The muramyl dipeptide analog GMTP-N-DPG preferentially induces cellular immunity to soluble antigens

GMTP-N-DPG (N-acetylglucosaminyl-N-acetylmuramyl-L-alanyl-D-isoglutamyl- L-alanyl-dipalmitoylpropylamide) is a lipophilic derivative of the immunologically active compound MDP and has adjuvant properties. GMTP-N-DPG was compared with other adjuvants in model vaccine systems using ovalbumin (OVA) and a synthetic peptide derived from pp89 of murine cytomegalovirus as antigens. When serum from C57/Bl mice immunized with OVA was tested for the presence of anti-OVA antibody, samples from mice immunized with OVA plus GMTP-N-DPG had ELISA optical density (O.D.) readings twice as high as those from mice immunized with antigen alone. In contrast, samples from mice immunized with the liposomal monophosphoryl lipid A (MPL) formulation exhibited ELISA O.D. readings tenfold higher than samples from mice immunized with antigen alone. Relative levels of specific antibody in serum samples from mice immunized with OVA plus the saponin adjuvant QS-21 were equal to the GMTP-N-DPG samples. When spleen cells from immunized mice were tested for their proliferative response to OVA, we found that liposomal MPL was again the optimal adjuvant, whereas the proliferative responses of cells from mice immunized with GMTP-N-DPG or QS-21 were no better than cells from mice immunized with OVA alone. In contrast to the relatively low antibody and proliferation levels, spleen cells from mice immunized with GMTP-N-DPG and OVA demonstrated the highest level of anti-OVA CTL activity. Spleen cells from mice immunized with the pp89 peptide plus GMTP-N-DPG also exhibited CTL activity. Using antibody and complement mediated cytotoxicity it was determined that the CTL were CD8+. Based on these results, we believe that GMTP-N-DPG may be an excellent candidate adjuvant in vaccines for diseases in which a strong cell-mediated response is desired.