Cytotoxic T cells generated against heteroclitic peptides kill primary tumor cells independent of the binding affinity of the native tumor antigen peptide

Recent Findings on Therapeutic Cancer Vaccines: An Updated Review

Cancer remains one of the global leading causes of death and various vaccines have been developed over the years against it, including cell-based, nucleic acid-based, and viral-based cancer vaccines. Although many vaccines have been effective in in vivo and clinical studies and some have been FDA-approved, there are major limitations to overcome: (1) developing one universal vaccine for a specific cancer is difficult, as tumors with different antigens are different for different individuals, (2) the tumor antigens may be similar to the body's own antigens, and (3) there is the possibility of cancer recurrence. Therefore, developing personalized cancer vaccines with the ability to distinguish between the tumor and the body's antigens is indispensable. This paper provides a comprehensive review of different types of cancer vaccines and highlights important factors necessary for developing efficient cancer vaccines. Moreover, the application of other technologies in cancer therapy is discussed. Finally, several insights and conclusions are presented, such as the possibility of using cold plasma and cancer stem cells in developing future cancer vaccines, to tackle the major limitations in the cancer vaccine developmental process.

Dissection of tumor antigens and immune landscape in clear cell renal cell carcinoma: Preconditions for development and precision medicine of mRNA vaccine

Accumulating evidence reveals that mRNA-type cancer vaccines could be exploited as cancer immunotherapies in various solid tumors. However, the use of mRNA-type cancer vaccines in clear cell renal cell carcinoma (ccRCC) remains unclear. This study aimed to identify potential tumor antigens for the development of an anti-ccRCC mRNA vaccine. In addition, this study aimed to determine immune subtypes of ccRCC to guide the selection of patients to receive the vaccine. Raw sequencing and clinical data were downloaded from The Cancer Genome Atlas (TCGA) database. Further, the cBioPortal website was used to visualize and compare genetic alterations. GEPIA2 was employed to evaluate the prognostic value of preliminary tumor antigens. Moreover, the TIMER web server was used to evaluate correlations between the expression of specific antigens and the abundance of infiltrated antigen-presenting cells (APCs). Single-cell RNA sequencing data of ccRCC was used to explore the expression of potential tumor antigens at single-cell resolution. The immune subtypes of patients were analyzed by the consensus clustering algorithm. Furthermore, the clinical and molecular discrepancies were further explored for a deep understanding of the immune subtypes. Weighted gene co-expression network analysis (WGCNA) was used to cluster the genes according to the immune subtypes. Finally, the sensitivity of drugs commonly used in ccRCC with diverse immune subtypes was investigated. The results revealed that the tumor antigen, LRP2, was associated with a good prognosis and enhanced the infiltration of APCs. ccRCC could be divided into two immune subtypes (IS1 and IS2) with distinct clinical and molecular characteristics. The IS1 group showed a poorer overall survival with an immune-suppressive phenotype than the IS2 group. Additionally, a large spectrum of differences in the expression of immune checkpoints and immunogenic cell death modulators were observed between the two subtypes. Lastly, the genes correlated with the immune subtypes were involved in multiple immune-related processes. Therefore, LRP2 is a potential tumor antigen that could be used to develop an mRNA-type cancer vaccine in ccRCC. Furthermore, patients in the IS2 group were more suitable for vaccination than those in the IS1 group.

Epitope-based minigene vaccine targeting fibroblast activation protein α induces specific immune responses and anti-tumor effects in 4 T1 murine breast cancer model

Fibroblast activation protein (FAPα) is a tumor stromal antigen expressed by cancer-associated fibroblasts (CAFs) in more than 90 % of malignant epithelial carcinomas. FAPα-based immunotherapy has been reported and showed that FAPα-specific immune response can remold immune microenvironment and contribute to tumor regression. Many FAPα-based vaccines have been investigated in preclinical trials, which can elicit strong and durable cytolytic T lymphocytes (CTL) with good safety. However, epitope-based FAPα vaccines are rarely reported. To break tolerance against self-antigens, analogue epitopes with modified peptides at the anchor residues are typically used to improve epitope immunogenicity. To investigate the feasibility of a FAPα epitope-based vaccine for cancer immunotherapy in vivo, we conducted a preclinical study to identify a homologous CTL epitope of human and mouse FAPα and obtained its analogue epitope in BALB/c mice, and explored the anti-tumor activity of their minigene vaccines in 4 T1 tumor-bearing mice. By using in silico epitope prediction tools and immunogenicity assays, immunodominant epitope FAP.291 (YYFSWLTWV) and its analogue epitope FAP.291I9 (YYFSWLTWI) were identified. The FAP.291-based epitope minigene vaccine successfully stimulated CTLs targeting CAFs and exhibited anti-tumor activity in a 4 T1 murine breast cancer model. Furthermore, although the analogue epitope FAP.291I9 enhanced FAP.291-specific immune responses, improvement of anti-tumor immunity effects was not observed. Check of immunosuppressive factors revealed that the high levels of IL-10, IL-13, myeloid-derived suppressor cells and iNOS induced by FAP.291I9 increased, which considered the main cause of the failure of the analogue epitope-based vaccine. Thus, we demonstrated for the first time that the FAP.291 minigene vaccine could induce mouse CTLs and also function as a tumor regression antigen, providing the basis for future studies of FAPα epitope-based vaccines. This study may also be valuable for further improvement of the immunogenicity of analogue epitope vaccines.

Identification of Tumor Antigens and Immune Landscape in Glioblastoma for mRNA Vaccine Development

Background: Clinical benefits from standard therapies against glioblastoma (GBM) are limited in part due to the intrinsic radio- and chemo-resistance. As an essential part of tumor immunotherapy for adjunct, therapeutic tumor vaccines have been effective against multiple solid cancers, while their efficacy against GBM remains undefined. Therefore, this study aims to find the possible tumor antigens of GBM and identify the suitable population for cancer vaccination through immunophenotyping. Method: The genomic and responding clinical data of 169 GBM samples and five normal brain samples were obtained from The Cancer Genome Atlas (TCGA). The mRNA_seq data of 940 normal brain tissue were downloaded from Genotype-Tissue Expression (GTEx). Potential GBM mRNA antigens were screened out by differential expression, copy number variant (CNV), and mutation analysis. K-M survival and Cox analysis were carried out to investigate the prognostic association of potential tumor antigens. Tumor Immune Estimation Resource (TIMER) was used to explore the association between the antigens and tumor immune infiltrating cells (TIICs). Immunophenotyping of 169 samples was performed through consensus clustering based on the abundance of 22 kinds of immune cells. The characteristics of the tumor immune microenvironment (TIME) in each cluster were explored through single-sample gene set enrichment analysis based on 29 kinds of immune-related hallmarks and pathways. Weighted gene co-expression network analysis (WGCNA) was performed to cluster the genes related to immune subtypes. Finally, pathway enrichment analyses were performed to annotate the potential function of modules screened through WGCNA. Results: Two potential tumor antigens selected were significantly positively associated with the antigen-presenting immune cells (APCs) in GBM. Furthermore, the expression of antigens was verified at the protein level by Immunohistochemistry. Two robust immune subtypes, immune subtype 1 (IS1) and immune subtype 2 (IS2), representing immune status "immune inhibition" and "immune inflamed", respectively, had distinct clinical outcomes in GBM. Conclusion: ARPC1B and HK3 were potential mRNA antigens for developing GBM mRNA vaccination, and the patients in IS2 were considered the most suitable population for vaccination in GBM.

Identification of tumor antigens and immune subtypes in lower grade gliomas for mRNA vaccine development

BACKGROUND

As an important part of tumor immunotherapy for adjunct, therapeutic tumor vaccines have been effective against multiple solid cancers, while their efficacy against lower grade glioma (LGG) remains undefined. Immunophenotyping of tumors is an essential tool to evaluate the immune function of patients with immunodeficiency or autoimmunity. Therefore, this study aims to find the potential tumor antigen of LGG and identify the suitable population for cancer vaccination based on the immune landscape.

METHOD

The genomic and clinical data of 529 patients with LGG were obtained from TCGA, the mRNA_seq data of normal brain tissue were downloaded from GTEx. Differential expression gene and mutation analysis were performed to screen out potential antigens, K-M curves were carried out to investigate the correlation between the level of potential antigens and OS and DFS of patients. TIMER dataset was used to explore the correlation between genes and immune infiltrating cells. Immunophenotyping of 529 tumor samples was based on the single-sample gene sets enrichment analysis. Cibersort and Estimate algorithm were used to explore the tumor immune microenvironment characteristics in each immune subtype. Weighted gene co-expression network analysis (WGCNA) clustered immune-related genes and screened the hub genes, and pathway enrichment analyses were performed on the hub modules related to immune subtype in the WGCNA.

RESULTS

Selecting for the mutated, up-regulated, prognosis- and immune-related genes, four potential tumor antigens were identified in LGG. They were also significantly positively associated with the antigen-presenting immune cells (APCs). Three robust immune subtypes, IS1, IS2 and IS3, represented immune status "desert", "immune inhibition", and "inflamed" respectively, which might serve as a predictive parameter. Subsequently, clinicopathological features, including the codeletion status of 1p19q, IDH mutation status, tumor mutation burden, tumor stemness, etc., were significantly different among subtypes.

CONCLUSION

FCGBP, FLNC, TLR7, and CSF2RA were potential antigens for developing cancer vaccination, and the patients in IS3 were considered the most suitable for vaccination in LGG.

Novel Survivin Peptides Screened With Computer Algorithm Induce Cytotoxic T Lymphocytes With Higher Cytotoxic Efficiency to Cancer Cells

The identification of novel biomarkers and therapeutic targets in advanced cancer is critical for improving cancer diagnosis and therapeutics. Survivin (SV) is highly expressed predominantly in most cancer cells and tissues but is absent or undetectable in terminally differentiated normal adult tissues. Therefore, it functions as an almost universal tumor antigen. Peptides are short chains of amino acids linked by peptide bonds. To obtain novel SV decamers that are able to induce SV-specific cytotoxic T lymphocytes (CTLs) with a higher cytotoxic efficiency against cancer cells, major histocompatibility complex (MHC) peptide binding algorithms were conducted to predict nine modified SV₉₅ decamers (from SV_95–2 to SV_95–10) based on the natural SV_95–104 peptide sequence of ELTLGEFLKL (here defined as SV_95–1). The fluorescent density of each SV₉₅ peptide was determined by a MHC stability assay, followed by the generation of SV₉₅-specific CTLs with each SV₉₅ peptide (from SV_95–1 to SV_95–10) and human dendritic cells (DCs) loaded with Poly(lactic-co-glycolic) acid (PLGA) nanoparticles encapsulated with SV₉₅ peptide. Finally, IFN-γ ELISpot and CytoTox 96^® Non-Radioactive Cytotoxicity Assays were employed to verify their cytotoxic efficiency of the SV₉₅-specific CTLs generated with the corresponding artificial antigen presenting cells (aAPCs) containing SV₉₅ (SV_95–1 to SV_95–10) peptide. Furthermore, the cytotoxicity of the SV₉₅ specific CTLs generated with nine mutated SV₉₅ peptides was compared to the one generated with natural SV_95–1 peptide and TIL2080 cells. The results indicated that the HLA-A2-restricted mutated SV₉₅ epitope decamers (SV_95–6 and SV_95–7) showed significant higher binding ability compared to natural peptide SV_95–1 in MHC stability assay. More importantly, SV_95–specific CTLs with higher cytotoxicity were successfully induced with both SV_95–6 and SV_95–7 peptides, which significantly eliminated target cells (not only SV_95–1 peptide pulsed T2 cells, but also both HLA-A2 and SV positive cancer cells) when compared to those generated with natural SV_95–1 peptide and TIL2080 cells. These findings suggest that the SV_95–6 and SV_95–7 peptides are two novel HLA-A2-restricted CTL epitopes and may be useful for the immunotherapy for patients with survivin expressing cancer.

An effective peptide vaccine strategy circumventing clonal MHC heterogeneity of murine myeloid leukaemia

BACKGROUND

Therapeutic cancer vaccines are an attractive approach for treating malignant tumours, and successful tumour eradication depends primarily on controlling tumour immunosuppression status as well as heterogeneity of tumour cells driven by epigenetic alterations.

METHODS

Peptide-loaded dendritic cell (DC) prime and non-infectious peptide booster heterologous immunisations were assessed for the immunogenicity of polo-like kinase-1 (PLK1)-derived peptides. Heterologous vaccination regimen targeting multiple shared tumour antigens simultaneously with PD-L1 blockade was assessed against murine myeloid leukaemia.

RESULTS

A synthetic PLK1122 (DSDFVFVVL)-based heterologous vaccination generated large numbers of long-lasting antigen-specific CD8 T-cells eliciting therapeutic effects against various established tumours. The therapeutic efficacy of single antigen-targeting PLK1122-based vaccine with sufficient endurance of PD-L1 blockade toward C1498 leukaemia relied on the heterogeneous clonal levels of MHC-I and PD-L1 expression. A novel multi-peptide-based vaccination targeting PLK1 and survivin simultaneously along with PD1 blockade led to complete tumour eradication and long-term survival in mice with clonally heterologous C1498 myeloid leukaemia.

CONCLUSIONS

Our findings suggest that PLK1 could be an attractive immunotherapeutic target antigen for cancer immunotherapy, and that similar strategies would be applicable for the optimisation of cancer vaccines for the treatment of numerous viral diseases and malignant tumours.

Melanoma vaccines: clinical status and immune endpoints

It has been known for decades that the immune system can be spontaneously activated against melanoma. The presence of tumor infiltrating lymphocytes in tumor deposits is a positive prognostic factor. Cancer vaccination includes approaches to generate, amplify, or skew antitumor immunity. To accomplish this goal, tested approaches involve administration of tumor antigens, antigen presenting cells or other immune modulators, or direct modulation of the tumor. Because the success of checkpoint blockade can depend in part on an existing antitumor response, cancer vaccination may play an important role in future combination therapies. In this review, we discuss a variety of melanoma vaccine approaches and methods to determine the biological impact of vaccination.

Personalized adoptive immunotherapy for patients with EBV-associated tumors and complications: Evaluation of novel naturally processed and presented EBV-derived T-cell epitopes

Morbidity and mortality of immunocompromised patients are increased by primary infection with or reactivation of Epstein-Barr virus (EBV), possibly triggering EBV⁺ post-transplant lymphoproliferative disease (PTLD). Adoptive transfer of EBV-specific cytotoxic T cells (EBV-CTLs) promises a non-toxic immunotherapy to effectively prevent or treat these complications. To improve immunotherapy and immunomonitoring this study aimed at identifying and evaluating naturally processed and presented HLA-A*03:01-restricted EBV-CTL epitopes as immunodominant targets. More than 15000 peptides were sequenced from EBV-immortalized B cells transduced with soluble HLA-A*03:01, sorted using different epitope prediction tools and eleven candidates were preselected. T2 and Flex-T peptide-binding and dissociation assays confirmed the stability of peptide-MHC complexes. Their immunogenicity and clinical relevance were evaluated by assessing the frequencies and functionality of EBV-CTLs in healthy donors (n > 10) and EBV⁺ PTLD-patients (n = 5) by multimer staining, Eli- and FluoroSpot assays. All eleven peptides elicited EBV-CTL responses in the donors. Their clinical applicability was determined by small-scale T-cell enrichment using Cytokine Secretion Assay and immunophenotyping. Mixtures of these peptides when added to the EBV Consensus pool revealed enhanced stimulation and enrichment efficacy. These EBV-specific epitopes broadening the repertoire of known targets will improve manufacturing of clinically applicable EBV-CTLs and monitoring of EBV-specific T-cell responses in patients.

Discovery of immunodominant T-cell epitopes reveals penton protein as a second immunodominant target in human adenovirus infection

Background

Human adenovirus (HAdV) infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation (HSCT). Efficient antiviral T-cell responses are necessary to clear infection, which is hampered by delayed immune reconstitution and medical immunosuppression after HSCT. Protective immunity may be conferred by adoptive transfer of HAdV-specific T cells. For identification of patients at risk and monitoring of treatment responses diligent assessment of anti-HAdV cellular immune responses is crucial. The HAdV-derived protein hexon has been recognized as a major immunodominant target across HAdV species. We aimed at identifying further targets of protective anti-HAdV immune response and characterizing immunogenic epitopes.

Methods

Nineteen candidate nonamers from hexon and penton proteins were identified by epitope binding prediction. Peptides were synthesized and tested for in vivo immunogenicity by screening peripheral blood mononuclear cells from healthy volunteers (n = 64) and HAdV-infected stem cell recipients (n = 26) for memory T cells recognizing the candidate epitopes in the context of most common HLA alleles.

Results

Functional CD8⁺ T cells recognizing seven epitopes were identified, among them four penton-derived and two hexon-derived peptides. The HLA-A*01-restricted penton-derived peptide STDVASLNY (A01Penton_STDV) and HLA-A*02-restricted hexon-derived peptide TLLYVLFEV (A02Hexon_TLLY) were recognized by more than half of the persons carrying the respective HLA-type.

Conclusions

Thus, the HAdV-derived penton protein is a novel major target of the anti-HAdV immune response. Identification of new immunodominant epitopes will facilitate and broaden immune assessment strategies to identify patients suitable for T-cell transfer. Knowledge of additional target structures may increase T-cell recovery in manufacturing processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1042-2) contains supplementary material, which is available to authorized users.

Specific cytotoxic T-cell immune responses against autoantigens recognized by chronic lymphocytic leukaemia cells

Mounting evidence suggests that autoreactivity and inflammatory processes are involved in the pathogenesis of chronic lymphocytic leukaemia (CLL). Cytoskeletal proteins, including non-muscle myosin heavy chain IIA (MYHIIA), vimentin (VIM) and cofilin-1 (CFL1), exposed on the surface of apoptotic cells have been identified as autoantigens that are recognized by the specific B-cell receptors of the CLL cells. In 212 CLL patients analysed with quantitative reverse transcriptase-polymerase chain reaction we found CFL1 overexpression and low expression of MYH9 in comparison with healthy volunteers. We detected specific cytotoxic immune responses for peptides derived from MYHIIA in 66·7%, VIM in 87·5% and CFL1 in 62·5% CLL patients in an Enzyme-Linked ImmunoSpot assay. Low frequencies of autoreactive peptide-specific T cells were detected against MYHIIA, VIM and CFL1 in CLL patients ex vivo; most of the detected cells had an effector-memory phenotype. Our findings support the existence of cytotoxic immune responses against three autoantigens that have been identified as targets of CLL clonotypic B-cell receptors. The presence of autoreactive CD8(+) T cells against MYHIIA, VIM and CFL1 in CLL patients indicates the involvement of antigen-specific autoreactive T cells in the pathogenesis of CLL.

Overview on poly(ADP-ribose) immuno-biomedicine and future prospects

Poly(ADP-ribose), identified in 1966 independently by three groups Strassbourg, Kyoto and Tokyo, is synthesized by poly(ADP-ribose) polymerases (PARP) from NAD(+) as a substrate in the presence of Mg(2+). The structure was unique in that it has ribose-ribose linkage. In the early-1970s, however, its function in vivo/in vitro was still controversial and the antibody against it was desired to help clear its significance. Thereupon, the author tried to produce antibody against poly(ADP-ribose) in rabbits and succeeded in it for the first time in the world. Eventually, this success has led to the following two groundbreaking papers in Nature: "Naturally-occurring antibody against poly(ADP-ribose) in patients with autoimmune disease SLE", and "Induction of anti-poly(ADP-ribose) antibody by immunization with synthetic double-stranded RNA, poly(A)·poly(U)".On the way to the publication of the first paper, a reviewer gave me a friendly comment that there is "heteroclitic" fashion as a mechanism of the production of natural antibody. This comment was really a God-send for me, and became a train of power for publication of another paper, as described above. Accordingly, I thought this, I would say, episode is worth describing herein. Because of its importance in biomedical phenomena, a certain number of articles related to "heteroclitic" have become to be introduced in this review, although they were not always directly related to immuno-biological works on poly(ADP-ribose). Also, I tried to speculate on the future prospects of poly(ADP-ribose), product of PARP, as an immuno-regulatory molecule, including either induced or naturally-occurring antibodies, in view of "heteroclitic".

Analogue peptides for the immunotherapy of human acute myeloid leukemia

The use of peptide vaccines, enhanced by adjuvants, has shown some efficacy in clinical trials. However, responses are often short-lived and rarely induce notable memory responses. The reason is that self-antigens have already been presented to the immune system as the tumor develops, leading to tolerance or some degree of host tumor cell destruction. To try to break tolerance against self-antigens, one of the methods employed has been to modify peptides at the anchor residues to enhance their ability to bind major histocompatibility complex molecules, extending their exposure to the T-cell receptor. These modified or analogue peptides have been investigated as stimulators of the immune system in patients with different cancers with variable but sometimes notable success. In this review we describe the background and recent developments in the use of analogue peptides for the immunotherapy of acute myeloid leukemia describing knowledge useful for the application of analogue peptide treatments for other malignancies.

Heteroclitic Peptides Increase Proliferation and Reduce Evidence of Human Immunodeficiency Virus-Specific CD8⁺ T Cell Dysfunction

Human immunodeficiency virus (HIV)-specific CD8(+) T cell dysfunction parallels disease progression; therefore, restoring potent HIV-specific CD8(+) T cell responses is a key therapeutic goal. Certain CD8(+) T cell peptide epitope variants, termed heteroclitic, enhance cytokine production by the HIV-specific CD8(+) T cells of some individuals. In this study, we investigated whether heteroclitic peptides that enhance cytokine production by HIV-specific CD8(+) T cells also reduce functional and phenotypic evidence of HIV-specific CD8(+) T cell exhaustion in those instances. Twenty-four variant peptides of human histocompatibility-linked leukocyte antigen (HLA)-A2-restricted reference HIV peptide epitopes designated as A2-7; Nef 83→91, A2-8; Nef 135→143, A2-Gag; Gag 77→85 and A2-9; Gag 433→440 were synthesized with conservative and semiconservative amino acid substitutions at positions 3, 5, and 7 or 3, 5, and 8 of Gag 433→440. Variants that enhanced interferon-gamma (IFN-γ) and/or interleukin-2 (IL-2) production in enzyme-linked immunospot assays (29 cases overall) were subsequently tested by 7-day in vitro peptide stimulation for their effects on HIV-specific CD8(+) T cell proliferation and programmed death-1 (PD-1) expression. Heteroclitic variants enhanced HIV-specific CD8(+) T cell proliferation by >20% in 13/29 cases tested, reduced PD-1 expression on proliferating cells by 15-50% in 10 cases, and reduced PD-1 expression on proliferating cells by >50% in 3 cases. In five cases, the same heteroclitic peptide increased proliferation by >20% and reduced PD-1 expression by >15%. These data demonstrate that heteroclitic peptides can alter the magnitude and character of HIV-specific CD8(+) cell responses relative to reference peptides and may have a unique immunotherapeutic value in therapeutic vaccines.

Enhancing Human Immunodeficiency Virus-Specific CD8(+) T Cell Responses with Heteroclitic Peptides

Human immunodeficiency virus (HIV)-specific CD8(+) T cells play a critical role in containing HIV replication and delaying disease progression. However, HIV-specific CD8(+) T cells become progressively more "exhausted" as chronic HIV infection proceeds. Symptoms of T cell exhaustion range from expression of inhibitory receptors and selective loss of cytokine production capacity through reduced proliferative potential, impaired differentiation into effector cells and increased susceptibility to apoptosis. While effective combination antiretroviral therapy (cART) durably reduces HIV viremia to undetectable levels, this alone does not restore the full pluripotency of HIV-specific CD8(+) T cells. In a number of studies, a subset of peptide epitope variants categorized as heteroclitic, restimulated more potent cellular immune responses in vitro than did the native, immunizing peptides themselves. This property of heteroclitic peptides has been exploited in experimental cancer and chronic viral infection models to promote clearance of transformed cells and persistent viruses. In this review, we consider the possibility that heteroclitic peptides could improve the efficacy of therapeutic vaccines as part of HIV immunotherapy or eradication strategies. We review literature on heteroclitic peptides and illustrate their potential to beneficially modulate the nature of HIV-specific T cell responses toward those found in the small minority of HIV-infected, aviremic cART-naïve persons termed elite controllers or long-term non-progressors. Our review suggests that the efficacy of HIV vaccines could be improved by identification, testing, and incorporation of heteroclitic variants of native HIV peptide epitopes.

Paradigm shifts in the management of poor-risk chronic lymphocytic leukemia

With the growing complexity of treatment options for chronic lymphocytic leukemia (CLL) and variables that influence the underlying biology of this disease, providing allogeneic stem cell transplant (alloSCT) to appropriate candidates poses a challenge for transplant physicians. Novel small molecule inhibitors hold unprecedented promise for poor-risk subgroups, which will likely alter decision-making and referral patterns for transplant. In this review, we analyze what is known and may still remain true about indications for transplant based on outcomes reported in the literature recently and over the last decade.

An unstable Th epitope of P. falciparum fosters central memory T cells and anti-CS antibody responses

Malaria is transmitted by Plasmodium-infected anopheles mosquitoes. Widespread resistance of mosquitoes to insecticides and resistance of parasites to drugs highlight the urgent need for malaria vaccines. The most advanced malaria vaccines target sporozoites, the infective form of the parasite. A major target of the antibody response to sporozoites are the repeat epitopes of the circumsporozoite (CS) protein, which span almost one half of the protein. Antibodies to these repeats can neutralize sporozoite infectivity. Generation of protective antibody responses to the CS protein (anti-CS Ab) requires help by CD4 T cells. A CD4 T cell epitope from the CS protein designated T* was previously identified by screening T cells from volunteers immunized with irradiated P. falciparum sporozoites. The T* sequence spans twenty amino acids that contains multiple T cell epitopes restricted by various HLA alleles. Subunit malaria vaccines including T* are highly immunogenic in rodents, non-human primates and humans. In this study we characterized a highly conserved HLA-DRβ1*04:01 (DR4) restricted T cell epitope (QNT-5) located at the C-terminus of T*. We found that a peptide containing QNT-5 was able to elicit long-term anti-CS Ab responses and prime CD4 T cells in HLA-DR4 transgenic mice despite forming relatively unstable MHC-peptide complexes highly susceptible to HLA-DM editing. We attempted to improve the immunogenicity of QNT-5 by replacing the P1 anchor position with an optimal tyrosine residue. The modified peptide QNT-Y formed stable MHC-peptide complexes highly resistant to HLA-DM editing. Contrary to expectations, a linear peptide containing QNT-Y elicited almost 10-fold lower long-term antibody and IFN-γ responses compared to the linear peptide containing the wild type QNT-5 sequence. Some possibilities regarding why QNT-5 is more effective than QNT-Y in inducing long-term T cell and anti-CS Ab when used as vaccine are discussed.

Cross-reactivity of T cells and its role in the immune system

T-cell receptors recognize peptides presented by the major histocompatibility complex (MHC) on the surface of antigen-presenting cells (APC). The ability of the T-cell receptor (TCR) to recognize more than one peptide-MHC structure defines cross-reactivity. Cross-reactivity is a documented phenomenon of the immune system whose importance is still under investigation. There are a number of rational arguments for cross-reactivity. These include the discrepancy between the theoretical high number of pathogen-derived peptides and the lower diversity of the T-cell repertoire, the need for recognition of escape variants, and the intrinsic low affinity of this receptor-ligand pair. However, quantifying the phenomenon has been difficult, and its immunological importance remains unknown. In this review, we examined the cases for and against an important role for cross reactivity. We argue that it may be an essential feature of the immune system from the point of view of biological robustness.

Heteroclitic peptides enhance human immunodeficiency virus-specific CD8(+) T cell responses

The inability of human immunodeficiency virus (HIV)-specific CD8(+) T cells to durably control HIV replication due to HIV escape mutations and CD8(+) T cell dysfunction is a key factor in disease progression. A few HIV-infected individuals termed elite controllers (EC) maintain polyfunctional HIV-specific CD8(+) T cells, minimal HIV replication and normal CD4(+) T lymphocyte numbers. Thus, therapeutic intervention to sustain or restore CD8(+) T cell responses similar to those persisting in EC could relieve terminal dependence on antiretrovirals. Vaccination with HIV peptides is one approach to achieve this and our objective in this study was to determine whether certain HIV peptide variants display antigenic superiority over the reference peptides normally included in vaccines. Eight peptide sets were generated, each with a reference peptide and six variants harboring conservative or semi-conservative amino acid substitutions at positions predicted to affect T cell receptor interactions without affecting human class I histocompatibililty-linked antigen (HLA) binding. Recognition across peptide sets was tested with >80 HIV-infected individuals bearing the appropriate HLA alleles. While reference peptides were often the most antigenic, cross-reactivity with variants was common and in many cases, peptide variants were superior at stimulating interferon-γ production or selectively enhanced interleukin-2 production. Although such heteroclitic activity was not generalized for all individuals bearing the HLA class I allele involved, these data suggest that heteroclitic peptide variants could improve the efficacy of therapeutic peptide vaccines in HIV infection.

The only proposed T-cell epitope derived from the TEL-AML1 translocation is not naturally processed

Adoptive therapy with T-cell receptor (TCR)-engineered T cells is a promising approach in cancer treatment. While usage of T cells specific for tumor-associated antigens (TAAs) can lead to serious side effects because of autoimmunity, targeting true tumor-specific mutations, such as the products of translocations in leukemias, should reduce such a risk. A potentially ideal target might be the chimeric protein TEL-AML1, which results from the chromosomal translocation 12;21 and represents the most common fusion gene in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Within the fusion region of TEL-AML1, a single epitope has been described by reverse immunology as immunogenic in HLA-A*0201 restriction settings. As a potential source of TCRs specific for this TEL-AML1 epitope, we have used mice expressing a human TCR-αβ repertoire and human MHC class I. Surprisingly, we have found that, although a specific functional CD8(+) T-cell response against this peptide could be evoked, the described epitope was in fact not endogenously processed. Analyses done with a potent antigen-presenting cell line, as well as with purified human proteasomes, support the conclusion that this peptide cannot be proposed as a potential target in immunotherapy of ALL in HLA-A*0201-restricted fashion.

Enhanced presentation of MHC class Ia, Ib and class II-restricted peptides encapsulated in biodegradable nanoparticles: a promising strategy for tumor immunotherapy

Background

Many peptide-based cancer vaccines have been tested in clinical trials with a limited success, mostly due to difficulties associated with peptide stability and delivery, resulting in inefficient antigen presentation. Therefore, the development of suitable and efficient vaccine carrier systems remains a major challenge.

Methods

To address this issue, we have engineered polylactic-co-glycolic acid (PLGA) nanoparticles incorporating: (i) two MHC class I-restricted clinically-relevant peptides, (ii) a MHC class II-binding peptide, and (iii) a non-classical MHC class I-binding peptide. We formulated the nanoparticles utilizing a double emulsion-solvent evaporation technique and characterized their surface morphology, size, zeta potential and peptide content. We also loaded human and murine dendritic cells (DC) with the peptide-containing nanoparticles and determined their ability to present the encapsulated peptide antigens and to induce tumor-specific cytotoxic T lymphocytes (CTL) in vitro.

Results

We confirmed that the nanoparticles are not toxic to either mouse or human dendritic cells, and do not have any effect on the DC maturation. We also demonstrated a significantly enhanced presentation of the encapsulated peptides upon internalization of the nanoparticles by DC, and confirmed that the improved peptide presentation is actually associated with more efficient generation of peptide-specific CTL and T helper cell responses.

Conclusion

Encapsulating antigens in PLGA nanoparticles offers unique advantages such as higher efficiency of antigen loading, prolonged presentation of the antigens, prevention of peptide degradation, specific targeting of antigens to antigen presenting cells, improved shelf life of the antigens, and easy scale up for pharmaceutical production. Therefore, these findings are highly significant to the development of synthetic vaccines, and the induction of CTL for adoptive immunotherapy.

Chromogranin A as potential target for immunotherapy of malignant pheochromocytoma

Currently, no effective treatment for malignant pheochromocytoma exists. The aim of our study was to investigate the role of chromogranin A (CgA) as a specific target molecule for immunotherapy in a murine model for pheochromocytoma. Six amino acid-modified and non-modified CgA peptides were used for dendritic cell vaccination. Altogether, 50 mice received two different CgA vaccination protocols; another 20 animals served as controls. In vitro tetramer analyses revealed large increases of CgA-specific cytotoxic T cells (CTL) in CgA-treated mice. Tumors of exogenous applied pheochromocytoma cells showed an extensive infiltration by CD8+ T cells. In vitro, CTL of CgA-treated mice exhibited strong MHC I restricted lysis capacities towards pheochromocytoma cells. Importantly, these mice showed strongly diminished outgrowth of liver tumors of applied pheochromocytoma cells. Our data clearly demonstrate that CgA peptide-based immunotherapy induces a cytotoxic immune response in experimental pheochromocytoma, indicating potential for therapeutic applications in patients with malignant pheochromocytoma.

The microenvironment differentially impairs passive and active immunotherapy in chronic lymphocytic leukaemia - CXCR4 antagonists as potential adjuvants for monoclonal antibodies

Direct contact with stromal cells protects chronic lymphocytic leukaemia (CLL) B cells from chemotherapy-induced apoptosis in vitro. Blockade of CXCR4 signalling antagonizes stroma-mediated interactions and restores CLL chemosensitivity. In vivo, administration of CXCR4 antagonists effectively mobilizes haematopoietic progenitor cells. Therefore, combinations of CXCR4 blockade and cytoreductive treatment with selective activity on CLL cells may avoid potential haematotoxicity. Hence, we tested CXCR4 antagonists in the context of passive and active immunotherapeutic approaches. We evaluated how efficiently rituximab, alemtuzumab and cytotoxic T cells killed CLL cells cocultured with stromal cells in the presence and absence of a CXCR4 antagonist. Stromal cell contact attenuated rituximab- and alemtuzumab-induced complement-dependent cytotoxicity of CLL cells. Addition of CXCR4 antagonists abrogated the protective effect of stroma. In contrast, stromal cells did not impair antibody-dependent cell-mediated cytotoxicity and cytotoxicity induced by activated T cells. Destruction of microtubules in CLL target cells restored the protective effect of stroma coculture for CLL cells during Natural Killer cell attack by preventing mitochondrial relocalization towards the immunological synapse. Our data identify the combination of CXCR4 antagonists with passive - but not active - immunotherapy as a promising potential treatment concept in CLL.

Bridging innate and adaptive antitumor immunity targeting glycans

Effective immunotherapy for cancer depends on cellular responses to tumor antigens. The role of major histocompatibility complex (MHC) in T-cell recognition and T-cell receptor repertoire selection has become a central tenet in immunology. Structurally, this does not contradict earlier findings that T-cells can differentiate between small hapten structures like simple glycans. Understanding T-cell recognition of antigens as defined genetically by MHC and combinatorially by T cell receptors led to the “altered self” hypothesis. This notion reflects a more fundamental principle underlying immune surveillance and integrating evolutionarily and mechanistically diverse elements of the immune system. Danger associated molecular patterns, including those generated by glycan remodeling, represent an instance of altered self. A prominent example is the modification of the tumor-associated antigen MUC1. Similar examples emphasize glycan reactivity patterns of antigen receptors as a phenomenon bridging innate and adaptive but also humoral and cellular immunity and providing templates for immunotherapies.

Identification of SARS-COV spike protein-derived and HLA-A2-restricted human CTL epitopes by using a new muramyl dipeptidederivative adjuvant

Severe acute respiratory syndrome (SARS) spread during the winter of 2003, and attempts have been made to develop vaccines against SARS corona virus (SARS-CoV). The present study provides a strategy to rapidly identify SARS-CoV-derived antigenic peptides recognized by HLA-A2-restricted cytotoxic T lymphocytes (CTLs). Forty-three candidate peptides having HLA-A2-binding motifs were selected in silico and HLA-A2/Db chimeric MHC class I-transgenic mice were immunized with these peptides and a new derivative of muramyl dipeptide that can induce upregulation of HLA-DR, CD80, CD86, and CD40 in human CD14+ antigen presenting cells, was administered as an adjuvant. Six HLAA2-restricted mouse CTL epitopes were identified, including two new epitopes which have never been reported before. One of the novel peptides was naturally processed and successfully induced HLAA2-restricted specific CTLs in both HLA transgenic mice and healthy donors. The method was useful, convenient and efficient for rapid identification of CTL epitopes derived from SARS-CoV proteins and will be possibly applicable for other pathogens to develop a peptide-based vaccine.

Identification of human idiotype-specific T cells in lymphoma and myeloma

Idiotype protein, among the first identified tumor-specific antigens, has been found to stimulate both humoral and cellular responses in lymphoma and myeloma patients. With the increasing use of B cell depletion treatments such as rituximab in clinic, the cellular response mediated by idiotype-specific T cells has become increasingly important as an adjunct therapy for lymphoma and myeloma. Here, we review the idiotype protein as a tumor antigen and the characteristics of the T cell response elicited idiotype vaccination. We also analyze the T cell epitopes that have been identified in idiotype protein and introduce our new findings of additional T cell epitopes derived from the Ig light chain. Finally, we propose new directions in the generation of idiotype-specific T cells for tumor therapy.

Vaccine therapy and chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (CLL) should be an ideal target for immune-mediated responses. CLL arises from B cells that can act as antigen-presenting cells (APCs), expresses unique tumour antigens, and has been shown to be a target of the allogeneic T cells which mediate a graft-versus-leukaemia effect. Despite these potential benefits, immune responses against CLL cells have been difficult to elicit. CLL induces immune defects in the host, the tumour cells are inefficient APCs, and therapies given to patients with CLL are themselves immunosuppressive. Successful vaccination approaches in this disease will require steps to overcome these difficulties, including identification of the targets of immune responses in this disease to enable monitoring of the immune response after vaccination, improved presentation of antigens, and steps to improve the immune defects that accompany this disease.

Amino acid-modified calcitonin immunization induces tumor epitope-specific immunity in a transgenic mouse model for medullary thyroid carcinoma

Up to now, no relevant tumor antigen has been identified in medullary thyroid carcinoma (MTC). The aim of the present study was to prove the concept of an immunization with an amino acid-modified calcitonin (CT) for the treatment of MTC in a transgenic mouse model. Amino acid-modified (human) CT has been chosen for vaccination because of its higher binding affinity to the murine H2-Kb-MHC molecule. Mice were immunized over 6 months with monthly injections of amino acid-modified CT-pulsed dendritic cells. For enumeration of tumor epitope-specific CD8+ cytotoxic T cells, tetramer analyses were performed. CT peptide-treated mice revealed a mean 0.73 +/- 0.45 and 0.91 +/- 0.59% positive cells, depending on the two tetramers tested, whereas no increase was seen in control protein-immunized mice (0.08-0.12% tetramer-positive cells). Importantly, the subset of CT-specific CD8+ T cells also showed a high expression of interferon-gamma. In line with these results, CT-immunized mice also showed an intratumor infiltration with CD8+ T lymphocytes. Importantly, we also found a diminished tumor outgrowth of -57% and a decrease of the serum CT levels (2.0 +/- 0.1 pg/ml) compared with control protein-immunized Ret/Cal mice (3.0 +/- 0.4 pg/ml). In summary, we show that amino acid-modified CT is recognized from the immune system leading to a specific antitumor immune response and a diminished tumor outgrowth in transgenic MTC mice. The results are of potential importance because they might be applicable to patients with metastatic spread of a MTC.

Cellular immune therapy for chronic lymphocytic leukemia

Although chemotherapy can induce complete responses in patients with chronic lymphocytic leukemia (CLL), it is not considered curative. Treated patients generally develop recurrent disease requiring additional therapy, which can cause worsening immune dysfunction, myelosuppression, and selection for chemotherapy-resistant leukemia-cell subclones. Cellular immune therapy promises to mitigate these complications and potentially provide for curative treatment. Most experience with this is in the use of allogeneic hematopoietic stem-cell transplantation (allo-HSCT), in which graft-versus-leukemia (GVL) effects can be observed and shown responsible for long-term disease-free survival. However, use of allo-HSCT for CLL is limited because of the lack of suitable donors and the treatment-related morbidity/mortality for elderly patients, who constitute the majority at risk for developing this disease. The GVL effect, however, suggests there are specific CLL-associated antigens that could be targeted in autologous cellular immune therapy. Effective strategies for this will have to overcome the disease-related acquired immune deficiency and the capacity of the leukemia-cell to induce T-cell tolerance, thereby compromising the activity of even conventional vaccines in patients with this disease. We will discuss the different strategies being developed to overcome these limitations that might provide for effective cellular immune therapy of CLL.

Review of current knowledge on HPV vaccination: an appendix to the European Guidelines for Quality Assurance in Cervical Cancer Screening

The recognition of a strong etiological relationship between infection with high-risk human papillomavirusses and cervical cancer has prompted research to develop and evaluate prophylactic and therapeutic vaccines. One prophylactic quadrivalent vaccine using L1 virus-like particles (VLP) of HPV 6, 11, 16 and 18 is available on the European market since the end of 2006 and it is expected that a second bivalent vaccine containing VLPs of HPV16 and HPV18 will become available in 2007. Each year, HPV16 and HPV18 cause approximately 43,000 cases of cervical cancer in the European continent. Results from the phase-IIb and III trials published thus far indicate that the L1 VLP HPV vaccine is safe and well-tolerated. It offers HPV-naive women a very high level of protection against HPV persistent infection and cervical intra-epithelial lesions associated with the types included in the vaccine. HPV vaccination should be offered to girls before onset of sexual activity. While prophylactic vaccination is likely to provide important future health gains, cervical screening will need to be continued for the whole generation of women that is already infected with the HPV types included in the vaccine. Phase IV studies are needed to demonstrate protection against cervical cancer and to verify duration of protection, occurrence of replacement by non-vaccine types and to define future policies for screening of vaccinated cohorts. The European Guidelines on Quality Assurance for Cervical Cancer Screening provides guidance for secondary prevention by detection and management of precursors lesions of the cervix. The purpose of the appendix on vaccination is to present current knowledge. Developing guidelines for future use of HPV vaccines in Europe, is the object of a new grant offered by the European Commission.