Disclosed is an in vitro method for producing IFN-&lambda； and/or for generating or obtaining a population of IFN-&lambda； producing CD8+ or eCD8+ conventional dendritic cells, wherein said eCD8+ cDCs express Clec9a and/or Necl2, comprising 5 the steps of: (a) providing a population of cells comprising CD8+ and/or eCD8+ conventional dendritic cells； (b) contacting said conventional dendritic cells with a double-stranded (ds) nucleic acid or analog thereof and, optionally, (c) contacting said population of cells with an agent that increases the level of said conventional dendritic cells, preferably Flt3-ligand or M-CSF receptor ligand； (d) isolating IFN-&lambda； and/or IFN-&lambda； producing Clec9a und Necl2-positive cells from said CD8+ and/or eCD8+ conventional dendritic cells. Further disclosed the use of a composition comprising a double-stranded (ds) nucleic acid or analog thereof in the manufacture of a medicament for the prevention and/or treatment of a disease for which IFN-&lambda； is beneficial for a subject who suffers from such disease, whereby the ds nucleic acid induces IFN-&lambda； production in CD8+ and/or eCD8+ conventional dendritic cells (cDCs) and wherein said eCD8+ cDCs express Clec9a and/or Necl2, wherein said disease is an infectious disease, in particular a viral infection, preferably a persistant viral infection, more preferably a viral infection of the liver and/or a Herpes virus infection, most preferably a Hepatitis virus infection； and/or cancer； and/or a disease of blood, spleen, lung, tonsils, lymph nodes, colon and/or liver.
