Abstract: Non-naturally occurring vector for gene therapy are provided, comprised of chemically defined reagents, where the vector is self-assembling and where the vector comprises (1) a core complex comprising a nucleic acid and (2) at least one complex forming reagent, where the vector has fusogenic activity. The vector optionally may contain reagents permitting fusion with cell membranes and nuclear uptake. The vector also may contain an outer shell moiety that is anchored to the core complex, whereby the outer shell stabilizes the complex, protects it from unwanted interactions and enhances delivery of the nucleic acid into a target tissue or cell. The outer shell optionally may be sheddable, that is, it may be designed such that it dissociates from the vector upon entry into the target cell or tissue.