The present disclosure relates to synthetic alpha-galactosyl ceramide (α-GalCer) analogs, and their use as immunotherapies. In one aspect, a method of activating a cytokine response in a subject includes administering an effective amount of a compound to a subject, wherein the subject has an adaptive immune system that includes a population of cells, the population including at least one lymphocyte and at least one antigen-presenting cell, and wherein the compound is represented by the structure of formula 1: wherein, n is 0 to 25; X is selected from O and S; R1 is selected from H, CH3, and phenyl, where phenyl is optionally substituted with H, OH, OCH3, F, CF3, phenyl, phenyl-F, C1-C6 alkyl, or C2-C6 branched alkyl; R2 is selected from OH and H; R3 is selected from C1-C15 alkyl, and phenyl, where phenyl is optionally substituted with H, OH, OCH3, F, CF3, phenyl, C1-C6 alkyl, or C2-C6 branched alkyl; R4 is selected from OH, OSO3H, OSO3Na, and OSO3K; and R5 is selected from CH2OH and CO2H; or a pharmaceutically acceptable salt thereof; forming a complex between the compound and the antigen-presenting cell, wherein the formation of the complex results in the activation of a receptor on the lymphocyte; and activating the lymphocyte to produce the cytokine response.