Abstract: The present invention relates to a recombinant Orthopox viral vector comprising, in operable linkage a first promoter comprising or consisting of (i) at least one viral early promoter element and optionally at least one viral late promoter element; or (ii) at least one viral late promoter element and at least three viral early promoter elements, and b) a first nucleic acid sequence encoding at least one immunostimulatory protein. The present invention also relates to cells comprising the recombinant Orthopox viral vectors and to compositions comprising the recombinant Orthopox viral vector or the cells; and optionally a further recombinant viral vector comprising a nucleic acid sequence encoding a check-point inhibitor, a nucleic acid encoding a checkpoint inhibitor or a checkpoint inhibitor. Moreover, the present invention provides the recombinant Orthopox viral vectors, and cells and compositions comprising the same for use in medicine, in particular for use in treating, ameliorating or preventing cancer.