[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.

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 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.

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.

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.

CD4 promotes breadth in the TCR repertoire.

A diverse population of MHC class II-restricted CD4 lineage T cells develops in mice that lack expression of the CD4 molecule. In this study, we show that the TCR repertoire selected in the absence of CD4 is distinct, but still overlapping in its properties with that selected in the presence of CD4. Immunization of mice lacking CD4 caused the clonal expansion of T cells that showed less breadth in the range of Ag-binding properties exhibited by their TCRs. Specifically, the CD4-deficient Ag-specific TCR repertoire was depleted of TCRs that demonstrated low-affinity binding to their ligands. The data thus suggest a key role for CD4 in broadening the TCR repertoire by potentiating productive TCR signaling and clonal expansion in response to the engagement of low-affinity antigenic ligands.

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.

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.

T-cell responses to immunodominant LACK antigen do not play a critical role in determining susceptibility of BALB/c mice to Leishmania mexicana.

Although BALB/c mice develop lesions when infected with Leishmania mexicana, the mechanisms which are responsible for susceptibility to this parasite have not been elucidated. In contrast, susceptibility of BALB/c mice to Leishmania major has been shown to depend on the early production of interleukin-4 (IL-4) by T cells which react to the parasitic LACK antigen. Here, we demonstrate that the lesions induced by L. mexicana are delayed compared to those induced by L. major but rapidly develop at later time points. Interestingly, while LACK-tolerant BALB/c-derived IE-LACK transgenic mice were resistant to L. major, they were susceptible to L. mexicana and developed lesions similar to those observed in wild-type BALB/c mice. The latter result was observed despite the fact that (i) LACK was expressed by L. mexicana, (ii) splenocytes from BALB/c mice were able to stimulate LACK-specific T-cell hybridoma cells when incubated with live L. mexicana promastigotes, and (iii) LACK-specific T cells contributed to IL-4 production in L. mexicana-infected BALB/c mice. Thus, in contrast to what was observed for L. major-infected mice, LACK-specific T cells do not play a critical role in determining susceptibility to L. mexicana. Although BALB/c mice are susceptible to both L. major and L. mexicana, the mechanisms which are responsible for susceptibility to these parasites are likely to be different.

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.

Priming by microbial antigens from the intestinal flora determines the ability of CD4+ T cells to rapidly secrete IL-4 in BALB/c mice infected with Leishmania major.

Infection of BALB/c mice with Leishmania major results in the rapid accumulation of IL-4 transcripts within CD4(+) T cells that react to the parasite Leishmania homologue of mammalian RACK1 (LACK) Ag. Because memory/effector cells secrete IL-4 more rapidly than naive cells, we sought to analyze the phenotype of these lymphocytes before infection. Indeed, a fraction of LACK-specific CD4(+) T cells expressed a typical CD62 ligand(low)CD44(high)CD45RB(low) phenotype in uninfected mice. LACK-specific T cells were primed in gut-associated lymphoid tissues by cross-reactive microbial Ags as demonstrated by their reactivity with bacterial extracts and by the ability of APCs from the mesenteric LN of BALB/c mice to induce their proliferation. Also, mice in which the digestive tract has been decontaminated exhibited a reduced proportion of LACK-specific T cells expressing a memory/effector phenotype and did not exhibit the early accumulation of IL-4 transcripts induced by L. major. Thus, LACK-specific T cells represent a subset of CD4(+) T cells which have acquired the ability to rapidly secrete IL-4 as the result of their priming by cross-reactive microbial Ags. Tracking the fate of these cells may provide information about the regulation of cell-mediated immune responses to gut Ags in physiological and pathological situations.

The role of antigen and IL-12 in sustaining Th1 memory cells in vivo: IL-12 is required to maintain memory/effector Th1 cells sufficient to mediate protection to an infectious parasite challenge.

IL-12 plays a central role in both the induction and magnitude of a primary Th1 response. A critical question in designing vaccines for diseases requiring Th1 immunity such as Mycobacterium tuberculosis and Leishmania major is the requirements to sustain memory/effector Th1 cells in vivo. This report examines the role of IL-12 and antigen in sustaining Th1 responses sufficient for protective immunity to L. major after vaccination with LACK protein (LP) plus rIL-12 and LACK DNA. It shows that, after initial vaccination with LP plus rIL-12, supplemental boosting with either LP or rIL-12 is necessary but not sufficient to fully sustain long-term Th1 immunity. Moreover, endogenous IL-12 is also shown to be required for the induction, maintenance, and effector phase of the Th1 response after LACK DNA vaccination. Finally, IL-12 is required to sustain Th1 cells and control parasite growth in susceptible and resistant strains of mice during primary and secondary infection. Taken together, these data show that IL-12 is essential to sustain a sufficient number of memory/effector Th1 cells generated in vivo to mediate long-term protection to an intracellular pathogen.

Requirements for the maintenance of Th1 immunity in vivo following DNA vaccination: a potential immunoregulatory role for CD8+ T cells.

Protective immunity against Leishmania major generated by DNA encoding the LACK (Leishmania homologue of receptor for activated C kinase) Ag has been shown to be more durable than vaccination with LACK protein plus IL-12. One mechanism to account for this may be the selective ability of DNA vaccination to induce CD8+ IFN-gamma-producing T cells. In this regard, we previously reported that depletion of CD8+ T cells in LACK DNA-vaccinated mice abrogated protection when infectious challenge was done 2 wk postvaccination. In this study, we extend these findings to study the mechanism by which CD8+ T cells induced by LACK DNA vaccination mediate both short- and long-term protective immunity against L. major. Mice vaccinated with LACK DNA and depleted of CD8+ T cells at the time of vaccination or infection were unable to control infection when challenge was done 2 or 12 wk postvaccination. Remarkably, it was noted that depletion of CD8+ T cells in LACK DNA-vaccinated mice was associated with a striking decrease in the frequency of LACK-specific CD4+ IFN-gamma-producing T cells both before and after infection. Moreover, data are presented to suggest a mechanism by which CD8+ T cells exert this regulatory role. Taken together, these data provide additional insight into how Th1 cells are generated and sustained in vivo and suggest a potentially novel immunoregulatory role for CD8+ T cells following DNA vaccination.

Listeria monocytogenes as a short-lived delivery system for the induction of type 1 cell-mediated immunity against the p36/LACK antigen of Leishmania major.

Listeria monocytogenes has been used as an experimental live vector for the induction of CD8-mediated immune responses in various viral and tumoral experimental models. Susceptibility of BALB/c mice to Leishmania major infection has been correlated to the preferential development of Th2 CD4 T cells through an early production of interleukin 4 (IL-4) by a restricted population of CD4 T cells which react to a single parasite antigen, LACK (stands for Leishmania homologue of receptors for activated C kinase). Experimental vaccination with LACK can redirect the differentiation of CD4(+) T cells towards the Th1 pathway if LACK is coadministrated with IL-12. As IL-12 is known to be induced by L. monocytogenes, we have tested the ability of a recombinant attenuated actA mutant L. monocytogenes strain expressing LACK to induce the development of LACK-specific Th1 cells in both B10.D2 and BALB/c mice, which are resistant and susceptible to L. major, respectively. After a single injection of LACK-expressing L. monocytogenes, IL-12/p40 transcripts showed a rapid burst, and peaks of gamma interferon (IFN-gamma)-secreting LACK-specific Th1 cells were detected around day 5 in the spleens and livers of mice of both strains. These primed IFN-gamma-secreting LACK-reactive T cells were not detected ex vivo after day 7 of immunization but could be recruited and detected 15 days later in the draining lymph node after an L. major footpad challenge. Although immunization of BALB/c mice with LACK-expressing L. monocytogenes did not change the course of the infection with L. major, immunized B10.D2 mice exhibited significantly smaller lesions than nonimmunized controls. Thus, our results demonstrate that, in addition of its recognized use for the induction of effector CD8 T cells, L. monocytogenes can also be used as a live recombinant vector to favor the development of potentially protective IFN-gamma-secreting Th1 CD4 T lymphocytes.

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.

Selective activation and expansion of high-affinity CD4+ T cells in resistant mice upon infection with Leishmania major.

Using multimers of MHC class II molecules linked to a peptide derived from the Leishmania LACK antigen, we have compared the fate of parasite-specific CD4+ T cells in resistant and susceptible mice transgenic for the beta chain of a LACK-specific TCR. Activated T cells were readily detected in the draining lymph nodes of infected animals. Although the kinetics of activation and expansion were similar in both strains, T cells from susceptible and resistant mice expressed low- and high-affinity TCR, respectively. As T cells from resistant mice produced more IFN-gamma and less IL-4 than those from susceptible animals, our results suggest that differences in TCR usage between MHC-matched animals may influence the development of the antiparasite immune response.

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.

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.