1. A composition comprising a compound of formula I:! ! where: R1 is —H or —OH, R2 is —H or —OH, x is an integer from 18 to 26, and n is an integer from 10 to 15.! 2. The composition according to claim 1, in which x = 23.! 3. The composition according to claim 1, in which x = 21.! 4. The composition according to any one of claims 1 to 3, in which n = 13.! 5. The composition according to claim 1, additionally containing antigen. ! 6. The composition according to claim 1 in combination with an antigen, designed to enhance the immune response to the antigen in a subject, and the immune response to the antigen in the subject increases relative to the immune response to the antigen in the control. ! 7. The composition according to claim 1 in combination with an antigen, designed to enhance the immune response to an antigen in a subject, the antigen and composition according to claim 1 are administered intramuscularly, and the immune response to the antigen in the subject increases relative to the immune response to the antigen in the control. ! 8. The composition according to claim 1 in combination with an antigen for use according to claim 6 or 7, wherein the subject's immune response increases by at least 50% relative to the control. ! 9. The composition according to claim 1 in combination with an antigen for use according to claim 6 or 7, wherein the subject's immune response increases by at least 100% relative to the control. ! 10. The composition according to claim 1 in combination with an antigen for use according to claim 6 or 7, wherein the subject's immune response increases by at least 1000% relative to the control. ! 11. The composition according to claim 1 in combination with an antigen for use according to claim 6 or 7, wherein the antigen and composition according to claim 1 are administered simultaneously. !12. The composition according to claim 1 in combination with an antigen for use according to any one of claims 6-11, wherein the composition is adminis
