Regulatory role of CD8 in major histocompatibility complex-unrestricted tumoricidal activity of mouse T cells activated with anti-CD3 monoclonal antibody

Challenges and future perspectives of T cell immunotherapy in cancer

Since the formulation of the tumour immunosurveillance theory, considerable focus has been on enhancing the effectiveness of host antitumour immunity, particularly with respect to T cells. A cancer evades or alters the host immune response by various ways to ensure its development and survival. These include modifications of the immune cell metabolism and T cell signalling. An inhibitory cytokine milieu in the tumour microenvironment also leads to immune suppression and tumour progression within a host. This review traces the development in the field and attempts to summarize the hurdles that the approach of adoptive T cell immunotherapy against cancer faces, and discusses the conditions that must be improved to allow effective eradication of cancer.

A mechanism of hypoxia-mediated escape from adaptive immunity in cancer cells

Immune escape is a fundamental trait of cancer in which mechanistic knowledge is incomplete. Here, we describe a novel mechanism by which hypoxia contributes to tumoral immune escape from cytotoxic T lymphocytes (CTL). Exposure of human or murine cancer cells to hypoxia for 24 hours led to upregulation of the immune inhibitory molecule programmed cell death ligand-1 (PD-L1; also known as B7-H1), in a manner dependent on the transcription factor hypoxia-inducible factor-1α (HIF-1α). In vivo studies also demonstrated cellular colocalization of HIF-1α and PD-L1 in tumors. Hypoxia-induced expression of PD-L1 in cancer cells increased their resistance to CTL-mediated lysis. Using glyceryl trinitrate (GTN), an agonist of nitric oxide (NO) signaling known to block HIF-1α accumulation in hypoxic cells, we prevented hypoxia-induced PD-L1 expression and diminished resistance to CTL-mediated lysis. Moreover, transdermal administration of GTN attenuated tumor growth in mice. We found that higher expression of PD-L1 induced in tumor cells by exposure to hypoxia led to increased apoptosis of cocultured CTLs and Jurkat leukemia T cells. This increase in apoptosis was prevented by blocking the interaction of PD-L1 with PD-1, the PD-L1 receptor on T cells, or by addition of GTN. Our findings point to a role for hypoxia/HIF-1 in driving immune escape from CTL, and they suggest a novel cancer immunotherapy to block PD-L1 expression in hypoxic-tumor cells by administering NO mimetics.

Effect of Lactobacillus brevis KB290 on the cell-mediated cytotoxic activity of mouse splenocytes: a DNA microarray analysis

Lactic acid bacteria confer a variety of health benefits. Here, we investigate the mechanisms by which Lactobacillus brevis KB290 (KB290) enhances cell-mediated cytotoxic activity. Female BALB/c mice aged 9 weeks were fed a diet containing KB290 (3 × 10(9) colony-forming units/g) or starch for 1 d. The resulting cytotoxic activity of splenocytes against YAC-1 cells was measured using flow cytometry and analysed for gene expression using DNA microarray technology. KB290 enhanced the cell-mediated cytotoxic activity of splenocytes. DNA microarray analysis identified 327 up-regulated and 347 down-regulated genes that characterised the KB290 diet group. The up-regulated genes were significantly enriched in Gene Ontology terms related to immunity, and, especially, a positive regulation of T-cell-mediated cytotoxicity existed among these terms. Almost all the genes included in the term encoded major histocompatibility complex (MHC) class I molecules involved in the presentation of antigen to CD8(+) cytotoxic T cells. Marco and Signr1 specific to marginal zone macrophages (MZM), antigen-presenting cells, were also up-regulated. Flow cytometric analysis confirmed that the proportion of MZM was significantly increased by KB290 ingestion. Additionally, the over-represented Kyoto Encyclopedia of Genes and Genomes pathways among the up-regulated genes were those for natural killer (NK) cell-mediated cytotoxicity and antigen processing and presentation. The results for the selected genes associated with NK cells and CD8(+) cytotoxic T cells were confirmed by quantitative RT-PCR. These results suggest that enhanced cytotoxic activity could be caused by the activation of NK cells and/or of CD8(+) cytotoxic T cells stimulated via MHC class I presentation.

Role of NK1.1+ and AsGm-1+ cells in oral immunoregulation of experimental colitis

NK1.1 and AsGm-1 expressing cells play a role in immunomodulation. Our purpose was to determine the role of NK1.1+ and AsGm-1+ expressing cells in the inflammatory/tolerance paradigm in experimental colitis. Oral tolerance towards colitis-extracted proteins had previously been shown to alleviate experimental colitis. Colitis was induced in C57/B6 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Oral tolerance was induced via five oral doses of proteins extracted from TNBS-colitis colonic wall. Clinical, macroscopic, and microscopic scores were used for colitis assessment. To evaluate the putative role of AsGm-1 in tolerance induction, depletion of AsGm-1 expressing cells was performed. To evaluate the mechanism of tolerance induction, liver-associated NKT lymphocytes were harvested 14 days following tolerance induction, and cultured with concanavalin A (con A) and colitis-extracted proteins. T cell subsets were measured by flow cytometry. Cytokine expression was measured by intracellular staining and enzyme-linked immunosorbent assay (ELISA). Orally tolerized mice exhibited significant alleviation of the clinical, macroscopic, and microscopic parameters of colitis, with increased CD4+ILA+/CD4+IFNgamma+ lymphocyte ratio, increased IL-4, and decreased IFNgamma and IL-12 serum levels. In contrast, orally fed mice that were AsGm-1 depleted showed evidence of severe colitis. These mice exhibited significant decreased CD4 +IL4+/CD4+IFNgamma+ ratios, and an increase in IFNgamma and IL-12, with decreased IL-4 levels. NKT cells harvested from tolerized mice secreted high levels of antiinflammatory cytokines. In contrast, in nontolerized mice, NKT cells mainly secreted proinflammatory cytokines. In a tolerized environment, both NK1.1 and AsGm-1 expressing cells are essential for disease alleviation. In contrast, in a nontolerized environment, AsGm-1 expressing cells support an antiinflammatory immune paradigm, while NKT lymphocytes support a proinflammatory shift.

Dose-dependent enhancing and inhibitory effects of A77 1726 (leflunomide) on cytotoxic T lymphocyte induction

Leflunomide is an immunosuppressive prodrug which prevents allograft rejection in several animal model systems and may, therefore, have clinical application in organ transplant recipients. Although cytotoxic T lymphocytes (CTL) are an important component of the allograft rejection response, the effect of leflunomide on CTL development has not been thoroughly explored. In this study we have determined the effect of A77 1726, the active metabolite of leflunomide, on CTL induction in C57BL/6 mouse T cell cultures stimulated with anti-CD3 monoclonal antibody. Conjugate formation with P815 target cells, granzyme B enzymatic activity in CTL lysates, and P815 cytolysis in a 51Cr-release assay were used as determinants of in vitro CTL function. At high concentrations (10-20 microM), A77 1726 strongly inhibited CTL generation. In contrast, a low concentration (0.5 microM) of A77 1726 promoted CTL development. These dose-dependent opposing effects of A77 1726 on CTL induction could not be attributed to alterations in CD8+ lymphocyte percentages, interleukin-2 or CD25 expression, or the ability to conjugate with P815 target cells. However, both interferon-gamma and granzyme B expression were significantly decreased when CTL were induced in the presence of 10-20 microM A77 1726, and were slightly, but not always significantly, elevated in the presence of 0.5 microM A77 1726. We conclude that at high concentrations A77 1726 is a potent inhibitor of CTL induction, but a low concentration of A77 1726 enhances CTL development.