Lymphocyte activation and regulation of three adhesion molecules with supposed function in homing: LECAM-1 (MEL-14 antigen), LPAM-1/2 (alpha 4-integrin) and CD44 (Pgp-1)

Inhibition of renalase drives tumour rejection by promoting T cell activation

BACKGROUND

Although programmed cell death protein 1 (PD-1) inhibitors have revolutionised treatment for advanced melanoma, not all patients respond. We previously showed that inhibition of the flavoprotein renalase (RNLS) in preclinical melanoma models decreases tumour growth. We hypothesised that RNLS inhibition promotes tumour rejection by effects on the tumour microenvironment (TME).

METHODS

We used two distinct murine melanoma models, studied in RNLS knockout (KO) or wild-type (WT) mice. WT mice were treated with the anti-RNLS antibody, m28, with or without anti-PD-1. 10X single-cell RNA-sequencing was used to identify transcriptional differences between treatment groups, and tumour cell content was interrogated by flow cytometry. Samples from patients treated with immunotherapy were examined for RNLS expression by quantitative immunofluorescence.

RESULTS

RNLS KO mice injected with wild-type melanoma cells reject their tumours, supporting the importance of RNLS in cells in the TME. This effect was blunted by anti-cluster of differentiation 3. However, MØ-specific RNLS ablation was insufficient to abrogate tumour formation. Anti-RNLS antibody treatment of melanoma-bearing mice resulted in enhanced T cell infiltration and activation and resulted in immune memory on rechallenging mice with injection of melanoma cells. At the single-cell level, treatment with anti-RNLS antibodies resulted in increased tumour density of MØ, neutrophils and lymphocytes and increased expression of IFNγ and granzyme B in natural killer cells and T cells. Intratumoural Forkhead Box P3 + CD4 cells were decreased. In two distinct murine melanoma models, we showed that melanoma-bearing mice treated with anti-RNLS antibodies plus anti-PD-1 had superior tumour shrinkage and survival than with either treatment alone. Importantly, in pretreatment samples from patients treated with PD-1 inhibitors, high RNLS expression was associated with decreased survival (log-rank P = 0.006), independent of other prognostic variables.

CONCLUSIONS

RNLS KO results in melanoma tumour regression in a T-cell-dependent fashion. Anti-RNLS antibodies enhance anti-PD-1 activity in two distinct aggressive murine melanoma models resistant to PD-1 inhibitors, supporting the development of anti-RNLS antibodies with PD-1 inhibitors as a novel approach for melanomas poorly responsive to anti-PD-1.

Leukocyte adhesion molecules in animal models of inflammatory bowel disease

The dysregulated recruitment of leukocytes into the intestine is required for the initiation and maintenance of inflammatory bowel disease (IBD). Several families of molecules regulate the influx of these cells into sites of inflammation. Interference with some of these molecules has already shown efficacy in the clinics and antibodies that target the molecules involved have been approved by the FDA for use in Crohn's disease (CD), multiple sclerosis (i.e., natalizumab), and psoriasis (i.e., efalizumab). Here, we discuss basic aspects of the different families of relevant molecules and compile a large body of preclinical studies that supported the targeting of specific steps of the leukocyte adhesion cascade for therapeutic purposes in colitis and in novel models of CD-like ileitis.

L-Selectin, α4β1, and α4β7 Integrins Participate in CD4+ T Cell Recruitment to Chronically Inflamed Small Intestine

CD4+ T cells are essential for development and perpetuation of Crohn's disease, a chronic immune-mediated condition that affects primarily the small intestine. Using novel models of Crohn's disease-like ileitis (i.e., SAMP1/YitFc and CD4+ T cell transfer models), we have begun to understand the adhesive pathways that mediate lymphocyte trafficking to the chronically inflamed small bowel. Expansion of the CD4/beta7+ population and increased mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression were observed within the intestinal lamina propria with disease progression. However, Ab blockade of the beta7 integrin, the alpha4beta7 heterodimer, MAdCAM-1, or L-selectin did not attenuate inflammation. Blockade of two pathways (L-selectin and MAdCAM-1 or alpha4 integrins) was required to improve ileitis. Further analyses showed that 55 +/- 7% of the mesenteric lymph node alpha4beta7+CD4 expressed L-selectin. These L-selectin+ T cells were the main producers of TNF-alpha and the predominant ileitis-inducing subpopulation. Mechanistically, combined blockade of L-selectin and MAdCAM-1 depleted the intestinal lamina propria of CD4+ T cells that aberrantly coexpressed alpha4beta7 and alpha4beta1 integrins, markedly decreasing local production of TNF-alpha and IFN-gamma. Thus, pathogenic CD4+ T cells not only use the physiologic alpha4beta7/MAdCAM-1 pathway, but alternatively engage alpha4beta1 and L-selectin to recirculate to the chronically inflamed small intestine.

Recent thymic emigrants (CD4+) continuously migrate through lymphoid organs: within the tissue they alter surface molecule expression

T-cell progenitors migrate from bone marrow (BM) into the thymus. After maturation they are released as recent thymic emigrants (RTE) into the periphery ensuring the diversification of the T-cell repertoire. Both the kinetics with which RTE migrate through the periphery and the surface molecules they express are still unclear. In 1- and 18-month-old Lewis rats CD4+ RTE were identified in blood, spleen, lymph node, and thoracic duct lymph by flow cytometry (CD45RC- and CD90+), were differentiated from CD4+ naive (CD45RC+) and memory T cells (CD45RC-CD90-), and were characterized regarding the expression of surface molecules. Both in 1- and 18-month-old animals the percentage of RTE among the CD4+ population in blood was comparable to that in all other compartments. Surprisingly, RTE expressed alpha4-integrin, LFA-1, and interleukin (IL)-2 receptor at a significantly higher level than naive T cells and more comparable to memory T cells. Within lymphoid tissues RTE, naive, and memory T cells significantly upregulated the expression of CD44 and ICAM-1, and downregulated the expression of L-selectin. These changes were reversed before the cells re-entered the blood. Thus, our data indicate that CD4+ RTE travel through the periphery of young and old rats like mature T cells, continuously modulating their surface molecule expression.

Possible role of L-selectin in T lymphocyte alveolitis in patients with active pulmonary sarcoidosis

A number of adhesion molecules participate in the recruitment of inflammatory cells to the site of inflammation, and selectins together with their ligands are important in the early transient adhesion phase. In this study, we evaluated the role of L-selectin in T lymphocyte alveolitis in patients with active pulmonary sarcoidosis. We measured serum and bronchoalveolar lavage fluid (BALF) concentrations of soluble (s)L-selectin using an ELISA. Serum and BALF concentrations of sL-selectin were significantly elevated in patients with sarcoidosis compared with control healthy subjects and idiopathic pulmonary fibrosis (IPF) patients (P < 0.05 and P < 0. 01, respectively). The lymphocyte surface marker was also examined in peripheral blood and BALF by flow cytometric analysis. The percentage of CD3+CD62L+ cells (L-selectin-bearing T lymphocytes) was significantly lower in peripheral blood of sarcoidosis than in that of healthy subjects (P < 0.01). In contrast, the percentage of CD3+CD62L- cells (L-selectin-negative T lymphocytes) in BALF of patients with sarcoidosis was significantly higher than in healthy subjects (P < 0.05) and IPF patients (P < 0.01). Furthermore, there was a significant correlation between serum concentrations of sL-selectin and the number of L-selectin-negative T lymphocytes in BALF (r = 0.535, P < 0.01). Our results suggest that L-selectin may be involved in T lymphocyte alveolitis in patients with active pulmonary sarcoidosis.

Altered migration of gut-derived T lymphocytes after activation with concanavalin A

Although activation of lymphocytes is known to be associated with profound changes in homing behavior, it remains unclear how activation alters migration of gut-derived lymphocytes in lymphoid and nonlymphoid organs. The objectives of this study were 1) to compare migration of naive and concanavalin A (ConA)-activated T lymphocytes into the gut mucosa, spleen, and liver and 2) to define the role of specific adhesion molecules in this homing process. Fluorescently labeled T lymphocytes collected from rat intestinal lymph were injected into the jugular vein, and the kinetics of appearance of the infused lymphocytes were monitored in ileal Peyer's patches, spleen, and liver. The migration of naive and ConA-activated T lymphocytes into microvessels were compared using an intravital microscope. ConA stimulation significantly increased the rolling velocity of T lymphocytes in postcapillary venules of Peyer's patches, and ConA-stimulated lymphocytes exhibited a loss of the selective adherence properties in Peyer's patches that is normally observed with naive T cells. ConA activation also suppressed the accumulation of T cells in the spleen. On the other hand, the adherence of T cells to hepatic sinusoidal endothelium was significantly increased after ConA activation, especially in the periportal area, and this increase was attenuated by an anti-intercellular adhesion molecule (ICAM)-1 antibody. Flow cytometry analysis revealed a decline in L-selectin expression and an increase in CD11a expression and ICAM-1 on the surface of ConA-treated T cells. In conclusion, activation of gut-derived T lymphocytes with ConA significantly alters their migration path, with a diminished localization to Peyer's patches and spleen and a preferential accumulation in hepatic sinusoids. This altered migration pattern likely results from changes in the expression of leukocyte adhesion molecules such as L-selectin and CD11a.

Tissue inhibitor of metalloproteinases-3 inhibits shedding of L-selectin from leukocytes

Although the enzyme or enzymes mediating shedding of L-selectin have not yet been identified, this activity can be blocked by synthetic hydroxamic acid-based inhibitors of metalloproteinases such as Ro 31-9790. However, the endogenous matrix metalloproteinase inhibitor tissue inhibitor of metalloproteinases (TIMP)-1 does not block L-selectin shedding. Here, we report that TIMP-3, but not TIMP-2, inhibits L-selectin shedding from mouse and human lymphocytes, Jurkat T cells, and human monocytes. TIMP-3 has an IC50 of 0.3-0.4 microM on these cell types compared with 0.7-4.8 microM for Ro 31-9790. A metalloproteinase (tumor necrosis factor-alpha (TNF-alpha)-converting enzyme; ADAM17) has recently been identified which cleaves the pro-form of TNF-alpha to produce soluble cytokine. We compared inhibition of L-selectin shedding by TIMPs and Ro 31-9790 with inhibition of TNF-alpha shedding from human monocytes. TIMP-3 inhibited TNF-alpha shedding (IC50 of 0.1 microM), as did Ro 31-9790 (IC50 of 0.4 microM). TIMP-2 had a partial effect, and TIMP-1 did not inhibit. This study confirms that L-selectin sheddase is a metalloproteinase, but not a matrix metalloproteinase, and investigates the relationship between shedding of L-selectin and TNF-alpha.

Mechanisms for induction of L-selectin loss from T lymphocytes by a cryptococcal polysaccharide, glucuronoxylomannan

Disseminated cryptococcosis is accompanied by cryptococcal polysaccharides in the serum and the lack of cellular infiltrates in infected tissues. Cryptococcal polysaccharides given intravenously to mice inhibit the influx of T lymphocytes into the sites of cell-mediated immune response. The focus here was to determine whether cryptococcal polysaccharides modulate the expression of molecules, such as L-selectin, that are important in extravasation of T cells. Cryptococcal glucuronoxylomannan (GXM), but not galactoxylomannan or mannoprotein, was found to cause loss of L-selectin from freshly isolated human T cells of both CD4 and CD8 subsets and from Jurkat cells. With the signaling-pathway inhibitors staurosporine (which inhibits protein kinase C) and herbimycin A (which inhibits protein tyrosine kinases), we showed that GXM or the cryptococcal culture filtrate antigen CneF directly induces L-selectin loss from CD4(+) and CD8(+) T cells via a herbimycin A-sensitive pathway(s) presumably involving one or more protein tyrosine kinases but not via a pathway involving protein kinase C. Loss of L-selectin from the T cells before the T cells have a chance to bind to L-selectin ligands on endothelial cells would be expected to prevent T-cell migration into inflamed tissues and/or lymph organs.

Metalloproteinase-mediated regulation of L-selectin levels on leucocytes

Leucocyte (L)-selectin can be proteolytically cleaved in the membrane proximal extracellular region to yield a soluble fragment that contains the functional lectin and epidermal growth factor domains. A variety of stimuli are known to stimulate L-selectin shedding including chemoattractants, phorbol esters, and L-selectin cross-linking; however, the enzymes that regulate L-selectin expression are not characterized. In this study we have used phorbol ester to stimulate endoproteolytic release of L-selectin and identified a major role for a cell surface metalloproteinase (L-selectin sheddase) in this process. The hydroxamic acid-based inhibitor of zinc-dependent matrix metalloproteinases Ro 31-9790 completely prevented shedding of cell surface L-selectin from leucocytes in mouse, rat, and man. L-selectin was susceptible to cleavage by known matrix metalloproteinases. Recombinant human fibroblast collagenase (MMP1) reduced the number of L-selectin-positive lymphocytes to a similar extent as phorbol ester activation, and stromelysin (MMP3) had a partial effect on L-selectin expression. Gelatinases A (MMP2) and B (MMP9) were without effect. Lymphocytes did not express fibroblast collagenase or stromelysin at the cell surface, and tissue inhibitor of metalloproteinases (TIMP) did not affect L-selectin levels. L-selectin sheddase was not detected in media harvested from phorbol ester-stimulated lymphocytes and was only able to cleave L-selectin in the cis but not the trans configuration. These results suggest that endoproteolytic release of L-selectin from the leucocyte surface is mediated by a metalloproteinase (L-selectin sheddase), which is distinguishable from known matrix metalloproteinases. Understanding the regulation of L-selectin sheddase will be critical for controlling leucocyte migration from the blood.

Cerebrospinal fluid soluble L-selectin (sCD62L) in meningoencephalitis

The leucocyte adhesion molecule L-selectin (CD62L) is rapidly cleaved off proteolytically after cell activation, generating soluble L-selectin (sCD62L) molecules. sCD62L concentrations were determined in 185 cerebrospinal fluid (CSF) samples obtained from children aged 1 month to 17 years. In 36 CSF samples of children with meningoencephalitis, sCD62L was significantly higher (median 209 fmol/ml) than in samples of children with other febrile diseases (n = 67, median 50 fmol/ml) or non-febrile disorders (n = 82, median 44 fmol/ml). There was a positive correlation between CSF protein and CSF sCD62L (rS = 0.68), suggesting that a disturbed blood-brain barrier contributes to raised sCD62L concentrations in the CSF. However, the CSF sCD62L/protein ratio of children with meningoencephalitis was significantly higher than in children with other febrile diseases or non-febrile disorders, indicating that sCD62L concentrations in children with meningoencephalitis were higher than expected from plasma leakage alone. It is concluded that both an impaired blood-brain barrier and the generation of sCD62L by infiltrating leucocytes contribute to raised CSF sCD62L concentrations in children with meningoencephalitis.

Recirculation, phenotype and functions of lymphocytes in mice treated with monoclonal antibody MEL-14

The effect of a single injection of an antibody against the peripheral lymph node (PLN) homing receptor or L-selectin (gp90MEL-14) was studied in vivo in C57BL/6 mice. L-selectin is known to be rapidly shed from leukocytes in humans and in mice following activation or cross-linking in vitro. Here we demonstrate that in vivo a single injection of MEL-14 antibody induces a rapid, almost complete and reversible down-regulation of L-selectin expression on both T and B cells. This modulation is dose dependent, specific for L-selectin and lasts for 10 days. On neutrophils, L-selectin expression was moderately decreased, and the injected antibody was detectable on the cell surface for several days. Thus, L-selectin expression after antibody binding in vivo was affected differently on neutrophils and lymphocytes. MEL-14 treatment induces profound alterations of cell traffic. Loss of L-selectin on lymphocytes leads to drastic PLN depletion and increased spleen cellularity. Depleted PLN were highly enriched in MEL-14-/lo, CD44hi and CD11ahi cells, which may represent transiently sessile memory/activated cells. The unresponsiveness in mixed lymphocyte reaction of PLN cells from treated animals and of purified L-selectin- PLN T cells from normal mice supports this view. However, PLN and spleen cells from treated animals responded normally to non-antigen-specific stimuli.

Functional studies on MEL-14+ and MEL-14- T cells in peripheral lymphoid tissues

Functions of MEL-14+ T cells and MEL-14- T cells in peripheral lymphoid tissues were analyzed and compared. The MEL-14- T cells, representing a minor subpopulation of spleen and lymph node T cells, generated considerably higher mixed lymphocyte reaction and mitogen responses than the MEL-14+ T cells in any lymphoid tissues studied. Furthermore, upon stimulation with ConA the MEL-14- CD8+ T cells produced significantly larger amounts of IL-2 and IFN-gamma than MEL-14+ CD8+ T cells did. A similar but less marked observation was obtained with the CD4+ T cell population. Furthermore, when B10.BR mice were immunized with AKR (Mls-1a) spleen cells, the proportion of the Mls-1a reactive V beta 6+ T cells from draining lymph nodes increased and a substantial proportion of the increasing V beta 6+ T cells was shown to be MEL-14-. The present findings on the whole indicate that MEL-14- T cells in the peripheral lymphoid tissues are at functionally high levels and may represent memory cells which have been previously stimulated in vivo.

Expression of an adhesion molecule and homing in B-cell chronic lymphocytic leukaemia: II. L-selectin expression mediated cell adhesion revealed by immobilized analogue carbohydrates in B-cell chronic lymphocytic leukaemia and monoclonal lymphocytosis of undetermined significance

The L-selectin mediated adhesion of freshly isolated peripheral blood mononuclear cells (PBMCs) to phosphonomonoester core polysaccharide (PPME) and fucoidin derivatized gels was investigated in seven cases of monoclonal lymphocytosis of undetermined significance (B-MLUS) and 12 cases of chronic lymphocytic leukaemia: B-CLL, patients with peripheral lymphocytosis (LY-patients), lymph node enlargement (LN-patients) and splenomegaly (SM-patients). PBMCs isolated from the peripheral blood of 10 healthy donors served as controls. The binding to PPME and fucoidin correlated well (n = 19, P = 0.01). Adhesion of PBMCs from B-MLUS and B-CLL showed a greater variability than controls. A higher number of cells, on average, bound to PPME and fucoidin derivatized polyacrylamide gels in B-MLUS than in B-CLL. However, the differences observed were not statistically significant. In four cases with B-CLL, the stimulatory effect of interferon-alpha on the function of L-selectin and some other accessory molecules was also studied. The increased binding of PBMCs to immobilized analogue molecules (PPME, fucoidin) and to high endothelial venules (HEVs) in the in vitro HEV-binding assay supports the notion that interferon-alpha not only increases the expression of the adhesion molecules, but also results in an enhanced adhesive function.

Expression of an adhesion molecule and homing in B-cell chronic lymphocytic leukaemia: I. Application of the HEV-binding assay to a clinical series

High endothelial venule (HEV)-binding of peripheral blood mononuclear cells (PBMCs) from 43 patients with B-cell chronic lymphocytic leukaemia (B-CLL) was investigated with a HEV-binding in vitro assay. Immunophenotyping of HEV-adherent PBMCs proved that most of them belonged to the B-cell proliferation. B-CLL cells stringently expressed CD44 molecules (Hermes-1, -3 and H90). The patients were subgrouped according to Binet's classification, as well as according to the organ manifestations, i.e. patients with B-cell monoclonal lymphocytosis of undetermined significance (B-MLUS) and patients with lymphocytosis (LY), lymph node enlargement (LN) and splenomegaly (SM). The HEV-binding activity of the cells was the highest in Binet stage A patients and in patients with B-MLUS (p < 0.05 in B-MLUS versus B-CLL LY, LN, SM). Based on these findings it is suggested that B-CLL patients show not only a clinical and immunophenotypical heterogeneity, but a diverse function of adhesion molecules.

Diminished cord blood lymphocyte L-selectin expression in neonatal bacterial infection

L-Selectin, a leukocyte surface glycoprotein involved in white blood cell extravasation, is rapidly down-regulated after leukocyte activation. We prospectively determined lymphocyte L-selectin expression in freshly obtained cord blood samples of 98 neonates (gestational age 25-42 weeks). In eight infants with bacterial infection, the mean percentage of L-selectin(high) lymphocytes was 32.5% (SD 20.1%), compared to 60.1% (SD 18.7%) in the control group (P < 0.01). A percentage of L-selectin(high) lymphocytes of less than 42% had a sensitivity of 75% and a specificity of 82% in identifying infected newborns. Cord blood lymphocyte L-selectin expression was independent of gestational age, birth weight, umbilical artery pH, hematocrit, white blood cell count, absolute neutrophil count, C-reactive protein level, or maternal fever before delivery while there was a weak correlation with the newborn's immature/total ratio and platelet count. To our knowledge, this is the first report demonstrating downregulation of human lymphocyte L-selectin expression following activation of the immune system in vivo.

Cloning and expression of mouse integrin beta p(beta 7): a functional role in Peyer's patch-specific lymphocyte homing

Lymphocytes express integrin receptors, termed lymphocyte Peyer's patch high endothelial venule (HEV) adhesion molecules (LPAMs), that mediate their organ-specific adhesion to specialized HEVs found in mucosal lymphoid organs (Peyer's patches). LPAM-1 consists of a murine integrin alpha 4 noncovalently associated with integrin beta p. Here, we describe the cloning and expression of a mouse cDNA encoding beta p, which is an 806-amino acid transmembrane glycoprotein. The genomic Southern blot analysis indicates that beta p is the murine homologue of human beta 7. The function of alpha 4 beta 7 as a Peyer's patch-specific adhesion molecule was tested directly by expression of the murine beta 7 cDNA in an alpha 4+ beta 7-B-cell line or coexpression of the alpha 4 and beta 7 cDNAs in an alpha 4-beta 7-T-cell line. The transfected cells exhibited a new Peyer's patch-specific adhesive phenotype that could be specifically blocked by monoclonal antibodies against alpha 4 and beta 7. Moreover, an anti-beta 7 monoclonal antibody specifically blocked binding of normal lymphocytes to Peyer's patch HEV but did not inhibit their binding to peripheral lymph node HEVs, indicating that beta 7 is a unique component of the Peyer's patch-specific homing receptor.