CpG
oligodeoxynucleotides (
CpG ODN) have been shown to have potent adjuvant activity for a wide range of
antigens. The purpose of this study was to determine the potential benefit of using
liposomes as a delivery vehicle to enhance the adjuvant activity of
CpG ODN with
Leishmania major stress-inducible protein 1 (LmSTI1)
antigen in induction of the Th1 response in a murine model of
leishmaniasis. BALB/c mice were immunized subcutaneously three times in 3-week intervals with liposomal recombinant LmSTI1 (Lip-rLmSTI1), rLmSTI1 coencapsulated with
CpG ODN in a
liposome (Lip-rLmSTI1-CpG ODN), rLmSTI1 plus
CpG ODN in
phosphate-buffered saline (PBS), rLmSTI1 plus non-
CpG ODN in PBS, rLmSTI1 in PBS, empty
liposome, or PBS. The intensity of
infection induced by L. major promastigote challenge was measured by footpad swelling. A significant (P < 0.001) inhibition of
infection in mice immunized with Lip-rLmSTI1-CpG ODN was shown compared to the other groups, and no parasite was detected in the spleens of this group 14 weeks after challenge. The highest
immunoglobulin G2a (
IgG2a) titer and the highest
IgG2a/
IgG1 ratio were also shown in the sera of mice immunized with Lip-rLmSTI1-CpG ODN before and 14 weeks after challenge. The results indicated the superiority of
CpG ODN in its liposomal form over its soluble form to induce the Th1 response when used in association with rLmSTI1
antigen. It seems that using a
liposome delivery system carrying
CpG ODN as an adjuvant coencapsulated with Leishmania
antigen plays an important role in
vaccine development strategies against
leishmaniasis.