The use of combination vaccinia vaccines and dual-gene vaccinia vaccines to enhance antigen-specific T-cell immunity via T-cell costimulation

Strategies for the development of PSA-based vaccines for the treatment of advanced prostate cancer

Prostate cancer is the second leading cause of cancer death in males in the USA. Vaccine strategies represent a novel therapeutic approach. One potential target for a prostate cancer vaccine is prostate-specific antigen (PSA), due to its restricted expression in prostate cancer and normal prostatic epithelial cells. A number of PSAspecific epitopes have been identified that can activate cytotoxic T-lymphocytes (CTLs) and in turn lead to the killing of tumor targets by the peptide-specific CTLs. Strategies have now been employed in clinical trials using RNA-pulsed dendritic cell vaccines, recombinant protein vaccines, and recombinant viral vector delivery of vaccines. Newer approaches incorporating costimulatory molecules that enhance Tcell activation are also being investigated.

Therapeutic cancer vaccines

Therapeutic cancer vaccines have the potential of being integrated in the therapy of numerous cancer types and stages. The wide spectrum of vaccine platforms and vaccine targets is reviewed along with the potential for development of vaccines to target cancer cell "stemness," the epithelial-to-mesenchymal transition (EMT) phenotype, and drug-resistant populations. Preclinical and recent clinical studies are now revealing how vaccines can optimally be used with other immune-based therapies such as checkpoint inhibitors, and so-called nonimmune-based therapeutics, radiation, hormonal therapy, and certain small molecule targeted therapies; it is now being revealed that many of these traditional therapies can lyse tumor cells in a manner as to further potentiate the host immune response, alter the phenotype of nonlysed tumor cells to render them more susceptible to T-cell lysis, and/or shift the balance of effector:regulatory cells in a manner to enhance vaccine efficacy. The importance of the tumor microenvironment, the appropriate patient population, and clinical trial endpoints is also discussed in the context of optimizing patient benefit from vaccine-mediated therapy.

Clinical development directions in oncolytic viral therapy

Oncolytic virotherapy is an emerging experimental treatment platform for cancer therapy. Oncolytic viruses are replicative-competent viruses that are engineered to replicate selectively in cancer cells with specified oncogenic phenotypes. Multiple DNA and RNA viruses have been clinically tested in a variety of tumors. This review will provide a brief description of these novel anticancer biologics and will summarize the results of clinical investigation. To date oncolytic virotherapy has shown to be safe, and has generated clinical responses in tumors that are resistant to chemotherapy or radiotherapy. The major challenge for researchers is to maximize the efficacy of these viral therapeutics, and to establish stable systemic delivery mechanisms.

Immune modulators with defined molecular targets: cornerstone to optimize rational vaccine design

Vaccination remains the most valuable tool for preventing infectious diseases. However, the performance of many existing vaccines should be improved and there are diseases for which vaccines are still not available. The use of well-defined antigens for the generation of subunit vaccines has led to products with an improved safety profile. However, purified antigens are usually poorly immunogenic, making essential the use of adjuvants. Despite the fact that adjuvants have been used to increase the immunogenicity of vaccines for more than 70 years, only a handful has been licensed for human use (e.g., aluminium salts, the micro-fluidized squalene-in-water emulsion MF59 and monophosphoryl lipid A). Thus, the development of new adjuvants which are able to promote broad and sustained immune responses at systemic and mucosal levels still remains as a major challenge in vaccinology. Recent advances in our understanding of the immune system have facilitated the identification of new biological targets for screening programs aimed at the discovery of novel immune stimulators. This resulted in the identification of new candidate adjuvants, which made possible the modulation of the immune responses elicited according to specific needs. A number of promising adjuvants which are currently under preclinical or clinical development will be described in this chapter.

Intratumoral delivery of vector mediated IL-2 in combination with vaccine results in enhanced T cell avidity and anti-tumor activity

Systemic IL-2 is currently employed in the therapy of several tumor types, but at the price of often severe toxicities. Local vector mediated delivery of IL-2 at the tumor site may enhance local effector cell activity while reducing toxicity. To examine this, a model using CEA-transgenic mice bearing established CEA expressing tumors was employed. The vaccine regimen was a s.c. prime vaccination with recombinant vaccinia (rV) expressing transgenes for CEA and a triad of costimulatory molecules (TRICOM) followed by i.t. boosting with rF-CEA/TRICOM. The addition of intratumoral (i.t.) delivery of IL-2 via a recombinant fowlpox (rF) IL-2 vector greatly enhanced anti-tumor activity of a recombinant vaccine, resulting in complete tumor regression in 70-80% of mice. The anti-tumor activity was shown to be dependent on CD8(+) cells and NK1.1(+). Cellular immune assays revealed that the addition of rF-IL-2 to the vaccination therapy enhanced CEA-specific tetramer(+) cell numbers, cytokine release and CTL lysis of CEA(+) targets. Moreover, tumor-bearing mice vaccinated with the CEA/TRICOM displayed an antigen cascade, i.e., CD8(+) T cell responses to two other antigens expressed on the tumor and not the vaccine: wild-type p53 and endogenous retroviral antigen gp70. Mice receiving rF-IL-2 during vaccination demonstrated higher avidity CEA-specific, as well as higher avidity gp70-specific, CD8(+) T cells when compared with mice vaccinated without rF-IL-2. These studies demonstrate for the first time that the level and avidity of antigen specific CTL, as well as the therapeutic outcome can be improved with the use of i.t. rF-IL-2 with vaccine regimens.

4-1BB ligand enhances tumor-specific immunity of poxvirus vaccines

PURPOSE

Recombinant poxvirus vaccines have been explored as tumor vaccines. The immunogenicity of these vaccines can be enhanced by co-expressing costimulatory molecules and tumor-associated antigens. While the B7-CD28 interaction has been most comprehensively investigated, other costimulatory molecules utilize different signaling pathways and might provide further cooperation in T cell priming and survival. 4-1BB (CD137) is a TNF family member and is critical for activation and long-term maintenance of primed T cells. This study was conducted to determine if a poxvirus expressing the ligand for 4-1BB (4-1BBL) could further improve the immune and therapeutic responses of a previously reported poxvirus vaccine expressing a triad of costimulatory molecules (B7.1, ICAM-1, and LFA-3).

EXPERIMENTAL DESIGN

A recombinant vaccinia virus expressing 4-1BBL was generated and characterized in an in vitro infection system. This vaccine was then used alone or in combination with a vaccinia virus expressing CEA, B7.1, ICAM-1, and LFA-3 in CEA-transgenic mice bearing established MC38 tumors. Tumor growth and immune responses against CEA and other tumor-associated antigens were determined. The level of anti-apoptotic proteins in responding T cells was determined by flow cytometry on tetramer selected T cells.

RESULTS

The combination of 4-1BBL with B7.1-based poxvirus vaccination resulted in significantly enhanced therapeutic effects against CEA-expressing tumors in a CEA-transgenic mouse model. This was associated with an increased level of CEA-specific CD4(+) and CD8(+) T cell responses, induction of antigen spreading to p53 and gp70, increased accumulation of CEA-specific T cells in the tumor microenvironment, and increased expression of bcl-X(L) and bcl-2 in CD4(+) and CD8(+) T cells in vaccinated mice.

CONCLUSION

4-1BBL cooperates with B7 in enhancing anti-tumor and immunologic responses in a recombinant poxvirus vaccine model. The inclusion of costimulatory molecules targeting distinct T cell signaling pathways provides a mechanism for enhancing the therapeutic effectiveness of tumor vaccines.

Local Delivery of Vaccinia Virus Expressing Multiple Costimulatory Molecules for the Treatment of Established Tumors

Successful immunotherapy of established tumors depends on overcoming the suppressive influence of the local tumor microenvironment. The direct injection of vaccinia virus expressing the B7.1 (CD80) costimulatory molecule into melanoma lesions resulted in local and systemic immunity with associated clinical responses. Therefore, we sought to evaluate the effects of a vaccinia virus expressing three costimulatory molecules, B7.1, ICAM-1, and LFA-3 (rV-TRICOM), in patients with metastatic melanoma. A standard dose escalation phase I clinical trial was performed. Thirteen patients were enrolled and 12 were available for follow-up. Local vaccination was feasible, with only low-grade injection site reactions associated with mild fatigue and myalgia reported. There was one occurrence of grade 1 vitiligo. Overall there was a 30.7% objective clinical response, with one patient achieving a complete response for more than 22 months. An inverse association was detected between anti-vaccinia antibody and anti-vaccinia T cell responses. Patients who failed to respond to vaccination but received high-dose interleukin-2 had a trend toward improved survival. Collectively, these results confirm the safety profile and feasibility of direct injection of vaccinia virus expressing multiple costimulatory molecules in patients with established tumors. Further clinical investigation is needed to better define the role of antigen, adjuvant cytokines, costimulation, and cross-presentation in the host immune response to local vaccination with vaccinia viruses expressing immunomodulatory molecules.

Vaccines with enhanced costimulation maintain high avidity memory CTL

The avidity of Ag-specific CTL is a critical determinant for clearing viral infection and eliminating tumor. Although previous studies have demonstrated that vaccines using enhanced costimulation will enhance the level and avidity of Ag-specific T cells from naive mice, there are conflicting data about the effects of vaccines using enhanced costimulation (vector or dendritic cell based) on the survival of memory T cells. In this study we have first extended previous observations that primary vaccination with a recombinant vaccinia virus (rV-) expressing a model Ag (LacZ) and a triad of T cell costimulatory molecules (B7-1, ICAM-1, and LFA-3 (designated TRICOM)) enhances the level and avidity of T cells from naive vaccinated C57BL/6 (Thy1.2) mice. Adoptive transfer of Thy1.1 memory CD8(+) T cells into naive Thy1.2 C57BL/6 mice was followed by booster vaccinations with a recombinant fowlpox (rF-)-expressing LacZ (rF-LacZ) or booster vaccinations with rF-LacZ/TRICOM. Analysis of levels of beta-galactosidase tetramer-positive T cells and functional assays (IFN-gamma expression and lytic activity) determined that booster vaccinations with rF-LacZ/TRICOM were superior to booster vaccinations with rF-LacZ in terms of both maintenance and enhanced avidity of memory CD8(+) T cells. Antitumor experiments using a self-Ag (carcinoembryonic Ag (CEA) vaccines in CEA transgenic mice bearing CEA-expressing tumors) also demonstrated that the use of booster vaccinations with vaccines bearing enhanced costimulatory capacity had superior antitumor effects. These studies thus have implications in the design of more effective vaccine strategies.

The requirement of multimodal therapy (vaccine, local tumor radiation, and reduction of suppressor cells) to eliminate established tumors

PURPOSE

Numerous immune-based strategies are currently being evaluated for cancer therapy in preclinical models and clinical trials. Whereas many strategies look promising in preclinical models, they are often evaluated before or shortly following tumor implantation. The elimination of well-established tumors often proves elusive. Here we show that a multimodal immune-based therapy can be successfully employed to eliminate established tumors.

EXPERIMENTAL DESIGN

This therapy consists of vaccines directed against a self-tumor-associated antigen, the use of external beam radiation of tumors to up-regulate Fas on tumor cells, and the use of a monoclonal antibody (mAb) to reduce levels of CD4+CD25+ suppressor cells.

RESULTS

We show here for the first time that (a) antigen-specific immune responses induced by vaccines were optimally augmented when anti-CD25 mAb was given at the same time as vaccination; (b) anti-CD25 mAb administration in combination with vaccines equally augmented T-cell immune responses specific for a self-antigen as well as those specific for a non-self antigen; (c) whereas the combined use of vaccines and anti-CD25 mAb enhanced antigen-specific immune responses, it was not sufficient to eliminate established tumors; (d) the addition of external beam radiation of tumors to the vaccine/anti-CD25 mAb regimen was required for the elimination of established tumors; and (e) T cells from mice receiving the combination therapy showed significantly higher T-cell responses specific not only for the antigen in the vaccine but also for additional tumor-derived antigens (p53 and gp70).

CONCLUSIONS

These studies reported here support the rationale for clinical trials employing multimodal immune-based therapies.

Analyses of recombinant vaccinia and fowlpox vaccine vectors expressing transgenes for two human tumor antigens and three human costimulatory molecules

PURPOSE

The poor immunogenicity of tumor antigens and the antigenic heterogeneity of tumors call for vaccine strategies to enhance T-cell responses to multiple antigens. Two antigens expressed noncoordinately on most human carcinomas are carcinoembryonic antigen (CEA) and MUC-1. We report here the construction and characterization of two viral vector vaccines to address these issues.

EXPERIMENTAL DESIGN

The two viral vectors analyzed are the replication-competent recombinant vaccinia virus (rV-) and the avipox vector, fowlpox (rF-), which is replication incompetent in mammalian cells. Each vector encodes the transgenes for three human costimulatory molecules (B7-1, ICAM-1, and LFA-3, designated TRICOM) and the CEA and MUC-1 transgenes (which also contain agonist epitopes). The vectors are designated rV-CEA/MUC/TRICOM and rF-CEA/MUC/TRICOM.

RESULTS

Each of the vectors is shown to be capable of faithfully expressing all five transgenes in human dendritic cells (DC). DCs infected with either vector are shown to activate both CEA- and MUC-1-specific T-cell lines to the same level as DCs infected with CEA-TRICOM or MUC-1-TRICOM vectors. Thus, no evidence of antigenic competition between CEA and MUC-1 was observed. Human DCs infected with rV-CEA/MUC/TRICOM or rF-CEA/MUC/TRICOM are also shown to be capable of generating both MUC-1- and CEA-specific T-cell lines; these T-cell lines are in turn shown to be capable of lysing targets pulsed with MUC-1 or CEA peptides as well as human tumor cells endogenously expressing MUC-1 and/or CEA.

CONCLUSION

These studies provide the rationale for the clinical evaluation of these multigene vectors in patients with a range of carcinomas expressing MUC-1 and/or CEA.

Multiple costimulatory modalities enhance CTL avidity

Recent studies in both animal models and clinical trials have demonstrated that the avidity of T cells is a major determinant of antitumor and antiviral immunity. In this study, we evaluated several different vaccine strategies for their ability to enhance both the quantity and avidity of CTL responses. CD8(+) T cell quantity was measured by tetramer binding precursor frequency, and avidity was measured by both tetramer dissociation and quantitative cytolytic function. We have evaluated a peptide, a viral vector expressing the Ag transgene alone, with one costimulatory molecule (B7-1), and with three costimulatory molecules (B7-1, ICAM-1, and LFA-3), with anti-CTLA-4 mAb, with GM-CSF, and combinations of the above. We have evaluated these strategies in both a foreign Ag model using beta-galactosidase as immunogen, and in a "self" Ag model, using carcinoembryonic Ag as immunogen in carcinoembryonic Ag transgenic mice. The combined use of several of these strategies was shown to enhance not only the quantity, but, to a greater magnitude, the avidity of T cells generated; a combination strategy is also shown to enhance antitumor effects. The results reported in this study thus demonstrate multiple strategies that can be used in both antitumor and antiviral vaccine settings to generate higher avidity host T cell responses.

Induction of an antigen cascade by diversified subcutaneous/intratumoral vaccination is associated with antitumor responses

PURPOSE

Cancer vaccines targeting tumor-associated antigens are being investigated for the therapy of tumors. Numerous strategies, including the direct intratumoral (i.t.) vaccination route, have been examined. For tumors expressing carcinoembryonic antigen (CEA) as a model tumor-associated antigen, we previously designed poxviral vectors that contain the transgenes for CEA and a triad of T-cell costimulatory molecules, B7-1, intercellular adhesion molecule-1, (ICAM-1), and leukocyte function associated antigen-3 (LFA-3) (CEA/TRICOM). Two types of poxvirus vectors were developed: replication-competent recombinant vaccinia and replication-defective recombinant fowlpox. We have shown previously that a vaccine regimen composed of priming mice s.c. with recombinant vaccinia-CEA/TRICOM and boosting i.t. with recombinant fowlpox-CEA/TRICOM was superior to priming and boosting vaccinations using the conventional s.c. route in inducing T-cell responses specific for CEA. These studies also showed that CEA was needed to be present both in the vaccine and in the tumor for therapeutic effects.

EXPERIMENTAL DESIGN

To determine specific immune responses associated with vaccination-mediated tumor regression, CEA-transgenic mice bearing CEA(+) tumors were vaccinated with the CEA/TRICOM s.c./i.t. regimen, and T-cell immune responses were assessed.

RESULTS

In CEA(+) tumor-bearing mice vaccinated with the CEA/TRICOM s.c./i.t. regimen, T-cell responses could be detected not only to CEA encoded in vaccine vectors but also to other antigens expressed on the tumor itself: wild-type p53 and an endogenous retroviral epitope of gp70. Moreover, the magnitude of CD8(+) T-cell immune responses to gp70 was far greater than that induced to CEA or p53. Finally, the predominant T-cell population infiltrating the regressing CEA(+) tumor after therapy was specific for gp70.

CONCLUSION

These studies show that the breadth and magnitude of antitumor immune cascades to multiple antigens could be critical in the therapy of established tumors.

Targeting the local tumor microenvironment with vaccinia virus expressing B7.1 for the treatment of melanoma

Immunotherapy for the treatment of metastatic melanoma remains a major clinical challenge. The melanoma microenvironment may lead to local T cell tolerance in part through downregulation of costimulatory molecules, such as B7.1 (CD80). We report the results from the first clinical trial, to our knowledge, using a recombinant vaccinia virus expressing B7.1 (rV-B7.1) for monthly intralesional vaccination of accessible melanoma lesions. A standard 2-dose-escalation phase I clinical trial was conducted with 12 patients. The approach was well tolerated with only low-grade fever, myalgias, and fatigue reported and 2 patients experiencing vitiligo. An objective partial response was observed in 1 patient and disease stabilization in 2 patients, 1 of whom is alive without disease 59 months following vaccination. All patients demonstrated an increase in postvaccination antibody and T cell responses against vaccinia virus. Systemic immunity was tested in HLA-A*0201 patients who demonstrated an increased frequency of gp100 and T cells specific to melanoma antigen recognized by T cells 1 (MART-1), also known as Melan-A, by ELISPOT assay following local rV-B7.1 vaccination. Local immunity was evaluated by quantitative real-time RT-PCR, which suggested that tumor regression was associated with increased expression of CD8 and IFN-gamma. The local delivery of vaccinia virus expressing B7.1 was well tolerated and represents an innovative strategy for altering the local tumor microenvironment in patients with melanoma.

Oncolytic viral therapies

Molecular research has vastly advanced our understanding of the mechanism of cancer growth and spread. Targeted approaches utilizing molecular science have yielded provocative results in the treatment of cancer. Oncolytic viruses genetically programmed to replicate within cancer cells and directly induce toxic effect via cell lysis or apoptosis are currently being explored in the clinic. Safety has been confirmed and despite variable efficacy results several dramatic responses have been observed with some oncolytic viruses. This review summarizes results of clinical trials with oncolytic viruses in cancer.

Phase I study of sequential vaccinations with fowlpox-CEA(6D)-TRICOM alone and sequentially with vaccinia-CEA(6D)-TRICOM, with and without granulocyte-macrophage colony-stimulating factor, in patients with carcinoembryonic antigen-expressing carcinomas

PURPOSE

Our previous clinical experience with vaccinia and replication-defective avipox recombinant carcinoembryonic antigen (CEA) vaccines has demonstrated safety and clinical activity with a correlation between CEA-specific immune response and survival. Preclinical evidence demonstrated that the addition of the transgenes for three T-cell costimulatory molecules (B7-1, ICAM-1, LFA-3, designated TRICOM) results in a significant improvement in antigen-specific T-cell responses and antitumor activity. We describe here the first trial in humans of the CEA-TRICOM vaccines (also including an enhancer agonist epitope within the CEA gene).

PATIENTS AND METHODS

Fifty-eight patients with advanced CEA-expressing cancers were accrued to eight cohorts that involved vaccinations with the following: replication-defective fowlpox recombinant (rF)-CEA(6D)-TRICOM; primary vaccination with recombinant vaccinia (rV)-CEA(6D)-TRICOM plus rF-CEA(6D)-TRICOM booster vaccinations; and rV-CEA(6D)-TRICOM and then rF-CEA(6D)-TRICOM, plus granulocyte-macrophage colony-stimulating factor (GM-CSF) with vaccines, or with divided doses of vaccine with GM-CSF. Vaccines were administered every 28 days for six doses and then once every 3 months. Reverting to treatments every 28 days was allowed if patients progressed on the 3-month schedule.

RESULTS

In this phase I study, no significant toxicity was observed. Twenty-three patients (40%) had stable disease for at least 4 months, with 14 of these patients having prolonged stable disease (> 6 months). Eleven patients had decreasing or stable serum CEA, and one patient had a pathologic complete response. Enhanced CEA-specific T-cell responses were observed in the majority of patients tested.

CONCLUSION

We demonstrated that the CEA-TRICOM vaccines are safe and can generate significant CEA-specific immune responses, and they seem to have clinical benefit in some patients with advanced cancer.

A novel multivalent human CTL peptide construct elicits robust cellular immune responses in HLA-A*0201 transgenic mice: implications for HTLV-1 vaccine design

Cytotoxic T-lymphocytes are critical in the clearance of chronic viral infections such as HTLV-1. Peptide-based vaccines may have potential application in invoking antiviral CTL responses. In the development of vaccination strategies, it is becoming increasingly important to elicit a broad immune response against several epitopes simultaneously that may provide large population coverage. In the present study, we addressed this issue, namely the processing and presentation of multiple CTL epitopes simultaneously for the generation of multispecific CTL responses. We designed a novel multivalent peptide consisting of three HLA-A(*)0201 restricted CTL epitopes, with intervening double arginine residues in tandem. These epitopes were derived from the HTLV-1 regulatory protein Tax, which is an attractive target for vaccine development against HTLV-1. Arginine residues were included to provide cleavage sites for proteasomes, to generate the intended MHC Class I ligands. Proteasomal digestion studies and mass spectrometry analysis showed cleavage of the multivalent construct to generate the individual epitopes. Immunization of HLA-A(*)0201 transgenic mice with this construct efficiently elicited cellular responses to each intended epitope in vivo, further validating the applicability of this approach. These data may have potential in the development of immunotherapeutic strategies for the treatment of HTLV-1 disease and in the future design of multivalent subunit peptide vaccines.

A triad of costimulatory molecules synergize to amplify T-cell activation in both vector-based and vector-infected dendritic cell vaccines

The activation of a T cell has been shown to require two signals via molecules present on professional antigen presenting cells: signal 1, via a peptide/MHC complex, and signal 2, via a costimulatory molecule. Here, the role of three costimulatory molecules in the activation of T cells was examined. Poxvirus (vaccinia and avipox) vectors were employed because of their ability to efficiently express multiple genes. Murine cells provided with signal 1 and infected with either recombinant vaccinia or avipox vectors containing a TRIad of COstimulatory Molecules (B7-1/ICAM-1/LFA-3, designated TRICOM) induced the activation of T cells to a far greater extent than cells infected with vectors expressing any one or two costimulatory molecules. Despite this T-cell "hyperstimulation" using TRICOM vectors, no evidence of apoptosis above that seen using the B7-1 vector was observed. Results employing the TRICOM vectors were most dramatic under conditions of either low levels of first signal or low stimulator cell to T-cell ratios. Experiments employing a four-gene construct also showed that TRICOM recombinants could enhance antigen-specific T-cell responses in vivo. These studies thus demonstrate the ability of vectors to introduce three costimulatory molecules into cells, thereby activating both CD4+ and CD8+ T-cell populations to levels greater than those achieved with the use of only one or two costimulatory molecules. This new threshold of T-cell activation has broad implications in vaccine design and development. Dendritic cells infected with TRICOM vectors were found to greatly enhance naïve T-cell activation, and peptide-specific T-cell stimulation. In vivo, peptide-pulsed DCs infected with TRICOM vectors induced cytotoxic T lymphocyte activity markedly and significantly greater than peptide-pulsed DCs.

Vector-based delivery of tumor-associated antigens and T-cell co-stimulatory molecules in the induction of immune responses and anti-tumor immunity

It has now been demonstrated in both experimental models and recent clinical trials that certain "self" antigens, which are functionally non-immunogenic in the host, can become immunogenic if presented to the immune system in a certain way. Here, we describe recombinant vaccines and vaccine strategies that have been developed to induce and potentiate T-cell responses of the host to such self-antigens. These strategies include: (a) the use of recombinant poxvirus vectors in which the tumor-associated antigen (TAA) is inserted as a transgene. Recombinant vaccinia vaccines and recombinant avipox (replication-defective) vaccines have been employed to break tolerance to a self-antigen; (b) the use of diversified prime and boost strategies using different vaccines; and (c) the insertion of multiple T-cell co-stimulatory molecules into recombinant poxvirus vectors, along with the TAA gene, to enhance T-cell immune responses to the TAA and induce anti-tumor immunity.

Phase I study of a vaccine using recombinant vaccinia virus expressing PSA (rV-PSA) in patients with metastatic androgen-independent prostate cancer

BACKGROUND

A Phase I trial of recombinant vaccinia prostate specific antigen (rV-PSA) in patients with advanced metastatic prostate cancer was conducted. This report describes 42 patients who were treated with up to three monthly vaccinations.

METHODS

All patients were entered on a dose-escalation phase I study of recombinant vaccinia containing the gene for PSA (rV-PSA). The primary objective of this study was to determine the safety of this vaccine in metastatic androgen-independent prostate cancer patients. A secondary objective was to assess evidence of anti-tumor activity by PSA measurements, radiologic findings, and immunologic methods.

RESULTS

There was no significant treatment-related toxicity apart from erythema, tenderness, and vesicle formation that lasted several days at the site of injection in some patients. There were immunologic responses, in selected patients, as evidenced by an increase in the proportion of PSA-specific T cells after vaccination. Furthermore, we show that these patients' T cells can lyse PSA-expressing tumor cells in vitro.

CONCLUSION

Given the low toxicity profile and the evidence of immunologic activity, we believe future study is warranted with PSA-based vaccines in prostate cancer. New PSA-based vaccines and vaccine strategies are currently being evaluated.

Expression of immunomodulating molecules by recombinant viruses: can the immunogenicity of live virus vaccines be improved?

Several obstacles exist for the development and use of live attenuated vaccines, including difficulty in achieving a proper balance between attenuation of viral replication and immunogenicity; inducing a strong T-helper 1 response in early life when the immune system is T helper 2 biased and immunization is sometimes associated with immunopathology and the immunosuppressive effect of maternal antibodies in infants. For some viral infections, the immune response to natural infection does not confer solid protection, complicating the task of vaccine development. The development of methods for generation of recombinant viruses provided new opportunities for improving the immunogenicity of live virus vaccine candidates, including the construction of viruses that express cytokines or other immunomodulating molecules. Depending on the choice of immunomodulating molecule, various stages of the immune response can be affected, such as antigen presentation or T-cell proliferation and differentiation. In addition to using the approach for development of viral live attenuated vaccines, it is currently being explored for the development of antitumor vaccines. For this type of vaccine, expression of tumor antigens and one or more immunomodulating molecules by one or several recombinant viruses has been proposed.

Towards the rational design of Th1 adjuvants

Finding adjuvants in order to enhance immune responses against target immunogens has been a major and recurrent issue for the vaccine industry. It is yet to be solved, most particularly in the context of a growing interest in designing new types of vaccines capable of eliciting Th1 immune responses. A review of synthetic adjuvants which have been (or are being) tested in clinical studies is presented. Importantly, recent advances in our understanding of the physiology of immune responses offer new avenues to design and test candidate adjuvants, based on either synthetic or natural molecules, with the aim to mimic and recapitulate pro-inflammatory signals initiating both innate and adaptative immune effector mechanisms. Thus, adjuvants of the future might be a mixture of molecules selected singularly for a capacity to attract, target or activate professional antigen presenting cells. Used as a combination, such molecules should facilitate antigen presentation by professional APCs and lead to a potent induction of T cell-mediated effector and immune memory mechanisms.

Induction of virus-specific cytotoxic T lymphocytes by in vivo electric administration of peptides

Generally, major histocompatibility complex (MHC) class I presentation of peptide antigens only occur for proteins' which are actively synthesized and processed intracellularly, so that immunization with a cytotoxic T lymphocyte (CTL) target peptide does not usually elicit effective CTL responses. In the present study, we explored the use of epitope peptides by in vivo electroporation to introduce directly into the cytoplasm for the vaccine elicitation of virus-specific CTLs in a mouse system. BALB/c mice were immunized with human immunodeficiency virus (HIV) env (P18, residues 311-320) or hepatitis C virus (HCV) NS5 (P17, residues 2423-2434) with or without electric pulses. Effector cells against peptide-labeled target cells were elicited in mice immunized with peptides with electric administration but not without electric administration. Moreover, cytolytic activities of CTL against peptide-labeled target cells were enhanced by the addition of plasmid having the immunostimulatory sequence (ISS) or cDNA of the B7-1 molecule in electric administration of peptides. The results of the present study suggest that a peptide vaccine against a virus using electric administration is effective in eliciting virus specific CTLs.

Recombinant viruses as a tool for therapeutic vaccination against human cancers

Viral vectors can be used to express a variety of genes in vivo, that encode tumor associated antigens, cytokines, or accessory molecules. For vaccination purposes, the ideal viral vector should be safe and enable efficient presentation of expressed antigens to the immune system. It should also exhibit low intrinsic immunogenicity to allow for its re-administration in order to boost relevant specific immune responses. Furthermore, the vector system must meet criteria that enable its industrialization. The characteristics of the most promising viral vectors, including retroviruses, poxviruses, adenoviruses, adeno-associated viruses, herpes simplex viruses, and alphaviruses, will be reviewed in this communication. Such recombinant viruses have been successfully used in animal models as therapeutic cancer vaccines. Based on these encouraging results, a series of clinical studies, reviewed herein, have been undertaken. Human clinical trials, have as of today, allowed investigators to establish that recombinant viruses can be safely used in cancer patients, and that such recombinants can break immune tolerance against tumor-associated antigens. These promising results are now leading to improved immunization protocols associating recombinant viruses with alternate antigen-presentation platforms (prime-boost regimens), in order to elicit broad tumor-specific immune responses (humoral and cellular) against multiple target antigens.

Enhanced activation of T cells by dendritic cells engineered to hyperexpress a triad of costimulatory molecules

BACKGROUND

Activation and proliferation of T cells are essential for a successful cellular immune response to an antigen. Antigen-presenting cells (APCs) activate T cells through a two-signal mechanism. The first signal is antigen specific and causes T cells to enter the cell cycle. The second signal involves a costimulatory molecule that interacts with a ligand on the T-cell surface and leads to T-cell cytokine production and their proliferation. Dendritic cells express several costimulatory molecules and are believed to be the most potent APCs. Two recombinant poxvirus vectors (replication-defective avipox [fowlpox; rF] and a replication-competent vaccinia [rV]) have been engineered to express a triad of costimulatory molecules (B7-1, intercellular adhesion molecule-1, and leukocyte function-associated antigen-3; designated TRICOM). This study was designed to determine if dendritic cells infected with these vectors would have an enhanced capacity to stimulate T-cell responses.

METHODS

Murine dendritic cells (of both intermediate maturity and full maturity) were infected with rF-TRICOM or rV-TRICOM and were used in vitro to stimulate naive T cells with the use of a pharmacologic agent as signal 1, to stimulate T cells in allospecific mixed lymphocyte cultures, and to stimulate CD8(+) T cells specific for a peptide from the ovalbumin (OVA) protein. In addition, dendritic cells infected with TRICOM vectors were pulsed with OVA peptide and used to vaccinate mice to examine T-cell responses in vivo. All statistical tests were two-sided.

RESULTS

Dendritic cells infected with either rF-TRICOM or rV-TRICOM were found to greatly enhance naive T-cell activation (P<.001), allogeneic responses of T cells (P<.001), and peptide-specific T-cell stimulation in vitro (P<.001). Peptide-pulsed dendritic cells infected with rF-TRICOM or rV-TRICOM induced cytotoxic T-lymphocyte activity in vivo to a markedly greater extent than peptide-pulsed dendritic cells (P =.001 in both).

CONCLUSIONS

The ability of dendritic cells to activate both naive and effector T cells in vitro and in vivo can be enhanced with the use of poxvirus vectors that potentiate the hyperexpression of a triad of costimulatory molecules. Use of either rF-TRICOM or rV-TRICOM vectors significantly improved the efficacy of dendritic cells in priming specific immune responses. These studies have implications in vaccine strategies for both cancer and infectious diseases.

Vaccination with a recombinant vaccinia vaccine containing the B7-1 co-stimulatory molecule causes no significant toxicity and enhances T cell-mediated cytotoxicity

B7-1 is a co-stimulatory molecule that provides a second signal for T-cell activation. Several studies have demonstrated that vaccination with a vector containing genes encoding B7-1 and an antigen appears to be efficacious at promoting immune responsiveness to the antigen. To evaluate the safety of such a protocol and determine the effect of the B7-1 vector on immune responsiveness, female C57BL/6 mice were administered Wyeth wild-type vaccinia virus (V-WT) or V-WT containing the gene for B7-1 (rV-B7-1) as a single s. c. injection or 3 monthly s.c. injections. Immunologic parameters were evaluated in half of the mice and general toxicity in the other half. Immunologic end points included determination of splenic lymphocyte phenotypes, mitogen-induced T- and B-cell proliferation, T-cell proliferation in response to alloantigens, cell-mediated cytotoxicity (CMC), natural killer cell activity and serum anti-nuclear antibody (ANA) titers. No significant signs of general toxicity were noted. The primary immunologic effect was an increase in the ability of spleen cells to lyse allogeneic targets and to proliferate in response to allogeneic stimulation. Numbers of splenic CD8(+) cells were also increased. These effects were more pronounced after 3 vaccinations than after a single vaccination. Minimal differences in ANA were observed between mice immunized with V-WT and rV-B7-1. In addition, no serum antibodies against B7-1 were detected in any mice. The data suggest that vaccination with rV-B7-1 augments CMC with minimal toxicity.

The diversity of T-cell co-stimulation in the induction of antitumor immunity

T-cell activation has now been shown to require at least two signals. The first signal is antigen-specific, is delivered through the T-cell receptor (TCR) via the peptide/major histocompatibility complex (MHC), and causes the T cell to enter the cell cycle. The second, or co-stimulatory, signal is required for cytokine production and proliferation, and is mediated through ligand interaction on the surface of the T cell. This chapter deals with: 1) comparative studies on the use of a dual-gene construct of a recombinant vaccinia (rV) vector containing a tumor-associated antigen (TAA) gene and a co-stimulatory molecule gene vs the use of admixtures of rV-TAA and rV containing the co-stimulatory molecule to induce anti-tumor immunity; 2) the use of an admixture of vaccinia viruses containing a TAA gene and the B7-1 co-stimulatory molecule gene to induce a therapeutic response in a lung metastasis tumor model; 3) the antitumor efficacy of whole-tumor-cell vaccines in which the B7-1 co-stimulatory molecule is expressed in a tumor-cell vaccine via a vaccinia vs a retroviral vector; 4) the use of recombinant poxviruses containing the genes for the co-stimulatory molecules ICAM-1 or LFA-3 to induce antitumor immunity; and 5) the use of poxvirus vectors containing a triad of co-stimulatory molecules (B7-1, ICAM-1 and LFA-3) that synergize to enhance both CD4+ and CD8+ T-cell responses to a new threshold.

Anti-tumor immunity elicited by a recombinant vaccinia virus expressing CD70 (CD27L)

CD70, a ligand of the T cell costimulatory receptor CD27, is expressed mainly on activated B cells and has been shown to increase cytotoxic activity and proliferation of preferentially unprimed T cells. Reported herein is the construction of a recombinant vaccinia virus encoding CD70 (designated rV-CD70) and a demonstration of its biological effect on naive T cells in vitro and in vivo. In a whole tumor cell vaccine model, the growth of CD70-negative murine colon adenocarcinoma (MC38) tumor cells infected with rV-CD70 (multiplicity of infection [MOI] of 0.1) and transplanted into syngeneic C57BL/6 mice was inhibited completely while control tumors infected with wild-type vaccinia grew rapidly and killed mice within 3-5 weeks. Tumor-free mice previously immunized with rV-CD70-infected tumors were partially protected against rechallenge with wild-type tumors, demonstrating the induction of systemic anti-tumor immunity. In addition, immunization of C57BL/6 mice with rV-CD70 admixed with vaccinia virus encoding carcinoembryonic antigen (rV-CEA) was superior to treatment with rV-CEA alone in inducing CEA-specific lymphoproliferative T cell responses and reducing growth of murine colon carcinomas transduced with CEA. These studies demonstrate for the first time the potential utility of a recombinant vaccinia virus expressing CD70 to enhance T cell responses and mediate anti-tumor immunity.