Neutrophil-neutrophil interactions under hydrodynamic shear stress involve L-selectin and PSGL-1. A mechanism that amplifies initial leukocyte accumulation of P-selectin in vitro

Leukocytes attach to and roll on inflamed endothelium and on leukocyte monolayers that form on the endothelial cells. Leukocyte-leukocyte interactions occurring under hydrodynamic shear stress are mediated by binding of L-selectin to unknown sialomucin-like glycoproteins. We show that purified neutrophil PSGL-1, a sialomucin glycoprotein that serves as a ligand for both P- and E-selectin, can also support the attachment and rolling of free flowing neutrophils in vitro. Neutrophil rolling on PSGL-1 was abolished by the anti-L-selectin mAb DREG200 and by the anti-PSGL-1 mAb PL1, indicating that L-selectin can interact directly with PSGL-1. Neutrophil rolling on neutrophil monolayers was also blocked by PL1 (60 +/- 9% SEM inhibition); however, DREG200 blocked more efficiently (93 +/- 7% SEM inhibition), suggesting that other L-selectin ligands may exist on the neutrophil surface. These studies demonstrate that PSGL-1 on the neutrophil surface is a major functional ligand for L-selectin. The avidity of this L-selectin-dependent adhesion event was sufficient to allow individual neutrophils rolling on P-selectin to capture free flowing neutrophils, which progressed to form linear strings and discrete foci of rolling neutrophils. Neutrophil accumulation on P-selectin accelerated with time as a result of neutrophil-assisted capture of free flowing neutrophils. When neutrophil-neutrophil interactions were blocked by DREG200, neutrophils accumulated on P-selectin in a random pattern and at a uniform rate. Thus, leukocyte-assisted capture of flowing leukocytes may play an important role in amplifying the rate of initial leukocyte recruitment at sites of inflammation.

Neutrophil rolling altered by inhibition of L-selectin shedding in vitro

The L-selectin adhesion molecule is involved in guiding leukocytes to sites of inflammation. L-selectin is cleaved by an unusual proteolytic activity at a membrane-proximal site resulting in rapid shedding from the cell surface. Although it has been demonstrated that L-selectin mediates, in part, the early event of leukocyte rolling under hydrodynamic flow, the contribution of shedding to L-selectin function has remained unknown. Here we show that hydroxamic acid-based metalloprotease inhibitors block L-selectin downregulation from the cell surface of stimulated neutrophils, without affecting Mac-1 mobilization or general neutrophil activation, and inhibit cleavage of L-selectin in a cell-free system. Unexpectedly, the hydroxamic acid-based inhibitors reduced neutrophil rolling velocity under hydrodynamic flow, resulting in increased neutrophil accumulation. These results suggest that L-selectin is cleaved in seconds--much faster than previously suspected--during the process of rolling under hydrodynamic flow, and that shedding of L-selectin may contribute significantly to the velocity of leukocyte rolling. L-selectin shedding during rolling interactions may be physiologically important for limiting leukocyte aggregation and accumulation at sites of inflammation.

Pluripotent stem cell-derived NK cells with high-affinity noncleavable CD16a mediate improved antitumor activity

Antibody-dependent cellular cytotoxicity (ADCC) is a key effector mechanism of natural killer (NK) cells that is mediated by therapeutic monoclonal antibodies (mAbs). This process is facilitated by the Fc receptor CD16a on human NK cells. CD16a appears to be the only activating receptor on NK cells that is cleaved by the metalloprotease a disintegrin and metalloproteinase-17 upon stimulation. We previously demonstrated that a point mutation of CD16a prevents this activation-induced surface cleavage. This noncleavable CD16a variant is now further modified to include the high-affinity noncleavable variant of CD16a (hnCD16) and was engineered into human induced pluripotent stem cells (iPSCs) to create a renewable source for human induced pluripotent stem cell-derived NK (hnCD16-iNK) cells. Compared with unmodified iNK cells and peripheral blood-derived NK (PB-NK) cells, hnCD16-iNK cells proved to be highly resistant to activation-induced cleavage of CD16a. We found that hnCD16-iNK cells were functionally mature and exhibited enhanced ADCC against multiple tumor targets. In vivo xenograft studies using a human B-cell lymphoma demonstrated that treatment with hnCD16-iNK cells and anti-CD20 mAb led to significantly improved regression of B-cell lymphoma compared with treatment utilizing anti-CD20 mAb with PB-NK cells or unmodified iNK cells. hnCD16-iNK cells, combined with anti-HER2 mAb, also mediated improved survival in an ovarian cancer xenograft model. Together, these findings show that hnCD16-iNK cells combined with mAbs are highly effective against hematologic malignancies and solid tumors that are typically resistant to NK cell-mediated killing, demonstrating the feasibility of producing a standardized off-the-shelf engineered NK cell therapy with improved ADCC properties to treat malignancies that are otherwise refractory.

Targeting natural killer cells to acute myeloid leukemia in vitro with a CD16 x 33 bispecific killer cell engager and ADAM17 inhibition

PURPOSE

The graft versus leukemia effect by natural killer (NK) cells prevents relapse following hematopoietic stem cell transplantation. We determined whether a novel bispecific killer cell engager (BiKE) signaling through CD16 and targeting CD33 could activate NK cells at high potency against acute myelogenous leukemia (AML) targets.

EXPERIMENTAL DESIGN

We investigated the ability of our fully humanized CD16 × CD33 (CD16 × 33) BiKE to trigger in vitro NK cell activation against HL60 (CD33(+)), RAJI (CD33(-)), and primary AML targets (de novo and refractory) to determine whether treatment with CD16 × 33 BiKE in combination with an ADAM17 inhibitor could prevent CD16 shedding (a novel inhibitory mechanism induced by NK cell activation) and overcome inhibition of class I MHC recognizing inhibitory receptors.

RESULTS

NK cell cytotoxicity and cytokine release were specifically triggered by the CD16 × 33 BiKE when cells were cultured with HL60 targets, CD33(+) de novo and refractory AML targets. Combination treatment with CD16 × 33 BiKE and ADAM17 inhibitor resulted in inhibition of CD16 shedding in NK cells, and enhanced NK cell activation. Treatment of NK cells from double umbilical cord blood transplant (UCBT) recipients with the CD16 × 33 BiKE resulted in activation, especially in those recipients with cytomegalovirus reactivation.

CONCLUSION

CD16 × 33 BiKE can overcome self-inhibitory signals and effectively elicit NK cell effector activity against AML. These in vitro studies highlight the potential of CD16 × 33 BiKE ± ADAM17 inhibition to enhance NK cell activation and specificity against CD33(+) AML, which optimally could be applied in patients with relapsed AML or for adjuvant antileukemic therapy posttransplantation.

Calmodulin regulates L-selectin adhesion molecule expression and function through a protease-dependent mechanism

Expression of the L-selectin adhesion molecule is rapidly down-regulated upon cell activation through proteolysis at a membrane-proximal site. Here we demonstrate that calmodulin, an intracellular calcium regulatory protein, specifically coprecipitates with L-selectin through a direct association with the cytoplasmic domain of L-selectin. Furthermore, calmodulin inhibitors disrupt L-selectin-dependent adhesion by inducing proteolytic release of L-selectin from the cell surface. The effects of the calmodulin inhibitors on L-selectin expression and function can be prevented by cotreatment with a hydroxamic acid-based metalloprotease inhibitor. Our results suggest a novel role for calmodulin in regulating the expression and function of an integral membrane protein through a protease-dependent mechanism. These findings may have broader implications for other cell surface proteins that also undergo regulated proteolysis.

Role of ADAM17 in the ectodomain shedding of TNF-alpha and its receptors by neutrophils and macrophages

TNF-alpha and its receptors TNFRI and TNFRII are cleaved from the surface of leukocytes by a proteolytic process referred to as ectodomain shedding. The role of a disintegrin and metalloproteinase 17 (ADAM17) in this process by the major professional phagocytes neutrophils and macrophages, the primary producers of TNF-alpha during inflammation induction, is based entirely on indirect evidence, and other sheddases have been implicated as well. As Adam17 gene-targeting in mice is lethal, we assessed the protease's relative contribution to TNF-alpha, TNFRI, and TNFRII shedding using radiation chimeric mice with leukocytes lacking functional ADAM17. We report ablated, soluble TNF-alpha, TNFRI, and TNFRII production by neutrophils and macrophages stimulated with various microbial antigens and greatly reduced TNF-alpha levels in vivo following inflammation induction. This is the first simultaneous analysis of TNF-alpha, TNFRI, and TNFRII shedding by neutrophils and macrophages and the first direct evidence that ADAM17 is a primary and nonredundant sheddase.

Shedding of the lymphocyte L-selectin adhesion molecule is inhibited by a hydroxamic acid-based protease inhibitor. Identification with an L-selectin-alkaline phosphatase reporter

Expression of the L-selectin adhesion molecule can be rapidly down-modulated by regulated proteolysis at a membrane-proximal site. The L-selectin secretase has remained undefined, and the secretase activity is resistant to a broad panel of common protease inhibitors. We have developed an L-selectin-alkaline phosphatase reporter, consisting of the ectodomain of human placental alkaline phosphatase fused to the membrane-proximal cleavage, transmembrane, and cytoplasmic domains of L-selectin, to aid in the screening for L-selectin secretase inhibitors. A hydroxamic acid-based metalloprotease inhibitor, KD-IX-73-4, inhibited release of the L-selectin-alkaline phosphatase reporter in a dose-dependent manner. The hydroxamic acid-based peptide was also found to inhibit wild type L-selectin down-regulation from the surfaces of phorbol myristate acetate-activated peripheral blood lymphocytes and phytohemagglutinin-stimulated lymphoblasts. Analysis of the proteolytic cleavage fragments of L-selectin confirmed that KD-IX-73-4 inhibited L-selectin proteolysis. Lymphocyte L-selectin was not down-regulated when co-cultured with formylmethionylleucylphenylalanine-stimulated neutrophils, suggesting that the putative secretase acts in cis with the membrane-bound L-selectin. These results suggest that the L-selectin secretase activity may involve a cell surface, zinc-dependent metalloprotease, although L-selectin shedding is not affected by EDTA and may be related to the recently described activity involved in processing of membrane-bound TNF-alpha.

A Genetically Engineered Primary Human Natural Killer Cell Platform for Cancer Immunotherapy

Enhancing natural killer (NK) cell cytotoxicity by blocking inhibitory signaling could lead to improved NK-based cancer immunotherapy. Thus, we have developed a highly efficient method for editing the genome of human NK cells using CRISPR/Cas9 to knock out inhibitory signaling molecules. Our method efficiently edits up to 90% of primary peripheral blood NK cells. As a proof-of-principle we demonstrate highly efficient knockout of ADAM17 and PDCD1, genes that have a functional impact on NK cells, and demonstrate that these gene-edited NK cells have significantly improved activity, cytokine production, and cancer cell cytotoxicity. Furthermore, we were able to expand cells to clinically relevant numbers, without loss of activity. We also demonstrate that our CRISPR/Cas9 method can be used for efficient knockin of genes by delivering homologous recombination template DNA using recombinant adeno-associated virus serotype 6 (rAAV6). Our platform represents a feasible method for generating engineered primary NK cells as a universal therapeutic for cancer immunotherapy.

Rapid activation-independent shedding of leukocyte L-selectin induced by cross-linking of the surface antigen

L-selectin (also termed LAM-1, Leu-8,TQ-1, gp90MEL-14, peripheral lymph node homing receptor and LECAM-1) is an adhesion protein thought to be important in leukocyte entry into lymphoid tissues and sites of inflammation. We, as well as others, have shown that leukocyte activation by chemotactic factors results in rapid shedding (release) of L-selectin from the cell surface. Here we have used flow cytometry, enzyme-linked immunosorbent assay, and SDS-PAGE/Western blot analysis to determine whether cross-linking of L-selectin in the absence of activation causes shedding. We found that rapid loss of leukocyte L-selectin expression (down-regulation) could be induced by treating cells with a chemical cross-linker [bis (sulfosuccinimidyl) suberate]. L-selectin down-regulation via cross-linking could occur at 4 degrees C and in the absence of detectable cell activation (increased expression of CD11b/18). The loss of L-selectin expression was due to shedding of the molecule from the leukocyte cell surface. Cross-linking of L-selectin with specific monoclonal antibodies also caused loss of surface expression of L-selectin at 37 degrees C. Finally, shed L-selectin was detected in the plasma of healthy adults whose peripheral blood leukocytes demonstrated no obvious signs of activation. Our results suggest that activation-independent shedding of leukocyte L-selectin may occur in vivo and a possible mechanism could involve cross-linking of leukocyte L-selectin. This provides a novel mechanism for rapid regulation of expression of a leukocyte-endothelial cell adhesion receptor.

Regulation of mature ADAM17 by redox agents for L-selectin shedding

L-selectin is constitutively expressed by neutrophils and plays a key role in directing these cells to sites of inflammation. Upon neutrophil activation, L-selectin is rapidly and efficiently down-regulated from the cell surface by ectodomain shedding. We have directly shown that A disintegrin and metalloprotease 17 (ADAM17) is a primary and nonredundant sheddase of L-selection by activated neutrophils in vivo. Following cell activation, intracellular signals lead to the induction of ADAM17's enzymatic activity; however, the target of this inducer mechanism remains unclear. Our study provides evidence of an activation mechanism that involves the extracellular region of the mature form of cell surface ADAM17 and not its intracellular region. We demonstrate that the catalytic activity of purified ADAM17 lacking a prodomain and its intracellular region is diminished under mild reducing conditions by DTT and enhanced by H(2)O(2) oxidation. Moreover, H(2)O(2) reversed ADAM17 inhibition by DTT. The treatment of neutrophils with H(2)O(2) also induced L-selectin shedding in an ADAM17-dependent manner. These findings suggest that thiol-disulfide conversion occurring in the extracellular region of ADAM17 may be involved in its activation. An analysis of ADAM17 revealed that within its disintegrin/cysteine-rich region are two highly conserved, vicinal cysteine sulfhydryl motifs (cysteine-X-X-cysteine), which are well-characterized targets for thiol-disulfide exchange in various other proteins. Using a cell-based ADAM17 reconstitution assay, we demonstrate that the cysteine-X-X-cysteine motifs are critical for L-selectin cleavage. Taken together, our findings suggest that reduction-oxidation modifications of cysteinyl sulfhydryl groups in mature ADAM17 may serve as a mechanism for regulating the shedding of L-selectin following neutrophil stimulation.

Identification of an ADAM17 cleavage region in human CD16 (FcγRIII) and the engineering of a non-cleavable version of the receptor in NK cells

CD16a and CD16b are IgG Fc receptors expressed by human natural killer (NK) cells and neutrophils, respectively. Both CD16 isoforms undergo a rapid down-regulation in expression by ADAM17-mediated proteolytic cleavage upon cell activation by various stimuli. We examined soluble CD16 released from activated NK cells and neutrophils by mass spectrometric analysis, and identified three separate cleavage sites in close proximity at P1/P1′ positions alanine195/valine196, valine196/serine197, and threonine198/isoleucine199, revealing a membrane proximal cleavage region in CD16. Substitution of the serine at position 197 in the middle of the cleavage region for a proline (S197P) effectively blocked CD16a and CD16b cleavage in cell-based assays. We also show that CD16a/S197P was resistant to cleavage when expressed in the human NK cell line NK92 and primary NK cells derived from genetically-engineered human induced pluripotent stem cells. CD16a is a potent activating receptor and despite blocking CD16a shedding, the S197P mutation did not disrupt IgG binding by the receptor or its activation of NK92 cells by antibody-treated tumor cells. Our findings provide further characterization of CD16 cleavage by ADAM17 and they demonstrate that a non-cleavable version of CD16a can be expressed in engineered NK cells.

ADAM17 deficiency by mature neutrophils has differential effects on L-selectin shedding

L-selectin directs neutrophils to sites of inflammation, and upon their activation, surface expression of the receptor is rapidly down-regulated by ectodomain shedding. Tumor necrosis factor-alpha-converting enzyme (TACE, or ADAM17) is a sheddase of L-selectin; however, Adam17 gene targeting (ADAM17(DeltaZn/DeltaZn)) in mice is perinatal lethal and its role in L-selectin shedding by mature neutrophils has not been determined. This was addressed here by using radiation-chimeric mice reconstituted with ADAM17(DeltaZn/DeltaZn) fetal liver cells. ADAM17-deficient neutrophils, monocytes, and lymphocytes failed to shed L-selectin in response to PMA, as did neutrophils infiltrating the inflamed peritoneum. In addition, the absence of functional ADAM17 resulted in significantly increased levels of L-selectin surface expression by peripheral-blood leukocytes, indicating the sheddase also plays a role in the constitutive cleavage of L-selectin. Interestingly, not all manners of L-selectin turnover required ADAM17. Plasma L-selectin levels were similar between ADAM17(DeltaZn/DeltaZn)-chimeric and control mice, as was the shedding of L-selectin by neutrophils undergoing spontaneous apoptosis. The latter process, however, was diminished by a metalloprotease inhibitor, indicating the role of a sheddase other than ADAM17. Together, our data reveal that L-selectin's surface density on neutrophils is regulated by ADAM17, but homeostatic L-selectin cleavage is not.

Lymphocyte function-associated antigen 1 is a receptor for Pasteurella haemolytica leukotoxin in bovine leukocytes

Pasteurella (Mannheimia) haemolytica leukotoxin (Lkt) causes cell type- and species-specific effects in ruminant leukocytes. Recent studies indicate that P. haemolytica Lkt binds to bovine CD18, the common subunit of all beta2 integrins. We designed experiments with the following objectives: to identify which member of the beta2 integrins is a receptor for Lkt; to determine whether Lkt binding to the receptor is target cell (bovine leukocytes) specific; to define the relationships between Lkt binding to the receptor, calcium elevation, and cytolysis; and to determine whether a correlation exists between Lkt receptor expression and the magnitude of target cell cytolysis. We compared Lkt-induced cytolysis in neutrophils from control calves and from calves with bovine leukocyte adhesion deficiency (BLAD), because neutrophils from BLAD-homozygous calves exhibit reduced beta2 integrin expression. The results demonstrate for the first time that Lkt binds to bovine CD11a and CD18 (lymphocyte function-associated antigen 1 [LFA-1]). The binding was abolished by anti-CD11a or anti-CD18 monoclonal antibody (MAb). Lkt-induced calcium elevation in bovine alveolar macrophages (BAMs) was inhibited by anti-CD11a or anti-CD18 MAb (65 to 94% and 37 to 98%, respectively, at 5 and 50 Lkt units per ml; P < 0.05). Lkt-induced cytolysis in neutrophils and BAMs was also inhibited by anti-CD11a or anti-CD18 MAb in a concentration-dependent manner. Lkt bound to porcine LFA-1 but did not induce calcium elevation or cytolysis. In neutrophils from BLAD calves, Lkt-induced cytolysis was decreased by 44% compared to that of neutrophils from control calves (P < 0.05). These results indicate that LFA-1 is a Lkt receptor, Lkt binding to LFA-1 is not target cell specific, Lkt binding to bovine LFA-1 correlates with calcium elevation and cytolysis, and bovine LFA-1 expression correlates with the magnitude of Lkt-induced target cell cytolysis.

Tumor-induced MDSC act via remote control to inhibit L-selectin-dependent adaptive immunity in lymph nodes

Myeloid-derived suppressor cells (MDSC) contribute to an immunosuppressive network that drives cancer escape by disabling T cell adaptive immunity. The prevailing view is that MDSC-mediated immunosuppression is restricted to tissues where MDSC co-mingle with T cells. Here we show that splenic or, unexpectedly, blood-borne MDSC execute far-reaching immune suppression by reducing expression of the L-selectin lymph node (LN) homing receptor on naïve T and B cells. MDSC-induced L-selectin loss occurs through a contact-dependent, post-transcriptional mechanism that is independent of the major L-selectin sheddase, ADAM17, but results in significant elevation of circulating L-selectin in tumor-bearing mice. Even moderate deficits in L-selectin expression disrupt T cell trafficking to distant LN. Furthermore, T cells preconditioned by MDSC have diminished responses to subsequent antigen exposure, which in conjunction with reduced trafficking, severely restricts antigen-driven expansion in widely-dispersed LN. These results establish novel mechanisms for MDSC-mediated immunosuppression that have unanticipated implications for systemic cancer immunity.

DOI:http://dx.doi.org/10.7554/eLife.17375.001

Bovine gamma/delta T cells bind E-selectin via a novel glycoprotein receptor: first characterization of a lymphocyte/E-selectin interaction in an animal model

E-Selectin is an inducible adhesion protein expressed by endothelial cells and recognized by leukocytes during their extravasation from the blood into inflamed tissues. Originally, E-selectin was defined as a myeloid cell-specific adhesion protein, but recent studies have shown it to be recognized by human lymphocytes as well. These lymphocytes represent a memory T cell subset and have been shown to express the HECA-452 carbohydrate epitope (CLA+ lymphocytes). We extend these findings and show that ruminant gamma/delta T cells bind E-selectin as well; and we provide preliminary evidence that this interaction is mediated by a novel glycoprotein receptor on the lymphocyte. Unlike conventional T cells (alpha/beta T cells), gamma/delta T cells from neonatal and mature animals bind E-selectin, suggesting that prior antigen stimulation and differentiation to a memory lymphocyte are not required for this interaction. Neuraminidase treatment of the gamma/delta T cells or addition of ethylenediaminetetraacetic acid (EDTA) to the assay abrogates binding, demonstrating the importance of sialic acid and divalent cations, which is consistent with other E-selectin-mediated adhesion events. However, previously defined E-selectin carbohydrate ligands, such as sialyl Lewis x on neutrophils and the HECA-452 epitope on human memory lymphocytes, are antigenically different than the carbohydrates on ruminant gamma/delta T cells since the mAbs CSLEX and HECA-452 do not recognize these cells. Protease treatment of gamma/delta T cells significantly inhibits their binding to E-selectin; however, previously characterized adhesion glycoproteins, such as L-selectin, CD44, and CD18, are not involved in the adhesive event. An E-selectin affinity column purifies a single glycoprotein of 250 kD (280 kD under reducing conditions) from gamma/delta T cell detergent lysates. Neuraminidase digestion of the 250-kD product as well as EDTA abolishes binding to E-selectin. Finally, E-selectin expression in vivo appears to mediate gamma/delta T cell accumulation. Stimulation of bovine skin with tumor necrosis factor alpha induced an increase in E-selectin expression that was associated with an influx of gamma/delta T cells at the same site.

Role of ADAM17 as a regulatory checkpoint of CD16A in NK cells and as a potential target for cancer immunotherapy

Human NK cell antitumor activities involve Ab-dependent cell-mediated cytotoxicity (ADCC), which is a key mechanism of action for several clinically successful tumor-targeting therapeutic mAbs. Human NK cells exclusively recognize these Abs by the Fcγ receptor CD16A (FcγRIIIA), one of their most potent activating receptors. Unlike other activating receptors on NK cells, CD16A undergoes a rapid down-regulation in expression by a proteolytic process following NK cell activation with various stimuli. In this review, the role of a disintegrin and metalloproteinase-17 (ADAM17) in CD16A cleavage and as a regulatory checkpoint is discussed. Several studies have examined the effects of inhibiting ADAM17 or CD16A cleavage directly during NK cell engagement of Ab-coated tumor cells, which resulted in strengthened Ab tethering, decreased tumor cell detachment, and enhanced CD16A signaling and cytokine production. However, the effects of either manipulation on ADCC have varied between studies, which may be due to dissimilar assays and the contribution of different killing processes by NK cells. Of importance is that NK cells under various circumstances, including in the tumor microenvironment of patients, down-regulate CD16A and this appears to impair their function. Considerable progress has been made in the development of ADAM17 inhibitors, including human mAbs that have advantages of high specificity and increased half-life in vivo. These inhibitors may provide a therapeutic means of increasing ADCC potency and/or antitumor cytokine production by NK cells in an immunosuppressive tumor microenvironment, and if used in combination with tumor-targeting Abs or NK cell-based adoptive immunotherapies may improve their efficacy.

ADAM17 cleaves CD16b (FcγRIIIb) in human neutrophils

CD16b (FcγRIIIb) is exclusively expressed by human neutrophils and binds IgG in immune complexes. Cell surface CD16b undergoes efficient ectodomain shedding upon neutrophil activation and apoptosis. Indeed, soluble CD16b is present at high levels in the plasma of healthy individuals, which appears to be maintained by the daily turnover of apoptotic neutrophils. At this time, the principal protease responsible for CD16b shedding is not known. We show that CD16b plasma levels were significantly decreased in patients administered a selective inhibitor targeting the metalloproteases ADAM10 and ADAM17. Additional analysis with inhibitors selective for ADAM10 or ADAM17 revealed that only inhibition of ADAM17 significantly blocked the cleavage of CD16b following neutrophil activation and apoptosis. CD16b shedding by ADAM17 was further demonstrated using a unique ADAM17 function-blocking mAb and a cell-based ADAM17 reconstitution assay. Unlike human CD16, however, mouse CD16 did not undergo efficient ectodomain shedding upon neutrophil stimulation or apoptosis, indicating that this mechanism cannot be modeled in normal mice. Taken together, our findings are the first to directly demonstrate that ADAM17 cleaves CD16 in human leukocytes.

Characterization of a functionally important and evolutionarily well-conserved epitope mapped to the short consensus repeats of E-selectin and L-selectin

Selectins represent a new family of adhesion molecules, expressed by leukocytes and endothelial cells, that are involved in the regulation of leukocyte traffic. Here we have characterized a new monoclonal antibody (mAb) (EL-246) that recognizes both human leukocyte L-selectin (previously called LAM-1, LECAM-1, or gp90MEL-14) and endothelial cell E-selectin (previously called ELAM-1). EL-246 recognized a 110-kD protein expressed on cells transfected with E-selectin cDNA and stained many postcapillary venules in inflamed human tonsil. EL-246 also stained human peripheral blood leukocytes and showed identity with anti-L-selectin mAb in two-color flow cytometric analysis. The expression of the leukocyte EL-246 antigen was regulated in the same manner as L-selectin and EL-246 recognized anti-L-selectin mAb affinity-purified antigen in SDS/PAGE Western blot analysis. Further, L-selectin cDNA transfectants were specifically stained by EL-246. EL-246 blocked greater than 95% of lymphocyte adhesion to peripheral lymph node high endothelial venules and greater than 90% of neutrophil adhesion to E-selectin transfectants. In addition to the EL-246 epitope being expressed on two different human selectins, it was detected on L-selectin from a variety of different animals. Interestingly, domain mapping studies localized the EL-246 epitope to the short consensus repeat (SCR) domains of L-selectin. EL-246 is the first mAb that recognizes two different selectins and potentially defines a functional epitope encoded by the SCR domains. Inhibitors of selectin function targeted to this region would be expected to have the added advantage of simultaneously blocking the activity of two distinct adhesion proteins involved in inflammation.

Expression of a Recombinant High Affinity IgG Fc Receptor by Engineered NK Cells as a Docking Platform for Therapeutic mAbs to Target Cancer Cells

Anti-tumor mAbs are the most widely used and characterized cancer immunotherapy. Despite having a significant impact on some malignancies, most cancer patients respond poorly or develop resistance to this therapy. A known mechanism of action of these therapeutic mAbs is antibody-dependent cell-mediated cytotoxicity (ADCC), a key effector function of human NK cells. CD16A on human NK cells has an exclusive role in binding to tumor-bound IgG antibodies. Though CD16A is a potent activating receptor, it is also a low affinity IgG Fc receptor (FcγR) that undergoes a rapid downregulation in expression by a proteolytic process involving ADAM17 upon NK cell activation. These regulatory processes are likely to limit the efficacy of tumor-targeting therapeutic mAbs in the tumor environment. We sought to enhance NK cell binding to anti-tumor mAbs by engineering these cells with a recombinant FcγR consisting of the extracellular region of CD64, the highest affinity FcγR expressed by leukocytes, and the transmembrane and cytoplasmic regions of CD16A. This novel recombinant FcγR (CD64/16A) was expressed in the human NK cell line NK92 and in induced pluripotent stem cells from which primary NK cells were derived. CD64/16A lacked the ADAM17 cleavage region in CD16A and it was not rapidly downregulated in expression following NK cell activation during ADCC. CD64/16A on NK cells facilitated conjugation to antibody-treated tumor cells, ADCC, and cytokine production, demonstrating functional activity by its two components. Unlike NK cells expressing CD16A, CD64/16A captured soluble therapeutic mAbs and the modified NK cells mediated tumor cell killing. Hence, CD64/16A could potentially be used as a docking platform on engineered NK cells for therapeutic mAbs and IgG Fc chimeric proteins, allowing for switchable targeting elements and a novel cancer cellular therapy.

In vivo role of leukocyte ADAM17 in the inflammatory and host responses during E. coli-mediated peritonitis

Inflammation is the body's initial response to infection, which is harmful when excessive, as exemplified in sepsis inflammatory syndromes. Ectodomain shedding by the membrane metalloprotease ADAM17 is an emerging regulator of inflammation, as it directs the activity of various inflammatory modulators. At this time, however, little is known about the in vivo function of ADAM17. Here, we show that ADAM17-deficient leukocytes afforded mice a survival benefit following Escherichia coli-mediated peritoneal sepsis, which was associated with a reduction in systemic proinflammatory cytokine levels and bacterial burden. A more rapid yet transitory neutrophil infiltration into the peritoneal cavity of conditional ADAM17 knockout mice was observed when compared with control mice, suggesting a mechanism for their enhanced clearance of bacteria. Preventing the shedding of L-selectin augments neutrophil recruitment, and we show that L-selectin shedding by peritoneal neutrophils in conditional ADAM17 knockout mice was impaired. Moreover, their peritoneal TNF-alpha levels were markedly lower than control mice following E. coli challenge. These events indicate key molecular processes involved in the altered time course of neutrophil recruitment in conditional ADAM17 knockout mice. Overall, our study provides novel in vivo evidence of the instrumental role of ADAM17 in modulating inflammation and host resistance during Gram-negative bacterial infection.

Engineering Anti-Tumor Monoclonal Antibodies and Fc Receptors to Enhance ADCC by Human NK Cells

Tumor-targeting monoclonal antibodies (mAbs) are the most widely used and characterized immunotherapy for hematologic and solid tumors. The significance of this therapy is their direct and indirect effects on tumor cells, facilitated by the antibody's antigen-binding fragment (Fab) and fragment crystallizable region (Fc region), respectively. The Fab can modulate the function of cell surface markers on tumor cells in an agonistic or antagonistic manner, whereas the Fc region can be recognized by an Fc receptor (FcR) on leukocytes through which various effector functions, including antibody-dependent cell-mediated cytotoxicity (ADCC), can be elicited. This process is a key cytolytic mechanism of natural killer (NK) cells. These innate lymphocytes in the human body recognize tumor-bound antibodies exclusively by the IgG Fc receptor CD16A (FcγRIIIA). Two allelic versions of CD16A bind IgG with either lower or higher affinity. Cancer patients homozygous for the higher affinity allele of CD16A have been reported to respond significantly better to mAb therapies for various malignancies. These studies revealed that mAb therapy efficacy positively correlates with higher affinity binding to CD16A. Approaches to enhance tumor antigen targeting by NK cells by modifying the Fc portion of antibodies or the FcR on NK cells are the focus of this review.

ADAM17 activity during human neutrophil activation and apoptosis

Substrates of the metalloprotease ADAM17 (also known as TNF-alpha converting enzyme or TACE) undergo ectodomain shedding and include various inflammatory modulators. Though polymorphonuclear leukocytes contribute significantly to inflammation, direct analyses of ADAM17 on human neutrophils are very limited. In addition, the current understanding of the processes regulating ADAM17 activity primarily relate to its rapid activation. Therefore, to extend insights into the mechanisms of ADAM17 activity, we examined its surface expression and the shedding of its substrates during extended periods of neutrophil activation and apoptosis. Contrary to studies with immortalized hematopoietic cell lines, we report that surface expression of ADAM17 is maintained by human neutrophils activated with formyl peptides or by FcR/complement receptor-mediated phagocytosis. Interestingly, bacterial phagocytosis resulted in a significant increase in ADAM17 expression several hours after pathogen engulfment. We provide novel evidence that ADAM17 surface expression is also maintained during spontaneous and anti-Fas-induced neutrophil apoptosis. The well-validated ADAM17 substrates L-selectin and proTNF-alpha were shed efficiently by neutrophils under each of the conditions tested. Our data thus indicate prolonged ADAM17 expression during neutrophil effector functions. The implications of this may be a role by ADAM17 in both the induction and down-regulation of neutrophil activity.

Hill CA, Walcheck B, Brooks JD. Increased expression of GCNT1 is associated with altered O-glycosylation of PSA, PAP, and MUC1 in human prostate cancers

BACKGROUND

Protein glycosylation is a common posttranslational modification and glycan structural changes have been observed in several malignancies including prostate cancer. We hypothesized that altered glycosylation could be related to differences in gene expression levels of glycoprotein synthetic enzymes between normal and malignant prostate tissues.

METHODS

We interrogated prostate cancer gene expression data for reproducible changes in expression of glycoprotein synthetic enzymes. Over-expression of GCNT1 was validated in prostate samples using RT-PCR. ELISA was used to measure core 2 O-linked glycan sialyl Lewis X (sLe(x) ) of prostate specific antigen (PSA), Mucin1 (MUC1), and prostatic acidic phosphatase (PAP) proteins.

RESULTS

A key glycosyltransferase, GCNT1, was consistently over-expressed in several prostate cancer gene expression datasets. RT-PCR confirmed increased transcript levels in cancer samples compared to normal prostate tissue in fresh-frozen prostate tissue samples. ELISA using PSA, PAP, and MUC1 capture antibodies and a specific core 2 O-linked sLe(x) detection antibody demonstrated elevation of this glycan structure in cancer compared to normal tissues for MUC1 (P = 0.01), PSA (P = 0.03) and near significant differences in PAP sLe(x) levels (P = 0.06). MUC1, PSA and PAP protein levels alone were not significantly different between paired normal and malignant prostate samples.

CONCLUSIONS

GCNT1 is over-expressed in prostate cancer and is associated with higher levels of core 2 O-sLe(x) in PSA, PAP and MUC1 proteins. Alterations of O-linked glycosylation could be important in prostate cancer biology and could provide a new avenue for development of prostate cancer specific glycoprotein biomarkers.

Ectodomain shedding of the cell adhesion molecule Nectin-4 in ovarian cancer is mediated by ADAM10 and ADAM17

We previously showed that the cell adhesion molecule Nectin-4 is overexpressed in ovarian cancer tumors, and its cleaved extracellular domain can be detected in the serum of ovarian cancer patients. The ADAM (adisintegrin and metalloproteinase) proteases are involved in ectodomain cleavage of transmembrane proteins, and ADAM17 is known to cleave Nectin-4 in breast cancer. However, the mechanism of Nectin-4 cleavage in ovarian cancer has not yet been determined. Analysis of ovarian cancer gene microarray data showed that higher expression of Nectin-4, ADAM10, and ADAM17 is associated with significantly decreased progression-free survival. We quantified Nectin-4 shedding from the surface of ovarian cancer cells after stimulation with lysophosphatidic acid. We report that ADAM17 and ADAM10 cleave Nectin-4 and release soluble Nectin-4 (sN4). Small molecule inhibitors and siRNA knockdown of both ADAM proteases confirmed these results. In matched samples from 11 high-grade serous ovarian cancer patients, we detected 2-20-fold more sN4 in ascites fluid than serum. Co-incubation of ovarian cancer cells with ascites fluid significantly increased sN4 shedding, which could be blocked using a dual inhibitor of ADAM10 and ADAM17. Furthermore, we detected RNA for Nectin-4, ADAM10, and ADAM17 in primary ovarian carcinoma tumors, secondary omental metastases, and ascites cells isolated from serous ovarian cancer patients. In a signaling pathway screen, lysophosphatidic acid increased phosphorylation of AKT, EGF receptor, ERK1/2, JNK1/2/3, and c-Jun. Understanding the function of Nectin-4 shedding in ovarian cancer progression is critical to facilitate its development as both a serum biomarker and a therapeutic target for ovarian cancer.

The cytoplasmic domain of L-selectin participates in regulating L-selectin endoproteolysis

Neutrophil recruitment at sites of inflammation is regulated by a series of adhesion and activation events. L-selectin (CD62L) is a leukocyte expressed adhesion protein that is important for neutrophil accumulation and rolling along the vascular endothelium. L-selectin is unique from other adhesion molecules involved in leukocyte transmigration in that its adhesiveness appears to be regulated partly by rapid endoproteolysis. Cleavage of L-selectin occurs within a membrane-proximal region that results in ectodomain shedding and retention of a 6-kDa transmembrane fragment. The cleavage domain of L-selectin has been well characterized through mutational analysis. Whether the cytoplasmic domain of L-selectin also plays a role in regulating shedding is controversial. We have previously shown that the Ca(2+)-sensing protein calmodulin (CaM) constitutively associates with the cytoplasmic domain of L-selectin in transfected cell lines. However, in the absence of mapping and mutational analysis of the CaM-binding region of L-selectin, there remains no direct evidence that this interaction affects shedding. Using synthesized peptides and expressed L-selectin constructs, we demonstrate that CaM binding activity occurs in the membrane-proximal region of the cytoplasmic domain. Mutations engineered in this region that prevent CaM binding increase the proteolytic turnover of L-selectin. Moreover, we demonstrate that CaM binding to the 6-kDa transmembrane fragment is greatly reduced compared with intact L-selectin in neutrophils, suggesting that CaM binding is regulated. These data imply that the cytoplasmic domain of L-selectin can regulate shedding by a mechanism in which bound CaM may operate as a negative effector.