A composition for use in parenteral administration in the treatment of cancer of a subject in need thereof, wherein the composition is in an acceptable pharmaceutical carrier and comprises: a. a therapeutically effective amount of a galactoarabino-rhamnogalacturonate comprising a 1,4-linked galacturonic acid (GalA) and methyl galacturonate (MeGalA) residues backbone linked to branched heteropolymers of alternating oligomers of α -1,2 linked rhamnose and α -1,4-linked GalA residues, the rhamnose residues carrying a primary branching of oligomers of 1,4- β -D-galactose residues, 1,5- α -L-arabinose residues, or a combination of 1,4- β -D-galactose and 1,5- α -L-arabinose residues, and wherein the 1,4-linked galacturonic acid and methyl galacturonate residues backbone represents between 55 to 85 molar percent of the total carbohydrate molar content, the branched heteropolymer of alternating α -1,2 linked rhamnose and α -1,4-linked GalA residues represents between 1 and 6 molar percent of the total carbohydrate molar content, the oligomer 1,4- β -D-galactose of the primary branching represents between 6 to 15 molar percent of the total carbohydrate molar content and the oligomer 1,5- α -L-arabinose of the primary branching represents between 2 to 8 molar percent of the total carbohydrate molar content, as characterized by gas chromatography/mass spectrometry, and wherein the galactoarabino-rhamnogalacturonate has an average molecular weight ranging from 20 kDa to 70 kDa; and b. a therapeutically effective amount of an antibody, wherein the antibody is an anti OX40/OX40L, anti-CTLA-4, anti-PD-1, anti PD-L1, anti PD-L2, anti 4-1BB/4-1BBL, anti- CD27, anti- CD70 or a combination of any of the foregoing. a. a therapeutically effective amount of a galactoarabino-rhamnogalacturonate comprising a 1,4-linked galacturonic acid (GalA) and methyl galacturonate (MeGalA) residues backbone linked to branched heteropolymers of alternating oligomers of α -1,2 linked rhamnose and α -1,4-linked GalA residues, the rhamnose residues carrying a primary branching of oligomers of 1,4- β -D-galactose residues, 1,5- α -L-arabinose residues, or a combination of 1,4- β -D-galactose and 1,5- α -L-arabinose residues, and wherein the 1,4-linked galacturonic acid and methyl galacturonate residues backbone represents between 55 to 85 molar percent of the total carbohydrate molar content, the branched heteropolymer of alternating α -1,2 linked rhamnose and α -1,4-linked GalA residues represents between 1 and 6 molar percent of the total carbohydrate molar content, the oligomer 1,4- β -D-galactose of the primary branching represents between 6 to 15 molar percent of the total carbohydrate molar content and the oligomer 1,5- α -L-arabinose of the primary branching represents between 2 to 8 molar percent of the total carbohydrate molar content, as characterized by gas chromatography/mass spectrometry, and wherein the galactoarabino-rhamnogalacturonate has an average molecular weight ranging from 20 kDa to 70 kDa; and b. a therapeutically effective amount of an antibody, wherein the antibody is an anti OX40/OX40L, anti-CTLA-4, anti-PD-1, anti PD-L1, anti PD-L2, anti 4-1BB/4-1BBL, anti- CD27, anti- CD70 or a combination of any of the foregoing.