B-cell functions in antitumor immunity are not well understood. In this study, we evaluated the role of B cells in the development of antitumor immunity using Friend murine leukemia virus gag-expressing mouse EL-4 (EL-4 gag), D5 mouse melanoma, or MCA304 mouse sarcoma cells. To screen tumors for susceptibility to B-cell-deficient immune environments, spleen cells from naive C57BL/6 [wild-type (WT)] and B-cell knockout (BKO) mice were cultured with irradiated tumor cells in vitro. When cells were stimulated with EL-4 gag or D5 (but not MCA304 tumors), IFN-γ production from CD8 T cells and natural killer cells was markedly decreased in WT compared with BKO cultures. IFN-γ production was correlated with CD40 ligand expression on the tumor and inversely with interleukin-10 (IL-10) production by B cells. Sorted WT B cells produced more IL-10 than CD40 knockout (CD40KO) B cells when cocultured with EL-4 gag or D5 (but not MCA304). IFN-γ production by BKO cells was reduced by the addition of sorted naive WT B cells (partially by CD40KO B cells) or recombinant mouse IL-10. In vivo tumor progression mirrored in vitro studies in that WT mice were unable to control tumor growth whereas EL-4 gag and D5 tumors (but not MCA304) were eliminated in BKO mice. Robust in vivo antitumor CTLs developed only in BKO tumor-challenged mice. Our studies provide the first mechanistic basis for the concept that B-cell depletion could therapeutically enhance antitumor immune responses to certain tumors by decreasing IL-10 production from B cells. (Cancer Res 2006; 66(15): 7741-7)

A new langerin ⁺ DC subset has recently been identified in murine dermis (langerin ⁺ dDC), but the lineage and functional relationships between these cells and langerin ⁺ epidermal Langerhans cells (LC) are incompletely characterized. Selective expression of the cell adhesion molecule EpCAM by LC allowed viable LC to be easily distinguished from langerin ⁺ dDC in skin and lymphoid tissue and ex vivo as well. Differential expression of EpCAM and langerin revealed the presence of at least 3 distinct skin DC subsets. We determined that LC and langerin ⁺ dDC exhibit different migratory capabilities in vitro and repopulate distinct anatomic compartments in skin at different rates after conditional depletion in vivo. Langerin ⁺ dDC, in contrast to LC, did not require TGFβ1 for development. Carefully timed gene gun immunization studies designed to take advantage of the distinct repopulation kinetics of langerin ⁺ dDC and LC revealed that langerin ⁺ dDC were required for optimal production of β-galactosidase-specific IgG2a/c and IgG2b in the acute phase. In contrast, immunization via LC-deficient skin resulted in persistent and strikingly reduced IgG1 and enhanced IgG2a Ab production. Our data support the concepts that LC and langerin ⁺ dDC represent distinct DC subsets that have specialized functions and that LC are important immunoregulatory cells. The presence of at least 3 functionally distinct skin DC subsets may have particular relevance for vaccines that are administered epicutaneously.