Main Inclusion Criteria:

          -  Biochemical recurrence (BCR) within 3 years of radical prostatectomy (RP) or
             definitive RT and no distant metastasis by standard CT imaging and bone scintigraphy,
             or locoregional recurrence (including lymph nodes) assessed by CT or multi-parametric
             magnetic resonance imaging (MRI) and confirmed with negative biopsy in case of prior
             RT.

          -  In case of BCR after RP all the following criteria should apply: a. PSA ≥0.2 ng/mL, b.
             PSA Doubling Time (PSADT) >3 months and <12 months

          -  In case of BCR after RT all the following criteria should apply: a. PSA >nadir + 2
             ng/mL, b. PSADT >3 months and <12 months

          -  ECOG performance status ≤2.

          -  Laboratory values obtained ≤30 days prior to first vaccination: Hemoglobin ≥5.6
             mmol/L; Absolute granulocyte count ≥1.5 x 109 /L, Platelets ≥100 x 109 /L., Total
             bilirubin ≤1.5 x upper limit of normal (ULN).

          -  Creatinine ≤1.5 x ULN.

          -  Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline
             phosphatase (ALP) ≤2.5 x ULN.

        Main Exclusion Criteria:

          -  Patients who are receiving androgen-deprivation therapy or considered a candidate for
             immediate anti-androgen deprivation therapy (ADT) as judged by the investigator.

          -  Patients who have received prior ADT are not eligible with the exception of those that
             received ADT ≤36 months in duration and ≥9 months before randomization and
             administered only in the neoadjuvant/adjuvant setting.

          -  Patient is planned for salvage therapy with RT or radical prostatectomy.

          -  Castrate level of serum testosterone <50 ng/dL at screening.

          -  PSA >10 ng/mL.