In vivo manipulation of dendritic cell migration and activation to elicit antitumour immunity.

Two approaches have been pursued to elicit antitumour immunity: (i) induce recruitment of immature dendritic cells or their precursors at a site of antigen delivery, and (ii) induce activation of tumour-infiltrating dendritic cells (DCs). The recruitment of selected DC subtype conditions the class of the immune response. Each immature DC population displays a unique spectrum of chemokine responsiveness. For examples, Langerhans cells (LCs) migrate selectively in response to CCL20/MIP-3alpha (through CCR6), blood CD11c+ DC to MCP chemokines (through CCR2). All these chemokines are inducible in response to inflammatory stimuli. CCL20/MIP-3alpha in particular is only detected within inflamed epithelium, at the site of antigen entry, which is infiltrated by immature DCs. Furthermore, to reach the site of injury, sequential responsiveness might operate, blood DC precursors are recruited by a set of chemokines (MIP, MCP) while within the tissue other chemokines will direct their navigation (CCL20/MIP-3alpha). Of interest, when injected in vivo together with antigen, MCP-4/CCL13, but not CCL20/MIP-3alpha, recruits blood monocytes or blood DC precursors that promptly differentiate into typical DCs and that improve antitumour immune responses. After antigen uptake, DCs acquire, upon maturation, responsiveness to CCR7 ligands (CCL21/SLC/6Ckine, CCL19/ELC/MIP-3beta) due to receptor up-regulation. In particular, in the periphery, CCL21/SLC/6Ckine expressed by lymphatic vessels may direct into the lymph stream, antigen-loaded maturing DCs leaving the site of infection; while within lymph-node, CCL21/SLC/6Ckine plays a critical role in the entry of naïve T cells from the blood through HEV. In regard to its central role, we decided to investigate whether the expression of CCL21/SLC/6Ckine in tumour may lead to antitumour immune responses. C26 colon carcinoma tumour cell line transduced with CCL21/SLC/6Ckine showed reduced tumorigenicity when injected in vivo into immunocompetent mice. The protection was CD8 dependent and associated with an important intratumoral infiltration of DCs. Most tumour infiltrating DCs (TIDCs) had an immature phenotype, were able to present TAA in the context of MHC class I, but were refractory to stimulation with the combination of LPS, IFNgamma and anti-CD40 antibody. TIDC paralysis could be reverted, however, by in vitro or in vivo stimulation with the combination of a CpG immunostimulatory sequence and an anti-interleukin 10 receptor (IL10R) antibody. CpG or anti-IL10R alone were inactive in TIDC, while CpG triggered activation in normal DC. In particular, CpG plus anti-IL10R enhanced the TAA-specific immune response and triggered de novo IL-12 production. Subsequently, CpG plus anti-IL10R treatment showed robust antitumour therapeutic activity exceeding by far that of CpG alone, and elicited antitumour immune memory.