Peptide-based vaccines for cancer: realizing their potential

Copresentation of Tumor Antigens and Costimulatory Molecules via Biomimetic Nanoparticles for Effective Cancer Immunotherapy

Nanoparticle (NP)-based cancer immunotherapy has been extensively explored. However, the efficacy of existing strategies is often limited by the lack of effective tumor-specific antigens or the inability to present costimulatory signal or both. Here, we report a novel approach to overcoming these limitations through surface coating with dendritic-tumor fusion cell membranes, which present whole repertories of tumor-associated antigens in the presence of costimulatory molecules. Because antigen-presenting and costimulatory molecules are displayed on their surface, these NPs can efficiently penetrate immune organs and activate T cells. We show that these NPs can be utilized to prevent tumor development and regress established tumors, including tumors in the brain. We demonstrate that encapsulation of immune adjuvants further improves their efficacy. Due to their significant efficacy, the whole tumor antigen-presenting costimulatory NPs have the potential to be translated into clinical applications for treatment of various cancers.

Evaluation of the Immunogenicity of a Potyvirus-Like Particle as an Adjuvant of a Synthetic Peptide

Improvement of current vaccines is highly necessary to increase immunogenicity levels and protection against several pathogens. Virus-like particles (VLPs) are promising approaches for vaccines because they emulate infectious virus structure, but lack any genetic material needed for replication. Plant viruses have emerged as a potential framework for VLP design, mainly because there is no preexisting immunity in mammals. In this study, we evaluated the scaffold of the papaya ringspot virus (PRSV) as a VLP adjuvant for a short synthetic peptide derived from the Hemagglutinin protein of AH1 N1 influenza virus-hemagglutinin (VLP-HA). Our results demonstrated that the adjuvant property of this VLP is highly similar to the trivalent influenza vaccine, showing comparable levels of IgG- and IgA-specific antibodies to HA-derived peptide in serum and feces of vaccinated mice, respectively. Furthermore, VLP-HA-immunized mice showed Th1-biased immune response as suggested by measuring IgG subclasses in comparison with the predominance of Th2-biased immune response in trivalent influenza vaccine dose-vaccinated mice. VLP-HA administration in mice induced comparable levels of activated CD4⁺- and CD8⁺-specific T lymphocytes for the HA-derived peptide. These results suggest the potential adjuvant capacity of the PRSV-VLP as a carrier for short synthetic peptides.

Dendritic-Tumor Fusion Cell-Based Cancer Vaccines

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that play a critical role in the induction of antitumor immunity. Therefore, various strategies have been developed to deliver tumor-associated antigens (TAAs) to DCs as cancer vaccines. The fusion of DCs and whole tumor cells to generate DC-tumor fusion cells (DC-tumor FCs) is an alternative strategy to treat cancer patients. The cell fusion method allows DCs to be exposed to the broad array of TAAs originally expressed by whole tumor cells. DCs then process TAAs endogenously and present them through major histocompatibility complex (MHC) class I and II pathways in the context of costimulatory molecules, resulting in simultaneous activation of both CD4⁺ and CD8⁺ T cells. DC-tumor FCs require optimized enhanced immunogenicity of both DCs and whole tumor cells. In this context, an effective fusion strategy also needs to produce immunogenic DC-tumor FCs. We discuss the potential ability of DC-tumor FCs and the recent progress in improving clinical outcomes by DC-tumor FC-based cancer vaccines.

Advances in inducing adaptive immunity using cell-based cancer vaccines: Clinical applications in pancreatic cancer

The incidence of pancreatic ductal adenocarcinoma (PDA) is on the rise, and the prognosis is extremely poor because PDA is highly aggressive and notoriously difficult to treat. Although gemcitabine- or 5-fluorouracil-based chemotherapy is typically offered as a standard of care, most patients do not survive longer than 1 year. Therefore, the development of alternative therapeutic approaches for patients with PDA is imperative. As PDA cells express numerous tumor-associated antigens that are suitable vaccine targets, one promising treatment approach is cancer vaccines. During the last few decades, cell-based cancer vaccines have offered encouraging results in preclinical studies. Cell-based cancer vaccines are mainly generated by presenting whole tumor cells or dendritic cells to cells of the immune system. In particular, several clinical trials have explored cell-based cancer vaccines as a promising therapeutic approach for patients with PDA. Moreover, chemotherapy and cancer vaccines can synergize to result in increased efficacies in patients with PDA. In this review, we will discuss both the effect of cell-based cancer vaccines and advances in terms of future strategies of cancer vaccines for the treatment of PDA patients.

Pancreatic cancer: role of the immune system in cancer progression and vaccine-based immunotherapy

Pancreatic cancer (PC) is the 5th leading cause of cancer related death in the developed world with more than 260,000 deaths annually worldwide and with a dismal 5-year survival. Surgery is the only potential hope of cure for PC, but, unfortunately, only 20% PC patients is resectable at the time of diagnosis. Therapeutic research efforts have mainly focused on improvements in radio/ chemo treatments and to date, there are only a few chemotherapeutic agents that have shown to be effective against PC, including gemcitabine with or without abraxane as well as a combination of 5-FU, leucovorin, oxaliplatin and irinotecan (the so-called FOLFIRINOX regimen). The survival of patients treated with these regimens is marginal and hence we are in urgent need of novel therapeutic approaches to treat pancreatic cancer. The success of immunotherapeutic strategies in other cancers and various evidences that pancreatic adenocarcinoma elicits antitumor immune responses, suggest that immunotherapies can be a promising alternative treatment modality for this deadly disease. PC immunotherapy treatments include passive immunotherapeutic approaches, such as the use of effector cells generated in vitro, and active immunotherapeutic strategies, which goal is to stimulate an antitumor response in vivo, by means of vaccination. In this review, we describe the immune suppressive mechanisms of pancreatic cancer and discuss recent preclinical and clinical efforts toward PC immunotherapy, including passive approaches, such as the use of antibodies and active strategies (vaccination), with a special mention of most recent treatment with CRS-207 and GVAX.

Therapeutic vaccines and cancer: focus on DPX-0907

In an attempt to significantly enhance immunogenicity of peptide cancer vaccines, we developed a novel non-emulsion depot-forming vaccine platform called DepoVax™ (DPX). Human leukocyte antigen (HLA)-A2 restricted peptides naturally presented by cancer cells were used as antigens to create a therapeutic cancer vaccine, DPX-0907. In a phase I clinical study, the safety and immune-activating potential of DPX-0907 in advanced-stage breast, ovarian, and prostate cancer patients were examined, following encouraging results in HLA-A2 transgenic mice. The DPX-0907 vaccine was shown to be safe and well tolerated, with injection-site reactions being the most commonly reported adverse event. Vaccinated cancer patients exhibited a 61% immune response rate, with higher response rates in the breast and ovarian cancer patient cohorts. In keeping with the higher immune efficacy of this vaccine platform, antigen-specific responses were detected in 73% of immune responders after just one vaccination. In 83% of responders, peptide-specific T-cells were detected at two or more time points post-vaccination, with 64% of these patients showing evidence of immune persistence. Immune monitoring also demonstrated the generation of antigen-specific T-cell memory, with the ability to secrete multiple type 1 cytokines. The novel DPX formulation promotes multifunctional effector/memory responses to peptide-based tumor-associated antigens. The data support the capacity of DPX-0907 to elicit type-1 biased immune responses, warranting further clinical development of the vaccine. In this review, we discuss the rationale for developing DPX-based therapeutic cancer vaccine(s), with a focus on DPX-0907, aimed at inducing efficient anti-tumor immunity that may eventually be shown to prolong patient survival.

Classification of human leukocyte antigen (HLA) supertypes

Identification of new antigenic peptides, derived from infectious agents or cancer cells, which bind to human leukocyte antigen (HLA) class I and II molecules, is of importance for the development of new effective vaccines capable of activating the cellular arm of the immune response. However, the barrier to the development of peptide-based vaccines with maximum population coverage is that the restricting HLA genes are extremely polymorphic resulting in a vast diversity of peptide-binding HLA specificities and a low population coverage for any given peptide-HLA specificity. One way to reduce this complexity is to group thousands of different HLA molecules into several so-called HLA supertypes: a classification that refers to a group of HLA alleles with largely overlapping peptide binding specificities. In this chapter, we focus on the state-of-the-art classification of HLA supertypes including HLA-I supertypes and HLA-II supertypes and their application in development of peptide-based vaccines.

Orchestration of CD4 T cell epitope preferences after multipeptide immunization

A detailed understanding of the molecular and cellular mechanisms that underlie epitope preferences in T cell priming is important for vaccines designed to elicit a broad T cell response. Protein vaccinations generally elicit CD4 T cell responses that are skewed toward a small fraction of epitopes, a phenomenon known as immunodominance. This characteristic of T cell responses, which limits the diversity of CD4 T cell recognition, is generally attributed to intracellular Ag processing. However, we recently discovered that immunodominance hierarchies persist even after vaccination with synthetic peptides. In this study, we probed the regulatory mechanisms that cause diminished CD4 T cell responses to subdominant peptides after such multipeptide immunization in mice. We have found that the delivery of subdominant and dominant epitopes on separate dendritic cells rescues expansion of less favored CD4 T cells. Furthermore, through the use of genetic models and inhibitors, we have found that selective losses in CD4 T cell responses are mediated by an IFN-γ-induced pathway, involving IDO, and that regulatory T cell activities may also regulate preferences in CD4 T cell specificity. We propose that after multipeptide immunization, the expansion and differentiation of dominant T cells initiate complex regulatory events that determine the final peptide specificity of the elicited CD4 T cell response.

What is recent in pancreatic cancer immunotherapy?

Pancreatic cancer (PC) represents an unresolved therapeutic challenge, due to the poor prognosis and the reduced response to currently available treatments. Pancreatic cancer is the most lethal type of digestive cancers, with a median survival of 4-6 months. Only a small proportion of PC patients is curative by surgical resection, whilst standard chemotherapy for patients in advanced disease generates only modest effects with considerable toxic damages. Thus, new therapeutic approaches, specially specific treatments such as immunotherapy, are needed. In this paper we analyze recent preclinical and clinical efforts towards immunotherapy of pancreatic cancer, including passive and active immunotherapy approaches, designed to target pancreatic-cancer-associated antigens and to elicit an antitumor response in vivo.

SYT-SSX breakpoint peptide vaccines in patients with synovial sarcoma: a study from the Japanese Musculoskeletal Oncology Group

In the present study, we evaluated the safety and effectiveness of SYT-SSX-derived peptide vaccines in patients with advanced synovial sarcoma. A 9-mer peptide spanning the SYT-SSX fusion region (B peptide) and its HLA-A*2402 anchor substitute (K9I) were synthesized. In Protocols A1 and A2, vaccines with peptide alone were administered subcutaneously six times at 14-day intervals. The B peptide was used in Protocol A1, whereas the K9I peptide was used in Protocol A2. In Protocols B1 and B2, the peptide was mixed with incomplete Freund's adjuvant and then administered subcutaneously six times at 14-day intervals. In addition, interferon-α was injected subcutaneously on the same day and again 3 days after the vaccination. The B peptide and K9I peptide were used in Protocols B1 and B2, respectively. In total, 21 patients (12 men, nine women; mean age 43.6 years) were enrolled in the present study. Each patient had multiple metastatic lesions of the lung. Thirteen patients completed the six-injection vaccination schedule. One patient developed intracerebral hemorrhage after the second vaccination. Delayed-type hypersensitivity skin tests were negative in all patients. Nine patients showed a greater than twofold increase in the frequency of CTLs in tetramer analysis. Recognized disease progression occurred in all but one of the nine patients in Protocols A1 and A2. In contrast, half the 12 patients had stable disease during the vaccination period in Protocols B1 and B2. Of note, one patient showed transient shrinkage of a metastatic lesion. The response of the patients to the B protocols is encouraging and warrants further investigation.

Transcutaneous immunization: an overview of advantages, disease targets, vaccines, and delivery technologies

Skin is an immunologically active tissue composed of specialized cells and agents that capture and process antigens to confer immune protection. Transcutaneous immunization takes advantage of the skin immune network by inducing a protective immune response against topically applied antigens. This mode of vaccination presents a novel and attractive approach for needle-free immunization that is safe, noninvasive, and overcomes many of the limitations associated with needle-based administrations. In this review we will discuss the developments in the field of transcutaneous immunization in the past decade with special emphasis on disease targets and vaccine delivery technologies. We will also briefly discuss the challenges that need to be overcome to translate early laboratory successes in transcutaneous immunization into the development of effective clinical prophylactics.

Current immunotherapeutic approaches in pancreatic cancer

Pancreatic cancer is a highly aggressive and notoriously difficult to treat. As the vast majority of patients are diagnosed at advanced stage of the disease, only a small population is curative by surgical resection. Although gemcitabine-based chemotherapy is typically offered as standard of care, most patients do not survive longer than 6 months. Thus, new therapeutic approaches are needed. Pancreatic cancer cells that develop gemcitabine resistance would still be suitable targets for immunotherapy. Therefore, one promising treatment approach may be immunotherapy that is designed to target pancreatic-cancer-associated antigens. In this paper, we detail recent work in immunotherapy and the advances in concept of combination therapy of immunotherapy and chemotherapy. We offer our perspective on how to increase the clinical efficacy of immunotherapies for pancreatic cancer.

Identification of HLA-A*0201-restricted cytotoxic T lymphocyte epitope from proliferating cell nuclear antigen

Peptide-based immunotherapy strategies appear promising as an approach to successfully induce an antitumor immune response and prolong survival in patients with various cancers. Protein antigens and their specific epitopes are formulation targets for anti-tumor vaccines. Bioinformatical approaches to predict major histocompatibility complex binding peptides can facilitate the resource-consuming effort of T cell epitope identification. Proliferating cell nuclear antigen including Ki-67 and PCNA, associated with the proliferation process of the cell, seems to be an attractive new target for tumor-specific immunotherapy. In this study, we predicted seven HLA-A*0201-restricted CTL candidate epitope of Ki-67 and eight epitope of PCNA by computer algorithm SYFPEITHI, BIMAS, and IEDB_ANN. Subsequently, biological functions of these peptides were tested by experiments in vitro. We found Ki-67((280-288)) (LQGETQLLV) had the strongest binding-affinity with HLA-A*0201. Further study revealed that Ki-67((280-288)) increased the frequency of IFN-γ-producing T cells compared to a negative peptide. Because Ki-67 was broadly expressed in most advanced malignant tumors, indicating a potential anti-tumor application in the future.

Carrageenan as an adjuvant to enhance peptide-based vaccine potency

New innovative therapies are urgently required in order to combat the high mortality and morbidity associated with advanced cancers. Antigen-specific cancer immunotherapy using peptide-based vaccination has emerged as an attractive approach for the control of cancers due to its simplicity and easy preparation. However, such an approach requires the employment of suitable adjuvants. In the current study, we explored the employment of a sulfated polysaccharide compound from red algae, carrageenan (CGN) as an adjuvant for their ability to generate antigen-specific immune responses and antitumor effects in mice vaccinated with human papillomavirus type 16 (HPV-16) E7 peptide vaccine. We found that carrageenan can significantly enhance the E7-specific immune responses generated by E7 peptide vaccination via the TLR4 activation pathway. In addition, carrageenan could enhance the protective and therapeutic antitumor effects generated by E7 peptide vaccination against E7-expressing tumors. Furthermore, the observed enhancement was not restricted to E7 antigen but was also applicable to other antigenic systems. We also found that other structurally similar compounds to CGN, such as dextran, also generated similar immune enhancement. Thus, our data suggest that CGN and its structurally related compounds may serve as innovative adjuvants for enhancing peptide-based vaccine potency.

The epidermal growth factor variant III peptide vaccine for treatment of malignant gliomas

Epidermal growth factor variant III (EGFRvIII) is the most common alteration of the epidermal growth factor (EGF) receptor found in human tumors. It is commonly expressed in glioblastoma multiforme (GBM), where it was initially identified. This constitutively active mutant receptor leads to unregulated growth, survival, invasion, and angiogenesis in cells that express it. EGFRvIII results from an in-frame deletion of exons 2 to 7 resulting in the fusion of exon 1 to exon 8 of the EGF receptor gene creating a novel glycine at the junction in the extracellular amino terminal domain. The juxtaposition of ordinarily distant amino acids in combination with the glycine that forms at the junction leads to a novel tumor-specific epitope that would make an ideal tumor-specific target. A peptide derived from the EGFRvIII junction can be used as a vaccine to prevent or induce the regression of tumors. This peptide vaccine has now proceeded to phase 1 and 2 clinical trials where it has been highly successful and is now undergoing investigation in a larger human clinical trial for patients who have newly diagnosed GBM. In this article, the authors discuss the preclinical data that led to the human trials and the exciting preliminary data from the clinical trials.

Identification of the transcription factor single-minded homologue 2 as a potential biomarker and immunotherapy target in prostate cancer

PURPOSE

Identification of novel biomarkers and immunotherapy targets for prostate cancer (PCa) is crucial to better diagnosis and therapy. We sought to identify novel PCa tumor-associated antigens (TAA) that are expressed in PCa, absent in nonprostate human tissue, and immunogenic for immune responses restricted by human HLA.

EXPERIMENTAL DESIGN AND RESULTS

Using microarray analysis of normal and cancerous human prostate tissues, we identified 1,063 genes overexpressed in PCa. After validating 195 transcripts in publicly available array data sets, we interrogated expression of these TAAs in normal human tissues to identify genes that are not expressed at detectable levels in normal, nonprostate adult human tissue. We identified 23 PCa TAA candidates. Real-time PCR confirmed that 15 of these genes were overexpressed in PCa (P< 0.05 for each). The most frequently overexpressed gene, single-minded homologue 2 (SIM2), was selected for further evaluation as a potential target for immunotherapy. ELISA assay revealed that a fraction of PCa patients exhibited immune responsiveness to SIM2 as evidenced by the presence of autoantibodies to SIM2 in their sera. We next showed binding of putative HLA-A2.1-restricted SIM2 epitopes to human A2.1, and immunization of transgenic HLA-A2.1 mice showed induction of SIM2-specific CTL responses in vivo.

CONCLUSIONS

Our findings that SIM2 is selectively expressed in PCa, that human HLA-A2.1-restricted SIM2 epitopes induce specific T cells in vivo, and that anti-SIM2 antibodies are detectable in PCa patients' sera implicate SIM2 as a PCa-associated antigen that is a suitable potential target for PCa immunotherapy.

Enhancing immune responses to tumor-associated antigens

The goal of vaccine-based cancer immunotherapy is to induce a tumor-specific immune response that ultimately reduces tumor burden. However, the immune system is often tolerant to antigens presented by the tumor, as the cancer originates from within a patient and is therefore recognized as self. This article reviews selected clinical strategies for overcoming this immune tolerance, and approaches to enhance generation of immunity to tumor-associated antigens by activating innate immunity, potentiating adaptive immunity, reducing immunosuppression, and enhancing tumor immunogenicity. Success in the field of cancer vaccines has yet to be fully realized, but intelligent choice of immunomodulators, tumor antigens and patient populations will likely lead to clinically relevant uses for cancer vaccines.

Ii-Key/HPV16 E7 hybrid peptide immunotherapy for HPV16+ cancers

Activation of antigen-specific CD4+ T cells is critical for vaccine design. We have advanced a novel technology for enhancing activation of antigen-specific CD4+ T helper cells whereby a fragment of the MHC class II-associated invariant chain (Ii-Key) is linked to an MHC class II epitope. An HLA-DR4-restricted HPV16 E7 epitope, HPV16 E7(8-22), was used to create a homologous series of Ii-Key/HPV16 E7 hybrids testing the influence of spacer length on in vivo enhancement of HPV16 E7(8-22)-specific CD4+ T lymphocyte responses. HLA-DR4-tg mice were immunized with Ii-Key/HPV16 E7(8-22) hybrids or the epitope-only peptide HPV16 E7(8-22). As measured by IFN-gamma ELISPOT assay of splenocytes from immunized mice, one of the Ii-Key/HPV16 E7(8-22) hybrids enhanced epitope-specific CD4+ T cell activation 5-fold compared to the HPV16 E7(8-22) epitope-only peptide. We further demonstrated that enhanced CD4+ T cell activation augments the CTL activity of a H-2D(b)-restricted HPV16 E7(49-57) epitope in HLA-DR4+ mice using an in vivo CTL assay. Binding assays indicated that the Ii-Key/HPV16 hybrid has increased affinity to HLA-DR4+ cells relative to the epitope-only peptide, which may explain its increased potency. In summary, Ii-Key hybrid modification of the HLA-DR4-restricted HPV16 E7(8-22) MHC class II epitope generates a potent immunotherapeutic peptide vaccine that may have potential for treating HPV16+ cancers in HLA-DR4+ patients.