Recombinant modified vaccinia Ankara primes functionally activated CTL specific for a melanoma tumor antigen epitope in melanoma patients with a high risk of disease recurrence

DNA and modified vaccinia Ankara prime-boost vaccination generates strong CD8+ T cell responses against minor histocompatibility antigen HA-1

Allogeneic immune responses underlie the graft-versus-leukaemia effect of stem cell transplantation, but disease relapse occurs in many patients. Minor histocompatibility antigen (mHAg) peptides mediate alloreactive T cell responses and induce graft-versus-leukaemia responses when expressed on patient haematopoietic tissue. We vaccinated nine HA-1-negative donors against HA-1 with a 'prime-boost' protocol of either two or three DNA 'priming' vaccinations prior to 'boost' with modified vaccinia Ankara (MVA). HA-1-specific CD8+ T cell responses were observed in seven donors with magnitude up to 1·5% of total CD8+ T cell repertoire. HA-1-specific responses peaked two weeks post-MVA challenge and were measurable in most donors after 12 months. HA-1-specific T cells demonstrated strong cytotoxic activity and lysed target cells with endogenous HA-1 protein expression. The pattern of T cell receptor (TCR) usage by HA-1-specific T cells revealed strong conservation of T cell receptor beta variable 7-9 (TRBV7-9) usage between donors. These findings describe one of the strongest primary peptide-specific CD8+ T cell responses yet recorded to a DNA-MVA prime-boost regimen and this may reflect the strong immunogenicity of mHAg peptides. Prime-boost vaccination in donors or patients may prove of substantial benefit in boosting graft-versus-leukaemia responses.

COVID-19 Vaccines (Revisited) and Oral-Mucosal Vector System as a Potential Vaccine Platform

There are several emerging strategies for the vaccination of COVID-19 (SARS-CoV-2) however, only a few have yet shown promising effects. Thus, choosing the right pathway and the best prophylactic options in preventing COVID-19 is still challenging at best. Approximately, more than two-hundred vaccines are being tested in different countries, and more than fifty clinical trials are currently undergoing. In this review, we have summarized the immune-based strategies for the development of COVID-19 vaccines and the different vaccine candidate platforms that are in clinical stages of evaluation, and up to the recently licensed mRNA-based COVID-19 vaccines of Pfizer-BioNtech and Moderna's. Lastly, we have briefly included the potentials of using the 'RPS-CTP vector system' for the development of a safe and effective oral mucosal COVID-19 vaccine as another vaccine platform.

Combination of vasculature targeting, hypofractionated radiotherapy, and immune checkpoint inhibitor elicits potent antitumor immune response and blocks tumor progression

Background

Tumor endothelial marker 1 (TEM1) is a protein expressed in the tumor-associated endothelium and/or stroma of various types of cancer. We previously demonstrated that immunization with a plasmid-DNA vaccine targeting TEM1 reduced tumor progression in three murine cancer models. Radiation therapy (RT) is an established cancer modality used in more than 50% of patients with solid tumors. RT can induce tumor-associated vasculature injury, triggering immunogenic cell death and inhibition of the irradiated tumor and distant non-irradiated tumor growth (abscopal effect). Combination treatment of RT with TEM1 immunotherapy may complement and augment established immune checkpoint blockade.

Methods

Mice bearing bilateral subcutaneous CT26 colorectal or TC1 lung tumors were treated with a novel heterologous TEM1-based vaccine, in combination with RT, and anti-programmed death-ligand 1 (PD-L1) antibody or combinations of these therapies, tumor growth of irradiated and abscopal tumors was subsequently assessed. Analysis of tumor blood perfusion was evaluated by CD31 staining and Doppler ultrasound imaging. Immunophenotyping of peripheral and tumor-infiltrating immune cells as well as functional analysis was analyzed by flow cytometry, ELISpot assay and adoptive cell transfer (ACT) experiments.

Results

We demonstrate that addition of RT to heterologous TEM1 vaccination reduces progression of CT26 and TC1 irradiated and abscopal distant tumors as compared with either single treatment. Mechanistically, RT increased major histocompatibility complex class I molecule (MHCI) expression on endothelial cells and improved immune recognition of the endothelium by anti-TEM1 T cells with subsequent severe vascular damage as measured by reduced microvascular density and tumor blood perfusion. Heterologous TEM1 vaccine and RT combination therapy boosted tumor-associated antigen (TAA) cross-priming (ie, anti-gp70) and augmented programmed cell death protein 1 (PD-1)/PD-L1 signaling within CT26 tumor. Blocking the PD-1/PD-L1 axis in combination with dual therapy further increased the antitumor effect and gp70-specific immune responses. ACT experiments show that anti-gp70 T cells are required for the antitumor effects of the combination therapy.

Conclusion

Our findings describe novel cooperative mechanisms between heterologous TEM1 vaccination and RT, highlighting the pivotal role that TAA cross-priming plays for an effective antitumor strategy. Furthermore, we provide rationale for using heterologous TEM1 vaccination and RT as an add-on to immune checkpoint blockade as triple combination therapy into early-phase clinical trials.

Heterologous prime-boost immunization co-targeting dual antigens inhibit tumor growth and relapse

Therapeutic cancer vaccines aim to induce an effective immune response against cancer, and the effectiveness of these vaccines is influenced by the choice of immunogen, vaccine type, and immunization strategy. Although treatment with cancer vaccines can improve tumor burden and survival, in most animal studies, it is challenging to achieve a complete response against tumor growth and recurrence, without the use of other therapies in combination. Here, we present a novel approach where dual antigens (survivin and MUC1) are co-targeted using three DNA vaccines, followed by a single booster of a recombinant modified vaccinia Ankara (MVA) vaccine. This heterologous vaccination strategy induced higher levels of interferon (IFN)-γ-secretion and stronger antigen-specific T-cell responses than those induced individually by the DNA vaccines and the MVA vaccine in mice. This strategy also increased the number of active tumor-infiltrating T cells that efficiently inhibit tumor growth in tumor-bearing mice. Heterologous DNA prime-MVA boost immunization was capable of inducing a robust antigen-specific immune-memory, as seen from the resistance to subsequent survivin- and MUC1-expressing tumors. Moreover, the therapeutic effects of DNA prime-MVA boost and DNA prime-adenovirus boost strategies were compared. DNA prime-MVA boost immunization performed better, as indicated by the T effector ratio and the induction of Th1 immunity. This study provides the basis for the use of heterologous DNA prime-MVA boost vaccination regime targeting two antigens simultaneously as a promising immunotherapeutic strategy against cancer.

Modified Vaccinia Virus Ankara Can Induce Optimal CD8+ T Cell Responses to Directly Primed Antigens Depending on Vaccine Design

A variety of strains of vaccinia virus (VACV) have been used as recombinant vaccine vectors with the aim of inducing robust CD8⁺ T cell immunity. While much of the pioneering work was done with virulent strains, such as Western Reserve (WR), attenuated strains such as modified vaccinia virus Ankara (MVA) are more realistic vectors for clinical use. To unify this literature, side-by-side comparisons of virus strains are required. Here, we compare the form of antigen that supports optimal CD8⁺ T cell responses for VACV strains WR and MVA using equivalent constructs. We found that for multiple antigens, minimal antigenic constructs (epitope minigenes) that prime CD8⁺ T cells via the direct presentation pathway elicited optimal responses from both vectors, which was surprising because this finding contradicts the prevailing view in the literature for MVA. We then went on to explore the discrepancy between current and published data for MVA, finding evidence that the expression locus and in some cases the presence of the viral thymidine kinase may influence the ability of this strain to prime optimal responses from antigens that require direct presentation. This extends our knowledge of the design parameters for VACV vectored vaccines, especially those based on MVA.IMPORTANCE Recombinant vaccines based on vaccinia virus and particularly attenuated strains such as MVA are in human clinical trials, but due to the complexity of these large vectors much remains to be understood about the design parameters that alter their immunogenicity. Previous work had found that MVA vectors should be designed to express stable protein in order to induce robust immunity by CD8⁺ (cytotoxic) T cells. Here, we found that the primacy of stable antigen is not generalizable to all designs of MVA and may depend where a foreign antigen is inserted into the MVA genome. This unexpected finding suggests that there is an interaction between genome location and the best form of antigen for optimal T cell priming in MVA and thus possibly other vaccine vectors. It also highlights that our understanding of antigen presentation by even the best studied of vaccine vectors remains incomplete.

Strong antigen-specific T-cell immunity induced by a recombinant human TERT measles virus vaccine and amplified by a DNA/viral vector prime boost in IFNAR/CD46 mice

Cancer immunotherapy is seeing an increasing focus on vaccination with tumor-associated antigens (TAAs). Human telomerase (hTERT) is a TAA expressed by most tumors to overcome telomere shortening. Tolerance to hTERT can be easily broken both naturally and experimentally and hTERT DNA vaccine candidates have been introduced in clinical trials. DNA prime/boost strategies have been widely developed to immunize efficiently against infectious diseases. We explored the use of a recombinant measles virus (MV) hTERT vector to boost DNA priming as recombinant live attenuated measles virus has an impressive safety and efficacy record. Here, we show that a MV-TERT vector can rapidly and strongly boost DNA hTERT priming in MV susceptible IFNAR/CD46 mouse models. The cellular immune responses were Th1 polarized. No humoral responses were elicited. The 4 kb hTERT transgene did not impact MV replication or induction of cell-mediated responses. These findings validate the MV-TERT vector to boost cell-mediated responses following DNA priming in humans.

Safety of an Oncolytic Myxoma Virus in Dogs with Soft Tissue Sarcoma

Many oncolytic viruses that are efficacious in murine cancer models are ineffective in humans. The outcomes of oncolytic virus treatment in dogs with spontaneous tumors may better predict human cancer response and improve treatment options for dogs with cancer. The objectives of this study were to evaluate the safety of treatment with myxoma virus lacking the serp2 gene (MYXVΔserp2) and determine its immunogenicity in dogs. To achieve these objectives, dogs with spontaneous soft tissue sarcomas were treated with MYXVΔserp2 intratumorally (n = 5) or post-operatively (n = 5). In dogs treated intratumorally, clinical scores were recorded and tumor biopsies and swabs (from the mouth and virus injection site) were analyzed for viral DNA at multiple time-points. In all dogs, blood, urine, and feces were frequently collected to evaluate organ function, virus distribution, and immune response. No detrimental effects of MYXVΔserp2 treatment were observed in any canine cancer patients. No clinically significant changes in complete blood profiles, serum chemistry analyses, or urinalyses were measured. Viral DNA was isolated from one tumor swab, but viral dissemination was not observed. Anti-MYXV antibodies were occasionally detected. These findings provide needed safety information to advance clinical trials using MYXVΔserp2 to treat patients with cancer.

Trial watch: DNA vaccines for cancer therapy

The foundation of modern vaccinology dates back to the 1790s, when the English physician Edward Jenner uncovered the tremendous medical potential of prophylactic vaccination. Jenner’s work ignited a wave of nationwide vaccination campaigns abating the incidence of multiple life-threatening infectious diseases and culminating with the eradication of natural smallpox virus, which was definitively certified by the WHO in 1980. The possibility of using vaccines against cancer was first proposed at the end of the 19th century by Paul Ehrlich and William Coley. However, it was not until the 1990s that such a hypothesis began to be intensively investigated, following the realization that the immune system is not completely unresponsive to tumors and that neoplastic cells express immunogenic tumor-associated antigens (TAAs). Nowadays, anticancer vaccines are rapidly moving from the bench to the bedside, and a few prophylactic and therapeutic preparations have already been approved by FDA for use in humans. In this setting, one interesting approach is constituted by DNA vaccines, i.e., TAA-encoding circularized DNA constructs, often of bacterial origin, that are delivered to patients as such or by means of specific vectors, including (but not limited to) liposomal preparations, nanoparticles, bacteria and viruses. The administration of DNA vaccines is most often performed via the intramuscular or subcutaneous route and is expected to cause (1) the endogenous synthesis of the TAA by myocytes and/or resident antigen-presenting cells; (2) the presentation of TAA-derived peptides on the cell surface, in association with MHC class I molecules; and (3) the activation of potentially therapeutic tumor-specific immune responses. In this Trial Watch, we will summarize the results of recent clinical trials that have evaluated/are evaluating DNA vaccines as therapeutic interventions against cancer.

A CD8 T-cell epitope variant enhances immune targeting to a recombinant picornavirus vaccine antigen

Recombinant virus vaccines are often less effective due to immunodominant responses against endogenous vector antigens. However, the use of small RNA virus vectors provides an opportunity to limit host exposure to endogenous virus antigens and focus immune responses on the desired vaccine antigen. Using the Daniel's strain of Theiler's murine encephalomyelitis virus, we have identified strategies to modulate responses to endogenous viral proteins by manipulating the host CD8+ T-cell repertoire prior to infection or through the use of mutations introduced into the virus genome. Both of these approaches enhance responses to vaccine antigens introduced into the picornavirus. However, the use of mutant immunodominant epitopes provides an opportunity for enhancing vaccine responses without further manipulation of the host. Using this strategy, we demonstrate that modification of the consensus MHC class I anchor residue within the virus genome can promote enhanced immunity to foreign antigens and self-antigens embedded in the virus genome.

Tumor-associated antigen/IL-21-transduced dendritic cell vaccines enhance immunity and inhibit immunosuppressive cells in metastatic melanoma

Dendritic cell (DC)-based vaccine approaches are being actively evaluated for developing immunotherapeutic agents against cancers. In this study, we investigated the use of engineered DCs expressing transgenic tumor-associated antigen hgp100 and the regulatory cytokine interleukin-21, namely DC-hgp100/mIL-21, as a therapeutic vaccine against melanoma. Tumor-bearing mice were injected intratumorally with transgenic DCs followed by three booster injections. Transgenic DC-hgp100/mIL-21 showed significant reduction in primary tumor growth and metastasis compared with DC-hgp100 alone and DC-mIL-21 alone. In vivo depletion of specific immune cell types (CD8(+) T, CD4(+) T and Natural killer (NK)-1.1(+) cells) effectively blocked the protective effect of this combinational vaccine. In adoptive transfer experiments, a survival rate of nearly 90% was observed at 60 days post-tumor inoculation for the combinational vaccine group. In contrast, all mice in the DC-hgp100 and DC-mIL-21-only groups died within 43-46 days after tumor challenge. Considerably increased levels of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, granulocyte macrophage colony-stimulating factor (GM-CSF) and cytotoxic T lymphocytes (CTLs) were detected with the combination vaccine group compared with other individual treatment groups. In comparison with the DC-hgp100 or mIL-21 groups, the combinational DC-hgp100/mIL-21 vaccine also drastically suppressed the myeloid-derived suppressor cells (MDSCs) and T-regulatory (Treg) cell populations. Our findings suggest that a combinational DC- and gene-based hgp100 and mIL-21 vaccine therapy strategy warrants further evaluation as a clinically relevant cancer vaccine approach for human melanoma patients.

Antitumor activity and immunogenicity of recombinant vaccinia virus expressing HPV 16 E7 protein SigE7LAMP is enhanced by high-level coexpression of IGFBP-3

We constructed recombinant vaccinia viruses (VACVs) coexpressing the insulin-like growth factor-binding protein-3 (IGFBP-3) gene and the fusion gene encoding the SigE7Lamp antigen. The expression of the IGFBP-3 transgene was regulated either by the early H5 promoter or by the synthetic early/late (E/L) promoter. We have shown that IGFBP-3 expression regulated by the H5 promoter yielded higher amount of IGFBP-3 protein when compared with the E/L promoter. The immunization with P13-SigE7Lamp-H5-IGFBP-3 virus was more effective in inhibiting the growth of TC-1 tumors in mice and elicited higher T-cell response against VACV-encoded antigen than the P13-SigE7Lamp-TK(-) control virus. We found that high-level production of IGFBP-3 enhanced virus replication both in vitro and in vivo, resulting in more profound antigen stimulation. Production of IGFBP-3 was associated with a higher adsorption rate of P13-SigE7Lamp-H5-IGFBP-3 to CV-1 cells when compared with P13-SigE7Lamp-TK(-). Intracellular mature virions (IMVs) of the IGFBP-3-expressing virus P13-SigE7Lamp-H5-IGFBP-3 have two structural differences: they incorporate the IGFBP-3 protein and they have elevated phosphatidylserine (PS) exposure on outer membrane that could result in increased uptake of IMVs by macropinocytosis. The IMV PS content was measured by flow cytometry using microbeads covered with immobilized purified VACV virions.

Phase I trial of recombinant modified vaccinia ankara encoding Epstein-Barr viral tumor antigens in nasopharyngeal carcinoma patients

Epstein-Barr virus (EBV) is associated with several malignancies including nasopharyngeal carcinoma, a high incidence tumor in Chinese populations, in which tumor cells express the two EBV antigens EB nuclear antigen 1 (EBNA1) and latent membrane protein 2 (LMP2). Here, we report the phase I trial of a recombinant vaccinia virus, MVA-EL, which encodes an EBNA1/LMP2 fusion protein designed to boost T-cell immunity to these antigens. The vaccine was delivered to Hong Kong patients with nasopharyngeal carcinoma to determine a safe and immunogenic dose. The patients, all in remission more than 12 weeks after primary therapy, received three intradermal MVA-EL vaccinations at three weekly intervals, using five escalating dose levels between 5 × 10(7) and 5 × 10(8) plaque-forming unit (pfu). Blood samples were taken during prescreening, immediately before vaccination, one week afterward and at intervals up to one year later. Immunogenicity was tested by IFN-γ ELIspot assays using complete EBNA1 and LMP2 15-mer peptide mixes and known epitope peptides relevant to patient MHC type. Eighteen patients were treated, three per dose level one to four and six at the highest dose, without dose-limiting toxicity. T-cell responses to one or both vaccine antigens were increased in 15 of 18 patients and, in many cases, were mapped to known CD4 and CD8 epitopes in EBNA1 and/or LMP2. The range of these responses suggested a direct relationship with vaccine dose, with all six patients at the highest dose level giving strong EBNA1/LMP2 responses. We concluded that MVA-EL is both safe and immunogenic, allowing the highest dose to be forwarded to phase II studies examining clinical benefit.

CD8+ T Lymphocyte Epitopes From The Herpes Simplex Virus Type 2 ICP27, VP22 and VP13/14 Proteins To Facilitate Vaccine Design And Characterization

CD8+ T cells have the potential to control HSV-2 infection. However, limited information has been available on CD8+ T cell epitopes or the functionality of antigen specific T cells during infection or following immunization with experimental vaccines. Peptide panels from HSV-2 proteins ICP27, VP22 and VP13/14 were selected from in silico predictions of binding to human HLA-A*0201 and mouse H-2Kd, Ld and Dd molecules. Nine previously uncharacterized CD8+ T cell epitopes were identified from HSV-2 infected BALB/c mice. HSV-2 specific peptide sequences stabilized HLA-A*02 surface expression with intermediate or high affinity binding. Peptide specific CD8+ human T cell lines from peripheral blood lymphocytes were generated from a HLA-A*02+ donor. High frequencies of peptide specific CD8+ T cell responses were elicited in mice by DNA vaccination with ICP27, VP22 and VP13/14, as demonstrated by CD107a mobilization. Vaccine driven T cell responses displayed a more focused immune response than those induced by viral infection. Furthermore, vaccination with ICP27 reduced viral shedding and reduced the clinical impact of disease. In conclusion, this study describes novel HSV-2 epitopes eliciting strong CD8+ T cell responses that may facilitate epitope based vaccine design and aid immunomonitoring of antigen specific T cell frequencies in preclinical and clinical settings.

Impact of anti-orthopoxvirus neutralizing antibodies induced by a heterologous prime-boost HIV-1 vaccine on insert-specific immune responses

BACKGROUND

The impact of anti-vector immunity on the elicitation of insert-specific immune responses is important to understand in vaccine development. HVTN 055 was a 150 person phase I randomized, controlled HIV vaccine trial of recombinant modified vaccinia Ankara (rMVA) and fowlpox (rFPV) with matched HIV-1 inserts which demonstrated increased CD8+ T-cell immune responses in the heterologous vaccine group. The controls used in this study were the empty vectors (MVA and FPV).

METHODS

Anti-MVA and anti-vaccinia neutralizing antibodies (NAbs) were measured and compared with cellular and humoral HIV-1-specific immune responses.

RESULTS

Elicitation of anti-vector responses increased with increasing dose of MVA and up to 2 administrations. Further inoculations of MVA (up to 5) did not increase the magnitude of the anti-MVA response but did delay the anti-vector NAb titre decay. There was no evidence that the insert impaired the anti-vector response, nor that anti-vector immunity attenuated the insert-specific responses.

CONCLUSION

Two doses of MVA may be ideal for the elicitation of orthopoxvirus immune responses with further doses maintaining increased titres against the vector. We found no evidence that eliciting HIV insert- or MVA vector-specific immune responses interfered with elicitation of immune responses to the other.

Deletion of specific immune-modulatory genes from modified vaccinia virus Ankara-based HIV vaccines engenders improved immunogenicity in rhesus macaques

Modified vaccinia virus Ankara (MVA) is a safe, attenuated orthopoxvirus that is being developed as a vaccine vector but has demonstrated limited immunogenicity in several early-phase clinical trials. Our objective was to rationally improve the immunogenicity of MVA-based HIV/AIDS vaccines via the targeted deletion of specific poxvirus immune-modulatory genes. Vaccines expressing codon-optimized HIV subtype C consensus Env and Gag antigens were generated from MVA vector backbones that (i) harbor simultaneous deletions of four viral immune-modulatory genes, encoding an interleukin-18 (IL-18) binding protein, an IL-1β receptor, a dominant negative Toll/IL-1 signaling adapter, and CC-chemokine binding protein (MVAΔ4-HIV); (ii) harbor a deletion of an additional (fifth) viral gene, encoding uracil-DNA glycosylase (MVAΔ5-HIV); or (iii) represent the parental MVA backbone as a control (MVA-HIV). We performed head-to-head comparisons of the cellular and humoral immune responses that were elicited by these vectors during homologous prime-boost immunization regimens utilizing either high-dose (2 × 10(8) PFU) or low-dose (1 × 10(7) PFU) intramuscular immunization of rhesus macaques. At all time points, a majority of the HIV-specific T cell responses, elicited by all vectors, were directed against Env, rather than Gag, determinants, as previously observed with other vector systems. Both modified vectors elicited up to 6-fold-higher frequencies of HIV-specific CD8 and CD4 T cell responses and up to 25-fold-higher titers of Env (gp120)-specific binding (nonneutralizing) antibody responses that were relatively transient in nature. While the correlates of protection against HIV infection remain incompletely defined, our results indicate that the rational deletion of specific genes from MVA vectors can positively alter their cellular and humoral immunogenicity profiles in nonhuman primates.

DNA fusion-gene vaccination in patients with prostate cancer induces high-frequency CD8(+) T-cell responses and increases PSA doubling time

We report on the immunogenicity and clinical effects in a phase I/II dose escalation trial of a DNA fusion vaccine in patients with prostate cancer. The vaccine encodes a domain (DOM) from fragment C of tetanus toxin linked to an HLA-A2-binding epitope from prostate-specific membrane antigen (PSMA), PSMA_27–35. We evaluated the effect of intramuscular vaccination without or with electroporation (EP) on vaccine potency. Thirty-two HLA-A2⁺ patients were vaccinated and monitored for immune and clinical responses for a follow-up period of 72 weeks. At week 24, cross-over to the immunologically more effective delivery modality was permitted; this was shown to be with EP based on early antibody data, and subsequently, 13/15 patients crossed to the +EP arm. Thirty-two HLA-A2⁻ control patients were assessed for time to next treatment and overall survival. Vaccination was safe and well tolerated. The vaccine induced DOM-specific CD4⁺ and PSMA₂₇-specific CD8⁺ T cells, which were detectable at significant levels above baseline at the end of the study (p = 0.0223 and p = 0.00248, respectively). Of 30 patients, 29 had a measurable CD4⁺ T-cell response and PSMA₂₇-specific CD8⁺ T cells were detected in 16/30 patients, with or without EP. At week 24, before cross-over, both delivery methods led to increased CD4⁺ and CD8⁺ vaccine-specific T cells with a trend to a greater effect with EP. PSA doubling time increased significantly from 11.97 months pre-treatment to 16.82 months over the 72-week follow-up (p = 0.0417), with no clear differential effect of EP. The high frequency of immunological responses to DOM-PSMA₂₇ vaccination and the clinical effects are sufficiently promising to warrant further, randomized testing.

Dissection of stromal and cancer cell-derived signals in melanoma xenografts before and after treatment with DMXAA

Background:

The non-malignant cells of the tumour stroma have a critical role in tumour biology. Studies dissecting the interplay between cancer cells and stromal cells are required to further our understanding of tumour progression and methods of intervention. For proof-of-principle of a multi-modal approach to dissect the differential effects of treatment on cancer cells and stromal cells, we analysed the effects of the stromal-targeting agent 5,6-dimethylxanthenone-4-acetic acid on melanoma xenografts.

Methods:

Flow cytometry and multi-colour immunofluorescence staining was used to analyse leukocyte numbers in xenografts. Murine-specific and human-specific multiplex cytokine panels were used to quantitate cytokines produced by stromal and melanoma cells, respectively. Human and mouse Affymetrix microarrays were used to separately identify melanoma cell-specific and stromal cell-specific gene expression.

Results:

5,6-Dimethylxanthenone-4-acetic acid activated pro-inflammatory signalling pathways and cytokine expression from both stromal and cancer cells, leading to neutrophil accumulation and haemorrhagic necrosis and a delay in tumour re-growth of 26 days in A375 melanoma xenografts.

Conclusion:

5,6-Dimethylxanthenone-4-acetic acid and related analogues may potentially have utility in the treatment of melanoma. The experimental platform used allowed distinction between cancer cells and stromal cells and can be applied to investigate other tumour models and anti-cancer agents.

Improving the MVA vaccine potential by deleting the viral gene coding for the IL-18 binding protein

BACKGROUND

Modified Vaccinia Ankara (MVA) is an attenuated strain of Vaccinia virus (VACV) currently employed in many clinical trials against HIV/AIDS and other diseases. MVA still retains genes involved in host immune response evasion, enabling its optimization by removing some of them. The aim of this study was to evaluate cellular immune responses (CIR) induced by an IL-18 binding protein gene (C12L) deleted vector (MVAΔC12L).

METHODOLOGY/PRINCIPAL FINDINGS

BALB/c and C57BL/6 mice were immunized with different doses of MVAΔC12L or MVA wild type (MVAwt), then CIR to VACV epitopes in immunogenic proteins were evaluated in spleen and draining lymph nodes at acute and memory phases (7 and 40 days post-immunization respectively). Compared with parental MVAwt, MVAΔC12L immunization induced a significant increase of two to three-fold in CD8(+) and CD4(+) T-cell responses to different VACV epitopes, with increased percentage of anti-VACV cytotoxic CD8(+) T-cells (CD107a/b(+)) during the acute phase of the response. Importantly, the immunogenicity enhancement was also observed after MVAΔC12L inoculation with different viral doses and by distinct routes (systemic and mucosal). Potentiation of MVA's CIR was also observed during the memory phase, in correlation with a higher protection against an intranasal challenge with VACV WR. Of note, we could also show a significant increase in the CIR against HIV antigens such as Env, Gag, Pol and Nef from different subtypes expressed from two recombinants of MVAΔC12L during heterologous DNA prime/MVA boost vaccination regimens.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates the relevance of IL-18 bp contribution in the immune response evasion during MVA infection. Our findings clearly show that the deletion of the viral IL-18 bp gene is an effective approach to increase MVA vaccine efficacy, as immunogenicity improvements were observed against vector antigens and more importantly to HIV antigens.

Vaccinia viruses: vaccines against smallpox and vectors against infectious diseases and tumors

Less than 200 years after its introduction, widespread use of vaccinia virus (VACV) as a smallpox vaccine has eradicated variola virus. Along with the remarkable success of the vaccination program, frequent and sometimes severe adverse reactions to VACV were encountered. After eradication, VACV has been reserved for select populations who might be at significant risk for orthopoxvirus infections. Events over the past decade have renewed concerns over the potential use of variola virus as a biological weapon. Accordingly, interest in VACV and attenuated derivatives has increased, both as vaccines against smallpox and as vectors for other vaccines. This article will focus on new developments in the field of orthopoxvirus immunization and will highlight recent advances in the use of vaccinia viruses as vectors for infectious diseases and malignancies.

Engineered Viruses as Vaccine Platforms

Many viruses have been investigated for the development of genetic vaccines and the ideal ones must be endowed with many properties, such as the quality and the quantity of the immunological response induced against the encoded antigens, safety and production on a large scale basis. Viral based vaccines must also deal with the potential problem of the pre-existing antivector immunity. Several viral vaccine vectors have emerged to date, all of them having relative advantages and limits depending on the proposed application. Recent successes reflect diverse improvements such as development of new adenovirus serotypes and prime-boost regimes. This chapter describes the features of four viral vector systems based on poxviruses, adenoviruses, alphaviruses and lentiviruses and recent results following their use with a particular emphasis on clinical research, highlighting the challenges and successes.

Dual neonate vaccine platform against HIV-1 and M. tuberculosis

Acquired immunodeficiency syndrome and tuberculosis (TB) are two of the world's most devastating diseases. The first vaccine the majority of infants born in Africa receive is Mycobacterium bovis bacillus Calmette-Guérin (BCG) as a prevention against TB. BCG protects against disseminated disease in the first 10 years of life, but provides a variable protection against pulmonary TB and enhancing boost delivered by recombinant modified vaccinia virus Ankara (rMVA) expressing antigen 85A (Ag85A) of M. tuberculosis is currently in phase IIb evaluation in African neonates. If the newborn's mother is positive for human immunodeficiency virus type 1 (HIV-1), the baby is at high risk of acquiring HIV-1 through breastfeeding. We suggested that a vaccination consisting of recombinant BCG expressing HIV-1 immunogen administered at birth followed by a boost with rMVA sharing the same immunogen could serve as a strategy for prevention of mother-to-child transmission of HIV-1 and rMVA expressing an African HIV-1-derived immunogen HIVA is currently in phase I trials in African neonates. Here, we aim to develop a dual neonate vaccine platform against HIV-1 and TB consisting of BCG.HIVA administered at birth followed by a boost with MVA.HIVA.85A. Thus, mMVA.HIVA.85A and sMVA.HIVA.85A vaccines were constructed, in which the transgene transcription is driven by either modified H5 or short synthetic promoters, respectively, and tested for immunogenicity alone and in combination with BCG.HIVA²²². mMVA.HIVA.85A was produced markerless and thus suitable for clinical manufacture. While sMVA.HIVA.85A expressed higher levels of the immunogens, it was less immunogenic than mMVA.HIVA.85A in BALB/c mice. A BCG.HIVA²²²–mMVA.HIVA.85A prime-boost regimen induced robust T cell responses to both HIV-1 and M. tuberculosis. Therefore, proof-of-principle for a dual anti-HIV-1/M. tuberculosis infant vaccine platform is established. Induction of immune responses against these pathogens soon after birth is highly desirable and may provide a basis for lifetime protection maintained by boosts later in life.

CTLA-4 blockade increases antigen-specific CD8(+) T cells in prevaccinated patients with melanoma: three cases

BACKGROUND

Anti-cytotoxic T-lymphocyte antigen-4 (CTLA-4) antibodies, such as ipilimumab, have generated measurable immune responses to Melan-A, NY-ESO-1, and gp100 antigens in metastatic melanoma. Vaccination against such targets has potential for immunogenicity and may produce an effector-memory T-cell response.

METHODS

To determine the effect of CTLA-4 blockade on antigen-specific responses following vaccination, in-depth immune monitoring was performed on three ipilimumab-treated patients prevaccinated with gp100 DNA (IMF-24), gp100(209-217) and tyrosinase peptides plus GM-CSF DNA (IMF-32), or NY-ESO-1 protein plus imiquimod (IMF-11); peripheral blood mononuclear cells were analyzed by tetramer and/or intracellular cytokine staining following 10-day culture with HLA-A*0201-restricted gp100(209-217) (ITDQVPFSV), tyrosinase(369-377) (YMDGTMSQV), or 20-mer NY-ESO-1 overlapping peptides, respectively. Tumors from IMF-32 were analyzed by immunohistochemistry to help elucidate mechanism(s) underlying tumor escape.

RESULTS

Following vaccination, patients generated weak to no CD4(+) or CD8(+) T-cell response specific to the vaccine antigen but demonstrated increases in effector-memory (CCR7(lo)CD45RA(lo)) tetramer(+)CD8(+) T cells. After ipilimumab induction, patients experienced a robust, although sometimes transient, antigen-specific response for gp100 (IMF-32 and IMF-24) or NY-ESO-1 (IMF-11) and produced polyfunctional intracellular cytokines. Primary and metastatic tumors expressed tyrosinase but not gp100 or class I/II MHC molecules.

CONCLUSION

Vaccination induced a measurable antigen-specific T-cell response that increased following CTLA-4 blockade, potentially "boosting" the vaccine-primed response. Tumor escape may be related to antigen loss or lack of MHC expression necessary for immune activity. These results in a limited number of patients support the need for further research into combining vaccination with ipilimumab and provide insight into mechanisms underlying tumor escape.

TAA polyepitope DNA-based vaccines: a potential tool for cancer therapy

DNA-based cancer vaccines represent an attractive strategy for inducing immunity to tumor associated antigens (TAAs) in cancer patients. The demonstration that the delivery of a recombinant plasmid encoding epitopes can lead to epitope production, processing, and presentation to CD8+ T-lymphocytes, and the advantage of using a single DNA construct encoding multiple epitopes of one or more TAAs to elicit a broad spectrum of cytotoxic T-lymphocytes has encouraged the development of a variety of strategies aimed at increasing immunogenicity of TAA polyepitope DNA-based vaccines. The polyepitope DNA-based cancer vaccine approach can (a) circumvent the variability of peptide presentation by tumor cells, (b) allow the introduction in the plasmid construct of multiple immunogenic epitopes including heteroclitic epitope versions, and (c) permit to enroll patients with different major histocompatibility complex (MHC) haplotypes. This review will discuss the rationale for using the TAA polyepitope DNA-based vaccination strategy and recent results corroborating the usefulness of DNA encoding polyepitope vaccines as a potential tool for cancer therapy.

Clinical and immunological responses in metastatic melanoma patients vaccinated with a high-dose poly-epitope vaccine

BACKGROUND

Safety and cellular immunogenicity of rising doses and varying regimens of a poly-epitope vaccine were evaluated in advanced metastatic melanoma. The vaccine comprised plasmid DNA and recombinant modified vaccinia virus Ankara (MVA) both expressing a string (Mel3) of seven HLA.A2/A1 epitopes from five melanoma antigens.

METHODS

Forty-one HLA-A2 positive patients with stage III/IV melanoma were enrolled. Patient groups received one or two doses of DNA.Mel3 followed by escalating doses of MVA.Mel3. Immunisations then continued eight weekly in the absence of disease progression. Epitope-specific CD8+ T cell responses were evaluated using ex-vivo tetramer and IFN-gamma ELISPOT assays. Safety and clinical responses were monitored.

RESULTS

Prime-boost DNA/MVA induced Melan-A-specific CD8+ T cell responses in 22/31 (71%) patients detected by tetramer assay. ELISPOT detected a response to at least one epitope in 10/31 (32%) patients. T cell responder rates were <50% with low-dose DNA/MVA, or MVA alone, rising to 91% with high-dose DNA/MVA. Among eight patients showing evidence of clinical benefit-one PR (24 months+), five SD (5 months+) and two mixed responses-seven had associated immune responses. Melan-A-tetramer+ immunity was associated with a median 8-week increase in time-to-progression (P = 0.037) and 71 week increase in survival (P = 0.0002) compared to non-immunity. High-dose vaccine was well tolerated. The only significant toxicities were flu-like symptoms and injection-site reactions.

CONCLUSIONS

DNA.Mel3 and MVA.Mel3 in a prime-boost protocol generated high rates of immune response to melanoma antigen epitopes. The treatment was well tolerated and the correlation of immune responses with patient outcomes encourages further investigation.

DNA vaccines: developing new strategies against cancer

Due to their rapid and widespread development, DNA vaccines have entered into a variety of human clinical trials for vaccines against various diseases including cancer. Evidence that DNA vaccines are well tolerated and have an excellent safety profile proved to be of advantage as many clinical trials combines the first phase with the second, saving both time and money. It is clear from the results obtained in clinical trials that such DNA vaccines require much improvement in antigen expression and delivery methods to make them sufficiently effective in the clinic. Similarly, it is clear that additional strategies are required to activate effective immunity against poorly immunogenic tumor antigens. Engineering vaccine design for manipulating antigen presentation and processing pathways is one of the most important aspects that can be easily handled in the DNA vaccine technology. Several approaches have been investigated including DNA vaccine engineering, co-delivery of immunomodulatory molecules, safe routes of administration, prime-boost regimen and strategies to break the immunosuppressive networks mechanisms adopted by malignant cells to prevent immune cell function. Combined or single strategies to enhance the efficacy and immunogenicity of DNA vaccines are applied in completed and ongoing clinical trials, where the safety and tolerability of the DNA platform are substantiated. In this review on DNA vaccines, salient aspects on this topic going from basic research to the clinic are evaluated. Some representative DNA cancer vaccine studies are also discussed.

Activation of human dendritic cells by recombinant modified vaccinia virus Ankara vectors encoding survivin and IL-2 genes in vitro

Modified vaccinia virus Ankara (MVA) has attracted significant attention as a safe, promising vector for immunotherapy. However, the precise effects of MVA infection on immune responses in humans remain largely unknown. We constructed recombinant MVA (rMVA) encoding both a human tumor-associated antigen (survivin) and the proinflammatory cytokine interleukin (IL)-2 and investigated their effects on human monocyte-derived dendritic cells (DCs). The results showed that infection with rMVA slightly impaired the upregulation of CD83 and reduced the production of IL-10 in DCs after lipopolysaccharide stimulation. However, rMVA-infected DCs were still able to express high levels of target genes and the costimulatory molecules CD80 and CD86 and to produce significant amounts of the proinflammatory cytokine tumor necrosis factor alpha. Moreover, rMVA-infected DCs exhibited a greater capacity than uninfected cells to stimulate T-cell proliferation and to reverse MVA-induced apoptosis in syngeneic T cells. Coculture of lymphocytes with rMVA-infected DCs significantly increased cytotoxic potential and interferon gamma production by cytotoxic T cells. These findings suggest that rMVA encoding survivin and IL-2 can effectively stimulate the activation of human DCs and overcome defects such as impairment of DC maturation and apoptosis of lymphocytes that are caused by vector alone. Thus, this study may provide a rational basis for further optimization of MVA vector.

Preclinical studies of a modified vaccinia virus Ankara-based HIV candidate vaccine: antigen presentation and antiviral effect

Poxvirus-based human immunodeficiency virus (HIV) vaccine candidates are currently under evaluation in preclinical and clinical trials. Modified vaccinia virus Ankara (MVA) vectors have excellent safety and immunogenicity records, but their behavior in human cell cultures remains only partly characterized. We studied here various virological and immunological aspects of the interactions of MVA-HIV, a vaccine candidate developed by the French National Agency for AIDS Research (ANRS), with primary human cells. We report that MVA-HIV infects and drives Gag expression in primary macrophages, dendritic cells (DCs), and epithelial and muscle cells. MVA-HIV-infected DCs matured, efficiently presented Gag, Pol, and Nef antigens, and activated HIV-specific cytotoxic T lymphocytes (CTLs). As expected with this type of vector, infection was cytopathic and led to DC apoptosis. Coculture of MVA-HIV-infected epithelial cells or myotubes with DCs promoted efficient Gag antigen major histocompatibility complex class I (MHC-I) cross-presentation without inducing direct infection and death of DCs. Antigen-presenting cells (APCs) infected with MVA-HIV also activated HIV-specific CD4(+) T cells. Moreover, exposure of DCs to MVA-HIV or to MVA-HIV-infected myotubes induced type I interferon (IFN) production and inhibited subsequent HIV replication and transfer to lymphocytes. Altogether, these results show that MVA-HIV promotes efficient MHC-I and MHC-II presentation of HIV antigens by APCs without facilitating HIV replication. Deciphering the immune responses to MVA in culture experiments will help in the design of innovative vaccine strategies.

Novel HIV-1 clade B candidate vaccines designed for HLA-B*5101(+) patients protected mice against chimaeric ecotropic HIV-1 challenge

Novel candidate HIV-1 vaccines have been constructed, which are tailor-designed for HLA-B*5101(+) patients infected with HIV-1 clade B. These vaccines employ novel immunogen HIVB-B*5101 derived from consensus HIV-1 clade B Gag p17 and p24 regions coupled to two Pol-derived B*5101-restricted epitopes, which are together with a third B*5101 epitope in Gag dominant in HIV-1-infected long-term non-progressing patients. Both plasmid DNA and modified vaccinia virus Ankara (MVA) vectors supported high expression levels of the HIVB-B*5101 immunogen in cultured cells. Heterologous DNA prime-recombinant MVA boost regimen induced efficiently HIV-1-specific CD8(+) T-cell responses in BALB/c mice. These vaccine-elicited T cells were multifunctional, killed efficiently target cells in vivo, and protected mice against challenge with ecotropic HIV-1/NL4-3 and ecotropic HIV-1/NDK chimaeric viruses with HIV-1 clade B or D backbones, respectively, and ecotropic murine leukemia virus gp80 envelope, and therefore did so in the absence of anti-HIV-1 gp120 antibodies. These results support further development of HIVB-B*5101 vaccines in combined heterologous-modality regimens. The use of allele-specific vaccines in humans is discussed in the context of other developments in the HIV-1 field.

In vitro host range, multiplication and virion forms of recombinant viruses obtained from co-infection in vitro with a vaccinia-vectored influenza vaccine and a naturally occurring cowpox virus isolate

Background

Poxvirus-vectored vaccines against infectious diseases and cancer are currently under development. We hypothesized that the extensive use of poxvirus-vectored vaccine in future might result in co-infection and recombination between the vaccine virus and naturally occurring poxviruses, resulting in hybrid viruses with unpredictable characteristics. Previously, we confirmed that co-infecting in vitro a Modified vaccinia virus Ankara (MVA) strain engineered to express influenza virus haemagglutinin (HA) and nucleoprotein (NP) genes with a naturally occurring cowpox virus (CPXV-NOH1) resulted in recombinant progeny viruses (H Hansen, MI Okeke, Ø Nilssen, T Traavik, Vaccine 23: 499–506, 2004). In this study we analyzed the biological properties of parental and progeny hybrid viruses.

Results

Five CPXV/MVA progeny viruses were isolated based on plaque phenotype and the expression of influenza virus HA protein. Progeny hybrid viruses displayed in vitro cell line tropism of CPXV-NOH1, but not that of MVA. The HA transgene or its expression was lost on serial passage of transgenic viruses and the speed at which HA expression was lost varied with cell lines. The HA transgene in the progeny viruses or its expression was stable in African Green Monkey derived Vero cells but became unstable in rat derived IEC-6 cells. Hybrid viruses lacking the HA transgene have higher levels of virus multiplication in mammalian cell lines and produced more enveloped virions than the transgene positive progenitor virus strain. Analysis of the subcellular localization of the transgenic HA protein showed that neither virus strain nor cell line have effect on the subcellular targets of the HA protein. The influenza virus HA protein was targeted to enveloped virions, plasma membrane, Golgi apparatus and cytoplasmic vesicles.

Conclusion

Our results suggest that homologous recombination between poxvirus-vectored vaccine and naturally circulating poxviruses, genetic instability of the transgene, accumulation of non-transgene expressing vectors or hybrid virus progenies, as well as cell line/type specific selection against the transgene are potential complications that may result if poxvirus vectored vaccines are extensively used in animals and man.

Expanding the repertoire of Modified Vaccinia Ankara-based vaccine vectors via genetic complementation strategies

Background

Modified Vaccinia virus Ankara (MVA) is a safe, highly attenuated orthopoxvirus that is being developed as a recombinant vaccine vector for immunization against a number of infectious diseases and cancers. However, the expression by MVA vectors of large numbers of poxvirus antigens, which display immunodominance over vectored antigens-of-interest for the priming of T cell responses, and the induction of vector-neutralizing antibodies, which curtail the efficacy of subsequent booster immunizations, remain as significant impediments to the overall utility of such vaccines. Thus, genetic approaches that enable the derivation of MVA vectors that are antigenically less complex may allow for rational improvement of MVA-based vaccines.

Principal Findings

We have developed a genetic complementation system that enables the deletion of essential viral genes from the MVA genome, thereby allowing us to generate MVA vaccine vectors that are antigenically less complex. Using this system, we deleted the essential uracil-DNA-glycosylase (udg) gene from MVA and propagated this otherwise replication-defective variant on a complementing cell line that constitutively expresses the poxvirus udg gene and that was derived from a newly identified continuous cell line that is permissive for growth of wild type MVA. The resulting virus, MVAΔudg, does not replicate its DNA genome or express late viral gene products during infection of non-complementing cells in culture. As proof-of-concept for immunological ‘focusing’, we demonstrate that immunization of mice with MVAΔudg elicits CD8+ T cell responses that are directed against a restricted repertoire of vector antigens, as compared to immunization with parental MVA. Immunization of rhesus macaques with MVAΔudg-gag, a udg⁻ recombinant virus that expresses an HIV subtype-B consensus gag transgene, elicited significantly higher frequencies of Gag-specific CD8 and CD4 T cells following both primary (2–4-fold) and booster (2-fold) immunizations as compared to the udg⁺ control virus MVA-gag, as determined by intracellular cytokine assay. In contrast, levels of HIV Gag-specific antibodies were elicited similarly in macaques following immunization with MVAΔudg-gag and MVA-gag. Furthermore, both udg⁻ and udg⁺ MVA vectors induced comparatively similar titers of MVA-specific neutralizing antibody responses following immunization of mice (over a 4-log range: 10⁴–10⁸ PFU) and rhesus macaques. These results suggest that the generation of MVA-specific neutralizing antibody responses are largely driven by input MVA antigens, rather than those that are synthesized de novo during infection, and that the processes governing the generation of antiviral antibody responses are more readily saturated by viral antigen than are those that elicit CD8+ T cell responses.

Significance

Our identification of a spontaneously-immortalized (but not transformed) chicken embryo fibroblast cell line (DF-1) that is fully permissive for MVA growth and that can be engineered to stably express MVA genes provides the basis for a genetic system for MVA. DF-1 cells (and derivatives thereof) constitute viable alternatives, for the manufacture of MVA-based vaccines, to primary CEFs – the conventional cell substrate for MVA vaccines that is not amenable to genetic complementation strategies due to these cells' finite lifespan in culture. The establishment of a genetic system for MVA, as illustrated here to allow udg deletion, enables the generation of novel replication-defective MVA mutants and expands the repertoire of genetic viral variants that can now be explored as improved vaccine vectors.

Boosting BCG vaccination with MVA85A down-regulates the immunoregulatory cytokine TGF-beta1

In clinical trials recombinant-modified vaccinia virus Ankara expressing the Mycobacterium tuberculosis antigen 85A (MVA85A) induces approximately 10 times more effector T cells than any other recombinant MVA vaccine. We have found that in BCG primed subjects MVA85A vaccination reduces transforming growth factor beta 1 (TGF-beta1) mRNA in peripheral blood lymphocytes and reduces TGF-beta1 protein in the serum, but increases IFN-gamma ELISPOT responses to the recall antigen SK/SD. TGF-beta1 is essential for the generation of regulatory T cells and we see a correlation across vaccinees between CD4+CD25hiFoxP3+ cells and TGF-beta1 serum levels. This apparent ability to counteract regulatory T cell effects suggests a potential use of MVA85A as an adjuvant for less immunogenic vaccines.

Dissociation between epitope hierarchy and immunoprevalence in CD8 responses to vaccinia virus western reserve

Understanding immunity to vaccinia virus (VACV) is important for the development of safer vaccines for smallpox- and poxvirus-vectored recombinant vaccines. VACV is also emerging as an outstanding model for studying CD8(+) T cell immunodominance because of the large number of CD8(+) T cell epitopes known for this virus in both mice and humans. In this study, we characterize the CD8(+) T cell response in vaccinated BALB/c mice by a genome-wide mapping approach. Responses to each of 54 newly identified H-2(d)-restricted T cell epitopes could be detected after i.p. and dermal vaccination routes. Analysis of these new epitopes in the context of those already known for VACV in mice and humans revealed two important findings. First, CD8(+) T cell epitopes are not randomly distributed across the VACV proteome, with some proteins being poorly or nonimmunogenic, while others are immunoprevalent, being frequently recognized across diverse MHC haplotypes. Second, some proteins constituted the major targets of the immune response by a specific haplotype as they recruited the majority of the specific CD8(+) T cells but these proteins did not correspond to the immunoprevalent Ags. Thus, we found a dissociation between immunoprevalence and immunodominance, implying that different sets of rules govern these two phenomena. Together, these findings have clear implications for the design of CD8(+) T cell subunit vaccines and in particular raise the exciting prospect of being able to choose subunits without reference to MHC restriction.

Immunogenicity and safety profiles of genetic vaccines against human Her-2/neu in cynomolgus monkeys

Her-2/neu is a well-characterized tumor-associated antigen, the overexpression of which in human carcinomas correlates with a poor prognosis. Here, we evaluated Her-2/neu-specific humoral and cellular immune responses in immunized monkeys after immunization with nonreplicating adenovirus (AdHM) expressing the extracellular and transmembrane domain of human Her-2/neu (HM) and/or naked DNA vaccine (pHM-hGM-CSF) expressing human granulocyte-macrophage colony-stimulating factor together with HM. Priming of monkeys with AdHM generated Her-2/neu-specific long-lasting antibody production. Furthermore, these Her-2/neu-specific antibodies produced by AdHM immunization, some of which shared epitope specificity with Herceptin, were able to induce antibody-dependent cellular cytotoxicity against Her-2-expressing target cells. Cellular immune responses were elicited in all monkeys immunized with Her-2/neu-expressing vaccine; interferon-gamma was secreted when these splenocytes were restimulated with Her-2/neu-expressing autologous cells, and immunization with AdHM induced Her-2/neu-specific lymphoproliferative responses. Further, immunization with pHM-hGM-CSF before AdHM immunization noticeably enhanced cytotoxic T-lymphocyte activity. In addition, we observed no abnormalities that would indicate that the genetic vaccines had toxic effects in the immunized monkeys. Thus, we can conclude that our genetic vaccines efficiently elicited Her-2/neu-specific humoral and cellular immune responses without causing severe adverse effects in nonhuman primates and that as such they warrant further clinical investigation.

DNA vaccines: precision tools for activating effective immunity against cancer

DNA vaccination has suddenly become a favoured strategy for inducing immunity. The molecular precision offered by gene-based vaccines, together with the facility to include additional genes to direct and amplify immunity, has always been attractive. However, the apparent failure to translate operational success in preclinical models to the clinic, for reasons that are now rather obvious, reduced initial enthusiasm. Recently, novel delivery systems, especially electroporation, have overcome this translational block. Here, we assess the development, current performance and potential of DNA vaccines for the treatment of cancer.

MHC-peptide-specific antibodies reveal inefficient presentation of an HLA-A*0201-restricted, Melan-A-derived peptide after active intracellular processing

MHC-peptide-specific Fab antibodies binding to HLA-A*0201 complexes presenting the wild-type EAAGIGILTV (EAA) or analogue Melan-A 10-mer ELAGIGILTV (ELA) peptide were generated to study efficacy of peptide processing and presentation. None of the selected Fab antibodies detected the naturally processed EAA/HLA-A*0201 complex on melanoma tumor cells, confirming the known low peptide number on the cell surface. To study the effect of peptide presentation and processing in more detail, genes coding for the A27L-mutated Melan-A protein or the processed ELA peptide were introduced into HLA-A*0201(+) B cells by infection with the respective recombinant vaccinia virus construct producing equimolar amounts of GFP-ubiquitin directly linked to the fragment of interest. Correlating GFP expression to actual numbers of peptide presented, 1100-2600 [corrected] ELA peptides had to be synthesized to be presented by a single MHC class I antigen-peptide complex. This number increased 10- to 20-fold when ELA peptide presentation from the A27L-mutated full length Melan-A protein was studied, since 16000-52000 [corrected] GFP molecules needed to be synthesized for the detection of one ELA peptide. Our results indicate that peptide processing rather than presentation is the rate-limiting step in our experimental setting and is much more ineffective for Melan-A than has been previously shown for other MHC class I-restricted epitopes.

Harnessing NKT cells for therapeutic applications

Activation of NKT cells leads to the maturation of dendritic cells and efficiently assists priming of antigen-specific immune responses. The lack of polymorphism of CDld molecules and the evolutionary conservation of NKT cell responses highlight the important role of these cells in bridging innate and adaptive immune responses and advocate the value of harnessing this system in clinical settings. Compounds capable of fine tuning NKT cell activation should be actively exploited as potent adjuvants in vaccination strategies or as immunomodulators of autoimmune diseases.

Comparative prime-boost vaccinations using Semliki Forest virus, adenovirus, and ALVAC vectors demonstrate differences in the generation of a protective central memory CTL response against the P815 tumor

Tumor-specific Ags are potential target molecules in the therapeutic treatment of cancer. One way to elicit potent immune responses against these Ags is to use recombinant viruses, which activate both the innate and the adaptive arms of the immune system. In this study, we have compared Semliki Forest virus (SFV), adenovirus, and ALVAC (poxvirus) vectors for their capacity to induce CD8(+) T cell responses against the P1A tumor Ag and to elicit protection against subsequent challenge injection of P1A-expressing P815 tumor cells in DBA/2 mice. Both homologous and heterologous prime-boost regimens were studied. In most cases, both higher CD8(+) T cell responses and better tumor protections were observed in mice immunized with heterologous prime-boost regimens, suggesting that the combination of different viral vectors is beneficial for the induction of an effective immune response. However, homologous immunization with SFV provided potent tumor protection despite a rather moderate primary CD8(+) T cell response as compared with mice immunized with recombinant adenovirus. SFV-immunized mice showed a rapid and more extensive expansion of P1A-specific CD8(+) T cells in the tumor-draining lymph node after tumor challenge and had a higher frequency of CD62L(+) P1A-specific T cells in the blood, spleen, and lymph nodes as compared with adenoimmunized mice. Our results indicate that not only the magnitude but in particular the quality of the CD8(+) T cell response correlates with tumor protection.

Viral vector vaccines make memory T cells against malaria

Vaccines that comprise attenuated viral vectors encoding antigens from target pathogens generate potent T-cell responses. One such pathogen is malaria, and in particular the liver stage of its life cycle. Immunogenicity and efficacy studies in animals and humans have revealed the generation of memory T cells of both the central and effector phenotypes, depending on the viral vectors used in the malaria vaccination regime (viral species and serotype, combination and sequence for prime-boost) and suggest a divergence in their protective role. Being able to influence the memory T-cell make-up in a rational manner may allow us to develop more efficacious vaccines.

Plasmid DNA and viral vector-based vaccines for the treatment of cancer

Plasmid DNA and viral vector-based cancer vaccines have many inherent features that make them promising cancer vaccine candidates. This review focuses on the use of plasmid DNA and viral vector vaccines to deliver tumour-specific antigens to induce a tumour-specific immune response. Examples of different antigen delivery systems that have been tested in recent clinical trials are summarised and advantages and disadvantages of a number of delivery systems and approaches are discussed. Finally, an outlook on how plasmid DNA and viral vectors might be developed further as cancer vaccines is provided.

Recombinant murine gammaherpesvirus 68 (MHV-68) as challenge virus to test efficacy of vaccination against chronic virus infections in the mouse model

Efficient vaccines against AIDS, Hepatitis C and other persistent virus infections are urgently needed. Vaccine development has been especially hampered by the lack of suitable small animal models to reliably test the protective capacity of candidate vaccines against such chronic viral infections. A natural mouse pathogen such as MHV-68 that persists lifelong after infection, appears to be a particularly promising candidate for a more relevant model system. Here, we investigated infections with recombinant MHV-68 as novel mouse challenge model to test the efficacy of heterologous vaccines based on recombinant modified vaccinia virus Ankara (MVA). To apply ovalbumin (OVA) as a model antigen, we constructed the recombinant virus MHV-68-OVA by BAC technology and characterized genetic stability and replicative capacity of the virus in vitro and in vivo. We demonstrated the ability of MHV-68-OVA to produce ovalbumin upon tissue culture infection. Moreover, the use of MHV-68-OVA-infected target cells allowed for efficient ex vivo amplification of OVA-specific, MHC class I-restricted CD8 T cells derived from MVA-OVA-vaccinated C57BL/6 mice. Finally, we immunized C57BL/6 mice with MVA-OVA and challenged the animals with MHV-68-OVA testing different time points and routes of infection. Vaccinated mice were infected with MHV-68-OVA but showed reduced viral loads in the acute and latent phase of challenge infection. These data strongly suggest the usefulness of the MHV-68 challenge model for further evaluation of recombinant vaccines against persisting virus infections.

Vaccination with recombinant modified vaccinia virus Ankara expressing bovine respiratory syncytial virus (bRSV) proteins protects calves against RSV challenge

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and calves. Bovine RSV (bRSV) is a natural pathogen for cattle, and bRSV infection in calves shares many features with the human infection. Thus, bRSV infection in cattle provides the ideal setting to evaluate the safety and efficacy of novel RSV vaccine strategies. Here, we have evaluated the efficacy and safety of modified vaccinia virus Ankara (rMVA)-based vaccine candidates, expressing the bovine RSV-F protein, either or not in combination with the G protein, in colostrums-deprived SPF calves born by caesarean section. Vaccination induced bRSV-specific IgG and CD8 T cell responses. Importantly, no IgE responses were detected. After bRSV challenge, rMVA vaccinated calves experienced less severe symptoms of lower respiratory tract disease compared to the mock-immunized control group. Immunized animals showed reduced pulmonary virus loads, and no eosinophilic infiltration or enhanced respiratory distress. In conclusion, candidate rMVA/bRSV vaccines induced protective and safe immune responses in calves.

Hepatitis B virus core antigen epitopes presented by HLA-A2 single-chain trimers induce functional epitope-specific CD8+ T-cell responses in HLA-A2.1/Kb transgenic mice

The potency of CD8+ cytotoxic T lymphocyte (CTL) responses toward core antigen has been shown to affect the outcomes of hepatitis B virus (HBV) infection. Since single-chain trimers (SCT) composed of peptide epitope beta2-microglobulin (beta2m) and major histocompatibility complex (MHC) class I heavy chain covalently linked together in a single molecule have been shown to stimulate efficient CTL responses, we investigated the properties of human leucocyte antigen (HLA)-A2 SCTs encoding the HBV core antigen (HBcAg) epitopes C(18-27) and C(107-115). Transfection of NIH-3T3 cells with pcDNA3.0-SCT-C(18-27) and SCT-C(107-115) leads to stable presentation of HBcAg epitopes at the cell surface. HLA-A2.1/Kb transgenic mice vaccinated with the SCT constructs, either as a DNA vaccine alone or followed by a boost with recombinant vaccinia virus, were shown to generate HBcAg-specific CTL responses by enzyme-linked immunospot assay (ELISPOT) and in vitro interferon-gamma release experiments. HBcAg-specific CTLs from vaccinated HLA-A2.1/Kb transgenic mice were able to inhibit HBV surface and e antigen expression as indicated by HepG2.2.15 cells. Our data indicate that a DNA vaccine encoding a human HLA-A2 SCT with HBV epitopes can lead to stable, enhanced HBV core antigen presentation, and may be useful for the control of HBV infection in HLA-A2-positive HBV carriers.

The human T cell response to melanoma antigens

The cornerstone of the concept of immunosurveillance in cancer should be the experimental demonstration of immune responses able to alter the course of in vivo spontaneous tumor progression. Elegant genetic manipulation of the mouse immune system has proved this tenet. In parallel, progress in understanding human T cell mediated immunity has allowed to document the existence in cancer patients of naturally acquired T cell responses to molecularly defined tumor antigens. Various attributes of cutaneous melanoma tumors, notably their adaptability to in vitro tissue culture conditions, have contributed to convert this tumor in the prototype for studies of human antitumor immune responses. As a consequence, the first human cytolytic T lymphocyte (CTL)-defined tumor antigen and numerous others have been identified using lymphocyte material from patients bearing this tumor, detailed analyses of specific T cell responses have been reported and a relatively large number of clinical trials of vaccination have been performed in the last 15 years. Thus, the "melanoma model" continues to provide valuable insights to guide the development of clinically effective cancer therapies based on the recruitment of the immune system. This chapter reviews recent knowledge on human CD8 and CD4 T cell responses to melanoma antigens.

Challenges for cancer vaccine development

The first generation of human cancer vaccines has been tested in phase III clinical trials, but only a few of these have demonstrated sufficient efficacy to be licensed for clinical use. This article reviews some of the mechanisms that could contribute to these limited clinical responses, and highlights the challenges faced for development of future vaccines.