Circulating DNA in higher organisms cancer detection brings back to life an ignored phenomenon.

The concept of circulating DNA is derived from the early transformation experiments on bacteria. We describe first experiments done with graft hybrids which could be due to circulating DNA. Work on uptake of foreign DNA by eukaryotic cells is then reported. This work led us to discover the phenomenon of transcession in plants and animals where we showed that bacterial DNA can spontaneously enter cells of eukaryotes and be transcribed. We then outline the fact that living cells spontaneously release DNA within a homeostatic mechanism. Finally we describe in more detail some experiments suggesting that an exchange of DNA between T and B lymphocytes may have immunological implications. In this work, nude mice injected with DNA excreted by antigen stimulated human T lymphocytes produced specific antibodies expressing human characteristics.