Induction of protective cytotoxic T cells to murine cytomegalovirus by using a nonapeptide and a human-compatible adjuvant (Montanide ISA 720)

Immuno-Enhancing Effect of Ginsenoside Rh2 Liposomes on Foot-and-Mouth Disease Vaccine

The adjuvant is essential for vaccines because it can enhance or directly induce a strong immune response associated with vaccine antigens. Ginsenoside Rh2 (Rh2) had immunomodulatory effects but was limited by poor solubility and hemolysis. In this study, Rh2 liposomes (Rh2-L) were prepared by ethanol injection methods. The Rh2-L effectively dispersed in a double emulsion adjuvant system to form a Water-in-Oil-in-Water (W/O/W) emulsion and had no hemolysis. The physicochemical properties of the adjuvants were tested, and the immune activity and auxiliary effects indicated by the Foot-and-Mouth disease (FMDV) antigen were evaluated. Compared with the mice vaccinated with the FMD vaccine prepared with the double emulsion adjuvant alone, those with the FMD vaccine prepared with the double emulsion adjuvant containing Rh2-L had significantly higher neutralizing antibody titer and splenocyte proliferation rates and showed higher cellular and humoral immune responses. The results demonstrated that Rh2-L could further enhance the immune effect of the double emulsion adjuvant against Foot-and-Mouth Disease.

Prime-boost-type PspA3 + 2 mucosal vaccine protects cynomolgus macaques from intratracheal challenge with pneumococci

BACKGROUND

Although vaccination is recommended for protection against invasive pneumococcal disease, the frequency of pneumococcal pneumonia is still high worldwide. In fact, no vaccines are effective for all pneumococcal serotypes. Fusion pneumococcal surface protein A (PspA) has been shown to induce a broad range of cross-reactivity with clinical isolates and afford cross-protection against pneumococcal challenge in mice. Furthermore, we developed prime-boost-type mucosal vaccines that induce both antigen-specific IgG in serum and antigen-specific IgA in targeted mucosal organs in previous studies. We investigated whether our prime-boost-type immunization with a fusion PspA was effective against pneumococcal infection in mice and cynomolgus macaques.

METHODS

C57BL/6 mice were intramuscularly injected with fusion PspA combined with CpG oligodeoxynucleotides and/or curdlan. Six weeks later, PspA was administered intranasally. Blood and bronchoalveolar lavage fluid were collected and antigen-specific IgG and IgA titers were measured. Some mice were given intranasal Streptococcus pneumoniae and the severity of infection was analyzed. Macaques were intramuscularly injected with fusion PspA combined with CpG oligodeoxynucleotides and/or curdlan at week 0 and week 4. Then, 13 or 41 weeks later, PspA was administered intratracheally. Blood and bronchoalveolar lavage fluid were collected and antigen-specific IgG and IgA titers were measured. Some macaques were intranasally administered S. pneumoniae and analyzed for the severity of pneumonia.

RESULTS

Serum samples from mice and macaques injected with antigens in combination with CpG oligodeoxynucleotides and/or curdlan contained antigen-specific IgG. Bronchial samples contained antigen-specific IgA after the fusion PspA boosting. This immunization regimen effectively prevented S. pneumoniae infection.

CONCLUSIONS

Prime-boost-type immunization with a fusion PspA prevented S. pneumoniae infection in mice and macaques.

Immune responses elicited by the recombinant Erp, HspR, LppX, MmaA4, and OmpA proteins from Mycobacterium tuberculosis in mice

Immunogenic potency of the recombinant Erp, HspR, LppX, MmaA4, and OmpA proteins from Mycobacterium tuberculosis (MTB), formulated with Montanide ISA 720 VG adjuvant, was evaluated in BALB/c mice for the first time in this study. The five vaccine formulations, adjuvant, and BCG vaccine were subcutaneously injected into mice, and the sera were collected at days 0, 15, 30, 41, and 66. The humoral and cellular immune responses against vaccine formulations were determined by measuring serum IgG and serum interferon-gamma (IFN-γ) and interleukin-12 (IL-12) levels, respectively. All formulations significantly increased IgG levels post-vaccination. The highest increase in IFN-γ level was provided by MmaA4 formulation. The Erp, HspR, and LppX formulations were as effective as BCG in enhancement of IFN-γ level. The most efficient vaccine boosting the IL-12 level was HspR formulation, especially at day 66. Erp formulation also increased the IL-12 level more than BCG at days 15 and 30. The IL-12 level boosted by MmaA4 formulation was found to be similar to that by BCG. OmpA formulation was inefficient in enhancement of cellular immune responses. This study showed that MmaA4, HspR, and Erp proteins from MTB are successful in eliciting both humoral and cellular immune responses in mice.

A fifty-year odyssey: prospects for a cytomegalovirus vaccine in transplant and congenital infection

INTRODUCTION

It has been almost fifty years since the Towne strain was used by Plotkin and collaborators as the first vaccine candidate for cytomegalovirus (CMV). While that approach showed partial efficacy, there have been a multitude of challenges to improve on the promise of a CMV vaccine. Efforts have been dichotomized into a therapeutic vaccine for patients with CMV-infected allografts, either stem cells or solid organ, and a prophylactic vaccine for congenital infection.

AREAS COVERED

This review will evaluate research prospects for a therapeutic vaccine for transplant recipients that recognizes CMV utilizing primarily T cell responses. Similarly, we will provide an extensive discussion on attempts to develop a vaccine to prevent the manifestations of congenital infection, based on eliciting a humoral anti-CMV protective response. The review will also describe newer developments that have upended the efforts toward such a vaccine through the discovery of a second pathway of CMV infection that utilizes an alternative receptor for entry using a series of antigens that have been determined to be important for prevention of infection.

EXPERT COMMENTARY

There is a concerted effort to unify separate therapeutic and prophylactic vaccine strategies into a single delivery agent that would be effective for both transplant-related and congenital infection.

The Breadth of Synthetic Long Peptide Vaccine-Induced CD8+ T Cell Responses Determines the Efficacy against Mouse Cytomegalovirus Infection

There is an ultimate need for efficacious vaccines against human cytomegalovirus (HCMV), which causes severe morbidity and mortality among neonates and immunocompromised individuals. In this study we explored synthetic long peptide (SLP) vaccination as a platform modality to protect against mouse CMV (MCMV) infection in preclinical mouse models. In both C57BL/6 and BALB/c mouse strains, prime-booster vaccination with SLPs containing MHC class I restricted epitopes of MCMV resulted in the induction of strong and polyfunctional (i.e., IFN-γ⁺, TNF⁺, IL-2⁺) CD8⁺ T cell responses, equivalent in magnitude to those induced by the virus itself. SLP vaccination initially led to the formation of effector CD8⁺ T cells (KLRG1^hi, CD44^hi, CD127^lo, CD62L^lo), which eventually converted to a mixed central and effector-memory T cell phenotype. Markedly, the magnitude of the SLP vaccine-induced CD8⁺ T cell response was unrelated to the T cell functional avidity but correlated to the naive CD8⁺ T cell precursor frequency of each epitope. Vaccination with single SLPs displayed various levels of long-term protection against acute MCMV infection, but superior protection occurred after vaccination with a combination of SLPs. This finding underlines the importance of the breadth of the vaccine-induced CD8⁺ T cell response. Thus, SLP-based vaccines could be a potential strategy to prevent CMV-associated disease.

The majority of infections with the betaherpesvirus human cytomegalovirus (HCMV) are clinically unnoticed, but in immunocompromised hosts HCMV infections can be severe and even fatal. Here we investigated in preclinical mouse models the efficacy and mechanisms of synthetic long peptide (SLP)-based vaccines eliciting mouse CMV (MCMV)-specific CD8⁺ T cells as a platform modality to protect against CMV infection. The percentages of MCMV-specific T cells in the circulation elicited by prime-booster SLP vaccination were equivalent or higher compared to those induced by the virus itself. We further show that the naive T cell precursor frequency rather than the functional avidity of T cells predicts the magnitude of SLP-induced CD8⁺ T cell responses. Superior protection against MCMV infection depends strongly on the combined use of distinct SLP vaccines leading to broader viral-specific responses. This finding highlights the importance of the breadth of vaccine-induced CD8⁺ T cell responses.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

Nasal Peptide Vaccination Elicits CD8 Responses and Reduces Viral Burden after Challenge with Virulent Murine Cytomegalovirus

Infection of BALB/c mice with murine cytomegalovirus (MCMV) leads to CD8 cell responses to an immunodominant epitope YPHFMPTNL. We presented this epitope as a nasal peptide vaccine in combination with cholera toxin adjuvant, and evaluated immune responses and protection from MCMV challenge. Vaccination of naive mice generated elevated numbers of peptide-specific interferon-gamma-secreting splenocytes (median 80/million, range 60 to 490), compared to control mice (median 2/million, range -4.5 to 8; P=0.008, Mann-Whitney test). Twelve days after challenge with virulent MCMV, vaccinated mice had a 1.1 log(10) reduction in salivary gland viral titer compared to unvaccinated controls (5.36+/-0.24 vs. 6.42+/-0.12, mean +/-SD log(10) plaque-forming-units; P <0.001, t -test). Mice with chronic MCMV infection had consistent responses to the peptide (183+/-24/million interferon-gamma-secreting splenocytes). Nasal peptide vaccination during chronic infection boosted peptide-specific responses in two of four mice to >900/million interferon-gamma-secreting splenocytes. Nasal peptide vaccination was immunogenic in naïve and MCMV-infected mice, and reduced viral burden in naive mice after virulent MCMV challenge. The nasal route may be useful for peptide presentation by novel human vaccines.

Adjuvants for enhancing the immunogenicity of whole tumor cell vaccines

Whole tumor cell lysates can serve as excellent multivalent vaccines for priming tumor-specific CD8(+) and CD4(+) T cells. Whole cell vaccines can be prepared with hypochlorous acid oxidation, UVB-irradiation and repeat cycles of freeze and thaw. One major obstacle to successful immunotherapy is breaking self-tolerance to tumor antigens. Clinically approved adjuvants, including Montanide™ ISA-51 and 720, and keyhole-limpet proteins can be used to enhance tumor cell immunogenicity by stimulating both humoral and cellular anti-tumor responses. Other potential adjuvants, such as Toll-like receptor agonists (e.g., CpG, MPLA and PolyI:C), and cytokines (e.g., granulocyte-macrophage colony stimulating factor), have also been investigated.

Long term stability of a recombinant Plasmodium falciparum AMA1 malaria vaccine adjuvanted with Montanide(®) ISA 720 and stabilized with glycine

Plasmodium falciparum apical membrane antigen 1 (AMA1) is an asexual blood-stage vaccine candidate against the malaria parasite. AMA1-C1/ISA 720 refers to a mixture of recombinant AMA1 proteins representing the FVO and 3D7 alleles in 1:1 mass ratio, formulated with Montanide(®) ISA 720 as a water-in oil emulsion. In order to develop the AMA1-C1/ISA 720 vaccine for human use, it was important to determine the shelf life of this formulation. Previously it was found 267 mM glycine stabilized the proteins in Montanide(®) ISA 720 formulations for a short period of time at 2-8°C [25]. We now test the long term stability of AMA1-C1 at 10 and 40 μg/mL formulated with Montanide(®) ISA 720 with 50mM glycine as a stabilizer. Stability of AMA1-C1/ISA 720 at different time points following formulation (0, 5, 12 or 18 months) was evaluated by determining the mean particle size (diameter of the mean droplet volume), total protein content by a Modified Lowry assay, identity and integrity using western blot and SDS-PAGE. Our results showed that the mean particle size of these emulsions increased over time, whereas protein content, as determined by an ELISA method using a monoclonal antibody against penta-his, decreased over time. For the 10 μg/mL AMA1-C1/ISA 720 vaccine, the protein content was 6.5±2.2 μg/mL, and for the 40 μg/mL AMA1-C1/ISA 720 vaccine, the protein content was only 8.2±2.3 μg/mL after 18 months of storage at 2-8°C. These results suggest that the integrity of the protein was affected by long-term storage. The results of the present study indicate that the AMA1-C1/ISA 720 emulsion was unstable after 12 months of storage, after which AMA1-C1 proteins were partially degraded.

Adjuvants for malaria vaccines

There is a renewed enthusiasm about subunit vaccines for malaria coincident with the formation of new alliances and partnerships raising international public awareness, attracting increased resources and the re-focusing of research programs on adjuvant development for infectious disease vaccines. It is generally accepted that subunit vaccines for malaria will require adjuvants to induce protective immune responses, and availability of suitable adjuvants has in the past been a barrier to the development of malaria vaccines. Several novel adjuvants are now in licensed products or in late stage clinical development, while several others are in the earlier development pipeline. Successful vaccine development requires knowing which adjuvants to use and knowing how to formulate adjuvants and antigens to achieve stable, safe, and immunogenic vaccines. For the majority of vaccine researchers this information is not readily available, nor is access to well-characterized adjuvants. In this minireview, we outline the current state of adjuvant research and development as it pertains to effective malaria vaccines.

New horizons in adjuvants for vaccine development

Over the last decade, there has been a flurry of research on adjuvants for vaccines, and several novel adjuvants are now in licensed products or in late stage clinical development. The success of adjuvants in enhancing the immune response to recombinant antigens has led many researchers to re-focus their vaccine development programs. Successful vaccine development requires knowing which adjuvants to use and knowing how to formulate adjuvants and antigens to achieve stable, safe and immunogenic vaccines. For the majority of vaccine researchers this information is not readily available, nor is access to well-characterized adjuvants. In this review, we outline the current state of adjuvant research and development and how formulation parameters can influence the effectiveness of adjuvants.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.

A mouse model for cytomegalovirus infection

This unit describes procedures for infecting newborn and adult mice with murine cytomegalovirus (mCMV). Methods are included for propagating mCMV in cell cultures and for preparing a more virulent form of mCMV from salivary glands of infected mice. A plaque-forming cell (PFC) assay is provided for measuring mCMV titers of infected tissues or virus stocks. In addition, a method is described for preparing the murine embryonic fibroblasts used for propagating mCMV and for the PFC assay.

Phase I trial of a CD8+ T-cell peptide epitope-based vaccine for infectious mononucleosis

A single blind, randomized, placebo-controlled, single-center phase I clinical trial of a CD8(+) T-cell peptide epitope vaccine against infectious mononucleosis was conducted with 14 HLA B*0801-positive, Epstein-Barr virus (EBV)-seronegative adults. The vaccine comprised the HLA B*0801-restricted peptide epitope FLRGRAYGL and tetanus toxoid formulated in a water-in-oil adjuvant, Montanide ISA 720. FLRGRAYGL-specific responses were detected in 8/9 peptide-vaccine recipients and 0/4 placebo vaccine recipients by gamma interferon enzyme-linked immunospot assay and/or limiting-dilution analysis. The same T-cell receptor Vbeta CDR3 sequence that is found in FLRGRAYGL-specific T cells from most EBV-seropositive individuals could also be detected in the peripheral blood of vaccine recipients. The vaccine was well tolerated, with the main side effect being mild to moderate injection site reactions. After a 2- to 12-year follow-up, 1/2 placebo vaccinees who acquired EBV developed infectious mononucleosis, whereas 4/4 vaccinees who acquired EBV after completing peptide vaccination seroconverted asymptomatically. Single-epitope vaccination did not predispose individuals to disease, nor did it significantly influence development of a normal repertoire of EBV-specific CD8(+) T-cell responses following seroconversion.

Highly protective in vivo function of cytomegalovirus IE1 epitope-specific memory CD8 T cells purified by T-cell receptor-based cell sorting

Reconstitution of antiviral CD8 T cells is essential for controlling cytomegalovirus (CMV) infection after bone marrow transplantation. Accordingly, polyclonal CD8 T cells derived from BALB/c mice infected with murine CMV protect immunocompromised adoptive transfer recipients against CMV disease. The protective population comprises CD8 T cells with T-cell receptors (TCRs) specific for defined and for as-yet-unknown viral epitopes, as well as a majority of nonprotective cells with unrelated specificities. Defined epitopes include IE1/m123 and m164, which are immunodominant in terms of the magnitude of the CD8 T-cell response, and a panel of subordinate epitopes (m04, m18, M45, M83, and M84). While cytolytic T-lymphocyte lines (CTLLs) were shown to be protective regardless of the immunodominance of the respective epitope, the individual contributions of in vivo resident epitope-specific CD8 T cells to the antiviral control awaited investigation. The IE1 peptide 168-YPHFMPTNL-176 is generated from the immediate-early protein 1 (IE1) (pp89/76) of murine CMV and is presented by the major histocompatibility complex class I (MHC-I) molecule Ld. To quantitate its contribution to the protective potential of a CD8-T memory (CD8-TM) cell population, IE1-TCR+ and IE1-TCR- CD8-TM cells were purified by epitope-specific cell sorting with IE1 peptide-loaded MHC-immunoglobulin G1 dimers as ligands of cognate TCRs. Of relevance for clinical approaches to an adoptive cellular immunotherapy, sorted IE1 epitope-specific CD8-TM cells were found to be exceedingly protective upon adoptive transfer. Compared with CTLLs specific for the same epitope and of comparable avidity and TCR beta-chain variable region (Vbeta)-defined polyclonality, sorted CD8-TM cells proved to be superior by more than 2 orders of magnitude.

Beneficial therapeutic effects with different particulate structures of murine polyomavirus VP1-coat protein carrying self or non-self CD8 T cell epitopes against murine melanoma

Polyomavirus-like-particles (PLPs) are empty, non-replicative, non-infectious particles that represent a potent antigen-delivery system against malignant disease. Protective anti-tumour immunity can be induced under therapy conditions by subcutaneous (s.c.) treatment with particulate antigenic structures like chimerical polyomavirus-pentamers (PPs). These PPs displaying an immunodominant H-2Kb-restricted ovalbumin (OVA)257-264 epitope evoked nearly complete tumour remission in MO5 (B16-OVA) melanoma-bearing C57BL/6 mice by two s.c. applications in a weekly interval. The immunotherapeutic intervention started at day 4 after melanoma implant. Furthermore, 40% of melanoma-bearing mice vaccinated with heterologous PPs carrying a H-2Kb-restricted cytotoxic T lymphocyte (CTL) epitope derived from of tyrosinase-related protein 2 (TRP2) survived similar treatment conditions. However, a late immunotherapeutic onset at day 10 post melanoma inoculation revealed no significant differences between the therapeutic values (40-60% survival) of VP1-OVA252-270 and VP1-TRP2180-192 PPs, respectively. These experiments underlined the capacity of PPs to break T cell tolerance against a differentially expressed self-antigen. As a correlate for preventive and therapeutic immunity against MO5 melanoma the number of OVA257-264- or TRP2180-188-specific CD8 T cells were significantly increased within the splenocyte population of treated mice as measured by H-2Kb-OVA257-264-PE tetramer staining or appropriate ELISPOT assays, respectively. These results reveal that heterologous PLPs and even chimerical PPs represent highly efficient antigen carriers for inducing CTL responses underlining their potential as immunotherapeutics against cancer.

Phase I/II study of immunotherapy with T-cell peptide epitopes in patients with stage IV melanoma

Previous studies in small groups of patients suggested that immunization of melanoma patients with peptide epitopes recognized by T cells could induce regression of melanoma. This approach was tested in 36 patients with stage IV melanoma. The (MHC class I-restricted) peptides were from gp100, MART-1, tyrosinase, and MAGE-3. The gp100 and MART-1 peptides had been modified to increase their immunogenicity. In half the patients (groups 3 and 4) the peptides were given in the adjuvant Montanide-ISA-720, and half the patients in both groups were given GM-CSF s.c. for 4 days following each injection. Treatment was well tolerated except for two severe erythematous responses to Montanide-ISA-720 and marked inflammatory responses at sites of GM-CSF administration in three patients. There were no objective clinical responses but stabilization of disease for periods from 3 to 12 months were seen in seven patients. Five of these were patients given the peptides in Montanide-ISA-720. Delayed-type hypersensitivity (DTH) skin test responses were also seen mainly in the patients given the peptides in Montanide-ISA-720. GM-CSF did not increase DTH responses in patients in the latter group but may have increased DTH responses in those not given peptides in Montanide-ISA-720. Inflammatory responses around s.c. metastases or regional lymph nodes were observed in two patients. These results suggest that the peptides are more effective when given in the adjuvant Montanide-ISA-720. Nevertheless, results from this study, together with those from a number of comparable studies, indicate that peptide vaccines are currently of minimal benefit to patients and support the need for ongoing development of new strategies in treatment of this disease.

Melanoma vaccines: prospects for the treatment of melanoma

A number of melanoma vaccines, made from whole melanoma cells or components of melanoma cells, are being tested in Phase II or III trials in patients after surgical removal of high risk primary or regional lymph node metastases, or in those with disseminated melanoma. During the progress of these trials, a number of melanoma antigens and their peptide epitopes that are recognised by human T-cells have been described. These findings and new information about antigen recognition by human T-cells have made it possible to explore the use of peptide epitopes targeted at T-cells as melanoma vaccines. Preliminary results are encouraging and suggest that it may soon be possible to use well defined vaccines, selected on the basis of the antigenic phenotype of the patient's melanoma and their HLA status. Equally exciting advances have been made preparing and using recombinant viral vectors containing genes that code for melanoma antigens. Experimental studies on the use of naked DNA as vaccines are also proceeding. Several fundamental obstacles preventing the effective use of T-cell epitope vaccines remain. These include selection of HLA and tumour antigen loss variants by the immune system, and conditioning of an ineffective immune response by the growing tumour. These aspects suggest that the development of effective vaccine therapy in the future may require a combination of strategies designed to stimulate HLA-restricted and -non-restricted effector cells, and judicious use of cytokines to obtain an effective immune response.

NY-ESO-1 protein formulated in ISCOMATRIX adjuvant is a potent anticancer vaccine inducing both humoral and CD8+ t-cell-mediated immunity and protection against NY-ESO-1+ tumors

NY-ESO-1 is a 180 amino-acid human tumor antigen expressed by many different tumor types and belongs to the family of "cancer-testis" antigens. In humans, NY-ESO-1 is one of the most immunogenic tumor antigens and NY-ESO-1 peptides have been shown to induce NY-ESO-1-specific CD8(+) CTLs capable of altering the natural course of NY-ESO-1-expressing tumors in cancer patients. Here we describe the preclinical immunogenicity and efficacy of NY-ESO-1 protein formulated with the ISCOMATRIX adjuvant (NY-ESO-1 vaccine). In vitro, the NY-ESO-1 vaccine was readily taken up by human monocyte-derived dendritic cells, and on maturation, these human monocyte-derived dendritic cells efficiently cross-presented HLA-A2-restricted epitopes to NY-ESO-1-specific CD8(+) T cells. In addition, epitopes of NY-ESO-1 protein were also presented on MHC class II molecules to NY-ESO-1-specific CD4(+) T cells. The NY-ESO-1 vaccine induced strong NY-ESO-1-specific IFN-gamma and IgG2a responses in C57BL/6 mice. Furthermore, the NY-ESO-1 vaccine induced NY-ESO-1-specific CD8(+) CTLs in HLA-A2 transgenic mice that were capable of lysing human HLA-A2(+) NY-ESO-1(+) tumor cells. Finally, C57BL/6 mice, immunized with the NY-ESO-1 vaccine, were protected against challenge with a B16 melanoma cell line expressing NY-ESO-1. These data illustrate that the NY-ESO-1 vaccine represents a potent therapeutic anticancer vaccine.

Efficacy of different commercial and new inactivated vaccines against ovine enzootic abortion

The protective efficacy of two inactivated commercial (A, B) and two new inactivated vaccines (M7, QS) against ovine enzootic abortion was determined in two separate experiments in sheep. Vaccine A contained chlamydiae propagated in chicken embryos, adjuvated with Marcol 82, and vaccine B contained chlamydiae cultured in cell monolayers, adjuvated with aluminium hydroxide. For the preparation of the experimental vaccines, Chlamydophila abortus AB7 strain was cultured in McCoy cells and adjuvated with QS-21 (QS) or Montanide ISA 773 (M7). The ewes were vaccinated twice subcutaneously and challenged at 90 days of gestation. Protection was evaluated by clinical, bacteriological and serological examinations, and compared to two control groups: one of infected but not vaccinated ewes, and another of vaccinated but not infected ewes. The experimental vaccines induced considerably better protection than the two commercial ones. The new vaccine M7 especially showed no abortions, a good antibody response, the highest newborn lamb weights and the lowest level of C. abortus shedding at lambing.

Dissecting the role of peptides in the immune response: theory, practice and the application to vaccine design

Analytical biochemistry and synthetic peptide based chemistry have helped to reveal the pivotal role that peptides play in determining the specificity, magnitude and quality of both humoral (antibody) and cellular (cytotoxic and helper T cell) immune responses. In addition, peptide based technologies are now at the forefront of vaccine design and medical diagnostics. The chemical technologies used to assemble peptides into immunogenic structures have made great strides over the past decade and assembly of highly pure peptides which can be incorporated into high molecular weight species, multimeric and even branched structures together with non-peptidic material is now routine. These structures have a wide range of applications in designer vaccines and diagnostic reagents. Thus the tools of the peptide chemist are exquisitely placed to answer questions about immune recognition and along the way to provide us with new and improved vaccines and diagnostics.

Antigens and immunoevasins: opponents in cytomegalovirus immune surveillance

CD8+ T cells are the main effector cells for the immune control of cytomegaloviruses. To subvert this control, human and mouse cytomegaloviruses each encode a set of immune-evasion proteins, referred to here as immunoevasins, which interfere specifically with the MHC class I pathway of antigen processing and presentation. Although the concerted action of immunoevasins prevents the presentation of certain viral peptides, other viral peptides escape this blockade conditionally or constitutively and thereby provide the molecular basis of immune surveillance by CD8+ T cells. The definition of viral antigenic peptides that are presented despite the presence of immunoevasins adds a further dimension to the prediction of protective epitopes for use in vaccines.

Induction of long-term memory CD8(+) T cells for recall of viral clearing responses against influenza virus

Induction of cytotoxic T-cell-mediated virus-clearing responses by influenza virus T cell determinant-containing peptide immunogens was examined. The most potent synthetic immunogens for eliciting pulmonary viral-clearing responses contained peptides representing determinants for CD4 and CD8 T cells (TH and CTL peptides, respectively) together with two or four palmitic acid (Pal) groups. Inoculated in adjuvant, these Pal2- or Pal4-CTL-TH lipopeptides and the nonlipidated CTL peptide induced equivalent levels of cytolytic activity in the primary effector phase of the response. The ability to recall lytic responses, however, diminished much more rapidly in CTL peptide-primed than in lipopeptide-primed mice. By 15 months postpriming, the recalled lytic activity in lipopeptide-inoculated mice remained potent, but the response induced by the CTL peptide was weak. Enumeration of specific gamma interferon-secreting CD8 T cells revealed that a greater number of these T cells had entered or remained in the memory pool in lipopeptide-primed mice, arguing for a quantitative rather than qualitative enhancement of the response on recall. Addition of either the lipid or the TH peptide to the CTL peptide was not sufficient to provide these long-lived antiviral responses, but inclusion of both components augmented the response. CD4 T cells elicited by the lipopeptides did not influence the rate of viral clearance upon challenge and most likely had a role in induction or maintenance of the memory response. It therefore appears that the lipopeptide immunogens, although not significantly superior at inducing primary effector CD8 T cells, elicit a much more effective memory population, the recall of which may account for their superiority in inducing pulmonary protection after viral challenge.

Induction of a cytotoxic T-cell response to HIV-1 proteins with short synthetic peptides and human compatible adjuvants

The goal of this study was the induction of a strong CTL response against multiple CTL epitopes present in HIV proteins using short synthetic peptides. Four HLA-A2.1 restricted peptides (RT 476-484, p17 77-85, gp41 814-823, RT 956-964) that showed stable binding to the HLA-A2.1 molecule in an in vitro binding assay were able to elicit a strong specific immune response in HLA-A2.1 transgenic mice when injected with IFA or Montanide. The use of biodegradable microspheres (MS) as adjuvant was also successfully tested for all peptides. When the peptides were injected as a mixture the response was weaker as compared to individual injections of the peptides indicating the occurrence of immunodominance (ID). We are currently investigating whether ID can be overcome by a combined injection of peptide loaded MS with different release patterns. Taken together, it seems feasible to induce a specific CTL response in HLA-A2.1 transgenic mice against several HIV proteins using short synthetic peptides and human compatible adjuvants.

Adjuvants designed for veterinary and human vaccines

Adjuvants play an important role in the efficacy of vaccines as the antigens become more and more purified. Indeed recombinant proteins or synthetic peptides are safer than crude inactivated micro-organism, but less immunogenic. This can be balanced by specific adjuvants. But there is no universal adjuvants and their action is not yet clear and rely on different mechanisms. Then, they must be adapted according to several criteria, like the target species, the antigens, the type of immune response, the route of inoculation, or the duration of immunity. For this purpose different type of emulsions have been developed. Water in oil (W/O) emulsions induce a strong and long term immune response. Those based on mineral oils are known to be very efficient but can sometimes induce local reactions with reactive antigens. Non mineral oils are well tolerated but less efficient with poor immunogens. Multiphasic (W/O/W) emulsions can induce short and long term immune responses with various antigens and oil in water (O/W) emulsions are well tolerated and induce a short term immune response. New generation of adjuvants are based on a new concept called 'immunosol' and stem from the association of nanoparticles with a new immunostimulant. They can be used when emulsions are not suitable to obtain a good balance between safety and immunogenicity.

Papillomavirus virus-like particles for the delivery of multiple cytotoxic T cell epitopes

Chimeric papillomavirus (PV) virus-like particles (VLPs) based on the bovine papillomavirus type 1 (BPV-1) L1 protein were constructed by replacing the 23-carboxyl-terminal amino acids of the BPV1 major protein L1 with an artificial "polytope" minigene, containing known CTL epitopes of human PV16 E7 protein, HIV IIIB gp120 P18, Nef, and reverse transcriptase (RT) proteins, and an HPV16 E7 linear B epitope. The CTL epitopes were restricted by three different MHC class I alleles (H-2(b), H-2(d), HLA-A*0201). The chimeric L1 protein assembled into VLPs when expressed in SF-9 cells by recombinant baculovirus. After immunization of mice with polytope VLPs in the absence of adjuvant, serum antibodies were detected which reacted with both polytope VLPs and wild-type BPV1L1 VLPs, in addition to the HPV16E7 linear B cell epitope. CTL precursors specific for the HPV16 E7, HIV P18, and RT CTL epitopes were also detected in the spleen of immunized mice. Polytope VLPs can thus deliver multiple B and T epitopes as immunogens to the MHC class I and class II pathways, extending the utility of VLPs as self-adjuvanting immunogen delivery systems.

Induction of CTL response by a minimal epitope vaccine in HLA A*0201/DR1 transgenic mice: dependence on HLA class II restricted T(H) response

CTL play a pivotal role in the immune response during viral infections. In this study, the HLA class II restricted T(H) requirement for optimal in vivo induction of HLA class I restricted CTL responses has been investigated. Towards this goal, transgenic mice expressing both HLA class I (A*0201 or A2.1) and class II (DRB1*0101 or DR1) molecules have been derived. Immunization of these mice with an HLA A*0201-restricted and CMV-specific CTL epitope (pp65(495-503)), and either of three different tetanus toxin-derived MHC class II-binding T(H) epitopes, resulted in a vigorous CTL response. CTL specific for the pp65(495-503) epitope were dramatically enhanced in mice expressing both the HLA-DR1 and HLA-A*0201 transgenes. Notably, preinjection of three TT peptides (TT(639-652), TT(830-843), and TT(947-967)) increased the capability of HLA A*0201/DR1 Tg mice to respond to subsequent immunization with the T(H) + CTL peptide mixture. These results indicate that the use of HLA A*0201/DR1 Tg mice constitute a versatile model system (in lieu of immunizing humans) for the study of both HLA class I and class II restricted T-cell responses. These studies provide a rational model for the design and assessment of new minimal-epitope vaccines based on their in vivo induction of a pathogen-specific CTL response.

Suppression of murine cytomegalovirus (MCMV) replication with a DNA vaccine encoding MCMV M84 (a homolog of human cytomegalovirus pp65)

The cytotoxic T-lymphocyte (CTL) response against the murine cytomegalovirus (MCMV) immediate-early gene 1 (IE1) 89-kDa phosphoprotein pp89 plays a major role in protecting BALB/c mice against the lethal effects of the viral infection. CTL populations specific to MCMV early-phase and structural antigens are also generated during infection, but the identities of these antigens and their relative contributions to overall immunity against MCMV are not known. We previously demonstrated that DNA vaccination with a pp89-expressing plasmid effectively generated a CTL response and conferred protection against infection (J. C. Gonzalez Armas, C. S. Morello, L. D. Cranmer, and D. H. Spector, J. Virol. 70:7921-7928, 1996). In this report, we have sought (i) to identify other viral antigens that contribute to immunity against MCMV and (ii) to determine whether the protective response is haplotype specific. DNA immunization was used to test the protective efficacies of plasmids encoding MCMV homologs of human cytomegalovirus (HCMV) tegument (M32, M48, M56, M82, M83, M69, and M99), capsid (M85 and M86), and nonstructural antigens (IE1-pp89 and M84). BALB/c (H-2(d)) and C3H/HeN (H-2(k)) mice were immunized by intradermal injection of either single plasmids or cocktails of up to four expression plasmids and then challenged with sublethal doses of virulent MCMV administered intraperitoneally. In this way, we identified a new viral gene product, M84, that conferred protection against viral replication in the spleens of BALB/c mice. M84 is expressed early in the infection and encodes a nonstructural protein that shares significant amino acid homology with the HCMV UL83-pp65 tegument protein, a major target of protective CTLs in humans. Specificity of the immune response to the M84 protein was confirmed by showing that immunization with pp89 DNA, but not M84 DNA, protected mice against subsequent infection with an MCMV deletion mutant lacking the M84 gene. The other MCMV genes tested did not generate a protective response even when mice were immunized with vaccinia viruses expressing the viral proteins. However, the M84 plasmid was protective when injected in combination with nonprotective plasmids, and coimmunization of BALB/c mice with pp89 and M84 provided a synergistic level of protection in the spleen. Viral titers in the salivary glands were also reduced, but not to the same extent as observed in the spleen, and the decrease was seen only when the BALB/c mice were immunized with pp89 plus M84 or with pp89 alone. The experiments with the C3H/HeN mice showed that the immunity conferred by DNA vaccination was haplotype dependent. In this strain of mice, only pp89 elicited a protective response as measured by a reduction in spleen titer. These results suggest that DNA immunization with the appropriate combination of CMV genes may provide a strategy for improving vaccine efficacy.

Immunogenicity of a killed whole Neospora caninum tachyzoite preparation formulated with different adjuvants

A killed whole Neospora caninum tachyzoite preparation was formulated with various adjuvants and tested for its immunogenicity in cattle. The adjuvants used were: Havlogen, a polymer of acrylic acid cross-linked with polyallylsucrose; Polygen, a non-particulate copolymer; a mixture of Havlogen and Bay R-1005, which is a preparation of free base synthetic glycolipids; and Montanide ISA 773, a water-in-oil emulsion made with a mixture of metabolisable and mineral oils. Immune responses in immunised cattle were compared with those of cattle experimentally infected with culture-derived N. caninum tachyzoites. The overall mean serum IFAT titres were significantly higher (P < 0.05) in experimentally infected cattle compared with all immunised cattle. Nonetheless, the maximum antibody titres of the immunised cattle, which were obtained following the third immunisation, were within the range of titres previously described for naturally infected cattle. The overall mean serum IFAT titres were significantly higher (P < 0.05) in cattle immunised with the killed tachyzoite preparation formulated with Polygen and with the mixture of Havlogen and Bay R-1005, compared with cattle immunised with the Havlogen- and Montanide-based preparations. Two of the four adjuvant preparations were able to induce cell-mediated immune responses similar to those of the experimentally infected cattle. The Havlogen-adjuvanted tachyzoite preparation elicited N. caninum-specific proliferation of peripheral blood mononuclear cells statistically similar (P = 0.095) to that of the infected animals. Peripheral blood mononuclear cells from animals immunised with the Polygen-adjuvanted tachyzoite preparation produced interferon-gamma concentrations of similar magnitude (P = 0.17) to those from the infected animals. Polygen was one of two adjuvants that elicited the highest antibody responses, and was the only adjuvant that induced interferon-gamma levels similar to those of the infected heifers.

Induction and tolerization of anti-male CD8+ cytotoxic T lymphocytes by in vivo immunization with an H-Y-derived peptide

We have analyzed the immune response induced by a 9mer synthetic peptide derived from the male histocompatibility antigen H-Y and containing Db-binding motifs in C57BL/6 mice. In this study we report that a single, subcutaneous injection of the peptide emulsified in IFA gave rise to the development of male-specific CD8+ T cells which displayed H-Y-specific proliferative response in vitro and showed a Tc1-type pattern of cytokine production (i.e. they secreted IFN-gamma and IL-2, but not IL-4 and IL-10). Development of a strong cytotoxic activity required in vitro stimulation with specific peptide and IL-2: under these culture conditions, we were able to generate potent CD8+ CTLs that lysed both male cells and peptide-pulsed female cells. Continuous administration of soluble peptide, delivered over a 7-day period by a mini-osmotic pump implanted subcutaneously, inhibited proliferative and cytotoxic responses and IFN-gamma production in lymph node cells from C57BL/6 mice subsequently primed with peptide in adjuvant. This decreased responses were associated with a strong increase in the secretion of IL-4 by antigen-specific CD8+ T lymphocytes. Subcutaneous administration of the H-Y-peptide in adjuvant significantly accelerates rejection of male skin graft, while continuous administration of peptide in soluble form did not modify the time course of rejection.

The V3 loop based multi-epitope polypeptide TAB9 adjuvated with montanide ISA720 is highly immunogenic in nonhuman primates and induces neutralizing antibodies against five HIV-1 isolates

In a previous work we selected montanide ISA720 (M-ISA720) among different adjuvants for the vaccination with a V3 loop based multi-epitope polypeptide TAB9. In this paper we present the evaluation of the toxicity and immunogenicity of this formulation in non-human primates. TAB9 in M-ISA720 was highly immunogenic in macaques (Macaca fascicularis) inducing antibodies against TAB9 in all animals after one inoculation and a strong anamnestic response after booster injections. Furthermore 97% of the V3 peptides included were recognized by TAB9 sera. No differences between doses of 200 microg and 1 mg of TAB9 in M-ISA720 were observed after four immunizations. Neutralizing antibodies against five HIV-1 isolates were detected in most animals. Animals remain healthy throughout the study and did not show lesions at the inoculation site.

Identification of murine cytotoxic T-lymphocyte epitopes of bovine herpesvirus 1

Major histocompatibility complex (MHC) class I molecules present endogenously derived viral peptides to CD8+ cytotoxic T-lymphocytes (CTLs). The objective of this study was to identify the H-2Dd- and H-2Kd-restricted CTL epitopes of bovine herpesvirus 1 (BHV-1), based on the allele-specific peptide motifs (ASPMs) of the above class I molecules. Nine sequences conforming to the H-2Dd and H-2Kd ASPMs were identified on BHV-1 proteins, and the respective peptides were synthesized. Five of these peptides exhibited moderate to strong binding to the Dd molecule. CTLs generated by BALB/c mice immunized with BHV-1 proteins emulsified in a suitable adjuvant effectively lysed peptide-pulsed syngeneic targets, indicating that these epitopes were generated in vivo. Mice immunized with these peptides emulsified in a suitable adjuvant also developed anti-BHV-1 CTLs. These CTLs identified three veritable CTL epitopes among the "potential epitopes" synthesized based on the ASPMs. The elucidation of the CTL epitopes of BHV-1 should aid in the development of efficacious vaccines against this virus.

Vaccine-induced cytotoxic T lymphocytes protect against retroviral challenge

The development of prophylactic vaccines against retroviral diseases has been impeded by the lack of obvious immune correlates for protection. Cytotoxic T-lymphocyte (CTL), CD4-lymphocyteS, chemokine and/or antibody responses have all been associated with protection against HIV and AIDS; however, effective and safe vaccination strategies remain elusive. Here we show that vaccination with a minimal ovine CTL peptide epitope identified within gp51 of the retrovirus bovine leukemia virus (BLV), consistently induced peptide-specific CTLs. Only sheep whose CTLs were also capable of recognizing retrovirus-infected cells were fully protected when challenged with BLV. This retrovirus displays limited sequence variation; thus, in the relative absence of confounding CTL escape variants, virus-specific CTLs targeting a single epitope were able to prevent the establishment of a latent retroviral infection.

Alphavirus-specific cytotoxic T lymphocytes recognize a cross-reactive epitope from the capsid protein and can eliminate virus from persistently infected macrophages

Persistent alphavirus infections in synovial and neural tissues are believed to be associated with chronic arthritis and encephalitis, respectively, and represent likely targets for CD8+ alphabeta cytotoxic T lymphocytes (CTL). Here we show that the capsid protein is a dominant target for alphavirus-specific CTL in BALB/c mice and that capsid-specific CTL from these mice recognize an H-2Kd restricted epitope, QYSGGRFTI. This epitope lies in the highly conserved region of the capsid protein, and QYSGGRFTI-specific CTL were cross reactive across a range of Old World alphaviruses. In vivo the acute primary viraemia of these highly cytopathic viruses was unaffected by QYSGGRFTI-specific CTL. However, in vitro these CTL were able to completely clear virus from macrophages persistently and productively infected with the arthrogenic alphavirus Ross River virus.

Cytotoxic T cells and neutralizing antibodies induced in rhesus monkeys by virus-like particle HIV vaccines in the absence of protection from SHIV infection

HIV Pr55gag has in the absence of other viral components the capacity to self assemble in budding noninfectious virus-like particles (VLP). The immunological spectrum of the HIV-1IIIB gag-derived VLP was expanded either by stable anchoring of chimeric modified gp 120 on the surface of the VLP (type 1) or by replacing sequences of the Pr55gag precursor by the V3 loop and a linear portion of the CD4 binding domain (type 2). This noninfectious antigen delivery system was evaluated for immunogenicity and efficacy in rhesus macaques without adjuvants. Intramuscular immunization with both types of VLP induced high titers of gag-specific antibodies ranging from 1/8000 to 1/510,000 for type 1 VLP and from 1/4000 to 1/16,000 for type 2 VLP. Only animals immunized with type 1 VLP developed substantial endpoint titers of env-specific antibodies (1/2000-1/32,000) with a neutralizing capacity at serum dilutions of 1/32-1/128. Gag- and env-specific cytotoxic T lymphocyte (CTL) activity was induced by both types of VLP at similar levels. Four weeks after the last immunization animals were challenged intravenously with 20 MID50 of the cell free homologous envelope simian/HIV-1IIIB chimeric challenge stock Despite HIV-1-specific neutralizing and CTL responses, all vaccinated animals became infected.

Human Melanoma Patients Recognize an HLA-A1-Restricted CTL Epitope from Tyrosinase Containing Two Cysteine Residues: Implications for Tumor Vaccine Development

To identify shared epitopes for melanoma-reactive CTL restricted by MHC molecules other than HLA-A*0201, six human melanoma patient CTL lines expressing HLA-A1 were screened for reactivity against the melanocyte differentiation proteins Pmel-17/gp100, MART-1/Melan-A, and tyrosinase, expressed via recombinant vaccinia virus vectors. CTL from five of the six patients recognized epitopes from tyrosinase, and recognition of HLA-A1+ target cells was strongly correlated with tyrosinase expression. Restriction by HLA-A1 was further demonstrated for two of those tyrosinase-reactive CTL lines. Screening of 119 synthetic tyrosinase peptides with the HLA-A1 binding motif demonstrated that nonamer, decamer, and dodecamer peptides containing the sequence KCDICTDEY (residues 243–251) all reconstituted the CTL epitope in vitro. Epitope reconstitution in vitro required high concentrations of these peptides, which was hypothesized to be a result of spontaneous modification of cysteine residues, interfering with MHC binding. Substitution of serine or alanine for the more N-terminal cysteine prevented modification at that residue and permitted target cell sensitization at peptide concentrations 2 to 3 orders of magnitude lower than that required for the wild-type peptide. Because spontaneous modification of sulfhydryl groups may also occur in vivo, tumor vaccines using this or other cysteine-containing peptides may be improved by amino acid substitutions at cysteine residues.

Immune responses and side effects of five different oil-based adjuvants in mice

In this study, five different oil based adjuvants were compared to assess efficacy and side effects. Mice were injected subcutaneously (s.c.) or intraperitoneally (i.p.) with a weak immunogen (synthetic peptide) emulsified in Freund's adjuvant (FA), Specol, RIBI, TiterMax or Montanide ISA50. Efficacy of adjuvants was evaluated based on their properties to induce peptide specific IgG1, IgG2a and total IgG antibodies, native protein cross-reactive antibodies and cytokine production. Side effects were evaluated based on clinical and behavioural abnormalities, and (histo)pathological changes. Although marked differences in isotype profile and height of titre are observed among the different adjuvants used, we found that FA, Montanide ISA50 and Specol worked equally well in the s.c. and i.p. route, TiterMax functioned only when given i.p. and RIBI also did not perform up to par. The number of cytokine (interferon-gamma and interleukin-4) producing spleen cells was significantly higher after injection of RIBI compared with other adjuvants. Injection of FA or TiterMax resulted in severe pathological changes while after RIBI injection minimal changes were observed. In conclusion, high peptide specific antibody levels with limited side effects can be obtained by s.c. injection of peptide combined with Montanide ISA50 or Specol as alternatives to FA.

Immunogenicity of Plasmodium falciparum circumsporozoite protein multiple antigen peptide vaccine formulated with different adjuvants

Only low antibody levels were obtained from vaccinating human volunteers with single-chain peptide from the Plasmodium falciparum circumsporozoite protein (PfCSP). This resulted in modest protection against sporozoite challenge. In addition, HLA restriction limits the probability of synthesis of a vaccine effective for a diverse population. We report immunization studies with a multiple antigen peptide (MAP) system consisting of multiple copies of a B-cell epitope from the central repeat region of the PfCSP in combination with a universal T-cell epitope, the P2P30 portion of tetanus toxin. This MAP4(NANP)6P2P30 vaccine was highly immunogenic in four different strains of mice when used with various safe and nontoxic adjuvants. When this MAP vaccine was encapsulated in liposomes with lipid A and adsorbed to aluminium hydroxide and given three times at 4-week intervals, the resultant antibody prevented 100% of sporozoites from invading and developing into liver stage infection. This high degree of immunogenicity of MAP4(NANP)6P2P30 vaccine formulated in liposomes, lipid A and aluminum hydroxide provides the foundation for consideration of human trials with this formulation.

Mucosal and parenteral vaccination against acute and latent murine cytomegalovirus (MCMV) infection by using an attenuated MCMV mutant

We used a live attenuated murine cytomegalovirus (MCMV) mutant to analyze mechanisms of vaccination against acute and latent CMV infection. We selected MCMV mutant RV7 as a vaccine candidate since this virus grows well in tissue culture but is profoundly attenuated for growth in normal and severe combined immunodeficient (SCID) mice (V. J. Cavanaugh et al., J. Virol. 70:1365-1374, 1996). BALB/c mice were immunized twice (0 and 14 days) subcutaneously (s.c.) with tissue culture-passaged RV7 and then challenged with salivary gland-passaged wild-type MCMV (sgMCMV) intraperitoneally (i.p.) on day 28. RV7 vaccination protected mice against challenge with 10(5) PFU of sgMCMV, a dose that killed 100% of mock-vaccinated mice. RV7 vaccination reduced MCMV replication 100- to 500-fold in the spleen between 1 and 8 days after challenge. We used the capacity to control replication of MCMV in the spleen 4 days after challenge as a surrogate for protection. Protection was antigen specific and required both live RV7 and antigen-specific lymphocytes. Interestingly, RV7 was effective when administered s.c., i.p., perorally, intranasally, and intragastrically, demonstrating that attenuated CMV applied to mucosal surfaces can elicit protection against parenteral virus challenge. B cells and immunoglobulin G were not essential for RV7-induced immunity since B-cell-deficient mice were effectively vaccinated by RV7. CD8 T cells, but not CD4 T cells, were critical for RV7-induced protection. Depletion of CD8 T cells by passive transfer of monoclonal anti-CD8 (but not anti-CD4) antibody abrogated RV7-mediated protection, and RV7 vaccination was less efficient in CD8 T-cell-deficient mice with a targeted mutation in the beta2-microglobulin gene. Although gamma interferon is important for innate resistance to MCMV, it was not essential for RV7 vaccination since gamma interferon receptor-deficient mice were protected by RV7 vaccination. Establishment of and/or reactivation from latency by sgMCMV was decreased by RV7 vaccination, as measured by diminished reactivation of MCMV from splenic explants. We found no evidence for establishment of splenic latency by RV7 after s.c. vaccination. We conclude that RV7 administered through both systemic and mucosal routes is an effective vaccine against MCMV infection. It may be possible to design human CMV vaccines with similar properties.

Multi-epitope DNA vaccines

The evolution of vaccine strategies has seen a move from whole organisms to recombinant proteins, and further towards the ultimate in minimalist vaccinology, the epitope. The epitope-based approach is clearly compelling as only a relatively tiny, but immunologically relevant, sequence is often capable of inducing protective immunity against a large and complex pathogen. The post-reductionist era in epitope-based vaccinology has seen a quest to re-construct complexity and design vaccines containing many epitopes. The hope is that such multi-epitope vaccines might induce immunity against multiple antigenic targets, multiple strain variants, and/or even multiple pathogens. The ability of DNA vaccination to co-deliver a series of antibody and/or CD4 T cell epitopes remains largely unexplored. Successful viral vector and DNA-based experimental vaccines coding for multiple contiguous CD8 CTL epitopes have, however, recently been described. This simple CTL poly-epitope (or polytope) strategy may find application in the design of vaccines against several diseases including EBV, HIV and cancer.

Phase I trial in humans of an oil-based adjuvant SEPPIC MONTANIDE ISA 720

Seppic MONTANIDE ISA 720 is a metabolizable oil adjuvant that has given good results in animals with recombinant malarial antigens. Twelve human volunteers were given increasing intramuscular doses of MONTANIDE ISA 720, ranging from 0.6 to 1.8 ml. The adjuvant was well tolerated with only minor local effects, including tenderness, local swelling and discomfort on use. MONTANIDE ISA 720 may prove to be an acceptable and effective adjuvant for use in people.

Adjuvants--a classification and review of their modes of action

Since early this century, various substances have been added to vaccines and certain formulations have been devised in an attempt to render vaccines more effective. Despite a plethora of options, only aluminium salts have gained acceptance as human vaccine adjuvants and even veterinary vaccines are largely dependent upon the use of aluminium salts. Currently, many new vaccines are under development and there is a desire to simplify vaccination schedules both by increasing the number of components per vaccine and decreasing the number of doses required for a vaccine course. New, more effective adjuvants will be required to achieve this.

Human cytotoxic T lymphocyte responses to Epstein-Barr virus infection

Epstein-Barr virus (EBV) provides one of the most informative systems with which to study cytotoxic T lymphocyte (CTL) responses in humans. The virus establishes a highly immunogenic growth-transforming infection of B lymphocytes, associated with the coordinate expression of six virus-coded nuclear antigens (EBNAs 1, 2, 3A, 3B, 3C, -LP) and two latent membrane proteins (LMPs 1 and 2). This elicits both primary and memory CT8+ CTL responses that are markedly skewed toward HLA allele-specific epitopes drawn from the EBNA3A, 3B, 3C subset of latent proteins, with reactivities to other antigens being generally much less frequent. This hierarchy of immunodominance among the different latent proteins may at least partly reflect their differential accessibility to the HLA class I-processing pathway. Furthermore, CTLs to some of the immunodominant epitopes involve highly conserved T cell receptor (TCR) usage, a level of focusing which evidence suggests could have immunopathological consequences from cross-reactive recognition of other target structures. EBV is associated with a range of human tumors, and there is increasing interest in the possibility of targeting such malignancies using virus-specific CTLs. The dramatic reversal of EBV-driven lymphoproliferations in bone marrow transplant patients following CTL infusion demonstrates the potential of this approach, and here we discuss prospects for its extension to other EBV-positive tumors in which the immunodominant EBNA3A, 3B, 3C proteins are not expressed.

Comparison of adjuvant formulations for cytotoxic T cell induction using synthetic peptides

We have investigated the capacity of synthetic peptides delivered in different adjuvant formulations to induce cytotoxic T lymphocyte (CTL) responses to a class I H-2Kd-restricted Plasmodium berghei circumsporozoite epitope, CS 252-260. Using three immunogen formulations: soybean emulsion; Montanide ISA720; and lipopeptide (P3-CS), we first evaluated the effects of immunization routes on CTL induction. No CTL response was induced in mice immunized s.c. or i.p. with CS peptide formulated in soybean emulsion. In contrast, immunization with lipopeptide P3-CS either s.c. or i.p. effectively primed for CTL. Interestingly, CS peptide emulsified in Montanide ISA720 induced a CTL response only when delivered s.c. and not i.p., indicating the critical influence of immunization routes on CTL induction. We then compared the effectiveness of eight adjuvant formulations to induce CTL response following a single s.c. immunization. Notably, lipopeptide P3-CS and CS peptide admixed with P3 or POE lipid molecules stimulated a vigorous CTL response. However, only mice immunized with P3-CS and CS peptide admixed with P3 molecule generated long-lived CTL which persisted in vivo for 5 months. Thus, based on a simultaneous comparison of the different adjuvant formulations, we demonstrated that the conjugated and unconjugated P3 lipopeptides were the most effective immunogens for eliciting primary and memory CTL in mice.