Ovalbumin lipid core peptide vaccines and their CD4 and CD8 T cell responses

The lipid core peptide (LCP) system has successfully been used in development of peptide-based vaccines against cancer and infectious diseases (such as group A streptococcal infection). CD8⁺ T cells are important targets for vaccines, however developing a vaccine that activates long-lasting immunity has proven challenging. The ability of LCP vaccines to activate antigen-specific CD8⁺ and/or CD4⁺ T cell responses was tested using compounds that contained two or four copies of OVA_257–264 and/or OVA_323–339 peptides conjugated to LCP, which are recognised by OTI (CD8⁺ specific) and OTII (CD4⁺ specific) T cells, respectively. The LCP–ovalbumin vaccines developed in this study were synthesised in 30% yields and showed no significant haemolytic effect on red blood cells (below 4% haemolysis when tested with compounds at up to 100 μM concentrations). Promising in vivo data in mice suggested that this LCP–ovalbumin vaccine system could act as a novel and potent vehicle for the stimulation of robust antigen-specific CD8⁺ T cell responses.     

T cell responses to bluetongue virus are directed against multiple and identical CD4+ and CD8+ T cell epitopes from the VP7 core protein in mouse and sheep

Bluetongue virus (BTV), an economically important orbivirus of the Reoviridae family, is a non-enveloped, dsRNA virus that causes a haemorrhagic disease mainly in sheep, but little is known of the cellular immunity elicited against BTV. We observed that vaccination of interferon type I-deficient mice (IFNAR^(−/−)), or inoculation of the wild type C57BL/6 strain with BTV-8, induced a strong T cell response. Therefore, we proceeded to identify some of the T cell epitopes targeted by the immune system. We selected, using H-2^b-binding predictive algorithms, 3 major histocompatibility complex (MHC)-class II-binding peptides and 7 MHC-class I binding peptides from the BTV-8 core protein VP7, as potential T cell epitopes. Peptide binding assays confirmed that all 7 MHC-class I predicted peptides bound MHC-class I molecules. Three MHC-class I and 2 MHC-class II binding peptide consistently elicited peptide-specific IFN-γ production (as measured by ELISPOT assays) in splenocytes from C57BL/6 BTV-8-inoculated mice and IFNAR^(−/−)-vaccinated mice. The functionality of these T cells was confirmed by proliferation and cytotoxicity assays. Flow cytometry analysis demonstrated that CD8⁺ T cells responded to MHC-class I binding peptides and CD4⁺ T cells to MHC-class II binding peptides. Importantly, these 5 epitopes were also able to induced IFN-γ production in sheep inoculated with BTV-8. Taken together, these data demonstrate the activation of BTV-specific T cells during infection and vaccination. The characterisation of these novel T cell epitopes may also provide an opportunity to develop DIVA-compliant vaccination approach to BTV encompassing a broad-spectrum of serotypes.     

Immunization of woodchucks (Marmota monax) with hepatitis delta virus DNA vaccine

We investigated the DNA immunization approach in order to induce a protective immune response against hepatitis delta virus (HDV) superinfection of chronically woodchuck hepatitis virus (WHV) infected woodchucks. The animals were immunized with an expression vector encoding HDAg by gene gun. T cell and humoral immune responses induced by this protocol were determined and compared with those induced by HDAg immunization using a CpG oligonucleotide as an adjuvant. After immunization the woodchucks were challenged with 10⁶ genome equivalents of HDV. The protein immunization with HDAg induced good humoral and T helper cell responses in the woodchucks, but did not protect them from HDV superinfection. The DNA immunized woodchucks were also not protected from HDV superinfection, however, the course of infection was modified: HDV viremia occurred later, the typical fluctuation of the HDV RNA titer with several peaks was absent, and antibodies to HDV were not detectable.     

Hepatitis B virus (HBV)-derived DRB1*0101-restricted CD4 T-cell epitopes help in the development of HBV-specific CD8+ T cells in vivo

We previously identified two HLA-DRB1*0101-restricted epitopes in hepatitis B virus (HBV) X protein (HBx) and in HBV envelope proteins (preS2). To evaluated their help in the development of CD8+ T-cell responses, mice transgenic for human class I and class II HLA molecules were immunized with HBV-T helper constructs. The preS2 epitope favored a well-balanced response with CD4+ and CD8+ T cells producing IFN-γ, IL-2 and TNF-α. The response was focused on CD8+ T cells with the HBx epitope. Fine characterization of helper activities may meet clinical needs in terms of enhancing the potency of preventive or therapeutic polyepitope vaccines.     

CD8 T cell response in HLA-A*0201 transgenic mice is elicited by epitopes from SARS-CoV S protein

Cytotoxic CD8⁺ T lymphocytes (CTLs) play an important role in antiviral immunity. Several human HLA-A*0201 restricted CTL epitopes of severe acute respiratory syndrome (SARS) spike (S) protein have been identified in HLA-A*0201 transgenic (Tg) mice, but the mechanisms and properties of immune responses are still not well understood. In this study, HLA-A*0201 Tg mice were primed intramuscularly with SARS S DNA and boosted subcutaneously with HLA-A*0201 restricted peptides. The lymphocytes from draining lymph nodes, spleens and lungs were stimulated with the cognate peptides. Three different methods (ELISA, ELISPOT and FACS) were used to evaluate the immune responses during short and long periods of time after immunization. Results showed that peptide-specific CD8⁺ T cells secreted IFN-γ, TNF-α and IL-2 and expressed CD107a/b on cell surface. IFN-γ⁺CD8⁺ T cells and CD107a/b⁺CD8⁺ T cells distributed throughout the lymphoid and non-lymphoid tissues, but the frequency of peptide-specific CD8⁺ T cells was higher in lungs than in spleens and lymph nodes. The phenotype of the CD8⁺ T cells was characterized based on the expression of IFN-γ. Most of the HLA-A*0201 restricted peptide-specific CD8⁺ T cells represented a memory subset with CD45RB^high and CD62L^low. Taken together, these data demonstrate that immunization with SARS S DNA and HLA-A*0201 restricted peptides can elicit antigen-specific CD8⁺ T cell immune responses which may have a significant implication in the long-term protection. We provide novel information in cellular immune responses of SARS S antigen-specific CD8⁺ T cells, which are important in the development of vaccine against SARS-CoV infection.     

Oral administration of a chimeric Hepatitis B Virus S/preS1 antigen produced in lettuce triggers infection neutralizing antibodies in mice

Hepatitis B Virus (HBV) infection can be prevented by vaccination. Vaccines containing the small (S) envelope protein are currently used in universal vaccination programs and achieve protective immune response in more than 90% of recipients. However, new vaccination strategies are necessary for successful immunization of the remaining non- or low-responders. We have previously characterized a novel HBV chimeric antigen, which combines neutralization epitopes of the S and the preS1 domain of the large (L) envelope protein (genotype D). The S/preS1^21–47 chimera produced in mammalian cells and Nicotiana benthamiana plants, induced a significantly stronger immune response in parenterally vaccinated mice than the S protein. Here we describe the transient expression of the S/preS1^21–47 antigen in an edible plant, Lactuca sativa, for potential development of an oral HBV vaccine. Our study shows that oral administration of adjuvant-free Lactuca sativa expressing the S/preS1^21–47 antigen, three times, at 1 μg/dose, was sufficient to trigger a humoral immune response in mice. Importantly, the elicited antibodies were able to neutralize HBV infection in an NTCP-expressing infection system (HepG2-NTCP cell line) more efficiently than those induced by mice fed on Lactuca sativa expressing the S protein. These results support the S/preS1^21–47 antigen as a promising candidate for future development as an edible HBV vaccine.     

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

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

A tumor-specific neoepitope expressed in homologous/self or heterologous/viral antigens induced comparable effector CD8+ T-cell responses by DNA vaccination

Somatic mutations in tumors often generate neoproteins that contain MHC-I-binding neoepitopes. Little is known if and how efficient tumor-specific neoantigens activate CD8⁺ T cells. Here, we asked whether a de novo generated neoepitope, encoded either within an otherwise conserved and ubiquitously expressed self-antigen or in a chimeric HBV core antigen expression platform, providing heterologous helper functions, induces CD8⁺ T cells in C57Bl/6J mice by DNA immunization. For it, we chose an established D^b/Sp_{244-252/R251H} neoepitope generated in the murine Endophilin-B2/SH3GLB2 (EndoB2-Sp) protein by a single amino acid exchange. We showed that a single injection of EndoB2-Sp expression vectors efficiently primed dimer/pentamer⁺, IFN-γ⁺ and cytolytic D^b/Sp_{244-252/R251H}-specific effector CD8⁺ T cells in C57Bl/6J mice. Priming of D^b/Sp_{244-252/R251H}-specific CD8⁺ T cells proceeded independent from CD4⁺ T-cell help in MHC-II-deficient Aα^-/- mice. As compared to the homologous EndoB2-Sp vaccine, the selective expression of the D^b/Sp_{244-252/R251H} neoepitope in chimeric particle-forming and assembly-deficient HBV core antigens induced comparable frequencies D^b/Sp_{244-252/R251H}-specific CD8⁺ T cells with the same cytolytic effector phenotype. The homologous EndoB2 carrier, but not the nine-residue neoepitope presented on chimeric HBV core particles, induced EndoB2-specific IgG antibody responses. The HBV core expression platform is thus an attractive option to selectively induce neoepitope-specific effector CD8⁺ T cells by DNA vaccination. These novel findings have practical implications for the design of heterologous/self and heterologous/viral cancer vaccines that prime and/or activate neoepitope-specific CD8⁺ T cells.     

A novel therapeutic hepatitis B vaccine induces cellular and humoral immune responses and breaks tolerance in hepatitis B virus (HBV) transgenic mice

Therapeutic vaccines are currently being developed for chronic hepatitis B and C. As an alternative to long-term antiviral treatment or to support only partially effective therapy, they should activate the patient's immune system effectively to fight and finally control the virus. A paradigm of therapeutic vaccination is the potent induction of T-cell responses against key viral antigens – besides activation of a humoral immune response. We have evaluated the potential of a novel vaccine formulation comprising particulate hepatitis B surface (HBsAg) and core antigen (HBcAg), and the saponin-based ISCOMATRIX™ adjuvant for its ability to stimulate T and B cell responses in C57BL/6 mice and its ability to break tolerance in syngeneic HBV transgenic (HBVtg) mice. In C57BL/6 mice, the vaccine induced multifunctional HBsAg- and HBcAg-specific CD8+ T cells detected by staining for IFNγ, TNFα and IL-2, as well as high antibody titers against both antigens. Vaccination of HBVtg animals induced potent HBsAg- and HBcAg-specific CD8+ T-cell responses in spleens and HBcAg-specific CD8+ T-cell responses in livers as well as anti-HBs seroconversion two weeks post injection. Vaccination further reduced HBcAg expression in livers of HBVtg mice without causing liver damage.     

Identification of two novel immunodominant UreB CD4 T cell epitopes in Helicobacter pylori infected subjects

An epitope-based vaccine is a promising option for treating Helicobacter pylori (H. pylori) infection. Epitope mapping is the first step in designing an epitope-based vaccine. A pivotal role of CD4⁺ T cells in protection against H. pylori has been accepted, but few Th epitopes have been identified. In this study, two novel UreB CD4⁺ T cell epitopes were identified using PBMCs obtained from two H. pylori infected subjects. We determined the restriction molecules by antibody blocking and used various Epstein–Barr virus-transformed B lymphocyte cell lines (BLCLs) with different HLA alleles as APCs to present peptides to CD4⁺ T cells. These epitopes were DRB1*1404-restricted UreB_373–385 and DRB1*0803-restricted UreB_438–452. The T cells specific to these epitopes not only recognized autologous DCs loaded with recombinant UreB but also those pulsed with H. pylori whole cell lysates, suggesting that these epitope peptides are naturally processed. These epitopes have important value for designing an effective H. pylori vaccine.     

Levamisole is a potential facilitator for the activation of Th1 responses of the subunit HBV vaccination

Chemical compounds activating innate responses may present potential adjuvants for the vaccine development. Levamisole (LMS), demonstrated as a potent adjuvant for DNA and viral killed vaccines in our previous studies, may activate such responses. To confirm this notion, LMS combined with the recombinant HBsAg (rHBsAg) was investigated. Compared to the vaccination with rHBsAg alone, LMS could up-regulate the expressions of TLR7&8, MyD88, IRF7 and their downstream pro-inflammatory cytokines including IFN-α and TNF-α, which promote DCs activation. Strikingly, we find that the combination of LMS and alum adjuvant synergistically enhances immunogenicity of rHBsAg and leads to a robust cell-mediated response demonstrated by the higher level of IgG2a/IgG1, T cell proliferation, and importantly, a high level of antigen-specific CTL and IFN-γ production within these activated CD8⁺ T cells. The achieved robust responses are at a comparative level with CpG + alum used as a positive control adjuvant in mice. The combination of LMS + alum with rHBsAg may provide a cost-effective, safe, and effective therapy to treat those individuals chronically infected by HBV, since antigen-specific cellular immunity is implicated for the clearance of HBV chronic infection.     

乙肝病毒前S基因变异与乙肝肝硬化的相关性研究

目的 探讨乙型肝炎病毒(hepatitis B virus,HBV)前S基因(preS)变异与HBV感染后肝硬化发生的相关性。方法 采用病例对照研究设计,对50例慢性乙型肝炎(chronic hepatitis B,CHB)患者和67例乙肝肝硬化(liver cirrhosis,LC)患者的血清HBVPreS基因进行扩增和测序,应用MEGA7软件进行序列比对,使用SPSS 16.0统计软件对PreS基因热点变异与LC的相关性进行单因素和多因素分析。结果 单因素分析结果表明,HBV基因组PreS区T3116m(χ²=8.470,P=0.004)、A49m(χ²=4.939,P=0.026)、T53m(χ²=6.683,P=0.010)、A109m(χ²=5.868,P=0.015)及PreS缺失变异(χ²=12.154,P=0.000)与LC发生显著相关。PreS缺失变异在失代偿期LC患者中的频率(63.16%)显著高于代偿期LC患者(31.03%)(P=0.007)。多因素分析结果表明,年龄越大(OR=1.07,95%CI:1.02~1.11)、T3116m(OR=4.18,95%CI:1.39~12.61)、PreS缺失变异(OR=7.20,95%CI:2.09~24.80)是LC的独立危险因素。结论 HBV PreS缺失变异与T3116m是乙型肝炎患者进展至LC的危险变异,还需要大样本人群进行验证。     

Prevention of infection of influenza virus in DQ6 mice, a human model, by a peptide vaccine prepared according to the cassette theory

We proposed a strategy (cassette theory) in which non-binding peptides for murine major histocompatibility complex (MHC) class II molecules are introduced into a MHC-binding component to render the resultant hybrid peptides bound to the MHC and thus immunogenic in animals carrying the relevant MHC. It was shown that 46F/HA127-133/54A(18mer) peptide which was prepared by introducing hemagglutinin (HA)127-133 of influenza virus into the H-2Ab binding component induced significant T cell responses and antibodies (Ab) specific for HA127-133 in H-2Ab mice. Further we found that the H-2Ab binding component had a supermotif for human class II molecules (i.e. HLA-DQ6). In the present study, a new peptide vaccine, H3-H3, was prepared by combining 46F/HA127-133/54A(18mer) as a carrier and HA127-133 attached to the C terminus of 46F/HA127-133/54A(18mer) as a hapten and the effect of vaccine was examined in DQ6 mice which carry HLA-DQ6 alone as MHC class II molecules and thus may be regarded as a model of the DQ6 positive individuals. Since 46F/HA127-133/ 54A(18mer) induced merely Ab against HA127-133, it was assumed that H3-H3 induced mainly HA127-133 specific Ab in DQ6 mice without undesirable Ab production against the carrier. Indeed, H3-H3 elicited T cell responses and induced HA127-133 specific Ab in DQ6 mice. Furthermore, administration of H3-H3 inhibited growth of influenza virus until 9 weeks after the last immunization in DQ6 mice.     

Establishment of animal models to analyze the kinetics and distribution of human tumor antigen-specific CD8 T cells

Many patients develop tumor antigen-specific T cell responses detectable in peripheral blood mononuclear cells (PBMCs) following cancer vaccine. However, measurable tumor regression is observed in a limited number of patients receiving cancer vaccines. There is a need to re-evaluate systemically the immune responses induced by cancer vaccines. Here, we established animal models targeting two human cancer/testis antigens, NY-ESO-1 and MAGE-A4. Cytotoxic T lymphocyte (CTL) epitopes of these antigens were investigated by immunizing BALB/c mice with plasmids encoding the entire sequences of NY-ESO-1 or MAGE-A4. CD8⁺ T cells specific for NY-ESO-1 or MAGE-A4 were able to be detected by ELISPOT assays using antigen presenting cells pulsed with overlapping peptides covering the whole protein, indicating the high immunogenicity of these antigens in mice. Truncation of these peptides revealed that NY-ESO-1-specific CD8⁺ T cells recognized D^d-restricted 8mer peptides, NY-ESO-1_81-88. MAGE-A4-specific CD8⁺ T cells recognized D^d-restricted 9mer peptides, MAGE-A4_265-273. MHC/peptide tetramers allowed us to analyze the kinetics and distribution of the antigen-specific immune responses, and we found that stronger antigen-specific CD8⁺ T cell responses were required for more effective anti-tumor activity. Taken together, these animal models are valuable for evaluation of immune responses and optimization of the efficacy of cancer vaccines.     

A T cell epitope-based vaccine protects against chlamydial infection in HLA-DR4 transgenic mice

Vaccination with recombinant chlamydial protease-like activity factor (rCPAF) has been shown to provide robust protection against genital Chlamydia infection. Adoptive transfer of IFN-γ competent CPAF-specific CD4⁺ T cells was sufficient to induce early resolution of chlamydial infection and reduction of subsequent pathology in recipient IFN-γ-deficient mice indicating the importance of IFN-γ secreting CD4⁺ T cells in host defense against Chlamydia. In this study, we identify CD4⁺ T cell reactive CPAF epitopes and characterize the activation of epitope-specific CD4⁺ T cells following antigen immunization or Chlamydia challenge. Using the HLA-DR4 (HLA-DRB1*0401) transgenic mouse for screening overlapping peptides that induced T cell IFN-γ production, we identified at least 5 CPAF T cell epitopes presented by the HLA-DR4 complex. Immunization of HLA-DR4 transgenic mice with a rCPAFep fusion protein containing these 5 epitopes induced a robust cell-mediated immune response and significantly accelerated the resolution of genital and pulmonary Chlamydia infection. rCPAFep vaccination induced CPAF-specific CD4⁺ T cells in the spleen were detected using HLA-DR4/CPAF-epitope tetramers. Additionally, CPAF-specific CD4⁺ clones could be detected in the mouse spleen following Chlamydia muridarum and a human Chlamydia trachomatis strain challenge using these novel tetramers. These results provide the first direct evidence that a novel CPAF epitope vaccine can provide protection and that HLA-DR4/CPAF-epitope tetramers can detect CPAF epitope-specific CD4⁺ T cells in HLA-DR4 mice following C. muridarum or C. trachomatis infection. Such tetramers could be a useful tool for monitoring CD4⁺ T cells in immunity to Chlamydia infection and in developing epitope-based human vaccines using the murine model.     

Delivery of antigenic candidates by a DNA/MVA heterologous approach elicits effector CD8T cell mediated immunity against Trypanosoma cruzi

In this study, we have characterized the immune mechanisms elicited by antigenic candidates, TcG2 and TcG4, delivered by a DNA-prime/MVA-boost approach, and evaluated the host responses to Trypanosoma cruzi infection in C57BL/6 mice. Immunization of mice with antigenic candidates elicited antigen-specific, high-avidity, trypanolytic antibody response (IgG2b > IgG1) and CD8⁺T cells that exhibited type-1 cytolytic effector (CD8⁺CD107a⁺IFN-γ⁺Perforin⁺) phenotype. The extent of TcG2-dependent type 1 B and T cell immunity was higher than that noted in TcG4-immunized mice, and expanded accordingly in response to challenge infection with T. cruzi. The progression of chronic phase in immunized mice was associated with persistence of IgGs, 55–90% reduction in the frequency of proinflammatory (IFN-γ⁺ or TNF-α⁺) CD8⁺T cells, and an increase or emergence of immunoregulatory (IL-10⁺) CD4/CD8 T cells. The tissue parasitism, infiltration of inflammatory infiltrate, parasite persistence, and fibrosis were decreased by 82–92% in heart and skeletal muscle of immunized/chronically infected mice. Control mice exhibited a significantly low antibody response, consistent activation of effector CD8⁺T cells dominated by pro-inflammatory phenotype and mixed cytokine profile (IFN-γ + TNF-α > IL-4 + IL-10), parasite persistence and pathologic damage in chagasic hearts. We conclude that delivery of TcG2 or TcG4 by DNA-rMVA approach elicits effective antibody and CD8⁺T cell mediated immunity against T. cruzi and Chagas disease. The emergence of type 2 cytokine and T cell response in chronic phase was indicative of prevention of clinical disease.     

Impaired hepatitis B vaccine responses during chronic hepatitis C infection: involvement of the PD-1 pathway in regulating CD4(+) T cell responses

Vaccination for hepatitis B virus (HBV) in the setting of hepatitis C virus (HCV) infection is recommended, but responses to vaccination are blunted when compared to uninfected populations. The mechanism for this failure of immune response in HCV-infected subjects remains unknown but is thought to be a result of lymphocyte dysfunction during chronic viral infection. We have recently demonstrated that PD-1, a novel negative immunomodulator for T cell receptor (TCR) signaling, is involved in T and B lymphocyte dysregulation during chronic HCV infection. In this report, we further investigated the role of the PD-1 pathway in regulation of CD4⁺ T cell responses to HBV vaccination in HCV-infected individuals. In a prospective HCV infected cohort, a poor response rate to HBV vaccination as assayed by seroconversion was observed in HCV-infected subjects (53%), while a high response rate was observed in healthy or spontaneously HCV-resolved individuals (94%). CD4⁺ T cell responses to ex vivo stimulations of anti-CD3/CD28 antibodies or hepatitis B surface antigen (HBsAg) were found to be lower in HBV vaccine non-responders compared to those responders in HCV-infected individuals who had received a series of HBV immunizations. PD-1 expression on CD4⁺ T cells was detected at relatively higher levels in these HBV vaccine non-responders than those who responded, and this was inversely associated with the cell activation status. Importantly, blocking the PD-1 pathway improved T cell activation and proliferation in response to ex vivo HBsAg or anti-CD3/CD28 stimulation in HBV vaccine non-responders. These results suggest that PD-1 signaling may be involved in impairing CD4⁺ T cell responses to HBV vaccination in subjects with HCV infection, and raise the possibility that blocking this negative signaling pathway might improve success rates of immunization in the setting of chronic viral infection.     

酶联免疫斑点法检测乙型肝炎病毒感染者抗原表位特异性细胞毒性T淋巴细胞

目的 通过观察乙型肝炎病毒(HBV)特异性细胞毒性T细胞(CTL)抗原表位肽刺激外周血单个核细胞(PBMC)产生γ干扰素(IFN-γ)的能力,分析不同类型HBV感染人群特异性CTL免疫应答差异.方法 合成4条人类白细胞抗原(HLA)-A2限制性HBV特异性CTL抗原表位肽[分别为多聚酶P的575-583序列FLLSLGIHL(Tp),HBsAg28-39序列IPQSLDSWVCTSL(Tel),HBsAg183-191序列FLLTRILTI(Te2)和HBcAg18-27序列FLPSDFFPSV(Tc)].流式细胞术鉴定HLA基因表型.用合成的CTL表位肽分别刺激慢性乙型肝炎组(CHB)、慢性乙型重型肝炎组(CSH),既往HBV感染者(N1)组和健康献血员(N2)的PBMC,采用酶联免疫斑点法(ELISPOT)检测分泌IFN-γ的CTL细胞的频率.结果 (1)HLA-A2基因分布频率:44例CHB组为45.5%(20/44),18例CSH组为55.6%(10/18),10例N1组为60%(6/10),10例N2组全部选择以往研究已确定的HLA-A2阳性者.(2)ELISPOT检测结果:①4条HBV特异性抗原多肽反应阳性率在CHB组、CSH组、N1组和N2组分别为50%(10/20)、10%(1/10)、83.3%(5/6)和10%(1/10).N1组反应阳性率高于CSH组(X2=9.000,P=0.008)和N2组(X2=9.000,P=0.008).②各组对Tp、Te1、Te2和Tc四条肽的平均反应强度用斑点形成细胞(SFC)/106PBMC表示,采用非参数秩和检验,N1组对Tp、Te1、Te2和Tc肽的平均反应强度大于CSH组和N2组(分别为77 SFC/106PBMC vs 10 SFC/106PBMC vs 15 SFC/106PBMC,59 SFC/106PBMC vs 0 SFC/106PBMC vs 0 SFC/106PBMC,100 SFC/106PBMC vs 0 SFC/106PBMC vs 22 SFC/106 PBMC和57 SFC/106 PBMC vs 20 SFC/106 PBMC vs 30 SFC/106 PBMC,均P<0.01).结论 各种类型HBV感染者不论病毒清除与否,都可对HBV特异性多肽产生T细胞免疫反应,这种免疫反应以既往感染者最强,慢性乙型肝炎组较弱,慢性乙型重型肝炎组缺乏,提示HBV特异性CTL应答可能是自身免疫机制清除病毒的重要因素.     

A modified epitope identified for generation and monitoring of PSA-specific T cells in patients on early phases of PSA-based immunotherapeutic protocols

Efficacy of vaccination in cancer patients on immunotherapeutic protocols can be difficult to evaluate. The aim of this study was therefore to identify a single natural or modified epitope in prostate-specific antigen (PSA) with the ability to generate high levels of PSA-specific T cells to facilitate monitoring in patients after vaccination against prostate cancer. To the best of our knowledge, this study describes for the first time the peptide specificity of T cells stimulated by endogenously processed PSA antigen. The peptide specificity of HLA-A*0201-restricted CD8⁺ T cells against human and rhesus PSA was investigated both in vivo after DNA vaccination in HLA-A*0201-transgenic mice and in vitro after repetitive stimulation of human T cells with DNA-transfected human dendritic cells (DCs). One of seven native PSA peptides, psa53–61, was able to activate high levels of PSA-specific CD8⁺ T cells in HLA-A*0201-transgenic mice after PSA DNA vaccination. Psa53–61 was also the only peptide that induced human T cells to produce IFNγ after stimulation with PSA transfected DCs, however not in all donors. Therefore, plasmids encoding modified epitopes in predicted HLA-A*0201 sequences were constructed. One of these modified PSA plasmids consistently induced IFNγ producing CD8⁺ T cells to the corresponding modified peptide as well as to the corresponding native peptide, in all murine and human T cell cultures. This study demonstrates a novel concept of introducing a modified epitope within a self-tumor antigen, with the purpose of eliciting a reliable T cell response from the non-tolerized immune repertoire, to facilitate monitoring of vaccine efficacy in cancer patients on immunotherapeutic protocols. The purpose of such a modified epitope is thus not to induce therapeutically relevant T cells but rather to, in case of weak or divergent T cell responses to self antigens/peptides, help answer questions about efficacy of vaccine delivery and about the possibility to induce immune responses in the selected and often immunosuppressed cancer patients.     

Towards an immunosense vaccine to prevent toxoplasmosis: protective Toxoplasma gondii epitopes restricted by HLA-A*0201

The ideal vaccine to protect against toxoplasmosis in humans would include antigens that elicit a protective T helper cell type 1 immune response, and generate long-lived IFN-γ-producing CD8⁺ T cells. Herein, we utilized a predictive algorithm to identify candidate HLA-A02 supertype epitopes from Toxoplasma gondii proteins. Thirteen peptides elicited production of IFN-γ from PBMC of HLA-A02 supertype persons seropositive for T. gondii infection but not from seronegative controls. These peptides displayed high-affinity binding to HLA-A02 proteins. Immunization of HLA-A*0201 transgenic mice with these pooled peptides, with a universal CD4⁺ epitope peptide called PADRE, formulated with adjuvant GLA-SE, induced CD8⁺ T cell IFN-γ production and protected against parasite challenge. Peptides identified in this study provide candidates for inclusion in immunosense epitope-based vaccines.