Interactions of tumor cells with dendritic cells: balancing immunity and tolerance

Tumor-educated CD11bhighIalow regulatory dendritic cells suppress T cell response through arginase I

Tumors can induce generation and accumulation of the immunosuppressive cells such as regulatory T cells in the tumor microenvironment, contributing to tumor escape from immunological attack. Although dendritic cell (DC)-based cancer vaccine can initiate antitumor immune response, regulatory DC subsets involved in the tolerance induction attracted much attention recently. Our previous studies demonstrate that the stromal microenvironment of the spleen, lung, and liver can program generation of CD11c(low)CD11b(high)Ia(low) DCs with regulatory function (CD11b(high)Ia(low) regulatory DCs). However, whether and how the tumor microenvironment can program generation of CD11b(high)Ia(low) regulatory DCs remain to be investigated. In this study, we used the freshly isolated tumor cells to mimic tumor microenvironment to coculture DCs and found that the freshly isolated tumor cells could drive DCs to differentiate into regulatory DCs with a CD11c(low)CD11b(high)Ia(low) phenotype and high expression of IL-10, NO, vascular endothelial growth factor, and arginase I. Tumor-educated CD11b(high)Ia(low) regulatory DCs inhibited CD4(+) T cell proliferation both in vitro and in vivo. 3LL lung cancer-derived TGF-beta and PGE(2) were responsible for the generation of regulatory DCs. PGE(2) was the main inducer of arginase I in regulatory DCs. Arginase I played a major role in the suppression of T cell response by regulatory DCs induced by 3LL lung cancer. A natural counterpart of CD11b(high)Ia(low) DCs was identified in tumor tissue, and CD11b(high)Ia(low) DCs sorted from 3LL lung cancer tissue expressed arginase I and inhibited T cell response. Therefore, tumors can educate DCs to differentiate into a regulatory DC subset, which contributes to constitution of the immunosuppressive tumor microenvironment and promotes tumor immune escape.

Monoclonal antibodies for cancer immunotherapy

Monoclonal antibodies are effective treatments for many malignant diseases. However, the ability of antibodies to initiate tumour-antigen-specific immune responses has received less attention than have other mechanisms of antibody action. We describe the rationale and evidence for the development of antibodies that can stimulate host tumour-antigen-specific immune responses. Such responses can be induced through the induction of antibody-dependent cellular cytotoxicity, promotion of antibody-targeted cross-presentation of tumour antigens, or by triggering of the idiotypic network. Future treatment modifications or combinations might be able to prolong, amplify, and shape these immune responses to increase the clinical benefits of antibody therapy for human cancer.

Dendritic cells: a critical player in cancer therapy?

Cancer immunotherapy seeks to mobilize a patient's immune system for therapeutic benefit. It can be passive, that is, transfer of immune effector cells (T cells) or proteins (antibodies), or active, that is, vaccination. Early clinical trials testing vaccination with ex vivo generated dendritic cells (DCs) pulsed with tumor antigens provide a proof-of-principle that therapeutic immunity can be elicited. Yet, the clinical benefit measured by regression of established tumors in patients with stage IV cancer has been observed in a fraction of patients only. The next generation of DC vaccines is expected to generate large numbers of high avidity effector CD8 T cells and to overcome regulatory T cells and suppressive environment established by tumors, a major obstacle in metastatic disease. Therapeutic vaccination protocols will combine improved DC vaccines with chemotherapy to exploit immunogenic chemotherapy regimens. We foresee adjuvant vaccination in patients with resected tumors but at high risk of relapse to be based on in vivo targeting of DCs with fusion proteins containing anti-DCs antibodies, antigens from tumor stem/propagating cells, and DC activators.

Cancer immunotherapy by dendritic cells

Cancerous lesions promote tumor growth, motility, invasion, and angiogenesis via oncogene-driven immunosuppressive leukocyte infiltrates, mainly myeloid-derived suppressor cells, tumor-associated macrophages, and immature dendritic cells (DCs). In addition, many tumors express or induce immunosuppressive cytokines such as TGF-beta and IL-10. As a result, tumor-antigen crosspresentation by DCs induces T cell anergy or deletion and regulatory T cells instead of antitumor immunity. Tumoricidal effector cells can be generated after vigorous DC activation by Toll-like receptor ligands or CD40 agonists. However, no single immunotherapeutic modality is effective in established cancer. Rather, chemotherapies, causing DC activation, enhanced crosspresentation, lymphodepletion, and reduction of immunosuppressive leukocytes, act synergistically with vaccines or adoptive T cell transfer. Here, I discuss the considerations for generating promising therapeutic antitumor vaccines that use DCs.

Cell competition and its possible relation to cancer

Cell competition can occur when cells of different genotypes share the same developing compartment, with one genotype displacing the other as a result of a proliferative advantage. Studies of cell competition in Drosophila have identified an active process of cell assassination and corpse engulfment, and also roles for Myc and the Warts/Hippo tumor suppressor pathway. Here, we discuss the possible relevance of cell competition to cancer.

Role of chaperones and FcgammaR in immunogenic death

Cell death under physiologic conditions does not lead to the induction of immunity. However recognition of stressed or opsonized cells can trigger immune responses. Recent studies have begun to illustrate the critical role of molecular chaperones such as inducible heat shock proteins in mediating immunogenicity of stressed cells. Immunity to opsonized cells depends in part on the engagement and the balance of activating and inhibitory FcgammaRs on antigen presenting dendritic cells. Understanding both these pathways of immunogenic cell death may yield novel approaches to regulate immunity.