Herein, we performed the validation of the polycationic phosphorus dendrimer-based approach for small interfering RNAs delivery in cancer stem cell in vitro. As a molecular target, we chose Lyn, a member of the Src family kinases as an example of a prominent enzyme class widely discussed as a potent anti-cancer intervention point. We then showed that anti-Lyn siRNA, delivered into Lyn-expressing tumor cell model reduces the cell viability, a fact that was not observed in a cell model that lacks Lyn-expression. Furthermore, we have found that the dendrimer itself influences various parameters of the cells such as the expression of surface markers PD-L1, TIM-3 and CD47, targets facilitating immune cell recognition.