1. Membrane vesicle, called Texosome, devoid of its natural environment, characterized in that (i) it derives from a dendritic cell; (ii) comprises a lipid bilayer which surrounds a cytosolic fraction, (iii) said vesicle presenting, on its surface, major histocompatibility complex (CMH) Class I and/or II molecules; (iv) having one or several CD63 molecules and (v) a size comprised between 60 and 100 nm. 2. Vesicle according to Claim 1, wherein said vesicle derives from dendritic cell sensibilized with antigen. 3. Vesicle according to any one of Claim 1 or 2, characterized in that it further comprises one or several CD82 or CD86 molecules. 4. Vesicle according to any one of Claim 1 to 3, which derives from an immature dendritic cell. 5. Vesicle according to any one of Claims 1 to 4, which derives from a dendritic cell carrying one or several antigenic peptides. 6. Vesicle according to Claim 5, characterized in that said vesicle derives from a dendritic cell incubated with vesicle called Texosome, said Texosome, derives from a tumor cell, comprises a lipid bilayer which surrounds a cytosolic fraction, which comprises tumor antigen molecules and/or immunomodulators and/or chemo-attractants and/or hormones and/or nucleic acids, exhibiting class I and/or class II major histocompatibility complex (CMH) molecules, comprising "Heat Shock" HSP70 protein and having a diameter of about 60-100 nm. 7. Vesicle according to any of Claims 1 to 4, which derives from an immortalized dendritic cell. 8. A method of preparing a vesicle according to any one of Claims 1 to 7, comprising: (i) a first step of providing dendritic cells or a cell culture comprising dendritic cells from monocyte or bone marrow precursors; (ii) a second step of sensitization of the cells by contacting said cells with peptides, antigens, cells, or membranes or vesicles expressing antigens or antigenic peptides, liposomes or nucleic acids, optionally incorporated into chemical or viral vectors under conditions allowing sensitisation of the dendritic cells; (iii) a third step comprising recuperation the vesicles produced by said dendritic cells from said cell cultures. 9. Method according to Claim 8, wherein the first step comprises the provision of immature dendritic cells, preferably human. 10. Method according to Claim 8 or 9, wherein the vesicles preparation step comprises an initial optional step of treatment of the cells. 11. Method according to Claim 10, wherein the dendritic cells are treated by culture in the presence of cytokines favouring the immature state, by irradiation, or by reducing the pH of the culture, or by combining these different types of treatment. 12. Method according to Claim 8, characterized in that the vesicles are collected by centrifugation, eletrophoresis, chromatography and/or nanofiltration. 13. Use of texosomes according to any one of Claims 1 to 7, for the in vitro stimulation and optionally amplification of T-lymphocytes specific for antigens contained in said texosomes, or of B-lymphocytes, and in particular for the in vitro stimulation and amplification of T-lymphocytes. 14. Use of texosomes according to any one of Claims 1 to 7, for the ex vivo selection of a T-lymphocyte repertoire, capable of recognizing specific antigens contained in said texosomes. 15. A medicine comprising, as active principle, one or several texosomes according to any one of Claims 1 to 7, in combination with a pharmaceutically acceptable vehicle. 16. A medicine according to Claim 15, for the treatment of cancer, infectious or parasitic diseases. 17. A medicine according to Claim 15 or 16, further comprising a stabilizing agent. 18. A composition, comprising texosomes according to any of Claims 1 to 7 and immunopotentiating addition for simultaneous, separate or parted in time use. 19. The use of texosomes according to any one of Claims 1 to 7 for preparation of pharmaceutical composition for the treatment of cancer, infectious or parasitic diseases.