This Phase Ib dose escalation study will evaluate BTH1704, a monoclonal antibody that targets an aberrantly glycosylated antigen Mucin 1, and Imprime PGG, a glucan contained in yeast that is essential in triggering a leukocyte-mediated cytotoxic response towards tumor cells, in combination with gemcitabine in patients with advanced PDAC. The three intravenous drugs are taken in tandem 4 times in a 28-day cycle. The MAD of BTH1704 (BTH, 3 dose levels) in combination with gemcitabine (Gem) and Imprime PGG (I) will be determined using a standard "3+3" design. Treatment continues until disease progression, unacceptable toxicity, physician discretion, or patient refusal.