Search PubMed⌕ Search

Biomedical subjects

D A Cheresh

Publications and source records attributed to D A Cheresh.

At least 127 records · Page 7Linked to original sources
PubMed1989

Functional properties and effect on growth suppression of human neuroblastoma tumors by isotype switch variants of monoclonal antiganglioside GD2 antibody 14.18.

A complete family of IgG isotype switch variant hybridomas was generated from the anti-GD2 monoclonal IgG3-producing hybridoma, 14.18, with the aid of the fluorescence-activated cell sorter. The IgG1, IgG2b, and IgG2a monoclonal antibodies (Mabs) produced by respective isotype switch variant hybridomas 14G1, 14G2b, or 14G2a, have binding activities for the biochemically defined GD2 antigen and GD2-expressing neuroblastoma target cell lines identical to that of IgG3 Mabs produced by the 14.18 parent cell line. This permitted us to examine the relative in vitro and in vivo cytotoxic capacities of each of the anti-GD2 antibodies for GD2-expressing neuroblastoma cells independent of antibody binding affinity or specificity. Mabs produced by 14.18, 14G2a, or 14G2b, but not 14G1, can direct efficient complement-dependent cytotoxicity against neuroblastoma tumor cells in the presence of human complement. Mabs produced by the parent 14.18 or by 14G2a are more efficient in directing antibody-dependent cell-mediated cytotoxicity than Mabs produced by 14G2b, and Mabs of 14G1 are inactive. However, despite these noted in vitro differences, antibodies produced by each member of this switch variant family suppress the growth of human neuroblastoma tumor cells in BALB/c athymic nu/nu mice. These studies suggest that a mechanism(s) other than Fc-directed complement-dependent cytotoxicity or antibody-dependent cell-mediated cytotoxicity may account for the in vivo antitumor effects of these particular antibodies.

Animals↗
PubMed1989

A novel vitronectin receptor integrin (alpha v beta x) is responsible for distinct adhesive properties of carcinoma cells.

Carcinoma cells express a novel integrin involved in cell adhesion to vitronectin, but not to fibrinogen or von Willebrand factor, whereas melanoma and endothelial cells express a vitronectin receptor (alpha v beta 3) that promotes cell attachment to all of these matrix components. The integrin responsible for this adhesive phenotype of carcinoma cells is composed of an alpha subunit that is indistinguishable from the alpha v of the vitronectin receptor and a beta subunit (beta x) that is distinct from any known integrin beta subunit. Accordingly, Northern blot analysis identifies an mRNA for alpha v, but not for beta 3 in carcinoma cells. This receptor appears to mediate cell adhesion to vitronectin as well as fibronectin since an antibody directed to its alpha subunit blocked carcinoma cell adhesion to both of these matrix proteins. These results suggest that homologous integrins with identical alpha subunits and structurally distinct beta subunits can account for the functional recognition of different matrixes by two cell types.

Adenocarcinoma↗
PubMed1989

Isolation and characterization of a platelet membrane protein related to the vitronectin receptor.

Glycoprotein IIb-IIIa is the most prominent Arg-Gly-Asp (RGD)-binding adhesion receptor on platelets. By affinity chromatography on an immobilized RGD peptide, we have investigated the possible existence of other platelet-associated adhesion receptors that bind RGD peptides. When an octyl glucoside extract of surface-radioiodinated platelets was applied to an affinity matrix of KYGRGDS-coupled Sepharose 4B, a 160-kDa-labeled protein (P160) and GPIIb-IIIa bound and were specifically eluted by soluble GRGDSP peptide, but not by the variant GRGESP peptide. Furthermore, a dodecapeptide corresponding to fibrinogen gamma 400-411 eluted only GPIIb-IIIa but not P160 from the RGD affinity matrix. Characterization of P160 by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by the O'Farrell gel electrophoresis system indicated that P160 is a component of platelet GPIc. GoH3, a monoclonal antibody recognizing the alpha subunit of the very late antigen-6, failed to immunoprecipitate P160 from the RGD eluate, indicating that it did not contain the very late antigen-6 alpha subunit. In immunoblots, P160 reacted specifically with a polyclonal anti-peptide antibody recognizing the alpha subunit of the vitronectin receptor (VnR), but not with the monoclonal anti-GPIIb antibody PMI-1, suggesting that P160 is the alpha subunit of platelet VnR. This possibility was further substantiated by the complete identity between the determined amino-terminal sequence of P160 and the known sequence of the VnR alpha subunit. Moreover, direct association of P160 with a beta subunit having an apparent molecular weight similar to that of GPIIIa was demonstrated by immunoprecipitation with LM609, an anti-VnR complex monoclonal antibody. These results indicate that the VnR complex is present on platelets and may play a functional role in platelet adhesive reactions.

Amino Acid Sequence↗
PubMed1989

RGD-dependent linkage between plant cell wall and plasma membrane: consequences for growth.

Soybean (Glycine max [L.] Merr. cv. Mandarin) root cells (SB-1 cell line) grown in suspension culture containing Glycyl-Arginyl-Glycyl-Aspartyl-Seryl-Proline (GRGDSP) (0.25 mg/ml), a synthetic peptide containing the RGD sequence found in many extracellular matrix adhesive proteins, demonstrated (a) significantly enhanced growth rate, and (b) aberrant cell wall/plasma membrane interactions and organization. Substitution of the Asp (D) by a Glu (E) amino acid in the hexapeptide, or inversion of the RGD sequence to GDR, abolished the morphological and growth effects observed for GRGDSP in plant cells. Immunoblots, which were prepared from beta-octylglucoside extracts of whole soybean cells and protoplasts, probed with polyclonal antibodies raised against human vitronectin receptor (hVNR) complex, demonstrated a single band with an apparent molecular mass of 70-72 kD. Chromatography of beta-octylglucoside extracts of SB-1 cells on a Gly-Arg-Gly-Asp-Ser-Pro-Lys-Sepharose affinity column demonstrated the retention of a single 70-72 kD polypeptide that reacted specifically with anti-hVNR antiserum. In contradistinction, no cross-reactivity was observed with antifibronectin receptor antiserum. Epifluorescence microscopy of whole soybean cells, after moderate treatment with pectinase, demonstrated punctate fluorescent patches at the cell membrane/wall boundary when probed with anti-hVNR and rhodamine-derivatized secondary antibodies. We propose that coordination and control of plant cell division and proper cell wall biosynthesis may be mediated by an RGD-dependent recognition system in which RGD binding protein(s) promote cell membrane-cell wall attachment.

Amino Acid Sequence↗
PubMed1989

Human melanoma cell attachment involves an Arg-Gly-Asp-directed adhesion receptor and the disialoganglioside GD2.

The disialogangliosides GD2 and GD3 play a major role in the ability of human melanoma cells to attach to Arg-Gly-Asp-containing substrates such as fibronectin and vitronectin, since pretreatment of these cells with monoclonal antibodies to the oligosaccharide of GD2 and GD3 can inhibit their attachment and spreading on such adhesive proteins. This report demonstrates that human melanoma cells (M21) synthesize and express a glycoprotein receptor that shares antigenic epitopes with the vitronectin receptor on human fibroblasts and is capable of specifically recognizing the Gly-Arg-Gly-Asp-Ser-Pro sequence. Biochemical evidence is presented indicating that the vitronectin receptor on M21 human melanoma cells contains associated calcium and GD2. This ganglioside copurified with the glycoprotein receptor for vitronectin on affinity columns containing either an Arg-Gly-Asp-containing peptide, Concanavalin A, or lentil lectin. This major Arg-Gly-Asp-directed receptor on M21 cells could be metabolically labeled with 45Ca++. Chelation of this ion with EDTA caused the dissociation of GD2 from the receptor and rendered the remaining glycoprotein incapable of binding to an Arg-Gly-Asp containing peptide. Reconstitution experiments demonstrated a requirement for calcium and not magnesium for receptor binding to Arg-Gly-Asp and indicated that addition of ganglioside can enhance this interaction.

Amino Acid Sequence↗
PubMed1988

The Arg-Gly-Asp binding domain of the vitronectin receptor. Photoaffinity cross-linking implicates amino acid residues 61-203 of the beta subunit.

We have employed photoaffinity cross-linking to examine RGD recognition by the human placental vitronectin receptor. The peptide GRGDSPK was coupled to a thiol-cleavable radioiodinatable aryl azide (sulfosuccinimidyl 2-(p-azido-salicylamido)-1,3'-dithiopropionate. When 125I-sulfosuccinimidyl 2-(p-azido-salicylamido)-1,3'-dithiopropionate-GRGDSPK was cross-linked to the vitronectin receptor in solution, 80% of the label was associated with the beta subunit. Cross-linking to both subunits of the receptor was highly specific and dependent upon the presence of divalent cations. Ca2+ and Mg2+ promoted RGD recognition by the receptor; however, the effects of each divalent cation were kinetically distinct. We have also identified and determined the amino acid sequence of chymotryptic and V8 protease-generated peptides of the beta subunit that were radiolabeled as a result of cross-linking. The results of these studies demonstrate that amino acid residues 61-203 are proximal to the RGD binding domain of the vitronectin receptor.

Affinity Labels↗
PubMed1987

Biosynthetic and functional properties of an Arg-Gly-Asp-directed receptor involved in human melanoma cell attachment to vitronectin, fibrinogen, and von Willebrand factor.

M21 human melanoma cells express an Arg-Gly-Asp-directed adhesion receptor composed of noncovalently associated alpha and beta chains. To establish the structural and functional properties of this receptor on M21 human melanoma cells, stable variant cell lines were selected that express altered alpha chain levels. One of these variants, M21-L, fails to synthesize alpha chain protein or its mRNA, yet does produce normal levels of the beta chain. In these cells the beta chain does not reach the cell surface but rather accumulates within the cell. M21-L cells lacking the alpha chain are incapable of attaching to vitronectin, von Willebrand factor, fibrinogen, or an Arg-Gly-Asp-containing heptapeptide yet attach normally to fibronectin, whereas the unselected M21 cells attach to all of these adhesive proteins. In addition, a monoclonal antibody, LM609 generated to a functional site on the intact receptor, is capable of preventing M21 cell attachment to vitronectin, von Willebrand factor, fibrinogen, and the Arg-Gly-Asp peptide but not to fibronectin. Following a 2-min biosynthetic pulse-label, the newly synthesized alpha chain remains in free form for 5 min and then associates with previously synthesized beta chain present in an intracellular pool. Once oligomerization takes place, the receptor gains the capacity to recognize Arg-Gly-Asp, and at this time the epitope recognized by monoclonal antibody LM609 is formed.

Cell Adhesion↗
PubMed1987

Analysis of effector cells in human antibody-dependent cellular cytotoxicity with murine monoclonal antibodies.

We examined purified human large granular lymphocytes, peripheral monocytes, and T cells for their ability to mediate antibody-dependent cellular cytotoxicity (ADCC) with murine monoclonal antibodies. We also evaluated the effects of pretreatment of cells with interleukin 2 and interferon to augment ADCC activity. MB3.6, a murine monoclonal antibody directed against the GD3 ganglioside, induced high levels of ADCC. This ADCC was mediated predominantly, if not completely, by human killer cells (large granular lymphocytes) whereas other effector cell populations demonstrated no significant cytotoxic activity in 6- or 18-hr assays. The IgG2a an anti-melanoma antibody 9.2.27 generated low or no ADCC with most normal donors or melanoma patients. IL 2 was a very potent booster of ADCC activity. Interferon alpha also was effective, whereas interferon gamma did not augment but rather inhibited reactivity. We tested a large panel of antibodies of various isotype against colon carcinoma cells and found that gamma-3 isotype antibodies more frequently generated ADCC and produced higher levels of cytotoxic activity than did IgG1 or IgG2 antibodies. It appears that a variety of parameters can affect ADCC reactions, including the type of effector cell and its level of activation, the isotype of the antibody, and properties of the target cell line such as its susceptibility to lysis.

Animals↗
PubMed1987

Disialoganglioside GD2 on human neuroblastoma cells: target antigen for monoclonal antibody-mediated cytolysis and suppression of tumor growth.

A murine monoclonal antibody 14.18 specifically recognizes disialoganglioside GD2, the major ganglioside expressed on the surface of human neuroblastoma cells. This monoclonal antibody (Mab) is of immunoglobulin G3 isotype, has an affinity constant (KA) of 3.5 X 10(8) M-1, and reacts preferentially with tumor cells and fresh frozen tumor tissues of neuroectodermal origin in enzyme-linked immunosorbent assay and immunoperoxidase assays, respectively. Mab 14.18 effectively lyses a number of human neuroblastoma cell lines by two distinct mechanisms, i.e., antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. There is a good correlation between the average number of antibody-binding sites per neuroblastoma cell and the amount of cell lysis observed in complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity. In addition, Mab 14.18 suppresses establishment as well as growth of progressively growing, established human neuroblastoma tumors in nude mice when injected 24 h and 9 days, respectively, after the initial s.c. inoculation of tumor cells. These data suggest that Mab 14.18 can mediate tumor cell killing in vivo and in vitro and may thereby prove useful for immunotherapy of human neuroblastoma.

Antibodies, Monoclonal↗
PubMed1987

Arg-Gly-Asp recognition by a cell adhesion receptor requires its 130-kDa alpha subunit.

A major Arg-Gly-Asp-directed receptor on M21 human melanoma cells is a heterodimer of alpha and beta chains which under reducing conditions have molecular masses of 130 and 105 kDa, respectively. This receptor is one member of a large family of cell adhesion receptors that shares antigenic determinants with the vitronectin receptor of fibroblasts and the platelet IIb X IIIa complex. Both subunits of the M21 cell adhesion receptor acquire high mannose-type oligosaccharides that are processed before transport to the cell surface. In addition, the alpha chain undergoes a proteolytic cleavage step. Pulse-chase immunoprecipitation analysis demonstrates that, following its synthesis, the beta chain remains unbound to alpha chain for 1-2 h and in this free form is unable to bind an Arg-Gly-Asp containing heptapeptide. Conversely, the biosynthetic precursor of the alpha chain is fully capable of binding the Arg-Gly-Asp-containing peptide immediately after its synthesis. Thus, Arg-Gly-Asp recognition by one member of this cell adhesion receptor family requires its 130-kDa alpha chain which appears to be functional prior to post-translational modifications.

Antibodies, Monoclonal↗
PubMed1987

Enhancement of cytotoxic and proliferative responses of lymphocytes from melanoma patients by incubation with monoclonal antibodies against ganglioside GD3.

Previous studies have shown that monoclonal antibodies (M.Ab) to the ganglioside GD3 may induce partial remissions in tumour growth in patients with melanoma. In vitro studies demonstrated that M.Abs to GD3 may also enhance lymphocyte responses to phytohemagglutinin and interleukin 2 (IL2). The present study extended these findings by showing that the IL2-dependent proliferative and cytotoxic response of T cell clones derived from a melanoma patient and a patient with the Vogt-Koyanagi-Harada syndrome were enhanced by pre-incubation of T cells with M.Ab to GD3. The degree of enhancement increased with the duration of pre-incubation from 2 to 24 h and applied to both T4+ and T8+ clones. The potentiation of these responses was not specific for M.Abs to GD3 but was also seen with M.Abs to GD2 and the T10 structure on T cells but not with M.Abs to the transferrin receptor or an isotype control M.Ab. Incubation of lymphocytes from a melanoma patient with M.Ab to GD3 during culture with autologous melanoma cells enhanced the proliferative response to the tumour. The expression of IL2 receptors (Tac epitope) on the T cells showed variable enhancement after incubation with M.Ab to GD3 but the significance of these findings in relation to the mechanism of the enhanced responses is not known. These results suggest that certain M.Abs may stimulate cell-mediated immune responses against tumour cells and that this may provide an additional mode of action of M.Abs against tumours in vivo.

Antibodies, Monoclonal↗
PubMed1987

Human endothelial cells synthesize and express an Arg-Gly-Asp-directed adhesion receptor involved in attachment to fibrinogen and von Willebrand factor.

Human umbilical vein endothelial cells express a heterodimeric adhesion receptor complex consisting of noncovalently associated alpha and beta subunits that under reducing conditions have molecular masses of 135 kDa and 115 kDa, respectively. This complex can be isolated in pure form from an affinity matrix consisting of an Arg-Gly-Asp-containing heptapeptide and is specifically immunoprecipitated with monoclonal antibodies (mAbs) directed against the vitronectin receptor of human melanoma cells. These data suggest that this complex is one member of a large family of cell adhesion receptors. One of the mAbs, LM609, inhibits the attachment of human endothelial cells to fibrinogen, von Willebrand factor, and vitronectin yet has no effect on the attachment of these cells to fibronectin, collagen, or laminin. In addition, mAb LM609 inhibits attachment of endothelial cells to an immobilized synthetic peptide containing the Arg-Gly-Asp sequence. This adhesion receptor appears structurally similar to the IIb/IIIa glycoprotein complex expressed on platelets yet is antigenically distinct, since mAb LM609 fails to recognize IIb/IIIa glycoproteins. This receptor organizes in clusters on endothelial cells during their attachment to von Willebrand factor, vitronectin, or the Arg-Gly-Asp-containing heptapeptide. The data presented in this report suggest that Arg-Gly-Asp recognition may play a significant role in biological events associated with vascular proliferation.

Antibodies, Monoclonal↗
PubMed1987

An Arg-Gly-Asp-directed receptor on the surface of human melanoma cells exists in an divalent cation-dependent functional complex with the disialoganglioside GD2.

The disialogangliosides GD2 and GD3 play a major role in the ability of human melanoma cells to attach to Arg-Gly-Asp-containing substrates such as fibronectin and vitronectin, since pretreatment of these cells with monoclonal antibodies to the oligosaccharide of GD2 and GD3 can inhibit their attachment and spreading on such adhesive proteins. This report demonstrates that human melanoma cells (M21) synthesize and express a glycoprotein receptor that shares antigenic epitopes with the vitronectin receptor on human fibroblasts and is capable of specifically recognizing the Gly-Arg-Gly-Asp-Ser-Pro sequence. In the presence of calcium, GD2, the major ganglioside of M21 cells, colocalized with this receptor on the surface of human melanoma cells and their focal adhesion plaques as demonstrated by double-label transmission immunoelectron microscopy and indirect immunofluorescence. Biochemical evidence is presented indicating that the vitronectin receptor on M21 human melanoma cells contains associated calcium and GD2. This ganglioside copurified with the glycoprotein receptor for vitronectin on affinity columns containing either an Arg-Gly-Asp-containing peptide, concanavalin A, or lentil lectin. This major Arg-Gly-Asp-directed receptor on M21 cells could be metabolically labeled with 45Ca2+. Chelation of this ion with EDTA caused the dissociation of GD2 from the receptor and rendered the remaining glycoprotein incapable of binding to an Arg-Gly-Asp-containing peptide. Reconstitution experiments demonstrated a requirement for calcium, and not magnesium, for receptor binding to Arg-Gly-Asp and indicated that addition of ganglioside can enhance this interaction.

Amino Acid Sequence↗
PubMed1986

Disialogangliosides GD2 and GD3 are involved in the attachment of human melanoma and neuroblastoma cells to extracellular matrix proteins.

Human melanoma cells express relatively large amounts of the disialogangliosides GD3 and GD2 on their surface whereas neuroblastoma cells express GD2 as a major ganglioside. Monoclonal antibodies (Mabs) directed specifically to the carbohydrate moiety of GD3 and GD2 inhibit melanoma and neuroblastoma cell attachment to various substrate adhesive proteins, e.g. collagen, vitronectin, laminin, fibronectin, and a heptapeptide, glycyl-L-arginyl-glycyl-L-aspartyl-L-seryl-L-prolyl-L-cysteine, which constitutes the cell attachment site of fibronectin. Cells that are preattached to a fibronectin substrate can also be induced to detach and round up in the presence of purified anti-ganglioside Mab. Moreover, when melanoma cells that contain both GD2 and GD3 are incubated with Mabs directed to both of these molecules an additive inhibition is observed. The specificity of this inhibition is demonstrated since Mabs of various isotypes directed to either protein or carbohydrate epitopes on a number of other major melanoma or neuroblastoma cell surface antigens have no effect on cell attachment. A study of the kinetics involved in this inhibition indicates that significant effects occur during the first 5 min of cell attachment, suggesting an important role for GD2 and GD3 in the initial events of cell-substrate interactions. The role of gangliosides in cell attachment apparently does not directly involve a strong interaction with fibronectin since we could not observe any binding of radiolabeled fibronectin or fragments of the molecule known to contain the cell attachment site to melanoma gangliosides separated on thin-layer chromatograms. An alternative explanation would be that gangliosides may play a role in the electrostatic requirements for cell-substrate interactions. In this regard, controlled periodate oxidation of terminal, unsubstituted sialic acid residues on the cell surface not only specifically destroys the antigenic epitopes on GD2 and GD3 recognized by specific Mabs but also inhibits melanoma cell and neuroblastoma cell attachment. In fact, the periodate-induced ganglioside oxidation and the inhibition of cell attachment are equally dose dependent. These data suggest that cell-substratum interactions may depend in part on the electrostatic environment provided by terminal sialic acid residues of cell surface gangliosides and possibly other anionic glycoconjugates.

Adenocarcinoma↗
PubMed1986

Disialoganglioside GD2 distributes preferentially into substrate-associated microprocesses on human melanoma cells during their attachment to fibronectin.

Human melanoma cells (M21) actively attach and spread on a fibronectin substrate. Indirect immunofluorescence assays with specific monoclonal antibodies directed to the disialoganglioside GD2, the major ganglioside expressed on M21 melanoma cells, indicate that during the cell attachment process this molecule redistributes into microprocesses that make direct contact with the fibronectin substrate. Scanning and transmission immunoelectron microscopic studies with anti-GD2 monoclonal antibodies and immuno-gold staining demonstrate that GD2 preferentially localizes into substrate-associated microprocesses that emanate from the plasma membrane of the M21 cells. Staining with monoclonal antibodies directed to other melanoma surface antigens fails to demonstrate a similar distribution pattern on these cells. Direct evidence is provided that GD2 is involved in M21 cell attachment to fibronectin, since treatment of these cells with anti-GD2 monoclonal antibodies causes cell rounding and detachment from a fibronectin substrate. Moreover, scanning electron microscopy demonstrates that this loss of attachment of fibronectin is characterized by a perturbation of the cell attachment-promoting microprocesses that in the presence of these antibodies lose contact with the fibronectin substrate.

Antibodies, Monoclonal↗
PubMed1986

Biosynthesis and expression of the disialoganglioside GD2, a relevant target antigen on small cell lung carcinoma for monoclonal antibody-mediated cytolysis.

Monoclonal antibodies (MAbs) 126 (immunoglobulin M) and 14.18 (immunoglobulin G3) react strongly with the cell surface of small cell carcinoma of the lungs (SCCL) and are unreactive with most normal tissues and other neoplasms with the notable exception of tumors derived from cells of neural crest origin. These MAbs react specifically with the oligosaccharide portion of the disialoganglioside GD2. Analysis of total gangliosides from cultured cell lines derived from SCCL indicates that GD2 is a predominant ganglioside. A comparison of the reactivities of MAbs against GD2 with those directed against gangliosides GM2 and GD3, each differing from GD2 by a single sugar residue, clearly indicates that GD2 is preferentially expressed by cultured cells derived from SCCL. Membranes isolated from these cells exhibit GD2 synthetase activity which specifically converts the precursor GD3 to GD2 in the presence of uridine diphosphate-N-acetyl galactosamine as the glycosyl donor. We present evidence that in SCCL, GD2 serves as a relevant target antigen for monoclonal antibody-mediated cytolysis. Specifically, we demonstrate that MAb 14.18 (immunoglobulin G3), can lyse small cell carcinoma of the lung targets by either complement- or antibody-dependent cellular cytotoxicity.

Antibodies, Monoclonal↗
PubMed1986

Potentiation of lymphocyte responses by monoclonal antibodies to the ganglioside GD3.

Previous studies have shown that the ganglioside GD3 is expressed in high concentrations on melanoma cells and that monoclonal antibodies (MAbs) against GD3 may induce partial remissions in tumor growth in patients with melanoma. The present studies indicated that incubation of interleukin 2 (IL2) dependent murine natural killer cells with several MAbs against the ganglioside GD3 potentiated the proliferative response to IL2. There was no effect on cell division in the absence of added IL2. Similarly the mitogenic response of human blood lymphocytes to phytohemagglutinin (PHA) or the T3 antigen was enhanced by coculture with these MAbs. This was noted when the MAbs to GD3 were added either before or up to 48 h after addition of PHA or MAb to T3. Kinetic analysis revealed that the potentiation of the PHA induced mitogenic response followed the expected response to PHA suggesting that the MAbs amplified normal activation pathways. These effects were also seen wih MAb to GD3 and the T10 structure on T-cells but not with MAbs to the transferrin receptor or isotype MAb controls. Studies on T-cell subsets suggested that the enhanced PHA responses were confined mainly to the T8 subset and responses of the T4 subset were not enhanced. Flow cytometric analysis revealed low levels of GD3 expression on blood lymphocytes which increased during culture with PHA. IL2 receptor (Tac epitope) expression did not show close correlation with the enhanced lymphocyte responses and the mechanism of the potentiation remains uncertain. These studies raise questions concerning the role of gangliosides in T-cell activation and whether these in vitro effects of MAbs to GD3 may account in part for their antitumor effects in patients with melanoma.

Antibodies, Monoclonal↗