The subject invention concerns a novel polysaccharide. RR1 is an .alpha.-D-glucan polysaccharide composed of a (1.fwdarw.4) linked back bone and (1.fwdarw.6) linked branches, which has been isolated from a medicinal herb, Tinospora cordifolia. RR1 exhibits unique immune-stimulating properties, is non-cytotoxic, and non-proliferating to normal lymphocytes, as well as tumor cell lines. The subject invention also concerns compositions containing an RR1 compound and methods for modulating an immune response in a subject using RR1 compounds. The present invention also provides methods for the use of an RR1 compound in conjunction with an antigen to stimulate an immune response, the RR1 compound providing an adjuvant-like activity in the generation of a Th1-type immune response to the antigen.