Dendritic cells infiltrating tumors cotransduced with granulocyte macrophage colony-stimulating factor (GM-CSF) and CD40 ligand genes take up and present endogenous tumor-associated antigens, and prime naive mice for a cytotoxic T lymphocyte response

We transduced BALB/c-derived C-26 colon carcinoma cells with granulocyte/ma crophage colony-stimulating factor (GM-CSF) and CD40 ligand (CD40L) genes t o favor interaction of these cells with host dendritic cells (DCs) and, the refore, cross-priming. Cotransduced cells showed reduced tumorigenicity, an d tumor take was followed by regression in some mice. In vivo tumors were h eavily infiltrated with DCs that were isolated, phenotyped, and tested in v itro for stimulation of tumor-specific cytotoxic T lymphocytes (CTLs). BALB /c C-26 carcinoma cells express the endogenous murine leukemia virus (MuLV) env gene as a tumor-associated antigen. This antigen is shared among solid tumors of BALB/c and C57BL/6 mice and contains two epitopes, AH-1 and KSP, recognized in the context of major histocompatibility complex class I mole cules H-2L(d) and H-2K(b), respectively. DCs isolated from C-26/GM/CD40L tu mors grown in (BALB/c X C57BL/6)F1 mice (H-2(dXb)) stimulated interferon ga mma production by both anti-AH-1 and KSP CTLs, whereas tumor-infiltrating D Cs (TIDCs) of BALB/c mice stimulated only anti-AH-1 CTLs. Furthermore, TIDC s primed naive mice for CTL activity as early as 2 d after injection into t he footpad, whereas double-transduced tumor cells required at least 5 d for priming; this difference may reflect direct DC priming versus indirect tum or cell priming. Immunohistochemical staining indicated colocalization of D Cs and apoptotic bodies in the tumors. These data indicate that DCs infiltr ating tumors that produce GM-CSF and CD40L can capture cellular antigens, l ikely through uptake of apoptotic bodies, and mature in situ to a stage sui table for antigen presentation. Thus, tumor cell-based vaccines engineered to favor the interaction with host DCs can be considered.