Dendritic cells generated in the presence of GM-CSF plus IL-15 prime potent CD8⁺ Tc1 responses in vivo

Dendritic cells (DC) comprise a system of professional antigen-presenting cells, which induce the stimulation of very rare antigen-specific naive T cells. DC progenitors can be stimulated to differentiate into immature DC by various growth factors, including GM-CSF and IL-4. Here we show that IL-15, in combination with GM-CSF is a growth factor for murine DC. Murine bone marrow cells, depleted of T cells, B cells, I-A⁺ cells and Gr-1⁺ granulocytes, and cultured in the presence of GM-CSF plus IL-15 (IL-15 DC), yielded DC expressing high levels of CD11c and MHC class II molecules, as well as CD11b. These cells expressed significant levels of CD40, CD80 and CD86, and could stimulate allogeneic CD4⁺ T cells efficiently. Interestingly, IL-15 DC were far superior to DC generated with GM-CSF plus IL-4 in stimulating allogeneic CD8⁺ T cells in vitro. Consistent with this, IL-15 DC induced much more potent antigen-specific CD8⁺ T cell responses with high levels of Th1 cytokines in vivo, compared to DC generated with GM-CSF plus IL-4, or with GM-CSF plus TGF-β, or with GM-CSF alone. Together, these data suggest that IL-15 promotes the development of DC, which induce potent Th1 and Tc1 responses in vivo. This suggests potential roles for these IL-15 DC cells in the immunotherapy of tumors and infectious diseases.