Biomedical subjects

R A Reisfeld

Publications and source records attributed to R A Reisfeld.

At least 55 records · Page 3Linked to original sources

PubMed1998

Phase I trial of a human-mouse chimeric anti-disialoganglioside monoclonal antibody ch14.18 in patients with refractory neuroblastoma and osteosarcoma.

PURPOSE: To evaluate the toxicity, immunogenicity, and pharmacokinetics of a human-mouse chimeric monoclonal antibody (mAb) ch 14.18 directed against disialoganglioside (GD2) and to obtain preliminary information on its clinical efficacy, we conducted a phase I trial in 10 patients with refractory neuroblastoma and one patient with osteosarcoma. PATIENTS AND METHODS: Eleven patients were entered onto this phase I trial. They received 20 courses of mAb ch 14.18 at dose levels of 10, 20, 50, 100, and 200 mg/m2. Dose escalation was performed in cohorts of three patients; intrapatient dose escalation was also permitted. RESULTS: The most prevalent toxicities were pain, tachycardia, hypertension, fever, and urticaria. Most of these toxicities were dose-dependent and rarely noted at dosages of 20 mg/m2 and less. Although the maximum-tolerated dose was not reached in this study, clinical responses were observed. These included one partial (PR) and four mixed responses (MRs) and one stable disease (SD) among 10 assessable patients. Biologic activity of ch 14.18 in vivo was shown by binding of ch 14.18 to tumor cells and complement-dependent cytotoxicity of posttreatment sera against tumor target cells. An anti-ch 14.18 immune response was detectable in seven of 10 patients studied. CONCLUSION: In summary, with the dose schedule used, ch 14.18 appears to be clinically safe and effective, and repeated mAb administration was not associated with increased toxicities. Further clinical trials of mAb ch 14.18 in patients with neuroblastoma are warranted.

Adult↗

PubMed1998

Antibody responses in melanoma patients immunized with an anti-idiotype antibody mimicking disialoganglioside GD2.

We initiated a clinical trial for patients with advanced malignant melanoma treated with an anti-idiotype antibody that mimics the disialoganglioside GD2. We report the clinical and immune responses of the first 12 patients entered into this trial. Patients received 1-, 2-, 4-, or 8-mg doses of the anti-idiotype antibody mixed with 100 microg of QS-21 adjuvant every other week, four times, and then monthly. Twelve patients have been on trial for 2-23 months, and all of them have generated immune responses. Patients were removed from the study if they demonstrated disease progression. Hyperimmune sera from all 12 patients revealed an anti-anti-idiotypic Ab3 response, as demonstrated by the inhibition of Ab2 binding to Ab1 by patients' immune sera. To further test the anti-anti-idiotypic response, patients' Ab3 antibodies were affinity purified on Sepharose 4B columns containing adsorbed immunizing anti-idiotype immunoglobulin. Purified Ab3 of all patients studied inhibited binding of Ab1 to a GD2-positive cell line. Purified Ab3 also inhibited binding of Ab1 to purified GD2, in a manner comparable to equal quantities of purified Ab1. The patient Ab3 was truly an Ab1' because it specifically bound to purified disialoganglioside GD2. The isotypic specificity of the Ab3 antibody was predominantly IgG, with only minimal IgM. The predominant IgG subclass was IgG1, with approximately equal quantities of IgG2, IgG3, and IgG4. These Ab3 antibodies reacted specifically with tumor cells expressing GD2 by immune flow cytometry and immunoperoxidase assays. Five patients' Ab3 antibodies studied for antibody-dependent cellular cytotoxicity were positive. One patient had a complete clinical response, with resolution of soft tissue disease, and six patients had stable disease, ranging from 9 to 23 months, and are being continued on vaccine therapy. Toxicity consisted of local reaction at the site of the injection, including induration and pain that generally resolved within a few days. Mild fever and chills were observed in 75% of the patients but rarely required acetaminophen. There was no additional toxicity, including abdominal pain that was previously seen with infusion of murine monoclonal anti-GD2 antibody. Current trials include patients with stage III melanoma and small cell lung cancer. Future trials will attempt to enhance the antitumor response by the addition of interleukin 2, granulocyte macrophage colony-stimulating factor, and other cytokines, together with the 1A7 vaccine.

Adult↗

PubMed1998

Suppression of human prostate carcinoma metastases in severe combined immunodeficient mice by interleukin 2 immunocytokine therapy.

Immunocytokines are antibody-cytokine fusion proteins that combine the unique targeting ability of antibodies with the multifunctional activities of cytokines to activate effector cells in the tumor microenvironment. Here, we demonstrate the therapeutic efficacy of a tumor-specific immunocytokine, huKS1/4-IL2, which effectively inhibited growth and dissemination of lung and bone marrow metastases of human prostate carcinoma in severe combined immunodeficient mice. This antitumor effect was specific and highly effective, irrespective of reconstitution of these mice with human lymphokine-activated killer cells. Survival times of mice treated with huKS1/4-IL2 were increased 4-fold as compared with animals treated with a mixture of the corresponding antibody and recombinant human interleukin-2 (rhIL2). A persistent antitumor response after treatment with the huKS1/4-IL2 immunocytokine in B, T, and natural killer cell-deficient severe combined immuodeficient-BEIGE mice, depleted of granulocytes, implies a major role for macrophages in this treatment effect. Our data demonstrate that immunocytokine-directed interleukin-2 therapy to tumor sites is an immunotherapeutic approach with potent effects against disseminated metastases of human prostate carcinoma and suggest that this treatment could be effective in an adjuvant setting for patients with minimal residual disease.

Animals↗

PubMed1997

Targeted interleukin-2 therapy for spontaneous neuroblastoma metastases to bone marrow.

BACKGROUND: Advanced (stage 4) cases of neuroblastoma, a childhood cancer of the nervous system, are associated with high relapse rates, even after intensive chemotherapy, radiotherapy, and autologous bone marrow transplantation. Therefore, the use of monoclonal antibodies directed against the neuroblastoma tumor marker disialoganglioside GD2 (GD2), in combination with recombinant human interleukin 2 (rhIL-2), is under clinical investigation. We hypothesize that targeted cytokine immunotherapy with a recombinant anti-GD2 antibody-interleukin 2 fusion protein (ch14.18-IL-2) is superior to a combination of ch14.18 and rhIL-2. Our purpose was as follows: 1) to develop a syngeneic model for murine neuroblastoma that expresses GD2 and features both experimental and spontaneous metastases to bone marrow and liver, and 2) to assess anti-GD2-targeted IL-2 therapy in this mode. METHODS: A hybrid neuroblastoma cell line was used to generate the GD2-positive NXS2 cell line. Bone marrow and liver metastases were quantified by reverse transcription-polymerase chain reaction for tyrosine hydroxylase and by organ weight or counts of macroscopic tumor foci, respectively. All P values reported are two-sided. RESULTS: Injection of NXS2 cells resulted in disseminated bone marrow and liver metastases exhibiting stable, but heterogeneous expression of GD2. Treatment with fusion protein (10 microg/day for 6 days) effectively suppressed growth of both experimental and spontaneous metastases to bone marrow and liver (P<.001). In contrast, a mixture of rhIL-2 and ch14.18 at equivalent dose levels was inefficient. Only mice treated with ch14.18-IL-2 showed a twofold prolongation in life span (P<.001). CONCLUSION: Targeted IL-2 therapy with a ch14.18-IL-2 fusion protein elicits an effective antitumor response. Our data suggest that a study of ch14.18-IL-2 as an adjuvant treatment in patients with minimal residual disease may be of value.

Animals↗

PubMed1997

Elimination of established murine colon carcinoma metastases by antibody-interleukin 2 fusion protein therapy.

A recombinant humanized antibody-interleukin 2 fusion protein (huKS1/4-IL-2) was used to direct IL-2 to the tumor microenvironment and elicit a T cell-mediated eradication of established pulmonary and hepatic CT26-KSA colon carcinoma metastases in syngeneic BALB/c mice. This antitumor effect was specific because a fusion protein, which was nonreactive with these tumor cells, failed to exert any such effect. The efficacy of the huKS1/4-IL-2 fusion protein in eliminating metastases was documented because mixtures of monoclonal antibody huKS1/4 with recombinant human IL-2 were ineffective and, at best, only partially reduced tumor load. Two lines of evidence indicated the eradication of metastases and the absence of minimal residual disease in animals treated with the fusion protein: first, the lack of detection of CT26-KSA cells by reverse transcription-PCR, which can detect one tumor cell in 10(6) liver cells; and second, the tripling of life span. The effector mechanism involved in this tumor eradication is dependent on T cells because the IL-2-directed therapy is ineffective in T cell-deficient SCID mice. The essential effector cells were further characterized as CD8+ T cells by in vivo depletion studies. Such T cells, isolated from tumor-bearing mice after fusion protein therapy, elicited MHC class I-restricted cytotoxicity in vitro against colon carcinoma target cells. Taken together, these data indicate that fusion protein-directed IL-2 therapy induces a T cell-dependent host immune response capable of eradicating established colon cancer metastases in an animal tumor model.

Animals↗

PubMed1997

A phase I/IB trial of murine monoclonal anti-GD2 antibody 14.G2a plus interleukin-2 in children with refractory neuroblastoma: a report of the Children's Cancer Group.

BACKGROUND: The murine monoclonal antibody (MoAb) 14.G2a recognizes GD2, a disialoganglioside expressed in tumors of neuroectodermal origin, and facilitates antibody dependent cellular cytotoxicity (ADCC) in vitro. When given in vivo, interleukin-2 (IL-2) can increase ADCC by enhancing the activity and number of circulating lymphocytes. METHODS: Thirty-three pediatric patients with GD2 positive malignancies, ranging in age from 2 to 17 years (median, 9.9 years), received IL-2 and 14.G2a in this Phase I/IB study of the Children's Cancer Group (CCG) and were monitored for toxicities and response to therapy. Seven of these patients also received granulocyte-macrophage-colony stimulating factor. RESULTS: The maximum tolerated dose (MTD) of 14.G2a with IL-2 was 15 mg/m2/day. The most prevalent Grade 3-4 toxicities were generalized pain (n = 14 [42%]) and fever without documented infection (n = 17 [52%]). IL-2 was thought to be the causative agent in most cases of fever. Toxicities attributed to 14.G2a included pain, allergic or anaphylactic reactions, and rash. Human antimouse antibodies were demonstrated in 9 of 21 evaluated patients. One patient with neuroblastoma had a partial response, and one patient with osteosarcoma had a complete response. Immunocytology demonstrated that the number of neuroblastoma cells in bone marrow decreased in three patients. CONCLUSIONS: The murine MoAb 14.G2a was well tolerated at the MTD and appeared to have some antitumor activity. Further development of this approach will involve additional engineered forms of the antibody as well as testing in the adjuvant and minimal residual disease setting.

Adjuvants, Immunologic↗

PubMed1997

Expression and regulation of the neural cell adhesion molecule L1 on human cells of myelomonocytic and lymphoid origin.

The neural cell adhesion molecule L1 has been implicated in a variety of neurologic processes, including neuritogenesis and cerebellar cell migration. Here we propose an expanded role for this cell adhesion molecule in the human immune system based on its expression on cells of myelomonocytic and lymphoid origin. Freshly isolated circulating monocytes had minimal L1 expression; however, activation of these effector cells by IFN-gamma, or as a result of density gradient isolation, resulted in a significant induction of L1 expression. Constitutive L1 expression was further evident on myelomonocytic cell lines but was absent on mature tissue macrophages. In further studies, positive selection with a L1-specific Ab enriched both B cells and dendritic precursor cells from peripheral blood. Significantly, L1 expression was not detected on mature dendritic cells but could be induced by treatment with LPS, PHA, and TNF-alpha. Immunohistochemical analysis further demonstrated significant L1 expression on follicular dendritic cells and on endothelial cells associated with the arterioles and red pulp of normal spleen. Based on these observations and known functions of L1, we propose that this cell adhesion molecule may contribute to cell-cell adhesion events associated with the effector function or extravasation of these immune effector cells. In support of the latter, we present evidence that L1 can be recognized by endothelial cells via the integrin alpha(v)beta3.

Cell Line↗

PubMed1997

Proteases and protease inhibitors in tumor progression.

Our understanding of the role of matrix degrading proteases in cancer has dramatically expanded over the last two decades. From correlative observations linking proteases to cancer progression, we have accumulated evidence supporting a causal role for proteases in various steps of tumor progression and have become increasingly aware of the complex interactions that exist among proteases. Specific natural inhibitors of these proteases have also been identified and their role as potent cytostatic agents in cancer has been suggested. In this article some of the concepts on the role of proteases in cancer are discussed and examples of cooperation between matrix metalloproteinases and the plasmin/plasminogen activators system are presented. The role of protease inhibitors such as tissue inhibitor of metalloproteinases-2 (TIMP-2) and plasminogen activator inhibitor-2 (PAI-2) as inhibitors of tumor growth, invasion and metastasis is discussed.

Amino Acid Sequence↗

PubMed1997

Matrix metalloproteinase-2 activation modulates glioma cell migration.

Stable transfection of U251.3 glioma cells with cDNA encoding MT-MMP-1 resulted in increased cell surface expression of MT-MMP-1 and TIMP-2, constitutive activation of MMP-2 proenzyme and increased collagen degradation. In tumor spheroid outgrowth assays, cell migration of MT-MMP-1 transfectants relative to control was enhanced on collagen and decreased on vitronectin and fibronectin. These effects were reversed by TIMP-2 and were not associated with any substantial changes in cell adhesion. Binding of U251.3 cells to the C-terminal domain of MMP-2 was specifically inhibited by anti-(alpha)vss3 integrin blocking antibody indicating that MMP-2 interacts with (alpha)vss3 through the enzyme's C-terminal portion at or near the integrin's matrix adhesion sites. We propose that these mechanisms could govern directed matrix degradation in the tumor cells' microenvironment by sequestration of active MMP-2 on the cell surface. Our data suggest that activation of MMP-2 and its proteolytic activity localized to the cell surface could differentially modulate tumor cell migration in response to particular matrix proteins by altering both composition of the extracellular matrix and expression of adhesion receptors on the cell surface.

Amino Acid Sequence↗

PubMed1997

Immunocytokines: a new approach to immunotherapy of melanoma.

Targeted interleukin-2 (IL-2) therapy with immunocytokines (i.e. antibody-cytokine fusion proteins) is effective in eradicating established hepatic and pulmonary metastases of melanoma in animal model systems. The effector mechanisms responsible for this antitumor effect in syngeneic, immunocompetent mice involves mainly CD8+ T cells. This was clearly indicated by immunohistochemical analyses, in vivo depletion studies and cytotoxicity tests. Such CD8+ T cells, isolated from tumor-bearing mice after immunocytokine therapy, exerted a major histocompatibility complex class I-restricted cytotoxicity against the same tumor in vitro. Because of this cellular immune response, antibody-directed IL-2 therapy can even address established metastases displaying extensive heterogeneity in the expression of the targeted antigen. The effector mechanisms induced by immunocytokines facilitate partial regressions of large subcutaneous melanoma exceeding more than 5% of the body weight. These results demonstrate the ability of immunocytokines to induce a T-cell-dependent host immune response capable of eradicating established melanoma metastases in clinically relevant organs and offers an effective, new tool for immunotherapy of malignant melanoma.

Animals↗

PubMed1997

Preclinical evaluation in nonhuman primates of murine monoclonal anti-idiotype antibody that mimics the disialoganglioside GD2.

The antiganglioside GD2 monoclonal antibody 14G2a (Ab1) served as an immunogen to generate the anti-idiotype (anti-Id) 1A7 (IgG1,kappa), which mimics GD2 both antigenically and biologically. Anti-Id 1A7 induced anti-GD2 antibodies in mice and rabbits. In this preclinical study, a pair of cynomolgus monkeys, immunized with 1A7 that had been mixed with QS-21 adjuvant, produced anti-anti-Id antibodies (Ab3), which reacted with the GD2-positive melanoma cell line M21/P6 cells but not with GD2-negative LS174-T cells. The Ab3 shared Ids with mAb 14G2a (Ab1), as demonstrated by their ability to inhibit binding of 1A7 to this Ab1. The Ab3 bound specifically to purified GD2 antigen and competed with the Ab1 14G2a in binding to a GD2-positive melanoma cell line or to purified GD2, suggesting that Ab1 and Ab3 may bind to the same epitope and may behave as an Ab1-like antibody (Ab1'). The isotype of the GD2-specific antibodies was mostly IgG in nature. The specificity of the antibodies for GD2 was further confirmed by dot blot analysis. These antisera also specifically lysed GD2-positive target cells in an antibody-dependent cellular cytotoxicity assay. The induction of anti-GD2 responses in monkeys did not cause any apparent side effects, despite the fact that GD2 antigen is expressed by many normal tissues of these animals. Taken together, these results suggest that anti-Id 1A7 can induce GD2-specific antibodies in nonhuman primates and can thus serve as a potential network antigen for triggering active anti-GD2 antibodies in patients with GD2-positive neuroectodermal tumors.

Adjuvants, Immunologic↗

PubMed1997

Phase IB trial of chimeric antidisialoganglioside antibody plus interleukin 2 for melanoma patients.

We conducted a Phase IB trial of antidisialoganglioside chimeric 14. 18 (ch14.18) antibody and interleukin 2 (IL-2) to determine the maximal tolerated dose (MTD), immunological effects, antitumor effects, and toxicity of this treatment combination. Twenty-four melanoma patients received immunotherapy with ch14.18 antibody and a continuous infusion of Roche IL-2 (1.5 x 10(6) units/m2/day) given 4 days/week for 3 weeks. The ch14.18 antibody (dose level, 2-10 mg/m2/day) was scheduled to be given for 5 days, before, during, or following initial systemic IL-2 treatment. The ch14.18 MTD was 7.5 mg/m2/day, and 15 patients were treated with the ch14.18 MTD. Immunological effects included the induction of lymphokine-activated killer activity and antibody-dependent cellular cytotoxicity by peripheral blood mononuclear cells. In addition, serum samples obtained following ch14.18 infusions were able to facilitate in vitro antibody-dependent cellular cytotoxicity. Antitumor activity included one complete response, one partial response, eight patients with stable disease, and one patient with >50% decrease of hepatic metastases in the face of recurrence of a s.c. lesion. Dose-limiting toxicities were a severe allergic reaction and weakness, pericardial effusion, and decreased performance status. Most patients treated at the MTD had abdominal, chest, or extremity pain requiring i.v. morphine. One patient had an objective peripheral neuropathy. This IL-2 and ch14.18 treatment combination induces immune activation in all patients and antitumor activity in some melanoma patients. We are attempting to enhance this treatment approach by addition of the anti-GD3 R24 antibody to this IL-2 and ch14.18 regimen.

Adult↗

PubMed1996

Long-lived and transferable tumor immunity in mice after targeted interleukin-2 therapy.

A major goal of tumor immunotherapy is the induction of tumor-specific T cell responses that are effective in eradicating disseminated tumor, as well as mounting a persistent tumor-protective immunity. We demonstrate here that a genetically engineered fusion protein consisting of human/mouse chimeric anti-ganglioside GD2 antibody and human interleukin-2 is able to induce eradication of established B78-D14 melanoma metastases in immunocompetent syngeneic C57BL/6J mice. This therapeutic effect is mediated by host immune cells, particularly CD8+ T cells and is associated with the induction of a long-lived immunity preventing tumor growth in the majority of animals when challenged up to four months later with B78-D14 cells. This effect was tumor-specific, since no cross-protection against syngeneic, ganglioside GD2+ EL-4 thymoma cells was observed. Furthermore, this tumor-specific protection can be transmitted horizontally to naive, syngeneic SCID mice by passive transfer of CD8+ T lymphocytes derived from immune animals. These results suggest that antibody-targeted delivery of cytokines provides a means to elicit effective immune responses against established tumors in the immunotherapy of neoplastic disease.

Animals↗

PubMed1996

Molecular cloning of a human melanoma-associated chondroitin sulfate proteoglycan.

A human melanoma-associated chondroitin sulfate proteoglycan (MCSP), recognized by mAb 9.2.27, plays a role in stabilizing cell-substratum interactions during early events of melanoma cell spreading on endothelial basement membranes. We report here the molecular cloning and nucleotide sequencing of cDNA encoding the entire core protein of human MCSP and provide its deduced amino acid sequence. This core protein contains an open reading frame of 2322 aa, encompassing a large extracellular domain, a hydrophobic transmembrane region, and a relatively short cytoplasmic tail. Northern blot analysis indicated that MCSP cDNA probes detect a single 8.0-kb RNA species expressed in human melanoma cell lines. In situ hybridization experiments with a segment of the MCSP coding sequence localized MCSP mRNA in biopsies prepared from melanoma skin metastases. Multiple human Northern blots with an MCSP-specific probe revealed a strong hybridization signal only with melanoma cells and not with other human cancer cells or a variety of human fetal and adult tissues. These data indicate that MCSP represents an integral membrane chondroitin sulfate proteoglycan expressed by human malignant melanoma cells. The availability of cDNAs encoding MCSP should facilitate studies designed to establish correlations between structure and function of this molecule and help to establish its role in the progression of human malignant melanoma.

Adult↗

PubMed1996

Characterization of an Ig VH idiotope that results in specific homophilic binding and increased avidity for antigen.

mAb against GD3 ganglioside demonstrate homophilic binding in which soluble anti-GD3 mAb bind, through the GD3 binding site, to a VH idiotope (designated IdHOM) on solid phase anti-GD3 mAb. In this way, homophilic binding provides a mechanism for amplifying the binding of mAb to cell surface GD3. We show that serine 52a, within CDR2, is required for IdHOM expression, homophilic binding, and high avidity binding to cell surface GD3. Computer modeling based on the crystal structure of anti-GD3 mAb R24 showed serine 52a situated at the mouth of the GD3 binding pocket, but not directly involved with GD3 binding. Substitutions at position 52a predicted to maintain the GD3 binding pocket (e.g., threonine) resulted in the loss of IdHOM expression and homophilic binding and markedly decreased binding to cell surface GD3, but maintained low avidity GD3 binding as measured by ELISA. All other substitutions at position 52a were predicted to significantly distort the GD3 binding pocket and resulted in the loss of both homophilic binding and any detectable avidity for GD3. We have structurally defined IdHOM and conclude that this idiotope is not required for the GD3 binding pocket, but that the idiotope is necessary for homophilic binding, which is required for high avidity binding to cell surface GD3. We speculate that selection of certain VH genes may result in the expression of idiotopes that allow homophilic binding, and this may represent a general mechanism for increasing the avidity of Abs against T cell-independent Ags.

Amino Acid Sequence↗

PubMed1996

An antibody-interleukin 2 fusion protein overcomes tumor heterogeneity by induction of a cellular immune response.

Antibody-based therapies for cancer rely on the expression of defined antigens on neoplastic cells. However, most tumors display heterogeneity in the expression of such antigens. We demonstrate here that antibody-targeted interleukin 2 delivery overcomes this problem by induction of a host immune response. Immunohistochemical analysis demonstrated that the antibody-interleukin 2 fusion protein-induced eradication of established tumors is mediated by host immune cells, particularly CD8+ T cells. Because of this cellular immune response, antibody-directed interleukin 2 therapy is capable to address established metastases displaying substantial heterogeneity in expression of the targeted antigen. This effector mechanism further enables the induction of partial regressions of large subcutaneous tumors that exceeded more than 5% of the body weight. These observations indicate that antibody-directed cytokine delivery offers an effective new tool for cancer therapy.

Animals↗

PubMed1996

T cell-mediated eradication of murine metastatic melanoma induced by targeted interleukin 2 therapy.

Induction of a T-cell mediated antitumor response is the ultimate goal for tumor immunotherapy. We demonstrate here that antibody-targeted IL2 therapy is effective against established pulmonary and hepatic melanoma metastases in a syngeneic murine tumor model. The effector mechanisms involved in this tumor eradication are not dependent on NK cells, since the therapeutic effect of antibody-IL2 fusion protein was not altered in NK cell-deficient mice. In contrast, T cells are essential for the observed antitumor effect, since therapy with antibody IL2 fusion proteins is unable to induce tumor eradication in T cell-deficient SCID mice. In vivo depletion studies characterized the essential effector cell population further as CD8 + T cells. Such CD8 + T cells, isolated from tumor bearing mice after antibody-directed IL2 therapy, exerted a MHC class I-restricted cytotoxicity against the same tumor in vitro. These data demonstrate the ability of antibody-targeted IL2 delivery to induce a T cell-dependent host immune response that is capable of eradicating established melanoma metastases in clinically relevant organs.

Animals↗

PubMed1996

Involvement of B lymphocytes in the growth inhibition of human pulmonary melanoma metastases in athymic nu/nu mice by an antibody-lymphotoxin fusion protein.

Antibody-cytokine fusion proteins can target biologically active cytokines to various tumor sites, achieving local concentrations sufficient to induce host immune responses leading to tumor elimination. Here, we demonstrate the therapeutic efficacy of a tumor-specific antibody-lymphotoxin fusion protein (ch225-LT) on xenografted pulmonary metastases of human melanoma. In vitro studies indicated a direct cytotoxic effect of such construacts on melanoma cells via the induction of apoptosis, as demonstrated by cell cycle analysis and DNA fragmentation. However, ch225-LT lacked any therapeutic effect in immune deficient C.B17 scid/beige and scid/scid mice, indicating the insufficiency of this direct mechanism in vivo. In contrast, in athymic nu/nu mice, ch225-LT completely inhibited outgrowth of the xenografted tumor. This therapeutic effect was accompanied by infiltrations of CD45+, Mac-1+, and asialo-GM1+ cells into the tumor; B220+ cells were present in the surrounding tissue and the periphery of the tumor. The functional role of asialo-GM2+ cells was confirmed by in vivo depletion studies. Our data indicate that an antibody-lymphotoxin fusion protein effectively inhibits the growth of disseminated melanoma metastases by mechanisms that function in the absence of mature T cells, but require B, NK, and other asialo-GM1+ cells.

Animals↗