The cellular and biochemical rules of lipid antigen presentation

Tumor Lipids of Pediatric Papillary Renal Cell Carcinoma Stimulate Unconventional T Cells

Papillary renal cell carcinoma (PRCC) is a rare entity in children with no established therapy protocols for advanced diseases. Immunotherapy is emerging as an important therapeutic tool for childhood cancer. Tumor cells can be recognized and killed by conventional and unconventional T cells. Unconventional T cells are able to recognize lipid antigens presented via CD1 molecules independently from major histocompatibility complex, which offers new alternatives for cancer immunotherapies. The nature of those lipids is largely unknown and α-galactosylceramide is currently used as a synthetic model antigen. In this work, we analyzed infiltrating lymphocytes of two pediatric PRCCs using flow cytometry, immunohistochemistry and qRT-PCR. Moreover, we analyzed the CD1d expression within both tumors. Tumor lipids of PRCC samples and three normal kidney samples were fractionated and the recognition of tumor own lipid fractions by unconventional T cells was analyzed in an in vitro assay. We identified infiltrating lymphocytes including γδ T cells and iNKT cells, as well as CD1d expression in both samples. One lipid fraction, containing ceramides and monoacylglycerides amongst others, was able to induce the proliferation of iNKT cells isolated from peripheral blood mononuclear cells (PBMCs) of healthy donors and of one matched PRCC patient. Furthermore, CD1d tetramer stainings revealed that a subset of iNKT cells is able to bind lipids being present in fraction 2 via CD1d. We conclude that PRCCs are infiltrated by conventional and unconventional T cells and express CD1d. Moreover, certain lipids, present in pediatric PRCC, are able to stimulate unconventional T cells. Manipulating these lipids and T cells may open new strategies for therapy of pediatric PRCCs.

Efficacy of targeted liposomes and nanocochleates containing imatinib plus dexketoprofen against fibrosarcoma

The main challenges in treating cancer using chemotherapeutics are insufficient dose at the target site and the development of drug resistance, while higher doses can induce side effects by damaging nontarget tissues. Combinatorial drug therapy may overcome these limitations by permitting lower doses and more specific targeting, thereby mitigating drug resistance and nontarget side effects. Recent reports indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) have anticancer potential and can be used together with conventional chemotherapeutics to improve efficacy and safety. In the present study, imatinib mesylate and dexketoprofen trometamol were selected as model drugs to develop targeted surface-modified liposome and nanocochleate formulations for fibrosarcoma treatment. The physicochemical properties and in vitro efficacy of various formulations were evaluated by measurement of particle size distribution, polydispersity index, zeta potential, encapsulation efficiency, diffusion through Caco-2 cells, and toxicity in culture. Selected formulations were then evaluated in fibrosarcoma-bearing model mice by histopathological observations and tyrosine kinase receptor inhibition assays. The most effective formulation on the fibrosarcoma model was a PEGylated nanocochleate formulation. These findings provide a foundation for developing more effective formulations and chemotherapeutic strategies for the treatment of fibrosarcoma and other types of cancer.

A new marine-derived sulfoglycolipid triggers dendritic cell activation and immune adjuvant response

Dendritic Cells (DCs) recognize infectious non-self molecules and engage the adaptive immune system thereby initiating long lasting, antigen-specific responses. As such, the ability to activate DCs is considered a key tool to enhance the efficacy and quality of vaccination. Here we report a novel immunomodulatory sulfolipid named β-SQDG18 that prototypes a class of natural-derived glycolipids able to prime human DCs by a TLR2/TLR4-independent mechanism and trigger an efficient immune response in vivo. β-SQDG18 induces maturation of DC with the upregulation of MHC II molecules and co-stimulatory proteins (CD83, CD86), as well as pro-inflammatory cytokines (IL-12 and INF-γ). Mice immunized with OVA associated to β-SQDG18 (1:500) produced a titer of anti-OVA Ig comparable to traditional adjuvants. In an experimental model of melanoma, vaccination of C57BL/6 mice with β-SQDG18-adjuvanted hgp10 peptide elicited a protective response with a reduction in tumour growth and increase in survival.

Nonclassical T cells and their antigens in tuberculosis

T cells that recognize nonpeptidic antigens, and thereby are identified as nonclassical, represent important yet poorly characterized effectors of the immune response. They are present in large numbers in circulating blood and tissues and are as abundant as T cells recognizing peptide antigens. Nonclassical T cells exert multiple functions including immunoregulation, tumor control, and protection against infections. They recognize complexes of nonpeptidic antigens such as lipid and glycolipid molecules, vitamin B2 precursors, and phosphorylated metabolites of the mevalonate pathway. Each of these antigens is presented by antigen-presenting molecules other than major histocompatibility complex (MHC), including CD1, MHC class I-related molecule 1 (MR1), and butyrophilin 3A1 (BTN3A1) molecules. Here, we discuss how nonclassical T cells participate in the recognition of mycobacterial antigens and in the mycobacterial-specific immune response.

Lipid antigens in immunity

Lipids are not only a central part of human metabolism but also play diverse and critical roles in the immune system. As such, they can act as ligands of lipid-activated nuclear receptors, control inflammatory signaling through bioactive lipids such as prostaglandins, leukotrienes, lipoxins, resolvins, and protectins, and modulate immunity as intracellular phospholipid- or sphingolipid-derived signaling mediators. In addition, lipids can serve as antigens and regulate immunity through the activation of lipid-reactive T cells, which is the topic of this review. We will provide an overview of the mechanisms of lipid antigen presentation, the biology of lipid-reactive T cells, and their contribution to immunity.

Immune system targeting by biodegradable nanoparticles for cancer vaccines

The concept of therapeutic cancer vaccines is based on the activation of the immune system against tumor cells after the presentation of tumor antigens. Nanoparticles (NPs) have shown great potential as delivery systems for cancer vaccines as they potentiate the co-delivery of tumor-associated antigens and adjuvants to dendritic cells (DCs), insuring effective activation of the immune system against tumor cells. In this review, the immunological mechanisms behind cancer vaccines, including the role of DCs in the stimulation of T lymphocytes and the use of Toll-like receptor (TLR) ligands as adjuvants will be discussed. An overview of each of the three essential components of a therapeutic cancer vaccine - antigen, adjuvant and delivery system - will be provided with special emphasis on the potential of particulate delivery systems for cancer vaccines, in particular those made of biodegradable aliphatic polyesters, such as poly(lactic-co-glycolic acid) (PLGA) and poly-ε-caprolactone (PCL). Some of the factors that can influence NP uptake by DCs, including size, surface charge, surface functionalization and route of administration, will also be considered.

Deciphering the role of CD1e protein in mycobacterial phosphatidyl-myo-inositol mannosides (PIM) processing for presentation by CD1b to T lymphocytes

Lipids are important antigens that induce T cell-mediated specific immune responses. They are presented to T lymphocytes by a specific class of MHC-I like proteins, termed CD1. The majority of the described CD1-presented mycobacterial antigens are presented by the CD1b isoform. We previously demonstrated that the stimulation of CD1b-restricted T cells by the hexamannosylated phosphatidyl-myo-inositol (PIM(6)), a family of mycobacterial antigens, requires a prior partial digestion of the antigen oligomannoside moiety by α-mannosidase and that CD1e is an accessory protein absolutely required for the generation of the lipid immunogenic form. Here, we show that CD1e behaves as a lipid transfer protein influencing lipid immunoediting and membrane transfer of PIM lipids. CD1e selectively assists the α-mannosidase-dependent digestion of PIM(6) species according to their degree of acylation. Moreover, CD1e transfers only diacylated PIM from donor to acceptor liposomes and also from membranes to CD1b. This study provides new insight into the molecular mechanisms by which CD1e contributes to lipid immunoediting and CD1-restricted presentation to T cells.

sPLA2-V inhibits EPCR anticoagulant and antiapoptotic properties by accommodating lysophosphatidylcholine or PAF in the hydrophobic groove

The endothelial protein C receptor (EPCR) plays an important role in cardiovascular disease by binding protein C/activated protein C (APC). EPCR structure contains a hydrophobic groove filled with an unknown phospholipid needed to perform its function. It has not been established whether lipid exchange takes place in EPCR as a regulatory mechanism of its activity. Our objective was to identify this phospholipid and to explore the possibility of lipid exchange as a regulatory mechanism of EPCR activity driven by the endothelially expressed secretory group V phospholipase A(2) (sPLA(2)-V). We identified phosphatidylcholine (PCh) as the major phospholipid bound to human soluble EPCR (sEPCR). PCh in EPCR could be exchanged for lysophosphatidylcholine (lysoPCh) and platelet activating factor (PAF). Remarkably, lysoPCh and PAF impaired the protein C binding ability of sEPCR. Inhibition of sPLA(2)-V, responsible for lysoPCh and PAF generation, improved APC binding to endothelial cells. EPCR-dependent protein C activation and APC antiapoptotic effect were thus significantly enhanced. In contrast, endothelial cell supplementation with sPLA(2)-V inhibited both APC generation and its antiapoptotic effects. We conclude that APC generation and function can be modulated by changes in phospholipid occupancy of its endothelial cell receptor.

High-frequency and adaptive-like dynamics of human CD1 self-reactive T cells

CD1 molecules present lipid antigens to T cells. An intriguing subset of human T cells recognize CD1-expressing cells without deliberately added lipids. Frequency, subset distribution, clonal composition, naïve-to-memory dynamic transition of these CD1 self-reactive T cells remain largely unknown. By screening libraries of T-cell clones, generated from CD4(+) or CD4(-) CD8(-) double negative (DN) T cells sorted from the same donors, and by limiting dilution analysis, we find that the frequency of CD1 self-reactive T cells is unexpectedly high in both T-cell subsets, in the range of 1/10-1/300 circulating T cells. These T cells predominantly recognize CD1a and CD1c and express diverse TCRs. Frequency comparisons of T-cell clones from sorted naïve and memory compartments of umbilical cord and adult blood show that CD1 self-reactive T cells are naïve at birth and undergo an age-dependent increase in the memory compartment, suggesting a naïve/memory adaptive-like population dynamics. CD1 self-reactive clones exhibit mostly Th1 and Th0 functional activities, depending on the subset and on the CD1 isotype restriction. These findings unveil the unanticipated relevance of self-lipid T-cell response in humans and clarify the basic parameters of the lipid-specific T-cell physiology.

Partial and ineffective activation of V gamma 9V delta 2 T cells by Mycobacterium tuberculosis-infected dendritic cells

Gammadelta T cells and dendritic cells (DCs) participate in early phases of immune response against Mycobacterium tuberculosis. We investigated whether a close functional relationship exists between these two cell populations using an in vitro coculture in a human system. Vgamma9Vdelta2 T cells induce full maturation of M. tuberculosis-infected immature DCs, as demonstrated by upregulation of the costimulatory CD80, CD86, CD40, and HLA-DR molecules on infected DCs after 24 h of coculture. Reciprocally, infected DCs induced substantial activation of Vgamma9Vdelta2 T cells upon coculture, which was cell-to-cell contact and TCR dependent, as demonstrated in transwell experiments. However, infected DCs selectively induced proliferative, but not cytokine or cytolytic, responses of Vgamma9Vdelta2 T cells, and this was associated with the expansion of phenotypically immature, central memory-type Vgamma9Vdelta2 T cells. Importantly, expansion of central memory Vgamma9Vdelta2 T cells and reduction of the pool of Vgamma9Vdelta2 T cells with immediate effector functions (effector memory and terminally differentiated cells) were also detected in vivo in the peripheral blood of patients with active tuberculosis, which reversed after antimycobacterial therapy. M. tuberculosis-infected DCs produced many different cytokines, but not IL-15, and addition of IL-15 to cocultures of infected DCs and Vgamma9Vdelta2 T cells caused efficient differentiation of these latter with generation of effector memory and terminally differentiated cells, which were capable of reducing the viability of intracellular M. tuberculosis. Overall, this study provides a further piece of information on the complex relationship between important players of innate immunity during mycobacterial infection.