1). To determine if we could protect mice against an M. tuberculosis infection using CFP exosome in a prime-boost model, mice were

again s.c. vaccinated with BCG, rested for 8 months then followed by a booster vaccination with exosomes or a second vaccination with BCG i.n. Mice were Alisertib given a low-dose aerosol infection with M. tuberculosis H37Rv 6 weeks after the last exosome booster vaccination. Six weeks later, all mice were sacrificed and mycobacterial counts were measured in lungs and spleens. As shown in Figure 8, the mice given only the prime BCG vaccination gave little to no significant protection. In contrast, the mycobacterial load in the BCG/CFP exosome vaccinated mice was significantly reduced both in the lungs and spleens in comparison with nonvaccinated or BCG primed vaccinated mice. Interestingly, mycobacterial numbers were significantly lower in the lungs of mice vaccinated with the high dose (40 see more μg/mouse) CFP exosomes compared to BCG prime/boost vaccinated mice. This same trend was observed in the spleen but the decrease was not statistically different (Fig. 8). Again, vaccination with exosomes isolated from uninfected macrophages gave no protection. There are currently

12 TB vaccine candidates in various phases of clinical trial. These vaccine candidates fall under three broad categories: (i) recombinant BCG or other mycobacteria species, (ii) viral vectors expressing various mycobacterial proteins, and (iii) recombinant mycobacterial proteins in conjugation with robust adjuvants. At present, it remains unclear whether these vaccine candidates will provide the effectiveness required for TB control [6]. However, recent data indicate that the MVA85A does not provide efficacious protection when used as a booster vaccine in HIV-negative Methocarbamol infants previously immunized with BCG [33]. Herein, we hypothesize that exosomes may provide a novel approach for TB vaccine development. Exosomes have a number of advantages including: (i)

stable conformational conditions for the proteins, (ii) effective molecular distribution due to the ability of microvesicles to recirculate in body fluids and reach distal organs, and (iii) a more efficient association of antigen with target cells [10]. The potential for using exosomes as a cell-free vaccine against TB has its roots in previous cancer vaccine studies. Three exosome-based vaccine candidates have already accomplished phase I clinical trials in the late-stage cancer patients, indicating that exosomes are safe in humans. One candidate is currently undergoing a phase II clinical trial for nonsmall cell lung cancer patients. [15-18]. However, these studies were performed using exosomes obtained from autologous cells, a process which would not be feasible for a TB vaccine.