The present invention provides a method of monitoring the efficacy of an immunotherapy in a mammalian subject, wherein the subject has been administered an immunotherapy, wherein the immunotherapy comprises a viral vector containing a polynucleotide encoding an antigen, wherein the viral vector is capable of transducing cells in the mammalian subject to cause the cells to express the antigen; the method comprising: (b) measuring, from a biological sample isolated from the subject, an immune response of the subject to the antigen and comparing the immune response of the subject to the antigen to a reference measurement of immune response to the antigen; (c) measuring, from a biological sample isolated from the subject, an immune response of the subject to the viral vector and comparing the immune response of the subject to the viral vector to a reference measurement of immune response to the viral vector; and (d) determining efficacy based on the comparisons of (b) and (c), wherein an elevated immune response to the antigen and a reduced immune response to the viral vector are indicative of an effective immunotherapy.