Subdominant Epitopes Research Articles

T cell responses targeting subdominant epitopes of Mycobacterium tuberculosis antigen ESAT-6 resist acquisition of bacteria-driven functionality and enhance protection in vivo. (75.8)

Abstract Immune-mediated pathology drives M.tuberculosis (Mtb) disease and transmission. Hyperconservation of dominant T cell epitopes in Mtb’s genome suggests that the T cell response to infection is actually evolutionarily beneficial to Mtb. Vaccine-induced CD4 T cells recognizing novel subdominant epitopes of ESAT-6 that are not targeted during natural infection can improve protective. We investigate differential characteristics of dominant vs subdominant T cells in protective immunity to Mtb in vivo. Methods. CB6F1 Mice were vaccinated with either rESAT-6 or a truncated ESAT-6, which lacks the dominant epitope and induces subdom T cell responses. Before and after Mtb infection, epitope-specific T cell responses were evaluated by proliferation, cytokine secretion, flow cytometric assays. Results. Pre-infection, subdom CD4 T cells had enhanced proliferation, but delayed cytokine kinetics. Post-infection, vaccine-induced T cells had a markedly different cytokine profile relative to infection-driven T cells, including memory-like polyfunctionality and IL-17 production. However, over time, a larger proportion of dominant T cells developed an infection-driven cytokine and KLRG1/PD-1 profile. Conclusion. Subdom epitope CD4 T cell have enhanced maintenance of vaccination-induced cytokine profile following infection in vivo, associated with their ability to enhance protection, and therefore may be uniquely able to resist bacterially-driven modulation and immune-mediated disease.

Induction of robust cellular immunity against HPV6 and HPV11 in mice by DNA vaccine encoding for E6/E7 antigen

Due to the strong relationship between the Human Papillomavirus (HPV) “high-risk” subtypes and cervical cancers, most HPV-related studies have been focusing on the “high-risk” HPV subtypes 16 and 18. However, it has been suggested that the “low-risk” subtypes of HPV, HPV6 and HPV11, are the major cause of recurrent respiratory papillomatosis and genital warts. In addition, HPV 6 and 11 are also associated with otolaryngologic malignancies, carcinoma of the lung, tonsil, larynx and low-grade cervical lesions. Therefore, development of HPV therapeutic vaccines targeting on subtypes 6 and 11 E6 or E7 are in great need. In this report, we describe two novel engineered DNA vaccines that encode HPV 6 and 11 consensus E6/E7 fusion proteins (p6E6E7 and p11E6E7) by utilizing a multi-phase strategy. Briefly, after generating consensus sequences, several modifications were performed to increase the expression of both constructs, including codon/RNA optimization, addition of a Kozak sequence and a highly efficient leader sequence. An endoproteolytic cleavage site was also introduced between E6 and E7 protein for proper protein folding and for better CTL processing. The expressions of both constructs were confirmed by western blot analysis and immunofluorescence assay. Vaccination with these DNA vaccines could elicit robust cellular immune responses. The epitope mapping assay was performed to further characterize the cellular immune responses induced by p6E6E7 and p11E6E7. The HPV 6 and 11 E6 or E7-specific immunodominant and subdominant epitopes were verified, respectively. The intracellular cytokine staining revealed that the magnitude of IFN-γ and TNF-α secretion in antigen-specific CD8+ cells was significantly enhanced, indicating that the immune responses elicited by p6E6E7 and p11E6E7 was heavily skewed toward driving CD8+ T cells. Such DNA immunogens are interesting candidates for further studies on HPV 6 and 11-associated diseases.

Identification of continuous epitopes of HuD antibodies related to paraneoplastic diseases/small cell lung cancer

HuD antibodies are associated with small cell lung cancer. To identify relevant epitopes of HuD antibodies, patient sera and a monoclonal antibody were analyzed for their reactivity to linear 20mer peptides spanning the human HuD protein. The HuD monoclonal antibody recognized a single fragment located in the first RNA recognition motif. Thorough analysis identified VRDKITQGSL as the actual epitope. Screening of anti-HuD positive patients and healthy controls identified eight peptides as potential subdominant epitopes. The majority of these peptides were located in the N-terminal end as well as in the linker region between the second and third RNA recognition motifs.

Re-Engaging Cross-Reactive Memory B Cells: The Influenza Puzzle

The emergence of a novel influenza A virus strain into humans poses a continuous public health threat. Vaccination is the most effective means of protection against influenza. The generation of memory B cells and long-lived plasma cells that can maintain protective levels of influenza-specific antibodies for protracted periods of time is the foundation for the success of such vaccines. Influenza vaccines elicit an antibody response that is primarily targeting viral surface glycoproteins. However, frequent amino acid mutations within the immunodominant epitopes allow the virus to efficiently escape neutralization by pre-existing antibodies and consequently cause annual epidemics and occasional pandemics. Recently, monoclonal antibodies (mAbs) that target subdominant influenza epitopes have been extensively characterized. These epitopes are immunogenic, can mediate virus neutralization, and most importantly are conserved among different influenza strains. It remains puzzling, however, that despite being repeatedly exposed to such conserved domains of influenza hemagglutinin (HA) either in the form of vaccination or natural infection, most humans do not develop immunological memory that can provide broad protection against emerging virus strains. Here we will discuss the conditions that may be required for engaging such cross-reactive memory B cells in the immune response to influenza infection and vaccination in humans.

Neonatal CD8 T-cell Hierarchy Is Distinct from Adults and Is Influenced by Intrinsic T cell Properties in Respiratory Syncytial Virus Infected Mice

Following respiratory syncytial virus infection of adult CB6F1 hybrid mice, a predictable CD8+ T cell epitope hierarchy is established with a strongly dominant response to a Kd-restricted peptide (SYIGSINNI) from the M2 protein. The response to KdM282-90 is ∼5-fold higher than the response to a subdominant epitope from the M protein (NAITNAKII, DbM187-195). After infection of neonatal mice, a distinctly different epitope hierarchy emerges with codominant responses to KdM282-90 and DbM187-195. Adoptive transfer of naïve CD8+ T cells from adults into congenic neonates prior to infection indicates that intrinsic CD8+ T cell factors contribute to age-related differences in hierarchy. Epitope-specific precursor frequency differs between adults and neonates and influences, but does not predict the hierarchy following infection. Additionally, dominance of KdM282-90 –specific cells does not correlate with TdT activity. Epitope-specific Vβ repertoire usage is more restricted and functional avidity is lower in neonatal mice. The neonatal pattern of codominance changes after infection at 10 days of age, and rapidly shifts to the adult pattern of extreme KdM282- 90 -dominance. Thus, the functional properties of T cells are selectively modified by developmental factors in an epitope-specific and age-dependent manner.

HIV-1: From escapism to conservatism

HIV-1: From escapism to conservatism

The Capacity of CMV-Specific T-Cells to Prevent Outgrowth of Clonogenic Human Colon Carcinoma Cells Co-Expressing CMVpp65 in-Vivo and Durably Suppress Established CMVpp65+ Tumor Xenografts Is Dose Dependant and Can Be Augmented by IL-15/IL-15Rα

Abstract 4307Adoptively transferred CMV-specific T cells (CMV-CTL) can effectively prevent CMV disease in HSCT recipients. However, data regarding the doses required to eradicate disease and the relative potency of T-cells (TC) specific for different epitopes are lacking. To test the capacity of T-cells specific for different CMV antigenic peptides to target and eliminate CMV+ cells in-vivo, and establish TC doses required for treatment we have developed an in-vivo model to assess specificity and efficacy of CMV-CTLs using human colon carcinoma cells transduced with CMVpp65 as a surrogate system.HLA A0201+ colon carcinoma cells transduced to express CMVpp65 and a GFP-firefly luciferase transgene (cocapp65) were injected subcutaneously (s.c.) into NOD/Scid-IL2Rgc-KO/J mice (NSG) at doses ranging from 104 – 106 (4 mice /group) and tumor growth followed for 4 weeks using bio-luminescent imaging and tumor measurements. Consistent engraftment was observed with 3 × 105 cells. Groups of NSG mice were then injected s.c with coca-pp65 (3 × 105) mixed with HLA A0201-restricted CMVpp65 specific T-cells (A2-CMV-CTLs) at E:T ratios of 50:1, 10:1, 2:1, 0.1:1, 0.01:1 and 0.001:1. To ascertain antigen specificity of A2-CMV-CTLs, groups of 4 NSG mice were subsequently co-injected s.c. with 3 tumor-TC combinations (E:T= 1:1) as follows: (i) A2-CMV- CTLs + 3 × 105 cocapp65 (ii) A2-CMV- CTLs + A2 tumor without CMVpp65 (iii) A2-Flu-CTLs + 3 × 105 cocapp65. Control animals were injected with the cocapp65 without TC. IL-2 (2000 U i.p) was given 2 × a week to all groups. Tumor growth was measured by bioluminescence. No growth of cocapp65 was detected in any animal co-injected with A2-CMV-CTLs at E:T ratios ≥ 1:1. At E:T ratios of 0.1:1, 0.01:1 and 0.001:1, 1/4, 2/4 and 3/4 animals demonstrated tumor growth respectively. In contrast, consistent tumor growth was seen in all control animals over 4 weeks. Thus, tumors in condition (i) were completely inhibited while (ii) and (iii) continued to grow similar to controls, thus demonstrating antigen specific activity of the infused CMV-CTLs.In subsequent experiments we assessed (1) the efficacy of titrated doses of intravenously administered CMV-CTLs in animals with established tumors using 20 × 106, 7× 106 or 2× 106 T-cells per mouse (2) the contribution of IL-15/15Rα complex in augmenting the efficacy of CMV-CTLs by injecting each mouse i.p. with irradiated Baf-3 cells transduced to express human IL-15/15Rα complex.Infusion of CMV-CTLs significantly suppressed growth of cocapp65 tumors at all doses tested. However after a period of 4 weeks, the tumors in animals receiving doses of 7 × 106 and 2 × 106 CMV-CTLs began to re-grow, while tumors in animals injected with 20 × 106 remained suppressed till the end of the experiment at 6–8 weeks. At autopsy, human CD45[+] CD3[+] T-cells were detected in tumors expressing CMVpp65 as documented by IHC staining, but not in tumors lacking CMVpp65 or HLA A0201. In mice injected with the Baf-3 cells expressing IL-15/IL-15Rα, the anti-tumor activity of the transferred T-cells was sustained even in animals treated with only 2×106 CMVpp65 specific CTLs. Differences in cytolytic capacity of CMV-CTLs reactive against dominant and subdominant epitopes are currently under study.These studies demonstrate that (1) CMV-CTLs can prevent outgrowth of clonogenic human carcinoma cells co-expressing an immunogenic viral antigen in-vivo at E:T ratios that are significantly lower than those required in-vitro (2) These CMV-CTLs can also induce sustained suppression of established tumor xenografts following intravenous transfer (3) Lower doses of intravenously transferred CMV-CTLs are effective, but may require additional dosing to maintain disease control, and (4) In contrast, IL-15/IL-15Rα supplementation can augment and sustain the in-vivo activity of low doses of CMVpp65-specific CTLs. This model thus provides an in vivo system for estimating the concentrations of antigen-specific T-cells over time required for effective adoptive immunotherapy, for comparative evaluations of virus-specific T-cells differing in phenotype or specificity, and for testing the potential of cytokines and other agents to increase or sustain virus-specific T-cell activity. Disclosures:No relevant conflicts of interest to declare.

Decline of influenza-specific CD8+ T cell repertoire in healthy geriatric donors

BackgroundWhile influenza vaccination results in protective antibodies against primary infections, clearance of infection is primarily mediated through CD8+ T cells. Studying the CD8+ T cell response to influenza epitopes is crucial in understanding the disease associated morbidity and mortality especially in at risk populations such as the elderly. We compared the CD8+ T cell response to immunodominant and subdominant influenza epitopes in HLA-A2+ control, adult donors, aged 21-42, and in geriatric donors, aged 65 and older.ResultsWe used a novel artificial Antigen Presenting Cell (aAPC) based stimulation assay to reveal responses that could not be detected by enzyme-linked immunosorbent spot (ELISpot). 14 younger control donors and 12 geriatric donors were enrolled in this study. The mean number of influenza-specific subdominant epitopes per control donor detected by ELISpot was only 1.4 while the mean detected by aAPC assay was 3.3 (p = 0.0096). Using the aAPC assay, 92% of the control donors responded to at least one subdominant epitopes, while 71% of control donors responded to more than one subdominant influenza-specific response. 66% of geriatric donors lacked a subdominant influenza-specific response and 33% of geriatric donors responded to only 1 subdominant epitope. The difference in subdominant response between age groups is statistically significant (p = 0.0003).ConclusionGeriatric donors lacked the broad, multi-specific response to subdominant epitopes seen in the control donors. Thus, we conclude that aging leads to a decrease in the subdominant influenza-specific CTL responses which may contribute to the increased morbidity and mortality in older individuals.

Precursor Frequency and Competition Dictate the HLA-A2–Restricted CD8+ T Cell Responses to Influenza A Infection and Vaccination in HLA-A2.1 Transgenic Mice

The human HLA-A2-restricted CD8(+) T cell response to influenza A virus (IAV) is largely directed against the matrix protein-derived M1(58-66) epitope and represents an archetypal example of CD8(+) T cell immunodominance. In this study, we examined the CD8(+) T cell hierarchy to M1(58-66) and two subdominant IAV-specific epitopes: NS1(122-130) and PA(46-55) in HLA-A2(+) human subjects and HLA-A2.1 transgenic (HHD) mice. Using epitope-based lipopeptides, we show that the CD8(+) T cell hierarchy induced by IAV infection could also be induced by lipopeptide vaccination in a context outside of viral infection when the Ag load is equalized. In the HHD HLA-A2.1 mouse model, we show that the naive T cell precursor frequencies, and competition at the Ag presentation level, can predict the IAV-specific CD8(+) T cell hierarchy. Immunization of mice with subdominant epitopes alone was unable to overcome the dominance of the M1(58-66)-specific response in the face of IAV challenge; however, a multiepitope vaccination strategy was most effective at generating a broad and multispecific response to infection.

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.

Development and preclinical safety evaluation of a new therapeutic HIV-1 vaccine based on 18 T-cell minimal epitope peptides applying a novel cationic adjuvant CAF01

Therapeutic immunization of HIV-1-infected individuals with or without anti-retroviral therapy is a new promising disease prevention. To induce a new cytotoxic T CD8 lymphocyte (CTL) immunity during chronic HIV-1 infection 15 infrequently targeted but conserved HLA-supertype binding CTL epitopes from Gag, Pol, Nef, Env, Vpu and Vif were identified. The 15 T CD8 and three T CD4 helper peptides were GMP synthesised and formulated with a new adjuvant CAF01 which is a synthetic two-component liposomic adjuvant comprising the quaternary ammonium dimethyl-dioctadecyl-ammonium (DDA) and the immune modulator trehalose 6,6′-dibehenate (TDB). Using IFN-γ ELISPOT assay, T-cell immune induction by the vaccine was found to both CD4 and CD8 T-cell restricted peptides in HLA-A2 transgenic mice. Comprehensive toxicity studies of the CAF01 adjuvant-alone and together with different vaccines showed that CAF01 when tested at human dose levels was safe and well tolerated with only local inflammation at the site of injection and no systemic reactions. No pharmacological safety issues were observed in Beagle dogs. The HIV-1 vaccine toxicity study in the Göttingen Minipig ® showed no systemic toxicity from five repetitive i.m. injections, each with a 2-week interval, of either the 18 HIV-1 peptide antigen solution (AFO18) or the AFO18–CAF01, in which the 18 HIV-1 peptides were formulated with the CAF01 adjuvant. Distinct inflammatory responses were observed in the injected muscles of the AFO18–CAF01 vaccine treated animals as a result of the immune stimulating effect of the adjuvant on the vaccine. The results of the toxicity studies provide optimism for phase I clinical trials evaluating the therapeutic HIV-1 T-cell vaccination approach using multiple subdominant minimal epitope peptides applying the novel cationic adjuvant CAF01.

Subdominant/Cryptic CD8 T Cell Epitopes Contribute to Resistance against Experimental Infection with a Human Protozoan Parasite

During adaptive immune response, pathogen-specific CD8+ T cells recognize preferentially a small number of epitopes, a phenomenon known as immunodominance. Its biological implications during natural or vaccine-induced immune responses are still unclear. Earlier, we have shown that during experimental infection, the human intracellular pathogen Trypanosoma cruzi restricts the repertoire of CD8+ T cells generating strong immunodominance. We hypothesized that this phenomenon could be a mechanism used by the parasite to reduce the breath and magnitude of the immune response, favoring parasitism, and thus that artificially broadening the T cell repertoire could favor the host. Here, we confirmed our previous observation by showing that CD8+ T cells of H-2a infected mice recognized a single epitope of an immunodominant antigen of the trans-sialidase super-family. In sharp contrast, CD8+ T cells from mice immunized with recombinant genetic vaccines (plasmid DNA and adenovirus) expressing this same T. cruzi antigen recognized, in addition to the immunodominant epitope, two other subdominant epitopes. This unexpected observation allowed us to test the protective role of the immune response to subdominant epitopes. This was accomplished by genetic vaccination of mice with mutated genes that did not express a functional immunodominant epitope. We found that these mice developed immune responses directed solely to the subdominant/cryptic CD8 T cell epitopes and a significant degree of protective immunity against infection mediated by CD8+ T cells. We concluded that artificially broadening the T cell repertoire contributes to host resistance against infection, a finding that has implications for the host-parasite relationship and vaccine development.

Protective Efficacy of Serially Up-Ranked Subdominant CD8+ T Cell Epitopes against Virus Challenges

Immunodominance in T cell responses to complex antigens like viruses is still incompletely understood. Some data indicate that the dominant responses to viruses are not necessarily the most protective, while other data imply that dominant responses are the most important. The issue is of considerable importance to the rational design of vaccines, particularly against variable escaping viruses like human immunodeficiency virus type 1 and hepatitis C virus. Here, we showed that sequential inactivation of dominant epitopes up-ranks the remaining subdominant determinants. Importantly, we demonstrated that subdominant epitopes can induce robust responses and protect against whole viruses if they are allowed at least once in the vaccination regimen to locally or temporally dominate T cell induction. Therefore, refocusing T cell immune responses away from highly variable determinants recognized during natural virus infection towards subdominant, but conserved regions is possible and merits evaluation in humans.

Sequence analysis of HIV-1 isolates from Guinea-Bissau: selection of vaccine epitopes relevant in both West African and European countries

For a CD8 epitope-based vaccine to match different geographic locations, the targeted epitopes for cytotoxic T-lymphocytes (CTLs) must be present in the local circulating HIV-1 strains. Secondly, the vaccine epitopes should match the host population HLA types. We characterized two new HIV-1 isolates from Guinea-Bissau. Also, we have identified 15 subdominant CD8 epitopes representing common HLA super-types theoretically covering most HLA alleles in any population. Herein we demonstrate that the selected vaccine epitopes are well conserved and simultaneously present in sequences from West Africa and Denmark. Use of the selected epitopes will likely ensure ≥10 immune targets in the majority of candidates for experimental therapeutic vaccination in both geographic regions. Our results warrant testing of the selected vaccine epitopes in both geographic locations.

The Immune Response to the RT181-189 Epitope in HIV-1-Infected Patients is Associated with Viral Sequence Polymorphism Flanking the Epitope

Many drug-resistance mutations in HIV-1 reverse transcriptase fall within cytotoxic T lymphocytes (CTL) epitopes, but studies of the response to these epitopes in patients with virological failure are lacking. We therefore compared IFN-γ ELISPOT responses to the YV9 epitope (RT181-189) covering the lamivudine resistance mutation, M184V, in HLA-A2(+) antiretroviral treatment (ART)-naive patients (n = 19), to those found in HLA-A2(+) patients with virological failure (n = 15). Ten ART-naive patients had an ELISPOT response to the wild-type epitope that cross-reacted with the mutant epitope. Two patients with virological failure showed a specific response to the 184V mutant epitope. Responses against YV9 were strongly associated (p = 0.005) with the presence of a 177E mutation, and the same tendency was observed in an independent cohort of patients (n = 22). These results indicate that variants in flanking residues may influence CTL responses to conserved subdominant HIV-1 epitopes.

Defining the Herpes Simplex Virus-Specific CD8+ T Cell Repertoire in C57BL/6 Mice

HSV type 1 (HSV-1) expresses its genes sequentially as immediate early (α), early (β), leaky late (γ1), and true late (γ2), where viral DNA synthesis is an absolute prerequisite only for γ2 gene expression. The γ1 protein glycoprotein B (gB) contains a strongly immunodominant CD8(+) T cell epitope (gB(498-505)) that is recognized by 50% of both the CD8(+) effector T cells in acutely infected trigeminal ganglia (TG) and the CD8(+) memory T cells in latently infected TG. Of 376 predicted HSV-1 CD8(+) T cell epitopes in C57BL/6 mice, 19 (gB(498-505) and 18 subdominant epitopes) stimulated CD8(+) T cells in the spleens and TG of HSV-1 acutely infected mice. These 19 epitopes identified virtually all CD8(+) T cells in the infected TG that represent all or the vast majority of the HSV-specific CD8(+) TCR repertoire. Only 11 of ∼84 HSV-1 proteins are recognized by CD8(+) T cells, and most (∼80%) are expressed before viral DNA synthesis. Neither the immunodominance of gB(498-505) nor the dominance hierarchy of the subdominant epitopes is due solely to MHC or TCR affinity. We conclude that the vast majority of CD8(+) T cells in HSV-1 acutely infected TG are HSV specific, that HSV-1 β and γ1 proteins that are expressed before viral DNA synthesis are favored targets of CD8(+) T cells, and that dominance within the TCR repertoire is likely due to the frequency or expansion and survival characteristics of CD8(+) T cell precursors.

Peptide-MHC stability regulates the efficiency and duration of cross-priming (100.4)

Abstract Mechanisms that regulate the recruitment and the accumulation of T cells can impact the magnitude of determinant-specific responses. In this study, we demonstrate that peptide-MHC stability is a regulator of CD8+ T cell cross-priming. We find that increasing the kinetic stability of pMHC for an immunorecessive determinant from SV40 large T antigen, designated site V, overcomes the immunorecessive nature of the determinant. Using an in vivo assay to measure the proportion of naïve T cells that are triggered by cross-priming, we found that enhanced immunogenicity was due to two independent mechanisms regulated by pMHC-stability. 1) Enhanced cross-priming resulted in more efficient recruitment of site V-specific T cells, and 2) extended duration of cross-priming was associated with greater accumulation of site V-specific T cells. Thus, our results suggest that pMHC-stability regulates the magnitude of the CD8+ T cell response by influencing the number of naïve T cells recruited and the extent of T cell expansion. These findings have implications for the design of multivalent CD8+ T cell vaccines targeting subdominant determinants.

Hypomorphic Mutation in the Site-1 Protease Mbtps1 Endows Resistance to Persistent Viral Infection in a Cell-Specific Manner

The prototypic arenavirus lymphocytic choriomeningitis virus (LCMV), which naturally persists in rodents, represents a model for HIV, HBV, and HCV. Cleavage of the viral glycoprotein precursor by membrane-bound transcription factor peptidase, site 1 (Mbtps1 or site-1 protease), is crucial for the life cycle of arenaviruses and therefore represents a potential target for therapy. Recently, we reported a viable hypomorphic allele of Mbtps1 (woodrat) encoding a protease with diminished enzymatic activity. Using the woodrat allele, we examine the role of Mbtps1 during persistent LCMV infection. Surprisingly, Mbtps1 inhibition limits persistent but not acute viral infection and is associated with an organ/cell type-specific decrease in viral titers. Analysis of bone marrow-derived dendritic cells from woodrat mice supports their specific role in resolving persistent viral infection. These results support in vivo targeting of Mbtps1 in the treatment of arenavirus infections and demonstrate a critical role for dendritic cells in persistent viral infections.

HIV fragment gag vaccine induces broader T cell response in mice

Broad T-cell response is considered critical for HIV-1 vaccines to compensate viral diversity. Usually, a limited number of immunodominant epitopes are recognized in natural infections, as well as in vaccinations. Here, we seek to overcome immunofocusing of CD8 T Cell responses to HIV-1 CN54 gag DNA (delivered as a plasmid) in BalB/C mice by splitting it into fragments for reducing competition of recognition between dominant and sub-dominant epitopes. As expected, mice immunized with mixture of DNA fragments elicited significantly broader T cell responses than whole-length gag. We also further studied the effects when fragments and full-length DNA vaccines are combined for prime–boost vaccination. Interestingly, mice primed with full-length gag and boosted with DNA vaccine fragments induced similar T-cell response breadth as mice both primed and boosted by fragments DNA. In contrast, mice primed with DNA vaccine fragments and boosted with full-length gag failed to broaden T cell responses, once again, only the dominant epitopes were recognized. In summary, our study demonstrated that “fragmentation strategy” can indeed broaden T cell responses. This enhancement is more likely achieved in boosting stage. This study offers a promising way to design a vaccine with higher chance covering the highly diversified circulating strains.

T Cell Therapy for Nasopharyngeal Carcinoma

Among the novel biologic therapeutics that will increase our ability to cure human cancer in the years to come, T cell therapy is one of the most promising approaches. However, with the possible exception of tumor-infiltrating lymphocytes therapy for melanoma, clinical trials of adoptive T-cell therapy for solid tumors have so far provided only clear proofs-of-principle to build on with further development. Epstein-Barr virus (EBV)-associated malignancies offer a unique model to develop T cell-based immune therapies, targeting viral antigens expressed on tumor cells. In the last two decades, EBV-specific cytotoxic T-lymphocytes (CTL) have been successfully employed for the prophylaxis and treatment of EBV-related lymphoproliferative disorders in immunocompromised hosts. More recently, this therapeutic approach has been applied to the setting of EBV-related solid tumors, such as nasopharyngeal carcinoma. The results are encouraging, although further improvements to the clinical protocols are clearly necessary to increase anti-tumor activity. Promising implementations are underway, including harnessing the therapeutic potential of CTLs specific for subdominant EBV latent cycle epitopes, and delineating strategies aimed at targeting immune evasion mechanisms exerted by tumor cells.