer was performed using VLP-PL conjugates to allow the expression of targeted gene. When HeLa cells were incubated with VLP-PL conjugate coupled with plasmid cytomegalovirus beta-galactosidase (pCMVbeta-gal), about 10% of cells were transfected and demonstrated beta-galactosidase activity. Hence chloramphenicol acetyltransferase activity was also expressed significantly in VLP-PL-plasmid simian virus 2 chloramphenicol acetyl transferase (pSV2CAT)-transfected cells, VLP-PL conjugate was tested whether it could transfer a tumor suppressor gene, pCMVp53, to HeLa cells and the exogenously provided p53 gene complexed to VLP-PL conjugate was detected from HeLa cells by polymerase chain reaction (PCR) analysis. Interestingly, additional increase of transfection efficiency was demonstrated in the presence of poloxamer 407 when C-33A cells were transfected with VLP-PL-pCMVbeta-gal complex. The result support the notion that VLP-PL conjugate may be a promising vector to transfer genetic materials into cancer cells and poloxamer 407 can be used for enhancing the transfection efficiency of VLP-PL conjugate.

DNA-carrier proteins for targeted gene delivery

The development of vectors for cell-specific gene delivery is a major goal of gene therapeutic strategies. Significant progress has been made in the construction of non-viral vectors that combine different functions required for gene transfer in an artificial complex. To some extent this can be achieved by complexing plasmid DNA with synthetic compounds such as lipids and polycations. Alternative approaches rely on the activities of natural or recombinant DNA-carrier proteins to achieve uptake and intracellular delivery of plasmid DNA. Nuclear proteins such as histones and members of the high mobility group protein family have been shown to condense DNA and transfect cultured cells. Some structural proteins of DNA viruses spontaneously assemble with plasmid DNA and form transfection-competent pseudocapsids. In addition, chimeric fusion proteins have been engineered that incorporate in a single polypeptide chain heterologous protein domains which facilitate binding to plasmid DNA, specific recognition of target cells, induction of receptor-mediated endocytosis, and DNA transport through intracellular compartments.

Gene delivery via polyomavirus major capsid protein VP(1), isolated from recombinant Escherichia coli

In this study we attempted to investigate the feasibility of transferring exogenous DNA into the recipient host via polyomavirus major capsid protein VP(1) pseudocapsids generated from recombinant Escherichia coli, designated PyVP(1,E), both in vitro and in vivo. NIH-3T3 and FR3T3 cells were transfected with pCMV beta and pPyMT-1 plasmid DNA, respectively. In vitro DNA transfection was carried out via Pseudofect- and PyVP(1,E)-mediated methods, or by co-precipitation with calcium phosphate. Expression of beta-galactosidase and PyMT reporter genes was examined by Western-blot analysis. Parallel experiments were performed in vivo by direct injection of pCMV beta and pPyMT-1 plasmid DNA, complexed with PyVP(1,E), into the livers of Wistar rats, followed by Western-blot analysis and histochemical staining. The results obtained from in vitro transfection experiments showed that expression of the reporter genes can be detected in the recipient cells at 48 h post-transfection. PyVP(1,E) was shown to exhibit similarly efficient in vitro DNA transfection properties to Pseudofect, which was obtained from recombinant baculovirus.

Duplicated DQ haplotypes increase the complexity of restriction element usage in cattle

The MHC of cattle encodes two distinct isotypes of class II molecules, DR and DQ. Unlike humans, cattle lack the DP locus and about half the common haplotypes express duplicated DQ genes. The number and frequency of DQA and DQB alleles means that most cattle are heterozygous. If inter- and/or intrahaplotype pairing of DQA and DQB molecules occurs, cattle carrying DQ-duplicated haplotypes may express more restriction elements than would be predicted by the number of expressed alleles. We are investigating whether duplicated haplotypes cause differences in immune response, particularly in terms of generating protective immunity. We have analyzed the Ag-presenting function of DQ molecules in two heterozygous animals, one of which carries a duplicated haplotype. We compared the class II isotype specificity of T cell clones recognizing a putative vaccinal peptide from foot-and-mouth disease virus (FMDV15). We show for the first time that bovine T cells can recognize Ag in the context of DQ molecules. We also present evidence that interhaplotype pairings of DQA and DQB molecules form functional restriction elements. Both animals showed distinct biases to usage of particular restriction elements. Mainly DQ-restricted clones were derived from the animal with duplicated DQ genes, whereas the majority of clones from the animal with a single DQ gene pair were DR restricted. Furthermore, haplotype bias was observed with both animals. These experiments show that understanding of class II chain pairing in addition to knowledge of the genotype may be important in vaccine design where effective epitope selection is essential.

Human immune responses to a novel norwalk virus vaccine delivered in transgenic potatoes

A new approach for delivering vaccine antigens is the use of inexpensive, plentiful, plant-based oral vaccines. Norwalk virus capsid protein (NVCP), assembled into virus-like particles, was used as a test antigen, to determine whether immune responses could be generated in volunteers who ingested transgenic potatoes. Twenty-four healthy adult volunteers received 2 or 3 doses of transgenic potato (n=20) or 3 doses of wild-type potato (n=4). Each dose consisted of 150 g of raw, peeled, diced potato that contained 215-751 microgram of NVCP. Nineteen (95%) of 20 volunteers who ingested transgenic potatoes developed significant increases in the numbers of specific IgA antibody-secreting cells. Four (20%) of 20 volunteers developed specific serum IgG, and 6 (30%) of 20 volunteers developed specific stool IgA. Overall, 19 of 20 volunteers developed an immune response of some kind, although the level of serum antibody increases was modest.

Humoral immunity to adeno-associated virus type 2 vectors following administration to murine and nonhuman primate muscle

Adeno-associated virus (AAV) is being developed as a vector capable of conferring long-term gene expression, which is useful in the treatment of chronic diseases. In most therapeutic applications, it is necessary to readminister the vector. This study characterizes the humoral immune response to AAV capsid proteins following intramuscular injection and its impact on vector readministration. Studies of mice and rhesus monkeys demonstrated the formation of neutralizing antibodies to AAV capsid proteins that persisted for over 1 year and then diminished, but this did not prevent the efficacy of vector readministration. More-detailed studies strongly suggested that the B-cell response was T cell dependent. This was further evaluated with a blocking antibody to human CD4, primatized for clinical trials, in a biologically compatible mouse in which the endogenous murine CD4 gene was functionally replaced with the human counterpart. Transient pharmacologic inhibition of CD4 T cells with CD4 antibody prevented an antivector response long after the effects of the CD4 antibody diminished; readministration of vector without diminution of gene expression was possible. Our studies suggest that truly durable transgene expression (i.e., prolonged genetic engraftment together with vector readministration) is possible with AAV in skeletal muscle, although it will be necessary to transiently inhibit CD4 T-cell function to avoid the activation of memory B cells.

Photodynamic therapy: tumor targeting with adenoviral proteins

A brief summary of the mechanisms involved in photodynamic therapy (PDT) and the role of delivery vehicles for photosensitizer targeting is addressed. Phthalocyanines (Pc) have been coupled to adenovirus type 2 capsid proteins including the hexon, the penton base and the fiber to enhance their target selectivity. Adenovirus penton base proteins contain the arginine-glycine-aspartic acid peptidic sequence (RGD) motif known to bind with great affinity and high specificity to integrin receptors, expressed by several types of cancer. Tetrasulfonated aluminum phthalocyanine (AlPcS4) was covalently coupled to the various capsid proteins via one or two caproic acid spacer chains (A1 or A2) in 7:1 up to 66:1 molar ratios. The capacity of the bioconjugates for singlet oxygen production, as measured by an L-tryptophan oxidation assay, was strongly reduced, likely reflecting scavenging by the carrier. Cell adsorption and in vitro photocytotoxicity assays were carried out using the A549 and HEp2 human cell lines expressing integrin receptors, and one murine, the EMT-6 cell line, which lacks receptors for the RGD sequence. The AlPcS4A2-protein complexes induced greater cytotoxicity as compared to the analogous AlPcS4A1 preparations. The penton base-AlPcS4A2 derivative was the more phototoxic for all cell lines tested. Tumor response studies using Balb/c mice with EMT-6 tumor implants demonstrated that the free AlPcS4A2 induced complete tumor regression at a dose of 1 mumol/kg and 400 J/cm2, which is comparable to the activity of the known AlPcS2adj. A mixture of adenovirus type 2 soluble proteins covalently labeled with AlPcS4A2 required 0.5 mumol/kg to induce the same response with the same light dose, suggesting that the high affinity RGD/receptor complex is able to target Pc for PDT.

Enhancement of the immunogenicity of a synthetic peptide bearing a VP3 epitope of hepatitis A virus

The immune responses elicited in mice by different forms of the VP3(110-121) B-epitope of the hepatitis A virus (HAV) were studied. Different forms of incorporation in liposomes were tested, encapsulation, rather than surface exposure, being the best antigenic preparation. Three larger peptides of the VP3 epitope, two of them containing a hepatitis B virus T-epitope, and a third containing a putative T-epitope of HAV (VP3(102-121)) were assayed. While this latter T-epitope induced an enhancement of the response against the VP3 B-epitope, the artificially coupled T-epitopes failed to induce a significant increase. The administration of two multiple antigenic peptide (MAP) constructs, the first containing the VP3(110-121) and VP1(11-25) HAV sequences and the second only the VP1(11-25) sequence, also suggested the presence of a T-epitope, since the response against the VP1 peptide was increased in the first construct.

A single dose immunization with rabbit haemorrhagic disease virus major capsid protein produced in Saccharomyces cerevisiae induces protection

The gene coding for the major capsid protein (VP60) from rabbit haemorrhagic disease virus was expressed in Saccharomyces cerevisiae under the phosphoglycerate kinase promoter. The recombinant VP60 produced in yeast was antigenically similar to the viral polypeptide as determined with a polyclonal serum. Electron microscopic observation of the recombinant yeast-derived antigen revealed the presence of virus-like particles similar in size and appearance to native capsids. Subcutaneous vaccination of rabbits with a single dose of this antigen in the absence of commercial adjuvants conferred complete protection against the haemorrhagic disease.

Vaccination of cattle with bovine papillomavirus type 4 L2 elicits the production of virus-neutralizing antibodies

Prophylactic vaccination of cattle with the N terminus (L2a, aa 11-200) of the minor capsid protein L2 completely prevented bovine papillomavirus type 4 (BPV-4) infection of the alimentary canal. To investigate the mechanisms underlying protection from viral infection, sera from vaccinated animals were analysed in neutralization assays both in the nude mouse xenograft system and in cattle. BPV-4 retained its infectivity when incubated with preimmune cattle sera, whereas, when incubated with immune sera from animals vaccinated with either whole L2 or its N terminus L2a, its infectivity was greatly reduced, indicating that the immune sera had neutralizing activity against the virus. This activity could be abrogated by absorbing the immune sera with L2 or L2a, thus indicating that virus neutralization was due to the presence in the immune sera of anti-L2 antibodies.

Immunization with recombinant protein: conditions for cytotoxic T cell and/or antibody induction

Safe vaccines should optimally induce both cell-mediated and humoral immunity. Recently, it has been shown that protective cytotoxic T cells (CTLs) can be induced not only with live vaccines, but also with recombinant viral proteins. This report shows in C57BL/6 (H-2b) mice that the recombinant nucleoprotein (N) of vesicular stomatitis virus (VSV) induced protective CTLs but no neutralizing antibodies in mice, whereas the recombinant glycoprotein (G) of VSV alone induced neutralizing antibodies but no CTLs. If the N and G of VSV were coinjected, both CTLs and a long-lasting neutralizing IgG response was measurable, demonstrating that mixed vaccines can be used to induce protective CTLs and antibodies with an efficiency comparable to live virus. In an attempt to define optimal conditions for CTL priming, the intravenous, intraperitoneal and subcutaneous route of injection were compared. Intravenous injection of recombinant VSV-N induced up to 30 times higher responses than the latter two routes. Finally, we tried to define conditions inducing only CTLs and no antibodies binding to the native protein form, or vice versa, only antibodies and no CTLs. Intravenous injection of boiled VSV-N induced a CTL response but no antibodies specific for the native VSV-N, whereas VSV-N injected subcutaneously in incomplete Freund's adjuvant induced high amounts of anti-VSV-N antibodies but virtually no CTLs. The conditions defined here permit vaccines to be designed which would function along selected and defined immunological effector pathways.

The S1 glycoprotein but not the N or M proteins of avian infectious bronchitis virus induces protection in vaccinated chickens

The S1, N and M proteins, obtained from the nephropathogenic N1/62 strain of infectious bronchitis virus (IBV) by immunoaffinity purification with monoclonal antibodies, were used for immunization of chickens. For all three antigens multiple immunizations were necessary for induction of an antibody response. Protection of chickens vaccinated with the S1 glycoprotein against virulent challenge was demonstrated by the complete absence of virus in tracheas and kidneys of vaccinated chickens. Following four immunizations with the S1 glycoprotein 71% and 86% of chickens were protected at the level of tracheas and kidneys, respectively. Three immunizations with the S1 glycoprotein protected 70% and 10% of chickens at the level of kidney and trachea, respectively. Neither the N nor the M antigen induced protection to a virulent challenge with the nephropathogenic N1/62 strain of IBV after four immunizations. Virus neutralizing, haemagglutination inhibiting and ELISA antibodies were detected in chickens immunized with the S1 glycoprotein and inactivated N1/62 virus, however there was no correlation between the presence of any of these antibodies and protection.

Resistance of mice vaccinated with rabies virus internal structural proteins to lethal infection

Mice were vaccinated with recombinant vaccinia virus (rVac) expressing the glycoprotein (G), nucleoprotein (N), phosphoprotein (NS) or matrix protein (M) of rabies virus and their resistance to peripheral lethal infection with street rabies virus was examined. Mice vaccinated with rVac-G or rVac-N developed strong antibody responses to the corresponding proteins and essentially all mice survived challenge infection. Mice vaccinated with rVac-NS or rVac-M developed only a slight antibody response, however, a significant protection (59%) was observed in the rVac-NS-vaccinated mice, whereas rVac-M-vaccinated mice were not protected. No anti-G antibodies were detected in the sera of mice which has been vaccinated with rVac-N or rVac-NS and survived challenge infection. Passive transfer of anti-N monoclonal antibodies (MAbs) recognizing an epitope located on amino acids 1-224 of the protein prior to challenge resulted in significant protection, although the protection was not complete even with a high amount of antibodies. In contrast, none of the mice given MAbs recognizing an epitope of amino acids 247-415 or F(ab')2 fragments from a protective MAb IgG were protected. Administration of anti-CD 8 MAb to rVac-N-vaccinated mice showed no significant effect on protection. Our observations suggest that a considerable part of the protection achieved by the vaccination with rVac-N can be ascribed to the intact anti-N antibodies recognizing an epitope located on amino acids 1-224 of the protein.