Computational prediction and experimental assessment of an HLA-A*0201-restricted cytotoxic T lymphocyte epitope from neutral endopeptidase

Protective CD8+ T-cell response against Hantaan virus infection induced by immunization with designed linear multi-epitope peptides in HLA-A2.1/Kb transgenic mice

Background

An effective vaccine that prevents disease caused by hantaviruses is a global public health priority, but up to now, no vaccine has been approved for worldwide use. Therefore, novel vaccines with high prophylaxis efficacy are urgently needed.

Methods

Herein, we designed and synthesized Hantaan virus (HTNV) linear multi-epitope peptide consisting of HLA-A*02-restricted HTNV cytotoxic T cell (CTL) epitope and pan HLA-DR-binding epitope (PADRE), and evaluated the immunogenicity, as well as effectiveness, of multi-epitope peptides in HLA-A2.1/K^b transgenic mice with interferon (IFN)-γ enzyme-linked immunospot assay, cytotoxic mediator detection, proliferation assay and HTNV-challenge test.

Results

The results showed that a much higher frequency of specific IFN-γ-secreting CTLs, high levels of granzyme B production, and a strong proliferation capacity of specific CTLs were observed in splenocytes of mice immunized with multi-epitope peptide than in those of a single CTL epitope. Moreover, pre-immunization of multi-epitope peptide could reduce the levels of HTNV RNA loads in the liver, spleen and kidneys of mice, indicating that specific CTL responses induced by multi-epitope peptide could reduce HTNV RNA loads in vivo.

Conclusions

This study may provide an important foundation for the development of novel peptide vaccines for HTNV prophylaxis.

A novel multi-epitope vaccine from MMSA-1 and DKK1 for multiple myeloma immunotherapy

The identification of novel tumour-associated antigens is urgently needed to improve the efficacy of immunotherapy for multiple myeloma (MM). In this study, we identified a membrane protein MMSA-1 (multiple myeloma special antigen-1) that was specifically expressed in MM and exhibited significantly positive correlation with MM. We then identified HLA-A*0201-restricted MMSA-1 epitopes and tested their cytotoxic T lymphocyte (CTL) response. The MMSA-1 epitope SLSLLTIYV vaccine was shown to induce an obvious CTL response in vitro. To improve the immunotherapy, we constructed a multi-epitope peptide vaccine by combining epitopes derived from MMSA-1 and Dickkopf-1 (DKK1). The effector T cells induced by multi-epitope peptide vaccine-loaded dendritic cells lysed U266 cells more effectively than MMSA-1/DKK1 single-epitope vaccine. In myeloma-bearing severe combined immunodeficient mice, the multi-epitope vaccine improved the survival rate significantly compared with single-epitope vaccine. Consistently, multi-epitope vaccine decreased the tumour volume greatly and alleviated bone destruction. The frequencies of CD4⁺ and CD8⁺ T cells was significantly increased in mouse blood induced by the multi-epitope vaccine, indicating that it inhibits myeloma growth by changing T cell subsets and alleviating immune paralysis. This study identified a novel peptide from MMSA-1 and the multi-epitope vaccine will be used to establish appropriate individualized therapy for MM.

Structure and Function of HLA-A*02-Restricted Hantaan Virus Cytotoxic T-Cell Epitope That Mediates Effective Protective Responses in HLA-A2.1/K(b) Transgenic Mice

Hantavirus infections cause severe emerging diseases in humans and are associated with high mortality rates; therefore, they have become a global public health concern. Our previous study showed that the CD8(+) T-cell epitope aa129-aa137 (FVVPILLKA, FA9) of the Hantaan virus (HTNV) nucleoprotein (NP), restricted by human leukocyte antigen (HLA)-A*02, induced specific CD8(+) T-cell responses that controlled HTNV infection in humans. However, the in vivo immunogenicity of peptide FA9 and the effect of FA9-specific CD8(+) T-cell immunity remain unclear. Here, based on a detailed structural analysis of the peptide FA9/HLA-A*0201 complex and functional investigations using HLA-A2.1/K(b) transgenic (Tg) mice, we found that the overall structure of the peptide FA9/HLA-A*0201 complex displayed a typical MHC class I fold with Val2 and Ala9 as primary anchor residues and Val3 and Leu7 as secondary anchor residues that allow peptide FA9 to bind tightly with an HLA-A*0201 molecule. Residues in the middle portion of peptide FA9 extruding out of the binding groove may be the sites that allow for recognition by T-cell receptors. Immunization with peptide FA9 in HLA-A2.1/K(b) Tg mice induced FA9-specific cytotoxic T-cell responses characterized by the induction of high expression levels of interferon-γ, tumor necrosis factor-α, granzyme B, and CD107a. In an HTNV challenge trial, significant reductions in the levels of both the antigens and the HTNV RNA loads were observed in the liver, spleen, and kidneys of Tg mice pre-vaccinated with peptide FA9. Thus, our findings highlight the ability of HTNV epitope-specific CD8(+) T-cell immunity to control HTNV and support the possibility that the HTNV-NP FA9 peptide, naturally processed in vivo in an HLA-A*02-restriction manner, may be a good candidate for the development HTNV peptide vaccines.

Major histocompatibility complex linked databases and prediction tools for designing vaccines

Presently, the major histocompatibility complex (MHC) is receiving considerable interest owing to its remarkable role in antigen presentation and vaccine design. The specific databases and prediction approaches related to MHC sequences, structures and binding/nonbinding peptides have been aggressively developed in the past two decades with their own benchmarks and standards. Before using these databases and prediction tools, it is important to analyze why and how the tools are constructed along with their strengths and limitations. The current review presents insights into web-based immunological bioinformatics resources that include searchable databases of MHC sequences, epitopes and prediction tools that are linked to MHC based vaccine design, including population coverage analysis. In T cell epitope forecasts, MHC class I binding predictions are very accurate for most of the identified MHC alleles. However, these predictions could be further improved by integrating proteasome cleavage (in conjugation with transporter associated with antigen processing (TAP) binding) prediction, as well as T cell receptor binding prediction. On the other hand, MHC class II restricted epitope predictions display relatively low accuracy compared to MHC class I. To date, pan-specific tools have been developed, which not only deliver significantly improved predictions in terms of accuracy, but also in terms of the coverage of MHC alleles and supertypes. In addition, structural modeling and simulation systems for peptide-MHC complexes enable the molecular-level investigation of immune processes. Finally, epitope prediction tools, and their assessments and guidelines, have been presented to immunologist for the design of novel vaccine and diagnostics.

Prediction and identification of HLA-A*0201-restricted epitopes from leukemia-associated protein MLAA-22 which elicit cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) play a critical role in the control of leukemia. However, few effective CTL epitopes have been identified to date yet. We previously reported that MLAA-22, a protein composed of 631 amino acid residues, is a novel acute myeloid leukemia (AML)-associated antigen. In the present study, ten high-score 9-mer peptides, which were selected from MLAA-22 by using ProPred1 and SYFPEITHI bioinformatics tools, were screened to identify HLA-A*0201-restricted-specific CTL epitopes. Monocyte-derived dendritic cells were generated in vitro to be used as antigen-presenting cells for the induction of CTLs. We found that peptide MLAA-22(379-387) (LLPNAIYKV) exhibited the highest binding affinity to HLA-A*0201 among all peptide candidates in the peptide-T2 binding assay. The percentage of positive T2 cells treated with MLAA-22(379-387) was about 96.3%, which is even higher than that of the positive control peptide CML28(173-181) (95.1%). MLAA-22(379-387)-induced CTLs showed the most significant cytotoxic activity and apparent killing effects on the cell lines including THP-1 (human acute monocytic leukemia), A549, T2, U937, and MCF-7, and the specific lysis ratios were 83.8, 32.6, 64.4, 64.4, and 32.6%, respectively, when the effector to target ratio (E/T) was 20:1. Specific lysis (%) of MLAA1 was significantly increased (P < 0.05, P < 0.001, respectively) in THP-1 cell than those in other cancer cell lines and were 28.5, 67.8, and 83.8% at ratio 5:1, 10:1, and 20:1, respectively. Hence, MLAA-22(379-387) is a potential tumor-associated antigen target for AML immunotherapy.