Identification of a dominant CD8+ CTL epitope in the SARS-associated coronavirus 2 spike protein

Coronavirus disease 2019 (COVID-19), which is caused by SARS-CoV-2, has been spreading throughout the world. To date, there are still no approved human vaccines for this disease. To develop an effective vaccine, the establishment of animal models for evaluating post-vaccination immune responses is necessary. In this study, we have identified a CTL epitope in the SARS-CoV-2 spike (S) protein that could be used to measure the cellular immune response against this protein. Potential predicted CTL epitopes of the SARS-CoV-2 S protein were investigated by immunizing BALB/c mice with a recombinant of the receptor-binding domain (RBD) of the S protein. Then, CD8⁺ T cells specific for S-RBD were detected by stimulating with potential epitope peptides and then measuring the interferon-gamma production. Truncation of this peptide revealed that S-RBD-specific CD8⁺ T cells recognized a H2-D^d-restricted S_526–533 peptide. In conclusion, this animal model is suitable for evaluating the immunogenicity of SARS-CoV-2 vaccines.     

Strategies to enhance immunogenicity of cDNA vaccine encoded antigens by modulation of antigen processing

Most vaccines are based on protective humoral responses while for intracellular pathogens CD8⁺ T cells are regularly needed to provide protection. However, poor processing efficiency of antigens is often a limiting factor in CD8⁺ T cell priming, hampering vaccine efficacy. The multistage cDNA vaccine H56, encoding three secreted Mycobacterium tuberculosis antigens, was used to test a complete strategy to enhance vaccine’ immunogenicity. Potential CD8⁺ T cell epitopes in H56 were predicted using the NetMHC3.4/ANN program. Mice were immunized with H56 cDNA using dermal DNA tattoo immunization and epitope candidates were tested for recognition by responding CD8⁺ T cells in ex vivo assays. Seven novel CD8⁺ T cell epitopes were identified. H56 immunogenicity could be substantially enhanced by two strategies: (i) fusion of the H56 sequence to cDNA of proteins that modify intracellular antigen processing or provide CD4⁺ T cell help, (ii) by substitution of the epitope’s hydrophobic C-terminal flanking residues for polar glutamic acid, which facilitated their proteasome-mediated generation. We conclude that this whole strategy of in silico prediction of potential CD8⁺ T cell epitopes in novel antigens, followed by fusion to sequences with immunogenicity-enhancing properties or modification of epitope flanking sequences to improve proteasome-mediated processing, may be exploited to design novel vaccines against emerging or ‘hard to treat’ intracellular pathogens.     

Immunoinformatics prediction of overlapping CD8+ T-cell,IFN-γ and IL-4 inducer CD4+ T-cell and linear B-cell epitopes based vaccines against COVID-19 (SARS-CoV-2)

At the beginning of the year 2020, the world was struck with a global pandemic virus referred to as SARS-CoV-2 (COVID-19) which has left hundreds of thousands of people dead. To control this virus, vaccine design becomes imperative. In this study, potential epitopes-based vaccine candidates were explored. Six hundred (6 0 0) genomes of SARS-CoV-2 were retrieved from the viPR database to generate CD8⁺ T-cell, CD4+ T-cell and linear B-cell epitopes which were screened for antigenicity, immunogenicity and non-allergenicity. The results of this study provide 19 promising candidate CD8⁺ T-cell epitopes that strongly overlap with 8 promising B-cells epitopes. Another 19 CD4⁺ T-cell epitopes were also identified that can induce IFN-γ and IL-4 cytokines. The most conserved MHC-I and MHC-II for both CD8⁺ and CD4⁺ T-cell epitopes are HLA-A*02:06 and HLA-DRB1*01:01 respectively. These epitopes also bound to Toll-like receptor 3 (TLR3). The population coverage of the conserved Major Histocompatibility Complex Human Leukocyte Antigen (HLA) for both CD8⁺ T-cell and CD4⁺ T-cell ranged from 65.6% to 100%. The detailed analysis of the potential epitope-based vaccine and their mapping to the complete COVID-19 genome reveals that they are predominantly found in the location of the surface (S) and membrane (M) glycoproteins suggesting the potential involvement of these structural proteins in the immunogenic response and antigenicity of the virus. Since the majority of the potential epitopes are located on M protein, the design of multi-epitope vaccine with the structural protein is highly promising though the whole M protein could also serve as a viable epitope for the development of an attenuated vaccine. Our findings provide a baseline for the experimental design of a suitable vaccine against SARS-CoV-2.     

Deciphering the protective role of adaptive immunity to CHIKV/IRES a novel candidate vaccine against Chikungunya in the A129 mouse model

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, recently re-emerged in Africa and spread to islands in the Indian Ocean, the Indian subcontinent, and to South East Asia. Viremic travelers have also imported CHIKV to the Western hemisphere highlighting the importance of CHIKV in public health. In addition to the great burden of arthralgic disease, which can persist for months or years, epidemiologic studies have estimated case-fatality rates of ∼0.1%, principally from neurologic disease in older patients. There are no licensed vaccines or effective therapies to prevent or treat human CHIKV infections. We have developed a live CHIKV vaccine (CHIKV/IRES) that is highly attenuated yet immunogenic in mouse models, and is incapable of replicating in mosquito cells. In this study we sought to decipher the role of adaptive immunity elicited by CHIKV/IRES in protection against wild-type CHIKV infection. A single dose of vaccine effectively activated T cells with an expansion peak on day 10 post immunization and elicited memory CD4⁺ and CD8⁺ T cells that produced IFN-γ, TNF-α and IL-2 upon restimulation with CHIKV/IRES. Adoptive transfer of CHIKV/IRES-immune CD4⁺ or CD8⁺ T cells did not confer protection against wtCHIKV-LR challenge. By contrast, passive immunization with anti-CHIKV/IRES immune serum provided protection, and a correlate of a minimum protective neutralizing antibody titer was established. Overall, our findings demonstrate the immunogenic potential of the CHIKV/IRES vaccine and highlight the important role that neutralizing antibodies play in protection against an acute CHIKV infection.     

DNA vaccination as a tool to identify subdominant CD8 T cell epitopes

DNA vaccination is highly efficient at inducing CD8⁺ T cell responses in animal models. Here we investigated whether DNA vaccine technology could be exploited to identify subdominant cytotoxic T lymphocytes (CTL) epitopes. Previous studies have shown that the Sendai virus HN protein does not induce a CD8⁺ T cell response in C57BL/6 mice. Thus, we vaccinated C57BL/6 mice with a DNA vaccine encoding Sendai virus hemagglutinin neuraminidase (HN) protein. The data show that this strategy elicited a potent D^b-restricted CD8⁺ CTL response against at least one subdominant HN-derived epitope. These CTL were able to lyse Sendai virus-infected target cells, demonstrating that the epitope was appropriately processed and present at sufficient levels for T cell recognition. However, these cells did not confer protection against lethal challenge with Sendai virus. These data demonstrate the capacity of DNA vaccine to raise CTL responses to subdominant epitopes, but show that such responses may be limited in their efficacy against non-persistent viruses.     

CTL epitopes for influenza A including the H5N1 bird flu; genome-, pathogen-, and HLA-wide screening

The purpose of the present study is to perform a global screening for new immunogenic HLA class I (HLA-I) restricted cytotoxic T cell (CTL) epitopes of potential utility as candidates of influenza A-virus diagnostics and vaccines. We used predictions of antigen processing and presentation, the latter encompassing 12 different HLA class I supertypes with >99% population coverage, and searched for conserved epitopes from available influenza A viral protein sequences. Peptides corresponding to 167 predicted peptide-HLA-I interactions were synthesized, tested for peptide-HLA-I interactions in a biochemical assay and for influenza-specific, HLA-I-restricted CTL responses in an IFN-gamma ELISPOT assay. Eighty-nine peptides could be confirmed as HLA-I binders, and 13 could be confirmed as CTL targets. The 13 epitopes, are highly conserved among human influenza A pathogens, and all of these epitopes are present in the emerging bird flu isolates. Our study demonstrates that present technology enables a fast global screening for T cell immune epitopes of potential diagnostics and vaccine interest. This technology includes immuno-bioinformatics predictors with the capacity to perform fast genome-, pathogen-, and HLA-wide searches for immune targets. To exploit this new potential, a coordinated international effort to analyze the precious source of information represented by rare patients, such as the current victims of bird flu, would be essential.     

Elicitation of broad CTL response against HIV-1 by the DNA vaccine encoding artificial multi-component fusion protein MultiHIV—Study in domestic pigs

Broad CTL response against HIV-1 is one factor that helps to control the viral replication. We have constructed a DNA vaccine that encodes a large artificial fusion protein (MultiHIV) and shown it to be immunogenic in mice, swine and macaques. Inbred mice revealed CTL response only against two epitopes due to limited MHC class I variability. To assess the quality of the CTL response we addressed this question in domestic swine. Number of presented epitopes varied between 7 and 14 among the five selected animals. Epitopes detected in swine are localised in the same antigenic regions recognised in humans. This can be explained by the fact that swine MHC-I (SLA-I) complex is remarkably similar to human HLA-I. These results also indicate that immunogenicity profile of vaccines in domestic swine may predict the outcome of human immunisation.     

Identification of HLA-I restricted epitopes in six vaccine candidates of Leishmania tropica using immunoinformatics and molecular dynamics simulation approaches

In spite of numerous studies on vaccination for various species of Leishmania, research on the development of an effective vaccine for L. tropica is very scarce. In silico epitope prediction is a new way to survey the best vaccine candidates. Here, we predicted the best epitopes of six L. tropica antigens with vaccine capability against this pathogen, using highly frequent HLA-I alleles. Based on the frequent HLA alleles, the protein sequences were screened individually using four different MHC prediction applications, namely SYFPEITHI, ProPredI, BIMAS, and IEDB. Several in silico assays including clustering, human similarity exclusion, epitope conservancy prediction, investigating in experimental records, immunogenicity prediction, and prediction of population coverage were performed to narrow the results and to find the best epitopes. The selected epitopes and their restricted HLA-I alleles were docked and the final epitopes with the lowest binding energy (the highest binding affinity) were chosen. Finally, the stability and the binding properties of the best epitope-HLA-I combinations were analyzed using molecular dynamics simulation studies. We found ten potential peptides with strong binding affinity to highly frequent HLA-I alleles that can be further evaluated as vaccine targets against L. tropica.     

Induction of cytotoxic T-cell responses by gene gun DNA vaccination with minigenes encoding influenza A virus HA and NP CTL-epitopes.

Cytotoxic T-lymphocyte (CTL) response is an important component of anti-viral immunity. CTLs are specific to short peptides presented by MHC-I molecules and immunisation with the exact peptide sequence introduced in the cytosol is therefore a minimal approach, which potentially affords a high degree of controllability. We have examined the induction of murine CTL's by this approach using DNA plasmid minigene vaccines encoding known mouse K(k) minimal CTL epitopes (8 amino acids) from the influenza A virus hemagglutinin and nucleoprotein. We here report that such an approach is feasible and that wild type influenza virus flanking amino acid sequences can influence the CTL response but are not essential for optimal CTL induction. We also examined the effect of different new amino acid sequences flanking the CTL epitopes. In one version, two CTL epitopes were linked together as 'string of beads'. This did not improve CTL induction. In another version, one CTL epitope was inserted into a known T-helper protein (HBsAg). This did significantly augment the response probably due to immunological help from HBsAg Th epitopes. Finally, the CTL inducing minigene DNA vaccines were compared with Flu-induced CTL responses and tested for their protective effect against a lethal influenza A virus infection in mice and no effect was found. We conclude that a specific and highly directed CTL induction is possible by unlinked minigene DNA immunisation, but that CTL induction solely is not always sufficient to provide protection.     

Optimization of epitope processing enhances immunogenicity of multiepitope DNA vaccines

Experimental DNA vaccines comprised of multiple minimal cytotoxic T lymphocytes (CTL) epitopes can effectively induce broad CTL responses; however, such constructs frequently exhibit significant variation in epitope immunogenicity. Antigenicity assays utilizing human cells transfected with one such multiepitope construct revealed that the epitopes with poor immunogenicity were inefficiently processed in transfected cells. Compilation of a database of 94 epitope/flanking region combinations, for which immunogenicity was measured experimentally, revealed that the type of residue immediately following the carboxyl-terminus of the epitope exerted a prominent effect on immunogenicity. Experiments utilizing a variety of HBV-specific vaccine constructs demonstrated epitope immunogenicity could be modulated by the insertion of a single amino acid and the effect on immunogenicity could be ascribed to modulation of processing efficiency. These findings demonstrate that multiepitope DNA vaccines can be engineered to enhance CTL immunogenicity by increasing processing efficiency.     

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.     

DNA/Ad5 vaccination with SIV epitopes induced epitope-specific CD4⁺ T cells, but few subdominant epitope-specific CD8⁺ T cells

The goals of a T cell-based vaccine for HIV are to reduce viral peak and setpoint and prevent transmission. While it has been relatively straightforward to induce CD8⁺ T cell responses against immunodominant T cell epitopes, it has been more difficult to broaden the vaccine-induced CD8⁺ T cell response against subdominant T cell epitopes. Additionally, vaccine regimens to induce CD4⁺ T cell responses have been studied only in limited settings. In this study, we sought to elicit CD8⁺ T cells against subdominant epitopes and CD4⁺ T cells using various novel and well-established vaccine strategies. We vaccinated three Mamu-A*01⁺ animals with five Mamu-A*01-restricted subdominant SIV-specific CD8⁺ T cell epitopes. All three vaccinated animals made high frequency responses against the Mamu-A*01-restricted Env TL9 epitope with one animal making a low frequency CD8⁺ T cell response against the Pol LV10 epitope. We also induced SIV-specific CD4⁺ T cells against several MHC class II DRBw*606-restricted epitopes. Electroporated DNA with pIL-12 followed by a rAd5 boost was the most immunogenic vaccine strategy. We induced responses against all three Mamu-DRB*w606-restricted CD4 epitopes in the vaccine after the DNA prime. Ad5 vaccination further boosted these responses. Although we successfully elicited several robust epitope-specific CD4⁺ T cell responses, vaccination with subdominant MHC class I epitopes elicited few detectable CD8⁺ T cell responses. Broadening the CD8⁺ T cell response against subdominant MHC class I epitopes was, therefore, more difficult than we initially anticipated.     

The immunologic dominance of an epitope within a rationally designed poly-epitope vaccine is influenced by multiple factors

IntroductionCD4⁺ T cells are essential for inducing optimal CD8⁺ T cell and antibody-producing B cell responses and maintaining their long-term immunological memory. Therefore, CD4⁺ T cells are a critical component in HIV vaccine development. Due to enormous viral gene variation and significant human host genetic diversity, HIV vaccines may need to be custom-made for different countries.MethodsPreviously, we designed a CD4⁺ T cell vaccine based on Chinese HIV isolates and HLA-DR alleles using bioinformatics tools and predicted that 20 epitopes could cover 98.1% of the Chinese population. In vivo testing of the poly-epitope antigen in mice only activated specific T cells for some epitopes. To elucidate the mechanism of the observed differential immunogenicity, we examined poly-epitope antigen processing and presentation using in vitro and in vivo analytical methods.ResultsEnzymatic digestion indicated that all 20 epitopes comprising the poly-epitope antigen could be liberated, but MHC II binding assays showed that neither binding affinity nor dissociation rate was associated with the magnitude of T cell immune responses elicited by each peptide epitope in vaccinated mice. Mass spectrometry analysis of MHC II-bound peptides suggested that the abundance of endogenously processed peptides bound to MHC II molecules was significantly associated with the relative immunodominance of these epitopes.ConclusionThese results provide a new rationale for improving the design and testing of poly-epitope vaccines for HIV and other diseases.     

Prediction and identification of novel IBV S1 protein derived CTL epitopes in chicken

Infectious bronchitis virus (IBV) is a major pathogen common in the poultry industry. Broad cytotoxic T lymphocyte (CTL) response against IBV is one of the crucial factors that help to control viral replication. Spike glycoproteins on the surface of the IBV virion harbor major T cell epitopes. In this study, based on the peptide-binding motifs of chicken MHC I molecules for the BF2*4, BF2*12, BF2*15, and BF2*19 haplotypes, potential CTL epitopes were predicted using S1 proteins from different IBV strains. Twenty-one peptides were predicted to be potential CTL epitopes; they were manually synthesized and the CTL responses to them tested in vitro. Spleen lymphocytes were collected from specific-pathogen free (SPF) chicken that had been immunized with the S1 protein expression plasmid, pV-S1, and were stimulated by the synthesized peptides. IFN-γ secretion and CD8⁺ T cell proliferation in chickens were tested by ELISpot array and flow cytometry, respectively. Four epitopes (P8_SRIQTATDP, P9_SRNATGSQP, P18_GAYAVVNV, and P19_SRIQTATQP) were identified to stimulate CD8⁺ T cell proliferation and IFN-γ secretion, indicating their efficacy as CTL epitopes in chicken. Poly-CTL-epitope DNA vaccine (pV-S1T) was constructed by inserting nucleotide sequences encoding the P8, P9, P18, and P19 CTL epitopes into the pVAX1 vector. Chickens were vaccinated with either pV-S1, pV-S1T, or pVAX1 and the protection efficacy was analyzed, revealing that ninety percent of chickens immunized with pV-S1T were protected after challenge with 10⁶ ELD₅₀ of IBV, demonstrating that these novel CTL epitopes were effective against IBV challenge. This study provides a new method to screen virus CTL epitopes in chicken and to develop poly-CTL-epitope DNA vaccines.     

Overlapping synthetic peptides encoding TPD52 as breast cancer vaccine in mice: Prolonged survival

Peptide-based vaccines, one of several anti-tumor immunization strategies currently under investigation, can elicit both MHC Class I-restricted (CD8⁺) and Class II-restricted (CD4⁺) responses. However, the need to identify specific T-cell epitopes in the context of MHC alleles has hampered the application of this approach. We have tested overlapping synthetic peptides (OSP) representing a tumor antigen as a novel approach that bypasses the need for epitope mapping, since OSP contain all possible epitopes for both CD8⁺ and CD4⁺ T cells. Here we report that vaccination of inbred and outbred mice with OSP representing tumor protein D52 (TPD52-OSP), a potential tumor antigen target for immunotherapy against breast, prostate, and ovarian cancer, was safe and induced specific CD8⁺ and CD4⁺ T-cell responses, as demonstrated by development of specific cytotoxic T cell (CTL) activity, proliferative responses, interferon (IFN)-γ production and CD107a/b expression in all mice tested. In addition, TPD52-OSP-vaccinated BALB/c mice were challenged with TS/A breast carcinoma cells expressing endogenous TPD52; significant survival benefits were noted in vaccine recipients compared to unvaccinated controls (p < 0.001). Our proof-of-concept data demonstrate the safety and efficacy of peptide library-based cancer vaccines that obviates the need to identify epitopes or MHC backgrounds of the vaccinees. We show that an OSP vaccination approach can assist in the disruption of self-tolerance and conclude that our approach may hold promise for immunoprevention of early-stage cancers in a general population.     

In vivo and in vitro immunogenicity of novel MHC class I presented epitopes to confer protective immunity against chronic HTLV-1 infection

Human T-cell leukemia virus type 1 (HTLV-1) has infected as many as 10 million people worldwide. While 90% are asymptomatic, 5% develop severe diseases including adult T-cell leukemia/lymphoka (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). No vaccine against HTLV-1 exists, and screening programs are not universal. However, patients with chronic HTLV-1 infection have high frequencies of HTLV-1-activated CD8+ T cells, and the two main HLA alleles (A2, A24) are present in 88% of infected individuals. We thus utilized an immunoproteomics approach to characterize MHC-I restricted epitopes presented by HLA-A2+, A24+ MT-2 and SLB-1 cell lines. Unlike traditional motif prediction algorithms, this approach identifies epitopes associated with cytotoxic T-cell responses in their naturally processed forms, minimizing differences in antigen processing and protein expression levels. Out of nine identified peptides, we confirmed six novel MHC-I restricted epitopes that were capable of binding HLA-A2 and HLA-A24 alleles and used in vitro and in vivo methods to generate CD8+ T cells specific for each of these peptides. MagPix MILLIPLEX data showed that in vitro generated epitope-specific CD8+ T cells secreted IFN-ɣ, granzyme B, MIP-1α, TNF-α, perforin and IL-10 when cultured in the presence of MT-2 cell line. Degranulation assay confirmed cytotoxic response through surface expression of CD107 on CD8+ T cells when cultured with MT-2 cells. A CD8+ T-cell killing assay indicated significant antiviral activity of CD8+ T cells specific against all identified peptides. In vivo generated CD8+ T cells similarly demonstrated immunogenicity on ELISpot, CD107 degranulation assay, and MagPix MILLIPLEX analysis. These epitopes are thus candidates for a therapeutic peptide-based vaccine against HTLV-1, and our results provide preclinical data for the advancement of such a vaccine.     

A novel DNA vaccine containing multiple TB-specific epitopes casted in a natural structure (ECANS) confers protective immunity against pulmonary mycobacterial challenge

Epitope-based DNA vaccines designed to induce T cell responses specific for Mycobacterium tuberculosis (M. tb) are being developed as a means of addressing vaccine potency. In this study, we predicted 4 T cell epitopes from ESAT-6, Ag85A/B and CFP-10 antigens and constructed an ECANS (epitopes casted in a natural structure) DNA vaccine by inserting the epitope DNA segments separately into the gene backbone of M. tb-derived HSP65 (heat shock protein 65) carrier. The immunogenicity and protective efficacy of pECANS DNA vaccine were assessed in BALB/c mice after intramuscular immunization with 4 doses of 50 μg ECANS DNA and followed by mycobaterial challenge 4 weeks after the last immunization. Compared to plasmid encoding HSP65, pECANS DNA immunization elicited remarkably higher levels of IFN-γ production by both CD4⁺ and CD8⁺ T cells, which were coupled with higher frequencies of antigen-specific T cells and higher CTL activity. Significantly enhanced levels of Th1 cytokines (IFN-γ and IL-12) and increased serum IgG2a/IgG1 ratio were also noted, indicating a predominant Th1 immune response achieved by pECANS DNA immunization. In the consequence, a better protection against Mycobacterium bovis BCG challenge was achieved which was evidenced by reduced bacterial loads in lungs and spleens and profound attenuation of lung inflammation and injury. Our results suggested that multi-T cell-epitope based ECANS gene vaccine induced T cell response to multiple T cell epitopes and led to enhanced protection against mycobacterial challenge. This strategy might be a useful platform to design multi-T cell epitope-based vaccine against M. tb infection.     

Mechanism for increased immunogenicity of vaccines that form in vivo immune complexes with the natural anti-Gal antibody

Anti-Gal constitutes ∼1% of circulating IgG in humans and interacts specifically with α-gal epitopes. We reported previously that expression of α-gal epitopes on HIV gp120 and influenza virus vaccines increases immunogenicity by ∼100-fold. We hypothesize that immunogenicity of any microbial vaccine can be markedly increased by linked α-gal epitopes due to in vivo formation of immune complexes with anti-Gal and the effective internalization of such immune complexes by APC, via Fc/FcγR interaction. The increased transport to lymph nodes and processing of anti-Gal complexed vaccines internalized by APC, results in effective activation of vaccine specific CD4⁺ and CD8⁺ T cells, and high cellular and humoral immune response. This universal mechanism for anti-Gal mediated increased immunogenicity is demonstrated in α1,3galactosyltransferase knockout mice with ovalbumin as a model vaccine.     

Effectiveness of a novel immunogenic nanoparticle platform for Toxoplasma peptide vaccine in HLA transgenic mice

We created and produced a novel self-assembling nanoparticle platform for delivery of peptide epitopes that induces CD8⁺ and CD4⁺T cells that are protective against Toxoplasma gondii infection. These self-assembling polypeptide nanoparticles (SAPNs) are composed of linear peptide (LP) monomers which contain two coiled-coil oligomerization domains, the dense granule 7 (GRA7_20–28 LPQFATAAT) peptide and a universal CD4⁺T cell epitope (derived from PADRE). Purified LPs assemble into nanoparticles with icosahedral symmetry, similar to the capsids of small viruses. These particles were evaluated for their efficacy in eliciting IFN-γ by splenocytes of HLA-B*0702 transgenic mice and for their ability to protect against subsequent T. gondii challenge. This work demonstrates the feasibility of using this platform approach with a CD8⁺ epitope that binds HLA-B7 and tests the biological activity of potentially protective peptides restricted by human major histocompatibility complex (HLA) class I molecules in HLA transgenic mice.