As seen in Trial #1, the vaccine improved the clinical symptoms of CVL dogs, whereas untreated dogs did not show improvement (Fig. 2). It is intriguing that the effectiveness of the vaccine depended on disease severity at the time of inclusion in the study. Severely sick dogs did not respond to the vaccine either clinically or immunologically (Fig. 2 and Fig. 3). The immunological hypo-responsiveness of the dogs may be due to an antigen-specific immunosuppressive status in severe CVL. It is accepted for dogs as well as for other mammalian hosts that a Th1 response is responsible for protection [34]. Production of Th1 cytokines such as IFN-γ, TNF, and IL-2 is associated

CP 690550 with protection against CVL [35] and [36]. For this reason we stimulated whole blood from the Study #2 dogs with antigen and attempted to measure IFN-γ production by ELISA. Unfortunately, the assay failed, and we were unable to detect IFN-γ production

with even con A stimulation on many samples. This was likely a technical issue because in a previous study the vaccine induced cell-mediated immune responses in dogs [26]. The disease severity-related hypo-responsiveness of these dogs to the vaccine may be related to an IL-10 down-regulation of the Th1 response. Because IL-10 levels increase in the spleen as CVL progresses [37], some dogs with advanced disease may be rendered less responsive to such an extent that the immune system Romidepsin is refractory to the Leish-111f + MPL-SE vaccine. Other strategies, such as giving a vaccine along with anti-IL-10 antibody, should be considered for immunotherapy of dogs with Cediranib (AZD2171) advanced CVL. The use of adjuvant alone also improved clinical outcomes in Study #2, and the efficacy was comparable to the vaccine (Fig. 2). Unlike with the Vaccine group, the single Adjuvant dog with a Day 0 CS ≥8 (whose CS changed by −2 vs. 0

for Vaccine) showed clinical improvement (Fig. 2) even though this dog exhibited no increased antibody titer to any of the antigens tested (Fig. 3A and data not shown). The clinical improvements observed in the Adjuvant group might be due to the immunostimulatory activity of MPL as a TLR4 ligand that directly activates cells within innate immune response pathways and, in conjunction with antigens present due to the existing parasite burden, may stimulate an effective anti-parasite, adaptive immune response. Such responses have previously been observed in immunotherapy settings; for example, in some cases the TLR ligands CpG oligonucleotides and imiquimod do not require exogenous antigens to improve clinical outcomes of leishmaniasis or to reduce parasite burdens [38], [39] and [40]. Similar results have been obtained in our human clinical trials of the Leish-111f + MPL-SE vaccine: Injection of adjuvant without antigen accelerated the cure of CL by chemotherapy (Piazza F et al.