CD40 ligand (CD40L), a strong stimulator of Th1 immune responses, acts via dendritic cells to trigger T-cell activation. AdCD40L therapy introduces the CD40L gene into the tumor microenvironment with an adenoviral vector and has shown promising results in experimental tumor models, dogs, and patients (phase I-II trials). The transduction efficiency of AdCD40L is dependent on the expression of CAR (coxsackie/adenovirus adhesion receptor), which is commonly downregulated on tumor cells. To enhance transduction efficiency, and therefore the therapeutic efficacy, a double-modified adenovirus was developed. The double-modified Ad5PTDf35(mCD40L) had a protein transduction domain (PTD) inserted into the hexon protein and the virus fiber is switched from serotype 5 to serotype 35. These modifications enable transduction of a wider range of cell types. In comparison with Ad5(mCD40L), Ad5PTDf35(mCD40L) showed increased transduction capacity on a variety of murine cells. Furthermore, antigen presentation was improved after transduction with Ad5PTDf35(mCD40L). This was demonstrated in an antigen presentation assay, both in vitro and in vivo, in which transduced dendritic cells were loaded with suboptimal concentrations of the human gp100 peptide and allowed to interact with gp100-specific transgenic T cells (pmel). Finally, Ad5PTDf35(mCD40L) could delay tumor growth in a murine cancer model at a particle load, wherein therapeutic efficacy of the Ad5(mCD40L) vector was lost. Hence, the Ad5PTDf35(CD40L) vector holds great promise as a second-generation immune stimulatory therapy, as it not only targets tumor cells but also antigen-presenting cells that are, among other cells, present in the tumor microenvironment.