The invention provides novel methods, materials and systems that can be used to generate viral vectors having altered tissue and cell targeting abilities. In illustrative embodiments of the invention, the specificity of lentiviral vectors was modulated by a thin polymer shell that synthesized and coupled to the viral envelope in situ. The polymer shell can confers such vectors with new targeting ability via agents such as cyclic RGD (cRGD) peptides that are coupled to the polymer shell. These polymer encapsulated viral vectors exhibit a number of highly desirable characteristics including a higher thermal stability, resistance to serum inactivation in vivo, and an ability to infect dividing and non-dividing cells with high efficiencies.