Use of monoclonal antibodies for expression cloning

This unit details the use of transient expression in mammalian cells to screen cDNA libraries with monoclonal antibodies (MAb) to isolate cDNA clones encoding cell-surface and intracellular proteins. The first protocol describes the cloning of cDNAs encoding cell-surface antigens. The second protocol is a modification that facilitates isolation of cDNAs encoding antigens that are expressed intracellularly. Both protocols are designed for use with the expression vector CDM8, which contains a polylinker for subcloning double-stranded cDNA.

Transient expression of proteins using COS cells

This unit describes the use of COS cells to efficiently produce a desired protein in a short period of time. These cells express high levels of the SV40 large tumor (T) antigen, which is necessary to initiate viral DNA replication at the SV40 origin. Each COS cell transfected with DNA encoding a cell-surface antigen (in the appropriate vector) or cytoplasmic protein will express several thousand to several hundred thousand copies of the protein 72 hr posttransfection. If the transfected DNA encodes a secreted protein, up to 10 mg of protein can be recovered from the supernatant of the transfected COS cells 1 week posttransfection. COS cell transient expression systems have also been used to screen cDNA libraries, to isolate cDNAs encoding cell-surface proteins, secreted proteins, and DNA binding proteins, and to test protein expression vectors rapidly prior to the preparation of stable cell lines.

Classification of mutations in the human CD40 ligand, gp39, that are associated with X-linked hyper IgM syndrome

The interaction between the T cell activation antigen gp39 and CD40, its receptor CD40 on B cells, plays a critical role in the regulation of humoral immune responses. Using a detailed three-dimensional model of the gp39 extracellular region, we have analyzed 20 mutations in gp39 that were, with one exception, isolated from patients with X-linked hyper IgM (XHIM) syndrome. On the basis of this analysis, the mutations were classified according to their predicted locations and effects. Twelve mutations are thought to compromise the gp39 structure by affecting interactions in hydrophobic core regions or at monomer interfaces, whereas seven others map closely to gp39 residues important for interaction with CD40. The latter mutations may thus, directly or indirectly, interfere with CD40 binding. One naturally occurring mutant whose carrier displays normal immune responses maps to a solvent-exposed position in a loop region of the molecule.

Scavenger receptor cysteine-rich domains 9 and 11 of WC1 are receptors for the WC1 counter receptor

Workshop cluster 1 (WC1) is a member of the scavenger receptor cysteine-rich (SRCR) superfamily that includes CD5, CD6, CD163, and M160. Bovine WC1 consists of 11 SRCR domains, a unique domain 1, and two homologous 5 SRCR domain cassettes, WC1 domains 2-6 and 7-11. The porcine orthologue of WC1 contains five SRCR domains with a different domain arrangement. Although the function of WC1 is unknown, WC1 is proposed to be an accessory or homing molecule. Thus, identification of cells that express the counter receptor for WC1 (WC1-CR) is critical to understanding the function of WC1. For this reason, we constructed WC1-human immunoglobulin G1 fusion proteins to identify the binding domain of WC1 and cells that express the WC1-CR. Immunohistochemical analysis revealed WC1 domains 9 and 11 bind cells with macrophage and dendritic cell morphology and cells in ellipsoids in the spleen. These results and the finding of conserved signaling motifs in the cytoplasmic tail suggest WC1 may be an accessory molecule.

Therapeutic intervention with inhibitors of co-stimulatory pathways in autoimmune disease

Many humanized antibodies and fusion proteins targeting T-cell co-stimulatory molecules are now in late-stage clinical development (phase II, phase III) or have recently completed phase III clinical trials. Both Amevive, an LFA-3-Ig fusion protein targeting CD2, and Xanelim, a humanized anti-CD11a antibody, have shown efficacy in pivotal phase III trials in patients with plaque psoriasis. These new medicines are poised to enter clinical use in 2002.

Retinoic acid and vitamin E modulate expression and release of CD178 in carcinoma cells: consequences for induction of apoptosis in CD95-sensitive cells

CD178 (CD95-ligand) is expressed on several tumor cells and likely influences the interaction of the tumor with the host immune system. However, little is known about the mechanisms that regulate its expression on the cell surface. We have evaluated the ability of various compounds and cytokines to regulate cell surface expression and release of soluble CD178 in various carcinoma cell lines. Vitamin E succinate (VES) and retinoic acid (RA) were found to reduce CD178 surface expression, whereas interferon-gamma stimulated a slight upregulation. At 48 h, the regulation of surface CD178 by VES and RA arose from a small decrease in CD178 mRNA and to a greater extent due to an increase in the release of soluble CD178; the latter was blocked by addition of a metalloproteinase inhibitor. Accordingly, VES and RA treatment diminished the ability of tumor cells to kill CD95-sensitive cells and this effect was markedly reduced by the presence of a metalloproteinase inhibitor. Our results indicate that, in vitro, CD178 expression on the cell surface of tumor cells can be regulated by agents that alter both expression and release of the ligand. In vivo, such treatments may play an important role in the outcome of tumor sensitivity or resistance to host immune mechanisms.

Tissue distribution of CD6 and CD6 ligand in cattle: expression of the CD6 ligand (CD166) in the autonomic nervous system of cattle and the human

We studied the tissue distribution of CD6(+) lymphocytes and cells expressing the CD6 ligand (also known as activated leukocyte cell adhesion molecule CD166) in calves by immunohistochemistry using an anti-bovine CD6 monoclonal antibody (mAb), a human CD6 (huCD6)-immunoglobulin G1 fusion protein (huCD6-Ig), and an anti-human CD166 (anti-huCD166) mAb. The huCD6-Ig and anti-huCD166 mAb bound to the sympathetic and parasympathetic nerve fibers but not to myelinated nerve fibers in the spinal nerve. Studies with human tissue using the anti-huCD166 mAb yielded identical patterns of labeling. Dense accumulations of CD6(+) lymphocytes were present in areas of the thymuses and spleens of calves, in areas innervated by huCD6-Ig(+) nerves. The cDNAs encoding the bovine CD166 and CD6 were isolated from the sympathetic ganglion and spleen, respectively. Predicted amino acid residues that are important for human and mouse CD6-CD166 binding were also conserved in bovine CD6 and CD166. Bovine CD166 transcripts were detected by reverse transcriptase-PCR in all the tissues that bound huCD6-Ig. These results show that the bovine orthologue of CD166 was constitutively expressed in the autonomic nervous systems of cattle and suggest that CD6(+) lymphocytes adhere to CD166(+) autonomic nerve terminals via CD6.

Differential regulation of CD40-mediated human B cell responses by antibodies directed against different CD40 epitopes

Ligation of CD40 using anti-CD40 or soluble CD40-ligand activates numerous intracellular kinases which transduce signals to the nucleus. The nature whereby these signaling events are coupled to distal functional events in B cells is poorly understood. In this study, using anti-CD40 monoclonal antibodies which recognize different epitopes on CD40, we compare the ability to activate the stress-activated protein kinases (SAPK) such as c-Jun NH(2) terminal kinase and p38 in human B cells with CD40 function. Activation of the SAPK pathway correlated with levels of activation of Rel/NF-kappaB transcription factors, but did not appear to be associated with rescue from anti-IgM induced apoptosis by suppressing caspase (CPP32) activity. Somewhat surprisingly, in the presence of IL-4, those antibodies to CD40 which failed to activate SAPK were most active in IgE production. IgE production was augmented in the presence of wortmannin. These studies suggest that rescue from apoptosis and IgE production mediated via CD40 may be independent of SAPK activation, induction of Rel/NF-kappaB, or suppression of CPP32 and that IgE production is, at least in part, regulated by signaling pathways that are dependent on phosphatidylinositol 3-kinase.

CD44 binds to the Shigella IpaB protein and participates in bacterial invasion of epithelial cells

Shigella entry into epithelial cells is characterized by a transient reorganization of the host cell cytoskeleton at the site of bacterial interaction with the cell membrane, which leads to bacterial engulfment in a macropinocytic process. Using affinity chromatography on HeLa cell extracts, we show here that the hyaluronan receptor CD44 associates with IpaB, a Shigella protein that is secreted upon cell contact. Overlay and solid-phase assays indicated that IpaB binds directly to the extracellular domain of CD44; binding is saturable and inhibitable, with a half-maximal inhibitory concentration of 175 nM. Immunoprecipitation experiments showed that IpaB associates with CD44 during Shigella entry. CD44 is recruited at bacterial entry sites and localizes at the plasma membrane of cellular extensions induced by Shigella. Pretreatment of cells with an anti-CD44 monoclonal antibody resulted in inhibition of Shigella-induced cytoskeletal reorganization, as well as inhibition of bacterial entry, whereas transfection of CD44 in cells that are deficient for CD44 results in increased bacterial binding to cells and internalization. The IpaB-CD44 interaction appears to be required for Shigella invasion by initiating the early steps of the entry process.

CD5 is A potential selecting ligand for B-cell surface immunoglobulin: a possible role in maintenance and selective expansion of normal and malignant B cells

Although the function of CD5 on B cells is unknown, previous studies suggested that CD5 interaction with V(H) framework regions of surface immunoglobulins (Igs) may contribute to survival and expansion of B cells. Here we used B-chronic lymphocytic leukemia (B-CLL) cells and transformed B-cell lines from normal and B-CLL patients to study CD5-Ig interactions. Immobilized Ig binds and permits isolation of CD5 from lysates of CD5-expressing cell lines. Immunoglobulins or Fab fragments of different V(H) families varied in their effectiveness as inhibitors of anti-CD5 staining of CLL cells, appendix and tonsil tissue sections. Human Ig also binds to purified recombinant CD5. We show here for the first time that the unconventional Ig-CD5 interaction maps to the extracellular CD5-D2 domain whereas conventional epitopes recognized by anti-CD5 antibodies are localized in the D1 domain of CD5. We propose that interactions of VH framework regions with CD5 as a ligand may maintain, select or expand normal, autoimmune or transformed B cells and also contribute to skewing of the normal V(H) repertoire.

Molecular cloning, genomic organization and cell-binding characteristics of mouse Spalpha

Several group B scavenger receptor cysteine-rich (SRCR) proteins have been shown to function as modulators in the immune response. Recently, we reported the cloning of a new member of this family, human Spalpha (hSpalpha). Herein we report the cloning and characterization of the mouse homologue of hSpalpha. Like its human counterpart, mouse Spalpha (mSpalpha), is a secreted protein containing three SRCR domains. Most lymphoid tissues express RNA transcripts encoding mSpalpha. Characterization of a genomic clone encoding the mature mSpalpha protein showed that each of the SRCR domains of mSpalpha is encoded by a single exon. Comparison of the sequence of mSPalpha with those of other published proteins indicates that it is the same as the recently reported protein named AIM (apoptosis inhibitor expressed by macrophages). Cell-binding studies with a mSpalpha immunoglobulin (mSpalpha-Rgamma) fusion protein indicated that mSpalpha is capable of binding to spleen-derived CD19+ B cells and minimally to peritoneal cavity-derived CD19+ B cells but not to peripheral blood-derived B cells. Spleen-derived CD3+ T cells also bound mSpalpha-Rgamma; however, no binding was observed to either peripheral blood mononuclear cells or peritoneal cavity-derived CD3+ T cells. The mSpalpha-Rgamma fusion protein was also shown to bind to the mouse cell lines WEHI3 (monocytic) and EL-4 (thymoma, T cell). The cloning of cDNA and genomic clones encoding mSpalpha and the identification of cells expressing a putative mSpalpha receptor(s) should facilitate in vivo studies designed to investigate the function of Spalpha in the immune compartment.

Colocalization of basic fibroblast growth factor and CD44 isoforms containing the variably spliced exon v3 (CD44v3) in normal skin and in epidermal skin cancers

Previous in vitro studies have shown CD44 isoforms containing the alternatively spliced exon v3 (CD44v3) to be modified with heparan sulphate (HS) and to bind HS-binding basic fibroblast growth factor (bFGF). Here, we demonstrate that exogenously added bFGF is also bound in vivo by CD44v3-positive keratinocytes in normal skin and by tumour cells in basal cell carcinoma and squamous cell carcinoma (SCC), two skin cancers of keratinocyte origin. bFGF binding and CD44v3 expression were colocalized in cultured human normal keratinocytes (HNK) and on the SCC cell line A431. By contrast, benign or malignant tumours of melanocyte origin failed to express CD44v3 and bound no bFGF. The bFGF binding to normal or transformed keratinocytes in vivo and in vitro was dependent on HS modification, as it was completely eliminated by pretreatment with heparitinase or by blocking with free heparin, whereas chondroitinase had no effect. In addition, specific removal of CD44v3 by antibody-induced shedding also diminished bFGF binding to keratinocytes. Furthermore, bFGF stimulated the proliferation of CD44v3-positive HNK and A431 in a dose-dependent fashion. This bFGF effect was again completely abolished by heparitinase or free heparin, but not by chondroitinase. In aggregate, our results suggest that a function of HS-modified CD44 isoforms such as CD44v3 in skin is to present the HS-binding growth factor bFGF, thereby stimulating the proliferation of normal or transformed keratinocytes.

The pleckstrin homology domain of the Wiskott-Aldrich syndrome protein is involved in the organization of actin cytoskeleton

In this study, we investigated the role of the pleckstrin homology (PH) domain of the Wiskott-Aldrich syndrome protein (WASP) in the regulation of actin cytoskeleton, which is defective in patients with Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT). Overexpression of the WASP in COS-7 cells cultured in the presence of fetal calf serum (FCS) resulted in large cluster formation of polymerized actin and WASP in the cytoplasm. In contrast, when the WASP transfected cells were cultured in the absence of FCS, activation with PMA or EGF was required to induce cluster formation. Overexpression of WASP with a missense mutation in the N-terminus of the PH domain failed to induce the large cluster formation in COS-7 cells even in the presence of FCS. We also found that phosphatidylinositol 4,5-bisphosphate (PIP(2)), which is known to regulate the actin cytoskeleton, binds to the PH domain of WASP, and the binding was abolished by the introduction of a missense mutation into the N-terminus but not the C-terminus of the PH domain. Together with the observations that most of the missense mutations observed in patients with WAS and XLT are located within the PH domain, these results indicate that the PH domain of WASP plays important roles in the regulation of actin cytoskeleton and suggested that the binding of PIP(2) to the PH domain is necessary for WASP to function properly.

CD44 is not an adhesive receptor for osteopontin

Osteopontin is a secreted glycoprotein with adhesive and migratory functions. Cellular interactions with osteopontin are mediated through integrin receptors which recognize the RGD domain. Recently, CD44, a non-integrin, multifunctional adhesion molecule was identified as an osteopontin receptor. CD44 is a ubiquitous surface molecule that exists as a number of different isoforms, generated by alternative splicing. To analyze which forms of CD44 mediate binding to osteopontin, we used the standard form of CD44 as CD44-human immunoglobulin fusion proteins and several splice variants in enzyme-linked immunosorbant assays. Multiple preparations of osteopontin were used including native osteopontin derived from smooth muscle cells, human urinary osteopontin, full-length recombinant osteopontin, and two recombinant osteopontin fragments expected to be formed following thrombin cleavage. Our data show that although the CD44-hlg fusion proteins could interact with hyaluronic acid as expected, there was no interaction between CD44H, CD44E, CD44v3,v8-v10, or CD44v3 with osteopontin. These studies suggest that CD44-osteopontin interactions may not be common in vivo and may be limited to a specific CD44 isoform(s), and/or a particular modified form of osteopontin.

Stimulation of CD40 on immunogenic human malignant melanomas augments their cytotoxic T lymphocyte-mediated lysis and induces apoptosis

Here, we report the functional expression of CD40 on human malignant melanomas (MMs). Comparison of tumor specimen from MM precursor lesions, primary tumors, and metastases revealed that CD40 surface expression is down-regulated during tumor progression. CD40 expression was confirmed in 7 human MM cell lines established from immunogenic primary tumors or metastases, whereas 11 cell lines established from advanced stages were CD40 negative. CD40 expression could be enhanced in CD40-positive MM by stimulation with IFN-gamma and tumor necrosis factor-alpha but not by interleukin (IL)-1beta or CD40 triggering. CD40 ligation on MM by CD40L-transfected murine L-cells or by a soluble CD40L fusion protein up-regulated their expression of intercellular adhesion molecule-1 and MHC class I and class II molecules and their secretion of IL-6, IL-8, tumor necrosis factor-a, and granulocyte macrophage colony-stimulating factor and also induced a rapid activation of the transcription factor nuclear factor kappaB. Furthermore, CD40 ligation of a HLA-A2+, MelanA/MART1+ MM cell line enhanced its susceptibility to specific lysis by a HLA-A2-restricted, MelanA/MART-1-specific CTL clone. Finally, CD40 ligation induced growth inhibition and apoptosis in MM. These results indicate that CD40-CD40L interactions may play an important role in augmenting antitumor immunity and inducing apoptosis in some CD40-positive immunogenic human MMs.

Characterization of the heparan sulfate and chondroitin sulfate assembly sites in CD44

Isoforms of CD44 are differentially modified by the glycosaminoglycans (GAGs) chondroitin sulfate (CS), heparan sulfate (HS), and keratan sulfate. GAG assembly occurs at serines followed by glycines (SG), but not all SG are utilized. Seven SG motifs are distributed in five CD44 exons, and in this paper we identify the HS and CS assembly sites that are utilized in CD44. Not all the CD44 SG sites are modified. The SGSG motif in CD44 exon V3 is the only HS assembly site; this site is also modified with CS. HS and CS attachment at that site was eliminated by mutation of the serines in the V3 motif to alanine (AGAG). Exon E5 is the only other CD44 exon that supports GAG assembly and is modified with CS. Using a number of recombinant CD44 protein fragments we show herein that the eight amino acids located downstream of the SGSG site in V3 are responsible for the specific addition of HS to this site. If the eight amino acids located downstream from the first SG site in CD44 exon E5 are exchanged with those located downstream of the SGSG site in exon V3, the SG site in E5 becomes modified with HS and CS. Likewise if the eight amino acids found downstream from the first SG in E5 are placed downstream from the SGSG in V3, this site is modified with CS but not HS. We also show that these sequences cannot direct the modification of CD44 with HS from a distance. Constructs containing CD44 exon V3 in which the SGSG motif was mutated to AGAG were not modified with HS even though they contained other SG motifs. Thus, a number of sequence and structural requirements that dictate GAG synthesis on CD44 have been identified.

Generation of artificial proteoglycans containing glycosaminoglycan-modified CD44. Demonstration of the interaction between rantes and chondroitin sulfate

All CD44 isoforms are modified with chondroitin sulfate (CS), while only those containing variably spliced exon V3 are modified with both CS and heparan sulfate (HS). The CS is added to a serine-glycine (SG) site in CD44 exon E5, while HS and CS are added to the SGSG site in exon V3. Site-directed mutagenesis and other molecular biology techniques were used to determine the minimal motifs responsible for the addition of CS and HS to CD44 (see accompanying paper (Greenfield, B., Wang, W.-C., Marquardt, H., Piepkorn, M., Wolff, E. A., Aruffo, A., and Bennett, K. L. (1999) J. Biol. Chem. 274, 2511-2517)). We have used this information to generate artificial proteoglycans containing the extracellular domain of the cell adhesion protein lymphocyte function-associated antigen-3 (LFA-3) (CD58) and CD44 motifs modified with CS or a combination of CS and HS. Analysis of the CD44-modified LFA-3 protein showed that it retains the ability to engage and trigger the function of its natural ligand CD2, resulting in T cell activation. In addition, the glycosaminoglycan-modified artificial proteoglycan is capable of binding the chemokine RANTES (regulated upon activation, normally T cell expressed and secreted) and delivering it to human T cells, resulting in enhanced T cell activation. These data demonstrate that artificial proteoglycans can be engineered with functional domains that have enhanced activity by codelivering glycosaminoglycan-binding molecules. The artificial proteoglycans were also used as a model system to explore the glycosaminoglycan binding properties of basic-fibroblast growth factor and the chemokine RANTES. While basic-fibroblast growth factor was shown to bind HS alone, this model revealed that RANTES binds not only HS, as has been demonstrated in the past, but also CS. Thus, artificial proteoglycans can be used for studying the glycosaminoglycan binding patterns of growth factors and chemokines and provide a means to manipulate the levels, types, and activity of glycosaminoglycan-binding proteins in vitro and in vivo.

The role of the CD40 pathway in alloantigen-induced hyporesponsiveness in vivo

Resting B (rB) cells are known to be incompetent APCs in vitro, which alone can induce specific unresponsiveness to single minor histocompatibility (miH) Ags and, when combined with CD40 pathway blockade, can induce hyporesponsiveness to MHC molecules in vivo. Here we show that anti-CD40 ligand (CD40L) mAb does not prevent the expression of B7-2 on allogeneic rB cells in vivo but did prolong donor-specific cardiac allograft survival. Moreover, pretreatment with professional APCs combined with anti-CD40L mAb induced hyporesponsiveness to alloantigens in vivo. rB cells from CD40 knockout mice were unable to induce unresponsiveness, while graft prolongation was achieved in CD40L knockout recipients pretreated with wild-type rB cells. These data suggest that CD40-CD40L interactions in the recipient play a critical role in the induction of hyporesponsiveness to alloantigens in vivo and that the effect of the CD40 pathway may be independent of its effect on the B7 costimulatory pathway.

Mutations of the CD40 ligand gene and its effect on CD40 ligand expression in patients with X-linked hyper IgM syndrome

X-linked hyper IgM syndrome (XHIM) is a primary immunodeficiency disorder caused by mutations of the gene encoding CD40 ligand (CD40L). We correlated mutations of the CD40L gene, CD40L expression, and the clinical manifestations observed in XHIM patients from 30 families. The 28 unique mutations identified included 9 missense, 5 nonsense, 9 splice site mutations, and 5 deletions/insertions. In 4 of 9 splice site mutations, normally spliced and mutated mRNA transcripts were simultaneously expressed. RNase protection assay demonstrated that 5 of 17 mutations tested resulted in decreased levels of transcript. The effect of the mutations on CD40L expression by activated peripheral blood mononuclear cells (PBMC) and T-cell lines or clones was assessed using one polyclonal and four monoclonal antibodies and a CD40-Ig fusion protein. In most patients, the binding of at least one antibody but not of CD40-Ig was observed, suggesting nonfunctional CD40L. However, activated PBMC from three patients and activated T-cell lines from two additional patients, each with different genotype, bound CD40-Ig at low intensity, suggesting functional CD40L. Thus, failure of activated PBMC to bind CD40-Ig is not an absolute diagnostic hallmark of XHIM and molecular analysis of the CD40L gene may be required for the correct diagnosis. Patients with genotypes resulting in diminished expression of wild-type CD40L or mutant CD40L that can still bind CD40-Ig appear to have milder clinical consequences.

Filamin binds to the cytoplasmic domain of the beta1-integrin. Identification of amino acids responsible for this interaction

Integrins play an important role in regulating cell adhesion, motility, and activation. In an effort to identify intracellular proteins expressed by activated T cells that interact with the cytoplasmic domain of beta1-integrin (CD29), we used the beta1-integrin cytoplasmic domain as bait in the yeast two-hybrid system. Here we report that the cytoplasmic domain of beta1-integrin specifically interacts with the cytoskeletal protein filamin. This interaction required all but the most carboxyl-terminal three residues of the cytoplasmic domain of beta1, and the carboxyl-terminal 477 residues of filamin containing the terminal 4. 5 approximately 96-residue tandem repeats of filamin. To verify this interaction in vivo, we showed that filamin specifically coprecipitated with beta1 in mammalian cells. We also showed that recombinant filamin chimeric proteins were able to bind to the beta1 cytoplasmic domain in vitro. We observed that a subset of single point mutations in the cytoplasmic domain of beta1, which had been previously reported to impair its function, disrupt the interaction between beta1 and filamin. Taken together, these findings suggest that the interaction between beta1 and filamin, which in turn can bind actin, provides a mechanism for the interaction of this cell surface receptor with cytoskeletal proteins and that this interaction plays a role in normal receptor function.

Transient inhibition of CD28 and CD40 ligand interactions prolongs adenovirus-mediated transgene expression in the lung and facilitates expression after secondary vector administration

Recombinant adenovirus vectors have been used to transfer genes to the lungs in animal models, but the extent and duration of primary transgene expression and the ability to achieve expression after repeated vector administration have been limited by the development of antigen-specific immunity to the vector and, in some cases, to vector-transduced foreign proteins. To determine if focused modulation of the immune response could overcome some of these limitations, costimulatory interactions between T cells and B cells/antigen-presenting cells were transiently blocked around the time of vector administration. Systemic treatment at the time of primary-vector administration with a monoclonal antibody (MR1) against murine CD40 ligand, combined with recombinant murine CTLA4Ig and intratracheal coadministration of an adenovirus vector transducing the expression of murine CTLA4Ig, prolonged adenovirus-transduced beta-galactosidase expression in the airways for up to 28 days and resulted in persistent alveolar expression for >90 days (the duration of the experiment). Consistent with these results, this treatment regimen reduced local inflammation and markedly reduced the T-cell and T-cell-dependent antibody response to the vector. A secondary adenovirus vector, administered >90 days after the last systemic dose of MR1 and muCTLA4Ig, resulted in alkaline phosphatase expression at levels comparable to those seen with primary-vector administration. Expression of the secondary transgene persisted in the alveoli (but not in the airways) for up to 24 days (the longest period of observation) at levels similar to those observed on days 3 to 4. These results indicate that transient inhibition of costimulatory molecule interactions substantially enhanced gene transfer to the alveoli but was much less effective in the airways. This suggests that there are differences in the efficiency or nature of mechanisms limiting transgene expression in the airways and in the alveoli.

Prolonged acceptance of concordant and discordant xenografts with combined CD40 and CD28 pathway blockade

BACKGROUND

The prompt and vigorous immune response to xenogenic tissue remains a significant barrier to clinical xenotransplantation. Simultaneous blockade of the CD28 and CD40 costimulatory pathways has been shown to dramatically inhibit the immune response to alloantigen.

METHODS

. In this study, we investigated the ability of simultaneous blockade of the CD28 and CD40 pathways to inhibit the immune response to xenoantigen in the rat-to-mouse and pig-to-mouse models.

RESULTS

Simultaneous blockade of the CD28 and CD40 pathways produced marked inhibition of the cellular response to xenoantigen in vivo and produced long-term acceptance of xenogeneic cardiac and skin grafts (rat-to-mouse), and markedly suppressed an evoked antibody response to xenoantigen. In addition, this strategy significantly prolonged the survival of pig skin on recipient mice.

CONCLUSIONS

Long-term hyporesponsiveness to xenoantigen across both a concordant and discordant species barrier, measured by the stringent criterion of skin grafting, can be achieved using a noncytoablative treatment regimen.

Analysis of the ligand binding site in Fas (CD95) by site-directed mutagenesis and comparison with TNFR and CD40

Fas and its ligand (FasL) are members of the tumor necrosis factor receptor (TNFR) and tumor necrosis factor (TNF) superfamilies, respectively. Fas-FasL interactions trigger controlled cell death (apoptosis) in the immune system and thus play a key role in the regulation of immune responses. Structural details of the Fas-Fas ligand interaction are currently unknown. Previously, six Fas residues were identified by mutagenesis as important for ligand binding. We have now extended our mutagenesis analysis and identified additional residues which contribute to the Fas-FasL interaction. Candidate and control residues were selected based on a molecular model of the Fas extracellular region. Although residues in all three extracellular domains were identified to contribute to binding, the Fas-FasL interaction is centered on the second TNFR-like domain. Important residues were compared to critical positions in TNFR and CD40, another member of the TNFR family.

Amplification of tumor immunity by gene transfer of the co-stimulatory 4-1BB ligand: synergy with the CD28 co-stimulatory pathway

We have explored the role of an activation-induced T cell molecule, 4-1BB (CDw137), in the amplification of tumor immunity by retrovirus-mediated transduction of the 4-1BB ligand (4-1BBL) into tumor cells. Mice inoculated with P815 tumor cells expressing 4-1BBL developed a strong cytotoxic T lymphocyte (CTL) response and long-term immunity against wild-type tumor. The optimal effect of 4-1BBL in CTL stimulation required B7-CD28 interaction since blockade of this interaction by antibodies down-regulated the expression of 4-1BB on T cells and decreased CTL activity. Furthermore, co-expression of 4-1BBL and B7-1 in the poorly immunogenic AG104A sarcoma enhanced the induction of effector CTL and the rejection of the wild-type tumor while neither 4-1BBL nor B7-1 single transfectants were effective, suggesting a synergistic effect between the 4-1BB and the CD28 co-stimulatory pathways. Our results underscore the importance of the 4-1BB T cell stimulation pathway in the amplification of an antitumor immune response.

Diminished expression of CD40 ligand may contribute to the defective humoral immunity in patients with MHC class II deficiency

Major histocompatibility complex (MHC) class II deficiency (bare lymphocyte syndrome, BLS) is a rare primary immunodeficiency classified as a subgroup of severe combined immunodeficiency. We studied T and B lymphocyte function by examining the CD40 ligand/CD40 system in three BLS patients from two unrelated families. CD40 ligand expression by maximally activated BLS T cells was diminished. This abnormality may represent immunological naïveté rather than a general T cell defect, since expression of activation marker CD69 and proliferative responses to PHA or anti-CD3 were normal, and BLS T cells primed and restimulated in vitro expressed normal amounts of CD40 ligand. BLS B cells proliferated and produced IgE if stimulated with anti-CD40 or soluble CD40 ligand and IL-4. Activation of BLS B cells with soluble CD40 ligand and IL-4 induced normal expression of activation markers, although MHC class II expression remained absent. Depressed antibody titers, lack of amplification and failure to undergo isotype switching in response to immunization with bacteriophage phi x 174 demonstrated defective T cell help. We conclude that BLS B cells are functionally normal if appropriately stimulated, and that the defective humoral immunity observed may be related to diminished expression of CD40 ligand on BLS T cells.

Agonistic activity of a CD40-specific single-chain Fv constructed from the variable regions of mAb G28-5

A single-chain Fv (sFv) was expressed from the variable regions of the CD40-specific mAb G28-5. The molecule bound CD40 with a high affinity (2.2 nM) and was a monomer in solution. Surprisingly, G28-5 sFv was a potent CD40 agonist that rapidly crosslinked CD40 on the cell surface but did not crosslink CD40-Ig in solution. G28-5 sFv was a more potent agonist than G28-5 IgG and was able to stimulate CD40 responses by B cells and monocytes. G28-5 IgG partially blocked, whereas G28-5 sFv augmented CD40 responses during stimulation with natural ligand (gp39-CD8 fusion protein). These results indicate that the functional activity of ligands built from the binding site of G28-5 is highly dependent upon the size and physical properties of the molecule both in solution and on the cell surfaces.

Identification of CD44 residues important for hyaluronan binding and delineation of the binding site

CD44 is a widely distributed cell surface protein that plays a role in cell adhesion and migration. As a proteoglycan, CD44 is also implicated in growth factor and chemokine binding and presentation. The extracellular region of CD44 is variably spliced, giving rise to multiple CD44 isoforms. All isoforms contain an amino-terminal domain, which is homologous to cartilage link proteins. The cartilage link protein-like domain of CD44 is important for hyaluronan binding. The structure of the link protein domain of TSG-6 has been determined by NMR. Based on this structure, a molecular model of the link-homologous region of CD44 was constructed. This model was used to select residues for site-specific mutagenesis in an effort to identify residues important for ligand binding and to outline the hyaluronan binding site. Twenty-four point mutants were generated and characterized, and eight residues were identified as critical for binding or to support the interaction. In the model, these residues form a coherent surface the location of which approximately corresponds to the carbohydrate binding sites in two functionally unrelated calcium-dependent lectins, mannose-binding protein and E-selectin (CD62E).

Protein superfamily members as targets for computer modeling: the carbohydrate recognition domain of a macrophage lectin

Members of protein superfamilies display similar folds, but share only limited sequence identity, often 25% or less. Thus, it is not straightforward to apply standard homology modeling methods to construct reliable three-dimensional models of such proteins. A three-dimensional model of the carbohydrate recognition domain of the rat macrophage lectin, a member of the calcium-dependent (C-type) lectin superfamily, has been generated to illustrate how information provided by comparison of X-ray structures and sequence-structure alignments can aid in comparative modeling when primary sequence similarities are low.

Analysis of the tyrosine phosphorylation and calcium fluxing of human CD6 isoforms with different cytoplasmatic domains

CD6 is a cell surface glycoprotein that functions both as a co-stimulatory and adhesion receptor on T cells. Recently we have described CD6 isoforms (CD6a, b, c, d, e) that arise via alternative splicing of exons encoding the cytoplasmic region of the molecule. CD6 becomes phosphorylated on tyrosine (Tyr) residues following stimulation through the T cell receptor (TCR) complex. Since the phosphorylation of Tyr residues renders some cell surface receptors competent for interactions with proteins of intracellular signaling pathways, we wanted to determine which region(s) and residues in the cytoplasmic domain of CD6 were important for phosphorylation on Tyr residues. We engineered and stably expressed chimeric receptors that consisted of the extracellular region of mouse CD6 and the cytoplasmic regions of either naturally occurring isoforms of human CD6, truncated proteins, or point mutants. We were able to demonstrate that of the nine Tyr residues in the cytoplasmic domain of the largest isoform CD6a, the two C-terminal Tyr residues (Tyr 629/662) are critical for the phosphorylation of CD6 following TCR cross-linking. Isoform CD6e, which is missing a region that contains two proline-rich motifs, is not phosphorylated. We further analyzed the ability of the different CD6 isoforms and truncated receptors to mobilize intracellular calcium after CD6/TCR co-ligation. All CD6 isoforms, including CD6e, as well as the truncation mutant delta 555, which is missing approximately the C-terminal half of the cytoplasmic domain, are able to increase Ca2+ influx. Taken together, these results suggest that the region of CD6 which is critical for Ca2+ mobilization is located N-terminal from amino acid 555 and is therefore different from the region located at the C terminus of CD6, which is necessary for tyrosine phosphorylation.

Deleted in colorectal carcinoma (DCC) binds heparin via its fifth fibronectin type III domain

DCC (deleted in colorectal carcinoma) is a broadly expressed cell-surface receptor. Netrin-1 was recently identified as a DCC ligand in brain, but the possibility of other DCC ligands was suggested by the finding that an anti-DCC antibody (clone AF5) neutralized netrin-1-dependent commissural axon outgrowth without blocking DCC/netrin-1 interactions. Here we have searched for alternative cell-surface DCC ligands. A DCC-Ig fusion protein bound to neural and epithelial derived cell lines, indicating that these lines express ligand(s) for DCC. The cell-surface binding activity was mediated by the loop between beta-strands F and G of the fifth fibronectin type III repeat FNIII-D5. The loop included the sequence KNRR, which resembles heparin-binding motifs in other proteins. Heparinase and heparitinase treatment of cells reduced binding of DCC-Ig, suggesting that heparan sulfate proteoglycans are cell-surface DCC ligand(s). This was further supported by heparin blocking experiments and by binding of DCC-Ig to immobilized heparan sulfate. The interaction between DCC-Ig and heparan sulfate/heparin, both on the surface of cells and immobilized on plastic, was blocked by the same anti-DCC antibody that blocks netrin-1-dependent commissural axon outgrowth. Taken together, these findings suggest that the DCC-Ig/heparin interaction may contribute to the biological activity of DCC.

Chondroitin sulphate composition and structure in alternatively spliced CD44 fusion proteins

Previous studies have indicated that CD44 isoforms, spliced with variant exons, are heterogeneously glycanated with chondroitin sulphate and heparan sulphate chains. Because such alternative splicing may regulate divergent biological effects of the specific isoforms, we analysed the consequences of this process on the composition and structure of the chondroitin-sulphate chains. Recombinant chimaeras were engineered with and without exons V3-10 or V3,8-10 and expressed as Ig fusion proteins in COS cells. In addition, the chondroitin sulphates of wild-type isoforms were contrasted with those of isoforms mutated with serine-to-alanine codon substitutions at a putative Ser-Gly-Ser-Gly glycosaminoglycan acceptor site within exon V3. The chondroitin sulphates contained both 4- and 6-sulphated galactosamine residues, although there was a high content of non-sulphated galactosamine-containing repeat units. Splicing of exons V4-7, which contain no Ser-Gly consensus motifs, resulted in increased glycanation with chondroitin-sulphate chains, as well as increased sulphation levels of the polymers. Comparison of wild-type and acceptor-site mutant isoforms showed that chondroitin-sulphate content declined by more than 60-80% in the mutant, indicating that assembly of chondroitin-sulphate chains occurs there, and a general decrease in the sulphation level of the remaining chains was observed. Undersulphation of the recombinant chondroitin sulphates was shown by parallel analyses with native human keratinocyte CD44 molecules and is most probably an artifact of transient expression in COS cells. Our data indicate that combinatorial exon splicing exerts complex and distal effects on glycanation patterns and structure, which presumably modulate those functions that may be mediated though the chondroitin-sulphate moieties, such as motility and matrix invasion.

CD6-ligand interactions: a paradigm for SRCR domain function?

The scavenger receptor cysteine-rich (SRCR) superfamily, which includes proteins expressed by leukocytes, can be subdivided into groups A and B. Group B contains the lymphocyte cell-surface receptor CD6. This article reviews recent progress in understanding the interaction between CD6 and its ligand, activated leukocyte cell adhesion molecule (ALCAM). Analysis of the CD6-ALCAM interaction may help to understand how other SRCR domains bind to their ligands.

Wiskott-Aldrich syndrome/X-linked thrombocytopenia: WASP gene mutations, protein expression, and phenotype

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT), caused by mutations of the WAS protein (WASP) gene, represent different phenotypes of the same disease. To demonstrate a phenotype/genotype correlation, we determined WASP gene mutations in 48 unrelated WAS families. Mutations included missense (20 families) and nonsense (eight) mutations located mostly in exons 1 to 4, and splice-site mutations (seven) and deletions and insertions (13) located preferentially in exons 7 to 11. Both genomic DNA and cDNA were sequenced and WASP expression was measured in cell lysates using peptide-specific rabbit anti-WASP antibodies. WASP was expressed in hematopoietic cell lines including bone marrow-derived CD34+ cells. Missense mutations located in exons 1 to 3 caused mild disease in all but one family and permitted WASP expression, although frequently at decreased concentration. Missense mutations affecting exon 4 were associated with classic WAS and, with one exception, barely detectable WASP. Nonsense mutations caused classic WAS and lack of protein. Insertions, deletions, and splice-site mutations resulted in classic WAS and absent, unstable, truncated, or multiply spliced protein. Using affinity precipitation, WASP was found to bind to Src SH3-containing proteins Fyn, Lck, PLC-gamma, and Grb2, and mutated WASP, if expressed, was able to bind to Fyn-glutathione S-transferase (GST) fusion protein. We conclude that missense mutations affecting the PH domain (exons 1 to 3) of WASP inhibit less important functions of the protein and result in a mild phenotype, and that missense mutations affecting exon 4 and complex mutations affecting the 3' portion of WASP interfere with crucial functions of the protein and cause classic WAS.

Sulfated galactocerebrosides as potential antiinflammatory agents

Native sulfatides, as well as many sulfated glycolipids, have been shown to avidly bind to the selectin receptors. In vivo, native sulfatides significantly block activity in selectin-dependent inflammatory responses. The fact that nonsulfated galactocerebrosides did not inhibit selectin-mediated adhesion identified a critical role for the anionic sulfate residue. We therefore initiated a program to evaluate the activity of position isomers. This study showed a binding selectivity for the positions 2 and 3 of the sulfate group on the carbohydrate ring as well as enhanced activity for the disulfated analogs. Furthermore, it was discovered that the attachment of lipophilic substituents on the carbohydrate ring was tolerated, consistent with the presence of a lipophilic pocket in the binding activity. This resulted in compounds with a 6-fold increased potency.

BMS-190394, a selectin inhibitor, prevents rat cutaneous inflammatory reactions

Selectin binding is the first step in extravasation of leukocytes through the endothelium. Infiltration of leukocytes is a hallmark of an inflammatory response. Blockade of selectin-dependent adhesion, therefore, represents a specific mechanism-based anti-inflammatory strategy. We have used the natural product sulfatide, one of the selectin ligands, as a template to design a novel selectin antagonist. BMS-190394, a structural analog of sulfatide, is an inhibitor of cell binding to P-, E- and L-selectin-Ig fusion proteins. BMS-190394 also inhibits binding mediated by native P-selectin expressed on the surface of activated platelets. Pharmacokinetic analysis of BMS-190394 showed that the compound remained in circulation with a T1/2 of 7 hr, long enough to inhibit the development of an acute inflammatory response. The in vitro activity and pharmacokinetic profile of this selectin-blocking compound led to the determination of its in vivo anti-inflammatory activity. BMS-190394 was a potent inhibitor of the dermal immune complex-induced reverse passive Arthus reaction in rats when delivered by the i.v. or i.p. route. The ED50 of the compound in the reverse passive Arthus reaction compares favorably to that for dexamethasone. BMS-190394 was also an effective inhibitor of the delayed-type hypersensitivity reaction in the rat. Compared with previous reports of the use of antibodies and complex oligosaccharides to inhibit the activity of the selectins, this low-molecular-weight inhibitor of the selectins presents a novel class of anti-inflammatory agents.

Mutational analysis of the CD6 ligand binding domain

CD6 belongs to the scavenger receptor cysteine-rich protein superfamily (SRCRSF), which includes a large number of cell surface proteins. The extracellular region of CD6 is composed of three SRCR domains. The membrane proximal SRCR domain of CD6 (CD6D3) specifically binds activated leukocyte cell adhesion molecule (ALCAM), a cell surface protein which is a member of the immunoglobulin superfamily (IgSF). CD6-ligand interactions have been implicated in immune cell adhesion, T cell maturation and the regulation of T cell activation. We tested 13 CD6D3 mutant proteins for binding to ALCAM and a panel of conformationally sensitive anti-CD6D3 monoclonal antibodies (mAbs). CD6D3 residues were classified according to their importance for structural integrity and ligand binding. The results were analyzed in the light of SRCR domain sequence comparison. A number of residues critical for ligand binding or important for structural integrity cluster in the C-terminal region of CD6D3 which is not conserved in other SRCR proteins.

CD6 recognizes the neural adhesion molecule BEN

CD6 and its ligand activated leukocyte cell adhesion molecule (ALCAM, CD166) have been detected on various immune cells and in the brain. CD6-ligand interactions have been implicated in the regulation of T cell function. ALCAM shares the same extracellular domain organization and significant sequence homology with the chicken neural adhesion molecule BEN. Although ALCAM's CD6 binding site is only partially conserved in BEN, CD6 specifically binds BEN, albeit with approximately 10-fold lower avidity than ALCAM. Differences in binding avidity are not detected when ALCAM and BEN fusion proteins containing the full-length extracellular regions are tested. Homotypic interactions between full-length forms are likely to account for these observations. The identified cross-species interaction between CD6 and BEN suggests that CD6-ligand interactions are highly conserved.

Thymus dysfunction and chronic inflammatory disease in gp39 transgenic mice

Expression of gp39 on activated T cells provides a co-stimulatory signal in peripheral lymphoid tissue that regulates humoral and cell-mediated immunity. The function of gp39 and its receptor CD40 in thymus remains uncertain. Here we report that overexpression of gp39 in transgenic mouse thymus caused a dose-dependent decline in thymocyte numbers (> 500 fold), loss of cortical epithelium and expansion of CD40+ medullary cells. Transplantation of transgenic bone marrow into normal mice indicated that gp39 significantly diminished thymocyte viability in the context of a 'normal' thymic environment. The peripheral tissues of transgenic mice also accumulated abnormalities in a transgene dose-dependent manner that involved inflammation and lymphoid tissue hypertrophy. Animals with the highest transgene copy numbers acquired a lethal inflammatory bowel disease marked by the infiltration of gp39+ T cells and CD40+ cells into diseased tissues. Examination of cells overexpressing gp39 suggested that these defects were caused, in part, by the saturation of a mechanism that sequesters gp39 inside non-activated cells and thus protects the immune system from inappropriate gp39-CD40 interaction. These results establish a regulatory role for gp39 in thymus function and a causal relationship in mediating chronic inflammatory disease.

4-1BB costimulatory signals preferentially induce CD8+ T cell proliferation and lead to the amplification in vivo of cytotoxic T cell responses

The 4-1BB receptor is an inducible type I membrane protein and member of the tumor necrosis factor receptor (TNFR) superfamily that is rapidly expressed on the surface of CD4+ and CD8+ T cells after antigen- or mitogen-induced activation. Cross-linking of 4-1BB and the T cell receptor (TCR) on activated T cells has been shown to deliver a costimulatory signal to T cells. Here, we expand upon previously published studies by demonstrating that CD8+ T cells when compared with CD4+ T cells are preferentially responsive to both early activation events and proliferative signals provided via the TCR and 4-1BB. In comparison, CD28-mediated costimulatory signals appear to function in a reciprocal manner to those induced through 4-1BB costimulation. In vivo examination of the effects of anti-4-1BB monoclonal antibodies (mAbs) on antigen-induced T cell activation have shown that the administration of epitope-specific anti-4-1BB mAbs amplified the generation of H-2d-specific cytotoxic T cells in a murine model of acute graft versus host disease (GVHD) and enhanced the rapidity of cardiac allograft or skin transplant rejection in mice. Cytokine analysis of in vitro activated CD4+ and CD8+ T cells revealed that anti-4-1BB costimulation markedly enhanced interferon-gamma production by CD8+ T cells and that anti-4-1BB mediated proliferation of CD8+ T cells appears to be IL-2 independent. The results of these studies suggest that regulatory signals delivered by the 4-1BB receptor play an important role in the regulation of cytotoxic T cells in cellular immune responses to antigen.

Monoclonal antibodies against the 4-1BB T-cell activation molecule eradicate established tumors

The 4-1BB glycoprotein is a member of the tumor necrosis factor receptor superfamily and binds to a high-affinity ligand (4-1BBL) expressed on several antigen-presenting cells such as macrophages and activated B cells. Expression of 4-1BB is restricted to primed CD4+ and CD8+ T cells, and 4-1BB signaling either by binding to 4-1BBL or by antibody ligation delivers a dual mitogenic signal for T-cell activation and growth. These observations suggest an important role for 4-1BB in the amplification of T cell-mediated immune responses. We now show that administration of anti-4-1BB monoclonal antibodies can eradicate established large tumors in mice, including the poorly immunogenic Ag104A sarcoma and the highly tumorigenic P815 masto cytoma. The immune response induced by anti-4- 1BB monoclonal antibodies is mediated by both CD8+ and CD4+ T cells and is accompanied by a marked augmentation of tumor-selective cytolytic T-cell activity. Our data suggest that a similar approach may be efficacious for immunotherapy of human cancer.

Characterization of mouse ALCAM (CD166): the CD6-binding domain is conserved in different homologs and mediates cross-species binding

Activated leukocyte cell adhesion molecule (ALCAM; CD166) is a member of the immunoglobulin gene superfamily (IgSF) which is expressed by activated leukocytes and thymic epithelial cells and is a ligand for the lymphocyte antigen CD6. Herein, we report on the isolation and characterization of cDNA clones encoding mouse ALCAM (mALCAM). Comparison of the predicted amino acid sequence of mALCAM and human ALCAM (hALCAM) showed an overall identity of 93%. Binding studies with truncated forms of the extracellular region of mALCAM showed that the CD6 binding site is located in the N-terminal Ig-like domain and that mALCAM is capable of binding both human and mouse CD6. Mutagenesis studies on hALCAM suggested that residues critical for CD6 binding map to the predicted A'GFCC'C" beta-sheet of ALCAM's N-terminal binding domain. Residue differences in the N-terminal domains of mALCAM and hALCAM were analyzed with the aid of a molecular model of ALCAM. All residues critical for CD6 binding are conserved in both mALCAM and hALCAM, whereas residue differences map to the predicted BED face which is opposite the CD6 binding site on hALCAM. These findings provide a molecular rationale for the observed cross-species CD6/ALCAM interaction and the apparent inability to generate monoclonal antibodies (mAb) against the CD6 binding site. RNA blot analysis showed that mRNA transcripts encoding mALCAM are expressed in the brain, lung, liver, and the kidney, as well as by activated leukocytes and a number of cell lines. A rat mAb specific for mALCAM was produced and by two-color immunofluorescence studies was shown to bind to both activated CD4+ and CD8+ T cells.

Transient immunomodulation with anti-CD40 ligand antibody and CTLA4Ig enhances persistence and secondary adenovirus-mediated gene transfer into mouse liver

Although recombinant adenovirus vectors offer a very efficient means by which to transfer genetic information into cells in vivo, antigen-dependent immunity limits the duration of gene expression and prevents retreatment. Recombinant murine CTLA4Ig and anti-CD40 ligand antibody block costimulatory interactions between T cells and antigen presenting cells. We previously reported that murine CTLA4Ig prolongs adenoviral-mediated gene transfer, but does not allow for secondary expression after readministration of the vector. In studies described here, when anti-CD40 ligand and recombinant murine CTLA4Ig were coadministered around the time of primary vector administration (i) prolonged adenovirus-mediated gene expression (length of experiment up to 1 year) from the livers of >90% of treated mice was observed, and (ii) secondary adenovirus-mediated gene transfer was achieved in >50% of the mice even after the immunosuppressive effects of these agents were no longer present. Nearly two-thirds of these mice had persistent secondary gene expression lasting for at least 200-300 days. Neither agent alone allowed transduction after secondary vector administration. Treated mice had decreased immune responses to the vector as shown by markedly decreased production of neutralizing antibodies, diminished spleen proliferation responses and IFN-gamma production in vitro, and reduced T cell infiltrates in the liver. These results suggest that it may be possible to obtain persistence as well as secondary adenoviral-mediated gene transfer with transient immunosuppressive therapies.

Identification of amino acid residues important for ligand binding to Fas

The interaction of Fas (CD95), a member of the tumor necrosis factor receptor (TNFR) family, and its ligand (FasL) triggers programmed cell death (apoptosis) and is involved in the regulation of immune responses. Although the Fas-FasL interaction is conserved across species barriers, little is currently known about the molecular details of this interaction. Our aim was to identify residues in Fas that are important for ligand binding. With the aid of a Fas molecular model, candidate amino acid residues were selected in the Fas extracellular domain 2 (D2) and D3 and subjected to serine-scanning mutagenesis to produce mutant Fas molecules in the form of Ig fusion proteins. The effects of these mutations on FasL binding was examined by measuring the ability of these proteins to inhibit FasL-mediated apoptosis of Jurkat cells and bind FasL in ELISA and BIAcore assays. Mutation of two amino acids, R86 and R87 (D2), to serine totally abolished the ability of Fas to interact with its ligand, whereas mutants K84S, L90S, E93S (D2), or H126S (D3) showed reduced binding compared with wild-type Fas. Two mutants (K78S and H95S) bound FasL comparably to wild type. Therefore, the binding of FasL involves residues in two domains that correspond to positions critical for ligand binding in other family members (TNFR and CD40) but are conserved between murine and human Fas.

Isolation and structure determination of sulfonoquinovosyl dipalmitoyl glyceride, a P-selectin receptor inhibitor from the alga Dictyochloris fragrans

Bioassay-guided fractionation of the marine alga Dictyochloris fragrans led to the isolation and identification of sulfonoquinovosyl dipalmitoyl glyceride (1). The structure of 1 was determined by a combination of spectroscopic methods. On the basis of P-selectin inhibition assays (i.e., P-selectin-IgG ELISA, cell binding assay of receptor globulin, and platelet:HL60 adhesion, it was demonstrated that 1 selectively blocks the P-selectin-ligand interaction in vitro and could be considered a lead compound for synthetic modification in order to design more potent inhibitors of cell adhesion processes that play important roles in development of inflammatory-mediated disease states.

Identification of the tumor antigen 90K domains recognized by monoclonal antibodies SP2 and L3 and preparation and characterization of novel anti-90K monoclonal antibodies

The tumor antigen 90K (Mac-2BP, L3 antigen), which has been shown to have T cell costimulatory activity, is a approximately 90 kDa secreted protein found in high levels in plasma, saliva, breast milk and other human fluids. The 90K antigen can be divided into three domains: an amino terminal scavenger receptor cysteine-rich (SRCR)-like domain (D1), followed by a heavily glycosylated mucin-like domain (D2) and a approximately 27 kDa carboxy-terminal domain (D3). In this study we report on the construction of six different 90K immunoglobulin (Ig) fusion proteins containing different 90K domain combinations. Initially these fusion proteins were used to identify which 90K domain contains the epitopes recognized by the anti-90K monoclonal antibodies (mAb) SP2 and L3. Both of these mAbs were found to recognize 90K-D2. A new panel of anti-90K mAb was then generated by immunizing mice with ascites derived 90K protein. The 90K domain specific fusion proteins were then used to identify novel anti-90K mAbs which recognize the amino terminal SRCR domain and the carboxy terminal approximately 27 kDa domain of 90K. Two novel anti-90K SRCR (D1) and one anti-90 27 kDa domain (D3) mAbs were obtained. These 90K-Ig fusion proteins, as well as the novel and existing anti-90K mAbs, provide a set of tools which will allow further dissection of the structure and function of this immune modulatory protein.

Analysis of 4-1BBL and laminin binding to murine 4-1BB, a member of the tumor necrosis factor receptor superfamily, and comparison with human 4-1BB

The T cell activation antigen 4-1BB (CDw137) is a distantly related member of the tumor necrosis factor receptor family of cell surface receptors. We previously reported that murine 4-1BB (m4-1BB) bound to extracellular matrix (ECM) proteins. Recently, a tumor necrosis factor-like ligand of m4-1BB, m4-1BBL, as well as the human counterparts of 4-1BB (ILA) and 4-1BBL (h4-1BB and h4-1BBL, respectively) have been cloned. No information is currently available on how binding of m4-1BB to ECM proteins affects its binding to m4-1BBL and vice versa and if the ability of m4-1BB to bind ECM proteins is conserved across species. We report that binding of m4-1BBL to m4-1BB blocked its ability to bind laminin (LN), while binding of m4-1BB to LN did not block its ability to bind m4-1BBL. Furthermore, binding of m4-1BBL to the m4-1BB.LN complex did not displace LN. These findings suggest the two ligands bind to proximal but distinct sites on m4-1BB. This is supported by the observation that six of eight anti-m4-1BB monoclonal antibodies blocked the interaction between 4-1BB and 4-1BBL, while seven blocked LN binding. Ligand and monoclonal antibody binding studies with a truncated protein lacking the amino-terminal LN-homologous domain of m4-1BB demonstrated that regions downstream of the LN-homologous domain participate in LN binding and that the intact protein is required for m4-1BBL binding. Studies with h4-1BB showed that h4-1BB only bound h4-1BBL, indicating that the ECM binding activity of 4-1BB is not conserved across species. This finding allowed the construction of murine/human 4-1BB chimeras, which permitted further dissection of the regions of 4-1BB involved in LN and 4-1BBL binding and suggests that sequence differences in the LN-homologous domain of h4-1BB in part account for the inability of h4-1BB to bind ECM proteins.