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A novel role for granzymes in anti-tumor immunity.

Hoves S, Sutton VR, Trapani JA - Oncoimmunology (2012)

Bottom Line: The cytotoxic properties of granzymes are well established, though recent publications suggest additional roles for granzymes in immunity.We demonstrated that granzymes can act as regulators of cross-presentation by dendritic cells by inducing critical "eat-me" signals on the dying tumor cell, resulting in efficient phagocytosis of cell-associated tumor antigen.

View Article: PubMed Central - PubMed

Affiliation: Ludwig Maximilian University of Munich; Division of Clinical Pharmacology and Medical Clinic; Munich, Germany.

ABSTRACT
The cytotoxic properties of granzymes are well established, though recent publications suggest additional roles for granzymes in immunity. We demonstrated that granzymes can act as regulators of cross-presentation by dendritic cells by inducing critical "eat-me" signals on the dying tumor cell, resulting in efficient phagocytosis of cell-associated tumor antigen.

No MeSH data available.


Related in: MedlinePlus

Figure 1. Cell-mediated killing of tumor cells by wild-type cytotoxic lymphocytes (WT CL) via granzymes A and B (GrAB) results in the exposure of yet unknown pro-phagocytic “eat-me” signals in addition to phosphatidlyserine exposure (PS). The CD8α+ DC engulf dying tumor cells and cross-present tumor antigen to naïve cytotoxic T lymphocytes (CTL), inducing in turn an adaptive immune response against the tumor. However, tumor cell death in the absence of GrAB (GrAB−/− CL) lacks PS exposure and other pro-phagocytic “eat-me” signals leading to reduced phagocytosis, cross-presentation and subsequent induction of tumor specific CTL.
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Figure 1: Figure 1. Cell-mediated killing of tumor cells by wild-type cytotoxic lymphocytes (WT CL) via granzymes A and B (GrAB) results in the exposure of yet unknown pro-phagocytic “eat-me” signals in addition to phosphatidlyserine exposure (PS). The CD8α+ DC engulf dying tumor cells and cross-present tumor antigen to naïve cytotoxic T lymphocytes (CTL), inducing in turn an adaptive immune response against the tumor. However, tumor cell death in the absence of GrAB (GrAB−/− CL) lacks PS exposure and other pro-phagocytic “eat-me” signals leading to reduced phagocytosis, cross-presentation and subsequent induction of tumor specific CTL.

Mentions: Tumor cells killed by GrAB-sufficient CL show morphological signs of apoptosis such as rounding, blebbing, lifting from the substrate and chromatin condensation.3 Furthermore, time-lapse microscopy confirmed the early exposure of phosphatidylserine (PS) followed some time later by loss of membrane integrity, indicating secondary necrosis. In contrast, CL deficient for GrAB showed morphological characteristics of apoptosis but lacked early PS exposure until the cell membrane became permeable for a DNA intercalating dye.3 As PS is regarded as one of the most critical signal for uptake of apoptotic cells, we explored the functional significance of tumor cell death in the absence or presence of GrAB. We used GrAB-sufficient or -deficient CTL to kill antigen-specific tumor cells carrying the model antigen ovalbumin (OVA) and co-cultured dying tumor cells with dendritic cells (DC).2 We found that CD8α+ DC showed a marked reduction in OVA cross-presentation in vitro and in vivo when exposed to tumor cells killed in the absence of GrAB. By contrast, the absence or presence of GrAB had no effect on the expression of activation makers and secretion of cytokines by the CD8α+ DC. Nevertheless, the MHC class I molecules of CD8α+ DC were significantly occupied by the OVA peptide SIINFEKL only when the DC were co-cultured with tumor cells killed by GrAB-sufficient CTL. Finally, we were able to pin down the impaired cross-presentation by DC to a marked reduction of phagocytosis of the dying tumor cells. By using Annexin V to block PS, we found that PS per se is not critical for tumor cell uptake by DC, confirming previous studies using UV-irradiated tumor cells.4 From these experiments, we further concluded that granzymes induce other pro-phagocytic “eat-me” signals apart from PS on the outer membrane of dying tumor cells (Fig. 1).2


A novel role for granzymes in anti-tumor immunity.

Hoves S, Sutton VR, Trapani JA - Oncoimmunology (2012)

Figure 1. Cell-mediated killing of tumor cells by wild-type cytotoxic lymphocytes (WT CL) via granzymes A and B (GrAB) results in the exposure of yet unknown pro-phagocytic “eat-me” signals in addition to phosphatidlyserine exposure (PS). The CD8α+ DC engulf dying tumor cells and cross-present tumor antigen to naïve cytotoxic T lymphocytes (CTL), inducing in turn an adaptive immune response against the tumor. However, tumor cell death in the absence of GrAB (GrAB−/− CL) lacks PS exposure and other pro-phagocytic “eat-me” signals leading to reduced phagocytosis, cross-presentation and subsequent induction of tumor specific CTL.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3377003&req=5

Figure 1: Figure 1. Cell-mediated killing of tumor cells by wild-type cytotoxic lymphocytes (WT CL) via granzymes A and B (GrAB) results in the exposure of yet unknown pro-phagocytic “eat-me” signals in addition to phosphatidlyserine exposure (PS). The CD8α+ DC engulf dying tumor cells and cross-present tumor antigen to naïve cytotoxic T lymphocytes (CTL), inducing in turn an adaptive immune response against the tumor. However, tumor cell death in the absence of GrAB (GrAB−/− CL) lacks PS exposure and other pro-phagocytic “eat-me” signals leading to reduced phagocytosis, cross-presentation and subsequent induction of tumor specific CTL.
Mentions: Tumor cells killed by GrAB-sufficient CL show morphological signs of apoptosis such as rounding, blebbing, lifting from the substrate and chromatin condensation.3 Furthermore, time-lapse microscopy confirmed the early exposure of phosphatidylserine (PS) followed some time later by loss of membrane integrity, indicating secondary necrosis. In contrast, CL deficient for GrAB showed morphological characteristics of apoptosis but lacked early PS exposure until the cell membrane became permeable for a DNA intercalating dye.3 As PS is regarded as one of the most critical signal for uptake of apoptotic cells, we explored the functional significance of tumor cell death in the absence or presence of GrAB. We used GrAB-sufficient or -deficient CTL to kill antigen-specific tumor cells carrying the model antigen ovalbumin (OVA) and co-cultured dying tumor cells with dendritic cells (DC).2 We found that CD8α+ DC showed a marked reduction in OVA cross-presentation in vitro and in vivo when exposed to tumor cells killed in the absence of GrAB. By contrast, the absence or presence of GrAB had no effect on the expression of activation makers and secretion of cytokines by the CD8α+ DC. Nevertheless, the MHC class I molecules of CD8α+ DC were significantly occupied by the OVA peptide SIINFEKL only when the DC were co-cultured with tumor cells killed by GrAB-sufficient CTL. Finally, we were able to pin down the impaired cross-presentation by DC to a marked reduction of phagocytosis of the dying tumor cells. By using Annexin V to block PS, we found that PS per se is not critical for tumor cell uptake by DC, confirming previous studies using UV-irradiated tumor cells.4 From these experiments, we further concluded that granzymes induce other pro-phagocytic “eat-me” signals apart from PS on the outer membrane of dying tumor cells (Fig. 1).2

Bottom Line: The cytotoxic properties of granzymes are well established, though recent publications suggest additional roles for granzymes in immunity.We demonstrated that granzymes can act as regulators of cross-presentation by dendritic cells by inducing critical "eat-me" signals on the dying tumor cell, resulting in efficient phagocytosis of cell-associated tumor antigen.

View Article: PubMed Central - PubMed

Affiliation: Ludwig Maximilian University of Munich; Division of Clinical Pharmacology and Medical Clinic; Munich, Germany.

ABSTRACT
The cytotoxic properties of granzymes are well established, though recent publications suggest additional roles for granzymes in immunity. We demonstrated that granzymes can act as regulators of cross-presentation by dendritic cells by inducing critical "eat-me" signals on the dying tumor cell, resulting in efficient phagocytosis of cell-associated tumor antigen.

No MeSH data available.


Related in: MedlinePlus