The role of granzymes in modulating target cell phagocytosis and immunogenicity
Final Report Abstract
Cytotoxic T lymphocytes (CTL) play a major role in elimination of virus-infecled or malignant cells and the induction of cell death is dependent on the proteases Granzymes A and B (GrAB) delivered by the pore-forming molecule Perforin. CTL from mice deficient in GrAB induce an alternate from of target cell death characterized by morphological changes normally seen in apoptosis, but do not induce exposure of the membrane lipid Phosphatidylserine (PS) on the outer membrane as seen in target cells killed by wild-type (WT-) CTL. As PS exposure is thought to be a key signal for uptake of dead/dying cells by phagocytes, we aimed to investigate the impact of the alternate from of cell death in regards of phagocytosis and ultimately the outcome of an immune response. We used dendritic cells as phagocytes as these highly specialized antigen-presenting cells are able to induce an immune response to engulfed antigens on MHC class I on the cell surface, allowing an immune response against virus infected or tumor cells. Using three separate models we cold show, that granzymes are critical determinants of target cell phagocytosis and subsequent antigen cross-presentation by DC. Firstly, ovalbumin-expressing MC38ova tumor cells killed by cognate CTLs deficient in GrAB (GrAB-/-.OT-l) were phagocytosed less efficiently in vitro by CD11c-highCD8a+ DC than cells killed by granzyme-sufficient WT CTLs (WT.OT-I). The DCs also showed a far stronger capacity for cross-presentation of the OVA peptide SllNFEKL following their uptake of target cells killed by WT.OT-I. Secondly (and consistent with these results), MC38ova cells killed by GrAB-/-.OT-l CTLs induced significantly less antigen cross-presentation in vivo, as determined by the proliferation of naive OT-l splenocytes co-injected into C57BL/6 recipients. Finally, unlike WT C57BL/6 mice, GrAB-/- mice failed to reject MC38ova tumors. Interestingly, continued tumor growth was associated with altered memory formation in GrAB-/-. Our study is the first to show a critical role for GrAB in profoundly altering immunogenicity by infiuencing the mode of target cell death.
Publications
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Lorne Cancer Conference, February 2008: In situ analysis of the antigen presenting machinery of AML blasts by tissue microarray
Hoves S, Aigner M, Pfeiffer C, Laumer M, Obermann EC & Mackensen A.
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2nd European Congress for Immunology in Berlin 13-16 September, 2009: A role for Granzymes A and B in target cell phagocytosis and antigen cross-presentation
Hoves S, Sutton VR, Haynes NM, Andrews DM, Stagg J, Hawkins ED, Sedelies K, Roczo S, Villadangos JA & Trapani JA
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2nd European Congress for Immunology in Berlin 13-16 September, 2009: Engulfment of dead or live target cells distinguished by the use of a pH-sensitive dye
Hoves S, Sutton VR, Roczo S, Sedelies K, Fielding K, Waterhouse NJ, Neeson P & Trapani JA
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Gordon Research Conference on "Apoptotic Cell Recognition & Clearance" in New London, NH, USA June/July 2009: A role for Granzymes A and B in target cell phagocytosis and antigen cross-presentation
Hoves S, Sutton VR, Haynes NM, Andrews DM, Stagg J, Hawkins ED, Sedelies K, Roczo S, Villadangos JA & Trapani JA
