Vitamin D-dependent induction of cathelicidin in human macrophages results in cytotoxicity against high-grade B cell lymphoma.

Infiltration by macrophages represents a characteristic morphological hallmark in high-grade lymphatic malignancies such as Burkitt's lymphoma (BL). Although macrophages can, in principle, target neoplastic cells and mediate antibody-dependent cellular cytotoxicity (ADCC), tumor-associated macrophages (TAMs) regularly fail to exert direct cytotoxic functions. The underlying mechanisms responsible for this observation remain unclear. We demonstrate that inflammatory M1 macrophages kill proliferating high-grade B cell lymphoma cells by releasing the antimicrobial peptide cathelicidin in a vitamin D-dependent fashion. We show that cathelicidin directly induces cell death by targeting mitochondria of BL cells. In contrast, anti-inflammatory M2 macrophages and M2-like TAMs in BL exhibit an altered vitamin D metabolism, resulting in a reduced production of cathelicidin and consequently in inability to lyse BL cells. However, treatment of M2 macrophages with the bioactive form of vitamin D, 1,25D3, or a vitamin D receptor agonist effectively induces cathelicidin production and triggers tumoricidal activity against BL cells. Furthermore, rituximab-mediated cytotoxicity of vitamin D-treated M2 macrophages is cathelicidin-dependent. Finally, vitamin D treatment of 25-hydroxyvitamin D (25D)-deficient volunteers in vivo or primary TAMs in vitro improves rituximab-mediated ADCC against B cell lymphoma cells. These data indicate that activation of the vitamin D signaling pathway activates antitumor activity of TAMs and improves the efficacy of ADCC.

CD47 Enhances In Vivo Functionality of Artificial Antigen-Presenting Cells.

PURPOSE: Artificial antigen-presenting cells, aAPC, have successfully been used to stimulate antigen-specific T-cell responses in vitro as well as in vivo. Although aAPC compare favorably with autologous dendritic cells in vitro, their effect in vivo might be diminished through rapid clearance by macrophages. Therefore, to prevent uptake and minimize clearance of aAPC by macrophages, thereby increasing in vivo functionality, we investigated the efficiency of "don't eat me" three-signal aAPC compared with classical two-signal aAPC. EXPERIMENTAL DESIGN: To generate "don't eat me" aAPC, CD47 was additionally immobilized onto classical aAPC (aAPC(CD47+)). aAPC and aAPC(CD47+) were analyzed in in vitro human primary T-cell and macrophage cocultures. In vivo efficiency was compared in a NOD/SCID T-cell proliferation and a B16-SIY melanoma model. RESULTS: This study demonstrates that aAPC(CD47+) in coculture with human macrophages show a CD47 concentration-dependent inhibition of phagocytosis, whereas their ability to generate and expand antigen-specific T cells was not affected. Furthermore, aAPC(CD47+)-generated T cells displayed equivalent killing abilities and polyfunctionality when compared with aAPC-generated T cells. In addition, in vivo studies demonstrated an enhanced stimulatory capacity and tumor inhibition of aAPC(CD47+) over normal aAPC in conjunction with diverging biodistribution in different organs. CONCLUSIONS: Our data for the first time show that aAPC functionalized with CD47 maintain their stimulatory capacity in vitro and demonstrate enhanced in vivo efficiency. Thus, these next-generation aAPC(CD47+) have a unique potential to enhance the application of the aAPC technology for future immunotherapy approaches.