Conventional dendritic cell (DC) vaccine strategies, in which DCs are loaded with antigens ex vivo, suffer biological issues such as impaired DC migration capacity and laborious GMP production... Show moreConventional dendritic cell (DC) vaccine strategies, in which DCs are loaded with antigens ex vivo, suffer biological issues such as impaired DC migration capacity and laborious GMP production procedures. In a promising alternative, antigens are targeted to DC-associated endocytic receptors in vivo with antibody-antigen conjugates co-administered with toll-like receptor (TLR) agonists as adjuvants. To combine the potential advantages of in vivo targeting of DCs with those of conjugated TLR agonists, we generated a multifunctional antibody construct integrating the DC-specific delivery of viral- or tumor-associated antigens and DC activation by TLR ligation in one molecule. We validated its functionality in vitro and determined if TLR ligation might improve the efficacy of such a molecule. In proof-of-principle studies, an alpha CD40 antibody containing a CMV pp65-derived peptide as an antigen domain (alpha CD40(CMV)) was genetically fused to the TLR5-binding D0/D1 domain of bacterial flagellin (alpha CD40.Flg(CMV)). The analysis of surface maturation markers on immature DCs revealed that fusion of flagellin to alpha CD40(CMV) highly increased DC maturation (3.4-fold elevation of CD80 expression compared to alpha CD40(CMV) alone) by specifically interacting with TLR5. Immature DCs loaded with alpha CD40.Flg(CMV) induced significantly higher CMVNLV-specific T cell activation and proliferation compared to alpha CD40(CMV) in co-culture experiments with allogeneic and autologous T cells (1.8-fold increase in % IFN-gamma/TNF-alpha(+) CD8(+) T cells and 3.9-fold increase in % CMVNLV-specific dextramer(+) CD8(+) T cells). More importantly, we confirmed the beneficial effects of flagellin-dependent DC stimulation using a tumor-specific neoantigen as the antigen domain. Specifically, the acute myeloid leukemia (AML)-specific mutated NPM1 (mNPM1)-derived neoantigen CLAVEEVSL was delivered to DCs in the form of alpha CD40(mNPM1) and alpha CD40.Flg(mNPM1) antibody constructs, making this study the first to investigate mNPM1 in a DC vaccination context. Again, alpha CD40.Flg(mNPM1)-loaded DCs more potently activated allogeneic mNPM1(CLA)-specific T cells compared to alpha CD40(mNPM1). These in vitro results confirmed the functionality of our multifunctional antibody construct and demonstrated that TLR5 ligation improved the efficacy of the molecule. Future mouse studies are required to examine the T cell-activating potential of alpha CD40.Flg(mNPM1) after targeting of dendritic cells in vivo using AML xenograft models. Show less
