The present invention provides an in vitro method of expressing an antigenic molecule or a part thereof on the surface of a dendritic cell using a PCI method with TPCS2a at a concentration of 0.020-0.1 μg/ml, using light of a wavelength of between 400 and 500 nm. Methods of treatment such as vaccination comprising this method, together with compositions comprising said cells and uses involving said cells expressing antigenic molecules are also provided.
