Glycosphingolipids (GSLs) from Sphingomonas paucimobilis Increase the Efficacy of Liposome-Based Nanovaccine against Acinetobacter baumannii-Associated Pneumonia in Immunocompetent and Immunocompromised Mice

Due to the high propensity of drug resistance in Acinetobacter baumannii, the number of currently available therapeutic drugs has become very limited. Thus, it becomes incredibly important to prepare an effective vaccine formulation capable of eliciting an effective immune response against A. baumannii. In this study, we prepared a liposomal vaccine formulation bearing glycosphingolipids (GSLs) from Sphingomonas paucimobilis and loaded with the whole cell antigen (WCAgs-GSLs-liposomes) of A. baumannii. The immune-stimulating potential and prophylactic efficacy of WCAgs-GSLs-liposomes were compared with those of WCAgs-liposomes (without GSLs) or free WCAgs in both immunocompetent and immunodeficient mice. The efficacy of vaccine formulations was determined by analyzing antibody titer, cytokine levels, and survival studies in the immunized mice. The findings revealed that vaccination with WCAgs-GSLs-liposomes stimulated a greater secretion of antibodies and cytokines, higher lymphocyte proliferation, and increased expression of the co-stimulatory molecules. Anti-sera from WCAgs-GSLs-liposomes-immunized mice remarkably reduced the biofilm formation by A. baumannii. Most importantly, WCAgs-GSLs-liposomes-vaccinated mice demonstrated a higher defiance against the pathogen, as compared to the immunizations with WCAgs-liposomes (without GSLs) or free WCAgs. Immunocompetent mice immunized with WCAgs-GSLs-liposomes showed a 100% survival rate, while those immunized with WCAgs-liposomes exhibited a 60% survival rate. The protective effect of WCAgs-GSLs-liposomes was also found to be higher in immunocompromised mice, as the immunized mice showed a 50% survival rate, which was greater than the 20% survival rate of those immunized with WCAgs-liposomes. The survival data was also supported by the findings of bacterial load and histological analysis that substantiated the greatest prophylactic potential of the WCAgs-GSLs-liposomes. These findings recommend that WCAgs-GSLs-liposomes may be reckoned as a prospective vaccine to protect the persons against A. baumannii infection.