The present invention relates to compositions comprising particles, each of the respective particles comprising particles formed by polyribonucleotides and polymers. Specifically, the composition comprises a complex of at least one double-stranded polyribonucleotide, such as polyinosinic-polycytidylic acid [poly(I:C)], and at least one linear polyalkyleneimine. The particles are also characterized by their monomodal diameter distribution and z-average diameter within specific ranges. The present invention additionally relates to methods of manufacturing the compositions, and further to related pharmaceutical compositions useful for the treatment of any cell growth disorder characterized by an abnormal growth of human or animal cells.