The vector-borne protozoan Leishmania infantum chagasi causes minimal inflammation after inoculation into skin but disseminates to cause fatal visceral leishmaniasis. To define the inflammatory response at the parasite inoculation site, we introduced metacyclic L. infantum chagasi promastigotes intradermally into BALB/c mouse ears and studied inflammatory cells over 7 days. Ly6G؉ neutrophils rapidly infiltrated the dermis, peaking after 6 to 24 h. Macrophages and NK cells next infiltrated the dermis, and NK followed by B cells expanded in draining lymph nodes. Parasite-containing phagocytes were tracked with fluorescent mCherry-labeled L. infantum chagasi. Ly6G؉ neutrophils contained the greatest proportion of intracellular parasites 6 to 24 h after inoculation, whereas dermal macrophages harbored the majority of intracellular parasites after 2 to 7 days. These observations were validated microscopically. Low doses of antibody transiently depleted mice of neutrophils, leaving other cells intact. Combined results of in vivo imaging, flow cytometry, and quantitative PCR showed that neutrophil depletion slowed the clearance of extracellular (luciferase-positive) promastigotes during the first 24 h after inoculation yet decreased the numbers of leukocytes containing intracellular (mCherry-positive) parasites. From 3 days onward, total L. infantum chagasi-containing dermal leukocytes and total L. infantum chagasi parasites in draining lymph nodes were similar in both groups. Nonetheless, a second wave of L. infantum chagasi-containing neutrophils occurred 7 days after parasite inoculation into neutrophildepleted mice, corresponding to the time of neutrophil recovery. Thus, neutrophils were recruited to the dermis even late after inoculation, and L. infantum chagasi trafficked through neutrophils in both neutrophil-depleted and control mice, albeit with different kinetics. Recruitment of neutrophils and transient parasite residence in neutrophils may play a role in nonulcerative forms of leishmaniasis.Parasites belonging to the genus Leishmania cause a spectrum of human diseases, the most deadly of which is visceral leishmaniasis. Leishmania infantum chagasi is one of the two most common etiologic agents of visceral leishmaniasis in humans. During natural infection, a bolus of metacyclic promastigotes is delivered into a hemorrhagic dermal lesion formed by a feeding female phlebotomine sand fly (5). Parasites quickly encounter soluble and cellular microbicidal immune elements. Rather than succumb, many are taken up by phagocytic host cells, where they transform to intracellular amastigotes, a form that can multiply and survive in phagolysosomes (9, 48).Although the majority of host cells harboring Leishmania sp. amastigotes are macrophages, intracellular amastigotes have been observed in other mammalian cell types as well, including dendritic cells (DCs), fibroblasts, and neutrophils (6,21,28,33). Recent studies suggest that neutrophils can promote the early establishment of intradermal infection with Leishmania major...

Increasing the long-term survival of memory T cells after immunization is key to a successful vaccine. In the past, the generation of large numbers of memory T cells in vivo has been difficult because Ag-stimulated T cells are susceptible to activation-induced cell death. Previously, we reported that OX40 engagement resulted in a 60-fold increase in the number of Ag-specific CD4+ memory T cells that persisted 60 days postimmunization. In this report, we used the D011.10 adoptive transfer model to examine the kinetics of Ag-specific T cell entry into the peripheral blood, the optimal route of administration of Ag and αOX40, and the Ag-specific Ab response after immunization with soluble OVA and αOX40. Finally, we compared the adjuvant properties of αOX40 to those of αCTLA-4. Engagement of OX-40 in vivo was most effective when the Ag was administered s.c. Time course studies revealed that it was crucial for αOX40 to be delivered within 24–48 h after Ag exposure. Examination of anti-OVA Ab titers revealed a 10-fold increase in mice that received αOX40 compared with mice that received OVA alone. Both αOX40 and αCTLA-4 increased the percentage of OVA-specific CD4+ T cells early after immunization (day 4), but αOX40-treated mice had much higher percentages of OVA-specific memory CD4+ T cells from days 11 to 29. These studies demonstrate that OX40 engagement early after immunization with soluble Ag enhances long-term T cell and humoral immunity in a manner distinct from that provided by blocking CTLA-4.

The tumor microenvironment of squamous cell carcinoma of the head and neck (SCCHN) has been shown to be immune suppressive. Therefore, strategies aimed at overcoming this issue could have a positive therapeutic impact. Hence, we investigated the expression of the known immune-modulatory proteins OX40, programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) in SCCHN on different T-cell subsets of tumor-infiltrating lymphocytes (TIL) to ascertain whether these proteins could potentially be targeted alone or in combination for future clinical trials. T cells from peripheral blood (PBL) and tumor were analyzed for the expression of OX40, PD-1 and CTLA-4 in 29 patients undergoing surgery. These proteins were all expressed significantly higher in T-cell subsets isolated from tumors compared with PBL of the same patient. OX40 expression was significantly greater in the TIL regulatory T-cell (Treg) population relative to conventional CD4 and CD8 TIL or the Treg isolated from PBL. PD-1 expression was increased in all T-cell subsets relative to PBL. CTLA-4 was also increased in all TIL subsets relative to blood, and similar to OX40, its highest level of expression was observed in the Treg TIL. The highest frequency of PD-1, CTLA-4 and OX40 triple-positive cells were found in the Treg population isolated from the tumor. We analyzed both human papilloma virus-positive and -negative patients and found similar levels and expression patterns of these two patient populations for all three proteins. These data suggest that there may be therapeutic advantages of targeting these pathways independently or in combination for patients with this disease.

Tumor necrosis factor receptor-associated factor 2 (TRAF2), an adapter protein that associates with the cytoplasmic tail of OX40, may play a critical role in OX40-mediated signal transduction. To investigate the in vivo role of TRAF2 in OX40-mediated generation of Ag-specific memory T cells, we bred OVA-specific TCR transgenic mice to TRAF2 dominant-negative (TRAF2 DN) mice. Following Ag stimulation and OX40 engagement of TRAF2 DN T cells in vivo, the number of long-lived OVA-specific T cells and effector T cell function was dramatically reduced when compared with wild-type T cells. We also demonstrate that CTLA-4 is down-regulated following OX40 engagement in vivo and the OX40-specific TRAF2 DN defect was partially overcome by CTLA-4 blockade in vivo. The data provide evidence that TRAF2 is linked to OX40-mediated memory T cell expansion and survival, and point to the down-regulation of CTLA-4 as a possible control element to enhance early T cell expansion through OX40 signaling.