Introduction: the immune response against dying cells

Can dendritic cells improve whole cancer cell vaccines based on immunogenically killed cancer cells?

Immunogenic cell death (ICD) offers interesting opportunities in cancer cell (CC) vaccine manufacture, as it increases the immunogenicity of the dead CC. Furthermore, fusion of CCs with dendritic cells (DCs) is considered a superior method for generating whole CC vaccines. Therefore, in this work, we determined in naive mice whether immunogenically killed CCs per se (CC vaccine) elicit an antitumoral immune response different from the response observed when immunogenically killed CCs are associated with DCs through fusion (fusion vaccine) or through co-incubation (co-incubation vaccine). After tumor inoculation, the type of immune response in the prophylactically vaccinated mice differed between the groups. In more detail, fusion vaccines elicited a humoral anticancer response, whereas the co-incubation and CC vaccine mainly induced a cellular response. Despite these differences, all three approaches offered a prophylactic protection against tumor development in the murine mammary carcinoma model. In summary, it can be concluded that whole CC vaccines based on immunogenically killed CCs may not necessarily require association with DCs to elicit a protective anticancer immune response. If this finding can be endorsed in other cancer models, the manufacture of CC vaccines would greatly benefit from this new insight, as production of DC-based vaccines is laborious, time-consuming and expensive.

Death-defining immune responses after apoptosis

Apoptosis is a programmed form of cell death whereby characteristic internal cellular dismantling is accompanied by the preservation of plasma membrane integrity. Maintaining this order during apoptosis prevents the release of cellular contents and ensures a noninflammatory death. Here, we consider examples of apoptosis in different contexts and discuss how the same form of cell death could have different immunological consequences. Multiple parameters such as cell death as a result of microbial infection, the nature of the inflammatory microenvironment, the type of responding phagocytic cells and the genetic background of the host organism all differentially influence the immunological consequences of apoptosis.

Various ways to improve whole cancer cell vaccines

Immunotherapy based on whole cancer cell vaccines is regarded as a promising avenue for cancer treatment. However, limited efficacy in the first human clinical trials calls for more optimized whole cancer cell vaccines and better patient selection. It is suggested that whole cancer cell vaccines consist preferably of immunogenically killed autologous cancer stem cells associated with dendritic cells. Adjuvants should stimulate both immune effector cells and memory cells, which could be achieved through their correct dosage and timing of administration. There are indications that whole cancer cell vaccination is less effective in patients who are immunocompromised, who have specific genetic defects in their immune or cancer cells, as well as in patients in an advanced cancer stage. However, such patients form the bulk of enrolled patients in clinical trials, prohibiting an objective evaluation of the true potential of whole cancer cell immunotherapy. Each key point will be discussed.

Overexpressing the CCL2 chemokine in an epithelial ovarian cancer cell line results in latency of in vivo tumourigenicity

The frequent loss of heterozygosity of chromosome (Chr) 17 in epithelial ovarian cancer (EOC), particularly high-grade ovarian serous carcinomas (HGOSCs), has been attributed to the disruption of known tumour suppressor genes, such as TP53 (17p13), as well as other genes on this chromosome that alone or in combination have a role in EOC. In a transcriptome analysis of Chr17 genes, we observed significant underexpression of the chemokine CCL2 (17q12) in a small set of HGOSC samples relative to normal ovarian surface epithelial cells and a significant upregulation of CCL2 in the TP53-mutated OV-90 EOC cell line rendered non-tumourigenic as a consequence of genetic manipulation. Here, we report that overexpressing CCL2 in OV-90 resulted in latency of tumour formation at intraperitoneal (i.p.) but not subcutaneous sites in a mouse xenograft model. Overexpressing CCL2 affected cell morphology and exerted modest, but not significant effects on cell viability, colony formation and cell migration. We report significant underexpression of CCL2 by transcriptome analysis (P=0.015) and by immunohistochemistry in 77% of HGOSC samples (n=65). Absent or a very low level of protein expression by immunohistochemistry was also observed in 71% of additional HGOSC samples (n=122). However, CCL2 protein expression did not significantly correlate with overall or disease-free survival. The epithelial cells of normal fallopian tubes, a purported origin of HGOSC, exhibited expression of CCL2 protein by immunohistochemistry. Our results affirm that CCL2 underexpression is a significant feature of HGOSC samples, and that CCL2 overexpression in an EOC cell line model affects tumourigenic potential in the i.p. setting.

Dendritic cells and their role in atherogenesis

Dendritic cells (DCs) are the most potent professional antigen-presenting cells with the unique ability of primary immune response initiation. DCs originate from bone marrow progenitors, which circulate in the peripheral blood and subsequently penetrate peripheral tissues, where they give rise to immature DCs. In peripheral tissues, DCs continuously monitor the microenvironment and, when the cells encounter 'danger' signals, DCs undergo differentiation and maturation. Maturing DCs usually migrate to lymphatic tissues, where they form contacts with T cells to initiate a primary immune response. DCs were identified in arteries in 1995 and since then, further knowledge has been gained about the peculiarities of vascular-associated DCs and their role in atherosclerosis. Immune reactions toward modified lipoproteins and other factors ignited by resident vascular DCs as well as by newly arrived DCs, which originate from blood monocytes, are believed to destabilize arterial homeostasis from very earlier stages of atherogenesis. There is a remarkable heterogeneity of DCs in atherosclerotic lesions. Some DCs mature and become capable of forming clusters with T cells directly within the arterial wall. The predictive value of the numbers of circulating DC precursors in coronary artery disease and in atherosclerosis has been assessed, and it has been shown that DCs have a role in plaque destabilization. Over recent decades, DCs have proven to be a valuable instrument in immunotherapy approaches against cancer and various autoimmune diseases, and this explains the demand that the accumulated knowledge be applied to the field of atherosclerosis immunotherapy.

The danger model in deciphering autoimmunity

Autoimmunity has been a topic of intensive research for several decades, yet amazingly, no uniform hypothesis exists to explain the basis for the spectrum of autoantibody specificities seen in autoimmune diseases. It therefore seems appropriate to consider whether our current framework for understanding tolerance, and thus the mechanisms controlling the initiation and perpetuation of autoimmunity, may be faulty. Adapting the paradigm of Matzinger-the 'danger model', a case can be made for a perspective that appreciates the fundamental role of the tissues in controlling immune response, favouring a shift of focus in studies on the initiation of autoimmunity. Applying the elements of this model, I set forth a number of scenarios for how autoreactivity could emerge, with emphasis on the likely sources of the involved autoantigens and the functional basis of their appearance. The emerging picture is one in which disruption of tissue homeostasis takes centre stage, with the antigen-presenting cells as the key players.

Innate immune recognition of infected apoptotic cells directs T(H)17 cell differentiation

Adaptive immune responses rely on differentiation of CD4 T helper cells into subsets with distinct effector functions best suited for host defence against the invading pathogen. Interleukin (IL)-17-producing T helper cells (T(H)17) are a recently identified subset, separate from the T helper type 1 (T(H)1) and T helper type 2 (T(H)2) subsets. Synergy between the cytokines transforming growth factor-beta and IL-6 in vitro induces development of T(H)17 cells in mouse and human systems, whereas IL-23 supports expansion of these cells. However, it is not known which conditions in vivo would induce this combination of cytokines. Furthermore, it is enigmatic that a combination of pro-inflammatory and anti-inflammatory cytokines would be required to generate an effector T(H)17 response. Here we show that the relevant physiological stimulus triggering this combination of cytokines is the recognition and phagocytosis of infected apoptotic cells by dendritic cells. Phagocytosis of infected apoptotic cells uniquely triggers the combination of IL-6 and transforming growth factor-beta through recognition of pathogen-associated molecular patterns and phosphatidylserine exposed on apoptotic cells, respectively. Conversely, phagocytosis of apoptotic cells in the absence of microbial signals induces differentiation of the closely related regulatory T cells, which are important for controlling autoimmunity. Blocking apoptosis during infection of the mouse intestinal epithelium with the rodent pathogen Citrobacter rodentium, which models human infections with the attaching and effacing enteropathogenic and enterohaemorrhagic Escherichia coli, impairs the characteristic T(H)17 response in the lamina propria. Our results demonstrate that infected apoptotic cells are a critical component of the innate immune signals instructing T(H)17 differentiation, and point to pathogens particularly adept at triggering apoptosis that might preferentially induce T(H)17-mediated immunity. Because T(H)17 cells have been correlated with autoimmune diseases, investigation of the pathways of innate recognition of infected apoptotic cells might lead to improved understanding of the causative defects in autoimmunity.