While in vitro observations suggest that cross-presentation of antigens is mediated primarily by CD8α + dendritic cells, in vivo analysis has been hampered by the lack of systems that selectively eliminate this cell lineage. Here we show that deletion of the transcription factor Batf3 ablated development of CD8α + dendritic cells, allowing us to examine their role in immunity in vivo. Dendritic cells from Batf3 -/-mice were defective in cross-presentation and Batf3 -/-mice lacked virusspecific CD8 + T cell responses to West Nile virus. Importantly, rejection of highly immunogenic syngeneic tumors was impaired in Batf3 -/-mice. These results suggest an important role for CD8α + dendritic cells and cross-presentation in responses to viruses and in tumor rejection.During antigen 'cross-presentation' (1), antigens generated in one cell are presented by MHC class I molecules of a second cell. It remains unclear whether all antigen presenting cells (APCs) use cross-presentation and whether this pathway plays a role in immune responses in vivo (2). Dendritic cells (DCs) are a heterogeneous group of APCs with two major subsets, plasmacytoid dendritic cells (pDCs) and conventional CD11c + dendritic cells (cDCs) (3). Subsets of cDCs include CD8α + , CD4 + , and CD8α -CD4 -populations that may exert distinct functions in immune responses. Evidence has suggested that CD8α + cDCs are important for cross-presentation during infections, but is based on ex vivo analysis (4-6) or in vitro antigen loading (7). Evidence both for and against a role for cross-presentation in responses against tumors has been reported (8-10).Attempts have been made to study the in vivo role of dendritic cells by selective depletion. Diphtheria toxin treatment can deplete all CD11c hi cells in one transgenic mouse model (11), but affects splenic macrophages and activated CD8 + T cells (12). Gene targeting of transcription factors (e.g., Irf2, Irf4, Irf8, Stat3 and Id2) has caused broad defects in several DC subsets, T cells and macrophages (13). To identify genes regulating DC development, we performed global gene expression analysis across many tissues and immune cells ( fig S1A). Batf3 (p21SNFT) (14) was highly expressed in cDCs, with low to absent expression in other *To whom correspondence should be addressed. E-mail murphy@pathology.wustl.edu. fig. S1B-D).In spleens of Batf3 -/-mice we found a selective loss of CD8α + cDCs, without abnormalities in other hematopoietic cell types or architecture (Fig. 1, fig. S2-S11). CD8α + cDC coexpress DEC205, CD24, and low levels of CD11b (3,15). Batf3 -/-mice lacked splenic CD11c hi CD8α + DEC205 + cells (Fig. 1A), showed a loss of CD11c hi CD11b dull cells and CD11c hi CD8α + CD24 + cells (Fig. 1B), but had normal populations of CD4 + and CD8α -CD4 -cDC subsets (Fig. 1B). Lymph nodes and thymi of Batf3 -/-mice lacked CD8α + DCs but had normal distributions of CD8α -CD11c + cells (Fig. 1C). DEC205 int and DEC205 hi DCs were present in lymph nodes draining the skin of Batf3 -/-mice (Fig. 1C), and show...

Dendritic cell responsiveness to type I interferon is required for the generation of antitumor T cell responses and tumor rejection.

'Cancer immunoediting' is a process wherein the immune system protects hosts against tumor development and facilitates outgrowth of tumors with reduced immunogenicity. Although interferon-gamma (IFN-gamma) is known to be involved in this process, the involvement of type I interferons (IFN-alpha/beta) has not been elucidated. We now show that, like IFN-gamma, endogenously produced IFN-alpha/beta was required for the prevention of the growth of primary carcinogen-induced and transplantable tumors. Although tumor cells are important IFN-gamma targets, they are not functionally relevant sites of the actions of the type I interferons. Instead, host hematopoietic cells are critical IFN-alpha/beta targets during development of protective antitumor responses. Therefore, type I interferons are important components of the cancer immunoediting process and function in a way that does not completely overlap the functions of IFN-gamma.

Herein we report the generation of mouse monoclonal antibodies (mAbs) specific for the IFNAR-1 subunit of the mouse interferon-alpha/beta (IFN-alpha/beta) receptor (MAR1 mAbs) that block type I IFN receptor signaling and biologic response induction in vitro and in vivo. These mAbs were generated from Ifnar1 (/) mice immunized by in vivo hydrodynamic transfection with a plasmid encoding the extracellular domain (ECD) of murine IFNAR-1. All MAR1 mAbs bound native receptor expressed on cell surfaces and immunoprecipitated IFNAR-1 from solubilized cells, and two mAbs also detected IFNAR-1 by Western blot analysis. in vitro, the mAbs prevented ligand-induced intracellular signaling and induction of a variety of type I IFN-induced biologic responses but had no effect on IFN-gamma-induced responses. The most effective in vitro blocker, MAR1-5A3, also blocked type I IFN-induced antiviral, antimicrobial, and antitumor responses in vivo. We also explored whether murine IFNAR-1 surface expression required the presence of Tyk2. In contrast to Tyk2-deficient human cell lines, comparable IFNAR-1 expression was found on primary cells derived either from wild-type or Tyk2 (/) mice. These mAbs represent much needed tools to more clearly elucidate the biochemistry, cell biology, and physiologic function of the type I IFNs and their receptor in mediating host-protective immunity and immunopathology.