Methods of substantially retaining or otherwise preserving the biological activity of a dsRNA, present in a cell, to post-transcriptionally silence the expression of a gene in a target organism, comprising the step of adding to the cell composition a compound having the function of a protein—or amine—cross linking agent and/or an acid, and compositions comprising the cells comprising dsRNA, and protein cross linking agents and/or acids, as well as the use of the cross linking agents and/or acids in the method.