Granulocyte-macrophage-colony stimulating factor (GM-CSF), can direct the activation, proliferation and differentiation of myeloid-derived cells. It is also responsible for maturation and function of professional antigen presenting cells thereby impacting adaptive immune responses, while assisting to maintain epithelial barrier function. GM-CSF in combination with other endogenous cytokines and secondary stimuli, such as tumor necrosis factor can modulate pro-inflammatory monocyte priming via chromatin remodeling and enhanced transcriptional responses, a concept termed "trained immunity". An increase in the incidence of opportunistic fungal infections was recently reported in patients with hematological cancers receiving treatment with the BTK inhibitor, Ibrutinib. Tec Kinase BTK is known to influence the expression of GM-CSFRα and regulates downstream signaling pathways, suggesting a role for GM-CSF in maintenance of defense against fungal infections in immune competent hosts. Further examination of the potential mechanism(s) of action for naturally occurring GM-CSF and recombinant human GM-CSF (rhu-GM-CSF) expressed in yeast (sargramostim) are reviewed.