Enhanced Activation of Human Dendritic Cells by Inducible CD40 and Toll-like Receptor-4 Ligation

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Abstract
Despite the potency of dendritic cells (DC) as antigen-presenting cells for priming adaptive immunity, DC-based cancer vaccines have been largely insufficient to effectively reduce tumor burden or prevent tumor progression in most patients. To enhance DC-based vaccines, we used the combination of a synthetic ligand-inducible CD40 receptor (iCD40) along with Toll-like receptor-4 (TLR-4) ligation in human monocyte-derived DCs. The iCD40 receptor permits targeted, reversible activation of CD40 in vivo, potentially bypassing the essential role of CD4+ T cells for activation of DCs. As a rigorous preclinical study of this approach, we evaluated key parameters of DC activation and function. Whereas neither iCD40 nor TLR-4 signaling alone led to high levels of interleukin (IL)-12p70 and IL-6, using iCD40 in combination with lipopolysaccharide (LPS) or monophosphoryl lipid A led to strongly synergistic production of both. Furthermore, this approach led to high expression of DC maturation markers, epitope-specific CTL and T helper 1 responses, as well as DC migration in vitro and in vivo. Moreover, use of iCD40-modified and LPS-stimulated DCs led to targeted expansion of autologous T cells against tumor-associated antigens, including prostate-specific membrane antigen, and elimination of preestablished tumors, supporting this technology as a potent strategy for DC-based cancer immunotherapy. [Cancer Res 2007;67(21):10528–10]