The present invention provides an in vitro method for obtaining and purifying regulatory T cells from thymic tissue (or thyTreg cells), which makes it possible to obtain more than 10 billion cells from a single thymus. These thyTregs obtained in the invention have a purity of more than 95% and very high suppressive capacity, survival and viability, in addition to being safe from a clinical viewpoint. The foregoing would not require the use of massive ex vivo cell expansion protocols. The transfer of these thyTreg cells to patients enables immune tolerance induction. Thus, said cells may be used as cell therapy to induce immune tolerance in the treatment and/or prevention of transplant rejections and in autoimmune diseases.