Co-cultures of human colorectal tumor spheroid with immune cells reveal therapeutic potential of MICA/ antibodies
Tristan Courau1, Mathieu Blery2, Thomas Aparicio1,3, Matthieu Allez1,3, Lionel Le Bourhis1 1U1160 Intestinal Immunity in Inflammation and Cancer, St Louis Hospital, Paris; 2Innate Pharma, Marseille; 3Gastroenterology department, St Louis Hospital, Paris
Relevant functional tests aimed at studying tumor-lymphocytes interactions and the efficacy of cancer immunotherapies in human remain scarce. 3D tumor cultures, called tumor spheroids, represent interesting models to study cancer treatments. Co-cultures of tumor spheroids with immune cells could thus be used to assess the efficacy and mechanisms of action of immuno-modulatory drugs. We developed co-culture systems with HT29 tumor cell line as well as primary colon tumor-derived spheroids to quantify by flow cytometry and live-cell imaging the infiltration, activation and function of immune cells toward tumors. Monocytes, T and NK cells from donor peripheral blood rapidly infiltrated HT29 spheroids, in which we found increased activated/effector cells compared to outside the spheroids. This infiltration induced immune-mediated tumor cells apoptosis, and adding of stimulatory cytokine IL-15 enhanced both immune infiltration and activation, leading to increased tumor cell apoptosis and spheroid destruction. NKG2D, a key molecule in anti-tumor immunity, can be subverted by tumors through chronic exposure to its ligands MICA/B. In our setting, NKG2D was engaged on infiltrating cells and its blockade dramatically reduced immune dependent spheroid destruction. We thus used these co-cultures to assess the therapeutic potential of a cytotoxic antibody specific for MICA/B. Anti-MICA/B strongly increased immune-dependent destruction of tumor spheroid in allogeneic as well as autologous conditions. NK cells infiltration was increased and their Fc receptors were engaged, advocating for an antibody dependent cell-mediated cytotoxicity process. Moreover, CD8 T cells were recruited and activated as well suggesting that the antitumor effect of the anti-MICA/B antibodies could depend on multiple mechanisms. Altogether, we show that tumor spheroids represent a relevant tool to study tumor-lymphocyte interactions and testing of immunotherapies such as anti-MICA/B. They can be easily used in allogeneic conditions, while autologous co-cultures could be of major importance to anticipate treatments efficacy in patients.
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