Administration of an anti-CD5 immunoconjugate to patients with rheumatoid arthritis: effect on peripheral blood mononuclear cells and in vitro immune function

OBJECTIVE

An immunoconjugate, CD5 Plus, composed of ricin A chain and murine IgG1 anti-CD5 monoclonal antibody is under investigation for treatment of rheumatoid arthritis. To understand better the mechanism of action of this agent, alterations in immune function and lymphocyte subpopulations were assessed in a subset of patients consecutively enrolled in 2-phase II clinical trials.

METHODS

Flow cytometric and in vitro functional analyses of peripheral blood mononuclear cells from 12 patients receiving 5 daily intravenous infusions of CD5 Plus at doses of 0.20 or 0.33 mg/kg were performed before, during and after treatment.

RESULTS

Peripheral CD3+ T cells were significantly depleted (p < 0.01) during treatment on Days 2 and 5 and returned towards baseline on Days 15 to 29; changes in CD5+ B cells occurred in parallel. There was no significant treatment effect on monocytes. All T cell subsets examined, including CD4, CD8, CD45RA, CD45RO, HLA-DR+, TCR-alpha beta and TCR-gamma delta, were affected equally through Day 15. On Day 29, the median CD4:CD8 ratio, elevated before treatment, was significantly decreased (p < 0.01), approaching the ratio observed in healthy controls. Proliferative responses to antigenic, allogeneic and mitogenic stimuli in vitro were depressed but detectable during the time of maximal T cell depletion and normalized to baseline values with recovery of T cell number. Spontaneous and pokeweed mitogen induced immunoglobulin secretion were unaffected in these patients.

CONCLUSION

Treatment associated effects of CD5 Plus were observed for both T and B cell populations which bear the CD5 antigen, and were reversible, as measured by in vitro assays of immune cell function, phenotype and number.

Evaluation of anti-CD5 ricin A chain immunoconjugate for prevention of acute graft-vs.-host disease after HLA-identical marrow transplantation

Anti-CD5 ricin A chain immunoconjugate (XZ-CD5) is an immunotoxin that inhibits proliferative and cytotoxic responses to alloantigen in vitro and has activity in the treatment of acute graft-vs.-host disease (GVHD). To determine if XZ-CD5 could be used to prevent acute GVHD, 11 adult recipients of HLA-identical allogeneic marrow received XZ-CD5 0.1 mg kg-1 day-1 intravenously with high-dose methyl-prednisolone for 10, 14 or 17 doses early post-transplant. Six additional patients received 17 doses of XZ-CD5 and cyclosporine (CSA). All patients engrafted. Severe capillary leak syndrome was the most common serious toxicity and occurred more frequently in patients receiving CSA (5/5 vs. 3/11, P = 0.03). All evaluable patients developed acute GVHD; 88% had grade II-IV GVHD. Flow cytometric analysis demonstrated a substantial number of circulating CD5+ and CD3+ lymphocytes during and early after administration of XZ-CD5. These results suggest that the immunotoxin did not eliminate alloreactive T cells in this setting.

Ricin: structure, mode of action, and some current applications

Ricin is an abundant protein component of Ricinus communis seeds (castor beans) that is exquisitely toxic to mammalian cells. It consists of an enzymic polypeptide that catalyzes the N-glycosidic cleavage of a specific adenine residue from 28S ribosomal RNA, joined by a single disulfide bond to a galactose (cell)-binding lectin. The enzymatic activity renders ribosomes containing depurinated 28S RNA incapable of protein synthesis. The bipartite molecular structure of ricin allows it to bind to the mammalian cell surface, enter via endocytic uptake, and deliver the catalytically active polypeptide into the cell cytosol where it irreversibly inhibits protein synthesis causing cell death. Because of its cytotoxic potency, modified ricin is being used for the selective killing of unwanted cells and for the toxigenic ablation of cell lineages in transgenic organisms.

Successful treatment of disseminated human Hodgkin's disease in SCID mice with deglycosylated ricin A-chain immunotoxins

To evaluate the effects of deglycosylated ricin A-chain (dgA) immunotoxins against disseminated Hodgkin's lymphoma, we used RFT5.dgA (CD25) and IRac.dgA (70 kD) to treat L540Cy Hodgkin cells in severely immunodeficient SCID mice. In this model, more than 90% of the animals developed multiple lymphomas in various organs such as the lymph nodes, liver, bone marrow, and extranodal sites that killed untreated animals after a mean survival time (MST) of 36.3 days. A single intraperitoneal injection of 8 micrograms of either immunotoxin rendered 95% (RFT5.dgA) and 93% (IRac.dgA), respectively, of mice tumor-free when applied 1 day after tumor challenge. The MST of the RFT5.dgA-treated group was extended by more than 80 days (P < .00001). SCID mice treated 12 days after tumor challenge had lower remission rates (46%), suggesting that the antitumor effect of the immunotoxins depends on the number of tumor cells present. We conclude that ricin A-chain immunotoxins have potent antitumor effects against disseminated Hodgkin's tumors in SCID mice and that this model is ideally suited for the evaluation of different immunotoxin treatment modalities.

Immunotoxin therapy of leptomeningeal neoplasia

Malignant tumors of the central nervous system can result from metastatic dissemination of a variety of cancers. Percutaneous intracisternal injection of an anti-idiotype monoclonal antibody (M6) ricin immunotoxin was shown to be moderately effective in prolonging the survival of tumor bearing animals supporting the use of immunotoxins for the treatment of central nervous system neoplasia (Zovickian J and Youle R.J. J. Neurosurg 68: 767, 1988). This report describes a method that significantly improves the survival of immunotoxin treated Strain 2 guinea pigs in a syngeneic animal model of leptomeningeal neoplasia. Strain 2 guinea pigs, implanted with subarachnoid catheters, received three courses of treatment with an (M6)-intract ricin immunotoxin following intracisternal inoculation of L2C leukemia tumor cells. Animals were treated with three to four micrograms of immunotoxin in three divided doses. This was found to be less toxic and more effective than single bolus administration of immunotoxin. These results demonstrate that a permanent indwelling catheter in this animal model facilitates multiple dose delivery of immunotoxin therapy allowing the assessment of various treatment schedules and the achievement of enhanced therapeutic effect. Furthermore, these results support the continued evaluation of immunotoxins for the treatment of central nervous system neoplasia.

Cytotoxic effect of diphtheria toxin used alone or in combination with other agents on human renal cell carcinoma cell lines

Treatment of renal cell carcinoma (RCC) by conventional chemotherapy and immunotherapy has resulted in minimal remissions. Alternative forms of therapy are therefore being sought. The present study investigated the sensitivity of RCC cell lines to several toxins used alone and in combination with other agents. RCC lines were relatively sensitive to the direct cytotoxic effect of diphtheria toxin (DTX), Pseudomonas aeruginosa exotoxin A (PEA) and ricin. Furthermore, DTX in combination with tumor necrosis factor-alpha (TNF-alpha) resulted in synergistic cytotoxic activity. The mechanism of synergy was examined. A possible mechanism of resistance to TNF-alpha in tumor cells is the expression of TNF-alpha mRNA or protein. R11 cells did not constitutively express mRNA for TNF-alpha, however, treatment of R11 cells with TNF-alpha induced the expression of TNF-alpha mRNA. When DTX was used in combination with TNF-alpha, the level of TNF-alpha mRNA induced by TNF-alpha was markedly reduced. These studies suggest that DTX in combination with TNF-alpha can overcome the resistance of RCC lines and that the marked downregulation of TNF-alpha mRNA by DTX may play a role in the enhanced cytotoxicity seen with the combination of DTX and TNF-alpha. Furthermore, the combination treatment might also potentiate the antitumor host responses. The implications of these findings in clinical therapy are discussed.

Use of the immunotoxin N901-blocked ricin in patients with small-cell lung cancer

In patients with small-cell lung cancer (SCLC), relapse with resistant disease often causes death. N901-blocked ricin (N901-bR), a murine monoclonal antibody (MAb)-blocked ricin immunotoxin, is a potential therapeutic for SCLC. N901-bR targets CD56, present on SCLC and cells of neuro-ectodermal origin. N901-bR kills up to 5 logs of CD56-positive cells at a concentration of 0.25 nM, while CD56-negative cells require 1000-fold more drug to achieve similar cell kill. We treated 21 patients with relapsed or refractory SCLC with a single 7-day course of N901-bR as a continuous infusion. We determined the MTD and toxicity profile, demonstrated drug binding to tumor cells in biopsies of lung, liver and bone marrow, and determined the time to development of human anti-mouse and anti-ricin antibodies. One patient had a documented PR and 6 patients demonstrated stable disease. Toxicity included transient elevation of liver enzymes, mild thrombocytopenia, hypoalbuminemia, fever, malaise, and evidence of capillary leak syndrome. Toxicities were controllable and reversible. No apparent drug-related central- or peripheral-nervous-system toxicity was noted by serial neurologic examinations, EMGs, and nerve conduction studies. Trials of N901-bR are planned in SCLC patients achieving CR and PR following chemoradiotherapy, and in relapsed/refractory patients. Anti-B4-bR will be added as an immunosuppressant in order to permit delivery of multiple courses of N901-bR. Additional trials will investigate synergy with conventional chemotherapeutics and the use of N901-bR as a sensitizing agent for chemotherapy-resistant tumors.

A phase I study of an anti-CD22-deglycosylated ricin A chain immunotoxin in the treatment of B-cell lymphomas resistant to conventional therapy

Twenty-six patients, whose B-cell lymphoma had relapsed after conventional therapies, were treated in a phase I dose escalation study with an immunotoxin consisting of a mouse CD22 monoclonal antibody (RFB4:IgG1K) coupled to chemically deglycosylated ricin A chain (dgA). Two to 12 doses of the immunotoxin were infused intravenously at 48-hour intervals. The peak serum concentration and half-life (T1/2) did not correlate directly with the dose and averaged 3.8 micrograms/mL and 7.8 hours, respectively. The main dose-limiting toxicity was caused by the vascular leak syndrome (VLS) consisting of weight gain, edema, serum albumin decrease, and critically by pulmonary edema. Myalgia occurred frequently and was only dose limiting in one patient who developed rhabdomyolysis. The presence of lymphoma cells in the blood (> or = 10(10)/L) and clinically detectable splenomegaly were associated with reduced toxicity and a shorter T1/2. Nine of 24 evaluable patients (37.5%) made antibody to either mouse Ig or dgA. There were five partial responses (PR) and one complete response (CR) lasting 30 to 78 days. High peak concentrations of immunotoxin in the serum, a long T1/2, and large areas under the curve (AUC) correlated with both clinical response and toxicity. None of three patients with CD5+ lymphomas (including two CLL patients) had more than mild toxicity or responded to the immunotoxin.

Combination graft-versus-host disease prophylaxis using immunotoxin (anti-CD5-RTA [Xomazyme-CD5]) plus methotrexate and cyclosporine or prednisone after unrelated donor marrow transplantation

Unrelated donor (URD) bone marrow transplantation (BMT) is associated with more frequent and more therapy-resistant graft-versus-host disease (GVHD). We tested an in vivo immunotoxin with direct cytolytic potency against CD5-expressing T lymphocytes (Xomazyme-CD5) for GVHD prophylaxis after URD BMT. The immunotoxin was given in vivo (0.1 mg/kg/day) for 3 weeks following transplantation in combination with methotrexate+prednisone (MXP; n = 16) or methotrexate+cyclosporine (MCX; n = 6). The 22 patients (10 phenotypically matched with their donors and 12 partially matched) received unmanipulated marrow. MXP was well tolerated, while MCX led to unacceptable nephrotoxicity, weight gain and edema. Four patients died of early complications. Thirteen of 17 evaluable patients achieved myeloid engraftment by 17-40 days (median 24 days). Acute GVHD developed in 9 of 15 evaluable patients (5 grade III/IV). Six of 8 evaluable patients developed chronic GVHD. Four patients survive 1.1-2 years after BMT. Although this immunotoxin has previously shown potency in prophylaxis of murine GVHD and therapy of human GVHD, in this trial inadequate immunosuppressive potency of the immunotoxin combinations was associated with unacceptable clinical toxicity. Aggressive immunoprophylaxis against GVHD is required to improve the success of URD BMT.

Eradication of large solid tumors in mice with an immunotoxin directed against tumor vasculature

Antibody-based therapy of solid tumors has met with limited success, chiefly because solid tumors are relatively impermeable to macromolecules. This problem could be circumvented by attacking the readily accessible endothelial cells of the tumor vascular bed. We have developed a model to test this "vascular targeting" approach in which cytokine gene transfection of the tumor cells causes them to induce an experimental marker selectively on tumor vascular endothelium. An anti-tumor endothelial cell immunotoxin caused complete occlusion of the tumor vasculature and dramatic regressions of large solid tumors. By contrast, a conventional anti-tumor cell immunotoxin of equivalent in vitro potency produced only minor, transient antitumor effects but, when combined, the two immunotoxins induced permanent complete remissions in over half of the animals. These experiments indicate that immunotoxins directed against recently described markers on vascular endothelial cells in human tumors could provide a general treatment for solid tumors in humans.

Effects of an anti-CD5 immunoconjugate (CD5-plus) in recent onset type I diabetes mellitus: a preliminary investigation. The CD5 Diabetes Project Team

Type-I (insulin-dependent) diabetes mellitus is an immunologically mediated disease that results in destruction of the insulin secreting beta cells of the pancreas. T cells have been implicated in the pathogenesis of this disease. One novel form of anti-T-cell therapy is the immunoconjugate CD5-Plus. This agent is composed of the murine IgG1 monoclonal antibody H65, which is directed toward the CD5+ antigen; and ricin A chain, a ribosomal inhibitor protein. We performed a pilot study to evaluate the safety of the immunoconjugate in subjects with type-I diabetes mellitus. We conducted a dose-escalation study using CD5-Plus given as an intravenous infusion for 5 consecutive days. Fifteen subjects (12 men and 3 women) with a mean age of 26 years, a mean duration of diabetes of 4.8 months, and a minimum stimulated C peptide of 0.3 pmol/mL were entered. Six subjects each were treated at the 0.1 and 0.2 mg/kg/day dosage levels, and three subjects were treated at the 0.33 mg/kg/day dose. Glycemic control was determined monthly by recording the glycohemoglobin, total daily insulin requirements, and fasting blood glucoses. Beta-cell function was measured by determining the C-peptide response to a mixed formula meal (Sustacal) at baseline and at 1,3,6,9, and 12 months after treatment. The area under the curve (AUC) of the C-peptide response was calculated and, to reduce variability, related to that of the same subject at baseline. An analysis of subjects who retained at least 80% of their baseline beta-cell function as measured by the AUC was performed.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-tumor activity of a blocked ricin immunotoxin with specificity against the cluster-5A antigen associated with human small-cell lung cancer

The monoclonal antibody (MAb SEN31, a mouse IgG1 which recognizes the cluster-5a antigen on small-cell lung cancer (SCLC) cells, was used to prepare a selective and potent blocked ricin immunotoxin. In a series of experiments in vitro and in a SCLC xenograft model in nude mice, the tumor localization potential of the radiolabeled antibody SEN31 and the anti-tumor activity of the immunotoxin SEN31-bR, the non-specific binding activity of which had been greatly reduced by blocking of the galactose binding domains of the B-chain, was determined. Radiolabeling of SEN31 was performed by linking a 67Ga-labeled desferrioxamine moiety to the oligosaccharide side chains of the antibody in order to preserve the specific cell-binding activity. 67Ga-SEN31 bound to the antigenic sites on cells of the SW2 SCLC cell line, with a dissociation constant of 3.5 nM and, when injected i.v., selectively localized at the site of s.c.-growing SW2 tumor xenografts in nude mice, with a tumor-to-blood ratio of 3.5. The immunotoxin SEN31-bR was potently and selectively active against SCLC cell lines both of classic and of variant morphologies. At a concentration of 300 pM the immunotoxin selectively eliminated 4.5 logs of clonogenic tumor cells. In nude mice, SEN31-bR was cleared from the blood with biphasic kinetics following i.v. injection and maintained a stable serum level during continuous i.p. infusion. The growth of s.c. SW2 solid-tumor xenografts was delayed following a single i.v. injection or a continuous i.p. infusion, each at a non-toxic dose.

Four ricin chain A-based immunotoxins directed against the common chronic lymphocytic leukemia antigen: in vitro characterization

The common B-chronic lymphocytic leukemia (B-CLL) antigen (cCLLa) appears to be ideal for targeted immunotherapy in that it is the most prevalent and disease-restricted marker in B-CLL. To assess this potential, we developed four immunotoxins (ITs) of anti-cCLLa monoclonal antibody CLL2m (an IgG2a kappa), using ricin chain A (RTA) or its deglycosylated derivative (dgA), each conjugated to either the whole IgG molecule or its Fab' fragment. Each IT was tested in vitro for specificity and cytotoxic activity (assessed by protein synthesis inhibition [PSI] and by cell kill [CK] in the clonogenic assay) against B-CLL cells. RTA-based anti-CD5 ITs and enriched normal B and T lymphocytes were used as controls. Each IT exhibited antigen-specific, dose-dependent activity. Thus, whereas B-CLL cells exhibited dose-dependent PSI and CK (whether the B-CLL clone was CD5+ or CD5-), normal B (cCLLa-/CD5-) and T lymphocytes (cCLLa-/CD5+) remained unaffected. IT potency was independent of toxin glycosylation, but was slightly influenced by antibody valence; divalent ITs were twice as potent as monovalent ITs (IC50, 2.3 v 7.1 x 10(-11) mol/L; CK, 2.6- v 2.0-log reached with 524 v 1,072 IT molecules bound/cell, respectively). In the presence of ammonium chloride or Verapamil, IT-induced CK was enhanced 10- to 80-fold. These data suggest that the cCLLa is a promising target for IT-based immunotherapy of B-CLL in vivo and ex vivo.

Restoration of interferon alpha potentiation of a recombinant ricin A chain immunotoxin following cytoreduction of xenografts of advanced ovarian tumors

BACKGROUND

We have demonstrated that, in the human ovarian carcinoma cell line (OVCAR-3), recombinant human interferon alpha (rHuIFN-alpha) potentiated in vitro inhibition of protein synthesis by immunotoxins. The antitumor activity of intracavitary immunotoxin administered to nude mice 5 days after tumor cell injection was enhanced by a nontherapeutic dose of rHuIFN-alpha, as evidenced by increased survival time.

PURPOSE

Our purpose was to determine the outcome of treatment with immunotoxin and rHuIFN-alpha in xenografts of more advanced tumors.

METHODS

At 10 or 15 days after tumor cell injection, nude mice with peritoneal OVCAR-3 xenografts were treated intraperitoneally with immunotoxin or with 454A12 monoclonal antibody (MAb) recombinant ricin A chain (rRA), alone or combined with a nontherapeutic dose of rHuIFN-alpha. The immunotoxin was composed of rRA covalently bound to an anti-CD71 (transferrin receptor) MAb. In other experiments, mice were treated intraperitoneally with cyclophosphamide and cisplatin to reduce tumor size on days 20 and 27 after tumor cell inoculation and then, beginning on day 40, with immunotoxin alone or combined with rHuIFN-alpha.

RESULTS

Initiation of treatment 10 days after OVCAR-3 transplantation significantly increased median survival from 41 to 89 days (10% survivors on day 120) with 454A12 MAb rRA alone and to more than 120 days (70% survivors) with 454A12 MAb rRA combined with rHuIFN-alpha (P < .0001). The increase in survival time between tumor-bearing mice treated with immunotoxin combined with rHuIFN-alpha and those treated with immunotoxin alone was statistically significant (P = .017). In contrast, the 15-day transplant tumors were not curable with immunotoxin therapy (survival, 72 days; 0% survivors) and were refractory to rHuIFN-alpha potentiation (survival, 75 days; 0% survivors). After the second course of chemotherapy to reduce the size of the advanced tumors (day 40), during the ascites cell count nadir, initiation of treatment with 454A12 MAb rRA alone or combined with rHuIFN-alpha resulted in significantly different survival times of 129 and 162 days, respectively (P = .0037). Pathologic examination of surviving mice treated with chemotherapy and 454A12 MAb rRA alone or in combination with rHuIFN-alpha revealed that one (17%) of six mice and 11 (65%) of 17 were tumor free, respectively.

CONCLUSIONS

The synergy between immunotoxins and IFN-alpha is dependent on tumor burden. These agents are less effective against large tumor burdens (i.e., advanced stage disease), but their beneficial effects re-emerge after cytoreduction by combination chemotherapy.

IMPLICATIONS

The ideal setting for testing the efficacy of intracavitary immunotoxin combined with rHuIFN-alpha after front-line chemotherapy is in patients with residual tumor refractory to additional chemotherapy or in those with toxic effects that prevent delivery of effective doses.

Overcoming tumor necrosis factor and drug resistance of human tumor cell lines by combination treatment with anti-Fas antibody and drugs or toxins

Monoclonal mouse anti-Fas antibody is directed against Fas antigen, a M(r) 36,000 encoded polypeptide that belongs to the family of cell surface proteins which includes nerve growth factor receptor, tumor necrosis factor (TNF) receptors, B-cell antigen CD40, and T-cell antigens OX40. Anti-Fas antibody mimics TNF-alpha in its cytolytic activity but not in other TNF-alpha-mediated activities. Thus, we examined if anti-Fas antibody synergizes in cytotoxicity with toxins and drugs. The present studies demonstrate that anti-Fas antibody in combination with diphtheria toxin (DTX), Adriamycin, or cis-platinum results in enhanced cytotoxicity and synergy and also overrides resistance to TNF, drugs, or toxins when tested against a battery of human tumor cell lines. Synergy with anti-Fas and DTX requires that DTX is enzymatically active, since inhibitors of DTX-mediated protein synthesis inhibition resulted in loss of synergy. When the plant toxin ricin was used, there was no synergy with anti-Fas antibody but rather an additive effect. The synergy was not obtained in a TNF receptor-negative line but was achieved with other anti-Fas-resistant lines. Cell lines resistant to either Adriamycin or cis-platinum were rendered sensitive by the combination of drug and anti-Fas antibody. Further, combination treatment of anti-Fas and Adriamycin overcame resistance of the gp 170-expressing, multidrug-resistant MDR ovarian line. In all cases, cytotoxicity was augmented by pretreatment of target cells with gamma-interferon which upregulates Fas antigen expression. These results show that anti-Fas antibody can synergize in cytotoxicity with toxins and chemotherapeutic drugs, and combination treatment can reverse resistance to TNF, toxins, and/or drugs.

Immunotoxin therapy of cancer

Differentiation antigens, hormones and growth factor receptors, and viral antigens are expressed on the surface of a variety of malignant and dysfunctional cells in humans. Murine and human monoclonal antibodies, recombinant hormone and growth factors, and recombinant soluble viral glycoprotein receptors have been generated that can target diseased human cells in vitro and in vivo. Highly potent peptide toxins that catalytically inactivate protein synthesis have been linked both chemically and genetically to these ligands to produce a new class of cancer therapeutic agents called immunotoxins. This article describes the structure, physiology, and initial clinical results with these molecules. Ongoing clinical studies are beginning to define a role for these unique agents in patients with malignancies of minimal bulk in combination with conventional chemoradiotherapy.

Adjuvant immunotoxin therapy with anti-B4-blocked ricin after autologous bone marrow transplantation for patients with B-cell non-Hodgkin's lymphoma

Anti-B-blocked ricin (anti-B4-bR) combines the specificity of the anti-B4 (CD19) monoclonal antibody with the protein toxin "blocked ricin." In blocked ricin, affinity ligands are attached to the ricin B-chain to attenuate its lectin binding capacity. In a phase I trial, Anti-B4-bR was administered by 7-day continuous infusion to 12 patients in complete remission after autologous bone marrow transplantation (ABMT) for relapsed B-cell non-Hodgkin's lymphoma (NHL). Patients were treated at 20, 40, and 50 micrograms/kg/d for 7 days. Potentially therapeutic serum levels could be sustained for 3 to 4 days. The maximum tolerated dose was 40 micrograms/kg/d for 7 days (total 280 micrograms/kg). The dose-limiting toxicities were reversible grade IV thrombocytopenia and elevation of hepatic transaminases. Mild capillary leak syndrome was manifested by hypoalbuminemia, peripheral edema (4 patients), and dyspnea (1 patient). Anti-immunotoxin antibodies developed in 7 patients. Eleven patients remain in complete remission between 13 and 26 months post-ABMT (median 17 months). These results show that Anti-B4-bR can be administered with tolerable, reversible toxicities to patients with B-cell NHL in complete remission following ABMT.

Immunotoxin therapy of small-cell lung cancer. N901-blocked ricin for relapsed small-cell lung cancer

Despite its initial chemosensitivity, small-cell lung cancer (SCLC) is rarely cured with chemotherapy alone, and fewer than 5% of patients are alive at 5 years. Immunotoxin therapy appears to offer promise in treating the minimal residual disease that remains after induction chemotherapy. We have studied N901-bR in patients with relapsed SCLS. N901-bR consists of the N901 monoclonal antibody (MoAb) and blocked ricin, an altered ricin molecule in which the galactose binding sites of the ricin B-chain which mediate nonspecific binding of the toxin are blocked through the covalent binding of ligands. N901 is an anti-NCAM (CD56) MoAb which binds to SCLC tumors and cell lines, cardiac muscle, natural killer (NK) cells, and peripheral nerve. N901-bR showed a 2.7 log greater in vitro cytotoxicity to the CD56-positive cell line SE-2 than to the antigen-negative Namalwa cell line. Nineteen patients with relapsed antigen-negative Namalwa cell line. Nineteen patients with relapsed and/or refractory SCLC have been entered into a phase I study at doses ranging from 5 to 40 micrograms/kg/day given as a 7-day continuous infusion. The dose-limiting toxicity is capillary leak syndrome observed in two thirds of the patients treated at 40 micrograms/kg/day. One patient at the maximum tolerated dose, 30 micrograms/kg/day x 7 days, has achieved a partial response to N901-bR. No patient has developed clinically significant peripheral or central neuropathy. We plan to begin a phase II study of N901-bR following induction chemotherapy in patients with SCLC.

Anti-B4-blocked ricin immunotoxin shows therapeutic efficacy in four different SCID mouse tumor models

Anti-CD19 monoclonal antibody anti-B4 (IgG1) conjugated to the novel toxin-blocked ricin forms a potent immunotoxin, anti-B4-blocked ricin, that kills greater than 4.5 logs of CD19-positive cells in vitro after a 24-h exposure to a conjugate concentration of 5 x 10(-9) M (1.11 micrograms/ml). The efficacy of anti-B4-blocked ricin in vivo was assessed in survival models of SCID mice bearing either a human B-cell lymphoma (Namalwa), a human non-T and non-B acute lymphoblastic leukemia (Nalm-6), or a murine B-cell lymphoma transfected with the human CD19 gene (300B4). In one model, 5 x 10(7) tumor cells were injected i.p., and 1 h later the mice were treated with i.v. bolus injections of anti-B4-blocked ricin at 100 micrograms/kg/day for 5 days. Controls included similar treatment with anti-B4 antibody (72 micrograms/kg/day or 2 mg/kg/day for 5 days) alone or with the isotype-matched nonspecific immunotoxin, N901-blocked ricin (100 micrograms/kg/day). In a second model, 4 x 10(6) tumor cells were injected i.v., and 7 days later mice were treated i.v. as above. Anti-B4-blocked ricin showed efficacy by killing in vivo up to 3 logs of tumor cells, which was manifested in significant prolongation of the life of the treated animals. Only very limited or no effects were observed in animals treated with either anti-B4 antibody alone or N901-blocked ricin control conjugate. The concentration of anti-B4-blocked ricin in the blood of animals was 150 ng/ml after the first i.v. injection and about 800 ng/ml following the fifth injection of conjugate. This increase may be due to damage to the reticuloendothelial system by anti-B4-blocked ricin, since the rate of clearance of carbon from blood also decreased 5-fold after five injections as compared to the rate after only one injection. These studies indicate that anti-B4-blocked ricin has the potential to increase survival times of hosts with malignant disease.

Efficacy of transferrin receptor-targeted immunotoxins in brain tumor cell lines and pediatric brain tumors

The efficacy and cytotoxic properties of immunotoxin conjugates directed against the transferrin receptor were examined in cell lines and operative specimens from pediatric brain tumors. Dose-response relationships were assessed for immunotoxin-mediated inhibition of protein synthesis for two immunotoxins, 454A12-rRA and anti-tfnR-CRM 107. Three target medulloblastoma cell lines (DAOY, D283MED, and D341MED), a glioblastoma (U373), and a neuroblastoma (SH-SY5Y) cell line exhibited similar sensitivity to both immunotoxins with IC50s in the 10(-9)-10(-10) M range. The time course of protein synthesis inhibition by the immunotoxins in DAOY cells showed that inhibition by anti-tfnR-CRM 107 was rapid and apparent by 6 h of incubation. In contrast, a response to 454A12-rRA was not observed until 16 h. Cell viability was decreased 30-40% by 24 h after removing 454A12-rRA (1 x 10(-9) M) and was maximally decreased 70-80% after 3 days. The efficacy of the immunotoxins on a variety of fresh specimens of pediatric brain tumors was also examined. The more aggressive and malignant tumor types such as glioblastoma multiforme and medulloblastoma had low IC50 values (10(-12) M), indicating that these tumors were extremely sensitive to transferrin receptor-targeted immunotoxins. In general, protein synthesis in slow-growing and benign tumors was not as greatly affected by immunotoxins. Immunoblots showed expression of transferrin receptors on the cell lines and tumors which correlated with in vitro sensitivity to immunotoxin. The results demonstrate that two immunotoxins targeted to the transferrin receptor are efficacious in killing brain tumor cell lines and primary tumor cultures at very low concentrations and that highly malignant tumors are especially sensitive to this cytotoxic response.

Differential patterns of response in patients with rheumatoid arthritis following administration of an anti-CD 5 immunoconjugate

As part of the clinical investigation of a new biologic agent in the treatment of rheumatoid arthritis (RA) various outcome measures were utilized to evaluate clinical activity in two multicenter open label protocols. These measures included the single criteria of joint tenderness and swelling counts and scores and composite criteria based on the Paulus analysis of four placebo-controlled CSSRD studies of second line agents in RA. Findings suggest a difference in the pattern of response between early and long-standing RA. Changes in both the swollen and tender joint counts should be utilized, especially in a population with sustained disease.

Biodistribution and in vivo antitumor efficacy of the systemically administered anti-human T-leukemia immunotoxins and potentiation of their efficacy by alpha-interferon

In this study, the systemically administered anti-human T-leukemia immunotoxins (ITs) are shown to be effective for tumor suppression in Ichikawa T-leukemia-bearing nude mice. In addition, their antitumor efficacy was markedly potentiated by recombinant human IFN-alpha. The combination of ITs and IFN-alpha effectively killed the tumor in the majority of the treated mice; 9 of the 12 treated mice survived tumor-free for as long as they were followed, i.e. for 140 days. Two different ITs, SN1-ricin A chain (RA) and SN2-RA, were used together to minimize the problem of tumor heterogeneity; monoclonal antibodies SN1 and SN2 are directed toward two different human T-leukemia associated cell surface antigens. In the biodistribution experiments, the paired label technique was used to include a reliable internal control. In an experiment, equal amounts of 125I-SN1-RA and 131I-labelled isotype-matching control IgG (IgG1-kappa)-RA were mixed and administered i.v. into tumor-bearing nude mice. In a separate experiment, a mixture of equal amounts of 125I-SN2-RA and 131I-control IgG-RA was administered i.v. This technique allowed us to distinguish the immunospecific uptake from the non-immunospecific uptake of ITs into individual organs. The present results clearly show that both SN1-RA and SN2-RA are specifically localized in tumors after systemic administration. For instance, 24 h after the administration of a radiolabelled mixture, the ratio of 125I/131I in the tumor was 7.0 and 23.5, respectively, for the SN1-RA/control IgG-RA mixture and the SN2-RA/control IgG-RA mixture. Such high ratios of 125I/131I were detected in the tumors throughout the experiments between 30 min and 24 h after the administration of the paired label mixture.

Cytotoxicity of CD3-ricin A chain immunotoxins in relation to cellular uptake and degradation kinetics

The cytotoxicity of WT32 (CD3)-ricin A immunotoxin (IT) to the acute lymphoblastic leukemia T-cell line Jurkat was compared with the rate of internalization and intracellular degradation of WT32 and WT32-ricin A during continuous exposure. Moreover, the influence of NH4Cl and monensin on these processes was studied. Based on protein synthesis inhibition ([3H]leucine incorporation), it appeared that cytotoxicity was not fully expressed directly after exposure to IT due to a delay in either the internalization of membrane-bound IT or the action of intracellular ricin A. Varying the duration of incubation and postponing [3H]leucine addition for up to 24 h after initiation showed that cytotoxicity occurred in two phases, rapid internalization of initially bound IT followed by a continuous but slower uptake, possibly due to reexpression of the CD3 antigen. No differences were found in the rate of internalization and degradation of 125I-labeled WT32 and WT32-ricin A. Internalization started rapidly after binding at 37 degrees C, was fastest during the first 12 h (+/- 360,000 molecules/cell), and continued for at least 24 h (+/- 420,000 molecules/cell). Exocytosis of intracellularly degraded molecules became measurable after 1 to 2 h of incubation at 37 degrees C and increased to approximately 400,000 molecules/cell in 24 h. After 4 h of incubation at 37 degrees C the number of internalized molecules exceeded the amount of WT32 that could maximally bind to the cell membrane (+/- 150,000 molecules/cell), confirming reexpression of antigen. The addition of NH4Cl and monensin enhanced the cytotoxicity of WT32-ricin A, probably due to an increased intracellular amount of IT. These agents appeared to reduce strongly the degradation of internalized WT32, resulting in an accumulation of intracellular molecules. NH4Cl was most effective during the first 12 h of incubation, whereas monensin increased the amount of intracellular WT32 molecules after 2 to 24 h. Our observations suggest that incubation conditions for the optimal cytotoxicity of IT treatment can be predicted by studying the internalization and degradation of the IT or respective monoclonal antibody.