Immune protection against Trypanosoma cruzi induced by TcVac4 in a canine model.

Chagas disease, caused by Trypanosoma cruzi, is endemic in southern parts of the American continent. Herein, we have tested the protective efficacy of a DNA-prime/T. rangeli-boost (TcVac4) vaccine in a dog (Canis familiaris) model. Dogs were immunized with two-doses of DNA vaccine (pcDNA3.1 encoding TcG1, TcG2, and TcG4 antigens plus IL-12- and GM-CSF-encoding plasmids) followed by two doses of glutaraldehyde-inactivated T. rangeli epimastigotes (TrIE); and challenged with highly pathogenic T. cruzi (SylvioX10/4) isolate. Dogs given TrIE or empty pcDNA3.1 were used as controls. We monitored post-vaccination and post-challenge infection antibody response by an ELISA, parasitemia by blood analysis and xenodiagnosis, and heart function by electrocardiography. Post-mortem anatomic and pathologic evaluation of the heart was conducted. TcVac4 induced a strong IgG response (IgG2>IgG1) that was significantly expanded post-infection, and moved to a nearly balanced IgG2/IgG1 response in chronic phase. In comparison, dogs given TrIE or empty plasmid DNA only developed high IgG titers with IgG2 predominance in response to T. cruzi infection. Blood parasitemia, tissue parasite foci, parasite transmission to triatomines, electrocardiographic abnormalities were significantly lower in TcVac4-vaccinated dogs than was observed in dogs given TrIE or empty plasmid DNA only. Macroscopic and microscopic alterations, the hallmarks of chronic Chagas disease, were significantly decreased in the myocardium of TcVac4-vaccinated dogs. We conclude that TcVac4 induced immunity was beneficial in providing resistance to T. cruzi infection, evidenced by control of chronic pathology of the heart and preservation of cardiac function in dogs. Additionally, TcVac4 vaccination decreased the transmission of parasites from vaccinated/infected animals to triatomines.

The thymus is required for the ability of FTY720 to prolong skin allograft survival across different histocompatibility MHC barriers.

The immunosuppressive effect of FTY720 is associated with the reversible sequestration of lymphocytes from the blood and the spleen into secondary lymphoid organs and reduced egress of mature thymocytes from the thymus. This work was designed to dissect the differential effect of FTY720 on CD4 and CD8 T cell-mediated mechanisms of skin graft rejection in the presence (euthymic) or absence (thymectomized) of thymic output. To that end, untreated and FTY720-treated euthymic (Euthy) and thymectomized (ATX) mice received skin allografts across a full, class II or class I major histocompatibility complex (MHC) mismatched (MM) barriers and graft survival was monitored. We demonstrate that a short course of FTY720 treatment significantly augments the survival of full, class I and class II MHC MM skin grafts compared to the nontreated controls. Interestingly, FTY720-treated Euthy recipients showed a significantly prolonged skin allograft survival compared to FTY720-treated ATX mice. These results together show that FTY720 impairs both CD4 and CD8 T cell-mediated mechanisms of rejection and, more importantly, the presence of the thymus is necessary for the ability of FTY720 to modulate skin allograft rejection across different histocompatibility MHC barriers.

Antibody-mediated signaling through PD-1 costimulates T cells and enhances CD28-dependent proliferation.

Programmed death-1 (PD-1, CD279) is a molecule expressed on activated T, B and myeloid cells. The role of the interaction of PD-1 ligands (PD-L1 and PD-L2) with PD-1 receptor and the type of signals (costimulatory or inhibitory) that are delivered is a subject of intense debate. Our study has characterized two monoclonal antibodies (mAb) against murine PD-1, termed clone 1H10 and clone 4F10, that recognized different epitopes from that of anti-PD-1, clone J43. We showed that neither of them inhibited anti-CD3-mediated proliferation, but 1H10 mAb induced direct T cell proliferation in the absence of any other stimulus. Moreover, PD-1 engagement with 1H10 mAb costimulated anti-CD3-mediated proliferation and enhanced anti-CD3/CD28 proliferation on both CD4+ and CD8+ T cells in the low range of anti-CD3 concentrations. Anti-PD-1-mediated proliferation induced with 1H10 mAb was also observed in vivo on CD4+ and CD8+ T cells, when CFSE-labeled splenocytes were adoptively transferred to irradiated syngeneic and allogeneic recipients. Overall, our data indicate that PD-1 might not only deliver negative signals to T cells upon interaction through one of its ligands, PD-L1 as reported, but also could costimulate T cells, suggesting a dual potential functional activity of the extracellular domains of this receptor.