 Pembrolizumab will be given on Day 1 of each 21 day cycle after Imprime PGG, and the RP2D dose of Imprime PGG will be given on Days 1, 8 and 15 of each 21 day cycle. Treatment will continue up to 16 cycles, or until disease progression, unacceptable toxicity, subject refusal, or subject death either from progression of disease, the therapy itself, or from other causes. 