Inflammation-Induced CCR7 Oligomers Form Scaffolds to Integrate Distinct Signaling Pathways for Efficient Cell Migration.

Host defense depends on orchestrated cell migration guided by chemokines that elicit selective but biased signaling pathways to control chemotaxis. Here, we showed that different inflammatory stimuli provoked oligomerization of the chemokine receptor CCR7, enabling human dendritic cells and T cell subpopulations to process guidance cues not only through classical G protein-dependent signaling but also by integrating an oligomer-dependent Src kinase signaling pathway. Efficient CCR7-driven migration depends on a hydrophobic oligomerization interface near the conserved NPXXY motif of G protein-coupled receptors as shown by mutagenesis screen and a CCR7-SNP demonstrating super-oligomer characteristics leading to enhanced Src activity and superior chemotaxis. Furthermore, Src phosphorylates oligomeric CCR7, thereby creating a docking site for SH2-domain-bearing signaling molecules. Finally, we identified CCL21-biased signaling that involved the phosphatase SHP2 to control efficient cell migration. Collectively, our data showed that CCR7 oligomers serve as molecular hubs regulating distinct signaling pathways.

CCR5 deficiency/CCR5Δ32: resistant to HIV infection at the cost of curtailed CD4+ T cell memory responses.

Orchestrated trafficking and activation by pathogen-derived peptides define the ability of CD4+ T helper cells to contribute to an effective adaptive immunity. In this issue of The EMBO Journal, Martín-Leal et al show that the inflammatory chemokine receptor CCR5, well known for its role in cell migration and HIV infection, regulates ceramide synthesis and TCR nanoclustering to promote memory CD4+ T cell activation.

Rapid increase in transferrin receptor recycling promotes adhesion during T cell activation.

BACKGROUND: T cell activation leads to increased expression of the receptor for the iron transporter transferrin (TfR) to provide iron required for the cell differentiation and clonal expansion that takes place during the days after encounter with a cognate antigen. However, T cells mobilise TfR to their surface within minutes after activation, although the reason and mechanism driving this process remain unclear. RESULTS: Here we show that T cells transiently increase endocytic uptake and recycling of TfR upon activation, thereby boosting their capacity to import iron. We demonstrate that increased TfR recycling is powered by a fast endocytic sorting pathway relying on the membrane proteins flotillins, Rab5- and Rab11a-positive endosomes. Our data further reveal that iron import is required for a non-canonical signalling pathway involving the kinases Zap70 and PAK, which controls adhesion of the integrin LFA-1 and eventually leads to conjugation with antigen-presenting cells. CONCLUSIONS: Altogether, our data suggest that T cells boost their iron importing capacity immediately upon activation to promote adhesion to antigen-presenting cells.

Heparin Specifically Interacts with Basic BBXB Motifs of the Chemokine CCL21 to Define CCR7 Signaling.

Chemokines are critically involved in controlling directed leukocyte migration. Spatiotemporal secretion together with local retention processes establish and maintain local chemokine gradients that guide directional cell migration. Extracellular matrix proteins, particularly glycosaminoglycans (GAGs), locally retain chemokines through electrochemical interactions. The two chemokines CCL19 and CCL21 guide CCR7-expressing leukocytes, such as antigen-bearing dendritic cells and T lymphocytes, to draining lymph nodes to initiate adaptive immune responses. CCL21-in contrast to CCL19-is characterized by a unique extended C-terminus composed of highly charged residues to facilitate interactions with GAGs. Notably, both chemokines can trigger common, but also ligand-biased signaling through the same receptor. The underlying molecular mechanism of ligand-biased CCR7 signaling is poorly understood. Using a series of naturally occurring chemokine variants in combination with newly designed site-specific chemokine mutants, we herein assessed CCR7 signaling, as well as GAG interactions. We demonstrate that the charged chemokine C-terminus does not fully confer CCL21-biased CCR7 signaling. Besides the positively charged C-terminus, CCL21 also possesses specific BBXB motifs comprising basic amino acids. We show that CCL21 variants where individual BBXB motifs are mutated retain their capability to trigger G-protein-dependent CCR7 signaling, but lose their ability to interact with heparin. Moreover, we show that heparin specifically interacts with CCL21, but not with CCL19, and thereby competes with ligand-binding to CCR7 and prevents signaling. Hence, we provide evidence that soluble heparin, but not the other GAGs, complexes with CCL21 to define CCR7 signaling in a ligand-dependent manner.

FAT10 localises in dendritic cell aggresome-like induced structures and contributes to their disassembly.

Dendritic cell (DC) aggresome-like induced structures (DALIS) are protein aggregates of polyubiquitylated proteins that form transiently during DC maturation. DALIS scatter randomly throughout the cytosol and serve as antigen storage sites synchronising DC maturation and antigen presentation. Maturation of DCs is accompanied by the induction of the ubiquitin-like modifier FAT10 (also known as UBD), which localises to aggresomes, structures that are similar to DALIS. FAT10 is conjugated to substrate proteins and serves as a signal for their rapid and irreversible degradation by the 26S proteasome similar to, yet independently of ubiquitin, thereby contributing to antigen presentation. Here, we have investigated whether FAT10 is involved in the formation and turnover of DALIS, and whether proteins accumulating in DALIS can be modified through conjunction to FAT10 (FAT10ylated). We found that FAT10 localises to DALIS in maturing DCs and that this localisation occurs independently of its conjugation to substrates. Additionally, we investigated the DALIS turnover in FAT10-deficient and -proficient DCs, and observed FAT10-mediated disassembly of DALIS. Thus, we report further evidence that FAT10 is involved in antigen processing, which may provide a functional rationale as to why FAT10 is selectively induced upon DC maturation.

CCR7 signalosomes are preassembled on tips of lymphocyte microvilli in proximity to LFA-1.

Leukocyte microvilli are elastic actin-rich projections implicated in rapid sensing and penetration across glycocalyx barriers. Microvilli are critical for the capture and arrest of flowing lymphocytes by high endothelial venules, the main lymph node portal vessels. T lymphocyte arrest involves subsecond activation of the integrin LFA-1 by the G-protein-coupled receptor CCR7 and its endothelial-displayed ligands, the chemokines CCL21 and CCL19. The topographical distribution of CCR7 and of LFA-1 in relation to lymphocyte microvilli has never been elucidated. We applied the recently developed microvillar cartography imaging technique to determine the topographical distribution of CCR7 and LFA-1 with respect to microvilli on peripheral blood T lymphocytes. We found that CCR7 is clustered on the tips of T cell microvilli. The vast majority of LFA-1 molecules were found on the cell body, likely assembled in macroclusters, but a subset of LFA-1, 5% of the total, were found scattered within 20 nm from the CCR7 clusters, implicating these LFA-1 molecules as targets for inside-out activation signals transmitted within a fraction of a second by chemokine-bound CCR7. Indeed, RhoA, the key GTPase involved in rapid LFA-1 affinity triggering by CCR7, was also found to be clustered near CCR7. In addition, we observed that the tyrosine kinase JAK2 controls CCR7-mediated LFA-1 affinity triggering and is also highly enriched on tips of microvilli. We propose that tips of lymphocyte microvilli are novel signalosomes for subsecond CCR7-mediated inside-out signaling to neighboring LFA-1 molecules, a critical checkpoint in LFA-1-mediated lymphocyte arrest on high endothelial venules.

CD44 engagement enhances acute myeloid leukemia cell adhesion to the bone marrow microenvironment by increasing VLA-4 avidity.

Adhesive properties of leukemia cells shape the degree of organ infiltration and the extent of leukocytosis. CD44 and the integrin VLA-4, a CD49d/CD29 heterodimer, are important factors of progenitor cell adhesion in bone marrow (BM). Here, we report their cooperation in acute myeloid leukemia (AML) by a novel non-classical CD44-mediated way of inside-out VLA-4 activation. In primary AML BM samples from patients and the OCI-AML3 cell line, CD44 engagement by hyaluronan induced inside-out activation of VLA-4 resulting in enhanced leukemia cell adhesion on VCAM-1. This was independent from VLA-4 affinity regulation but based on ligand-induced integrin clustering on the cell surface. CD44-induced VLA-4 activation could be inhibited by the Src family kinase inhibitor PP2 and the multikinase inhibitor midostaurin. In further consequence, the increased adhesion on VCAM-1 allowed AML cells to strongly bind stromal cells. Thereby VLA-4/VCAM-1 interaction promoted activation of Akt, MAPK, NF-kB and mTOR signaling and decreased AML cell apoptosis. Collectively, our investigations provide a mechanistic description of an unusual CD44 function in regulating VLA-4 avidity in AML, supporting AML cell retention in the supportive BM microenvironment.

In Vivo Function of the Lipid Raft Protein Flotillin-1 during CD8+ T Cell-Mediated Host Surveillance.

Flotillin-1 (Flot1) is an evolutionary conserved, ubiquitously expressed lipid raft-associated scaffolding protein. Migration of Flot1-deficient neutrophils is impaired because of a decrease in myosin II-mediated contractility. Flot1 also accumulates in the uropod of polarized T cells, suggesting an analogous role in T cell migration. In this study, we analyzed morphology and migration parameters of murine wild-type and Flot1-/- CD8+ T cells using in vitro assays and intravital two-photon microscopy of lymphoid and nonlymphoid tissues. Flot1-/- CD8+ T cells displayed significant alterations in cell shape and motility parameters in vivo but showed comparable homing to lymphoid organs and intact in vitro migration to chemokines. Furthermore, their clonal expansion and infiltration into nonlymphoid tissues during primary and secondary antiviral immune responses was comparable to wild-type CD8+ T cells. Taken together, Flot1 plays a detectable but unexpectedly minor role for CD8+ T cell behavior under physiological conditions.

A Versatile Toolkit for Semi-Automated Production of Fluorescent Chemokines to Study CCR7 Expression and Functions.

Chemokines guide leukocyte migration in different contexts, including homeostasis, immune surveillance and immunity. The chemokines CCL19 and CCL21 control lymphocyte and dendritic cell migration and homing to lymphoid organs. Thereby they orchestrate adaptive immunity in a chemokine receptor CCR7-dependent manner. Likewise, cancer cells that upregulate CCR7 expression are attracted by these chemokines and metastasize to lymphoid organs. In-depth investigation of CCR7 expression and chemokine-mediated signaling is pivotal to understand their role in health and disease. Appropriate fluorescent probes to track these events are increasingly in demand. Here, we present an approach to cost-effectively produce and fluorescently label CCL19 and CCL21 in a semi-automated process. We established a versatile protocol for the production of recombinant chemokines harboring a small C-terminal S6-tag for efficient and site-specific enzymatic labelling with an inorganic fluorescent dye of choice. We demonstrate that the fluorescently labeled chemokines CCL19-S6Dy649P1 and CCL21-S6Dy649P1 retain their full biological function as assessed by their abilities to mobilize intracellular calcium, to recruit ß-arrestin to engaged receptors and to attract CCR7-expressing leukocytes. Moreover, we show that CCL19-S6Dy649P1 serves as powerful reagent to monitor CCR7 internalization by time-lapse confocal video microscopy and to stain CCR7-positive primary human and mouse T cell sub-populations.

IL-4 receptor engagement in human neutrophils impairs their migration and extracellular trap formation.

BACKGROUND: Type 2 immunity serves to resist parasitic helminths, venoms, and toxins, but the role and regulation of neutrophils during type 2 immune responses are controversial. Helminth models suggested a contribution of neutrophils to type 2 immunity, whereas neutrophils are associated with increased disease severity during type 2 inflammatory disorders, such as asthma. OBJECTIVE: We sought to evaluate the effect of the prototypic type 2 cytokines IL-4 and IL-13 on human neutrophils. METHODS: Human neutrophils from peripheral blood were assessed without or with IL-4 or IL-13 for (1) expression of IL-4 receptor subunits, (2) neutrophil extracellular trap (NET) formation, (3) migration toward CXCL8 in vitro and in humanized mice, and (4) CXCR1, CXCR2, and CXCR4 expression, as well as (5) in nonallergic versus allergic subjects. RESULTS: Human neutrophils expressed both types of IL-4 receptors, and their stimulation through IL-4 or IL-13 diminished their ability to form NETs and migrate toward CXCL8 in vitro. Likewise, in vivo chemotaxis in NOD-scid-Il2rg-/- mice was reduced in IL-4-stimulated human neutrophils compared with control values. These effects were accompanied by downregulation of the CXCL8-binding chemokine receptors CXCR1 and CXCR2 on human neutrophils on IL-4 or IL-13 stimulation in vitro. Ex vivo analysis of neutrophils from allergic patients or exposure of neutrophils from nonallergic subjects to allergic donor serum in vitro impaired their NET formation and migration toward CXCL8, thereby mirroring IL-4/IL-13-stimulated neutrophils. CONCLUSION: IL-4 receptor signaling in human neutrophils affects several neutrophil effector functions, which bears important implications for immunity in type 2 inflammatory disorders.

ZAP70 expression enhances chemokine-driven chronic lymphocytic leukemia cell migration and arrest by valency regulation of integrins.

The ζ-associated protein of 70 kDa (ZAP70) is expressed in the aggressive form of B-cell chronic lymphocytic leukemia (CLL). Moreover, the integrin very late antigen (VLA)-1 is highly expressed on subtypes of CLL that are associated with high proliferation rates in the lymph node context. We herein identify a critical role for ZAP70 in chemokine-mediated, inside-out signaling to integrins in trisomy 12 carrying Ohio State University-CLL cell lines derived from a patient with previously treated CLL. We found that ZAP70-positive CLL cells migrated significantly better toward ligands of the lymph node homing chemokine receptors CCR7 and CXCR4 compared with ZAP70-negative cells. In addition, ZAP70-expressing CLL cells adhered more efficiently to integrin ligands under static conditions. We discovered that ZAP70 expression controls chemokine-driven clustering of the integrins VLA-4 and lymphocyte function-associated antigen-1. More precisely, chemokine stimulation resulted in a ZAP70-dependent integrin valency regulation on CLL cells, whereas high-affinity regulation of integrins was independent of ZAP70. Consequently, ZAP70-expressing CLL cells show increased chemokine-driven arrest on immobilized integrin ligands and on chemokine-presenting endothelial cells under physiologic flow conditions. Hence, we describe a novel mechanism showing how ZAP70 controls chemokine-driven valency regulation of integrins and arrest of CLL cells on endothelial cells, a process that might contribute to CLL disease progression.-Laufer, J. M., Lyck, R., Legler, D. F. ZAP70 expression enhances chemokine-driven chronic lymphocytic leukemia cell migration and arrest by valency regulation of integrins.

Immobilized chemokine fields and soluble chemokine gradients cooperatively shape migration patterns of dendritic cells.

Chemokines orchestrate immune cell trafficking by eliciting either directed or random migration and by activating integrins in order to induce cell adhesion. Analyzing dendritic cell (DC) migration, we showed that these distinct cellular responses depended on the mode of chemokine presentation within tissues. The surface-immobilized form of the chemokine CCL21, the heparan sulfate-anchoring ligand of the CC-chemokine receptor 7 (CCR7), caused random movement of DCs that was confined to the chemokine-presenting surface because it triggered integrin-mediated adhesion. Upon direct contact with CCL21, DCs truncated the anchoring residues of CCL21, thereby releasing it from the solid phase. Soluble CCL21 functionally resembles the second CCR7 ligand, CCL19, which lacks anchoring residues and forms soluble gradients. Both soluble CCR7 ligands triggered chemotactic movement, but not surface adhesion. Adhesive random migration and directional steering cooperate to produce dynamic but spatially restricted locomotion patterns closely resembling the cellular dynamics observed in secondary lymphoid organs.

Engineering of Nanobodies Recognizing the Human Chemokine Receptor CCR7.

The chemokine receptor CCR7 plays a pivotal role in health and disease. In particular, CCR7 controls homing of antigen-bearing dendritic cells and T cells to lymph nodes, where adaptive immune responses are initiated. However, CCR7 also guides T cells to inflamed synovium and thereby contributes to rheumatoid arthritis and promotes cancer cell migration and metastasis formation. Nanobodies have recently emerged as versatile tools to study G-protein-coupled receptor functions and are being tested in diagnostics and therapeutics. In this study, we designed a strategy to engineer novel nanobodies recognizing human CCR7. We generated a nanobody library based on a solved crystal structure of the nanobody Nb80 recognizing the ß2-adrenergic receptor (ß2AR) and by specifically randomizing two segments within complementarity determining region 1 (CDR1) and CDR3 of Nb80 known to interact with ß2AR. We fused the nanobody library to one half of split-YFP in order to identify individual nanobody clones interacting with CCR7 fused to the other half of split-YFP using bimolecular fluorescence complementation. We present three novel nanobodies, termed Nb1, Nb5, and Nb38, that recognize human CCR7 without interfering with G-protein-coupling and downstream signaling. Moreover, we were able to follow CCR7 trafficking upon CCL19 triggering using Nb1, Nb5, and Nb38.

Membrane lipid environment: Potential modulation of chemokine receptor function.

Migration of leukocytes is typically mediated by G protein-coupled receptors (GPCRs) upon activation by specific ligands that range from small peptides, chemokines to a variety of lipidic molecules. The heptahelical receptors are highly dynamic structures and the signaling efficiency largely depends on the discrete contact with the ligand. In addition, several allosteric modulators of receptor activity have been reported, which do not induce migration by themselves. Another important mechanism modulating the activity of GPCRs is their local environment. Not only the membrane lipid composition influences the activity, but also direct binding of lipids, in particular cholesterol, was shown to alter receptor signaling properties. Recent findings indicate that also chemokine receptor activity is modulated by membrane lipids. In this short review we discuss this new paradigm and potential consequences for chemokine-induced migration.

Epithelial chemokine CXCL14 synergizes with CXCL12 via allosteric modulation of CXCR4.

The chemokine receptor, CXC chemokine receptor 4 (CXCR4), is selective for CXC chemokine ligand 12 (CXCL12), is broadly expressed in blood and tissue cells, and is essential during embryogenesis and hematopoiesis. CXCL14 is a homeostatic chemokine with unknown receptor selectivity and preferential expression in peripheral tissues. Here, we demonstrate that CXCL14 synergized with CXCL12 in the induction of chemokine responses in primary human lymphoid cells and cell lines that express CXCR4. Combining subactive concentrations of CXCL12 with 100-300 nM CXCL14 resulted in chemotaxis responses that exceeded maximal responses that were obtained with CXCL12 alone. CXCL14 did not activate CXCR4-expressing cells (i.e., failed to trigger chemotaxis and Ca2+ mobilization, as well as signaling via ERK1/2 and the small GTPase Rac1); however, CXCL14 bound to CXCR4 with high affinity, induced redistribution of cell-surface CXCR4, and enhanced HIV-1 infection by >3-fold. We postulate that CXCL14 is a positive allosteric modulator of CXCR4 that enhances the potency of CXCR4 ligands. Our findings provide new insights that will inform the development of novel therapeutics that target CXCR4 in a range of diseases, including cancer, autoimmunity, and HIV.-Collins, P. J., McCully, M. L., Martínez-Muñoz, L., Santiago, C., Wheeldon, J., Caucheteux, S., Thelen, S., Cecchinato, V., Laufer, J. M., Purvanov, V., Monneau, Y. R., Lortat-Jacob, H., Legler, D. F., Uguccioni, M., Thelen, M., Piguet, V., Mellado, M., Moser, B. Epithelial chemokine CXCL14 synergizes with CXCL12 via allosteric modulation of CXCR4.

A structure-activity relationship linking non-planar PCBs to functional deficits of neural crest cells: new roles for connexins.

Migration of neural crest cells (NCC) is a fundamental developmental process, and test methods to identify interfering toxicants have been developed. By examining cell function endpoints, as in the 'migration-inhibition of NCC (cMINC)' assay, a large number of toxicity mechanisms and protein targets can be covered. However, the key events that lead to the adverse effects of a given chemical or group of related compounds are hard to elucidate. To address this issue, we explored here, whether the establishment of two overlapping structure-activity relationships (SAR)-linking chemical structure on the one hand to a phenotypic test outcome, and on the other hand to a mechanistic endpoint-was useful as strategy to identify relevant toxicity mechanisms. For this purpose, we chose polychlorinated biphenyls (PCB) as a large group of related, but still toxicologically and physicochemically diverse structures. We obtained concentration-dependent data for 26 PCBs in the cMINC assay. Moreover, the test chemicals were evaluated by a new high-content imaging method for their effect on cellular re-distribution of connexin43 and for their capacity to inhibit gap junctions. Non-planar PCBs inhibited NCC migration. The potency (1-10 µM) correlated with the number of ortho-chlorine substituents; non-ortho-chloro (planar) PCBs were non-toxic. The toxicity to NCC partially correlated with gap junction inhibition, while it fully correlated (p < 0.0004) with connexin43 cellular re-distribution. Thus, our double-SAR strategy revealed a mechanistic step tightly linked to NCC toxicity of PCBs. Connexin43 patterns in NCC may be explored as a new endpoint relevant to developmental toxicity screening.

Fluorescently Tagged CCL19 and CCL21 to Monitor CCR7 and ACKR4 Functions.

Chemokines are essential guidance cues orchestrating cell migration in health and disease. Cognate chemokine receptors sense chemokine gradients over short distances to coordinate directional cell locomotion. The chemokines CCL19 and CCL21 are essential for recruiting CCR7-expressing dendritic cells bearing pathogen-derived antigens and lymphocytes to lymph nodes, where the two cell types meet to launch an adaptive immune response against the invading pathogen. CCR7-expressing cancer cells are also recruited by CCL19 and CCL21 to metastasize in lymphoid organs. In contrast, atypical chemokine receptors (ACKRs) do not transmit signals required for cell locomotion but scavenge chemokines. ACKR4 is crucial for internalizing and degrading CCL19 and CCL21 to establish local gradients, which are sensed by CCR7-expressing cells. Here, we describe the production of fluorescently tagged chemokines by fusing CCL19 and CCL21 to monomeric red fluorescent protein (mRFP). We show that purified CCL19-mRFP and CCL21-mRFP are versatile and powerful tools to study CCR7 and ACKR4 functions, such as receptor trafficking and chemokine scavenging, in a spatiotemporal fashion. We demonstrate that fluorescently tagged CCL19 and CCL21 permit the visualization and quantification of chemokine gradients in real time, while CCR7-expressing leukocytes and cancer cells sense the guidance cues and migrate along the chemokine gradients.

Modulation of Chemokine Receptor Function by Cholesterol: New Prospects for Pharmacological Intervention.

Chemokine receptors are seven transmembrane-domain receptors belonging to class A of G-protein-coupled receptors (GPCRs). The receptors together with their chemokine ligands constitute the chemokine system, which is essential for directing cell migration and plays a crucial role in a variety of physiologic and pathologic processes. Given the importance of orchestrating cell migration, it is vital that chemokine receptor signaling is tightly regulated to ensure appropriate responses. Recent studies highlight a key role for cholesterol in modulating chemokine receptor activities. The steroid influences the spatial organization of GPCRs within the membrane bilayer, and consequently can tune chemokine receptor signaling. The effects of cholesterol on the organization and function of chemokine receptors and GPCRs in general include direct and indirect effects (Fig. 1). Here, we review how cholesterol and some key metabolites modulate functions of the chemokine system in multiple ways. We emphasize the role of cholesterol in chemokine receptor oligomerization, thereby promoting the formation of a signaling hub enabling integration of distinct signaling pathways at the receptor-membrane interface. Moreover, we discuss the role of cholesterol in stabilizing particular receptor conformations and its consequence for chemokine binding. Finally, we highlight how cholesterol accumulation, its deprivation, or cholesterol metabolites contribute to modulating cell orchestration during inflammation, induction of an adaptive immune response, as well as to dampening an anti-tumor immune response.

Regulation of Sec16 levels and dynamics links proliferation and secretion.

We currently lack a broader mechanistic understanding of the integration of the early secretory pathway with other homeostatic processes such as cell growth. Here, we explore the possibility that Sec16A, a major constituent of endoplasmic reticulum exit sites (ERES), acts as an integrator of growth factor signaling. Surprisingly, we find that Sec16A is a short-lived protein that is regulated by growth factors in a manner dependent on Egr family transcription factors. We hypothesize that Sec16A acts as a central node in a coherent feed-forward loop that detects persistent growth factor stimuli to increase ERES number. Consistent with this notion, Sec16A is also regulated by short-term growth factor treatment that leads to increased turnover of Sec16A at ERES. Finally, we demonstrate that Sec16A depletion reduces proliferation, whereas its overexpression increases proliferation. Together with our finding that growth factors regulate Sec16A levels and its dynamics on ERES, we propose that this protein acts as an integrator linking growth factor signaling and secretion. This provides a mechanistic basis for the previously proposed link between secretion and proliferation.

The STEAP1(262-270) peptide encapsulated into PLGA microspheres elicits strong cytotoxic T cell immunity in HLA-A*0201 transgenic mice--A new approach to immunotherapy against prostate carcinoma.

BACKGROUND: PLGA microsphere-based vaccination has been proven to be effective in immunotherapy of syngeneic model tumors in mice. The critical step for the translation to humans is the identification of immunogenic tumor antigens and potent vaccine formulations to overcome immune tolerance. METHODS: HLA-A*0201 transgenic mice were immunized with eight different human prostate cancer peptide antigens co-encapsulated with TLR ligands into PLGA microspheres and analyzed for antigen-specific and functional cytotoxic T lymphocyte responses. RESULTS: Only vaccination with STEAP1(262-270) peptide encapsulated in PLGA MS could effectively crossprime CTLs in vivo. These CTLs recognized STEAP1(262-270) /HLA-A*0201 complexes on human dendritic cells and prostate cancer cell lines and specifically lysed target cells in vivo. Vaccination with PLGA microspheres was much more potent than with incomplete Freund's adjuvant. CONCLUSIONS: Our data suggests that there exist great differences in the immunogenicity of human PCa peptide antigens despite comparable MHC class I binding characteristics. Immunogenic STEAP1(262-270) peptide encapsulated into PLGA microspheres however was able to induce vigorous and functional antigen-specific CTLs and therefore is a promising novel approach for immunotherapy against advanced stage prostate cancer.