Discovery of chemotherapy-associated ovarian cancer antigens by interrogating memory T cells.

According to the immunogenic cell death hypothesis, clinical chemotherapy treatments may result in CD8(+) and CD4(+) T-cell responses against tumor cells. To discover chemotherapy-associated antigens (CAAs), T cells derived from ovarian cancer (OC) patients (who had been treated with appropriate chemotherapy protocols) were interrogated with proteins isolated from primary OC cells. We screened for immunogenicity using two-dimensional electrophoresis gel-eluted OC proteins. Only the selected immunogenic antigens were molecularly characterized by mass-spectrometry-based analysis. Memory T cells that recognized antigens associated with apoptotic (but not live) OC cells were correlated with prolonged survival in response to chemotherapy, supporting the model of chemotherapy-induced apoptosis as an adjuvant of anti-tumor immunity. The strength of both memory CD4(+) and CD8(+) T cells producing either IFN-γ or IL-17 in response to apoptotic OC antigens was also significantly greater in Responders to chemotherapy than in nonresponders. Immunogenicity of some of these antigens was confirmed using recombinant proteins in an independent set of patients. The T-cell interrogation system represents a strategy of reverse tumor immunology that proposes to identify CAAs, which may then be validated as possible prognostic tumor biomarkers or cancer vaccines.

Mycobacteria exploit p38 signaling to affect CD1 expression and lipid antigen presentation by human dendritic cells.

Group I CD1 proteins are specialized antigen-presenting molecules that present both microbial and self lipid antigens to CD1-restricted alpha/beta T lymphocytes. The production of high levels of gamma interferon and lysis of infected macrophages by lipid-specific T lymphocytes are believed to play pivotal roles mainly in the defense against mycobacterial infections. We previously demonstrated that Mycobacterium tuberculosis and bacillus Calmette-Guérin (Mycobacterium bovis BCG) induce human monocytes to differentiate into CD1- dendritic cells (DC), which cannot present lipid antigens to specific T cells. Here, we show that in human monocytes mycobacteria trigger phosphorylation of p38 mitogen-activated protein kinase to inhibit CD1 expression in DC derived from infected monocytes. Pretreatment with a specific p38 inhibitor renders monocytes insensitive to mycobacterial subversion and allows them to differentiate into CD1+ DC, which are fully capable of presenting lipid antigens to specific T cells. We also report that one of the pathogen recognition receptors triggered by BCG to activate p38 is complement receptor 3 (CR3), as shown by reduced p38 phosphorylation and partial reestablishment of CD1 membrane expression obtained by CR3 blockade before infection. In conclusion, we propose that p38 signaling is a novel pathway exploited by mycobacteria to affect the expression of CD1 antigen-presenting cells and avoid immune recognition.

PD-L1 negatively regulates CD4+CD25+Foxp3+ Tregs by limiting STAT-5 phosphorylation in patients chronically infected with HCV.

CD4+CD25+Foxp3+ Tregs suppress autoimmune responses. In addition, they limit T cell responses during chronic infection, thereby minimizing T cell-dependent immunopathology. We sought to investigate how Tregs are regulated in the livers of patients chronically infected with HCV, where they control the balance between an adequate protective immune response and suppression of immunopathology. We found that, despite accumulating and proliferating at sites of infection in the livers of patients chronically infected with HCV, Tregs were relatively less expanded than CD4+CD25+Foxp3- effector T cells. The relative lower expansion of intrahepatic Tregs coincided with their upregulation of programmed death-1 (PD-1). PD-1 expression inversely correlated with both Treg proliferation and clinical markers of immune suppression in vivo. Consistent with the possibility that PD-1 controls Tregs, blockade of the interaction between PD-1 and programmed death-1 ligand 1 (PD-L1) enhanced the in vitro expansion and function of Tregs isolated from the livers of patients chronically infected with HCV. Blockade of the interaction between PD-L1 and B7.1 also improved the proliferation of these cells. Interestingly, both PD-1 and phosphorylated STAT-5 were overexpressed in intrahepatic Tregs in a parallel fashion in steady disease conditions, and in an alternate-fluctuating fashion during the course of severe hepatitis reactivation. Notably, PD-L1 blockade upregulated STAT-5 phosphorylation in Tregs ex vivo. These data suggest that PD-L1 negatively regulates Tregs at sites of chronic inflammation by controlling STAT-5 phosphorylation.

Cross-presentation of caspase-cleaved apoptotic self antigens in HIV infection.

We found that the proteome of apoptotic T cells includes prominent fragments of cellular proteins generated by caspases and that a high proportion of distinct T cell epitopes in these fragments is recognized by CD8+ T cells during HIV infection. The frequencies of effector CD8+ T cells that are specific for apoptosis-dependent epitopes correlate with the frequency of circulating apoptotic CD4+ T cells in HIV-1-infected individuals. We propose that these self-reactive effector CD8+ T cells may contribute to the systemic immune activation during chronic HIV infection. The caspase-dependent cleavage of proteins associated with apoptotic cells has a key role in the induction of self-reactive CD8+ T cell responses, as the caspase-cleaved fragments are efficiently targeted to the processing machinery and are cross-presented by dendritic cells. These findings demonstrate a previously undescribed role for caspases in immunopathology.