scholarly journals Lack of CD4+ T Cells Does Not Affect Induction of CD8+ T-Cell Immunity against Encephalitozoon cuniculi Infection

2000 ◽  
Vol 68 (11) ◽  
pp. 6223-6232 ◽  
Author(s):  
Magali Moretto ◽  
Lori Casciotti ◽  
Brigit Durell ◽  
Imtiaz A. Khan
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Cell Mediated Immunity ◽  
Wild Type ◽  
Encephalitozoon Cuniculi ◽  
Cell Immunity ◽  
Mouse Tissues

ABSTRACT Cell-mediated immunity has been reported to play an important role in defense against Encephalitozoon cuniculi infection. Previous studies from our laboratory have underlined the importance of cytotoxic CD8+ T lymphocytes (CTL) in survival of mice infected with E. cuniculi. In the present study, immune response against E. cuniculi infection in CD4+T-cell-deficient mice was evaluated. Similar to resistant wild-type animals, CD4−/− mice were able to resolve E. cuniculi infection even at a very high challenge dose (5 × 107 spores/mouse). Tissues from infected CD4−/− mice did not exhibit higher parasite loads in comparison to the parental wild-type mice. Conversely, at day 21 postinfection, susceptible CD8−/− mice had 1014 times more parasites in the liver compared to control wild-type mice. Induction of the CD8+ T-cell response in CD4−/− mice against E. cuniculi infection was studied. Interestingly, a normal antigen-specific CD8+T-cell response to E. cuniculi infection was observed in CD4−/− mice (precursor proliferation frequency, 1/2.5 × 104 versus 1/104 in wild-type controls). Lack of CD4+ T cells did not alter the magnitude of the antigen-specific CTL response (precursor CTL frequency; 1/1.4 × 104 in CD4−/− mice versus 1/3 × 104 in control mice). Adoptive transfer of immune CD8+ T cells from both CD4−/− and wild-type animals prevented the mortality in CD8−/− mice.E. cuniculi infection thus offers an example of an intracellular parasitic infection where CD8+ T-cell immunity can be induced in the absence of CD4+ T cells.

scholarly journals Lack of Interleukin-12 in p40-Deficient Mice Leads to Poor CD8+ T-Cell Immunity against Encephalitozoon cuniculi Infection

2010 ◽  
Vol 78 (6) ◽  
pp. 2505-2511 ◽  
Author(s):  
Magali M. Moretto ◽  
Elizabeth M. Lawlor ◽  
Imtiaz A. Khan
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Response ◽  
T Cell Response ◽  
Scid Mice ◽  
T Cell Immunity ◽  
Interleukin 12 ◽  
Cell Immune Response ◽  
Encephalitozoon Cuniculi ◽  
Cell Immunity

ABSTRACT A CD8+ T-cell response is critical for protection against Encephalitozoon cuniculi infection. However, the factors responsible for the generation of CD8+ T-cell immunity during E. cuniculi infection and the cytokines involved in this process have not been identified. In the present study, we demonstrated that p40-deficient animals, which are unable to produce interleukin-12 (IL-12), have a serious defect in expansion of the CD8+ T-cell response which compromises the survival of an infected host. Adoptive transfer of CD8+ T cells from immunocompetent donors protected SCID mice infected with E. cuniculi, whereas administration of CD8+ T cells from p40−/− mice failed to protect infected SCID mice. In vitro dendritic cell (DC) cultures from knockout mice pulsed with E. cuniculi spores were unable to develop a robust CD8+ T-cell immune response. Addition of exogenous IL-12 or transfer of CD8+ T cells that were initially primed with DC from p40−/− animals to DC cultures from immunocompetent mice (directly or via transwells) led to optimal expansion of these cells. This IL-12-mediated reinstatement of CD8+ T-effector immunity was independent of gamma interferon (IFN-γ) as addition of antibody to the cultures failed to have an effect. These studies demonstrated that IL-12 plays a predominant role in the expansion of effector CD8+ T-cell immunity against E. cuniculi, which is critical for host survival. These findings are very important for understanding the protective immune mechanisms needed to protect an immunocompromised host against an opportunistic infection and can be extended to other microsporidial pathogens.

scholarly journals Children and adults with mild COVID-19 symptoms develop memory T cell immunity to SARS-CoV-2

2021 ◽  
Author(s):  
Patricia Kaaijk ◽  
Veronica Olivo Pimentel ◽  
Maarten E. Emmelot ◽  
Martien Poelen ◽  
Alper Cevirgel ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Immune Memory ◽  
Effector Memory ◽  
Longitudinal Assessment ◽  
Memory T Cell ◽  
Cell Immunity

Background: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to considerable morbidity/mortality worldwide, but most infections, especially among children, have a mild course. However, it remains largely unknown whether infected children develop cellular immune memory. Methods: To determine whether a memory T cell response is being developed as an indicator for long-term immune protection, we performed a longitudinal assessment of the SARS-CoV-2-specific T cell response by IFN-γ ELISPOT and activation marker expression analyses of peripheral blood samples from children and adults with mild-to-moderate COVID-19. Results: Upon stimulation of PBMCs with heat-inactivated SARS-CoV-2 or overlapping peptides of spike (S-SARS-CoV-2) and nucleocapsid proteins, we found S-SARS-CoV-2-specific IFN-ɣ T cell responses in most infected children (83%) and all adults (100%) that were absent in unexposed controls. Frequencies of SARS-CoV-2-specific T cells were higher in infected adults, especially in those with moderate symptoms, compared to infected children. The S-SARS-CoV-2 IFN-ɣ T cell response correlated with S1-SARS-CoV-2-specific serum IgM, IgG, and IgA antibody concentrations. Predominantly, effector memory CD4+ T cells of a Th1 phenotype were activated upon exposure to SARS-CoV-2 antigens, which persisted for 4-8 weeks after symptom onset. We detected very low frequencies of SARS-CoV-2-reactive CD8+ T cells in these individuals. Conclusions: Our data indicate that an antigen-specific memory CD4+ T cell response is induced in children and adults with mild SARS-CoV-2 infection. T cell immunity induced after mild COVID-19 could contribute to protection against re-infection.

scholarly journals Assessment of T-cell immunity to SARS-CoV-2 in COVID-19 convalescents and vaccinated subjects, using TigraTest® SARS-CoV-2 ELISPOT kit

2021 ◽  
Vol 21 (3) ◽  
pp. 178-192
Author(s):  
D. A. Poteryaev ◽  
S. G. Abbasova ◽  
P. E. Ignatyeva ◽  
O. M. Strizhakova ◽  
S. V. Kolesnik ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Peripheral Blood ◽  
Cell Response ◽  
Human Peripheral Blood ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Cell Immunity

With the onset of the COVID-19 pandemic, a number of molecular-based tests have been developed to diagnose SARS-CoV-2 infection. However, numerous available serological tests lack sufficient sensitivity or specificity. They do not detect specific antibodies in a significant proportion of patients with PCR-confirmed COVID-19. There is evidence that some convalescents have a relatively short-lived humoral immunity. In contrast, a number of publications have shown that T-cell response to human coronaviruses, including SARS-CoV-1, MERS, and SARS-CoV-2, can be strong and long-term. Assessment of T-cell immunity to SARS-CoV-2 is important not only for stratification of risks and identification of potentially protected populations with immunity acquired as a result of previous infection, but also for determining immunogenicity and potential efficacy of vaccines under development. The existing methods of quantitative or semi-quantitative assessment of specific T-cell response are mainly used in scientific research and are not standardised. The aim of the study was to develop and verify experimentally a test kit to be used in a standardised procedure for in vitro determination of T-cells specific to SARS-CoV-2 antigens, in human peripheral blood. Materials and methods: the TigraTest® SARS-CoV-2 kit developed by GENERIUM, which determines the number of T-cells secreting interferon gamma in vitro, was tested in the study. Samples of venous blood of volunteers from three different groups were analysed in the study: presumably healthy volunteers; COVID-19 convalescents; individuals vaccinated against SARS-CoV-2. Results: the authors developed the TigraTest® SARS-CoV-2 kit for in vitro determination of T-cells specific to SARS-CoV-2 antigens in human peripheral blood, demonstrated its specificity and performed preliminary assessment of its sensitivity. The study analysed the range and magnitude of the T-cell response in convalescent and vaccinated individuals. A pronounced T-cell response was also shown in some individuals with no symptoms or with unconfirmed diagnosis. It was discovered that the mean T-cell response to peptides of the spike protein (S-protein) was higher in the vaccinated individuals than in the convalescent patients. A correlation was determined between the severity of the disease and the level of T-cell response. Specific contributions of various groups of antigens to the T-cell response after COVID-19 infection were also determined. Conclusions: the TigraTest® SARS-CoV-2 kit is a specific and sensitive tool for the assessment of T-cell immunity to the SARS-CoV-2 virus, which can also be used for vaccinated individuals. The kit may be used in clinical practice for comprehensive assessment of immunity to SARS-CoV-2.

scholarly journals High prevalence of S. pyogenes Cas9-specific T cell sensitization within the adult human population – A balanced effector/regulatory T cell response

2018 ◽  
Author(s):  
Dimitrios L. Wagner ◽  
Leila Amini ◽  
Desiree J. Wendering ◽  
Petra Reinke ◽  
Hans-Dieter Volk ◽  
...  
Keyword(s):  
Gene Therapy ◽  
T Cells ◽  
T Cell ◽  
Cell Response ◽  
Human Subjects ◽  
T Cell Response ◽  
Cell Mediated Immunity ◽  
Healthy Human ◽  
Cell Immunity

Summary ParagraphThe field of gene therapy has been galvanized by the discovery of the highly efficient and adaptable site-specific nuclease system CRISPR/Cas9 from bacteria.1,2 Immunity against therapeutic gene vectors or gene-modifying cargo nullifies the effect of a possible curative treatment and may pose significant safety issues.3-5 Immunocompetent mice treated with CRISPR/Cas9-encoding vectors exhibit humoral and cellular immune responses against the Cas9 protein, that impact the efficacy of treatment and can cause tissue damage.5,6 Most applications aim to temporarily express the Cas9 nuclease in or deliver the protein directly into the target cell. Thus, a putative humoral antibody response may be negligible.5 However, intracellular protein degradation processes lead to peptide presentation of Cas9 fragments on the cellular surface of gene-edited cells that may be recognized by T cells. While a primary T cell response could be prevented or delayed, a pre-existing memory would have major impact. Here, we show the presence of a ubiquitous memory/effector T cell response directed towards the most popular Cas9 homolog from Streptococcus pyogenes (SpCas9) within healthy human subjects. We have characterized SpCas9-reactive memory/effector T cells (TEFF) within the CD4/CD8 compartments for multi-effector potency and lineage determination. Intriguingly, SpCas9-specific regulatory T cells (TREG) profoundly contribute to the pre-existing SpCas9-directed T cell immunity. The frequency of SpCas9-reactive TREG cells inversely correlates with the magnitude of the respective TEFF response. SpCas9-specific TREG may be harnessed to ensure the success of SpCas9-mediated gene therapy by combating undesired TEFF response in vivo. Furthermore, the equilibrium of Cas9-specific TEFF and TREG cells may have greater importance in Streptococcus pyogenes-associated diseases. Our results shed light on the T cell mediated immunity towards the much-praised gene scissor SpCas9 and offer a possible solution to overcome the problem of pre-existing immunity.

scholarly journals CD8+ T Cell Immunity Is Compromised by Anti-CD20 Treatment and Rescued by Interleukin-17A

mBio ◽  
2020 ◽  
Vol 11 (3) ◽  
Author(s):  
Facundo Fiocca Vernengo ◽  
Cristian G. Beccaria ◽  
Cintia L. Araujo Furlan ◽  
Jimena Tosello Boari ◽  
Laura Almada ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Content Type ◽  
Cell Immunity ◽  
Anti Cd20

ABSTRACT Treatment with anti-CD20, used in many diseases in which B cells play a pathogenic role, has been associated with susceptibility to intracellular infections. Here, we studied the effect of anti-CD20 injection on CD8+ T cell immunity using an experimental model of Trypanosoma cruzi infection, in which CD8+ T cells play a pivotal role. C57BL/6 mice were treated with anti-CD20 for B cell depletion prior to T. cruzi infection. Infected anti-CD20-treated mice exhibited a CD8+ T cell response with a conserved expansion phase followed by an early contraction, resulting in a strong reduction in total and parasite-specific CD8+ T cell numbers at 20 days postinfection. Anti-CD20 injection increased the frequency of apoptotic CD8+ T cells, decreased the number of effector and memory CD8+ T cells, and reduced the frequency of proliferating and cytokine-producing CD8+ T cells. Accordingly, infected anti-CD20-treated mice presented lower cytotoxicity of T. cruzi peptide-pulsed target cells in vivo. All of these alterations in CD8+ T cell immunity were associated with increased tissue parasitism. Anti-CD20 injection also dampened the CD8+ T cell response, when this had already been generated, indicating that B cells were involved in the maintenance rather than the induction of CD8+ T cell immunity. Anti-CD20 injection also resulted in a marked reduction in the frequency of interleukin-6 (IL-6)- and IL-17A-producing cells, and recombinant IL-17A (rIL-17A) injection partially restored the CD8+ T cell response in infected anti-CD20-treated mice. Thus, anti-CD20 reduced CD8+ T cell immunity, and IL-17A is a candidate for rescuing deficient responses either directly or indirectly. IMPORTANCE Monoclonal antibody targeting the CD20 antigen on B cells is used to treat the majority of non-Hodgkin lymphoma patients and some autoimmune disorders. This therapy generates adverse effects, notably opportunistic infections and activation of viruses from latency. Here, using the infection murine model with the intracellular parasite Trypanosoma cruzi, we report that anti-CD20 treatment affects not only B cell responses but also CD8+ T cell responses, representing the most important immune effectors involved in control of intracellular pathogens. Anti-CD20 treatment, directly or indirectly, affects cytotoxic T cell number and function, and this deficient response was rescued by the cytokine IL-17A. The identification of IL-17A as the cytokine capable of reversing the poor response of CD8+ T cells provides information about a potential therapeutic treatment aimed at enhancing defective immunity induced by B cell depletion.

scholarly journals CD8+ T cell immunity is compromised by anti-CD20 treatment and rescued by IL-17A

2019 ◽  
Author(s):  
Facundo Fiocca Vernengo ◽  
Cristian G. Beccaria ◽  
Cintia L. Araujo Furlan ◽  
Jimena Tosello Boari ◽  
Laura Almada ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
B Cell Depletion ◽  
Cell Immunity ◽  
Anti Cd20

AbstractTreatment with anti-CD20, used in many diseases in which B cells play a pathogenic role, has been associated with susceptibility to intracellular infections. Here, we studied the effect of anti-CD20 injection on CD8+ T cell immunity using an experimental model of Trypanosoma cruzi infection, in which CD8+ T cells play a pivotal role. C57BL/6 mice were treated with anti-CD20 for B cell depletion prior to T. cruzi infection. Infected anti-CD20-treated mice exhibited a CD8+ T cell response with a conserved expansion phase followed by an early contraction, resulting in a strong reduction in total and parasite-specific CD8+ T cells at 20 days postinfection. Anti-CD20 injection decreased the number of effector and memory CD8+ T cells and reduced the frequency of proliferating and cytokine producing CD8+ T cells. Accordingly, infected anti-CD20-treated mice presented a lower cytotoxicity of T. cruzi peptide-pulsed target cells in vivo. All of these alterations in CD8+ T cell immunity were associated with increased tissue parasitism. Anti-CD20 injection also dampened an established CD8+ T cell response, indicating that B cells were involved in the maintenance rather than the induction of CD8+ T cell immunity. Anti-CD20 injection also resulted in a marked reduction in the frequency of IL-6- and IL-17A-producing cells, and only rIL-17A injection partially restored the CD8+ T cell response in infected anti-CD20-treated mice. Thus, anti-CD20 reduced CD8+ T cell immunity, and IL-17A is a candidate for rescuing deficient responses either directly or indirectly.ImportanceMonoclonal antibody targeting the CD20 antigen on B cells is used to treat the majority of Non-Hodgkin lymphoma patients and some autoimmune disorders. This therapy generates adverse effects, notably opportunistic infections and activation of viruses from latency. Here, using the infection murine model with the intracellular parasite Trypanosoma cruzi, we report that anti-CD20 treatment not only affects B cell response but also CD8+ T cells, the most important immune effectors involved in control of intracellular pathogens. Anti-CD20 treatment, directly or indirectly, affects cytotoxic T cell number and function and this deficient response was rescued by the cytokine IL-17A. The identification of IL-17A as the cytokine capable of reversing the poor response of CD8+ T cells provide information about a potential therapeutic treatment aimed at enhancing defective immunity induced by B cell depletion.

scholarly journals Optimal CD8 T-Cell Response against Encephalitozoon cuniculi Is Mediated by Toll-Like Receptor 4 Upregulation by Dendritic Cells

2010 ◽  
Vol 78 (7) ◽  
pp. 3097-3102 ◽  
Author(s):  
Elizabeth M. Lawlor ◽  
Magali M. Moretto ◽  
Imtiaz A. Khan
Keyword(s):  
Dendritic Cells ◽  
T Cell ◽  
Dendritic Cell ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Toll Like Receptor ◽  
Encephalitozoon Cuniculi ◽  
Toll Like Receptor 4 ◽  
Cell Immunity

ABSTRACT CD8+ T-cell immunity has been shown to play an important role in the protective immune response against Encephalitozoon cuniculi. Although earlier studies suggest that dendritic cells (DC) are important for the induction of this response, the factors responsible for initiation of the dendritic cell response against this pathogen have not been evaluated. In the current study, we demonstrate that E. cuniculi infection causes strong Toll-like receptor 4 (TLR4)-dependent dendritic cell activation and a blockade of this molecule reduces the ability of DC to prime an antigen-specific CD8+ T-cell response. Pretreatment of DC with anti-TLR4 antibody causes a defect in both in vitro and in vivo CD8+ T-cell priming. These findings, for the first time, emphasize the contribution of TLR4 in the induction of CD8+ T-cell immunity against E. cuniculi infection.

scholarly journals CD8+-T-Cell Immunity against Toxoplasma gondii Can Be Induced but Not Maintained in Mice Lacking Conventional CD4+ T Cells

2002 ◽  
Vol 70 (2) ◽  
pp. 434-443 ◽  
Author(s):  
Lori Casciotti ◽  
Kenneth H. Ely ◽  
Martha E. Williams ◽  
Imtiaz A. Khan
Keyword(s):  
Immune Response ◽  
T Cells ◽  
T Cell ◽  
Toxoplasma Gondii ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Immunity ◽  
Cell Immune Response ◽  
Cell Immunity ◽  
Ifn Γ

ABSTRACT T-cell immunity is critical for survival of hosts infected with Toxoplasma gondii. Among the cells in the T-cell population, CD8+ T cells are considered the major effector cells against this parasite. It is believed that CD4+ T cells may be crucial for induction of the CD8+-T-cell response against T. gondii. In the present study, CD4−/− mice were used to evaluate the role of conventional CD4+ T cells in the immune response against T. gondii infection. CD4−/− mice infected with T. gondii exhibited lower gamma interferon (IFN-γ) messages in the majority of their tissues. As a result, mortality due to a hyperinflammatory response was prevented in these animals. Interestingly, T. gondii infection induced a normal antigen-specific CD8+-T-cell immune response in CD4−/− mice. No difference in generation of precursor cytotoxic T lymphocytes (pCTL) or in IFN-γ production by the CD8+-T-cell populations from the knockout and wild-type animals was observed. However, the mutant mice were not able to sustain CD8+-T-cell immunity. At 180 days after infection, the CD8+-T-cell response in the knockout mice was depressed, as determined by pCTL and IFN-γ assays. Loss of CD8+-T-cell immunity at this time was confirmed by adoptive transfer experiments. Purified CD8+ T cells from CD4−/− donors that had been immunized 180 days earlier failed to protect the recipient mice against a lethal infection. Our study demonstrated that although CD8+-T-cell immunity can be induced in the absence of conventional CD4+ T cells, it cannot be maintained without such cells.

scholarly journals Mechanisms that allow vaccination against an oncolytic vesicular stomatitis virus-encoded transgene to enhance safety without abrogating oncolysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Amanda W. K. AuYeung ◽  
Robert C. Mould ◽  
Ashley A. Stegelmeier ◽  
Jacob P. van Vloten ◽  
Khalil Karimi ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Vesicular Stomatitis Virus ◽  
Cell Response ◽  
Viral Infections ◽  
T Cell Response ◽  
Oncolytic Viruses ◽  
Oncolytic Virotherapy ◽  
Cell Immunity ◽  
Vesicular Stomatitis

AbstractVaccination can prevent viral infections via virus-specific T cells, among other mechanisms. A goal of oncolytic virotherapy is replication of oncolytic viruses (OVs) in tumors, so pre-existing T cell immunity against an OV-encoded transgene would seem counterproductive. We developed a treatment for melanomas by pre-vaccinating against an oncolytic vesicular stomatitis virus (VSV)-encoded tumor antigen. Surprisingly, when the VSV-vectored booster vaccine was administered at the peak of the primary effector T cell response, oncolysis was not abrogated. We sought to determine how oncolysis was retained during a robust T cell response against the VSV-encoded transgene product. A murine melanoma model was used to identify two mechanisms that enable this phenomenon. First, tumor-infiltrating T cells had reduced cytopathic potential due to immunosuppression. Second, virus-induced lymphopenia acutely removed virus-specific T cells from tumors. These mechanisms provide a window of opportunity for replication of oncolytic VSV and rationale for a paradigm change in oncolytic virotherapy, whereby immune responses could be intentionally induced against a VSV-encoded melanoma-associated antigen to improve safety without abrogating oncolysis.

scholarly journals Growth, Virulence, and Immunogenicity of Listeria monocytogenes aro Mutants

2004 ◽  
Vol 72 (10) ◽  
pp. 5622-5629 ◽  
Author(s):  
Jochen Stritzker ◽  
Jozef Janda ◽  
Christoph Schoen ◽  
Marcus Taupp ◽  
Sabine Pilgrim ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
T Cell ◽  
Cell Response ◽  
Culture Media ◽  
Lethal Dose ◽  
T Cell Response ◽  
Wild Type ◽  
Protein Antigens ◽  
Cell Immunity ◽  
Virulence Attenuation

ABSTRACT Mutants of Listeria monocytogenes with deletions in genes of the common branch of the biosynthesis pathway leading to aromatic compounds were constructed as possible virulence-attenuated carrier strains for protein antigens or vaccine DNA. aroA, aroB, and in particular aroE mutants showed strongly reduced growth rates in epithelial cells and even in rich culture media. The metabolism of the aro mutants under these conditions was predominantly anaerobic. Aerobic metabolism and a wild-type growth rate were, however, regained upon the addition of vitamin K2, suggesting that the aro mutants are deficient in oxidative respiration due to the lack of menaquinone. Replication of the aro mutants in the host cell's cytosol and cell-to-cell spread were drastically slowed down, and all aro mutants showed high virulence attenuation in mice, i.e., the 50% lethal dose in BALB/c mice was increased at least 104-fold for the aroA, aroB, and aroA/B mutants and >105-fold for the aroE mutant compared to the parent strain. Nevertheless, mice preimmunized with aro mutant bacteria elicited good T-cell response and full protection against a subsequent challenge with the virulent wild-type strain. A total of 5 × 106 aroA, aroB, and aroA/B mutant bacteria were sufficient to obtain a protective T-cell response, while 5 × 108 aroE or aroA/E mutants were necessary to achieve comparable numbers of antigen-specific T cells. These numbers were well tolerated without causing any signs of disease, indicating that Listeria strains with deletions in genes of the basic branch of the aromatic amino acid pathway could be useful vaccine carriers for inducing T-cell immunity.

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