Flexibility in MHC and TCR Recognition: Degenerate Specificity at the T Cell Level in the Recognition of Promiscuous Th Epitopes Exhibiting No Primary Sequence Homology

Sequence similarity between SARS-CoV-2 nucleocapsid and multiple sclerosis-associated proteins provides insight into viral neuropathogenesis following infection

The novel coronavirus SARS-CoV-2 continues to cause death and disease throughout the world, underscoring the necessity of understanding the virus and host immune response. From the start of the pandemic, a prominent pattern of central nervous system (CNS) pathologies, including demyelination, has emerged, suggesting an underlying mechanism of viral mimicry to CNS proteins. We hypothesized that immunodominant epitopes of SARS-CoV-2 share homology with proteins associated with multiple sclerosis (MS). Using PEPMatch, a newly developed bioinformatics package which predicts peptide similarity within specific amino acid mismatching parameters consistent with published MHC binding capacity, we discovered that nucleocapsid protein shares significant overlap with 22 MS-associated proteins, including myelin proteolipid protein (PLP). Further computational evaluation demonstrated that this overlap may have critical implications for T cell responses in MS patients and is likely unique to SARS-CoV-2 among the major human coronaviruses. Our findings substantiate the hypothesis of viral molecular mimicry in the pathogenesis of MS and warrant further experimental exploration.

Removal of CD276+ cells from haploidentical memory T-cell grafts significantly lowers the risk of GVHD

Detrimental graft-versus-host disease (GVHD) still remains a major cause of death in hematopoietic stem cell transplantation (HSCT). The recently explored depletion of naive cells from mobilized grafts (CD45RA depletion) has shown considerable promise, yet is unable to eliminate the incidence of GVHD. Analysis of CD45RA-depleted haploidentical mixed lymphocytes culture (haplo-MLC) revealed insufficient suppression of alloresponses in the CD4⁺ compartment and identified CD276 as a marker for alloreactive memory Th1 T cells. Conclusively, depleting CD276⁺ cells from CD45RA-depleted haplo-MLC significantly attenuated alloreactivity to recipient cells while increasing antiviral reactivity and maintaining anti-third party reactivity in vitro. To evaluate these findings in vivo, bulk, CD45RA-depleted, or CD45RA/CD276-depleted CD4⁺ T cells from HLA-DR4^negative healthy humans were transplanted into NSG-Ab°DR4 mice, a sensitive human allo-GVHD model. Compellingly, CD45RA/CD276-depleted grafts from HLA-DR4^negative donors or in vivo depletion of CD276⁺ cells after transplant of HLA-DR4^negative memory CD4 T cells significantly delay the onset of GVHD symptoms and significantly alleviate its severity in NSG-Ab°DR4 mice. The clinical courses correlated with diminished Th1-cytokine secretion and downregulated CXCR6 expression of engrafted peripheral T cells. Collectively, mismatched HLA-mediated GVHD can be controlled by depleting recipient-specific CD276⁺ alloreacting T cells from the graft, highlighting its application in haplo-HSCT.

Immunological properties and protective efficacy of a single mycobacterial antigen displayed on polyhydroxybutyrate beads

In 2015, there were an estimated 10.4 million new tuberculosis (TB) cases and 1.4 million deaths worldwide. Bacille Calmette-Guérin (BCG), an attenuated strain of Mycobacterium bovis, is the vaccine available against TB, but it is insufficient for global TB control. This study evaluated the immunogenicity of the Mycobacterium tuberculosis antigen Rv1626 in mice while assessing the effect of co-delivering either Cpe30 (immunostimulatory peptide), CS.T3378-395 (promiscuous T helper epitope) or flagellin (TLR5 agonist) or a combination of all three immunostimulatory agents. Rv1626 and the respective immunostimulatory proteins/peptides were co-displayed on polyhydroxybutyrate beads assembled inside an engineered endotoxin-free mutant of Escherichia coli. Mice vaccinated with these beads produced immune responses biased towards Th1-/Th17-type responses, but inclusion of Cpe30, CS.T3378-395 and flagellin did not enhance immunogenicity of the Rv1626 protein. This was confirmed in a M. bovis challenge experiment in mice, where Rv1626 beads reduced bacterial cell counts in the lungs by 0.48 log10 compared with the adjuvant alone control group. Co-delivery of immunostimulatory peptides did not further enhance protective immunity.

The nonspecific face of adaptive immunity

Memory T cells generated by infection or immunization persist in the organism and mediate specific protection upon rechallenge with microbial pathogens expressing the same molecular structures. However, multiple lines of evidence indicate that previously encountered or persisting pathogens influence the immune response to unrelated pathogens. We describe the acquisition of non-antigen specific memory features by both innate and adaptive immune cells explaining these phenomena. We also focus on the different mechanisms (homeostatic or inflammatory cytokine-driven) that lead to acquisition of memory phenotype and functions by antigen-inexperienced T lymphocytes. We discuss the implications of these new concepts for host defense, auto-immunity and vaccination strategies.

The fully synthetic MAG-Tn3 therapeutic vaccine containing the tetanus toxoid-derived TT830-844 universal epitope provides anti-tumor immunity

Malignant transformations are often associated with aberrant glycosylation processes that lead to the expression of new carbohydrate antigens at the surface of tumor cells. Of these carbohydrate antigens, the Tn antigen is particularly highly expressed in many carcinomas, especially in breast carcinoma. We designed MAG-Tn3, a fully synthetic vaccine based on three consecutive Tn moieties that are O-linked to a CD4⁺ T cell epitope, to induce anti-Tn antibody responses that could be helpful for therapeutic vaccination against cancer. To ensure broad coverage within the human population, the tetanus toxoid-derived peptide TT830-844 was selected as a T-helper epitope because it can bind to various HLA-DRB molecules. We showed that the MAG-Tn3 vaccine, which was formulated with the GSK proprietary immunostimulant AS15 and designed for human cancer therapy, is able to induce an anti-Tn antibody response in mice of various H-2 haplotypes, and this response correlates with the ability to induce a specific T cell response against the TT830-844 peptide. The universality of the TT830-844 peptide was extended to new H-2 and HLA-DRB molecules that were capable of binding this T cell epitope. Finally, the MAG-Tn3 vaccine was able to induce anti-Tn antibody responses in cynomolgus monkeys, which targeted Tn-expressing tumor cells and mediated tumor cell death both in vitro and in vivo. Thus, MAG-Tn3 is a highly promising anticancer vaccine that is currently under evaluation in a phase I clinical trial.

The Unspecific Side of Acquired Immunity Against Infectious Disease: Causes and Consequences

Acquired immunity against infectious disease (AIID) has long been considered as strictly dependent on the B and T lymphocytes of the adaptive immune system. Consequently, AIID has been viewed as highly specific to the antigens expressed by pathogens. However, a growing body of data motivates revision of this central paradigm of immunology. Unrelated past infection, vaccination, and chronic infection have been found to induce cross-protection against numerous pathogens. These observations can be partially explained by the poly-specificity of antigenic T and B receptors, the Mackaness effect and trained immunity. In addition, numerous studies highlight the importance of microbiota composition on resistance to infectious disease via direct competition or modulation of the immune response. All of these data support the idea that a non-negligible part of AIID in nature can be nonspecific to the pathogens encountered and even of the antigens expressed by pathogens. As this protection may be dependent on the private T and B repertoires produced by the random rearrangement of genes, past immune history, chronic infection, and microbiota composition, it is largely unpredictable at the individual level. However, we can reasonably expect that a better understanding of the underlying mechanisms will allow us to statistically predict cross-protection at the population level. From an evolutionary perspective, selection of immune mechanisms allowing for partially nonspecific AIID would appear to be advantageous against highly polymorphic and rapidly evolving pathogens. This new emerging paradigm may have several important consequences on our understanding of individual infectious disease susceptibility and our conception of tolerance, vaccination and therapeutic strategies against infection and cancer. It also underscores the importance of viewing the microbiota and persisting infectious agents as integral parts of the immune system.

Are allergic multimorbidities and IgE polysensitization associated with the persistence or re-occurrence of foetal type 2 signalling? The MeDALL hypothesis

Allergic diseases [asthma, rhinitis and atopic dermatitis (AD)] are complex. They are associated with allergen-specific IgE and nonallergic mechanisms that may coexist in the same patient. In addition, these diseases tend to cluster and patients present concomitant or consecutive diseases (multimorbidity). IgE sensitization should be considered as a quantitative trait. Important clinical and immunological differences exist between mono- and polysensitized subjects. Multimorbidities of allergic diseases share common causal mechanisms that are only partly IgE-mediated. Persistence of allergic diseases over time is associated with multimorbidity and/or IgE polysensitization. The importance of the family history of allergy may decrease with age. This review puts forward the hypothesis that allergic multimorbidities and IgE polysensitization are associated and related to the persistence or re-occurrence of foetal type 2 signalling. Asthma, rhinitis and AD are manifestations of a common systemic immune imbalance (mesodermal origin) with specific patterns of remodelling (ectodermal or endodermal origin). This study proposes a new classification of IgE-mediated allergic diseases that allows the definition of novel phenotypes to (i) better understand genetic and epigenetic mechanisms, (ii) better stratify allergic preschool children for prognosis and (iii) propose novel strategies of treatment and prevention.

Intramolecular polyspecificity in CD4 T-cell recognition of Ad-restricted epitopes of proteoglycan aggrecan

T-cell recognition of MHC–peptide complexes shows a high degree of polyspecificity extending to recognition of a large number of structurally unrelated peptides. Examples of polyspecificity reported to date are confined to recognition of epitopes from distinct proteins or synthetic peptide libraries. Here we describe intramolecular polyspecificity of CD4 T cells specific for several epitopes within proteoglycan aggrecan, a structural glycoprotein of cartilage and candidate autoantigen in rheumatoid arthritis. T-cell hybridomas from aggrecan-immunized mice recognized four structurally unrelated epitopes from the G1 domain of aggrecan, but not other aggrecan epitopes or a variety of other peptide epitopes restricted by the same MHC class II allele. We also showed that the hierarchy of cross-reactivity broadly correlated with the strength of peptide binding to MHC class II. Similar polyspecificity was observed in responses of lymph node cells from peptide-immunized mice, suggesting polyspecificity of a significant proportion of the in vivo aggrecan specific T-cell repertoire. Polyspecific recognition of several epitopes within the same autoantigen may provide a novel mechanism to reach the activation threshold of low-affinity autoreactive T cells in the initiation of autoimmune diseases.

Depletion of naive T cells using clinical grade magnetic CD45RA beads: a new approach for GVHD prophylaxis

Depletion of naive T cells from donor leukapheresis products (LPs) aims at the reduction of alloreactivity, while preserving memory T-cell reactivity (for example, to pathogens). This study established the immunomagnetic depletion procedure under clean room conditions using CD45RA beads and analyzed LPs of six donors for cell composition and functional immune responses. CD45RA depletion resulted in 3.4-4.7 log (median 4.4) reduction of CD45RA(+) T cells, thereby eliminating naive and late effector T cells. B cells were also completely removed, whereas significant proportions of NK cells, monocytes and granulocytes persisted. CD45RA-depleted LPs contained effector and central memory CD4(+) and CD8(+) T cells that showed sustained IFN-γ secretion to CMV, EBV, Aspergillus and Candida Ags. Alloreactivity was measured in MLRs between donors with complete HLA-mismatch. Alloreactive CD8(+) T cells were strongly reduced (median >1-log) upon CD45RA depletion, whereas alloreactive CD4(+) T cells persisted in significant numbers. In conclusion, clinical grade depletion of CD45RA(+) naive T cells from donor LPs is feasible and highly efficient. The depleted products show sustained CD4(+) and CD8(+) T-cell reactivity to pathogens and effectively reduced CD8-mediated alloreactivity. Prophylactic and preemptive infusions after allogeneic SCT may improve T-cell reconstitution and pathogen-specific immunosurveillance, along with lower risk of inducing GVHD.

Immunological consequences of ischemic stroke: immunosuppression and autoimmunity

Stroke may be accompanied by immunological consequences including local autoimmunity and peripheral immune suppression. Since the blood brain barrier is disturbed cells of the immune system gain direct access to the brain parenchyma. Here local autoimmunity contributes to lesion formation and, in experimental stroke, inhibition of this immune response has been shown to be beneficial. More recently, however, stroke has been shown to also induce severe peripheral immune suppression which predisposes for subsequent bacterial infections that impair the clinical outcome. Here we summarize current knowledge on the immunological consequences of ischemic stroke and will discuss implications of these findings for our understanding of the immunopathogenesis of Multiple Sclerosis.

Gag- and Nef-specific CD4+ T cells recognize and inhibit SIV replication in infected macrophages early after infection

The precise immunological role played by CD4(+) T cells in retroviral infections is poorly defined. Here, we describe a new function of these cells, the elimination of retrovirus-infected macrophages. After experimental CD8(+) cell depletion, elite controlling macaques with set-point viral loads < or = 500 viral RNA copies/mL mounted robust Gag- and Nef-specific CD4(+) T cell responses during reestablishment of control with > or = 54% of all virus-specific CD4(+) T cells targeting these 2 proteins. Ex vivo, these simian immunodeficiency virus (SIV)-specific CD4(+) T cells neither recognized nor suppressed viral replication in SIV-infected CD4(+) T cells. In contrast, they recognized SIV-infected macrophages as early as 2 h postinfection because of presentation of epitopes derived from virion-associated Gag and Nef proteins. Furthermore, virus-specific CD4(+) T cells displayed direct effector function and eliminated SIV-infected macrophages. These results suggest that retrovirus-specific CD4(+) T cells may contribute directly to elite control by inhibiting viral replication in macrophages.

Degenerate TCR recognition and dual DR2 restriction of autoreactive T cells: implications for the initiation of the autoimmune response in multiple sclerosis

TCR degeneracy may facilitate self-reactive T cell activation and the initiation of an autoimmune response in multiple sclerosis (MS). MHC class II alleles of the DR2 haplotype DR2a (DRB5*0101) and DR2b (DRB1*1501) are associated with an increased risk for MS in Caucasian populations. In order to selectively expand and characterize T cells with a high degree of TCR degeneracy that recognize peptides in the context of disease-associated DR2 alleles, we developed DR2-anchored peptide mixtures (APM). We report here that DR2-APM have a high stimulatory potency and can selectively expand T cells with a degenerate TCR (TCR(deg)). Due to the low concentration of individual peptides in the mixtures, T cell clones' proliferative response to DR2-APM implies that multiple peptides stimulate the TCR, which is a characteristic of TCR(deg). The frequency of DR2-APM-reactive T cells is significantly higher in MS patients than in healthy controls, suggesting that they may play a role in the development of the autoimmune response in MS. DR2-APM-reactive cells have a dual DR2 restriction: they recognize DR2-APM in the context of both DR2a and DR2b molecules. The DR2-APM-reactive cells' IL-17 secretion, together with cross-reactivity against myelin peptides, may contribute to their role in the development of autoimmune response in MS.

Preservation of a critical epitope core region is associated with the high degree of flaviviral cross-reactivity exhibited by a dengue-specific CD4+ T cell clone

Dengue is a member of the Flaviviridae, a large group of related viruses some of which co-circulate in certain regions (e.g. dengue and Yellow fever in South America). Immune responses cross-reactive between different dengue serotypes are important in the pathogenesis of dengue disease but it is not known whether previous infection with one flavivirus might affect the clinical course of subsequent infections with other members of the family. CD4+ T cells have been shown to be important in the production of cytokines in response to dengue infection and can demonstrate significant epitope cross-reactivity. Here, we describe the generation and characterisation of CD4+ T cell clones from a patient experiencing acute dengue infection. These clones were DRB1*15+ and recognised epitope variants not only within other dengue viruses but certain other flaviviruses. This cross-reactivity was dependent upon the presence of a five-amino acid core region, consistent with structural observations of class II MHC binding to TCR demonstrating that only a subset of residues within an epitope bound to a class II molecule are "read out" by the TCR. This capacity of CD4+ T cell clones to recognise a given epitope despite considerable variation between viruses may be of pathological significance, particularly in regions where related viruses co-circulate.

Perpetuation of immunological memory through common MHC-I binding modes of peptidomimic and antigenic peptides

Understanding the molecular mechanisms of immunological memory assumes importance in vaccine design. We had earlier hypothesized a mechanism for the maintenance of immunological memory through the operation of a network of idiotypic and anti-idiotypic antibodies (Ab2). Peptides derived from an internal image carrying anti-idiotypic antibody are hypothesized to facilitate the perpetuation of antigen specific T cell memory through similarity in peptide-MHC binding as that of the antigenic peptide. In the present work, the existence of such peptidomimics of the antigen in the Ab2 variable region and their similarity of MHC-I binding was examined by bioinformatics approaches. The analysis employing three known viral antigens and one tumor-associated antigen shows that peptidomimics from Ab2 variable regions have structurally similar MHC-I binding patterns as compared to antigenic peptides, indicating a structural basis for memory perpetuation.

Engineered promiscuous T helper peptides for the induction of immune responses

Following recognition of antigens by T helper (Th) lymphocytes, T cell help is elicited to induce humoral and cellular immune responses. These antigens are presented as short peptides, T helper peptides (THP), bound to MHC class II molecules. Since both endogenous THP (from antigens of interest) or exogenous THP (not encompassed by the sequence of the antigen of interest) are able to elicit T cell help, we decided to engineer promiscuous exogenous THP capable of binding to several HLA-DR molecules, in order to cover an important proportion of the human population. Some of these exogenous THP were able to bind to all seven HLA-DR molecules tested and were immunogenic in vivo in HLA-DR4 transgenic mice. Among them, peptides p37, p62 and p45 elicited Th1 cytokine profiles in vivo, providing help for the induction of potent CTL responses. Finally, in vitro stimulation assays carried out using human cells, showed that these peptides could induce T cell responses using cells obtained from individuals with a broad spectrum of HLA-DR molecules. Thus, engineered exogenous THP may be a valuable tool for the induction of immune responses in a large proportion of human population.

Factors responsible for differences between asymptomatic subjects and patients presenting an IgE sensitization to allergens. A GA2LEN project

The synthesis of allergen-specific IgE is required for the development of allergic diseases including allergic rhinitis and allergic asthma (patients), but many individuals with allergen-specific IgE do not develop symptoms (asymptomatic subjects). Differences may exist between asymptomatic subjects and patients. Whether the presence of allergen-specific IgE translates into clinical allergy most likely depends on a complex interplay of multiple factors. These include a family history of atopy, the levels of total serum IgE and, allergen-specific IgE or IgG, epitope-specificity of IgE and their degree of polyclonality (mono- vs polysensitized), as yet unidentified serum factors, the balance of T regulatory cells (Treg) and Th1/Th2 cells, the polymorphisms of the high affinity receptor for IgE (FcepsilonRI) and other factors regulating the activation of FcepsilonRI-bearing cells. Asymptomatic subjects may be more often monosensitized than patients who may be more often polysensitized. There are many unanswered important questions that need to be addressed in order to better understand how IgE sensitization translates into clinical allergy. The assessment of differences between the asymptomatic and symptomatic groups of subjects represent one of the scientific programs of Global Allergy and Asthma European Network funded by the European Union and the hypotheses underlying these differences are presented in this paper.

Human T lymphocyte responses against lung cancer induced by recombinant truncated mouse EGFR

The induction of active cellular responses against EGFR should be a promising approach for the treatment of those receptor-positive tumors. However, the immunity against EGFR is presumably difficult to elicit by vaccine based on self or syngeneic EGFR due to the immune tolerance acquired during the development in immune system. We proposed a model to break immune tolerance against self-EGFR through an altered immunogen source based on xenogeneic homologous EGFR. We have previously shown human EGFR as a xenoantigen could induce specific immune responses in mouse and cross-react with mouse EGFR, and resulted in therapeutic benefits for EGFR-positive mouse tumor. Here, we show a recombinant form of extracellular domain of mouse EGFR, in the presence of DCs, could activate human peripheral T cells to proliferate, secret IFN-gamma, the induced responses could cross-react with human EGFR and kill autologous EGFR-positive lung cancer cells which could be blocked by anti-CD8 and anti-MHC class I antibody. There is no detectable cytotoxical activity against lung tissue, liver tissue and kidney tissue derived from paracancerous normal tissue. These observations suggest that antitumor immunity induced by the truncated mouse EGFR may be provoked in a cross-reaction between mouse EGFR and self-EGFR, and may provide insight into treatment of EGFR-positive tumors through induction of the autoimmune responses against EGFR.

T cell epitope-containing peptides of the major dog allergen Can f 1 as candidates for allergen immunotherapy

One prerequisite for developing peptide-based allergen immunotherapy is knowing the T cell epitopes of an allergen. In this study, human T cell reactivity against the major dog allergen Can f 1 was investigated to determine peptides suitable for immunotherapy. Seven T cell epitope regions (A-G) were found in Can f 1 with specific T cell lines and clones. The localization of the epitope regions shows similarities with those of the epitopes found in Bos d 2 and Rat n 1. On average, individuals recognized three epitopes in Can f 1. Our results suggest that seven 16-mer peptides (p15-30, p33-48, p49-64, p73-88, p107-122, p123-138, and p141-156), each from one of the epitope regions, show widespread T cell reactivity in the population studied, and they bind efficiently to seven HLA-DRB1 molecules (DRB1*0101, DRB1*0301, DRB1*0401, DRB1*0701, DRB1*1101, DRB1*1301, and DRB1*1501) predominant in Caucasian populations. Therefore, these peptides are potential candidates for immunotherapy of dog allergy.

Immunodominant viral peptides as determinants of cross-reactivity in the immune system--Can we develop wide spectrum viral vaccines?

When we look back to Edward Jenner vaccination of a young man in 1796, we cannot help thinking that he was both lucky and crazy. Crazy because he decided to test in a human being a hypothesis based mainly in the traditional belief that people who had acquired cowpox from the udders of a cow were thereafter resistant to smallpox, a quite devastating disease, and lucky because (even considering that he did not know this at that time) he succeeded to induce protection against a pathogen through the induction of an immune response directed against a different agent. Not only was he able to protect the young man but he took the first step towards the development of a vast new field, vaccination. It is acceptable to say that Jenner was lucky because he succeeded in promoting protection against smallpox using a cowpox virus and this induction of protection in a cross-reactive way is believed to be quite rare. Nevertheless, more and more examples of cross-reactive immune responses are being described and we are beginning to admit that cross-reactivity is far more common and important than we used to think. Here we review cross-reactivity in the immune system and the plasticity of T cell recognition. Based on the existence of T cell receptor promiscuous recognition and cross-recognition of conserved viral immunodominant epitopes, we propose two approaches to develop wide spectrum viral vaccines. The first one is based on the identification, characterization, and cloning of immunodominant viral epitopes able to stimulate responses against different viruses. The produced peptides could then be purified and serve as a basis for vaccine therapies. A second strategy is based on the identification of conserved patterns in immunodominant viral peptides and the production of synthetic peptides containing the amino acid residues necessary for MHC anchoring and TCR contact. Although we are still far from a complete knowledge of the cross-reactivity phenomenon in the immune system, the analysis of immunodominant viral epitopes and the identification of particular “viral patterns” seems to be important steps towards the development of wide spectrum viral vaccines.

Human cytomegalovirus-specific CD4(+) T-cell clones recognize cross-reactive peptides from the immediate early 1 protein

Human cytomegalovirus (HCMV) is a beta-herpes virus that persists in a latent state in immunocompetent individuals. Both CD4(+) and CD8(+) T lymphocytes have been reported to be present at a high frequency in HCMV-seropositive individuals and are involved in the control of infection. How such frequencies are maintained is not completely understood. We have observed that the canonical HLA-DR8 epitope of the immediate early 1 protein (IE1) contained in the IE1 (156--175) sequence shares homologies with an IE1 sequence contained in part in the previously reported HLA-DR3 epitope, IE1 (91-110). We thus wondered whether such homology in a single protein would translate into recognition of the IE1 homolog sequence by HLA-DR8-restricted CD4(+) cells in addition to the canonical epitope. We found that established HLA-DR8-restricted T cell clones are also able to cross-recognize the IE1 (91--110) peptide, as well as a shorter 14-mer, IE1 (91--104). Moreover, the homolog peptide IE1 (91-110) was able to generate, from a seropositive blood donor, new IE1-specific, HLA-DR8-restricted CD4(+) T cell clones that were also cross-reactive. Those findings may provide clues to the formation and regulation of the T-cell repertoire and memory.

Herpesvirus saimiri immortalization of Aotus T lymphocytes specific for an immunogenically modified peptide of Plasmodium falciparum merozoite surface antigen 2

The Plasmodium merozoite surface antigen 2 (MSA2) is one of several candidates for a protective vaccine against malaria. Previous studies have shown that antibodies directed against the MSA2 variable region are not protective and that constant regions are non-immunogenic. However, modified peptides derived from constant regions can be rendered immunogenic and partially protective in Aotus monkeys. In this study, we reveal the establishment, using in vitro Herpesvirus samiri (HVS) infection, of an Aotus monkey T-cell line (AnTMSA2) specific for a modified immunogenic and partially protective peptide derived from a constant and highly conserved region of MSA2 (SKYSNTFINNAYNMSIRRSM). AnTMSA2 is a CD4 T lymphocyte expressing high levels of MHC class II molecules, CD58 and CD2, which are important for proliferation and growth. AnTMSA2 proliferates specifically in response to the modified monomeric MSA2 peptide sequence. It is also capable of specific antigen recognition after glycine-cysteine-polymerized sequence processing and presentation by autologous APC. Interestingly, AnTMSA2 presents cross-reactivity with D-peptide analogues in which residues in positions 8 and 9 were changed for NDID residues. Therefore, at least for this particular sequence, polymerized D-peptides could be used for immunizing animals without losing the immunogenic epitope. AnTMSA2 presents a cytokine profile corresponding to a Th0-like pattern, which suggests that as a result of HVS immortalization AnTMSA2 is in transit from a Th2 to a Th1 pattern. Taken together our results suggest that Th2 T-cell induction and/or T-cell cross-reactivity generation by the modified peptide could be responsible for the immunogenic conversion observed in Aotus monkeys and that D-peptide analogues with longer half-lives could provide an alternative for inducing protective immunity.

Long-term multiepitopic cytotoxic-T-lymphocyte responses induced in chimpanzees by combinations of Plasmodium falciparum liver-stage peptides and lipopeptides

Preclinical immunogenicity studies of 12 malaria peptides, selected from four Plasmodium falciparum antigens (Ags), namely, LSA1, LSA3, SALSA, and STARP, that are expressed at the pre-erythrocytic (sporozoite and liver) stages of the human parasite were carried out in chimpanzees. To strengthen their immunogenicity, six of these synthetic peptides were modified by the C-terminal addition of a single palmitoyl chain (lipopeptides) and delivered without adjuvant, whereas the remaining six unmodified peptides were emulsified and delivered by using Montanide ISA51 adjuvant. We have previously reported that these peptides and lipopeptides induce high B-cell and CD4(+)-T-helper responses in chimpanzees. In this report, we show their ability to induce multiepitopic and long-lasting antigen-specific CD8(+) cytotoxic-T-lymphocyte (CTL) responses. The magnitude, consistency, and memory of CTL responses generated by LSA3 peptides point to the strong immunogenicity of this liver-stage Ag. These findings support the screening strategy used to select the four P. falciparum pre-erythrocytic Ags and emphasize their valuable immunogenic properties. The successful immunization of nonhuman primates with combinations of corresponding peptides in a mineral oil emulsion (ISA51) and lipopeptides in saline provide a vaccine formulation that can be tested in humans.

Induction of a protective capsular polysaccharide antibody response to a multiepitope DNA vaccine encoding a peptide mimic of meningococcal serogroup C capsular polysaccharide

Systemic infection by encapsulated organisms, such as Neisseria meningitidis, is a major cause of morbidity and mortality worldwide, especially in individuals less than 2 years of age. Antibodies directed at the capsular polysaccharide are shown to be protective against disease by inducing complement-dependent bactericidal activity. The current polysaccharide vaccine has been shown to be poorly immunogenic in high-risk groups and this is probably related to its T-independent properties. An alternative approach to eliciting a T-dependent serum immunoglobulin G (IgG) antibody response to encapsulated pathogens is DNA vaccination. We assessed the immunogenicity of a multiepitope DNA vaccine encoding a T-cell helper epitope and a peptide mimic of N. meningitidis serogroup C. The DNA construct induced a significant anti-polysaccharide antibody response that was bactericidal. Mice immunized with the DNA construct were subsequently protected against challenge with a lethal dose of N. meningitidis serogroup C.

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity

The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4(+) T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4(+) Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2(d) mice with the four newly identified CD4(+) Th1 peptide epitopes but not with four CD4(+) Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

In Vivo Priming Of HIV-Specific CTLs Determines Selective Cross-Reactive Immune Responses Against Poorly Immunogenic HIV-Natural Variants

Degeneracy of the TCR repertoire might allow for cross-recognition of epitope variants. However, it is unclear how the first encounter with HIV Ags determines recognition of emerging epitope variants. This question remains crucial in the choice of HIV vaccine sequences given the virus variability. In this study, we individualized nine natural mutations within an HIV-Nef(180-189) epitope selected from several HIV-infected individuals. These variants of Nef(180-189) sequence display slightly different HLA-A2 binding capacities and stabilities and we have shown that only two induced a strong CTL response in vivo in HLA-A2 transgenic mice after a single injection. We demonstrated that priming with these two immunogenic variants generated a specific pattern of cross-reactive CTL repertoire directed against poorly immunogenic peptides. Thus, the range of peptide variants recognized by HIV-specific CTL depends upon the Ag encountered during primary immunization of CD8 lymphocytes. These data have practical implications in the development of cross-reactive vaccines against HIV.