Vaccination with DNA encoding the immunodominant LACK parasite antigen confers protective immunity to mice infected with Leishmania major.

To determine whether DNA immunization could elicit protective immunity to Leishmania major in susceptible BALB/c mice, cDNA for the cloned Leishmania antigen LACK was inserted into a euykaryotic expression vector downstream to the cytomegalovirus promoter. Susceptible BALB/c mice were then vaccinated subcutaneously with LACK DNA and challenged with L. major promastigotes. We compared the protective efficacy of LACK DNA vaccination with that of recombinant LACK protein in the presence or absence of recombinant interleukin (rIL)-12 protein. Protection induced by LACK DNA was similar to that achieved by LACK protein and rIL-12, but superior to LACK protein without rIL-12. The immunity conferred by LACK DNA was durable insofar as mice challenged 5 wk after vaccination were still protected, and the infection was controlled for at least 20 wk after challenge. In addition, the ability of mice to control infection at sites distant to the site of vaccination suggests that systemic protection was achieved by LACK DNA vaccination. The control of disease progression and parasitic burden in mice vaccinated with LACK DNA was associated with enhancement of antigen-specific interferon-gamma (IFN-gamma) production. Moreover, both the enhancement of IFN-gamma production and the protective immune response induced by LACK DNA vaccination was IL-12 dependent. Unexpectedly, depletion of CD8(+) T cells at the time of vaccination or infection also abolished the protective response induced by LACK DNA vaccination, suggesting a role for CD8(+) T cells in DNA vaccine induced protection to L. major. Thus, DNA immunization may offer an attractive alternative vaccination strategy against intracellular pathogens, as compared with conventional vaccination with antigens combined with adjuvants.

Altered ligands reveal limited plasticity in the T cell response to a pathogenic epitope.

Experimental leishmaniasis offers a well characterized model of T helper type 1 cell (Th1)-mediated control of infection by an intracellular organism. Susceptible BALB/c mice aberrantly develop Th2 cells in response to infection and are unable to control parasite dissemination. The early CD4(+) T cell response in these mice is oligoclonal and reflects the expansion of Vbeta4/ Valpha8-bearing T cells in response to a single epitope from the parasite Leishmania homologue of mammalian RACK1 (LACK) antigen. Interleukin 4 (IL-4) generated by these cells is believed to direct the subsequent Th2 response. We used T cells from T cell receptor-transgenic mice expressing such a Vbeta4/Valpha8 receptor to characterize altered peptide ligands with similar affinity for I-Ad. Such altered ligands failed to activate IL-4 production from transgenic LACK-specific T cells or following injection into BALB/c mice. Pretreatment of susceptible mice with altered peptide ligands substantially altered the course of subsequent infection. The ability to confer a healer phenotype on otherwise susceptible mice using altered peptides that differed by a single amino acid suggests limited diversity in the endogenous T cell repertoire recognizing this antigen.

Resistance to Leishmania major induced by tolerance to a single antigen.

In mice, susceptibility to Leishmania major is associated with the early expansion of T helper 2 cells (TH2) cells, but nothing is known of the specificity of these cells. A previously identified antigen, Leishmania homolog of receptors for activated C kinase (LACK), was found to be the focus of this initial response. Mice made tolerant to LACK by the transgenic expression of the antigen in the thymus exhibited both a diminished TH2 response and a healing phenotype. Thus, T cells that are activated early and are reactive to a single antigen play a pivotal role in directing the immune response to the entire parasite.

Expression cloning of a protective Leishmania antigen.

Parasite-specific CD4+ T cells have been shown to transfer protection against Leishmania major in susceptible BALB/c mice. An epitope-tagged expression library was used to identify the antigen recognized by a protective CD4+ T cell clone. The expression library allowed recombinant proteins made in bacteria to be captured by macrophages for presentation to T cells restricted to major histocompatibility complex class II. A conserved 36-kilodalton member of the tryptophan-aspartic acid repeat family of proteins was identified that was expressed in both stages of the parasite life cycle. A 24-kilodalton portion of this antigen protected susceptible mice when administered as a vaccine with interleukin-12 before infection.

[The biological rationale for immunotherapy in cancer]. / Rationnel biologique de l'immunothérapie des cancers.

INTRODUCTION: Immunotherapy aims to promote the immune system's activity against malignant cells by stimulating the response to several tumor antigens. STATE OF THE ART: Immunosurveillance may adjust the immunogenicity of tumors. To be effective, immunity must induce the specific activation of CD4+ and CD8+ T lymphocytes, as well as activation of innate immunity. Activator and inhibitory costimulatory molecules regulate T lymphocyte activation at immunity checkpoints such as PD-1/PD-L1 and CTLA-4. Adaptive immune resistance confers tumour resistance to immunosurveillance through these immune checkpoints. PERSPECTIVES: Approaches involving the combination of several immunotherapies with each other or with chemotherapy and radiotherapy and antibodies against other molecules of costimulation are under development. The development of biomarkers, which can select a targeted population and predict therapeutic response, represents a major challenge. Tumour high-throughput sequencing could refine "immunoscore". Intratumoral T cell receptor seems to represent a promising biomarker. CONCLUSIONS: Numerous challenges still remain in developing research approaches for the development of immunotherapies.

Present difficulties and future promise of MHC multimers in autoimmune exploration.

Class I tetramers have been used to track cytotoxic T cells during bacterial and viral infections. During the past year, the use of such molecules has revealed important information about the role of CD8(+) T cells in autoimmune diabetes. Furthermore, class II multimers have been produced and successfully used to stain autoreactive CD4(+) T cells from patients with rheumatoid arthritis or Borrelia-burgdorferi-induced Lyme arthritis.

Paper alert. Immunology.

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.

Immunotherapy in Non-Small Cell Lung Cancer: Biological Principles and Future Opportunities.

Immunotherapy aims to amplify the anticancer immune response through reactivation of the lymphocytic response raised against several tumor neo-antigens. To obtain an effective immune response, this therapeutic approach requires that a number of immunological checkpoints be passed, such as the activation of excitatory costimulatory signals or the avoidance of coinhibitory molecules. Among the immune checkpoints, the interaction of the membrane-bound ligand PD-1 and its receptor PD-L1 has received much attention because of remarkable efficacy in numerous clinical trials for various cancer types, including non-small cell lung cancer (NSCLC). However, several limitations exist with these therapeutic agents when used as monotherapy, with objective responses observed in only 30-40% of patients, with the majority of patients demonstrating innate resistance, and approximately 25% of responders later demonstrating disease progression. Recent developments in the understanding of cancer immunology have the potential to identify mechanisms of innate and acquired resistance to immune checkpoint inhibitors through translational research in human samples. This review focuses on the biological basic principles for immunological checkpoint blockade, and highlights the current status and the perspectives of this therapeutic approach in NSCLC patients.

Bystander immunotherapy as a strategy to control allergen-driven airway inflammation.

Allergic asthma is a chronic inflammatory disease characterized by airway hyperresponsiveness (AHR), lung infiltration of Th2 cells, and high levels of IgE. To date, allergen-specific immunotherapy (SIT) is the only treatment that effectively alleviates clinical symptoms and has a long-term effect after termination. Unfortunately, SIT is unsuitable for plurisensitized patients, and highly immunogenic allergens cannot be used. To overcome these hurdles, we sought to induce regulatory CD4(+) T cells (Treg) specific to an exogenous antigen that could be later activated as needed in vivo to control allergic responses. We have established an experimental approach in which mice tolerized to ovalbumin (OVA) were sensitized to the Leishmania homolog of receptors for activated c kinase (LACK) antigen, and subsequently challenged with aerosols of LACK alone or LACK and OVA together. Upon OVA administration, AHR and allergic airway responses were strongly reduced. OVA-induced suppression was mediated by CD25(+) Treg, required CTLA-4 and ICOS signaling and resulted in decreased numbers of migrating airway dendritic cells leading to a strong impairment in the proliferation of allergen-specific Th2 cells. Therefore, inducing Treg specific to a therapeutic antigen that could be further activated in vivo may represent a safe and novel curative approach for allergic asthma.

The histological spectrum of visceral leishmaniasis caused by Leishmania infantum MON-1 in acquired immune deficiency syndrome.

Visceral leishmaniasis (VL) due to Leishmania infantum is endemic in Southern France and can be considered as an opportunistic infection in patients with acquired immunodeficiency syndrome (AIDS). Co-infection with Leishmania sp. and human immunodeficiency virus (HIV) is emerging, but pathological findings of leishmaniasis in AIDS have been poorly documented, and scattered case reports have include morphological descriptions. The clinicopathologic analysis of 16 patients with HIV and VL were evaluated. The clinical presentation was characteristic of VL, with fever, hepatosplenomegaly, and pancytopenia in 6 patients, and the diagnosis was confirmed by finding amastigotes of Leishmania sp. in bone marrow smears and biopsy specimens. In 4 patients, the initial diagnosis of VL was made fortuitously in gastrointestinal biopsies performed systematically (3 patients) or in case of diarrhea (1 patient). In one duodenal biopsy, Leishmania sp. and Mycobacteria sp. were associated. Liver biopsy allowed the diagnosis of VL in 3 cases. Autopsy was performed in 9 patients, showing a disseminated leishmaniasis with very unusual localizations (adrenal and heart) in 2 cases. Cutaneous leishmaniasis involvement was noted before (4 patients), at the same time (2 patient), or after (1 patient) the diagnosis of VL. Inflammatory infiltrates noted with Leishmania sp. infection were made by CD68 macrophages with (8 patients) or without (8 patients) associated CD8 positive lymphocytes. Immunoperoxidase study using polyclonal anti-Leishmania sp. antibodies contributed to the diagnosis in all cases. Electron microscopy of 2 digestive biopsy specimens showed the ultrastructural characteristics of Leishmania sp. amastigotes. The zymodeme MON-1 of L infantum was identified by isoenzyme electrophoresis in all patients. The mean of CD4 counts was 37/mm3 at the time of diagnosis, and the mean duration before the death was 8 months. As shown in this study, VL in AIDS can be diagnosed in gastrointestinal or liver biopsies. Diagnosis of VL was made when the CD4 count was very low and was correlated with a poor prognosis.

Langerin+ dendritic cells are responsible for LPS-induced reactivation of allergen-specific Th2 responses in postasthmatic mice.

Allergic asthma is a T cell-dependent inflammatory lung disease that results from complex interactions between genetic predisposition and environmental factors, including exposure to lipopolysaccharide (LPS). In this study, we have shown that airway LPS exposure was sufficient to induce airway hyperreactivity (AHR) and eosinophil recruitment in mice that had previously experienced an acute episode of allergic asthma. LPS-induced disease reactivation depended on the activation of allergen-specific CD4(+) T cells by a subset of lung langerin(+) dendritic cells (DCs) that retained the allergen. Upon LPS exposure, migration of langerin(+) DCs from lungs to draining lymph nodes increased and LPS-exposed langerin(+) DCs instructed CD4(+) T cells toward a T helper (Th) 2 response. Selective depletion of langerin(+) DCs prevented LPS-induced eosinophil recruitment and T-cell activation, further demonstrating a critical role for langerin(+) DCs in disease reactivation. This finding provides a possible explanation for the subclinical worsening of asthmatics following exposure to low-dose LPS.

The oral administration of bacterial extracts prevents asthma via the recruitment of regulatory T cells to the airways.

The prevalence of asthma has steadily increased during the last decade, probably as the result of changes in the environment, including reduced microbial exposure during infancy. Accordingly, experimental studies have shown that deliberate infections with live pathogens prevent the development of allergic airway diseases in mice. Bacterial extracts are currently used in children suffering from repeated upper respiratory tract infections. In the present study, we have investigated whether bacterial extracts, commercially available as Broncho-Vaxom (BV), could prevent allergic airway disease in mice. Oral treatment with BV suppressed airway inflammation through interleukin-10 (IL-10)-dependent and MyD88 (myeloid differentiation primary response gene (88))-dependent mechanisms and induced the conversion of FoxP3 (forkhead box P3)(-) T cells into FoxP3(+) regulatory T cells. Furthermore, CD4(+) T cells purified from the trachea of BV-treated mice conferred protection against airway inflammation when adoptively transferred into sensitized mice. Therefore, treatment with BV could possibly be a safe and efficient strategy to prevent the development of allergic diseases in children.

Breast milk immune complexes are potent inducers of oral tolerance in neonates and prevent asthma development.

Allergic asthma is a chronic lung disease resulting from an inappropriate T helper (Th)-2 response to environmental antigens. Early tolerance induction is an attractive approach for primary prevention of asthma. Here, we found that breastfeeding by antigen-sensitized mothers exposed to antigen aerosols during lactation induced a robust and long-lasting antigen-specific protection from asthma. Protection was more profound and persistent than the one induced by antigen-exposed non-sensitized mothers. Milk from antigen-exposed sensitized mothers contained antigen-immunoglobulin (Ig) G immune complexes that were transferred to the newborn through the neonatal Fc receptor resulting in the induction of antigen-specific FoxP3(+) CD25(+) regulatory T cells. The induction of oral tolerance by milk immune complexes did not require the presence of transforming growth factor-beta in milk in contrast to tolerance induced by milk-borne free antigen. Furthermore, neither the presence of IgA in milk nor the expression of the inhibitory FcgammaRIIb in the newborn was required for tolerance induction. This study provides new insights on the mechanisms of tolerance induction in neonates and highlights that IgG immune complexes found in breast milk are potent inducers of oral tolerance. These observations may pave the way for the identification of key factors for primary prevention of immune-mediated diseases such as asthma.

T cells that react to the immunodominant Leishmania major LACK antigen prevent early dissemination of the parasite in susceptible BALB/c mice.

Susceptibility of BALB/c mice to Leishmania major depends on the early production of IL-4 by CD4(+) T cells which react to the parasite LACK antigen. Here, we show that LACK-specific cells are rapidly recruited to the site of infection and favor the early dissemination of L. major to the internal organs.

A role for ID repetitive sequences in growth- and transformation-dependent regulation of gene expression in rat fibroblasts.

A set of mRNAs tagged by repetitive sequences of the ID family were found to accumulate following growth-factor-induced transition of normal (FR3T3) rat fibroblasts from a quiescent to a proliferative state. The levels of the same transcripts were also increased following transformation by polyoma virus and by ras and myc oncogenes. The presence of the ID element appeared to be determinant, since a similar pattern of expression was observed for a construct where one element had been inserted in the 3' noncoding region of a rabbit beta-globin gene expressed under control of an SV40 promoter.

CD4(+) T cells which react to the Leishmania major LACK antigen rapidly secrete interleukin-4 and are detrimental to the host in resistant B10.D2 mice.

Leishmania major induces the rapid production of interleukin-4 (IL-4) in both susceptible BALB/c and resistant B10.D2 mice. In both strains, IL-4 is produced by T cells which react to the parasite LACK (for Leishmania homolog of the receptor for activated C kinase) antigen. The rapid production of IL-4 in B10.D2 mice does not confer susceptibility but results in increased parasite burdens.

Increased levels of mitochondrial gene expression in rat fibroblast cells immortalized or transformed by viral and cellular oncogenes.

Steady-state levels of the mitochondrial (mt) mRNA encoding subunit II of cytochrome oxidase (COII) were increased 5-10 fold in fully transformed cell lines derived from rodent embryonic fibroblasts after transfer of polyoma virus DNA, and in immortalized cell lines established by transfer of plt (polyoma large T protein), E1A (adenovirus) and myc oncogenes. Increased mitochondrial gene expression was not related with active growth per se: it was low in fast-growing rat embryo cells, and it did not change upon serum starvation and subsequent stimulation of FR3T3 cells. The number of copies of mtDNA did not vary, and different mitochondrial mRNAs and rRNAs were increased in the same proportions, suggesting a change in the rate of accumulation of their common precursor.