Abstract: Novel chimeric molecules, termed “half-antibodies”, which are capable of self-assembling to form an epitope recognition site. Using these half-antibodies or a vesicle, a viral particle, a composition or a kit thereof, for therapeutic applications, such as the prevention or treatment of cancers, genetic diseases, infectious diseases, and for in vitro diagnostic applications and detecting biological molecules. The half-antibodies include at least two chimeric molecules A and B, each has a polypeptide domain characteristic of a variable domain of a heavy chain or of a light chain of an antibody, and a nucleotide domain, the nucleotide domain of A and that of B being capable of pairing into a double stranded structure. Biologically active nucleic sequences can be grafted onto these chimeric molecules to prevent the expression of target genes in the interior of a human or non-human mammalian cell.