Effective tumor immunotherapy directed against an oncogene-encoded product using a vaccinia virus vector

Vaccines as treatments for prostate cancer

Prostate cancer is a leading cause of death in men worldwide. For over 30 years, growing interest has focused on the development of vaccines as treatments for prostate cancer, with the goal of using vaccines to activate immune cells capable of targeting prostate cancer to either eradicate recurrent disease or at least delay disease progression. This interest has been prompted by the prevalence and long natural history of the disease and by the fact that the prostate is an expendable organ. Thus, an immune response elicited by vaccination might not need to target the tumour uniquely but could theoretically target any prostate tissue. To date, different vaccine approaches and targets for prostate cancer have been evaluated in clinical trials. Overall, five approaches have been assessed in randomized phase III trials and sipuleucel-T was approved as a treatment for metastatic castration-resistant prostate cancer, being the only vaccine approved to date by the FDA as a treatment for cancer. Most vaccine approaches showed safety and some evidence of immunological activity but had poor clinical activity when used as monotherapies. However, increased activity has been observed when these vaccines were used in combination with other immune-modulating therapies. This evidence suggests that, in the future, prostate cancer vaccines might be used to activate and expand tumour-specific T cells as part of combination approaches with agents that target tumour-associated immune mechanisms of resistance.

Coronavirus Pseudotypes for All Circulating Human Coronaviruses for Quantification of Cross-Neutralizing Antibody Responses

The novel coronavirus SARS-CoV-2 is the seventh identified human coronavirus. Understanding the extent of pre-existing immunity induced by seropositivity to endemic seasonal coronaviruses and the impact of cross-reactivity on COVID-19 disease progression remains a key research question in immunity to SARS-CoV-2 and the immunopathology of COVID-2019 disease. This paper describes a panel of lentiviral pseudotypes bearing the spike (S) proteins for each of the seven human coronaviruses (HCoVs), generated under similar conditions optimized for high titre production allowing a high-throughput investigation of antibody neutralization breadth. Optimal production conditions and most readily available permissive target cell lines were determined for spike-mediated entry by each HCoV pseudotype: SARS-CoV-1, SARS-CoV-2 and HCoV-NL63 best transduced HEK293T/17 cells transfected with ACE2 and TMPRSS2, HCoV-229E and MERS-CoV preferentially entered HUH7 cells, and CHO cells were most permissive for the seasonal betacoronavirus HCoV-HKU1. Entry of ACE2 using pseudotypes was enhanced by ACE2 and TMPRSS2 expression in target cells, whilst TMPRSS2 transfection rendered HEK293T/17 cells permissive for HCoV-HKU1 and HCoV-OC43 entry. Additionally, pseudotype viruses were produced bearing additional coronavirus surface proteins, including the SARS-CoV-2 Envelope (E) and Membrane (M) proteins and HCoV-OC43/HCoV-HKU1 Haemagglutinin-Esterase (HE) proteins. This panel of lentiviral pseudotypes provides a safe, rapidly quantifiable and high-throughput tool for serological comparison of pan-coronavirus neutralizing responses; this can be used to elucidate antibody dynamics against individual coronaviruses and the effects of antibody cross-reactivity on clinical outcome following natural infection or vaccination.

Cancer vaccines: translation from mice to human clinical trials

Therapeutic cancer vaccines have been a long-sought approach to harness the exquisite specificity of the immune system to treat cancer, but until recently have not had much success as single agents in clinical trials. However, new understanding of the immunoregulatory mechanisms exploited by cancers has allowed the development of approaches to potentiate the effect of vaccines by removing the brakes while the vaccines step on the accelerator. Thus, vaccines that had induced a strong T cell response but no clinical therapeutic effect may now reach their full potential. Here, we review a number of promising approaches to cancer vaccines developed initially in mouse models and their translation into clinical trials, along with combinations of vaccines with other therapies that might allow cancer vaccines to finally achieve clinical efficacy against many types of cancer.

High-Throughput, Protein-Targeted Biomolecular Detection Using Frequency-Domain Faraday Rotation Spectroscopy

A clinically relevant magneto-optical technique (fd-FRS, frequency-domain Faraday rotation spectroscopy) for characterizing proteins using antibody-functionalized magnetic nanoparticles (MNPs) is demonstrated. This technique distinguishes between the Faraday rotation of the solvent, iron oxide core, and functionalization layers of polyethylene glycol polymers (spacer) and model antibody-antigen complexes (anti-BSA/BSA, bovine serum albumin). A detection sensitivity of ≈10 pg mL^-1 and broad detection range of 10 pg mL^-1 ≲ c_BSA ≲ 100 µg mL^-1 are observed. Combining this technique with predictive analyte binding models quantifies (within an order of magnitude) the number of active binding sites on functionalized MNPs. Comparative enzyme-linked immunosorbent assay (ELISA) studies are conducted, reproducing the manufacturer advertised BSA ELISA detection limits from 1 ng mL^-1 ≲ c_BSA ≲ 500 ng mL^-1 . In addition to the increased sensitivity, broader detection range, and similar specificity, fd-FRS can be conducted in less than ≈30 min, compared to ≈4 h with ELISA. Thus, fd-FRS is shown to be a sensitive optical technique with potential to become an efficient diagnostic in the chemical and biomolecular sciences.

Randomized phase II trial of docetaxel with or without PSA-TRICOM vaccine in patients with castrate-resistant metastatic prostate cancer: A trial of the ECOG-ACRIN cancer research group (E1809)

Anti-tumor vaccines have demonstrated efficacy in patients with castration-resistant metastatic prostate cancer. One vaccine, Prostvac-VF®, using a heterologous prime-boost strategy with vaccinia and fowlpox viral vectors encoding PSA, is currently being evaluated in a registration phase III multinational clinical trial. The current trial was planned to assess the clinical efficacy of this vaccine in patients with castration-resistant metastatic prostate cancer receiving subsequent docetaxel chemotherapy. 10 patients with metastatic castration-resistant prostate cancer, with a predicted survival of at least 18 months, were enrolled out of a planned 144 patients. Eight of 10 patients were treated and were randomized to receive docetaxel chemotherapy alone (Arm B, n = 2) versus treatment with Prostvac-VF (days 1, 15, 29, 43, 57) followed by docetaxel (Arm A, n = 6) chemotherapy beginning at month 3. The primary endpoint of the trial was overall survival, and secondary endpoints included time to radiographic progression and immunological response. The trial was opened within the Eastern Cooperative Oncology Group, but due to slow accrual was closed by CTEP after only 10 patients were enrolled within 13 months.

RESULTS

Presented here are the safety, clinical, and immunological results from 8 eligible patients who underwent treatment. Two of 6 patients treated on Arm A, with vaccine followed by docetaxel, had a >50% PSA response, with one of these patients experiencing a PSA decline during treatment with vaccine. Significant PSA-specific CD4+ and CD8+ T-cell responses and IgG antibody responses specific for PSA were not detected. The primary endpoint of overall survival cannot be assessed due to limited accrual. The lack of T-cell responses, even in this small cohort, suggests that further validation and development of immune biomarkers will be important for future studies. Other trials remain ongoing to evaluate the role of anti-tumor vaccination in sequence with other traditional anti-tumor therapies.

Viral vectors for vaccine applications

Traditional approach of inactivated or live-attenuated vaccine immunization has resulted in impressive success in the reduction and control of infectious disease outbreaks. However, many pathogens remain less amenable to deal with the traditional vaccine strategies, and more appropriate vaccine strategy is in need. Recent discoveries that led to increased understanding of viral molecular biology and genetics has rendered the used of viruses as vaccine platforms and as potential anti-cancer agents. Due to their ability to effectively induce both humoral and cell-mediated immune responses, viral vectors are deemed as an attractive alternative to the traditional platforms to deliver vaccine antigens as well as to specifically target and kill tumor cells. With potential targets ranging from cancers to a vast number of infectious diseases, the benefits resulting from successful application of viral vectors to prevent and treat human diseases can be immense.

Inhibitors of C5 complement enhance vaccinia virus oncolysis

Genetically engineered tumor-selective vaccinia virus (VV) has been demonstrated to be a highly effective oncolytic agent, but immune clearance may limit its therapeutic potential. As previously demonstrated, immunosuppression can lead to significant enhancement of viral recovery and therapeutic effect, but the magnitude of complement-mediated viral inactivation has not been fully elucidated and warrants further investigation. Using fluorescent microscopy and quantitative plaque assays, we have determined complement's key role in viral clearance and its multi-faceted means to pathogen destruction. Complement can lead to direct viral destruction and inhibition of viral uptake into cells, even in the absence of anti-vaccinia antibodies. Our data demonstrate C5 to be integral to the clearance pathway, and its inhibition by Staphylococcal superantigen-like protein leads to a 90-fold and 150-fold enhancement of VV infectivity in both the presence and absence of anti-VV antibodies, respectively. This study suggests that complement inhibition may reduce vaccinia viral neutralization and may be critical to future in vivo work.

Poxviral vectors for cancer immunotherapy

INTRODUCTION

Poxviral vaccines have been given to over 1 billion people in the successful global eradication of smallpox. Recombinant poxviruses have been investigated extensively as a novel immunotherapy for cancer, undergoing several iterations to optimize their immunogenicity and efficacy. The current platform expressing multiple costimulatory molecules plus a tumor-associated antigen such as PSA, that is, PSA-TRICOM (PROSTVAC-V/F), is promising and is currently in a Phase III randomized, placebo-controlled clinical trial in metastatic castration-resistant prostate cancer.

AREAS COVERED

This review discusses the clinical development of poxviral-based cancer vaccines, with a particular focus on the rationale for combining vaccines with other treatment modalities, including radiotherapy, chemotherapy, hormonal therapy, other immune-based therapies and molecularly targeted therapy. We also discuss the importance of appropriate patient selection in clinical trial design.

EXPERT OPINION

Preclinical and early clinical studies employing poxviral-vector vaccines have shown promising results with this novel immunologic approach, both alone and combined with other therapies. The challenges of translating the science of immunotherapy to clinical practice include clinical trial design that includes appropriate patient selection, appropriate end points and identification of meaningful surrogate biomarkers.

Targeting dendritic cells with nano-particulate PLGA cancer vaccine formulations

Development of safe and effective cancer vaccine formulation is a primary focus in the field of cancer immunotherapy. The recognition of the crucial role of dendritic cells (DCs) in initiating anti-tumor immunity has led to the development of several strategies that target vaccine antigens to DCs as an attempt for developing potent, specific and lasting anti-tumor T cell responses. The main objective of this review is to provide an overview on the application of poly (d,l-lactic-co-glycolic acid) nanoparticles (PLGA-NPs) as cancer vaccine delivery system and highlight their potential in the development of future therapeutic cancer vaccines. PLGA-NPs containing antigens along with immunostimulatory molecules (adjuvants) can not only target antigen actively to DCs, but also provide immune activation and rescue impaired DCs from tumor-induced immuosupression.

PSA-based vaccines for the treatment of prostate cancer

Prostate cancer is the second leading cause of cancer-related death among men in the USA. Vaccine strategies represent a novel therapeutic approach. One potential target for a prostate cancer vaccine is prostate-specific antigen, owing to its restricted expression in prostate cancer and normal prostatic epithelial cells. A number of prostate-specific antigen-specific epitopes have been identified that can activate cytotoxic T lymphocytes and, in turn, result in the killing of tumor targets by the peptide-specific cytotoxic T lymphocytes. Strategies employed in clinical trials consist of dendritic cell vaccines, recombinant protein and recombinant DNA vaccines, as well as viral vector delivery of vaccines. New approaches incorporating a combination of a vaccine with traditional treatments for prostate cancer are also being investigated.

Immunotherapy for Prostate Cancer: What's the Future?

Prostate cancer is the most common noncutaneous cancer and second leading cause of cancer death among US men. A greater understanding of basic immunologic principles has led to a variety of new techniques,which has led to advancements in prostate cancer vaccines. This article discusses the rationale for the development of antibody-based therapy and vaccines therapy, including whole tumor cells, dendritic cells, and pox viral vectors. A summary of selected clinical studies incorporating these strategies and new approaches incorporating a combination of immunotherapy with traditional treatments for prostate cancer is presented.

Effect of Dose on Immune Response in Patients Vaccinated With an HER-2/neu Intracellular Domain Protein—Based Vaccine

Purpose

To evaluate the safety of an HER-2/neu intracellular domain (ICD) protein vaccine and to estimate whether vaccine dose impacts immunogenicity.

Patients and Methods

Twenty-nine patients with HER-2/neu—overexpressing breast or ovarian cancer and with no evidence of disease after standard therapy received a low- (25 μg), intermediate- (150 μg), or high-dose (900 μg) HER-2/neu ICD protein vaccine. The vaccine was administered intradermally, monthly for 6 months, with granulocyte-macrophage colony-stimulating factor as an adjuvant. Toxicity and both cellular and humoral HER-2/neu—specific immunity was evaluated.

Results

The vaccine was well tolerated. The majority of patients (89%) developed HER-2/neu ICD-specific T-cell immunity. The dose of vaccine did not predict the magnitude of the T-cell response. The majority of patients (82%) also developed HER-2/neu—specific immunoglobulin G antibody immunity. Vaccine dose did not predict magnitude or avidity of the HER-2/neu—specific humoral immune response. Time to development of detectable HER-2/neu—specific immunity, however, was significantly earlier for the high- versus low-dose vaccine group (P = .003). Over half the patients retained HER-2/neu—specific T-cell immunity 9 to 12 months after immunizations had ended.

Conclusion

The HER-2/neu ICD protein vaccine was well tolerated and effective in eliciting HER-2/neu—specific T-cell and antibody immunity in the majority of breast and ovarian cancer patients who completed the vaccine regimen. Although the dose of vaccine did not impact the magnitude of T-cell or antibody immunity elicited, patients receiving the highest dose developed HER-2/neu—specific immunity more rapidly than those who received the lowest dose.

Vaccine Therapy for a Patient with Androgen-Insensitive Prostate Cancer without Evidence of Measurable Disease on Scans

Androgen ablation therapy is the mainstay treatment of patients who have failed local therapy for prostate cancer. PSA is a serum marker commonly used to monitor patients who have undergone primary therapy for evidence of disease progression. However, there currently is no standard therapy for patients once they have demonstrated disease progression. We report a case of a 65-year-old man with castrate testosterone levels but a rising serum PSA level without radiographic evidence of metastasis. After failing prior antiandrogen therapy, he enrolled on a clinical trial comparing a PSA-based vaccine with nilutamide. When his PSA level rose on nilutamide, he commenced treatment with the vaccine therapy. He has continued to have a PSA response with the vaccine treatments with no radiographic evidence disease for >20 months.

HER-2 in breast cancer--methods of detection, clinical significance and future prospects for treatment

The Human Epidermal Growth Factor (HER-2) oncogene encodes a transmembrane tyrosine kinase receptor with extensive homology to the Epidermal Growth Factor Receptor (EGFR) which is the prototypal member of this family of receptor tyrosine kinases. HER-2 gene amplification is found in 20-30% of breast cancers. Various methods such as immunohistochemistry, southern and slot blotting, enzyme immunoassays and fluorescence in situ hybridization have all been employed to evaluate HER-2 gene and protein abnormalities. Of these immunohistochemistry is the most frequently employed but there are valid indications for the other avaliable methods. However, it is prudent that whichever methods employed are standardized, especially those that possess may have a degree of subjectivity in their assesment.

A chimeric multi-human epidermal growth factor receptor-2 B cell epitope peptide vaccine mediates superior antitumor responses

Immunotherapeutic approaches to cancer should focus on novel undertakings that modulate immune responses by synergistic enhancement of antitumor immunological parameters. Cancer vaccines should preferably be composed of multiple defined tumor Ag-specific B and T cell epitopes. To develop a multiepitope vaccine, 12 high ranking B cell epitopes were identified from the extracellular domain of the human epidermal growth factor receptor-2 (HER-2) oncoprotein by computer-aided analysis. Four novel HER-2 B cell epitopes were synthesized as chimeras with a promiscuous T cell epitope (aa 288-302) from the measles virus fusion protein (MVF). Two chimeric peptide vaccines, MVF HER-2(316-339) and MVF HER-2(485-503) induced high levels of Abs in outbred rabbits, which inhibited tumor cell growth. In addition, Abs induced by a combination of two vaccines, MVF HER-2(316-339) and MVF HER-2(628-647) down-modulated receptor expression and activated IFN-gamma release better than the individual vaccines. Furthermore, this multiepitope vaccine in combination with IL-12 caused a significant reduction (p = 0.004) in the number of pulmonary metastases induced by challenge with syngeneic tumor cells overexpressing HER-2. Peptide Abs targeting specific sites in the extracellular domain may be used for exploring the oncoprotein's functions. The multiepitope vaccine may have potential application in the treatment of HER-2-associated cancers.

Synthetic peptides as cancer vaccines

Effective cancer therapy or prevention has been the dream of physicians and scientists for many years. Although we are still very far from our ultimate goal of cancer prevention, significant milestones have been realized in terms of our knowledge base and understanding of the pathogenesis of cancerous cells and the involvement of the immune system against both self- and virus-associated tumor antigens. Immunotherapeutic strategies are now accepted to being superior in terms of the exquisite specificity that they offer in targeting only tumor cells as opposed to the existent chemotherapy or radiation therapy that is more general and invasive with many associated side effects. There are several immunotherapeutic strategies that are currently under investigation. This review primarily focuses on the significant advances made in the use of synthetic peptides in the development of subunit cancer vaccines. We have attempted to highlight some of the fundamental issues regarding antigen processing and presentation, Major Histocompatibility Complex (MHC) restriction, T-cell help, structural determinants in antibody recognition, and the use of these concepts in the rational design and delivery of peptide vaccines to elicit protective humoral and cell mediated immune responses. The recent use of costimulatory molecules and cytokines to augment immune responses also has been discussed along with the contributions of our laboratory to the field of synthetic peptide vaccine development.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.

Intratumoral administration of an adenovirus expressing a kinase dead form of ErbB-2 inhibits tumor growth

ErbB-2 is amplified or overexpressed in a number of different cancers including breast, ovarian, lung, prostate and stomach. This overexpression leads to enhanced receptor dimer formation and stabilization allowing the receptor to remain in an active state. The clinical consequences of ErbB-2 overexpression include increased tumor aggressiveness, poor prognosis, decreased patient survival and resistance to chemotherapy. As a result, a variety of different strategies are being examined to inhibit its function or expression. In this study, we explored the efficacy of a type 5 recombinant adenovirus encoding a kinase dead form of ErbB-2, AderbB-2 Delta tk, as a potential therapeutic agent for breast cancer using a murine breast model expressing constitutively active ErbB-2. Co-expression in tumor cells of the kinase dead form of ErbB-2 inhibits receptor activity and induces the death of cells expressing constitutively active ErbB-2. In addition, AderbB-2 Delta tk exhibits antitumor activity in both immune-competent and immune-deficient animals with increased antitumor activity in the immune-competent animals. The results suggest both immune and non-immune mechanisms contribute to the antitumor efficacy of this vector.

Efficacy of vaccination with plasmid DNA encoding for HER2/neu or HER2/neu-eGFP fusion protein against prostate cancer in rats

Despite early diagnosis and improved therapy, 31,500 men will die from prostate cancer (PC) this year. The HER2/neu oncoprotein is an important effector of cell growth found in the majority of high-grade prostatic tumors and is capable of rendering immunogenicity. The antigenicity of this oncoprotein might prove useful in the development of PC vaccines. Our goal is to prove the principle that a single DNA vaccine can provide reliable immunity against PC in the MatLyLu (MLL) translational tumor model. The parental rat MatLyLu PC cell line expresses low to moderate levels of the rat neu protein. To simulate in vivo human PC, MatLyLu cells were transfected with a truncated sequence of human HER2/neu cDNA cloned into the pCI-neo vector. This HER2/neu cDNA sequence encodes the first 433 amino acids of the extracellular domain (ECD). MatLyLu cells were also transfected with the same HER2/neu cDNA sequence cloned into the N1-terminal sequence of EGFP reporter gene to produce a fusion protein. The partial ECD sequence of HER2/neu includes five rat major histocompatibility (MHC)-II-restricted peptides with complete human-to-rat cross-species homology. The HER2/neu protein overexpression was documented by Western Blot analysis, and the expression of fusion protein was monitored by confocal microscopy and fluorimetry. Vaccination with a single injection of HER2/neu cDNA protected 50% of animals against HER2/neu-MatLyLu tumors (P < 0.01). When the tumor cells were engineered to express HER2/neu-EGFP fusion protein, the antitumor immunity was enhanced, as following vaccination with HER2/neu-EGFP cDNA, 80% of these rats rejected HER2/neu-EGFP-MatLyLu (P<0.001). Both vaccines induced HER2/neu-specific antibody titers. Rats vaccinated with EGFP-cDNA rejected 80% of EGFP-MatLyLu tumors and, interestingly, 40% of HER2/neu-MatLyLu tumors. None of the cDNA vaccines induced immunity against parental MatLyLu cells. Our data clearly demonstrate that a single injection of HER2/neu-EGFP cDNA is a very effective vaccine against PC tumors expressing the cognate tumor-associated antigen (TA). The antitumor immunity is significantly more pronounced if the tumors express xenogeneic HER2/neu-EGFP fusion protein as opposed to only the syngeneic HER2/neu oncoprotein. Our data suggests that the HER2/neu-EGFP-MatLyLu tumor is a potential animal tumor model for investigating therapeutic vaccine strategies against PC in vivo and demonstrates the limitations of a cDNA vaccine only encoding for MHC-II-restricted HER2/neu-ECD sequence peptides.

Inhibition of tumor growth by recombinant vaccinia virus expressing GA733/CO17-1A/EpCAM/KSA/KS1-4 antigen in mice

The human colorectal carcinoma (CRC)-associated GA733 antigen (Ag), also named CO17-1A/EpCAM/KSA/KS1-4, has been a useful target in passive immunotherapy of CRC patients with monoclonal antibody (mAb) and in active immunotherapy with anti-idiotypic antibodies or with recombinant protein. These approaches have targeted single epitopes (monoclonal anti-GA733 antibodies and anti-idiotypic antibodies) or extracellular domain epitopes (recombinant protein), primarily by B cells. To determine whether a reagent that induces immunity to a larger number of both B- and T-cell epitopes might represent a superior vaccine, we analyzed the capacity of full-length GA733 Ag expressing multiple potentially immunogenic epitopes and encoded by recombinant vaccinia virus (VV GA733-2) to induce humoral, cellular, and/or protective immunity in mice. VV GA733-2 induced Ag-specific antibodies that reacted predominantly to unknown epitopes on the Ag and lysed Ag-positive CRC targets in conjunction with murine peritoneal macrophages as effector cells. Immunized mice developed Ag-specific, proliferative and delayed-type hypersensitive lymphocytes. VV GA733-2 inhibited growth of ras-transformed syngeneic tumor cells expressing the human GA733 Ag in mice. These results suggest the potential of VV GA733-2 as a candidate vaccine for patients with CRC, possibly in combination with recombinant GA733-2-expressing adenovirus, which has been shown to induce cytolytic antibodies and T cells as well as tumor protective effects in mice. The combined vaccine approach may be superior to the use of either vaccine alone in patients who are pre-immune to both viruses.

Down regulation of B cells by immunization with a fusion protein of a self CD20 peptide and a foreign IgG.Fc fragment

In vivo studies of mice were performed to investigate whether auto-reactive antibodies specific for self CD20 antigen on B cells could be induced by immunizing with a CD20 peptide linked to a foreign, human IgG.Fc fragment through a T cell immunologically inert linker peptide and how such an auto-reactivity, if generated, would affect the levels of B cells. The dimeric Fc fusion protein containing the extracellular 44-amino acid portion of CD20, and the CH2-CH3 domains of human gamma 1 immunoglobulin were prepared. After several subcutaneous immunizations with this CD20-Fc protein, mice produced anti-CD20 antibodies that can bind to native CD20 on normal B cells and B-lymphoma cells. In mice immunized with the CD20-Fc protein, the fraction of B cells in total peripheral blood lymphocytes decreased to about 40%, significantly lower than that of mice immunized with human IgG. In addition, antibody response towards an irrelevant bystander antigen, chicken ovalbumin, was weakened compared with that of mice immunized with human IgG. These results show that auto-reactive antibodies specific for CD20 can be induced by immunizing with an autologous CD20 peptide fused with a foreign IgG.Fc and that the auto-antibodies can partially reduce the levels of B cells and their response to other antigens.

Immunization against endogenous retroviral tumor-associated antigens

Endogenous retroviral gene products have been found in some human tumors, and therefore, may serve as antigens for immunotherapy approaches. The murine colorectal carcinoma CT26 and melanoma B16 have recently been found to express the endogenous retroviral gene products gp70 and p15E, respectively, that can serve as antigens recognized by T cells. To date, though, there has been no demonstration of tumor treatment using an endogenous retroviral protein. In this study, we demonstrate that mice immunized with recombinant vaccinia encoding the gp70 H2-L(d)-restricted minimal determinant were protected from CT26 tumor challenge. Splenocytes from mice immunized with vaccinia gp70 specifically secreted IFN-gamma in response to gp70 peptide-pulsed stimulators. Although this strategy could protect against subsequent tumor challenge, it was ineffective against established tumors. Therefore, to investigate the treatment of established CT26 or B16 lung metastases, mice were treated with cultured dendritic cells (DCs) pulsed with gp70 or p15E peptide. Significant inhibition of established lung metastases required immunization with peptide-pulsed DCs pretreated with CD40 ligand that has been demonstrated to increase the T-cell stimulatory activity of DCs. The ability to immunize against endogenous retroviral tumor antigens may have relevance in the induction of antitumor immunity for some human cancers.

Characterization of tumor vaccines during product development

The term tumor vaccines encompasses a wide variety of diverse agents capable of interacting with the immune system to produce local inflammation, delayed type hypersensitivity reaction and/or tumor regression and, hopefully, a therapeutic effect. These vaccines may be grouped into the following general areas: (1) Cell-based vaccines such as manipulated tumor cells, activated peripheral blood or bone marrow-derived lymphocytes, dendritic cells or other antigen presenting cells (APC) and gene-modified tumor cells or other cells engineered to express cytokines, growth factors or tumor antigens. (2) Antigen preparations, such as synthetic peptides, purified antigens and tumor cell lysates. (3) Viral and plasmid vectors expressing therapeutic genes. (4) Liposome containing antigen, peptides, plasmids encoding tumor antigens. While no tumor vaccine has been licensed by the FDA, numerous clinical trials are ongoing and some products have advanced to Phase III pivotal stages of development. However, as with many novel products, major regulatory and scientific issues associated with clinical use of tumor vaccines remain to be addressed. In this paper, we address issues associated with different types of tumor vaccines and provide recommendations for the characterization of these vaccines at various stages of development.

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.

Prospects for the therapeutic use of anticancer vaccines

Although a century has passed since initial attempts were made to stimulate the immune system to destroy tumour, the immunotherapy of cancer is still in the early stages. Historically, a variety of specific and nonspecific immunostimulatory strategies have been administered with only modest clinical success. However, recent advances in tumour immunology, most notably the identification of genes encoding for cancer regression antigens, have paved the way for the development of a variety of novel and specific vaccine approaches. These include vaccines based on tumour cells, carbohydrates, peptides and heat-shock proteins, DNA-based vaccination, and the use of recombinant bacteria and viruses to deliver antigens or the DNA coding for them. While several of these approaches have yielded exciting clinical results, a number of immunological and host obstacles to the successful application of cancer vaccines remain. Further research is needed on the optimum choice of antigen, delivery vector, adjuvant and administration regimen.

Human HER-2/neu protein immunization circumvents tolerance to rat neu: a vaccine strategy for 'self' tumour antigens

Many newly defined tumour antigens are 'self' proteins. Immunizing cancer patients against these antigens may be difficult due to tolerance. The HER-2/neu oncogenic protein is such a 'self' tumour antigen. Rat neu is homologous with human HER-2/neu and provides a model system for studying vaccination strategies. Rats are tolerant to rat neu. Vaccination with this 'self' protein elicits no detectable immune response. The current studies evaluated whether tolerance to rat neu can be circumvented by immunizing with the highly homologous foreign human HER-2/neu protein. Rats were immunized with human HER-2/neu intracellular domain (hICD) protein that is 92% homologous to rat neu ICD. Animals immunized with hICD developed significant antibody and T-cell responses that were specific for both human HER-2/neu and rat neu. Neu-specific antibodies were present in titres of greater than 1:200,000. Analysis of the specificity of the antibody response using synthetic peptides demonstrated substantial reactivity to an epitope with 100% homology between rat and human protein. Significant T-cell responses (stimulation index > 10) to hICD and rat neu protein (stimulation index > 4) were detected. The T cells also responded to both human and rat ICD. The results imply that immunization with foreign proteins, which are highly homologous to 'self' tumour antigens, may be an effective vaccine strategy for 'self' tumour antigens.

HER-2/neu protein: a target for antigen-specific immunotherapy of human cancer

The HER-2/neu oncogenic protein is a tumor antigen. Some patients with cancer have a preexistent immune response directed against the HER-2/neu protein. Effective cancer vaccines targeting HER-2/neu will be able to boost this immunity to potentially therapeutic levels. In addition, HER-2/neu-directed monoclonal antibody therapy has been effective in eradicating malignancy in animal models and has shown benefit in the treatment of human HER-2/neu-overexpressing cancers. This review outlines studies that define HER-2/neu-specific immunity in patients with cancer and overviews the current vaccine strategies for generating or augmenting neu-specific immunity. The potential problems associated with eliciting HER-2/neu-specific immunity are addressed, including the question of precipitating autoimmune toxicity against this "self" -protein and the mechanisms of immunological escape that may play a role in preventing effective function of the HER-2/neu-specific immune response. Finally, antibody-based HER-2/neu-directed therapies are overviewed. HER-2/neu is a prototype antigen for groups investigating innovative modifications of monoclonal antibody technology, and cutting edge therapies targeting this antigen are being contemplated for clinical use in the treatment of human malignancy. Immune-based treatments designed to target the HER-2/neu oncogenic protein will soon give the clinical oncologist new therapeutic weapons, directed against a biologically relevant tumor-related protein, with which to fight cancer.

Genetically engineered poxviruses for recombinant gene expression, vaccination, and safety

Vaccinia virus, no longer required for immunization against smallpox, now serves as a unique vector for expressing genes within the cytoplasm of mammalian cells. As a research tool, recombinant vaccinia viruses are used to synthesize and analyze the structure-function relationships of proteins, determine the targets of humoral and cell-mediated immunity, and investigate the types of immune response needed for protection against specific infectious diseases and cancer. The vaccine potential of recombinant vaccinia virus has been realized in the form of an effective oral wild-life rabies vaccine, although no product for humans has been licensed. A genetically altered vaccinia virus that is unable to replicate in mammalian cells and produces diminished cytopathic effects retains the capacity for high-level gene expression and immunogenicity while promising exceptional safety for laboratory workers and potential vaccine recipients.

Strategies for the development of recombinant vaccines for the immunotherapy of breast cancer

The development of recombinant vaccines for specific immunotherapy of carcinoma represents a novel approach for the treatment of breast cancer and other tumor types. This article reviews the various parameters that should be considered in the development of recombinant vaccines. Several breast cancer associated antigens are also discussed which may provide potential target molecules. The human carcinoembryonic antigen (CEA), which is expressed on approximately 50% of breast cancers, represents one such target for immunotherapy. To enhance the immunogenicity of this antigen, a recombinant CEA-vaccinia vaccine, designated rV-CEA, was produced. To study the effects of this vaccine in an animal model, a murine colon carcinoma cell line was transduced with CEA and transplanted into immunocompetent mice for protection and therapy studies. Pre-clinical toxicity studies were also conducted in non-human primates. The results of these studies showed the rV-CEA vaccine to be immunogenic and safe in both rodents and primates, and to elicit good anti-tumor responses in the rodent model. In a Phase I clinical trial in metastatic breast, lung, and colorectal cancer patients involving three immunizations of rV-CEA, at three dose levels, enhancement of T-cell and antibody responses to vaccinia virus proteins were observed with no toxicity. Specific T-cell responses were studied via stimulation of peripheral blood lymphocytes with specific peptide epitopes from the CEA molecule. These studies demonstrated clear cut differences in establishment of T-cell lines pre- versus post-immunization. The T-cell lines were shown to be CD8+ and/or CD4+/CD8+, to lyse EBV transformed B-cells transduced with the CEA gene, and to lyse CEA positive carcinoma cells in a HLA restricted manner. Thus, in a Phase I clinical trial the rV-CEA vaccine has been shown to stimulate a CTL response specific for CEA defined epitopes in cancer patients.

The next wave of recombinant and synthetic anticancer vaccines

The identification of tumor-associated antigens (TAA) recognized by T lymphocytes makes the development of antigen-specific synthetic and recombinant vaccines possible. The expression of TAA within a recombinant vector increases control over the kinetics and quantity, the molecular form, and the subcellular location of the immunogen delivered. The next generation of antitumor vaccines employs cytokines and costimulatory molecules expressed in concert with TAA that are capable of augmenting the activation and proliferation of antitumor immune responses. The ultimate goal of these new strategies, the treatment of established cancer, is now being realized in animal models.

Immunization by direct DNA inoculation induces rejection of tumor cell challenge

Direct DNA inoculation is the basis for a new technology that has been successfully used for in vivo induction of both humoral and cellular immune responses. However, the immunological parameters of this new approach remain to be evaluated in detail. We report here that direct DNA inoculation can induce protection from malignant tumor cell challenge through the generation of specific immune responses directed against antigens displayed on the tumor cells. The protected mice remain tumor-free for more than 1 year post-challenge. Memory responses upon tumor rechallenge were observed for both humoral and cellular immunity. Inoculated animals were able to reject otherwise lethal tumors several months following the original DNA inoculation protocol. These in vivo protective responses suggest that further analysis of this technology for vaccine development or immune therapeutic strategies is warranted.

In vivo delivery of interleukin-4 by a recombinant vaccinia virus prevents tumor development in mice

To study the immunotherapeutic potential of interleukin-4 (IL-4) delivered in vivo via a recombinant vaccinia virus, a thymidine kinase-negative (TK-) vaccinia virus that expressed the murine IL-4 gene (VV1/IL-4) was constructed. When mice were inoculated with 10(7) plaque-forming units (pfu) of VV1/IL-4 subcutaneously (s.c.), 10(5) pfu/cm2 were found in skin, and smaller numbers in liver and kidney between 1 and 7 days after infection; few viral pfu were found in spleen and lung, or in any organ after intravenous infection. This suggested that recombinant vaccinia viruses might be most efficient at delivery of cytokine genes to the skin. Because IL-4 has recently been found to have potent anti-tumor activity, the effect of recombinant virus infection on the development of s.c. tumors was studied. A single s.c. inoculation with VV1/IL-4 delayed the development of NCTC 2472 tumors, but when VV1/IL-4 was inoculated s.c. weekly for 8 weeks, tumor development was completely prevented in 93% of mice. Similarly, the development of M-3 melanoma tumors was also prevented by weekly s.c. inoculations of VV1/IL-4. About 40% of mice treated with control VV2/beta gal by the same regimen also failed to develop tumors. Weekly virus treatment did not prevent NCTC 2472 tumor development in athymic nu/nu mice, suggesting that mature T cells are required for expression of VV1/IL-4 induced antitumor activity. Thus, recombinant vaccinia viruses may be especially well suited for convenient therapeutic delivery of immunomodulator genes to skin-related sites.

Protective cellular immunity against a spontaneous mammary carcinoma from ras transgenic mice

Mammary carcinomas of v-Ha-ras transgenic mice closely resemble human breast cancer in their multi-step nature and in the requirement of genetic, hormonal and somatic mutational events for full-scale malignancy. We demonstrate that spontaneous breast cancers derived from v-Ha-ras transgenic FVB (H-2q) mice are highly immunogenic and that they elicit a protective T cell response. A continuous tumor cell line OM-2 has been established from a progressively growing mammary tumor and three sublines OM-10, OM-12 and OM-14 have been derived by in vivo passage of OM-2. All lines express the v-Ha-ras gene product and surface MHC class I. The parental OM-2 line is highly immunogenic and behaves like a regressor tumor. The regression of OM-2 is mediated by CD8+ T lymphocytes, although CD4+ lymphocytes also appear to play a limited role. Cytotoxic T lymphocytes (CTLs) obtained from mice immunized with OM-2 show MHC class I-restricted, specific T cell cytotoxicity against OM-2 but not normal fibroblasts derived from ras transgenic mice. The anti-OM-2 CTLs lyse the OM-2 sublines OM-12 and OM-14, although to a lesser degree than OM-2, and do not lyse OM-10, in spite of the fact that all cell lines express comparable levels of activated ras and MHC class I. Our studies represent the first analysis of protective T cell response to breast cancer and demonstrate that contrary to expectation, the spontaneous breast cancers are highly immunogenic and that the immune response does not appear to be directed to activated ras.

DNA inoculation as a novel vaccination method against human retroviruses with rheumatic disease associations

There are a number of rheumatologic manifestations of human retroviral infections associated with human immunodeficiency virus type I (HIV-I) and the human T-cell leukemia virus type I (HTLV-I) including arthritis, Sjøgren's syndrome-like symptoms as well as other varied autoimmune phenomena. Infection with HTLV-1 may be directly involved in the etiology and/or pathogenesis of an arthritic condition similar to rheumatoid arthritis. We have been characterizing a new vaccination strategy against human retroviral infections, designated DNA inoculation. This procedure involves the intramuscular injection of DNA plasmids which express specific human retroviral antigens. This technique results in the development of humoral and cellular immune responses against these proteins. Specifically, this method has been successfully used to develop immune responses against HIV-I and HTLV-I. The availability of rat and rabbit infection models for HTLV-I, coupled with the successful development of immune responses in these animals after DNA inoculation with an HTLV-I envelope expressing plasmid, will allow the efficacy of this vaccination technique to be evaluated with protection against in vivo viral challenge as an endpoint.

Genetic infection induces protective in vivo immune responses

Drug-induced abortive retroviral infection has been reported to induce both T-cell and B-cell immunity in vivo. We sought to analyze if replication-incompetent retroviruses could induce the development of similarly protective in vivo immune responses in a more desirable fashion. To evaluate retroviral transduction vaccination (genetic infection), a plasmid encoding human CD4 in a retroviral vector was transfected into the pA317 amphotropic retroviral packaging system. The resulting replication defective retrovirus was used to transduce BALB/c mice prior to tumor challenge with human CD4. Immunization elicited specific humoral and cellular anti-human CD4 responses. We evaluated anti-cell responses using a tumor model system. We observed that BALB/c mice challenged with SP2/0 lymphoma cells develop lethal tumors and die within 7 weeks of challenge. Cloned SP2/0 cells stably transfected with the human cell-surface antigen CD4 also develop tumors in naive mice and succumb to the tumors in a similar manner to SP2/0 inoculated animals. In contrast, CD4 retrovirus-transduced animals, when challenged with the CD4-expressing SP2/0 cells, demonstrated a low incidence of tumors and significantly enhanced survival compared to the mice immunized similarly with human CD8 retrovirus. These results establish an in vivo tumor challenge system with relevance to the development of protective in vivo immune responses, and indicate that genetic infection is a useful technique for inducing protective immunity.

Activated oncogenes and putative tumor suppressor genes involved in human breast cancers

Cytogeneticists first proposed that the karyotypic abnormalities identified on chromosomes 1, 3, 6, 11, 13, 16, 17, and 18 supported a genetic basis for breast cancer. Such abnormal banding patterns, however, may represent either loss-of-function or gain-of-function molecular events. RFLP analyses have since confirmed that 20-60% of primary and spontaneous human breast tumors exhibit allelic losses on these same chromosomes, although the exact genes involved at these chromosomal sites remain largely unknown. Knowledge gained about the Rb-1 and p53 tumor suppressor genes at 13q14 and 17p13 in breast and other human tumors supports the paradigm that for any chromosomal locus, allelic loss associated with a mutation in the remaining tumor allele signifies an involved tumor suppressor gene. Given this paradigm, there are nearly a dozen putative breast tumor suppressor genes under active investigation, with most investigators now focusing on various chromosome 17 loci. Among the known proto-oncogenes found activated in breast cancer, amplification of c-erbB-2 at 17q21 is the most widely studied and clinically significant gain-of-function event uncovered to date, occurring in about 20% of all primary breast tumors. The involvement of this overexpressed membrane receptor has engendered interest in related tyrosine kinase receptors, such as EGFR, IR, and IGF-I-R, as well as their respective ligands, which may be overexpressed in a greater fraction of tumors, contributing to the autocrine and paracrine regulation of breast cancer growth and metastasis. New attention is being given to the potentially oncogenic function of structurally altered nuclear transactivating steroid hormone receptors, such as ER, whose overexpression has long been used to determine endocrine therapy and prognosis for individual breast cancer patients. While c-myc was one of the first known proto-oncogenes to be found amplified and overexpressed in human breast cancers, the actual incidence and clinical significance of its activation remain disputed and in need of further study. Lastly, we can expect greater clarification about the importance of various 11q13 genes found coamplified in nearly 20% of primary breast cancers, and pursuit into the intriguing possibility that a cyclin-encoding gene represents the overexpressed locus of real interest in this amplicon. Virtually all of these important genetic abnormalities identified thus far are associated with but not restricted to human breast cancers. The absence of identifiable molecular defects relating to the tissue specificity of this malignancy must be considered a substantial gap in our basic understanding of breast carcinogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Update on tumor vaccines

Vaccination against tumor has always been an attractive idea for the treatment of patients bearing tumor. By harnessing the host's own immune response the attack on tumor cells would act on a continuing basis, with emerging tumor cells stimulating their own destruction. However, the approach has been hampered by our poor understanding of the nature of tumor antigens and of the pathways by which immune cells might operate against tumor growth. Recent developments in molecular biology and immunology are remedying this deficiency and bringing vaccination to the forefront of new approaches to treatment of a range of tumors. Results obtained in B-cell tumors, where the idiotypic immunoglobulin at the cell surface provides a well-defined tumor antigen, are already indicating exciting possibilities as well as delineating problems. There is considerable clinical evidence that patients have some intrinsic ability to control tumor growth and that certain tumors remain dormant for long periods. Attempts to understand and perhaps stimulate the mechanisms involved are being made through the use of biological modifiers and by manipulating potential effector cells in vitro. Ideally this approach, which may include non-specific and specific elements, could be combined with specific vaccination in order to combat the apparent ability of many tumor cells to evade host defences.