Applying TLR Synergy in Immunotherapy: Implications in Cutaneous Leishmaniasis

Abstract

Therapy of intracellular pathogens can be complicated by drug toxicity, drug resistance and the need for prolonged treatment regimens. One approach which has shown promise is immunotherapy. Leishmaniasis, a vector-borne disease ranked among the six most important tropical infectious diseases by the WHO, has been treated clinically with crude or defined vaccine preparations or cytokines such as IFN-γ and GM-CSF in combination with chemotherapy. We have attempted to develop an improved and defined immunotherapeutic using a mouse model of cutaneous leishmaniasis. We hypothesized that immunotherapy may be improved by using TLR synergy to enhance the parasite-specific immune response. We formulated L110f, a well-established Leishmania poly-protein vaccine candidate, in conjunction with either monophosphoryl lipid A (MPL), a TLR 4 agonist, or CpG, a TLR 9 agonist, or a combination of these and evaluated anti-leishmania immune responses in absence or presence of active disease. Only mice treated with L110f + MPL-CpG were able to induce a strong effective T cell response during disease and subsequently cured lesions and reduced parasite burden when compared to mice treated with L110f and either single adjuvant. Our data help to define a correlate of protection during active infection and indicate TLR synergy to be a potentially valuable tool in treating intracellular infections.

Regulatory Actions of Toll-Like Receptor 2 (TLR2) and TLR4 in Leishmania donovani Infection in the Liver

“…The contrasting effects of TLR2 and TLR4 signaling implied that engaging TLR2 would promote infection, while blockading TLR2 or triggering TLR4 would strengthen resistance and produce antileishmanial activity. These assumptions were tested in WT mice with established infection by injecting Pam3CSK4 (27,(52)(53)(54), anti-TLR2 MAb (36,37), or GLA-SE, a TLR4 agonist (33).…”

Dendritic Cells Interactions with the Immune System – Implications for Vaccine Development

“…Raman et al have demosntrated that achieving strong and effective T cell responses against cutaneous leishmaniasis in mice required the combination of MPLA and CpG along with the antigen. However, the administration of the antigen with each adjuvant separately did not produce an optimal response [80]. In the same way, Zhu et al found that mice immune response upon vaccination against HIV using envelope peptide along with macrophage-activating lipoprotein 2 (MALP2, TLR2/6), poly(I:C), CpG was importantly improved [81].…”

Local Delivery of the Toll-Like Receptor 9 Ligand CpG Downregulates Host Immune and Inflammatory Responses, Ameliorating Established Leishmania (Viannia) panamensis Chronic Infection

“…Previous studies have utilized CpG alone (15) or in combination with other adjuvants or L. major antigen for both treatment and prevention of experimental leishmaniasis (68). However, therapeutic treatment by CpG alone of L. major is controversial, and both healing and the absence of an effect have been reported (14,15); where healing was observed, however, this was accompanied by a Th1 response. In the current study, we employed a high dose of CpG, administered locally after the development of lesions, which induces a regulatory response and effectively ameliorates L. (V.) panamensis infection.…”

“…Generally, treatment of leishmaniasis (vaccine immunotherapy or adjuvant alone) with CpG or other TLR ligands directed the host immune response toward Th1-like (higher levels of IFN-␥) or multifunctional T cell responses, which were associated with healing (14,24,26,27). However, ligation of TLRs can activate or downregulate the immune response; studies indicate that the precise effect can be dose dependent.…”

“…This approach could be especially appropriate for leishmaniasis, as the immune response is directly linked to outcome of infection. Indeed, immunotherapy has been tried in different modalities for several Leishmania species, with various results (8)(9)(10)(11)(12)(13)(14)(15). Understanding the immune response that leads to healing is important for the development of appropriate modulation methods.…”