The invention provides formulations that contain an immunogenic or immunostimulatory cargo, delivery moiety and/or lipid, and a lipid that functions to reduce or prevent induction in a subject of an immune response which would otherwise occur when the immunogenic or immunostimulatory cargo, delivery moiety and/or lipid is administered to a subject as a component of an appropriate control formulation lacking the immune response reducing lipid. Specific immune response reducing lipids and uses thereof are further provided.