A pharmaceutical composition, including at least one nucleic acid, a Tyrode's medium having 140 mM NaC1, 6 mM KC1, 3 mM CaC12, 2 mM MgC12, 10 mM Hepes, pH 7.4, and 10 mM glucose; and a tetrafunctional copolymer of formula (I): where x and y represent, independently of one another, an integer of between 1 and 500, the tetrafunctional copolymer is in a form of a mineral salt wherein said tetrafunctional copolymer is in a cationic form. The compound of formula (I) has a molecular weight of between 1,000 and 25,000 g/mol and an EO/PO ratio of 0.8 to 1.2.