<p>Disclosed is a drug delivery system or method or pharmaceutical composition which can suppress the barrier mechanism against the transfer of a substance to transfer a medicinal substance at any part of the body in a non-invasive and bloodless manner. A factor capable of suppressing the expression of a tricellulin gene or the function of a tricellulin protein; a drug delivery system or method using the factor; a pharmaceutical composition comprising the factor; and a non-human animal having a knockout tricellulin gene.</p>
