There is provided a biologically-active agent, in particular, for the early diagnosis and/or preventative therapy of virally-infected living cells, the efficacy of which is selective for the cell membranes of the virally-infected cells, which are modified after viral infection. The agent includes at least one component, selected from a group of materials, including recombinant human histone H1 or at least an H1 subtype or the active portion thereof. The appropriate biological activity for killing a virally-infected cell at the modified cell membrane thereof through cooperation with similarly or differently active agent components may be achieved, which together form a biologically-effective complex with increased biological activity.
