MHC Class I-restricted Peptide Research Articles

Abstract P006: Novel machine-learning tools improve cost-effective development of personalised immunotherapies: Lowering false positive rates in the search for actionable (personalised and largely shared) immunogenic neoantigens

Abstract Personalised immunotherapy approaches rely on the ability of tumour-derived neoantigens to elicit a T-cell immune reaction able to recognise and kill the tumour cells expressing them. Clinical attempts to leverage the power of neoantigens have however yielded mixed results. This can mostly be attributed to the difficulty of finding truly immunogenic peptides from the set of novel peptides generated by mutations in a given cancer patient. In silico approaches can help alleviate this heavy cost by reducing the neoantigen search space, prioritising epitopes based on various parameters such as epitope expression or MHC binding likelihood. Here we present a suite of tools aimed at further assisting clinicians in selecting the most actionable peptides from a set of potential candidates. We developed neoMS, a neural network algorithm able to predict epitope presentation at the cell surface with unparalleled performance. The model achieves up to 0.61 precision at recall 0.4 on its test set, vastly outperforming the current industry standards. In addition, due to his sequence-based comparison method, neoMS exhibits extrapolation capabilities, achieving non-zero predictive power when evaluated on ground truth ligandome data derived from an HLA allele completely absent from the training set. In some cancer indications we showed, moreover, that the neoMS-predicted rate of neoantigen presentation can be used in combination with tumour mutational burden as a high-specificity predictor of response to immune checkpoint inhibitor treatment. Furthermore, the neoIM algorithm is able to discriminate, in an HLA-agnostic fashion, which of the presented peptides will elicit a T-cell immune reaction. This first-in-class algorithm is a random forest classifier specifically trained to classify short peptides of length 9-11 amino acids as immunogenic or non-immunogenic. neoIM vastly outperforms the currently available methods and can predict peptide immunogenicity with high accuracy (AUC=0.88). Interestingly, neoIM confirmed ELISPOT data obtained by Dillon et al. (2017) showing a response in 4 out of 11 breast cancer patients to a vaccine consisting of 9 MHC class-I restricted breast cancer-associated peptides. The 2 antigens that resulted in a CD8+ T-cell specific response were predicted by neoIM as the highest scoring showing its potential in finding the truly immunogenic neoantigens. Taken together, these tools decrease false positive rates significantly as they enable improved identification of immunogenic peptides and the predictions correlate with intensity of immune response and clinical benefits. As such, these tools represent a cost-efficient preliminary step in the search for actionable, immunogenic neoantigens. Citation Format: Cedric Bogaert, Lena Pfitzer, Nil Adell Mill, Bruno Fant. Novel machine-learning tools improve cost-effective development of personalised immunotherapies: Lowering false positive rates in the search for actionable (personalised and largely shared) immunogenic neoantigens [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P006.

Vγ9Vδ2 T Cells Concurrently Kill Cancer Cells and Cross-Present Tumor Antigens.

The human Vγ9Vδ2 T cell is a unique cell type that holds great potential in immunotherapy of cancer. In particular, the therapeutic potential of this cell type in adoptive cell therapy (ACT) has gained interest. In this regard optimization of in vitro expansion methods and functional characterization is desirable. We show that Vγ9Vδ2 T cells, expanded in vitro with zoledronic acid (Zometa or ZOL) and Interleukin-2 (IL-2), are efficient cancer cell killers with a trend towards increased killing efficacy after prolonged expansion time. Thus, Vγ9Vδ2 T cells expanded for 25 days in vitro killed prostate cancer cells more efficiently than Vγ9Vδ2 T cells expanded for 9 days. These data are supported by phenotype characteristics, showing increased expression of CD56 and NKG2D over time, reaching above 90% positive cells after 25 days of expansion. At the early stage of expansion, we demonstrate that Vγ9Vδ2 T cells are capable of cross-presenting tumor antigens. In this regard, our data show that Vγ9Vδ2 T cells can take up tumor-associated antigens (TAA) gp100, MART-1 and MAGE-A3 - either as long peptide or recombinant protein – and then present TAA-derived peptides on the cell surface in the context of HLA class I molecules, demonstrated by their recognition as targets by peptide-specific CD8 T cells. Importantly, we show that cross-presentation is impaired by the proteasome inhibitor lactacystin. In conclusion, our data indicate that Vγ9Vδ2 T cells are broadly tumor-specific killers with the additional ability to cross-present MHC class I-restricted peptides, thereby inducing or supporting tumor-specific αβTCR CD8 T cell responses. The dual functionality is dynamic during in vitro expansion, yet, both functions are of interest to explore in ACT for cancer therapy.

Harnessing neoantigen specific CD4 T cells for cancer immunotherapy.

The goal of precision immunotherapy is to direct a patient's T cell response against the immunogenic mutations expressed on their tumors. Most immunotherapy approaches to-date have focused on MHC class I-restricted peptide epitopes by which cytotoxic CD8+ T lymphocytes (CTL) can directly recognize tumor cells. This strategy largely overlooks the critical role of MHC class II-restricted CD4+ T cells as both positive regulators of CTL and other effector cell types, and as direct effectors of antitumor immunity. In this review, we will discuss the role of neoantigen specific CD4+ T cells in cancer immunotherapy and how existing treatment modalities may be leveraged to engage this important T cell subset.

A Random Forest based approach to MHC class I epitope prediction and analysis

Abstract Background Increased hydrophobicity of the contact regions between MHC class I-restricted peptides and TCR is associated with increased immunogenicity. To improve prediction of antigenic peptides and to identify additional biochemical properties associated with immunogenicity, we have created a random forest (RF)-based computational model that evaluates target epitopes using 66 parameters that cover a range of amino acid biochemical properties. Method A dataset of publicly available 9 mer epitopes with experimentally defined immunogenicity (n=29,874) and/or HLA binding (n=108,069) were collected from IEDB and the MassIVE database. Epitopes restricted to target HLA alleles were scored based on the biochemical parameters of each amino acid, and used to train a RF model specific to that HLA. For biochemical property analysis, redundant features were removed with a wrapper algorithm before being used to train the RF model. Results The RF model specific for HLA-A*02:01 (n=5500) was evaluated for HLA binding and immunogenicity prediction accuracy using a mutually-exclusive testing set of HLA-restricted peptides that were non-immunogenic, immunogenic, or non-binders. The model showed an immunogenicity prediction accuracy of 83% with an AUC of 0.88, and a HLA binding prediction accuracy of 97.4%, with a sensitivity of 95.2% and specificity of 99.9%. The RF model confirmed that hydrophobic interactions at peptide positions 4 and 8 as well as H-bonding at position 1 were important for immunogenicity. Conclusion RF-based algorithms can be used to identify biochemical parameters associated with immunogenic class I-restricted T cell epitopes. This model is being expanded to other HLA alleles.

A pilot study of the immunogenicity of a 9-peptide breast cancer vaccine plus poly-ICLC in early stage breast cancer

BackgroundBreast cancer remains a leading cause of cancer death worldwide. There is evidence that immunotherapy may play a role in the eradication of residual disease. Peptide vaccines for immunotherapy are capable of durable immune memory, but vaccines alone have shown sparse clinical activity against breast cancer to date. Toll-like receptor (TLR) agonists and helper peptides are excellent adjuvants for vaccine immunotherapy and they are examined in this human clinical trial.MethodsA vaccine consisting of 9 MHC class I-restricted breast cancer-associated peptides (from MAGE-A1, −A3, and -A10, CEA, NY-ESO-1, and HER2 proteins) was combined with a TLR3 agonist, poly-ICLC, along with a helper peptide derived from tetanus toxoid. The vaccine was administered on days 1, 8, 15, 36, 57, 78. CD8+ T cell responses to the vaccine were assessed by both direct and stimulated interferon gamma ELIspot assays.ResultsTwelve patients with breast cancer were treated: five had estrogen receptor positive disease and five were HER2 amplified. There were no dose-limiting toxicities. Toxicities were limited to Grade 1 and Grade 2 and included mild injection site reactions and flu-like symptoms, which occurred in most patients. The most common toxicities were injection site reaction/induration and fatigue, which were experienced by 100% and 92% of participants, respectively. In the stimulated ELIspot assays, peptide-specific CD8+ T cell responses were detected in 4 of 11 evaluable patients. Two patients had borderline immune responses to the vaccine. The two peptides derived from CEA were immunogenic. No difference in immune response was evident between patients receiving endocrine therapy and those not receiving endocrine therapy during the vaccine series.ConclusionsPeptide vaccine administered in the adjuvant breast cancer setting was safe and feasible. The TLR3 adjuvant, poly-ICLC, plus helper peptide mixture provided modest immune stimulation. Further optimization is required for this multi-peptide vaccine/adjuvant combination.Trial registrationClinicalTrials.gov(posted 2/15/2012): NCT01532960. Registered 2/8/2012.https://clinicaltrials.gov/show/NCT01532960

Glycolipid-peptide conjugate vaccines enhance CD8+ T cell responses against human viral proteins

An important goal of vaccination against viruses and virus-driven cancers is to elicit cytotoxic CD8+ T cells specific for virus-derived peptides. CD8+ T cell responses can be enhanced by engaging help from natural killer T (NKT) cells. We have produced synthetic vaccines that induce strong peptide-specific CD8+ T cell responses in vivo by incorporating an NKT cell-activating glycolipid. Here we examine the effect of a glycolipid-peptide conjugate vaccine incorporating an NKT cell-activating glycolipid linked to an MHC class I-restricted peptide from a viral antigen in human peripheral blood mononuclear cells. The vaccine induces CD1d-dependent activation of human NKT cells following enzymatic cleavage, activates human dendritic cells in an NKT-cell dependent manner, and generates a pool of activated antigen-specific CD8+ T cells with cytotoxic potential. Compared to unconjugated peptide, the vaccine upregulates expression of genes encoding interferon-γ, CD137 and granzyme B. A similar vaccine incorporating a peptide from the clinically-relevant human papilloma virus (HPV) 16 E7 oncoprotein induces cytotoxicity against peptide-expressing targets in vivo, and elicits a better antitumor response in a model of E7-expressing lung cancer than its unconjugated components. Glycolipid-peptide conjugate vaccines may prove useful for the prevention or treatment of viral infections and tumors that express viral antigens.

Exosome-driven transfer of tumor-associated Pioneer Translation Products (TA-PTPs) for the MHC class I cross-presentation pathway

ABSTRACTCellular immune reactions against non-self-epitopes require activation of cytotoxic CD8+ T-cells via cross-presentation of MHC class I-restricted peptides by professional antigen presenting cells (pAPCs), with the consequent detection and elimination of cells expressing the same antigens via the endogenous (direct) pathway. The source of peptides for the endogenous pathway is constituted of alternative mRNA translation products; however, it is still unclear which source of peptides is used for cross-presentation. Furthermore, the presentation of non-canonical translation products, produced during a non-conventional translation event, on class I molecules of tumor cells has been reported but how these peptides are generated, presented to pAPCs, and their capacity to stimulate CD8+ T cells is still not known. Here, we report that pioneer translation peptides (PTPs) derived from intron or exon pre-mRNAs can serve as tumor-associated antigens (TA-PTPs) and are delivered from the producing tumor cells to pAPCs via exosomes where they are processed by the cytosolic pathway. Injection of TA-PTPs and tumor-derived exosomes efficiently induce CD8+ T-cell proliferation and prevent tumor growth in mice. Our results show that TA-PTPs represent an efficient source of antigenic peptides for CD8+ T cell activation and that full-length proteins are not required for cross-presentation. These findings can have interesting implications for generating tolerance and for designing vectors to generate vaccines.

Abstract B059: Slow maturation of early phagosomes promotes a TAP independent antigen cross-presentation pathway

Abstract Early phagocytic compartments play a role in protein sorting, signaling and neutralizing pathogens. In addition, certain subsets of dendritic cells (DCs) load peptides derived from exogenous antigens on to MHC class-I molecules in early phagosomes. This process plays a key role in antigen cross-presentation, a process particularly important in the activation of naïve CD8+ T-cells when it is known as cross-priming and is essential for mounting an immune response against tumor and viral antigens. The functional properties of early phagosomes that facilitate cross-presentation remain unclear. Here we show that the expression of Rab GTPase mutants (Rab5CA, Rab7DN and Rab22CA) that impair maturation of phagosomes enhance antigen cross-presentation efficiency of DCs as well as an engineered derivative of 293T cells capable of cross-presentation. Enhanced antigen cross-presentation observed upon expression of the Rab5CA, Rab7DN and Rab22CA mutants remains dependent on proteasome activity. However, expression of the mutants renders cross-presentation independent of the activity of Transporter associated with antigenic peptide (TAP). These findings taken together reveal a novel TAP independent but proteasome dependent mechanism of MHC class I-restricted antigen processing and peptide loading that is facilitated by slow maturation of endocytic compartments. Citation Format: Debrup Sengupta, Peter Cresswell. Slow maturation of early phagosomes promotes a TAP independent antigen cross-presentation pathway. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B059.

P4.05 - The study of CD8+ T cell response to MHC class I-restricted universal tumoral peptide in accompany with viral peptide

ABSTRACT Background: Breast cancers likes as other human cancers are immunogenic and express tumor-associated proteins that can stimulate and generate immune responses in cancer. One of the important antigen that is express in tumors especially in Brest cancers is human Telomerase reverse transcriptase (hTERT). There are some databases that store the information about T cell epitopes, and we used them to identify immunogenic epitopes in proteins that bind in Class I MHC. in this study we used a peptide derived of hTERT molecule accompany with viral peptide derived of influenza that restricted to HLA-A2 (common MHC class I in Iran) for induction of T CD8+ responses in breast cancer patients. Material and Methods: PBMCs were obtained from blood sample of HLA-A2 positive breast cancer patient incubated with tumor cell line that were transloaded with synthetic peptides from hTERT and viral peptides. Proliferation of T cells analyzed with MTT reaction. After this step, supernatants from previous step evaluated for IFN-γ production by ELISA test. Final step in this study was cytotoxicity assay by measuring LDH on supernatants from first step. Results: As we expected in this study, stimulation and proliferation of T cells occurred. MTT data showed that proliferation of PBMCs incubated with tumoral and viral peptide more than proliferation of PBMCs incubated with tumoral peptide alone. IFN-γ ELISA assessment and LDH cytotoxicity assay confirmed the MTT assay. Conclusion: Our findings showed that the viral peptide intensified CTLs responses to tumoral peptide.

Immunologic hierarchy, class II MHC promiscuity, and epitope spreading of a melanoma helper peptide vaccine.

Immunization with a combination melanoma helper peptide (6MHP) vaccine has been shown to induce CD4(+) T cell responses, which are associated with patient survival. In the present study, we define the relative immunogenicity and HLA allele promiscuity of individual helper peptides and identify helper peptide-mediated augmentation of specific CD8(+) T cell responses. Thirty-seven participants with stage IIIB-IV melanoma were vaccinated with 6MHP in incomplete Freund's adjuvant. The 6MHP vaccine is comprised of 6 peptides representing melanocytic differentiation proteins gp100, tyrosinase, Melan-A/MART-1, and cancer testis antigens from the MAGE family. CD4(+) and CD8(+) T cell responses were assessed in peripheral blood and in sentinel immunized nodes (SIN) by thymidine uptake after exposure to helper peptides and by direct interferon-γ ELIspot assay against 14 MHC class I-restricted peptides. Vaccine-induced CD4(+) T cell responses to individual epitopes were detected in the SIN of 63 % (22/35) and in the peripheral blood of 38 % (14/37) of participants for an overall response rate of 65 % (24/37). The most frequently immunogenic peptides were MAGE-A3281-295 (49 %) and tyrosinase386-406 (32 %). Responses were not limited to HLA restrictions originally described. Vaccine-associated CD8(+) T cell responses against class I-restricted peptides were observed in 45 % (5/11) of evaluable participants. The 6MHP vaccine induces both CD4(+) and CD8(+) T cell responses against melanoma antigens. CD4(+) T cell responses were detected beyond reported HLA-DR restrictions. Induction of CD8(+) T cell responses suggests epitope spreading and systemic activity mediated at the tumor site.

A Randomized Phase II Trial of Multiepitope Vaccination with Melanoma Peptides for Cytotoxic T Cells and Helper T Cells for Patients with Metastatic Melanoma (E1602)

This multicenter randomized trial was designed to evaluate whether melanoma helper peptides augment cytotoxic T lymphocyte (CTL) responses to a melanoma vaccine and improve clinical outcome in patients with advanced melanoma. One hundred seventy-five patients with measurable stage IV melanoma were enrolled into 4 treatment groups, vaccinated with 12 MHC class I-restricted melanoma peptides to stimulate CTL (12 MP, group A), plus a tetanus peptide (group B), or a mixture of 6 melanoma helper peptides (6 MHP, group C) to stimulate helper T lymphocytes (HTL), or with 6 melanoma helper peptide (6 MHP) alone (group D), in incomplete Freund's adjuvant plus granulocyte macrophage colony-stimulating factor. CTL responses were assessed using an in vitro-stimulated IFN-γ ELIspot assay, and HTL responses were assessed using a proliferation assay. In groups A to D, respectively, CTL response rates to 12 melanoma peptides were 43%, 47%, 28%, and 5%, and HTL response rates to 6 MHP were in 3%, 0%, 40%, and 41%. Best clinical response was partial response in 7 of 148 evaluable patients (4.7%) without significant difference among study arms. Median overall survival (OS) was 11.8 months. Immune response to 6 MHP was significantly associated with both clinical response (P = 0.036) and OS (P = 0.004). Each vaccine regimen was immunogenic, but MHPs did not augment CTL responses to 12 melanoma peptides. The association of survival and immune response to 6 MHP supports further investigation of helper peptide vaccines. For patients with advanced melanoma, multipeptide vaccines should be studied in combination with other potentially synergistic active therapies.

Unexpected T‐cell recognition of an altered peptide ligand is driven by reversed thermodynamics

The molecular basis underlying T-cell recognition of MHC molecules presenting altered peptide ligands is still not well-established. A hierarchy of T-cell activation by MHC class I-restricted altered peptide ligands has been defined using the T-cell receptor P14 specific for H-2D(b) in complex with the immunodominant lymphocytic choriomeningitis virus peptide gp33 (KAVYNFATM). While substitution of tyrosine to phenylalanine (Y4F) or serine (Y4S) abolished recognition by P14, the TCR unexpectedly recognized H-2D(b) in complex with the alanine-substituted semiagonist Y4A, which displayed the most significant structural modification. The observed functional hierarchy gp33 > Y4A > Y4S = Y4F was neither due to higher stabilization capacity nor to differences in structural conformation. However, thermodynamic analysis demonstrated that while recognition of the full agonist H-2D(b) /gp33 was strictly enthalpy driven, recognition of the weak agonist H-2D(b) /Y4A was instead entropy driven with a large reduction in the favorable enthalpy term. The fourfold larger negative heat capacity derived for the interaction of P14 with H-2D(b) /gp33 compared with H-2D(b) /Y4A can possibly be explained by higher water entrapment at the TCR/MHC interface, which is also consistent with the measured opposite entropy contributions for the interactions of P14 with both MHCs. In conclusion, this study demonstrates that P14 makes use of different strategies to adapt to structural modifications in the MHC/peptide complex.

Two Preferentially Expressed Proteins Protect Vascular Endothelial Cells from an Attack by Peptide-Specific CTL

Vascular endothelial cells (EC) are an exposed tissue with intimate contact with circulating Ag-specific CTL. Experimental in vitro and clinical data suggested that endothelial cells present a different repertoire of MHC class I-restricted peptides compared with syngeneic leukocytes or epithelial cells. This endothelial-specific peptide repertoire might protect EC from CTL-mediated cell death. The HLA-A*02-restricted peptide profile of human EC and syngeneic B lymphoblastoid cells was biochemically analyzed and compared. For EC selective peptides, source protein expression, peptide binding affinity, and peptide-HLA-A*02 turnover were measured. The significance of abundant peptide presentation for target cell recognition by immunodominant CTL was tested by small interfering RNA treatment of EC to knock down the source proteins. High amounts of two peptides, PTRF(56-64) and CD59(106-114), were consistently detected in EC. This predominance of two endothelial peptides was explained by cell type-specific source protein expression that compensated for poor HLA-A*02 binding affinity and short half-live of peptide/HLA-A*02 complexes. Knocking down the source proteins containing the abundant endothelial peptide motifs led to a nearly 100-fold increase of surface expression of SMCY(311-319), an immunodominant minor histocompatibility Ag, as detected by cytotoxicity assays using SMCY(311-319)-specific CTL. We conclude that EC express and present preferentially two distinct HLA-A*02-restricted peptides at extraordinary high levels. These abundant self-peptides may protect EC from CTL-mediated lysis by competing for HLA-A*02 binding sites with immunodominant scarcely expressed antigenic peptides.

Global evaluation of the role of ubiquitin in MHC Class I-restricted antigen processing. (106.35)

Abstract The multicatalytic proteasome plays an indispensable role in cellular proteolysis and in the production of most MHC class I-restricted antigenic peptides. Although ubiquitinylation was originally considered to be necessary for directing substrates to proteasomal destruction, growing evidence supports a role for ubiquitin-independent degradation as a substantial portion of intracellular proteolysis. To explore the importance of ubiquitin in MHC class I-restricted antigen processing, we have employed an inducible vaccinia virus system to overexpress wild-type and dominant-negative lysineless forms of ubiquitin (Ub) in mammalian cells. We have previously shown that abrogation of polyubiquitination in this manner inhibited epitope presentation from endoplasmic reticulum-targeted model antigens but had little impact on antigen presentation from cytosolic proteins. We are now seeking to elucidate the selective role of ubiquitin in MHC class I antigen processing by global evaluation of MHC class I-associated peptide display in the presence or absence of polyubiquitination, using mass spectrometric identification of peptides and comparative analysis of parent protein families.

Enhanced immunogenicity of MHC class I-restricted tumor-associated altered peptide ligands

Enhanced immunogenicity of MHC class I-restricted tumor-associated altered peptide ligands

Linkage of Bacterial Protein Synthesis and Presentation of MHC Class I-Restricted Listeria monocytogenes-Derived Antigenic Peptides

The processing and MHC class I-restricted presentation of antigenic peptides derived from the p60 protein of the facultative intracellular bacterium Listeria monocytogenes is tightly linked to bacterial protein synthesis. We used non-linear regression analysis to fit a mathematical model of bacterial antigen processing to a published experimental data set showing the accumulation and decay of p60-derived antigenic peptides in L. monocytogenes-infected cells. Two alternative models equally describe the experimental data. The simulation accounting for a stable and a hypothetical rapidly degraded form of antigen predicts that the antigenic peptides p60 217–225 and p60 449–457 are derived from a putative instable form of p60 with an average intracellular half-life of approximately 3 minutes accounting for approximately 31% of all p60 molecules synthesized. The alternative model predicts that both antigenic peptides are processed from p60 degraded intracellularly with a half-life of 109 min and that antigen processing only occurs as long as bacterial protein synthesis is not inhibited. In order to decide between both models the intracellular accumulation of p60 in infected cells was studied experimentally and compared with model predictions. Inhibition of p60 degradation by the proteasome inhibitor epoxomicin revealed that during the first 3 h post infection approximately 30% of synthesized p60 molecules were degraded. This value is significantly lower than the approximately 50% degradation of p60 that would be expected in the presence of the predicted putative short-lived state of p60 and also fits precisely with the predictions of the alternative model, indicating that the tight connection of bacterial protein biosynthesis and antigen processing and presentation of L. monocyctogenes-derived antigenic peptides is not caused by the presence of a highly instable antigenic substrate.

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

BackgroundMany 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.MethodsTo 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.ResultsWe 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.ConclusionEncapsulating 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.

Long-Term WT1 Peptide Vaccination Over 7 Years for 3 AML Patients with Molecular Relapse

AbstractAbstract 3295WT1 (Wilms' tumor gene 1) encodes a transcription factor, which regulates various types of genes and plays an important role in cell proliferation and differentiation. WT1 is highly expressed in leukemia and various types of solid tumors. In vivo immunization of mice with MHC class I-restricted 9-mer WT1 peptide elicited WT1-specific cytotoxic T lymphocytes (CTLs) and rejected WT1-expressing leukemia cells, demonstrating that WT1 is a tumor rejection antigen. Next, identification of human HLA class I-restricted WT1 peptides was performed, and WT1 235 (235-243 aa) and WT1 126 (126-134 aa) were determined as an HLA-A*2402- or HLA-A*0201- restricted WT1 peptide, respectively, by using in vitro WT1-specific CTL induction assay.On the basis of these fundamental experiments, we performed for the first time a phase I clinical trial of WT1 peptide immunotherapy with the approval of our ethical committee. A total of 26 patients with acute myeloid leukemia (AML), myelodysplastic syndrome, breast or lung cancer were intradermally injected with a HLA-A*2402-restricted natural or modified 9-mer WT1 peptide emulsified with Montanide ISA51 adjuvant at 0.3, 1.0 or 3.0 mg at 2-week intervals. As shown in Table1, 12 AML patients were WT1-vaccinated and eight of the 12 AML patients were evaluable for clinical effect because of the existence of minimal residual disease (MRD) assessed by WT1 mRNA assay. Since four of the eight patients had obvious clinical response with the decrease in WT1 mRNA within three injections of WT1 vaccine, WT1 vaccination was repeated for them afterward (in the case that clinical response was not obvious within three injections of WT1 vaccine, WT1 vaccination was discontinued). However, one patient (No. 20) had re-increase in WT1 mRNA and WT1 vaccination was discontinued. The remaining three patients (Nos. 21, 23 and 24) have been repeatedly receiving WT1 vaccination (intervals were changed from 2 weeks to one month) over 7 years until now. WT1 mRNA levels, which directly reflected the amount of leukemic blast cells, were abnormally high and 102-103 copies/mg RNA in PB (normal level is < 50 copies/mg RNA) before WT1 vaccination in these three AML patients, showing that the patients were at molecular relapse with MRD. In nos. 21 and 23 patients, a decrease and increase in WT1 mRNA levels were repeated during early stages of WT1 vaccination. However, afterward, WT1 mRNA levels gradually decreased and reached normal level approximately three and a half years after the beginning of WT1 vaccination and have been maintained at normal level until now. In patient no. 24, high levels of WT1 mRNA (near 103 copies) gradually decreased by repeated WT1 vaccination and returned to normal level approximately 5 years after the beginning of WT1 vaccination although it was much delayed. Thus, these three patients had achieved continuous complete remission regardless of high risk for clinical relapse. [Display omitted] WT1-specific immune responses were evaluated by WT1 tetramer assay. Frequencies of WT1-specific cytotoxic T lymphocytes (CTLs) (WT1 tetramer+ CD8+ T cells) in the patients were already higher before WT1 vaccination, compared to those in healthy volunteers, which was a frequent phenomenon in WT1-expressing tumor-bearing patients, but the WT1-specific CTLs were a IFN-g− inactivated form. After WT1 vaccination, a IFN- g+ activated from of WT1-specific CTLs appeared and was maintained until now.No adverse effects except local erythema and eruption at the injection sites of WT1 vaccine were observed regardless of repeated long-term WT1 vaccination over 7 years. These finding indicated that WT1-specific CTLs could attack WT1-expressing leukemic blast cells but ignored WT1-expressing normal cells such as podocytes of kidney and progenitor cells of various types of organs.In conclusion, we presented here the first report of promising clinical outcome of very long-term WT1 vaccination for AML patients with high risk for relapse. WT1 peptide immunotherapy should have good prospects as a cure-oriented therapy for AML and could be the first choice of the treatments for AML patients who had still MRD after induction chemotherapy, especially for elder patients who were intolerable to intensive chemotherapy. WT1 peptide immunotherapy may be also a better choice of treatments for AML patients who have high risk for relapse but are intolerable to allogeneic hematopoietic stem cell transplantation. Disclosures:No relevant conflicts of interest to declare.

Bryostatin-I: A dendritic cell stimulator for chemokines induction and a promising adjuvant for a peptide based cancer vaccine

Bryostatin-1 (Bryo-1), a PKC modulator, was previously shown to activate monocytes and lymphocytes to produce cytokines. In this report, we investigated the adjuvanticity of Bryo-1 both in vitro and in vivo. First, Bryo-1 was found to induce the release of CCL2 and CCL3 from mouse bone marrow-derived dendritic cells (BMDC) in a dose-dependent manner. As little as 0.1 nM Bryo-I induced release of chemokines from BMDC and the maximal induction could be achieved at 5–10 nM. Both PKC and ERK inhibitors attenuated the release of CCL2 and CCL3. Consistently, Western blot indicated that Bryo-I activated ERK in a dose- and time-dependent manner. Experiments with the NF-κB inhibitor, MG-132, demonstrated that NF-κB was involved in the induction of CCL2 but not CCL3. Because chemokines have been demonstrated to have profound effects on immune reactions by regulating the trafficking of DC and other lymphocytes into lymphoid organs, Bryo-I was tested as an adjuvant in an E7 peptide (MHC class I-restricted peptide epitope derived from human papillomavirus (HPV) 16 E7 protein)-based cancer vaccine. Mice immunized by s.c. injection with Bryo-I/E7 had enlarged draining lymph nodes and showed an antigen specific T-cell response demonstrated by the release of IFN-γ from isolated splenocytes and in vivo CTL activity. Finally, immunization with Bryo-I/E7 totally prevented the E7-expressing TC-1 tumor growth in mice. In conclusion, for the first time, we demonstrated that Bryo-I induced chemokine release from dendritic cell and was an effective adjuvant for peptide cancer vaccine.

CpG‐enhanced CD8+ T‐cell responses to peptide immunization are severely inhibited by B cells

Synthetic peptides encoding protective pathogen-derived epitopes represent--in principle--an ideal approach to T-cell vaccination. Empirically, however, these strategies have not been successful. In the current study, we profiled the early activation of CD8+ T cells by MHC class I-restricted peptide immunization to better understand the biology of this response. We found that CD8+ T cells proliferated robustly in response to low doses of short synthetic peptides in PBS, but failed to acquire effector function or form memory populations in the absence of the TLR ligand CpG. CpG was unique among TLR ligands in its ability to enhance the response to peptide and its adjuvant effects had strict temporal requirements. Interestingly, CpG treatment modulated T-cell expression of the surface receptors PD-1 and CD25, providing insight into its possible adjuvant mechanism. The effects of CpG on peptide immunization were dramatically enhanced in the absence of B cells, demonstrating a unique system of regulation of T-cell responses by these lymphocytes. The results reported here provide insight into the complex response to a simple vaccination regimen, as well as a framework for a rational peptide-based vaccine design to both exploit and overcome targeted aspects of the immune response.