Recombinant plasmids usable for the transfection of eukaryotic and prokaryotic cells are described; such plasmids have a length comprised between 7 and 12 kbases and comprise a sequence encoding the heavy chain of an immunoglobulin; in particular, they may be used: in a process of transfection of prokaryotic or eukaryotic cells (ex vivo) which can be inoculated into higher organisms in order to induce a prophylactic or therapeutic immune response; in a protocol of direct inoculation (in vivo) in higher organisms in genic immunization methodologies with the aim of evoking prophylactic or therapeutic immune responses.