Artificially synthesized helper/killer-hybrid epitope long peptide (H/K-HELP): preparation and immunological analysis of vaccine efficacy

SARS-CoV-2 spike protein-derived immunogenic peptides that are promiscuously presented by several HLA-class II molecules and their potential for inducing acquired immunity

The current coronavirus disease 2019 (COVID-19) pandemic that is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a significant threat to public health. Although vaccines based on the mRNA of the SARS-CoV-2 spike protein have been developed to induce both cellular and humoral immunity against SARS-CoV-2, there have been some concerns raised about their high cost, particularly in developing countries. In the present study, we aim to identify an immunogenic peptide in the SARS-CoV-2 spike protein to activate cellular immunity, particularly CD4+ helper T lymphocytes (Th cells), which are a commander of immune system. SARS-CoV-2 spike protein-derived peptides Spike448-477 and Spike489-513(N501Y)-specific CD4+ Th cell lines were generated by repetitive stimulation of healthy donor-derived CD4+T-cells with each peptide. Their HLA-restrictions were addressed by using blocking antibodies against HLA and HLA-transfected L-cells. The epitopes of Spike448-477-specific CD4+ Th cell lines were defined using a series of 7-14-mer overlapping truncated peptides and alanine-substituted epitope peptides. To address responsiveness of these CD4+ Th cell lines to several SARS-CoV-2 variants, we stimulated the CD4+ Th cell lines with mutated peptides. We addressed whether these identified peptides were useful for monitoring T-cell-based immune responses in vaccinated donors using the IFN-γ ELISpot assay. The Spike448-477 peptide was found to be a promiscuous peptide presented by HLA- DRB1*08:02, DR53, and DPB1*02:02. Although HLA-DPB1*02:02-restricted CD4+ Th cells did not response to some peptides with the L452R and L452Q mutations, the other CD4+ Th cells were not affected by any mutant peptides. We developed two tetramers to detect HLA-DRB1*08:02/Spike449-463- and Spike449-463(L452R/Y453F)-recognizing CD4+ Th cells. Spike489-513(N501Y) peptide was also a promiscuously presented to HLA-DRB1*09:01 and DRB1*15:02. The T-cell responses specific to both peptides Spike448-477 and Spike489-513 were detected in PBMCs after vaccinations. In addition, we observed that the Spike448-477 peptide activated both CD8+ T-cells and CD4+ Th cells in individuals receiving mRNA vaccines. SARS-CoV-2 spike protein-derived peptides, Spike448-477 and Spike489-513, include several epitopes that are presented by multiple HLA-class II alleles to activate CD4+ Th cells, which are considered useful for monitoring the establishment of acquired immunity after vaccination.

Antitumor Peptide-Based Vaccine in the Limelight

The success of the immune checkpoint blockade has provided a proof of concept that immune cells are capable of attacking tumors in the clinic. However, clinical benefit is only observed in less than 20% of the patients due to the non-specific activation of immune cells by the immune checkpoint blockade. Developing tumor-specific immune responses is a challenging task that can be achieved by targeting tumor antigens to generate tumor-specific T-cell responses. The recent advancements in peptide-based immunotherapy have encouraged clinicians and patients who are struggling with cancer that is otherwise non-treatable with current therapeutics. By selecting appropriate epitopes from tumor antigens with suitable adjuvants, peptides can elicit robust antitumor responses in both mice and humans. Although recent experimental data and clinical trials suggest the potency of tumor reduction by peptide-based vaccines, earlier clinical trials based on the inadequate hypothesis have misled that peptide vaccines are not efficient in eliminating tumor cells. In this review, we highlighted the recent evidence that supports the rationale of peptide-based antitumor vaccines. We also discussed the strategies to select the optimal epitope for vaccines and the mechanism of how adjuvants increase the efficacy of this promising approach to treat cancer.

Development of a novel T cell-oriented vaccine using CTL/Th-hybrid epitope long peptide and biodegradable microparticles, against an intracellular bacterium

Antigen-specific CD8+ T-lymphocytes (cytotoxic T-lymphocytes: CTL), as well as CD4+ T-lymphocytes (helper T-lymphocytes: Th), simultaneously play an important role in the elimination of intracellular bacteria such as Mycobacterium tuberculosis and Listeria monocytogenes. Administration of T-cell epitope short peptide needs large numbers of peptides for effective vaccination due to its easily degradable nature in vivo. In this respect, biocompatible and biodegradable microparticles combined with CTL/Th-hybrid epitope long peptide (long peptide) have been used to diminish the degradation of loaded peptide. The aim of this study is to develop a novel T cell-oriented vaccine against intracellular bacteria that is composed of long peptide and poly (lactic-co-glycolic acid) (PLGA) microparticles. Mouse bone marrow-derived dendritic cells (BMDCs) were loaded with L. monocytogenes listeriolysin O (LLO)-derived or ovalbumin (OVA)-derived long peptide/PLGA or other comparative antigens. The antigen-loaded BMDCs were injected subcutaneously into the flank of mice twice, and then, the spleens were collected and lymphocyte proliferation and interferon-γ production were evaluated. The median diameter of the PLGA spheres was 1.38 μm. Both LLO- and OVA-long peptide/PLGA showed significantly more robust CTL and Th proliferations with higher interferon-γ production than the long peptide alone or CTL and Th short peptides/PLGA vaccination. Furthermore, the LLO-long peptide/PLGA vaccination showed a significantly lower bacterial burden in spleens compared with the long peptide alone or the CTL and Th short peptides/PLGA vaccination after the challenge of lethal amounts of L. monocytogenes. These results suggest that the novel vaccine taking advantages of CTL/Th-hybrid epitope long peptide and PLGA microparticle is effective for protection against intracellular bacteria.

New Strategies for Therapeutic Cancer Vaccines

BACKGROUND

Patients with low response rates to cancer vaccines, short duration of anti-tumor response after vaccination, and relatively weak curative effects are problems that have not been resolved effectively during the development and application of cancer vaccines. With the continuous improvement of knowledge and awareness regarding the immune system and cancer cells, many researches have helped to explain the reasons for poor vaccine efficacy. Input from researchers accompanied by some newly emerged strategies could bring hope to improve the therapeutic effects of vaccines.

METHODS

Data were collected from Web of Science, Medline, Pubmed, through searching of these keywords: "cancer vaccine", "cancer stem cell", "targeted agent", "immune checkpoint blockade" and "neoantigen".

RESULTS

It may be more effective in immunotherapy of human cancers, including cancer stem cell vaccines, combination vaccines with targeted agents or immune checkpoint blockade, and neoantigen-based vaccines.

CONCLUSION

Personalized vaccines will become the mainstream solution of cancer treatment program with the continuous improvement of human understanding of the immune system and the progress of related experiments.

Cancer vaccines: designing artificial synthetic long peptides to improve presentation of class I and class II T cell epitopes by dendritic cells

There is now a consensus that efficient peptide vaccination against cancer requires that peptides should (i) be exclusively presented by professional APC and (ii) stimulate both CD4 and CD8-specific T cell responses. To this aim, in recent trials, patients were vaccinated with pools of synthetic long peptides (SLP) (15–30 aa long) composed of a potential class I epitope(s) elongated at both ends with native antigen sequences to also provide a potential class II epitope(s). Using MELOE-1 as a model antigen, we present an alternative strategy consisting in linking selected class I and class II epitopes with an artificial cathepsin-sensitive linker to improve epitope processing and presentation by DC. We provide evidence that some linker sequences used in our artificial SLPs (aSLPs) could increase up to 100-fold the cross-presentation of class I epitopes to CD8-specific T cell clones when compared to cross-presentation of the corresponding native long peptide. Presentation of class II epitopes were only slightly increased. We confirmed this increased cross-presentation after in vitro stimulation of PBMC from healthy donors with aSLP and assessment of CD8-specific responses and also in vivo following aSLP vaccination of HLA*A0201/HLA-DRB0101 transgenic mice. Finally, we provide some evidence that vaccination with aSLP could inhibit the growth of transplanted tumors in mice. Our data thus support the use of such aSLPs in future cancer vaccination trials to improve anti-tumor CD8 T cell responses and therapeutic efficacy.

A new peptide vaccine OCV-501: in vitro pharmacology and phase 1 study in patients with acute myeloid leukemia

Wilms’ tumor 1 (WT1) is a promising target of new immunotherapies for acute myeloid leukemia (AML) as well as for other cancers. OCV-501 is a helper peptide derived from the WT1 protein. OCV-501 induced OCV-501-specific Type 1 T-helper (Th1) responses dose-dependently and stimulated helper activity of the specific Th1 cells in peripheral blood mononuclear cells from healthy donors. OCV-501 also enhanced the increase in WT1-killer peptide-specific cytotoxic T lymphocytes. OCV-501 stimulated the OCV-501-specific Th1 clones in an HLA class-II restricted manner and formed a complex with HLA class-II protein. OCV-501-specific Th1 clones demonstrated significant OCV-501-specific cytolytic activity against OCV-501-pulsed B-lymphoblastoid cell line cells. Based on the pre-clinical results, phase 1 clinical trial was conducted. The result of this trial suggested that the subcutaneous administration of OCV-501 once weekly for 4 weeks at doses of 0.3, 1, and 3 mg in older patients with AML during complete remission was safe and well tolerated. The maximum tolerated dose was considered to be ≥3 mg. Of the nine subjects enrolled, neither relapse nor blast cells were observed during the study. Immunological responses were observed in OCV-501-specific delayed-type hypersensitivity test. This trial was registered at http://www.clinicaltrials.gov as NCT 01440920.

Improvement of Peptide-Based Tumor Immunotherapy Using pH-Sensitive Fusogenic Polymer-Modified Liposomes

To establish peptide vaccine-based cancer immunotherapy, we investigated the improvement of antigenic peptides by encapsulation with pH-sensitive fusogenic polymer-modified liposomes for induction of antigen-specific immunity. The liposomes were prepared by modification of egg yolk phosphatidylcholine and l-dioleoyl phosphatidylethanolamine with 3-methyl-glutarylated hyperbranched poly(glycidol) (MGlu-HPG) and were loaded with antigenic peptides derived from ovalbumin (OVA) OVA-I (SIINFEKL), and OVA-II (PSISQAVHAAHAEINEAP_βA), which bind, respectively, to major histocompatibility complex (MHC) class I and class II molecules on dendritic cell (DCs). The peptide-loaded liposomes were taken up efficiently by DCs. The peptides were delivered into their cytosol. Administration of OVA-I-loaded MGlu-HPG-modified liposomes to mice bearing OVA-expressing E.G7-OVA tumors induced the activation of OVA-specific CTLs much more efficiently than the administration of free OVA-I peptide did. Mice strongly rejected E.G7-OVA cells after immunization with OVA-I peptide-loaded MGlu-HPG liposomes, although mice treated with free OVA-I peptide only slightly rejected the cells. Furthermore, efficient suppression of tumor volume was observed when tumor-bearing mice were immunized with OVA-I-peptide-loaded liposomes. Immunization with OVA-II-loaded MGlu-HPG-modified liposomes exhibited much lower tumor-suppressive effects. Results indicate that MGlu-HPG liposomes might be useful for improvement of CTL-inducing peptides for efficient cancer immunotherapy.

Vaccination with liposome-coupled glypican-3-derived epitope peptide stimulates cytotoxic T lymphocytes and inhibits GPC3-expressing tumor growth in mice

Because therapeutic manipulation of immunity can induce tumor regression, anti-cancer immunotherapy is considered a promising treatment modality. We previously reported that glypican-3 (GPC3), an oncofetal antigen overexpressed in hepatocellular carcinoma (HCC), is a useful target for cytotoxic T lymphocyte (CTL)-mediated cancer immunotherapy, and we have performed clinical trials using the GPC3-derived peptide vaccine. Although vaccine-induced GPC3-peptide-specific CTLs were often tumor reactive in vitro and were correlated with overall survival, no complete response was observed. In the current study, we synthesized liposome-coupled GPC3-derived CTL epitope peptide (pGPC3-lipsome) and investigated its antitumor potential. Vaccination with pGPC3-liposome induced peptide-specific CTLs at a lower dose than conventional vaccine emulsified in incomplete Freund's adjuvant. Coupling of pGPC3 to liposomes was essential for effective priming of GPC3-specific CTLs. In addition, immunization with pGPC3-liposome inhibited GPC3-expressing tumor growth. Thus, vaccination with tumor-associated antigen-derived epitope peptides coupled to the surfaces of liposomes may be a novel therapeutic strategy for cancer.