Abstract Introduction: Given the pre-eminent role of dendritic cells (DCs) as antigen-presenting cells, their exploitation as natural adjuvants in vaccination protocols for the treatment of various malignancies and infectious diseases is not surprising. Nevertheless, inadequate or unsustained activation has likely limited response rates in clinical trials. We previously reported a potent synthetic dimerizer drug-inducible CD40 (iCD40) receptor that permits temporally controlled DC-specific activation within the context of an immunological synapse (Hanks et al, Nat Med, 2005). We showed that when combined with Toll-like Receptor (TLR) adjuvants, iCD40-modified DCs (iCD40-DCs) have enhanced survival, co-stimulatory marker expression, migration, IL-12 production, antigen (Ag)-specific T cell stimulatory capacity and anti-tumor responses (Lapteva et al, Cancer Res, 2007). A phase I/II clinical trial based on iCD40-DCs to treat castration-resistant, metastatic prostate cancer began enrolling patients in August 2009. Procedures: To simplify this approach, we have developed a unified, inducible DC switch, called “iCD40. MyD88”, which combines signaling elements from costimulatory molecule, CD40, and TLR adapter, MyD88, fused to tandem FK506-binding binding proteins (FKBP12v36). Activation is initiated in vitro or in vivo by lipid-permeable dimerizing ligands (i.e. AP1903 or AP20187). Results: Both murine and human iCD40. MyD88-DCs secrete high (ng) levels of IL-12 and maturation markers in a ligand-dependent fashion without the need for exogenous adjuvants. iCD40. MyD88 activation is associated with synergistic activation of IKKα/β and p38. Moreover, tumor-bearing mice treated with antigen-pulsed, iCD40. MyD88-DCs show a potent anti-tumor immune response, consistent with expansion of antigen-specific CTLs in vivo. Bicistronic vectors combining iCD40. MyD88 along with tumor-associated antigens are underway. Conclusion: This “combo-switch” permits potent, targeted activation of antigen-pulsed DCs in vivo, leading to improved anti-tumor immunity with a high likelihood for reduced side effects. Production of a single vector that combines a potent DC switch with tumor antigen is the first requisite step leading to economically viable, “off-the-shelf”, vaccine therapies for cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4761.