Real time PCR for the assessment of CD8+ T cellular immune response after prophylactic vaccinia vaccination.

BACKGROUND: The magnitude of specific CD8+ T cell reactivity responsible for vaccine-induced protection against smallpox infection has not yet been fully elucidated. Among other techniques, RT-PCR for the monitoring of cytokine release in effector T cells against tumor and viral antigens has demonstrated a novel promising method. OBJECTIVE: To determine the functional status of antigen specific CD8+ T cells in healthy participants before and 4 weeks after prophylactic vaccination (Lister strain) against smallpox using quantitative real-time PCR (qRT-PCR). STUDY DESIGN: Changes of interferon-gamma (IFNgamma) mRNA expression levels on short term ex vivo peptide antigen stimulation were measured. The corresponding specific CD8+ T cell reactivity was then displayed as CD8-normalized IFN-gamma levels (IFN-gamma/CD8 ratio). RESULTS: We found a 5-9 fold increase of CD8+ T cell reactivity in three out of four vaccinated individuals. The kinetics and strength determined in responders reveal a virus specific T cell effector repertoire pre-vaccination and a corresponding functional state after immunization comparable also to data obtained from tetramer- and ELISPOT analysis. CONCLUSIONS: Apart from protective vaccinia-specific neutralizing antibodies, the presence of antigen-specific CD8+ T-cells has been demonstrated after vaccinia vaccination. In concordance with others, results from this PCR-based study indicate that this smallpox vaccine induces strong vaccinia virus-specific CD8+ and IFN-gamma producing T cell responses.     

Neutralization assay using a modified vaccinia virus Ankara vector expressing the green fluorescent protein is a high-throughput method to monitor the humoral immune response against vaccinia virus

Vaccination against smallpox is again considered in order to face a possible bioterrorist threat, but the nature and the level of the immune response needed to protect a person from smallpox after vaccination are not totally understood. Therefore, simple, rapid, and accurate assays to evaluate the immune response to vaccinia virus need to be developed. Neutralization assays are usually considered good predictors of vaccine efficacy and more informative with regard to protection than binding assays. Currently, the presence of neutralizing antibodies to vaccinia virus is measured using a plaque reduction neutralization test, but this method is time-consuming and labor-intensive and has a subjective readout. Here, we describe an innovative neutralization assay based on a modified vaccinia virus Ankara (MVA) vector expressing the green fluorescent protein (MVA-gfp). This MVA-gfp neutralization assay is rapid and sensitive and has a high-throughput potential. Thus, it is suitable to monitor the immune response and eventually the efficacy of a large campaign of vaccination against smallpox and to study the vector-specific immune response in clinical trials that use genetically engineered vaccinia viruses. Most importantly, application of the highly attenuated MVA eliminates the safety concern in using the replication-competent vaccinia virus in the standard clinical laboratory.     

A vaccinia virus renaissance: New vaccine and immunotherapeutic uses after smallpox eradication

In 1796, Edward Jenner introduced the concept of vaccination with cowpox virus, an Orthopoxvirus within the family Poxviridae that elicits cross protective immunity against related orthopoxviruses, including smallpox virus (variola virus). Over time, vaccinia virus (VACV) replaced cowpox virus as the smallpox vaccine, and vaccination efforts eventually led to the successful global eradication of smallpox in 1979. VACV has many characteristics that make it an excellent vaccine and that were crucial for the successful eradication of smallpox, including (1) its exceptional thermal stability (a very important but uncommon characteristic in live vaccines), (2) its ability to elicit strong humoral and cell-mediated immune responses, (3) the fact that it is easy to propagate, and (4) that it is not oncogenic, given that VACV replication occurs exclusively within the host cell cytoplasm and there is no evidence that the viral genome integrates into the host genome. Since the eradication of smallpox, VACV has experienced a renaissance of interest as a viral vector for the development of recombinant vaccines, immunotherapies, and oncolytic therapies, as well as the development of next-generation smallpox vaccines. This revival is mainly due to the successful use and extensive characterization of VACV as a vaccine during the smallpox eradication campaign, along with the ability to genetically manipulate its large dsDNA genome while retaining infectivity and immunogenicity, its wide mammalian host range, and its natural tropism for tumor cells that allows its use as an oncolytic vector. This review provides an overview of new uses of VACV that are currently being explored for the development of vaccines, immunotherapeutics, and oncolytic virotherapies.     

Microarray assay for evaluation of the genetic stability of modified vaccinia virus Ankara B5R gene

Adverse events associated with the use of live smallpox vaccines have led to the development of a new generation of attenuated smallpox vaccines that are prepared in cultured cells as alternatives. The inability to conduct direct clinical evaluation of their efficacy in humans demands that licensure be based on animal studies and exhaustive evaluation of their in vitro properties. One of the most important characteristics of live viral vaccines is their genetic stability, including reversion of the vaccine strain to more virulent forms, recombination with other viral sequences to produce potentially pathogenic viruses, and genetic drift that can result in decrease of immunogenicity and efficacy. To study genetic stability of an immunoessential vaccinia virus gene in a new generation smallpox vaccine, an advanced oligonucleotide microchip was developed and used to assay for mutations that could emerge in B5R gene, a vaccinia virus gene encoding for a protein that contains very important neutralizing epitopes. This microarray contained overlapping oligonucleotides covering the B5R gene of modified vaccinia virus Ankara (MVA), a well-studied candidate smallpox vaccine. The microarray assay was shown to be able to detect even a single point mutation, and to differentiate between vaccinia strains. At the same time, it could detect newly emerged mutations in clones of vaccinia strains. In the work described here, it was shown that MVA B5R gene was stable after 34 passages in Vero and MRC-5 cells that were proposed for use as cell substrates for vaccine manufacture. Potentially, the proposed method could be used as an identity test and could be extended for the entire viral genome and used to monitor consistency of vaccine production.     

DNA/MVA HIV-1/AIDS vaccine elicits long-lived vaccinia virus-specific immunity and confers protection against a lethal monkeypox challenge

Modified vaccinia Ankara (MVA) is being tested in humans as an alternative to the current smallpox vaccine Dryvax. Here, we compare the magnitude and longevity of protective immune responses elicited by a DNA/MVA HIV-1 vaccine with those elicited by Dryvax using a monkeypox virus/macaque model. The DNA/MVA vaccine elicited similar levels of vaccinia virus (VV)-specific antibody and 5-10-fold lower levels of VV-specific cellular responses than Dryvax. This MVA-elicited cellular and humoral immunity was long-lived. A subset of the DNA/MVA- and Dryvax-vaccinated macaques were subjected to a lethal monkeypox virus challenge at 3 years after vaccination. All of the vaccinated monkeys survived, whereas the unvaccinated controls succumbed to monkeypox. The viral control correlated with early postchallenge levels of monkeypox-specific neutralizing antibody but not with VV-specific cellular immune response. Thus, our results demonstrate the elicitation of long lasting protective immunity for a lethal monkeypox challenge by a DNA/MVA HIV-1 vaccine.     

Comparison of methods for detection of vaccinia virus in patient specimens

We analyzed a shell vial culture assay (SVA), real-time PCR, and a direct fluorescent antibody assay (DFA) for rapid detection of vaccinia virus from vaccination sites of Dryvax vaccine recipients. Of 47 samples assayed, 100% were positive by PCR, 89% were positive by SVA, and 40% were positive by DFA. DFA was limited by the need for adequate numbers of cells, with 32% of samples inadequate for interpretation. DFA performed better with specimens from patients who had not previously received the vaccine. PCR was positive for longer times postvaccination than was SVA. Infectious virus could be recovered after 45 min of acetone fixation of shell vial coverslips. Commercially available polyclonal antibodies cross-reacted with other orthopoxviruses and herpes simplex 1, but commercially available monoclonal antibodies were specific for vaccinia virus. In summary, PCR was the most sensitive test for detecting vaccinia virus in clinical specimens, while the DFA was the most rapid but the least sensitive test.     

The nonreplicating smallpox candidate vaccines defective vaccinia Lister (dVV-L) and modified vaccinia Ankara (MVA) elicit robust long-term protection

Current smallpox vaccines are live vaccinia viruses that replicate in the vaccinee inducing immunity against the deadly disease smallpox. Replication resulting in virus spread within the host, however, is the major cause of severe postvaccinal adverse events. Therefore, attenuated strains such as modified vaccinia Ankara (MVA) or LC16m8 are candidates as next generation vaccines. These strains are usually grown in primary cells in which mass production is difficult and have an unknown protective potential in humans. Proven vaccine strains of defined origin and modern production techniques are therefore desirable. In this study, defective vaccinia virus (dVV) lacking a gene essential for replication (derived from the Lister vaccine in a complementing cell line) was compared with the Wyeth smallpox vaccine strain and with MVA in mouse animal models using cowpox and ectromelia virus challenge. Similar to MVA, prime-boost immunizations with defective vaccinia induced robust long-term immunity, suggesting it as a promising next generation smallpox vaccine.     

Enhanced immunogenicity and protective effect conferred by vaccination with combinations of modified vaccinia virus Ankara and licensed smallpox vaccine Dryvax in a mouse model

Significant adverse events are associated with vaccination with the currently licensed smallpox vaccine. Candidate new-generation smallpox vaccines such as the replication-defective modified vaccinia virus Ankara (MVA) produce very few adverse events in experimental animals and in limited human clinical trials conducted near the end of the smallpox eradication campaign. Efficacy evaluation of such new-generation vaccines will be extraordinarily complex, however, since the eradication of smallpox precludes a clinical efficacy trial and the correlates of protection against smallpox are unknown. A combination of relevant animal efficacy studies along with thorough comparative immunogenicity studies between traditional and new-generation smallpox vaccines will be necessary for vaccine licensure. In the present study, a variety of immune responses elicited by MVA and the licensed smallpox vaccine Dryvax in a murine model were compared, with a focus on mimicking conditions and strategies likely to be employed in human vaccine trials. Immunization of mice with MVA, using several relevant vaccination routes including needle-free delivery, elicited humoral and cellular immune responses qualitatively similar to those elicited by vaccination with Dryvax. Similar levels of vaccinia-specific IgG and neutralizing antibody were elicited by Dryvax and MVA when higher doses (approximately 1 log) of MVA were used for immunization. Antibody levels peaked at about 6 weeks post-immunization and remained stable for at least 15 weeks. A booster immunization of either MVA or Dryvax following an initial priming immunization with MVA resulted in an enhanced IgG titer and neutralizing antibody response. In addition, both Dryvax and various MVA vaccination protocols elicited antibody responses to the extracellular enveloped form of the virus and afforded protection against a lethal intranasal challenge with vaccinia virus WR.     

Identification of vaccinia CD8+ T-cell epitopes conserved among vaccinia and variola viruses restricted by common MHC class I molecules, HLA-A2 or HLA-B7

Immunization with vaccinia virus results in long-lasting protection against smallpox and is an approach that has been successfully used to eliminate natural smallpox infections worldwide. Today, vaccinia virus is very important not only as a vaccine virus to protect human against smallpox, but also as an expression vector for immunization against other infectious diseases, such as HIV and cancer. In this article, we identify three new vaccinia human CD8+ T-cell epitopes conserved among vaccinia and variola viruses restricted by HLA-A2, HLA-B7, or HLA-B*3502, which belongs to the HLA-B7 supertype. Identification of these CD8+ T-cell epitopes restricted by common HLA alleles will help to quantitate human CD8+ T-cell responses to licensed and experimental smallpox vaccines and to vaccinia virus vectors. CD8+ T-cell responses specific to these epitopes can also be used to quantitate cellular immune responses, especially with new smallpox vaccines that do not induce a "take," such as the modified vaccinia virus Ankara strain. Combined with previous reports by us and others, these results show that there are some vaccinia viral proteins containing multiple epitopes restricted by different MHC molecules of humans and mice.     

Laboratory confirmation of generalized vaccinia following smallpox vaccination

The reinitiation of smallpox vaccination has renewed interest in implementing modern diagnostic methods to assess orthopoxvirus infection and adverse events following vaccination. We report here the laboratory confirmation of vaccinia virus in pustular lesions of a healthy adult vaccinee by use of a two-tier algorithm incorporating TaqMan PCR and electron microscopy.     

Cell-mediated immune responses to smallpox vaccination

We report that vaccine dilution (1:1 or 1:10) and previous vaccinia virus vaccination status had no significant effect on cell-mediated immune responses (i.e., the immediate vaccinia virus-specific gamma interferon-producing T-cell response measured by enzyme-linked immunospot assay) 1 month after smallpox vaccination (Lancy-Vaxina; Berna Biotech, Switzerland).     

The N-terminal domain of the vaccinia virus E3L-protein is required for neurovirulence, but not induction of a protective immune response

Encephalitis is a rare, but serious complication from vaccination against smallpox using replication competent strains of vaccinia virus. In this report we describe mutants of vaccinia virus, containing N-terminal deletions of the vaccinia virus interferon resistance gene, E3L, that are attenuated for neuropathogenesis in a mouse model system. These recombinant viruses replicated to high titers in the nasal mucosa after intra-nasal infection of C57BL/6 mice but failed to spread to the lungs or brain. These viruses demonstrated reduced pathogenicity after intra-cranial infection as well, indicating a decrease in neurovirulence. Intra-nasal inoculation or inoculation by scarification with a low dose of recombinant virus containing a deletion of the entire N-terminal domain of E3L protected against challenge with a high dose of wild-type vaccinia virus, suggesting that this replication competent, but attenuated strain of vaccinia virus may have promise as an improved vaccine for protecting against smallpox, and as a vector for inducing mucosal immunity to heterologous pathogenic organisms.     

Identification and preliminary characterization of vaccinia virus (Dryvax) antigens recognized by vaccinia immune globulin

Using vaccinia immune globulin (VIG), a high-titer antibody preparation from immunized subjects, we demonstrate that the humoral immune response in humans is directed against numerous antigens in the Dryvax vaccine strain. Western blot and immunoprecipitation analyses revealed highly antigenic proteins associated with both the extracellular enveloped virus and intracellular mature virus forms. The modified vaccinia virus Ankara (MVA), a new generation smallpox vaccine that is attenuated for replication in humans, expresses most, but not all, of the major vaccinia antigens recognized by antibodies in VIG, lacking the highly antigenic protein corresponding to the A-type inclusion body protein. Since new-generation smallpox vaccines such as MVA will require extensive comparison to traditional smallpox vaccines in animal models of immunogenicity and protection, we compared the vaccinia virus antigens recognized by VIG to those recognized by sera from Dryvax and MVA immunized mice. The humoral immune response in immunized mice is qualitatively similar to that in humans.     

Detection of vaccinia virus DNA on the LightCycler by fluorescence melting curve analysis

After eradication of variola virus the worldwide vaccination program was stopped to avoid the severe complications observed in a small fraction of vaccinees. Hence, there is at least one non-vaccinated generation in the human population that is immunologically naive with respect to variola virus infections. The possibility of a deliberate release of variola virus by bioterrorist attacks has led to the resumption of vaccination of hospital employees and military personnel with vaccinia virus in certain parts of the world. However, the appearance of a single confirmed smallpox case worldwide would result in vaccination of possible contact persons with vaccinia virus. Therefore, reliable confirmation of vaccinia virus in patients presenting with smallpox-like syndromes is required. A vaccinia virus-specific single nucleotide polymorphism was identified in the gene B8R coding for a vaccinia virus IFNgamma receptor. Based on this polymorphism, the LightCycler real-time PCR assay detects vaccinia virus DNA in a linear range from 10(6) to 10 genome equivalents and discriminates vaccinia virus from other orthopoxviruses by fluorescence melting curve analysis (DeltaT = 9 degrees C). While the assay amplifies generically DNA of all orthopoxviruses tested, amplification curves are only displayed for vaccinia virus strains including strains formerly used for vaccination. In addition, an internal amplification control is described that allows reliable interpretation of results.     

Neutralization Assay Using a Modified Vaccinia Virus Ankara Vector Expressing the Green Fluorescent Protein Is a High-Throughput Method To Monitor the Humoral Immune Response against Vaccinia Virus

Vaccination against smallpox is again considered in order to face a possible bioterrorist threat, but the nature and the level of the immune response needed to protect a person from smallpox after vaccination are not totally understood. Therefore, simple, rapid, and accurate assays to evaluate the immune response to vaccinia virus need to be developed. Neutralization assays are usually considered good predictors of vaccine efficacy and more informative with regard to protection than binding assays. Currently, the presence of neutralizing antibodies to vaccinia virus is measured using a plaque reduction neutralization test, but this method is time-consuming and labor-intensive and has a subjective readout. Here, we describe an innovative neutralization assay based on a modified vaccinia virus Ankara (MVA) vector expressing the green fluorescent protein (MVA-gfp). This MVA-gfp neutralization assay is rapid and sensitive and has a high-throughput potential. Thus, it is suitable to monitor the immune response and eventually the efficacy of a large campaign of vaccination against smallpox and to study the vector-specific immune response in clinical trials that use genetically engineered vaccinia viruses. Most importantly, application of the highly attenuated MVA eliminates the safety concern in using the replication-competent vaccinia virus in the standard clinical laboratory.     

Smallpox: residual antibody after vaccination

Of all the microorganisms and toxins, poxviruses (Orthopoxvirus) have the greatest potential for use by terrorists. These viruses can spread rapidly through the environment following initial infection. In 1980, the World Health Organization Eradication Program discontinued vaccination for smallpox and declared that the disease had been eliminated. With the threat of smallpox virus as a bioterrorism weapon, questions have been asked about the persistence of protection (as offered by antibodies) following vaccination with vaccinia virus vaccine. To address this, sera from 204 adults vaccinated as children were tested by enzyme immunoassay (EIA) for the presence of vaccinia virus antibody. Of the 204 individuals whose sera were examined for the presence of vaccinia antibody, 165 (80.9%) had been vaccinated once and 39 (19.1%) had been vaccinated at least twice. Of the 165 sera from individuals vaccinated once, 112 (67.9%) were positive. Of the 39 sera from individuals vaccinated more than once, 31 (79.5%) were positive. The presence of a vaccination scar at the time of blood collection was not determined. Fifty-six nonvaccinated individuals, under 30 years of age, were tested by EIA; four of these (7.1%) were positive for vaccinia virus antibody by EIA. Forty-four EIA-positive and 16 EIA-negative sera were also tested by serum neutralization (SN) as a comparison with the EIA test results; one serum (negative by EIA) was SN positive. No attempt was made to ascertain any demographics other than age (date of birth) and "remembered" times of vaccination.     

Subcutaneous Administration of a Recombinant Vaccinia Virus Vaccine Expressing Multiple Envelopes of HIV-1

A critical goal of HIV vaccine development is the identification of safe and immunogenic vectors. Recombinant vaccinia virus is a highly effective vaccine vector, with demonstrated capacity to protect animals from various viral pathogens, including rabies. Unlike many other candidate vaccine vectors, vast human experience exists with the parenteral smallpox vaccine. However, consideration of recombinant vaccinia virus as a modern vaccine is complicated by the relatively high prevalence of immunocompromised persons compared to such prevalence 4 or more decades ago (when smallpox vaccination was still routine). Administering vaccine by the subcutaneous (SQ) route, rather than the traditional scarification route, could address these concerns. SQ administration could prevent transmission of vaccinia virus to potentially vulnerable persons; it could also avoid the most common adverse events, which are cutaneous in nature. However, previous studies suggest that elicitation of immune response against passenger gene products following SQ administration requires development of a superficial pox lesion, defeating the intention of SQ administration. This is the first report to demonstrate that SQ administration of recombinant vaccinia virus does elicit immune response to the passenger protein in the absence of a cutaneous pox lesion. Results further show that a multi-envelope HIV vaccine can elicit antibody responses toward heterologous HIV-1 not represented by primary sequence in the vaccine. These findings have global implications because they support the consideration of recombinant vaccinia virus as a valuable HIV vaccine vector system.     

Performance of virus isolation and Directigen Flu A to detect influenza A virus in experimental human infection.

BACKGROUND: Few data exist to assess the sensitivity of different specimen types for viral detection during the course of influenza virus infection. OBJECTIVES: This study assessed the relationships between quantitative influenza A virus replication and antigen detectability by the enzyme immunosorbent assay (EIA) Directigen Flu A in different type of samples during experimental human infection. STUDY DESIGN: Fourteen volunteers were inoculated with influenza A virus A/Texas/36/91 (H1N1). Four specimens types were collected in sequence for quantitative isolation in cell culture and antigen testing from days 1 to 8 after inoculation. RESULTS: Seventy-one (63%) of nasopharyngeal wash specimens were culture positive, compared to 51 (46%) of throat gargles, 51 (46%) of nasal swabs, and 27 (24%) of throat swabs. All subjects shed virus in their nasopharyngeal wash at least one day and 86% of subjects had a positive nasopharyngeal wash culture on day 2 after inoculation. The mean viral titers were highest on day 2 post inoculation for all specimen types and averaged 3.6 log10 TCID50/ml for nasal washes, 1.2 log10 TCID50/ml for throat gargles, 1.8 log10 TCID50/ml for the nasopharyngeal swabs, and 0.6 log10 TCID50/ml for the throat swabs. Mean viral titers in the nasal washes were significantly different (P<0.05) compared to other specimen types. The peak of sensitivity of EIA (compared to culture) was the second day after inoculation. Nasopharyngeal and throat swab results were combined for this analysis and considered positive by culture if positive in either or both samples. Thus, on day 2 the number of EIA positive samples relative to the number culture positive was 9/12 (75%) for nasopharyngeal wash specimens, 2/9 (22%) for throat gargles, and 7/11 (64%) for the combined throat and nasal swabs specimens. CONCLUSIONS: Nasopharyngeal washes are the most sensitive sample type detecting influenza A virus in adults. For rapid diagnosis the Directigen Flu A is an alternative with a sensitivity compared to culture ranging between 64 and 78% if performed on nasopharyngeal specimens on day two or three after experimental infection in adults. However, if performed on other specimens or later in the course of infection the sensitivity is lower.     

Failure of the Smallpox Vaccine To Develop a Skin Lesion in Vaccinia Virus-Na?ve Individuals Is Related to Differences in Antibody Profiles before Vaccination,Not After

Successful vaccination against smallpox with conventional vaccinia virus is usually determined by the development of a vesicular skin lesion at the site of vaccinia inoculation, called a “take.” Although previous vaccination is known to be associated with attenuation of the take, the immunology that underlies a no-take in vaccinia-naïve individuals is not well understood. We hypothesized that antibody profiling of individuals before and after receiving vaccinia virus would reveal differences between takes and no-takes that may help better explain the phenomenon. Using vaccinia virus proteome microarrays and recombinant protein enzyme-linked immunosorbent assays (ELISAs), we first examined the antibody response in vaccinia-naïve individuals that failed to take after receiving different doses of the replication-competent DryVax and Aventis Pasteur (APSV) smallpox vaccines. Most that received diluted vaccine failed to respond, although four no-takes receiving diluted vaccine and four receiving undiluted vaccine mounted an antibody response. Interestingly, their antibody profiles were not significantly different from those of controls that did show a take. However, we did find elevated antibody titers in no-takes prior to receiving DryVax that were significantly different from those of takes. Although the sample size studied was small, we conclude the failure to take in responders correlates with preexisting immunity of unknown etiology that may attenuate the skin reaction in a way similar to previous smallpox vaccination.     

A rapid, high-throughput vaccinia virus neutralization assay for testing smallpox vaccine efficacy based on detection of green fluorescent protein

Virus neutralization remains a vital tool in assessment of vaccine efficacy for smallpox in the absence of animal smallpox models. In this regard, development of a rapid, sensitive, and high-throughput vaccinia neutralization assay has been sought for evaluating alternative smallpox vaccines, use in bridging studies, as well as understanding the effects of anti-viral immunotherapeutic regimes. The most frequently used method of measuring vaccinia virus neutralization by plaque reduction is time, labor, and material intensive, and therefore limiting in its utility for large scale, high-throughput analysis. Recent advances provide alternative methods that are less labor intensive and higher throughput but with limitations in reagents needed and ease of use. An innovative neutralization assay is described based on a modified Western Reserve vaccinia vector expressing green fluorescent protein (WR-GFP) and an adherent cell monolayer in multi-well plate format. The assay is quick, accurate, provides a large dynamic range and is well suited for large-scale vaccination studies using standard adherent cell lines.