TNF-related apoptosis-inducing ligand (TRAIL/Apo-2L): A novel mechanism for CpG ODN and BCG-induced anti-tumor activity

Currently, there are agents in clinical trials or use, such as CpG oligodeoxynucleotides (ODN) and Mycobacterium bovis bacillus Calmette-Guerin (BCG), respectively, that elicit tumoricidal activity through unknown mechanisms. These two therapeutic agents have important similarities in that both induce a strong TH1 response by stimulating the production of interferons and IL-12. Interestingly, interferons induce the expression of the tumoricidal TNF family member TNF-related apoptosis-inducing ligand (TRAIL/Apo-2L) on multiple subsets of immune cells, such as monocytes, T cells, and NK cells.; We proposed that TRAIL/Apo-2L is responsible for the tumoricidal activity of CpG ODN and BCG immunotherapy via an interferon-dependent mechanism. We discovered that CpG-A or -B ODN stimulated PBMC exhibited tumoricidal activity via a TRAIL/Apo-2L-dependent mechanism. IFN-alpha, produced by plasmacytoid DC, was necessary in upregulating the surface expression of TRAIL/Apo-2L on all PBMC subsets. These studies define an IFN-alpha-dependent mechanism by which CpG ODN stimulated PBMC function through TRAIL/Apo-2L-mediated tumoricidal activity.; In 1984, Tokunaga et al. described the immunostimulatory properties of BCG DNA. Subsequent studies determined that CpG motifs were responsible for stimulating immune cells, and Mycobacterial species contain high amounts of CpG dinucleotide content. Because of BCG's use in treating bladder cancer, ability to stimulate IFN, and high amounts of CpG motifs, we hypothesized that BCG's antitumor activity is dependent on IFN and TRAIL/Apo-2L like that of CpG ODN. Our lab described the presence of soluble TRAIL/Apo-2L in the urine of BCG immunotherapy bladder cancer responders. The source of the TRAIL/Apo-2L was examined by analyzing the leukocytes present in the urine for TRAIL/Apo-2L expression. Neutrophils were the only cells expressing TRAIL/Apo-2L, leading us to examine the direct effects of BCG on neutrophils. We discovered that neutrophils have an intracellular store of soluble, functional TRAIL/Apo-2L. Although IFN-alpha did not affect the expression or release of TRAIL/Apo-2L from neutrophils, it was a potent stimulus for the synthesis of intracellular TRAIL/Apo-2L. These results describe a role for neutrophils, TRAIL/Apo-2L, and IFN in implementing an antitumor response during BCG immunotherapy.