The present disclosure is directed to the stabilization of nucleated cells in a whole blood sample ex-vivo, effected by an additive being a liquid composition for stabilizing an analyte in intact nucleated cells of a whole-blood sample ex-vivo, the composition being an aqueous solution, the solution comprising an anticoagulant, a phosphate salt, a cell-metabolizable sugar, adenine, and an antioxidant, wherein the antioxidant comprises a mitochondria-targeted antioxidant, preferably a mitochondria-targeted antioxidant selected from the group consisting of SkQ1, MitoQ, SS-31, and a mixture thereof. In a specific embodiment, the liquid composition further comprises a protease inhibitor. Further provided is advantageous use of the composition for stabilizing an analyte selected from DNA, RNA and protein in intact nucleated cells of the whole-blood sample ex-vivo, as well as kits including the composition for practicing said use. Additionally, specific methods are provided for stabilizing intact nucleated cells of a whole-blood sample ex-vivo.
