Immunodominant AH1 Antigen-Deficient Necroptotic, but Not Apoptotic, Murine Cancer Cells Induce Antitumor Protection.

Immunogenic cell death (ICD) occurs when a dying cell releases cytokines and damage-associated molecular patterns, acting as adjuvants, and expresses Ags that induce a specific antitumor immune response. ICD is studied mainly in the context of regulated cell death pathways, especially caspase-mediated apoptosis marked by endoplasmic reticulum stress and calreticulin exposure and, more recently, also in relation to receptor-interacting protein kinase-driven necroptosis, whereas unregulated cell death like accidental necrosis is nonimmunogenic. Importantly, the murine cancer cell lines used in ICD studies often express virally derived peptides that are recognized by the immune system as tumor-associated Ags. However, it is unknown how different cell death pathways may affect neoepitope cross-presentation and Ag recognition of cancer cells. We used a prophylactic tumor vaccination model and observed that both apoptotic and necroptotic colon carcinoma CT26 cells efficiently immunized mice against challenge with a breast cancer cell line that expresses the same immunodominant tumor Ag, AH1, but only necroptotic CT26 cells would mount an immune response against CT26-specific neoepitopes. By CRISPR/Cas9 genome editing, we knocked out AH1 and saw that only necroptotic CT26 cells were still able to protect mice against tumor challenge. Hence, in this study, we show that endogenous AH1 tumor Ag expression can mask the strength of immunogenicity induced by different cell death pathways and that upon knockout of AH1, necroptosis was more immunogenic than apoptosis in a prophylactic tumor vaccination model. This work highlights necroptosis as a possible preferred ICD form over apoptosis in the treatment of cancer.

Differential effects of FcRn antagonists on the subcellular trafficking of FcRn and albumin.

The homeostasis of IgG is maintained by the neonatal Fc receptor, FcRn. Consequently, antagonism of FcRn to reduce endogenous IgG levels is an emerging strategy for treating antibody-mediated autoimmune disorders using either FcRn-specific antibodies or an engineered Fc fragment. For certain FcRn-specific antibodies, this approach has resulted in reductions in the levels of serum albumin, the other major ligand transported by FcRn. Cellular and molecular analyses of a panel of FcRn antagonists have been carried out to elucidate the mechanisms leading to their differential effects on albumin homeostasis. These analyses have identified 2 processes underlying decreases in albumin levels during FcRn blockade: increased degradation of FcRn and competition between antagonist and albumin for FcRn binding. These findings have potential implications for the design of drugs to modulate FcRn function.

Severity of doxorubicin-induced small intestinal mucositis is regulated by the TLR-2 and TLR-9 pathways.

Intestinal mucositis is a serious complication of cancer chemotherapy and radiotherapy; it frequently compromises treatment and dramatically reduces the quality of life of patients. Different approaches to limit the damage to the intestine during anti-cancer therapy have been largely ineffective due to insufficient knowledge of the mechanism of mucositis development. This study aimed to define the role of TLR-2 and TLR-9 in the modulation of small intestinal damage in a model of doxorubicin-induced mucositis. Doxorubicin-induced intestinal damage was verified by a histological score (HS), analysis of leukocyte influx into the lamina propria, and determination of the number of apoptotic cells. Additionally, the activation status of glycogen synthase kinase 3ß (GSK-3ß) was assessed. Wild-type (WT) mice injected with doxorubicin demonstrated severe intestinal damage (HS 8.0 ± 0.81), reduction of villus length to 43.9% ± 13.7% of original length, and increased influx of leukocytes as compared to vehicle-injected mice (HS 1.33 ± 1.15). The protective effect of TLR-2 or TLR-9 deficiency was associated with a significant decrease of the HS as compared to WT mice. In the ileum, a minor reduction of villus length and a decreased number of infiltrating leukocytes and TUNEL-positive cells was observed. We demonstrate that the TLR-9 antagonist ODN2088 reduces doxorubicin-induced intestinal damage. Furthermore, we show that GSK-3ß activity is inhibited in the absence of TLR-2. The protective capacity of GSK-3ß suppression was observed in WT mice by inhibiting it with the specific inhibitor SB216763. Overall, our findings demonstrate that the TLR-2/GSK-3ß and TLR-9 signalling pathways play a central role in the development of intestinal mucositis and we suggest a new therapeutic strategy for limiting doxorubicin-induced intestinal inflammation.

Ionizing radiation results in a mixture of cellular outcomes including mitotic catastrophe, senescence, methuosis, and iron-dependent cell death.

Radiotherapy is commonly used as a cytotoxic treatment of a wide variety of tumors. Interestingly, few case reports underlined its potential to induce immune-mediated abscopal effects, resulting in regression of metastases, distant from the irradiated site. These observations are rare, and apparently depend on the dose used, suggesting that dose-related cellular responses may be involved in the distant immunogenic responses. Ionizing radiation (IR) has been reported to elicit immunogenic apoptosis, necroptosis, mitotic catastrophe, and senescence. In order to link a cellular outcome with a particular dose of irradiation, we performed a systematic study in a panel of cell lines on the cellular responses at different doses of X-rays. Remarkably, we observed that all cell lines tested responded in a similar fashion to IR with characteristics of mitotic catastrophe, senescence, lipid peroxidation, and caspase activity. Iron chelators (but not Ferrostatin-1 or vitamin E) could prevent the formation of lipid peroxides and cell death induced by IR, suggesting a crucial role of iron-dependent cell death during high-dose irradiation. We also show that in K-Ras-mutated cells, IR can induce morphological features reminiscent of methuosis, a cell death modality that has been recently described following H-Ras or K-Ras mutation overexpression.

Vaccination with Necroptotic Cancer Cells Induces Efficient Anti-tumor Immunity.

Successful immunogenic apoptosis in experimental cancer therapy depends on the induction of strong host anti-tumor responses. Given that tumors are often resistant to apoptosis, it is important to identify alternative molecular mechanisms that elicit immunogenic cell death. We have developed a genetic model in which direct dimerization of FADD combined with inducible expression of RIPK3 promotes necroptosis. We report that necroptotic cancer cells release damage-associated molecular patterns and promote maturation of dendritic cells, the cross-priming of cytotoxic T cells, and the production of IFN-γ in response to tumor antigen stimulation. Using both FADD-dependent and FADD-independent RIPK3 induction systems, we demonstrate the efficient vaccination potential of immunogenic necroptotic cells. Our study broadens the current concept of immunogenic cell death and opens doors for the development of new strategies in cancer therapy.

Characterization of neutralizing profiles in HIV-1 infected patients from whom the HJ16, HGN194 and HK20 mAbs were obtained.

Several new human monoclonal antibodies (mAbs) with a neutralizing potential across different subtypes have recently been described. Three mAbs, HJ16, HGN194 and HK20, were obtained from patients within the HIV-1 cohort of the Institute of Tropical Medicine (ITM). Our aim was to generate immunization antibodies equivalent to those seen in plasma. Here, we describe the selection and characterization of patient plasma and their mAbs, using a range of neutralization assays, including several peripheral blood mononuclear cell (PBMC) based assays and replicating primary viruses as well as cell line based assays and pseudoviruses (PV). The principal criterion for selection of patient plasma was the activity in an 'extended incubation phase' PBMC assay. Neutralizing Abs, derived from their memory B cells, were then selected by ELISA with envelope proteins as solid phase. MAbs were subsequently tested in a high-throughput HOS-PV assay to assess functional neutralization. The present study indicates that the strong profiles in the patients' plasma were not solely due to antibodies represented by the newly isolated mAbs. Although results from the various assays were divergent, they by and large indicate that neutralizing Abs to other epitopes of the HIV-1 envelope are present in the plasma and synergy between Abs may be important. Thus, the spectrum of the obtained mAbs does not cover the range of cross-reactivity seen in plasma in these carefully selected patients irrespective of which neutralization assay is used. Nevertheless, these mAbs are relevant for immunogen discovery because they bind to the recombinant glycoproteins to which the immune response needs to be targeted in vivo. Our observations illustrate the remaining challenges required for successful immunogen design and development.