Andrew J. Currie

The Cationic Antimicrobial Peptide LL-37 Modulates Dendritic Cell Differentiation and Dendritic Cell-Induced T Cell Polarization

Dendritic cells (DC) are instrumental in orchestrating an appropriately polarized Th cell response to pathogens. DC exhibit considerable phenotypic and functional plasticity, influenced by lineage, Ag engagement, and the environment in which they develop and mature. In this study, we identify the human cationic peptide LL-37, found in abundance at sites of inflammation, as a potent modifier of DC differentiation, bridging innate and adaptive immune responses. LL-37-derived DC displayed significantly up-regulated endocytic capacity, modified phagocytic receptor expression and function, up-regulated costimulatory molecule expression, enhanced secretion of Th-1 inducing cytokines, and promoted Th1 responses in vitro. LL-37 may be an attractive therapeutic candidate for manipulating T cell polarization by DC.

Innate immunity in human newborn infants: prematurity means more than immaturity

Neonates, particularly those born prematurely, are exquisitely vulnerable to life-threatening infections. This increased susceptibility to infection is maintained into childhood. Despite the considerable human and economic cost of infection-related neonatal morbidity and mortality, the mechanisms underlying this heightened susceptibility are only partly understood. It is increasingly recognised that innate immune responses are key to the protection against infection early in life, and emerging data suggest that such responses are deficient in the newborn and especially in preterm infants. Here we review the current understanding of the maturation of the innate immune response in human neonates highlighting the clinical relevance and possible avenues for therapeutic intervention.

Tumor eradication after cyclophosphamide depends on concurrent depletion of regulatory T cells: a role for cycling TNFR2-expressing effector-suppressor T cells in limiting effective chemotherapy

Tumor cell death potentially engages with the immune system. However, the efficacy of anti-tumor chemotherapy may be limited by tumor-driven immunosuppression, e.g., through CD25+ regulatory T cells. We addressed this question in a mouse model of mesothelioma by depleting or reconstituting CD25+ regulatory T cells in combination with two different chemotherapeutic drugs. We found that the efficacy of cyclophosphamide to eradicate established tumors, which has been linked to regulatory T cell depletion, was negated by adoptive transfer of CD25+ regulatory T cells. Analysis of post-chemotherapy regulatory T cell populations revealed that cyclophosphamide depleted cycling (Ki-67hi) T cells, including foxp3+ regulatory CD4+ T cells. Ki-67hi CD4+ T cells expressed increased levels of two markers, TNFR2 and ICOS, that have been associated with a maximally suppressive phenotype according to recently published studies. This suggest that cyclophosphamide depletes a population of maximally suppressive regulatory T cells, which may explain its superior anti-tumor efficacy in our model. Our data suggest that regulatory T cell depletion could be used to improve the efficacy of anti-cancer chemotherapy regimens. Indeed, we observed that the drug gemcitabine, which does not deplete cycling regulatory T cells, eradicates established tumors in mice only when CD25+ CD4+ T cells are concurrently depleted. Cyclophosphamide could be used to achieve regulatory T cell depletion in combination with chemotherapy.

Cranking the Immunologic Engine with Chemotherapy: Using Context to Drive Tumor Antigen Cross-Presentation towards Useful Antitumor Immunity

This review shows how tumor antigen cross-presentation is affected by the major therapeutic modalities including chemotherapy, radiotherapy, and surgery. We argue that this process could affect the way that a tumor works as its own cellular vaccine, and that it is differentially modulated by the choice of treatment.

Locally Administered TLR7 Agonists Drive Systemic Antitumor Immune Responses That Are Enhanced by Anti-CD40 Immunotherapy

Topical application of tumors with the TLR7 agonist imiquimod is an effective adjunct treatment for a range of primary dermatological cancers. However, for therapy to be effective against a broad range of solid tumor types, it must promote a strong systemic antitumor response that targets metastases in addition to primary tumor. We therefore investigated the potential of locally delivered imiquimod to stimulate an effective systemic antitumor response in a murine model of malignant mesothelioma (AB1-HA) with primary and distal tumors (dual tumor). Persistent delivery of imiquimod into primary tumor significantly retarded tumor growth in all treated mice compared with vehicle control. This local antitumor immune response required both CD8 T cells and NK cells, but not CD4 T cells, and was reliant on type I IFN induction. In vivo CTL studies and Ly6A/E staining of lymphocytes suggested that local imiquimod treatment had indeed induced a systemic, Ag-specific CD8 response. However, notably this response was not sufficient to retard the growth of an untreated distal tumor. Because local imiquimod treatment did not induce significant CD4 T cell responses, we investigated the efficacy of combining imiquimod with agonistic CD40 Ab (as a surrogate for CD4 T cell help). Combination of locally delivered imiquimod with systemic anti-CD40 immunotherapy not only significantly enhanced the local antitumor response, with 30% complete resolution, but it was also effective at significantly retarding growth of distal tumor. These results demonstrate that antitumor responses induced by locally delivered TLR7 agonists can be harnessed systemically for treating distal tumor.

Cyclophosphamide Chemotherapy Sensitizes Tumor Cells to TRAIL-Dependent CD8 T Cell-Mediated Immune Attack Resulting in Suppression of Tumor Growth

Background Anti-cancer chemotherapy can be simultaneously lymphodepleting and immunostimulatory. Pre-clinical models clearly demonstrate that chemotherapy can synergize with immunotherapy, raising the question how the immune system can be mobilized to generate anti-tumor immune responses in the context of chemotherapy. Methods and Findings We used a mouse model of malignant mesothelioma, AB1-HA, to investigate T cell-dependent tumor resolution after chemotherapy. Established AB1-HA tumors were cured by a single dose of cyclophosphamide in a CD8 T cell- and NK cell-dependent manner. This treatment was associated with an IFN-α/β response and a profound negative impact on the anti-tumor and total CD8 T cell responses. Despite this negative effect, CD8 T cells were essential for curative responses. The important effector molecules used by the anti-tumor immune response included IFN-γ and TRAIL. The importance of TRAIL was supported by experiments in nude mice where the lack of functional T cells could be compensated by agonistic anti-TRAIL-receptor (DR5) antibodies. Conclusion The data support a model in which chemotherapy sensitizes tumor cells for T cell-, and possibly NK cell-, mediated apoptosis. A key role of tumor cell sensitization to immune attack is supported by the role of TRAIL in tumor resolution and explains the paradox of successful CD8 T cell-dependent anti-tumor responses in the absence of CD8 T cell expansion.

Neonatal immune responses to coagulase-negative staphylococci

Purpose of review Coagulase-negative staphylococci have emerged as the most common nosocomial pathogen in neonatal intensive care units worldwide. Our understanding of the interactions between coagulase-negative staphylococci and the immune system is incomplete, especially in the newborn. This review summarizes current knowledge on the human immune response to coagulase-negative staphylococci, with particular emphasis on the neonatal innate immune system. Recent findings There are very limited data on innate immune responses to coagulase-negative staphylococci in neonates. Levels of serum proteins, including transplacental anti-coagulase-negative staphylococci immunoglobulin and complement, correlate with gestational age, and this relative deficiency in preterm infants contributes to their suboptimal opsonization and impaired bacterial killing of coagulase-negative staphylococci. In adults, coagulase-negative staphylococci elicit significant cytokine responses in vitro, which are probably partly mediated by Toll-like receptors, including Toll-like receptor type 2, but these pathways have not been characterized in the high-risk neonatal population. Summary The susceptibility of human preterm neonates to coagulase-negative staphylococci relates partly to the immaturity of the neonatal immune response. Strategies to reduce the burden of coagulase-negative staphylococci infections require a thorough understanding of host–pathogen interactions, particularly the engagement of coagulase-negative staphylococci by the neonatal innate immune system.

Targeting the Effector Site with IFN-αβ-Inducing TLR Ligands Reactivates Tumor-Resident CD8 T Cell Responses to Eradicate Established Solid Tumors

Effective antitumor CD8 T cell responses may be activated by directly targeting the innate immune system within tumors. We investigated this response by injecting a range of TLR agonists into established tumors using a mouse model of malignant mesothelioma stably transduced with the hemagglutinin (HA) gene as a marker Ag (AB1-HA). Persistent delivery of the dsRNA mimetic poly(I:C) into established AB1-HA tumors resulted in complete tumor resolution in 40% of mice, with the remaining mice also showing a significant delay in tumor progression. Experiments in athymic nude mice along with CD8 depletion and IFN-αβ blocking studies revealed that tumor resolution required both CD8 T cells and type I IFN induction, and was associated with local changes in MHC class I expression. Surprisingly, however, tumor resolution was not associated with systemic dissemination or tumor infiltration of effector CD8 T cells. Instead, the antitumor response was critically dependent on the reactivation of tumor-resident CD8 T cell responses. These studies suggest that, once reactivated, pre-existing local CD8 T cell responses are sufficient to resolve established tumors and that in situ type I IFN is a determining factor.

Partial, but not Complete, Tumor-Debulking Surgery Promotes Protective Antitumor Memory when Combined with Chemotherapy and Adjuvant Immunotherapy

Resection alone is rarely curative for advanced tumors, but the outcome generally improves with adjuvant therapy. We have previously shown that a combination of traditional chemotherapy (gemcitabine) and immunotherapy (anti-CD40/FGK-45) without surgery is synergistic and can lead to long-term cure when applied to small tumors. Such cured animals have immunologic memory and are protected from rechallenge. Here we investigate the effectiveness of combination chemotherapy and immunotherapy after partial or complete surgical debulking of large tumors. We found that complete resection followed by combination chemotherapy/immunotherapy led to a high rate of cure (>80%) but failed to induce a long-term, tumor-specific memory. Partial debulking followed by combination therapy elicited the same proportion of cured animals but in contrast to complete resection, a memory response was invoked. We postulate that chemotherapy induced apoptosis of the residual tumor cells following incomplete resection is absolutely required for the induction of long-term immunologic memory.

Alveolar macrophages bind and phagocytose allergen-containing pollen starch granules via C-type lectin and integrin receptors: implications for airway inflammatory disease.

Recent studies suggest that IgE-independent mechanisms of airway inflammation contribute significantly to the pathophysiology of allergic airway inflammatory diseases such as asthma. Such mechanisms may involve direct interactions between inhaled allergens and cells of the respiratory tract such as macrophages, dendritic cells, and epithelial cells. In this study, we investigated receptor-mediated interactions occurring between alveolar macrophages and allergen-containing pollen starch granules (PSG). We report here that PSG are released from a range of grass species and are rapidly bound and phagocytosed by alveolar macrophages. Human monocyte-derived dendritic cells also bound PSG but no internalization was observed. Phagocytosis of PSG was dependent on Mg2+ and Ca2+ and was inhibited by neo-glycoproteins such as galactose-BSA and N-acetylgalactose-BSA. Partial inhibition of phagocytosis was also seen with the Arg-Gly-Asp-Ser (RGDS) motif and with an anti-CD18 mAb (OX42). The combination of both neo-glycoprotein and anti-CD18 achieved the greatest degree of inhibition (>90%). Together, these data suggest a role for both C-type lectins and β2-integrins in the binding and internalization of PSG. The consequences of this interaction included a rapid up-regulation of inducible NO synthase mRNA and subsequent release of NO by alveolar macrophages. Thus, receptor-mediated recognition of inhaled allergenic particles by alveolar macrophages may represent a potential mechanism for modulating the inflammatory response associated with allergic airway diseases such as asthma.