Molecular mechanisms of phagocytic uptake in mammalian cells.

Phagocytosis is a highly conserved, complex process that has evolved to counter the constant threat posed by pathogens, effete cells and debris. Classically defined as a mechanism for internalising and destroying particles greater than 0.5 mum in size, it is a receptor-mediated, actin-driven process. The best-studied phagocytic receptors are the opsono-receptors, FcgammaR and CR3. Phagocytic uptake involves actin dynamics including polymerisation, bundling, contraction, severing and depolymerisation of actin filaments. Recent evidence points to the importance of membrane remodelling during phagocytosis, both in terms of changes in lipid composition and delivery of new membrane to the sites of particle binding. Here we review the molecular mechanisms of phagocytic uptake and some of the strategies developed by microbial pathogens to manipulate this process.

The urinary corticoid:creatinine ratio (UCCR) in healthy cats undergoing hospitalisation.

Thirty-one healthy pet cats had voided urine samples collected prior to, during and after a brief period of hospitalisation. Urinary corticoids were measured, both prior to and following an extraction technique, and the urinary corticoid:creatinine ratio (UCCR) was calculated. Associations between the UCCR and age, sex, breed and time of urine collection were investigated. There was no significant relationship established between age, sex and breed and the UCCR. A significant increase in the UCCR, however, did occur between the first home collected and first hospitalised urine sample, but only when comparing extracted corticoid results. A normal range for feline UCCR is established for the chemiluminescent immunoassay used in this study.

Cardiac troponin I in cats with hypertrophic cardiomyopathy.

The molecular structure of cardiac troponin I (cTnI) is highly conserved across mammalian species and assays developed for its measurement in human patients have been validated in a number of veterinary species. A raised concentration of circulating cTnI is a sensitive and specific marker of cardiac myocyte injury. Raised levels have been documented in a variety of cardiac diseases in both human and veterinary patients. This study compared serum cTnI concentrations between 16 cats diagnosed with hypertrophic cardiomyopathy (HCM) using echocardiography and 18 control cats. The results show that cats with HCM have significantly higher concentration of serum cTnI (median 0.95 ng/ml, range 0.2-4.1 ng/ml) than control cats (median <0.2 ng/ml, range <0.2-0.25 ng/ml) [P<0.0001]. Furthermore in cats with cardiomyopathy a weak correlation was found between the thickness of the left ventricular freewall in diastole measured by ultrasound and serum cTnI concentration (r(2)=0.28;P=0.036). These results suggest that measurement of serum cTnI concentration may enable cats with cardiomyopathy to be distinguished from normal cats using the assay described here.

Concurrent tirapazamine and radiotherapy for advanced head and neck carcinomas: a Phase II study.

PURPOSE: To evaluate the efficacy and toxicity of tirapazamine, a hypoxic cytotoxin, combined with conventional radiotherapy (RT) for advanced head and neck carcinomas. MATERIALS AND METHODS: From Oct. 1994 to Nov. 1996, 40 patients with stage III or IV carcinomas of the head and neck were enrolled in a Phase II trial to receive conventional RT (70 Gy in 7 weeks) with concurrent tirapazamine (159 mg/m2 intravenously, 3 times per week for 12 doses). One patient subsequently withdrew from the protocol treatment, and was excluded from analyses. Among the 39 cases, the primary sites were located in the oropharynx (n = 28), supraglottic larynx (n = 6), or hypopharynx (n = 5). Twenty-seven patients had T3 or T4, and 27 had N2 or N3 disease. RESULTS: Thirty-two (82%) patients received full 12 drug doses. Thirty-two patients (82%) received full 70 Gy of RT. The most frequent drug toxicities were muscle cramps (77%) and nausea/vomiting (62%), usually grade 1 or 2. Overall, 13 patients (33%) experienced grade 3 or 4 drug-related toxicities. No excessive RT-associated acute normal tissue reactions were observed. With a median follow-up of 13 months, the 1-year and 2-year local control rate was 64% and 59% respectively. CONCLUSION: The tirapazamine regimen was well tolerated with a compliance rate of 82%. The toxicity of RT with concurrent tirapazamine was acceptable in treating advanced head and neck carcinomas. The disease control trend was encouraging. Further clinical studies are warranted.

Intraventricular immunotoxin therapy for leptomeningeal neoplasia.

OBJECTIVE: The goals of this clinical trial of intraventricular 454A12-rRA therapy were to identify dose-limiting toxicities, to evaluate the pharmacokinetics of single-dose intraventricular 454A12-rRA, and to detect antitumor activity. METHODS: We performed a pilot study of intraventricular therapy with the immunotoxin 454A12-rRA in eight patients with leptomeningeal spread of systemic neoplasia. The immunotoxin 454A12-rRA is a conjugate of a monoclonal antibody against the human transferrin receptor and recombinant ricin A chain, the enzymatically active subunit of the protein toxin ricin. Patients were treated with single doses of 454A12-rRA ranging from 1.2 to 1200 micrograms. RESULTS: The early phase half-life of 454A12-rRA in ventricular cerebrospinal fluid (CSF) averaged 44 +/- 21 minutes, and the late phase half-life averaged 237 +/- 86 minutes. The clearance of the immunotoxin was faster than the clearance of coinjected technetium-99m-diethylenetriamine penta-acetic acid, averaging approximately 2.4-fold greater. No 454A12-rRA degradation was detected by Western blot analysis of ventricular CSF for a period of 24 hours, and bioactivity was retained in CSF paralleling the concentration of immunotoxin. No acute or chronic drug toxicity was identified in patients who received less than or equal to 38 micrograms of 454A12-rRA by intraventricular injection. Doses more than or equal to 120 micrograms caused a CSF inflammatory response that was associated with transient headache, vomiting, and altered mental status. This acute syndrome was responsive to steroids and CSF drainage. No systemic toxicity was detected. In four of the eight patients, a greater than 50% reduction of tumor cell counts in the lumbar CSF occurred within 5 to 7 days after the intraventricular dose of 454A12-rRA; however, no patient had their CSF cleared of tumor, and clinical or magnetic resonance imaging evidence of tumor progression was demonstrated in seven of the eight patients after treatment. CONCLUSION: Tumoricidal concentrations of the immunotoxin 454A12-rRA can be attained safely in the CSF of patients with leptomeningeal tumor spread.

Epidural analgesia for labour in a patient with Ebstein's anomaly.

Ebstein's anomaly is an uncommon congenital cardiac defect which is associated with cyanosis and arrhythmias. There have been very few previous reported cases of successful outcome in pregnancy in women with this disorder. We describe the successful analgesic management of an obstetric patient who had been known to have Ebstein's anomaly since childhood. Her first pregnancy was uneventful and analgesia during labour was provided by an epidural. During her second pregnancy she presented to our hospital as her condition had deteriorated. Symptomatic control was achieved with digoxin. Despite this, several episodes of hospitalization were needed pre-partum for rest and oxygen therapy. After the onset of spontaneous labour, analgesia was managed by an epidural using bupivacaine. Invasive monitoring was not deemed appropriate due to increased risk and questionable usefulness. Vaginal delivery was managed with elective lift-out forceps to minimize the stress of pushing. When reviewed two months post-partum she still required digoxin although her symptoms had improved considerably. The successful management of Ebstein's anomaly in pregnancy should include team management from early in pregnancy.

Patients' knowledge of anaesthetic practice and the rôle of anaesthetists.

Patients were questioned pre-operatively to assess the level of their knowledge with regard to anaesthetic qualifications, anaesthesia and the role of anaesthetists. Thirty-five percent did not realise that anaesthetists were qualified doctors and only 25% could mention any duties that anaesthetists might have outside the operating theatre. However, those questioned were better informed about the anaesthetist's role in monitoring the patient during surgery and recovery.

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.

Phase I study of antilipopolysaccharide human monoclonal antibody MAB-T88.

Monoclonal antibody MAB-T88 is a human monoclonal immunoglobulin M antibody directed at the lipopolysaccharide of gram-negative bacteria. In this study, nine patients who were expected to become neutropenic from antineoplastic chemotherapy received an infusion of MAB-T88, three patients at each of three doses: 1, 4, and 8 mg/kg of body weight. MAB-T88 was shown to be safe, with an effective half-life in plasma of 25.4 h, and no patient developed immunoglobulin G antibody to MAB-T88.

Intravenous administration of recombinant human macrophage colony-stimulating factor to patients with metastatic cancer: a phase I study.

PURPOSE: Recombinant human macrophage colony-stimulating factor (M-CSF) has been shown to stimulate specifically macrophage lineage differentiation in vitro and to induce cells capable of antitumor activity alone or in combination with an antibody. The administration of M-CSF to mice has demonstrated antitumor therapeutic effects in vivo. Therefore, a phase I trial of M-CSF administration to patients with metastatic cancer was undertaken. PATIENTS AND METHODS: M-CSF was given by intermittent intravenous bolus infusion every 8 hours for 7 days; the treatment cycle was repeated once after a week of rest. Cohorts of three patients underwent dose escalation from 10 to 100,000 micrograms/m2/d; 23 patients received 27 courses of M-CSF administration. All patients had metastatic solid tumors refractory to conventional therapy, including renal cell carcinoma (RCC) (nine), melanoma (seven), and colorectal carcinoma (seven). RESULTS: Treatment-related toxicity was minimal; five patients developed transient signs of ocular or periorbital inflammation, with iridocyclitis as the most severe manifestation. At the highest doses, platelet counts decreased with therapy (but remained > 100,000/mm3) and the absolute monocyte count increased during the course of therapy. Only at 30,000 and 100,000 micrograms/m2/d was treatment limited because of toxicity (iritis and malaise). Pharmacokinetic studies demonstrated up to a 1,000-fold increase in circulating serum M-CSF after bolus infusion; half-life varied from 1 to 6 hours. Complete regression of mediastinal adenopathy and multiple pulmonary metastases were observed in one patient with RCC. CONCLUSION: Recombinant M-CSF can be administered safely to patients with metastatic cancer at doses that demonstrate biologic activity.

Interferon-gamma induced by administration of recombinant interleukin-2 to patients with cancer: kinetics, dose dependence, and correlation with physiological and therapeutic response.

The administration of recombinant interleukin-2 as an i.v. bolus at dose levels of from 1 to 30 MIU/m2 to patients with cancer induces easily measurable serum interferon-gamma levels of 1 to 500 U/ml. After a lag of 1 h, interferon-gamma rises to a maximum at 4 h and then slowly decreases. The peak values are poorly correlated with the dose of interleukin-2, and thus must be also be dependent on other factors. Successive administration of interleukin-2 typically increases the peak level of interferon-gamma fourfold, but does not diminish the lag period. Peak levels of interferon-gamma are also increased by concurrent administration of interferon-beta with interleukin-2. Continuous i.v. infusion of 1.5 to 20 MIU/m2 of interleukin-2/day results in interferon-gamma levels of 1 to 7 U/ml. Hypotension, which is characteristically associated with interleukin-2 administration, is correlated with interferon-gamma levels in only some patients. There was no apparent correlation between tumor regression and serum interferon-gamma levels.

Phase I trial of recombinant macrophage colony-stimulating factor by rapid intravenous infusion in patients with cancer.

Fourteen patients were entered into a phase I dose-escalation trial of macrophage colony-stimulating factor (M-CSF). M-CSF was administered to inpatients by rapid 15 min i.v. infusion every 8 h x 5 days, repeated after a 9-day rest. Dose levels evaluated were 20, 40, 80, 330, and 1,100 micrograms/m2. Monitoring of patients every 4 h included vital signs, daily complete blood count (CBC), and serum chemistries (SGOT, creatinine, and bilirubin) while receiving M-CSF. No clinical or laboratory evidence of toxicity was seen. The average serum t1/2 varied with dose level. At 330 and 1,100 micrograms/m2, the serum t1/2 was 25 and 84 min, respectively, implying a saturable mechanism of clearance. After 5 days of treatment, the t1/2 decreased by twofold, consistent with enhancement of the saturable mechanism. Monocyte cytotoxicity against the A375 melanoma cell line was evaluated pretreatment and day 5 of each cycle. No consistent enhancement of monocyte cytotoxicity was seen. No effect on peripheral blood monocyte number was seen until the 1,100 micrograms/m2 dose level. At this dose level, the mean monocyte number on day 5 was increased compared to baseline (1,300 mm3 vs. 300/mm3). Clinical activity was seen in two patients with previously progressive leiomyosarcoma metastatic to the liver. A partial response (PR) lasting 7 months occurred at the 330 micrograms/m2 dose level while a patient treated at 1,100 micrograms/m2 has had stable disease for 20+ months. The maximum tolerated dose (MTD) of M-CSF was not determined. Based on clinical responses, a phase II trial is warranted in patients with metastatic soft tissue sarcoma.

Suppression and transient induction of lymphokines in cancer patients after administration of polyethylene glycolated interleukin-2.

Polyethylene glycolated (pegylated) interleukin-2 (PEG IL-2) was administered as a weekly i.v. bolus to patients with metastatic cancer in a phase-I trial. Efficacy, toxicity and pharmacokinetics have been described previously. To explore mechanism of IL-2 action and discover predictors of efficacy, the levels of several lymphokines were measured in pharmacokinetic serum samples. IL-1 beta and IL-6 were elevated in many patients before PEG IL-2 administration, forming a continuous, log-normal distribution among patients. The levels of the two lymphokines were strongly correlated. However, no significant correlation could be found between these levels, clinical chemistry, or tumor regression seen after PEG IL-2 administration. Three hours after PEG IL-2 administration, IL-1 beta and IL-6 levels, if elevated, fell to normal. In all patients, independent of initial levels, IL-6 and IFN-gamma, but not IL-1 beta, increased 4 to 6 h after the injection and then fell rapidly, even though PEG IL-2 levels were high and often changed only slightly during this period. This suggests an active shut down of lymphokine synthesis, or an increase in elimination rate. After the fourth administration of PEG IL-2, the peak level of IFN-gamma was 2 to 20 times higher than after the first, while the peak level of IL-6 did not change in a consistent direction. Responding patients had typical peak levels of IL-6 and IFN-gamma. Low levels of TNF and IL-4 were occasionally seen before and after PEG IL-2 administration, but no consistent pattern was evident.

A phase I trial of recombinant human macrophage colony-stimulating factor by rapid intravenous infusion in patients with refractory malignancy.

Twenty patients with advanced cancer for which there was no effective standard therapy or whose disease was refractory to standard therapy were treated with recombinant macrophage colony-stimulating factor (rM-CSF). The rM-CSF was administered by intravenous bolus infusion for 5 consecutive days every other week for 2 treatment weeks. The doses administered ranged from 30 to 33,000 micrograms/m2/day. There was no intrapatient dose escalation. There were minimal to no systemic side effects seen, except for acute dyspnea noted in three patients. The dyspnea was felt to be related to the rate of infusion and did not recur in one patient given additional rM-CSF at a slower infusion rate. The major hematologic effect seen was a mild decrease in platelet count, which began to recover while the patients continued to receive the rM-CSF. The clearance of rM-CSF was dose dependent. Lower doses resulted in a saturable mechanism felt to represent cellular uptake. Clearance at higher doses demonstrated both a first-order mechanism at high serum rM-CSF concentrations, representing renal clearance, as well as a saturable mechanism at low serum concentrations. The maximum mean serum half-life was reached at dose levels of greater than or equal to 3,690 micrograms/m2 and was in the range of 234-258 min. By this route of administration, rises in absolute monocyte count were slight and seen only at doses of greater than or equal to 450 micrograms/m2 during the second therapy week. The maximum tolerated dose was not reached in this study because of lack of availability of rM-CSF.

Phase I trial of recombinant human macrophage colony-stimulating factor in patients with invasive fungal infections.

A phase I dose escalation trial of recombinant human macrophage colony-stimulating factor (rhM-CSF) in combination with conventional antifungal therapy was conducted in 24 marrow transplant recipients with invasive fungal infection. Daily doses ranged from 100 to 2,000 micrograms/m2/d. Toxicity, such as constitutional symptoms, directly ascribed to rhM-CSF was not observed; however, transient, dose-related thrombocytopenia was observed. Patients who received 2,000 micrograms/m2/d of rhM-CSF had a mean reduction in platelet count of 61,000/mm3 during the rhM-CSF infusion period, which was significant when compared with patients who received lower doses of rhM-CSF (P = .008). Fourteen of the 16 patients who received rhM-CSF after undergoing allogeneic bone marrow transplantation had no change in the severity of graft-versus-host disease (GVHD) while receiving rhM-CSF. One had an increase in the severity of GVHD and one had a decrease. There were no effects on neutrophil, monocyte, or lymphocyte counts. Six patients had resolution of their infections, 12 were not evaluable for response, and six did not respond. Ten patients survived 100 days after initiation of rhM-CSF and 14 died. Further trials with rhM-CSF to assess antifungal activity are indicated.

Detection and quantification of human immunodeficiency virus RNA in patient serum by use of the polymerase chain reaction.

Human immunodeficiency virus (HIV) RNA was detected and quantified in the serum of HIV-seropositive individuals using the polymerase chain reaction (PCR) and a nonisotopic enzyme-linked affinity assay. Of 55 HIV-infected patients who were not receiving therapy, serum HIV RNA was detected in 9 of 19 who were asymptomatic, 11 of 16 with AIDS-related complex (ARC), and 18 of 20 with AIDS, with copy numbers ranging from 10(2) to greater than or equal to 5 x 10(4) 200 microliters of serum based on a relationship between absorbance and known copy number of gag gene RNA. Linear regression analysis demonstrated a correlation between infectious titer in 42 patient sera cocultured with donor peripheral blood mononuclear cells (PBMC) and PCR product absorbance (r = .70, P less than .01). Serum HIV RNA detected by PCR also correlated with serum p24 antigen positivity, CD4 counts less than 400/mm3, and the presence of HIV-related symptoms or disease. Quantification of infectious HIV RNA in cell-free serum by PCR may be useful as a marker for for disease progression or in monitoring antiviral therapy.

Inhibition of human immunodeficiency virus gene amplification by heparin.

Gene amplification of virus-specific sequences is widely used as a method to detect or confirm human immunodeficiency virus (HIV) infection. In this study we used an enzyme-linked affinity assay to quantify polymerase chain reaction products from whole blood, plasma, and separated mononuclear cells collected in the presence of four common anticoagulants: acid citrate dextrose, sodium EDTA, potassium oxalate, and sodium heparin. Attenuation of the product signal was observed after amplification of nucleic acid extraction from whole blood, washed mononuclear cells, and plasma from specimens collected in sodium heparin. These inhibitory effects on gene amplification could be reversed with heparinase. The addition of as little as 0.05 U of heparin completely inhibited amplification of an HLA-DQa sequence from placental DNA. We conclude that heparin can cause attenuation or inhibition of gene amplification. Acid citrate dextrose and EDTA, which lack inhibitory activity, are the most appropriate anticoagulants for clinical blood samples when polymerase chain reaction amplification is anticipated.

Enhanced therapeutic efficacy against an ovarian tumor xenograft of immunotoxins used in conjunction with recombinant alpha-interferon.

The antitumor effects of two immunotoxins were evaluated in vitro and in vivo against the human ovarian carcinoma cell line, OVCAR-3. The immunotoxins used were composed of recombinant ricin A chain (rRTA) covalently attached to a monoclonal antibody directed toward the human transferrin receptor (45412/rRTA, also called 454A12 MAB-rRTA by Cetus Corporation) or Pseudomonas exotoxin coupled to an anticarcinoma monoclonal antibody (NR-LU-10/PE). Preliminary characterization of the NR-LU-10 antigen by immunoprecipitation and cellular fluorescence demonstrated two dominant cell surface polypeptide moieties with molecular weights of 40,000 and 45,000 and a minor component with a molecular weight of 33,000. The immunotoxins were used alone or in combination with recombinant human alpha-interferon (rhIFN-alpha). Protein synthesis was inhibited in a dose-dependent manner in OVCA-3 cells incubated in vitro with either NR-LU-10/PE or 454A12/rRTA (50% inhibitory concentrations, 1 and 75 ng/ml, respectively). Unconjugated NR-LU-10 or 454A12 abrogated the activity of the relevant immunotoxins. Concomitant incubation in vitro of OVCAR-3 cells with NR-LU-10/PE or 454A12/rRTA and a noncytotoxic concentration of rhIFN-alpha potentiated the inhibitory activity of the immunotoxins via a mechanism independent of antigenic upregulation. This potentially synergistic combination was then tested in vivo. The median survival time (MST) of mice given injections i.p. of 4 x 10(6) OVCAR-3 cells was 46 days. Cohorts of mice that received intracavitary treatment beginning 5 days posttumor cell inoculation with either 0.25 or 0.5 microgram of NR-LU-10/PE every other day for a total of 10 treatments exhibited a significantly increased MST of 63 and 104 days, respectively (P less than 0.0001). Likewise, the i.p. injection of either 2.5 or 10 micrograms of 454A12/rRTA given in an identical schedule resulted in a MST of 89 and greater than 120 days, respectively (P less than 0.0001). When rhIFN-alpha was administered i.p. in conjunction with those doses of either immunotoxin, a significant increase in the MST was observed in comparison with mice given immunotoxin alone. The combination of 5 x 10(4) units of rhIFN-alpha and 0.25 microgram of NR-LU-10/PE resulted in 67% long-term survivors (greater than 120 days) compared with only 13% survival of mice given the immunotoxin alone. Similarly, 2.5 micrograms of 454A12/rRTA plus rhIFN-alpha resulted in an enhanced therapeutic response (89% long-term survivors) when compared with 454A12/rRTA alone (29%).(ABSTRACT TRUNCATED AT 400 WORDS)

Phase I evaluation of an anti-breast carcinoma monoclonal antibody 260F9-recombinant ricin A chain immunoconjugate.

Four women with metastatic breast cancer were treated with monoclonal antibody 260F9-recombinant ricin A chain, a ricin A chain immunoconjugate (IC) which targets a Mr 55,000 antigen expressed by human mammary carcinomas. Patients were treated by daily, 1-h i.v. injections for 6 to 8 consecutive days. Two patients were treated with 10 micrograms/kg daily and the two others were treated with 50 micrograms/kg daily. The trial was suspended after four patients had been treated because patients treated with a continuous infusion schedule with this IC had developed significant neurological toxicity at doses similar to those used in this study. The half-life of the IC showed a t 1/2 alpha of approximately 1.8 h, a t 1/2 beta of approximately 8.3 h, and a peak concentration of about 200 ng/ml, at the lower dose level, and showed a t 1/2 alpha of approximately 2.5 h, t 1/2 beta of about 10.4 h, and a peak concentration of 500 and 850 ng/ml for the two patients at the higher dose level. All four patients developed evidence of a human anticonjugate antibody response within 16 days of the onset of therapy. The treatment was associated with significant toxicity, manifested by a syndrome consisting of weight gain, edema, hypoalbuminemia, and dyspnea. Similar symptoms were observed in patients treated by continuous infusions of the IC. This clinical syndrome, seen at doses of IC which were insufficient to saturate antigen-expressing malignant tumor deposits in this trial, has been seen in other IC therapy trials and in clinical trials using the cytokine interleukin 2. To investigate a possible mechanism responsible for this toxicity, human monocytes were incubated with varying concentrations of IC. There was detectable binding of IC to human monocytes at IC concentrations which were achieved clinically in this trial. Furthermore, the binding appeared to be abrogated by preincubation of the monocytes with pooled human immunoglobulin, thus suggesting that binding occurs via Fc gamma receptor-mediated mechanisms. Binding was not affected if different linkers between recombinant ricin A chain and the antibody were used or if a different antibody moiety was used in the IC preparation. Chemically linked dimers of MOPC-21 bound to human monocytes at least as well as the ICs; this binding was not abrogated by preincubation with pooled human immunoglobulin. Since the IC preparations used in this clinical trial contained small percentages of dimers and/or multimers, the clinical toxicity syndromes which we observed may be related to this series of observations.(ABSTRACT TRUNCATED AT 400 WORDS)