Background: Phase I/II studies of pTVG-HP showed safety and increases in prostatic acid phosphatase (PAP)-specific T cells. Based on these, we conducted a multi-center, randomized phase II trial using pTVG-HP with GM-CSF adjuvant vs GM-CSF alone in patients with PSA-recurrent, non-metastatic, non-castrate, prostate cancer (stage M0). Methods: 99 patients with M0 prostate cancer (negative CT and bone scan) with PSA doubling time (DT) of < 12m were randomly assigned to pTVG-HP + GM-CSF vs GM-CSF. Treatments were every 2 wk x 6, and then quarterly for up to 24m. Primary endpoint was 2-year MFS. Secondary endpoints included median MFS, changes in PSA DT, and immune response to PAP antigen. Additional analysis included quantitative changes in bone lesion activity by NaF PET/CT. Results: Few grade 3/4 events were observed and were not statistically different between arms. 2-year MFS between control and pTVG-HP was 42.3% and 41.8% (p = 0.97). Median MFS was not different (18.3m control versus 18.9m pTVG-HP, HR = 1.6, p = 0.13). Changes in PSA DT, and immunity to the PAP target, were not different between study arms. A pre-planned subset analysis showed median MFS was significantly longer in patients with rapid PSA DT ( < 3m) treated with pTVG-HP (6.1m versus 12.0m, n = 21, HR = 4.4, p = 0.03). In patients with baseline metastases detected on NaF PET/CT, total activity (SUVtotal) increased 17% with GM-CSF alone, but decreased 29% with pTVG-HP from baseline to month 6 (n = 27, p = 0.07). Conclusions: This trial did not demonstrate an overall increase in 2-year MFS following treatment with pTVG-HP, but suggested a modest effect in patients with rapidly progressive disease. NaF PET/CT imaging suggests that pTVG-HP has a detectable effect on decreasing metastatic activity in bone. A separate trial suggests that pTVG-HP is an immune activating agent that improves activity of PD-1 blockade. A trial using pTVG-HP in combination with nivolumab in patients with M0 prostate cancer is currently underway. Clinical trial information: NCT01341652