Induction of protection in mice against a respiratory challenge by a vaccine formulated with the Chlamydia major outer membrane protein adjuvanted with IC31®

IC31®, a novel adjuvant, has been shown to be effective by increasing the levels of IFN-γ in animal models when delivered with several antigens. Here, we tested the ability of IC31®, to enhance the protective ability of the Chlamydia trachomatis native major outer membrane protein (nMOMP). BALB/c mice were immunized by the intramuscular (i.m.) and subcutaneous (s.c.) routes with nMOMP + IC31®. Another group of animals was immunized with nMOMP + Alum and as a negative control mice were immunized with ovalbumin (Ova) + IC31®. Animals immunized with nMOMP + IC31® developed high Chlamydia-specific IgG titers. The serum levels of IgG1 were higher than those of the IgG2a. T cells, from the spleens of mice immunized with IC31®-adjuvanted nMOMP demonstrated a strong lymphoproliferative reaction to Chlamydia elementary bodies (EB) compared with the groups immunized with nMOMP + Alum or Ova + IC31®. A similar comparison between these groups of mice revealed that the levels of IFN-γ in the supernatants from stimulated T-cells were significantly higher in animals immunized with nMOMP + IC31®. Following an intranasal challenge with C. trachomatis, the mice immunized with IC31®-adjuvanted nMOMP showed significant protection. The change in body weight, an indication of the severity of the infection, was significantly less reduced in mice immunized with nMOMP + IC31®. Furthermore, the weight of the lungs, as well as the pulmonary Chlamydia burden, was significantly lower in the animals immunized with nMOMP + IC31® when compared with the groups immunized with nMOMP + Alum or with Ova + IC31®. In conclusion, these results provide the rationale for further preclinical testing of IC31® using other chlamydial antigens, and support the potential evaluation of this adjuvant in human vaccines against Chlamydia.