Preparation and characterization of monoclonal antibodies against placental alkaline phosphatase and other human trophoblast-associated determinants

Radioimmunotherapy Trials in Germ Testicular Carcinoma: A Phase I Study

Two patients with germ cell testicular cancer were submitted to radioimmunotherapy (RIT) by using the monoclonal antibody 131I-radiolabelled (MoAb) H17E2, raised against placental alkaline phosphatase (PLAP).

Both patients had been previously treated with repeated chemotherapy regimens assisted by autologous bone marrow transplant (ABMT), that, in the end were unsuccessful, thus necessitating further experimental treatment.

RIT was well tolerated and the targeting of multiple neoplastic lesions was satisfactory. Nevertheless, the clinical results of treatment were minimal owing to the extension of the tumour.

The data obtained suggest the possibility of applying this form of treatment in patients with minimal residual disease after previous traditional chemotherapy regimens.

Modulation of antibody pharmacokinetics by chemical polysialylation

Chemical coupling of a variety of polymers to therapeutic proteins has been studied as a way of improving their pharmacokinetics and pharmacodynamics in vivo. Conjugates have been shown to possess greater stability, lower immunogenicity, and a longer blood circulation time due to the chemicophysical properties of these hydrophilic long chain molecules. Naturally occurring colominic acid (polysialic acid, PSA) has been investigated as an alternative to synthetic polymers such as poly(ethylene glycol) (PEG) due to its lower toxicity and natural metabolism. Antibodies and their fragments are a good example of the types of proteins which benefit from pharmacokinetic engineering. Here, we chemically attached differing amounts and differing lengths of short (11 kDa) and longer (22 kDa) chain colominic acid molecules to the antitumor monoclonal antibody H17E2 Fab fragment. Different coupling ratios and lengths were seen to alter the electrophoretic mobility of the Fab fragment but have a minor effect on the antibody immunoreactivity toward the placental alkaline phosphatase (PLAP) antigen. Polysialylation generally increased Fab fragment blood half-life resulting in higher tumor uptake in a KB human tumor xenograft mouse model. One H17E2 Fab-PSA conjugate had over a 5-fold increase in blood exposure and over a 3-fold higher tumor uptake with only a marginal decrease in tumor/blood selectivity ratio compared to the unconjugated Fab. This conjugate also had a blood bioavailability approaching that of a whole immunoglobulin.

A recombinant cytotoxic chimera based on mammalian deoxyribonuclease-I

A number of mammalian proteins with suitable biological activities have been considered for use in targeted tumour therapy. Deoxyribonuclease-I (DNase-I), an endonuclease that degrades double-stranded DNA, represents an attractive candidate for tumour targeting since it is normally non-toxic yet could be highly cytotoxic when redirected to the cell nucleus. Our aim was to investigate the cytotoxic potential of mammalian DNase-I and its possible use in tumour-targeting strategies for cancer therapy. A chimeric molecule comprising a scFv reactive against the human placental alkaline phosphatase (hPLAP) and bovine pancreatic DNase-I was designed and investigated. The development of a tightly controlled system for the bacterial expression of DNase-I and its chimera is described. The production and purification of active DNase-I from the soluble cell fraction and significant yields from the insoluble fraction by isolation and refolding are described. The construction, expression, purification and in vitro characterisation of an anti-PLAP scFv-DNase-I chimera is also described. This molecule was shown to possess both antigen-binding and DNA-degrading activity in in vitro assays, thus combining the specific cell-targeting properties of the scFv and the potent, highly catalytic activity of the endonuclease. Furthermore, this chimeric molecule was highly cytotoxic in vitro in cells expressing the PLAP antigen. Targeting mammalian DNase-I provides a novel therapeutic strategy for selective cell killing, with the promise of less systemic toxicity and immunogenicity than currently used immunotoxins.

Radioimmunoscintigraphy in patients with ovarian cancer

The targeting potential of three different monoclonal antibodies (MAbs) was assessed in patients with ovarian cancer. HMFG1, OC-125 and H17E2 labelled with 111In or 123I were evaluated prospectively for their ability to localize ovarian tumour. Forty two patients with ovarian cancer, aged 40-78 years (median = 58 years) were studied using OC-125 (n = 9), HMFG1 (n = 11) and H17E2 (n = 22). Imaging data were compared with the CT and the surgical findings. Presence of tumour was confirmed in 35/42 (83%) patients (8/9 OC-125, 10/11 HMFG1 and 17/22 H17E2) and correlated well with the conventional radiology diagnostic methods. One patient with a negative H17E2 scan and a large abdominal mass detected at laparotomy revealed a PLAP-negative tumour on immunohistochemistry. Scintigraphy revealed the presence of active disease, confirmed by laparotomy/laparoscopy in 6/8 patients considered to be in clinical remission. The sensitivity of the method was high enough and the diagnostic contribution of this approach should be further evaluated.

In vitro cytotoxicity following specific activation of amygdalin by beta-glucosidase conjugated to a bladder cancer-associated monoclonal antibody

We describe a novel version of antibody-directed enzyme prodrug therapy (ADEPT), with the use of amygdalin as prodrug. Amygdalin is a naturally occurring cyanogenic glycoside, which can be cleaved by sweet almond beta-glucosidase to yield free cyanide. If amygdalin could be activated specifically at the tumour site, then malignant cells would be killed without the systemic toxicity usually associated with chemotherapy. To this end, we have conjugated beta-glucosidase to a tumour-associated monoclonal antibody (MAb) (HMFG1) and the conjugate has been tested in vitro for specificity and cytotoxicity subsequent to activation of amygdalin. Amygdalin was cytotoxic to HT1376 bladder cancer cells only at high concentrations, whereas the combination of amygdalin with HMFG1-beta-glucosidase enhanced the cytotoxic effect of amygdalin by 36-fold. When 2 concentrations of HMFG1-beta-glucosidase were compared, the toxic effect was dose dependent. The cytotoxicity of amygdalin was also enhanced by the MAb-enzyme conjugate even when the unbound conjugate was removed from the medium prior to exposure to amygdalin and the cells were washed. In addition to the cytotoxic effect, we also demonstrated specificity, using a MAb-enzyme conjugate that does not recognise the HT1376 bladder cancer cells. Finally, we studied the cytotoxic effect of the conjugate in co-culture of HMFG1-positive and-negative cell lines (HT 1376 and U87MG cells). We demonstrated that the rate of surviving cells corresponds well to the percentage of U87MG (HMFG1-negative) cells in the flask. Our findings indicate that ADEPT is more effective than non-directed enzyme activation of a prodrug and can result in a non-toxic cancer therapy.

Design, characterization and anti-tumour cytotoxicity of a panel of recombinant, mammalian ribonuclease-based immunotoxins

Bovine seminal ribonuclease (BSRNase) is an unusual member of the ribonuclease superfamily, because of its remarkable anti-tumour and immunosuppressive properties. We describe here the construction, expression, purification and characterization of a panel of six immunotoxins based upon this enzyme and show that we can increase its anti-tumour activity by over 2 x 10(4)-fold. This is achieved by improving tumour cell targeting using a single-chain Fv (scFv) directed against the oncofetal antigen placental alkaline phosphatase. As well as the simple scFv-BSRNase fusion protein, we have constructed five other derivatives with additional peptides designed to improve folding and intracellular trafficking and delivery. We find that the molecule most cytotoxic to antigen (PLAP)-positive cells in vitro is one that contains a C-terminal 'KDEL' endoplasmic reticulum retention signal and a peptide sequence derived from diphtheria toxin. All these molecules are produced in Escherichia coli (E. coli) as insoluble inclusion bodies and require extensive in vitro processing to recover antigen binding and ribonuclease activity. Despite incomplete ribonuclease activity and quaternary assembly, these molecules are promising reagents for specific chemotherapy of cancer and are potentially less harmful and immunogenic than current immunotoxins.

GaLV pseudotyped vectors and cationic lipids transduce human CD34+ cells

High transduction frequency of hematopoietic stem/progenitor cells is essential to derive clinical benefits for treating certain inherited and acquired diseases. We demonstrate here stable gene transfer into human bone marrow-derived CD34+ progenitors using cationic lipids to facilitate GaLV and amphotroic pseudotyped retroviral-mediated transductions. Furthermore, the transgene was detected only in the progeny of flow cytometer sorted CD34+ population transduced by the LAPSN (PG13) viral vector in the presence of cationic lipids but not when transduction was facilitated with conventional polycations Polybrene or protamine sulfate. Thus, a combination of GaLV pseudotyped vectors and cationic lipids results in increased transduction frequencies of the CD34+ cells without a requirement of extended in vitro culture, or co-cultivation with producer cell lines. These improvements may result in the production of therapeutically significant quantities of genetically modified hematopoietic cells.

Construction, expression and characterisation of a single chain anti-tumour antibody (scFv)-IL-2 fusion protein

We describe the production and preliminary characterisation of a fusion protein between interleukin-2 and a single-chain Fv version of the H17E2 anti-placental alkaline phosphatase (PLAP) antibody. This molecule could be used to target interleukin-2 to PLAP-expressing tumours.

Maternal serum placental alkaline phosphatase level and risk for preterm delivery

OBJECTIVE

The purpose of this study was to determine whether elevated midtrimester serum placental alkaline phosphatase levels are predictive of preterm delivery.

STUDY DESIGN

By use of banked serum specimens from a sample of women who had received maternal serum alpha-fetoprotein screening, placental alkaline phosphatase values for multiples of the median were obtained from 270 mothers who had experienced a preterm delivery and from 1598 mothers of term, appropriate-for-gestational-age infants. Specimens were analyzed for placental alkaline phosphatase by means of a monoclonal antibody enzyme-linked immunosorbent assay. Logistic regression was used to determine whether placental alkaline phosphatase was associated with preterm birth, while potential confounders were controlled for.

RESULTS

Women with placental alkaline phosphatase levels > or = 2.0 multiples of the median were significantly more likely to be delivered of a preterm infant in the current pregnancy compared with women with levels < 2.0 multiples of the median (odds ratio 2.9, 95% confidence interval 2.1 to 3.9). The likelihood of preterm birth increased significantly with higher multiples of the median (p < 0.001).

CONCLUSION

Women with elevated placental alkaline phosphatase levels are at increased risk for preterm delivery. Additional studies are needed to evaluate the clinical utility of placental alkaline phosphatase testing as a means of identifying mothers at risk for preterm birth.

Peroperative radioimmunodetection of ovarian carcinoma using a hand-held gamma detection probe

Radioimmunoscintigraphy (RIS) can be used in the preoperative localisation of ovarian carcinoma to demonstrate uptake of radiolabelled monoclonal antibodies into neoplastic tissue. The tissue uptake of radiotracer was evaluated at laparotomy in 16 patients with suspected ovarian cancer who had preoperative RIS using technetium-99m-labelled monoclonal antibodies SM3 and H17E2. A gamma detection probe (gamma DP) was used to measure uptake in possible tumour deposits at operation and also the uptake in tissues resected for histology. The percentage uptake of the initial injected dose of radiotracer was also measured in resected tissues. Activity was found to be significantly higher in malignant than in non-neoplastic tissue by all three methods of evaluation. The gamma DP used peroperatively yielded a 82% sensitivity with a 72% specificity for an uptake ratio of 1.5:1. When tissue was examined immediately after resection, for a 100% specificity the sensitivity was 64%. In vitro measurements of monoclonal antibody uptake by tissue similarly gave a 65% sensitivity with a 100% specificity. Peroperative and immediate post-operative measurements of tissue radioactivity can be performed quickly and conveniently, and in some cases may be of benefit in the localisation of tumour at laparotomy and in providing extra information when tissue is examined by frozen section.

Genetically engineered antibodies for diagnostic pathology

Antibody genes can be cloned, genetically manipulated, and expressed in both homologous and heterologous expression systems to produce viable antigen-binding proteins complete with natural effector functions. Manipulation of antibody genes permits the expression of fusion proteins or truncated proteins that retain antigen-binding activity. The new antibody technologies are becoming increasingly sophisticated, permitting the alteration of antigen-binding responses, the transfer of antigen specificity between antibodies, and the expression of minimal-size antigen-binding protein domains. These new molecules have been made mostly for studies on function or to provide molecules suited for in vivo diagnosis and therapy; very few have been specifically designed for, or used for, diagnostic histopathology. We describe here the adaptation of small antibody derivatives for use in immunohistochemistry. Molecules suitable for this purpose need only to possess specific antigen-binding ability and some means of detection of antigen-bound material. Detection could be by recognition of a genetically fused flag or tag epitope, by the fusion of an enzyme whose activity can be assayed, or by fusion with a protein that can interact with pre-existing histopathological reagents.

Characterisation of the differential expression of marker antigens by normal and malignant endometrial epithelium

In order to examine the production of marker proteins, a reproducible method has been established for culturing purified epithelial cells from normal and malignant endometrium. We have examined the differential expression of secretory proteins using immunohistochemistry in frozen tissue sections, immunocytochemistry in cell cultures derived from the same specimens and protein assays on the culture supernatants. Placental protein 14 (PP14) was produced by normal premenopausal epithelium but not by the post-menopausal or malignant endometrial epithelium. In contrast, placental alkaline phosphatase (PLAP) was produced by endometrial cancers and the endometrial adenocarcinoma-derived cell line Ishikawa, but not by the normal endometrial epithelium. Other markers such as CA-125, which was produced by both normal and malignant endometrium but not by the cell line, and human chorionic gonadotrophin (beta-hCG), which was produced by Ishikawa cells but not by any of the fresh tissues, were less cancer specific. Placental alkaline phosphatase is a direct product of endometrial cancers that can be readily assayed in serum using this two-site assay to test its clinical usefulness in monitoring patients at risk for endometrial cancer.

Production of placental alkaline phosphatase (PLAP) and PLAP-like material by epithelial germ cell and non-germ cell tumours in vitro

Placental and placental-like alkaline phosphatase (PLAP) levels in the culture media of 87 cell lines of neoplastic and 'normal' origin were measured by a conventional immunosorbent enzymatic assay (IAEA) and by a new immunoradiometric assay (IRMA). The IRMA detected immunoreactive PLAP in 37 of 80 (46%) human epithelial and germ cell cultures, while the IAEA detected PLAP in only 25 (33%). Of the 52 non-germ cell tumour cultures, the IRMA detected expression in 24 (46%) and the IAEA in only 16 (31%). In 17 cases (21%) the IRMA recorded levels double that of the IAEA, while in five cultures (6%) the reverse was true. The IRMA was much more robust than the IAEA and had considerably lower inter- and intra-assay coefficients of variation (3.75-8.5% vs 5.2-46%). Detection of PLAP(-like) expression by IAEA is dependent on neoplastic expression of enzymatically functional molecules and quantification assumes constant enzyme kinetics. PLAP-like material has a higher catalytic rate constant than PLAP and thus will give higher values on a stoichiometric basis in an IAEA. The higher detection rate and levels of PLAP-like material in neoplastic cultures when measured by the IRMA clearly demonstrate ectopic expression of non-enzymatic PLAP and PLAP-like genes. The incidence of PLAP(-like) expression by non-germ cell and possible germ cell tumours has been underestimated and its utility as a tumour marker should be re-examined using assays which measure antigen mass rather than phosphatase activity.

Targeting of tumours with murine and reshaped human monoclonal antibodies against placental alkaline phosphatase: immunolocalisation, pharmacokinetics and immune response

Anti-tumour monoclonal murine and humanised (reshaped human) antibodies (H17E2 and Hu2PLAP, respectively) against placental alkaline phosphatase (PLAP), radioactively labelled with indium-111 (111In) and iodine-123 (123I), were evaluated for their ability to localise mainly testicular and ovarian tumours in sequential pilot studies of the Hammersmith Oncology Group. 33 patients with active primary and/or metastatic testicular cancer were studied with the [111In]- or [123I]H17E2 antibody. 8 patients with testicular cancer were studied with the same antibody after being rendered free of disease after induction chemotherapy and surgical resection of residual tumour. 3 additional patients, 2 with ovarian cancer and 1 with testicular seminoma, were studied with [111In]H17E2 via a macrocyclic chelating agent (DOTA). 7 patients; 5 with ovarian cancer, 1 with breast cancer, and 1 with gastric cancer, received the reshaped human Hu2PLAP antibody [111In]DOTA labelled. One of these was imaged twice, with H17E2- and Hu2PLAP-DOTA-111In, respectively. In the initial 33 patients with active primary and/or metastatic testicular cancer, the presence of tumour was confirmed and correlated well with conventional radiological diagnostic methods, and in addition, the antibody scan revealed the presence of active disease in 2 patients with negative conventional imaging, but elevated serum tumour markers. In the 8 patients with complete remission (CR), imaging studies with the radiolabelled antibody did not show any localisation. The best images were obtained at 24 and 48 h after the [123I]- and [111In]H17E2, respectively. None of these patients developed human anti-mouse antibody responses (HAMA). Successful imaging with the reshaped human antibody, Hu2PLAP-DOTA-111In, was seen in 3 patients with PLAP-positive tumours (2 ovarian and 1 gastric cancer). The 3 negative patients were 1 in complete remission, 1 with PLAP-negative tumour and 1 who cleared the Hu2PLAP antibody immediately after infusion due to the presence of anti-chelating agent (anti-DOTA) antibodies from a previous H17E2-DOTA-111In scan. One patient with PLAP-negative breast carcinoma had a false-positive scan with Hu2PLAP, showing localisation to the pleural effusion. Antibody pharmacokinetics showed a mean t1/2 beta = 73.1 +/- 30.2 h (n = 5) for Hu2PLAP versus t1/2 beta = 27.2 +/- 5.9 h (n = 3) for H17E2 (P < 0.05). 2 patients receiving Hu2PLAP were excluded due to the rapid clearance of the radiolabel as a result of the presence of high HAMA and anti-chelate antibody levels, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Construction, characterisation and kinetics of a single chain antibody recognising the tumour associated antigen placental alkaline phosphatase

The murine monoclonal antibody H17E2 recognises placental alkaline phosphatase (PLAP), an antigen present in the human term placenta and also expressed by many tumours. The antibody is of value in both immunoscintigraphy and radioimmunotherapy in testicular and ovarian cancer. The small size of genetically engineered single chain antibodies (SCAs) should give diagnostic and therapeutic advantages of improved tumour penetration and increased blood clearance compared to IgG. Employing recombinant DNA techniques a SCA based on H17E2 has been expressed in Escherichia coli and has been shown to bind placental alkaline phosphatase specifically. When administered to nude mice bearing human tumour xenografts, the H17E2 SCA effectively localised to tumour whilst a co-administered non-specific SCA did not. H17E2 SCA achieves tumour: blood ratios that are superior to those achieved with whole IgG, probably owing to its rapid blood clearance. We conclude that the H17E2 SCA is suitable for further investigation as an agent for clinical imaging and therapy. Additionally, the SCA can also be used for the construction of antibody based fusion proteins to target other effector functions to tumour cells.

Measurement of placental alkaline phosphatase activity in benign and malignant pleural effusions

The usefulness of placental alkaline phosphatase (PLAP) as a diagnostic marker of malignancy was assessed in pleural fluid from 60 patients with effusions. Pleural fluid PLAP activities were measured by an enzyme linked immunoassay (ELISA) using the two monoclonal antibodies H17E2 and H317. Similar values were found in groups of patients with primary bronchial tumours (n = 12), secondary malignancies (n = 23), and "benign" conditions (n = 25). The highest values were found in a small subgroup of patients with metastatic ovarian carcinoma. However, the production of this enzyme by normal lung makes the measurement of PLAP in pleural fluid unhelpful as a diagnostic aid to distinguish "benign" from malignant effusions.

Engineering antibodies for therapy

Success in the generation of an antibody-based therapeutic requires careful consideration of the binding site, to achieve specificity and high affinity; of the effector, to produce the desired therapeutic effect; of the means of attachment of the effector to the binding site; production of the end product; and the response made by the patient to the administered compound. Each of these areas is receiving attention by antibody-engineering techniques. The number of potentially useful monoclonal antibodies developed over the last 10 years, and currently in clinical trials or preregistration, is now being increased by these engineered newcomers. It will be interesting to see over the next few years how many of these antibodies, and of which kind, emerge as products.

Germ cell alkaline phosphatase in human seminal plasma following vasectomy

Germ cell alkaline phosphatase (also termed placental-like alkaline phosphatase or Nagao isoenzyme) was assayed in seminal plasma using monoclonal antibody-based enzyme immunoassays in samples obtained both before and after vasectomy. In all cases, germ cell alkaline phosphatase fell to undetectable levels within 14 days of operation. A fall in seminal plasma germ cell alkaline phosphatase may thus be an early indication of successful vasectomy.

Tumour localisation with a radioactively labelled reshaped human monoclonal antibody

A genetically reshaped human IgG1 monoclonal antibody (Hu2PLAP) with anti-tumour specificity, was radiolabelled with Indium-111 by chelation with a new macrocyclic compound (DOTA) which allows the production of stable radioimmunoconjugates for in vivo application. This was used to image seven patients with malignant disease, of whom two had been previously exposed to mouse monoclonal antibodies and had developed human anti-mouse antibodies (HAMA). Successful tumour localisation was seen in the four patients with active disease and antigen positive tumours. No patient showed any antibody responses against Hu2PLAP, but three out of six patients tested showed an immune response against the macrocycle DOTA. Reshaped human monoclonal antibodies with anti-tumour specificity may facilitate repeated administrations of radioactive antibodies, thus allowing new possibilities, both in the diagnosis and treatment of cancer.

Human ovarian cancer xenografts in nude mice: characterization and analysis of antigen expression

We have characterized 13 different human ovarian cancer xenografts grown subcutaneously in nude mice. The tumor lines represented 5 histological subtypes: serous (4), mucinous (4), clear-cell carcinoma (1), carcinosarcoma (1) and undifferentiated (3). The specific histology and the degree of differentiation resembled those of the original patients' tumors and were maintained upon serial transfer. Volume doubling times of the xenografts ranged from 3.5 to 15 days. The xenografts were also analyzed for their antigen expression using 20 monoclonal antibodies (MAbs) reactive with 15 tumor-associated antigens. Immunohistochemical examination of tissue sections showed a positive reaction pattern with MAbs 115D8, 140C1, 139H2, 175C5, HMFG1 and HMFG2, each recognizing episialin, as well as with MAbs AUA1, 358.4.32 and 199-157 in xenografts of the serous, mucinous and clear-cell carcinoma subtype. MAb OC125 was reactive with xenografts of the serous subtypes. Other antibodies, such as 494 and OV-TL3 infrequently demonstrated positive reactions. Reactivity of all MAbs was low in the carcinosarcoma and undifferentiated tumor lines. With the exception of AUA1, 495 and 126E5, all MAbs revealed a heterogeneous staining pattern. MAbs against episialin and OC125 predominantly stained the apical site of the tumor cells. Strongest reactivity with almost all histological subtypes was observed with MAbs 115D8, 140C1, 139H2 and AUA1. In cases where we were able to compare the patients' tumor tissue with the respective xenografts, retention of antigen expression was demonstrated in each instance. Release of tumor-associated antigens was shown for CA125 in 2 serous-tumor lines, for CA15.3 in 1 serous-tumor line, and for CEA in 3 lines of the mucinous subtype. This panel of human tumor xenografts could be a valuable tool to determine the potential usefulness of MAb-guided therapy in ovarian cancer.

Expression of placental alkaline phosphatase in gastric and colorectal cancers. An immunohistochemical study using the prepared monoclonal antibody

The authors developed monoclonal antibodies (MoAb) against human placental alkaline phosphatase (PLAP). Four specific MoAb reacting only with PLAP and two nonspecific MoAb reacting equally with isozymes of alkaline phosphatase (hepatic, intestinal, and placental) were obtained. Immunohistochemical staining with the specific MoAb showed that the cell membrane and cytoplasm of cancer cells were stained in gastric and colorectal carcinoma. The incidence of PLAP positivity was 23% (25 of 107) of all gastric carcinomas. Among gastric carcinomas, the 42% (13 of 31) positivity of highly differentiated carcinoma (papillary adenocarcinoma and well-differentiated tubular adenocarcinoma) was a significantly higher rate than that found in poorly differentiated carcinoma (poorly differentiated adenocarcinoma and signet-ring cell carcinoma, five of 41, 12%). The incidence of PLAP positivity was 11% (four of 35) in colorectal carcinoma. In contrast, gastric adenoma, intestinal metaplasia, and noncancerous tissue adjacent to cancer did not show staining. These results indicated that expression of PLAP was apt to occur in more highly differentiated gastric carcinoma and was highly specific for carcinoma in the gastrointestinal tract, although its incidence was not high.

Immunoaffinity purification and characterisation of p29--an estrogen receptor related protein

p29, a 29 kDa protein recognised by D5, a monoclonal antibody prepared against partially purified cytosolic estrogen receptor (ER), has been purified to homogeneity from ZR-75-1, a human breast cancer cell line. Ammonium sulphate fractionation followed by immunoaffinity chromatography on a three column system using Protein A-Sepharose coupled D5, produced purified p29. Silver stained SDS one-dimensional polyacrylamide gel electrophoresis (PAGE) and two-dimensional PAGE showed p29 to have been purified to homogeneity. Amino acid analysis showed no unusual characteristics. Partial N-terminal sequencing studies showed that purified p29 shared a 100% homology with the sequence of a pp89, murine cytomegaloviral protein.

The expression of placental alkaline phosphatase (PLAP) and PLAP-like enzymes in normal and neoplastic human tissues. An immunohistological survey using monoclonal antibodies

The immunohistological expression of placental alkaline phosphatase (PLAP) and PLAP-like enzyme was studied in frozen sections from a wide variety (n = 254) of normal and malignant tissues using monoclonal antibodies reactive with PLAP (H317) and PLAP/PLAP-like enzyme (H17E2; H315). PLAP/PLAP-like reactivity was seen in normal thymus, and foetal and neonatal testis, and in 21 out of 22 malignant germ cell tumours (GCTs), but was also found in normal endocervix, normal Fallopian tube and in 28 out of 167 non-GCTs (particularly in ovarian and proximal gastrointestinal tract tumours). Positivity for true PLAP (as demonstrated with H317) was seen in term placenta, in endocervix, and in Fallopian tube (but not in other normal tissues) and was commonly found in ovarian and proximal gastrointestinal tract tumours. Reactivity with H317 was unusual in malignant GCTs (2 out of 22 cases). These findings confirm that PLAP/PLAP-like positivity is a highly sensitive immunohistological marker for malignant GCTs, but one which by itself is of only moderate specificity. Furthermore, expression of true PLAP is rare in GCTs and favours instead an origin from the ovary or proximal gastrointestinal tract. The results also indicate that the predominant heat-stable alkaline phosphatase species in normal foetal and neonatal testis, and in thymus has a similar immunohistological profile to that found in malignant GCTs, and is a PLAP-like enzyme ("germ cell alkaline phosphatase") distinct from true PLAP. The occurrence of this marker in GCTs would appear to reflect increased eutopic production of an enzyme present in trace amount in corresponding normal tissues rather than a genuine example of ectopic expression.

Heat-stable alkaline phosphatase as a marker for human and monkey type-I pneumocytes

The expression of the heat-stable isoenzyme of alkaline phosphatase in the human and monkey (Macaca mulatta, M. fascicularis) lung was investigated at the light- and electron-microscopic level, using cytochemical techniques and immunocytochemical procedures based on monoclonal and polyclonal antibodies against human term-placental alkaline phosphatase. Both in man and monkey, the enzyme was present in type-I pneumocytes. In the monkey, the enzyme was found in all type-I cells. In man, strong staining was observed only in some type-I cells and in certain cuboidal respiratory bronchiolar cells. Staining was localized on the apical and basal plasma membrane, in apical and basal caveolae, and in the underlying basement membrane. The level of heat-stable alkaline phosphatase expression in the human lung was 10-fold lower than in the monkeys studied. In human fetal lung, the onset of heat-stable alkaline phosphatase expression was associated with the development of the alveolar epithelium from 17-20 weeks gestation onward. It is concluded that: (1) heat-stable alkaline phosphatase is a specific constituent of type-I pneumocytes in man and monkeys; and (2) its subcellular localization may explain its rapid appearance in the circulation under certain conditions.

In vivo imaging of rat lymphocytes with an indium 111-labelled anti-T cell monoclonal antibody: a comparison with indium 111-labelled lymphocytes

An indium 111-labelled mouse anti-rat T cell monoclonal antibody, MRC OX-19, was injected intravenously into rats to establish the usefulness of radiolabelled anti-lymphocyte antibodies in imaging lymphoid tissues. Antibody binding in vivo, measured by immunofluorescence analysis of cell suspensions made from lymphoid tissues, was detectable on lymphocytes in blood, spleen and lymph nodes. The extent of binding was time and antibody-dose dependent. Doses of antibody above 80 micrograms/kg body weight resulted in modulation, i.e. loss of CD 5 (T1) molecules from the cell surface, although the cells remained in the circulation. Modulation was demonstrable within 2 h and for at least 24 h after a single injection of antibody. Intravenous injection of 111In-MRC OX-19 resulted in levels of in vivo binding comparable with those seen with unlabelled antibody. Scintillation imaging showed early splenic localisation persisting over 48 h, a more gradual localisation in the lymph nodes seen clearly at 24 h and a steady background. Comparison of the in vivo distribution of labelled antibody and 111In-tropolone-labelled lymphocytes showed that both could be used for external imaging of lymphocytes by scintillation camera.

Placental alkaline phosphatase in developing normal and abnormal gonads and in germ-cell tumours

The evolution of the gonads during intra-uterine development has been followed by immunohistochemical demonstration of placental-like alkaline phosphatase (PLAP) at the germ-cell level. PLAP immunopositivity was restricted to the limited period when germ cells were not surrounded by granulosa or Sertoli cells. Abnormal fetuses or neonates presenting with chromosomal anomalies frequently had disorganized gonads where germ cells retained their membrane PLAP immunopositivity. This abnormal immunopositivity is similar to that expressed by abnormal germ cells in testicular in situ carcinoma, in gonadoblastoma (case of 45,XO/46,XY mosaic) and in seminoma. The pattern of positivity for other germ-cell tumours was highly variable. We suggest that in abnormal gonads, dysgenetic or neoplastic, an early embryonic property is retained by abnormal germ cells. Its importance in the process of neoplastic induction remains to be defined.

Investigation of expression of 5T4 antigen in cervical cancer

A monoclonal antibody detecting amniotrophoblastic antigen 5T4 has shown reactivity against various neoplastic cell lines and tumour specimens but with a relatively restricted normal tissue expression. This antibody has been investigated as a potential indicator of premalignant changes identified as cervical intra-epithelial neoplasia and malignant cervical lesions using immunohistochemistry on frozen tissue biopsies. The basal cells of normal cervical stratified epithelium exhibited faint staining, but a general increase in intensity and extent of specific labeling of this tissue was seen from the first premalignant stage through to carcinoma. In most cases, this was in accordance with the distribution of dysplastic cells, and was accompanied by increased specific staining of the stromal tissue. All invasive squamous carcinomas of the cervix were 5T4 antigen positive. Common inflammatory non-malignant diseases did show a certain degree of epithelial and stromal reactivity. These results, showing 5T4 reactivity with neoplastic and pre-neoplastic lesions, may provide a quantitative basis for its potential use as a tumour marker in the immunochemical detection on immunoassay of cervical cancer.

Human placentae: view from an immunological bias

Human placentae form a major part of the interface between maternal and embryonic tissues. Placentae are morphologically complex organs that are lined with a trophoblastic tissue that provides anatomical constraints over which flows maternal blood. Maternal antibodies and immune cells thus contact the lining syncytiotrophoblast, and this paper considers some of the antigens that maternal immune components might encounter. The antigens have been grouped into those of unknown function, major histocompatibility antigens, and antigens of suspected function. The paper also details certain antigens of cytotrophoblasts. We discuss consequences of maternal immune responses to extraembryonic antigens and present evidence for amplification of these responses through the activation of hemostasis and fibrinolysis within the placenta and placental bed.

Monoclonal antibodies reactive with human breast or ovarian carcinoma: in vivo applications

Monoclonal antibodies (MoAbs) are unique and useful bioprobes that allow in vivo targeting of membrane-associated or circulating antigens. Most of the clinical trials to date have used low dosages of radiolabeled MoAb given in a single dose. Newer studies have included antibody fragments, repeated injections, intraperitoneal (IP) administration, and other labels such as 90Y. Clinical MoAb trials are often arduous, expensive, and time-consuming to perform. Before human use, animal studies and extensive MoAb characterization are required. The production of pharmaceutical grade, radiolabeled MoAb is technically difficult and costly. Clinical trials require administrative and patient consent as well as extensive written protocols. These studies necessitate interdepartmental and intradepartmental cooperation and coordination. Furthermore, the use of in vivo radiolabeled probes impacts many levels of health care providers from janitorial, nursing, and technical staff to laboratories and physicians. Simple blood tests or disposal of body excretions may concern nursing or technical staff with the possibility of radiation exposure. The responsibility for study design, personnel involvement, and prospective use in patients without a definitive cancer diagnosis ultimately rests with the physician. While many issues have been addressed, additional clinical trials, consideration of safety issues, and standardization between institutions will be necessary before the use of radiolabeled MoAb for diagnosis, management, or therapy of human tumors becomes routine. Continued cooperation and funding should ensure its achievement.

Isolation and characterization of a multipotent clone of human embryonal carcinoma cells

Histopathological studies suggest that the stem cells of human teratomas may be classified into two major categories: nullipotent stem cells, and multipotent stem cells, capable both of self-renewal and differentiation into a wide range of somatic and extraembryonic cell types. We have isolated a multipotent stem cell clone from the human teratoma cell line GCT 27, and compared its properties to a nullipotent clone derived from the same strain. The multipotent clone GCT 27 X-1 gave rise to colonies of mixed cell morphology in vitro. Analysis of cell surface, cytostructural and extracellular matrix markers in GCT 27 X-1 cells showed that the stem cells of this line were very similar in phenotype to nullipotent cells. The two cell clones were predominantly hypotriploid, and contained several marker chromosomes in common. GCT 27 X-1 was feeder-cell-dependent for continuous growth in vitro; removal of the feeder layer resulted in differentiation of the stem cells into a variety of cell types, some with characteristics of extraembryonic endoderm, others showing neuronal properties. When transplanted into nude mice, GCT 27 X-1 cells gave rise to teratocarcinomas containing embryonal carcinoma stem cells, and many other cell types: yolk sac carcinoma cells; cells producing alphafetoprotein or human chorionic gonadotrophin; glandular, columnar, cuboidal, and squamous epithelium; primitive mesenchyme and cartilage; neuroectodermal cells. Nullipotent GCT 27 C-1 cells could form colonies in the absence of feeder layers, but multipotent GCT 27 X-1 cells could not. While a range of known growth factors and related substances failed to substitute for feeder layers in supporting the growth of GCT 27 X-1 stem cells, supernatants from yolk sac carcinoma cell line GCT 44 could partially replace the feeder cell requirement. Thus, the results revealed a basic difference in growth control between these multipotent and nullipotent human embryonal carcinoma cells, and suggested a possible paracrine regulatory pathway between multipotent stem cells and yolk sac carcinoma cells.

Monoclonal antibodies to enzymes

The production, identification, and utilisation of monoclonal antibodies to enzymes are reviewed. Such antibodies may be produced in vitro by the mouse-hybridoma technique, may occur naturally in vivo as enzyme-binding immunoglobulins and may be produced in the laboratory from the lymphocytes of patients whose sera contains such immunoglobulins. The diagnostic application of monoclonal antibodies to enzymes is considered, with special reference to their use in the measurement of the MB-isoenzyme of creatine kinase, pancreatic isoamylase, prostatic acid phosphatase, and the isoenzymes of alkaline phosphatase.

A Preliminary Study of Brain Gliomas with H17E2 Monoclonal Antibody: Immunoscintigraphy and Pharmacokinetics

Ten patients with relapsing high grade brain gliomas and one patient with low grade glioma were studied with a monoclonal antibody (H17E2) against placental alkaline phosphatase. In addition 2 patients with relapsing high grade glioma were studied with a non specific antibody (4D513/2118). 1 mCi of Iodine-131-labelled H17E2 was administered intracarotidly (i.c.) in two, and intravenously (i.v.) in 9 patients. Immunoscintigrams were taken at 0, 2, 24, 48 and 72 hours. Radioactivity was monitored in blood and urine. Tumour/non-tumour ratios were estimated (max. 2.45). All high grade gliomas receiving specific antibody irrespective of the route of administration, gave a positive immunoscintigraphic pattern, increasing in intensity with time.

Disappearance of radioactivity in blood was biexpontential with a long component over 30 hours. Urinary excretion of radioactivity ranged from 3.7–21.7% of administered dose/day. The patient with low grade glioma and the patients receiving non specific monoclonal antibody showed a negative pattern, a fast blood clearance and a high urinary excretion. We conclude that a) Iodine-131 labelled H17E2 proved to be stable in vivo and produced satisfactory tumour localisation and b) i.v. route was as good as i.c.

Labelling monoclonal antibodies with yttrium-90

Using the cyclic DTPA derivatisation procedure developed by Hnatowich, conditions have been optimised for labelling three tumour-associated monoclonal antibodies with 90Y. High labelling efficiencies (greater than 95%) at modest specific activities (1 mCi/mg) could be routinely obtained. Radiochemical stability of the radiolabelled preparations in vitro was good, but radiolysis resulted in early losses of antibody immunoreactivity.

Intraperitoneal radioimmunotherapy for ovarian cancer

Twenty-eight patients with assessable residual ovarian cancer after cytoreductive surgery and chemotherapy received intraperitoneal I-131 labelled monoclonal antibodies. There was no response in eight patients with tumour nodules greater than 2 cm, a partial response in two of the 15 patients with tumour nodules less than 2 cm, and a complete response in three of the other five patients with positive peritoneal washings. A further six patients received Y-90 labelled monoclonal antibodies for residual ovarian cancer. There was no response in one patient with nodules greater than 2 cm, and a partial response in one of the other five patients with tumour nodules less than 2 cm. The non-specific radiation dose in the peritoneal cavity from the infused isotope was measured by lithium fluoride thermoluminescent dosimetry (TLD). The radiation dose received by the peritoneal serosa was less than 500 cGy and was not sufficient to account for the observed tumour response. Significant bone marrow suppression was observed with I-131 activities greater than 120 mCi and with Y-90 activities greater than 13 mCi. The haemopoietic bone marrow is the dose-limiting organ in patients receiving radioimmunotherapy.

Intraperitoneal radioimmunotherapy for ovarian cancer: pharmacokinetics, toxicity, and efficacy of I-131 labeled monoclonal antibodies

Thirty-six patients with ovarian cancer were treated with intraperitoneal I-131 labeled monoclonal antibodies to tumor associated antigens. The activity of I-131 administered was increased from 20 mCi to 158 mCi and the pharmacokinetics and toxicity evaluated. Five patients who had developed HAMA (Human Antimouse Antibodies) were retreated, and the pharmacokinetics and toxicity of the first and second treatment compared. Patients receiving their first therapy (HAMA negative), had a maximum of 25% (range 19.8-39.8%) of the injected activity in their circulation. This was accompanied by severe marrow suppression at I-131 activities over 120 mCi. The 5 HAMA positive patients had only 5% injected activity in the systemic circulation (range 3.8-6%), with rapid urinary excretion and neglible marrow suppression. In 31 patients with assessable disease there were no responses in 8 patients with gross disease (nodules greater than 2 cms), partial responses in 2 out of 15 patients with nodules less than 2 cms, and complete responses in 3 out of 6 patients with microscopic disease. The non specific radiation dose to the peritoneal cavity was estimated to be less than 500 cGy by lithium fluoride TLD, and could not be expected to account for the responses seen.

Locoregional immunotherapy of human ovarian cancer: preliminary results

Ten patients with advanced ovarian carcinoma (5 in FIGO stage III and 5 in stage IV), following the failure of repeated chemotherapy courses, were submitted to i.p. radioimmunotherapy (RIT). Several antibodies (HMFG1, HMFG2, H17E2, B72.3) were employed. The antibody choice was made on the basis both of immunohistochemistry and immunoscintigraphy results. The mean dose administered in each single course was 17 mg, 3 patients underwent two treatments and 2 patients were injected three times. The isotope employed was 131I (mean dose 92 mCi). The early or late untoward effects were negligible. All patients developed anti-mouse antibodies (HAMA) which reduced, during the further RIT, the MoAbs' effective half-life. The estimated radiation dose delivered to the tumour ranged from 2910 to 11,000 cGy. Both wholebody and liver radiation burden resulted in tolerable limits while the thyroid irradiation was high. In 3 patients the RIT result was ineffective; in 2 cases a temporary ascitis staunch was obtained. In 2 cases the tumour growth was slower than expected and in 3 patients instrumental evidence of partial tumour reduction, still lasting after 4-11 months, was observed.

Serum placental-like alkaline phosphatase (PLAP): a novel combined enzyme linked immunoassay for monitoring ovarian cancer

A new combined enzyme linked immunoassay (ELISA) was developed to measure both serum placental-like alkaline phosphatase (PLAP) activity (PLAPA) and concentration (PLAPC) in the same microtitre plate using an Imperial Cancer Research Fund monoclonal antibody, designated H17E2. PLAP A and PLAP C were determined together with an existing marker, CA125 in 397 serial samples from 87 patients with epithelial ovarian cancer. Retrospective assessment showed the sensitivity to increase from 73% with CA125 alone, to 88% using CA125 and PLAP A, and to 93% with all three markers in 261 samples from the patients with known active disease at the time of sampling. When the results for all 397 samples were included in the analysis, however, the specificity, sensitivity, accuracy and predictive powers of this monoclonal antibody were not sufficiently high to assist in the prospective follow up of patients with ovarian cancer. This was due to a significant number of false positive and false negative results. Our data indicate that PLAP A or PLAP C estimation with H17E2 may, therefore, only be of value in the management of those patients with known active disease who are already known to be "marker positive" for this antigen.

Clinical applications of monoclonal antibodies against ovarian cancer-associated antigens

Monoclonal antibodies (McAbs), reactive with tumour-associated antigens (TAAs) present on tumour cells, appear to offer new possibilities in the diagnosis and treatment of cancer (Table I). In addition to these prospects for clinical application, monoclonal antibodies also serve as useful instruments in basic cancer research. The hybridoma technology initiated by Köhler and Milstein in 1975, underwent a very rapid development and has now shown its potential in the field of oncology. This technique made it possible to produce very large quantities of homogeneous antibodies of a stable quality. These McAbs often recognize only one antigenic determinant, or epitope, of cell surface and other molecules. This high specificity is essential for in vivo applications, especially in therapeutic immunotargeting. A central question is whether the antibodies can reach and identify those antigens on ovarian tumour cells that are not shared with normal tissues. Various antibodies have been described in the field of gynaecological oncology, which are assumed to be capable of recognizing such ovarian tumour-related antigens. These McAbs, single or in combination, are capable of showing, unambiguously, the presence of various tumour-associated antigens on ovarian carcinoma cells either in tissue or, when antigen shedding occurs, in blood. However, these McAbs may also react with tumour-associated antigens present on endometrial, cervical, colorectal, breast or other carcinoma cells. The original immunogens used to generate these McAbs differ as to their origin: ovarian cancer cells, breast cancer cells, human milk-fat preparations, trophoblastic cells, endometrial cancer cells have been used as well as osteogenic sarcoma cells, epidermoid carcinoma cells and small-cell lung cancer, colorectal, pancreatic and laryngeal carcinoma cells. The histological distribution patterns of the antigens recognized by these McAbs vary widely: cross-reactions with normal tissue and with carcinomas different from those used as immunogen are frequently seen.

Development of anti-idiotypic antibodies against tumour antigens and autoantigens in ovarian cancer patients treated intraperitoneally with mouse monoclonal antibodies

Repeated intraperitoneal administration of therapeutic amounts of radiolabelled (iodine-131) murine monoclonal antibodies leads to the development of an immune response in the recipient, part of which is directed against the variable region (idiotype) of the administered antibody (anti-Id1 response). Human immunoglobulin purified from these patients inhibits binding of the original murine monoclonal antibody to its target tumour antigen and therefore represents an "internal image" of the tumour antigen. Furthermore, this study recorded the development of human antibodies that themselves bind to the tumour antigen, with a specificity identical or similar to that of the injected monoclonal antibody. These human antitumour antibodies are probably generated by way of the idiotypic network and confirm the existence of the idiotypic network. Accompanying this antitumour response the transient development of autoantibodies that react with connective tissue components of liver, kidney, spleen, and diaphragm was also observed.

A 72 kD trophoblast glycoprotein defined by a monoclonal antibody

A novel trophoblast cell surface antigen has been defined by a monoclonal antibody 5T4, raised following immunisation with wheat germ agglutinin (WGA) purified glycoproteins from deoxycholate (DOC) solubilised human syncytiotrophoblast plasma membrane (StMPM). The distribution of the antigen was determined by indirect immunoperoxidase staining of sections of normal organ and placental tissues as well as immunofluorescence and radiobinding assays with a wide variety of cell lines representing differing normal and tumour cell types. In frozen sections of normal full term placenta, 5T4 is strongly expressed only by the syncytiotrophoblast, some extravillous cytotrophoblast and the amniotic epithelium. The 5T4 antigen is apparently not expressed by any maternal component of the placenta nor is it detected in adult liver, lung, bronchus, heart, testis, ovary, brain, or muscle. The antigen is apparently expressed by several specialised epithelia. Immunoprecipitation of radiolabelled StMPM indicated that 5T4 molecules are glycoproteins of mol. wt of approximately 72 kD on SDS-PAGE. 5T4 antigen is selectively expressed by diverse tumour cell lines, including those of developmental origin. The molecular characteristics, relatively restricted normal tissue distribution and expression by certain tumour cell types make this antigen worthy of future study for use as a diagnostic marker of malignancy.

Measurement of placental alkaline phosphatase in maternal plasma as an indicator of subsequent low birthweight outcome

Placental alkaline phosphatase (P-ALP) was measured by a specific monoclonal antibody-based immunoassay in plasma samples of 117 women who subsequently were delivered of an infant of birthweight less than 2.5 kg. P-ALP values greater than twice the normal median were found in 32% of maternal plasma samples from low birthweight cases in one series and in 35% in another series, while in normal outcome controls the corresponding value was 8%. The differences were highly significant. The proportion of low birthweight cases with elevated maternal P-ALP values appears to be very similar between 15 and 34 weeks gestation. At 16-18 weeks gestation there is a significant positive correlation (r = 0.40) between P-ALP and maternal plasma alpha-fetoprotein (AFP) values in low birthweight cases. The use of P-ALP assay in combination with AFP assay appears to improve the detection of pregnancies with subsequent low birthweight outcome.

Production of monoclonal antibodies to placental alkaline phosphatase: preliminary characterisation includes identification of one antibody reactive with routinely fixed histological preparations

We describe the production and preliminary characterisation of a set of monoclonal antibodies (MAbs) raised against placental alkaline phosphatase (PLAP). Different forms of antigen presentation, PLAP or PLAP-like expressing whole cells, placental membranes or purified PLAP were used to immunise BALB/c mice. Initial screening was carried out against the immunising material by ELISA, against fresh frozen placental sections by immunostaining and against purified PLAP using an enzyme capture assay. The most successful fusions were those following whole cell immunisation, producing 27 antibodies that all reacted with both the placental and testicular form of enzyme. These all showed a broadly similar pattern of reactivity when tested against a range of human malignant cell lines. Further characterisation identified one antibody, 8B6, as strongly reactive with formalin-fixed paraffin-embedded placental sections. This antibody also performed well when tested against a range of normal and malignant routinely fixed tissue sections. Of 14 antibodies analysed for immunoglobulin isotype, 10 were of the IgGI subclass. In competitive binding studies with 7 antibodies to discriminate epitopes, at least 4 distinct binding sites were identified. By Scatchard analysis on 4 of these antibodies, binding constants of 3 were within the range 3.5-5.3 x 10(-9)M. Unusually the 4th antibody appeared to recognise 2 separate antigen sites with binding constants of 2.1 and 7.5 x 10(-9)M. In a preliminary study to compare patterns of reactivity of a selection of the new antibodies with a limited number of sera from smokers and seminoma patients, results indicate their potential for further typing within the placental group of enzymes.

Antibody-guided diagnosis and therapy of malignant lesions

Tumour associated monoclonal antibodies (MAbs) HMFG1, HMFG2 and H17E2, labelled with 123iodine or 111indium, were used to detect primary and metastatic cancer by external body scintigraphy in patients with ovarian, breast and non-small cell lung cancer (NSCC). Successful localisation was seen in all patients with primary and 80% of the metastatic NSCC, 50% of primary and 70% of metastatic breast cancer lesions and in 80% of patients with metastatic ovarian cancer. On the other hand, imaging carried with a radiolabelled non-specific MAb produced positive results in 3 out of 5 cases with primary NSCC. Therefore, non-specific imaging should be further studied in clinical research for the evaluation of the specificity of radioimmunodetection. A therapeutic procedure which has shown promise is that of intracavity administration of radiolabelled antibodies. Twenty-nine patients with resistant ovarian cancer have been treated with intraperitoneal 131I-labelled MAbs (HMFG1, HMFG2, AUA1, H17E2). There were no significant responses in 8 patients with gross disease. There were 2 responses in 15 assessable patients with tumour nodules of less than 2 cm in diameter. Out of 6 patients with microscopic disease, 4 are disease-free with follow-up time of 6-40 months (mean = 17.5 months).

Monoclonal antibodies to placental alkaline phosphatase: preclinical evaluation in a human xenograft tumour model of F(ab')2 and Fab fragments

Six new placental alkaline phosphatase monoclonal antibodies (MAbs) have been evaluated in order to select a potentially clinically useful antibody fragment for use in immunoscintigraphy or therapy. Initially, 3 antibodies were identified by trial pepsin digestion as likely to give satisfactory F(ab')2 yield. The corresponding intact antibodies were then compared for ability to localise human xenograft tumours in athymic mice. Of the best of these, designated 3F6, F(ab')2 and Fab fragments were then evaluated in similar xenograft experiments. In intact antibody biodistribution comparisons, 3F6 showed good tumour retention and satisfactory specific/non-specific ratios at 8 days. In similar fragment biodistribution experiments 3F6 F(ab')2 gave the highest tumour/blood ratio (10) and tumour/organ ratios (19) and the best specific/non-specific localisation. This fragment also showed higher absolute uptake in the tumour than intact antibody, 18.9% and 14.4% respectively of the injected dose. As expected, fragments showed much faster blood clearance rates than whole antibody. For Fab the in vivo instability by 6 hr was also demonstrated.

Human amnion cells: modulation of expression of specific antigens

Antigen expression by fetal cells near the mother is of interest because of the possibility that some antigens may stimulate beneficial maternal immune responses or may prevent the development of harmful responses. The recent generation of monoclonal antibodies to amnion and trophoblast antigens together with the finding that class I histocompatibility antigen (HLA) expression by amnion cells can be manipulated provided an opportunity to determine if any relationships exist among expression of HLA, amnion antigens, and trophoblast antigens. The results of the present study demonstrate that: class I HLA and amnion-specific antigens are co-expressed by IFN-gamma-modulated amnion cells, so neither prevents expression of the other; EGF enhances expression of two amnion-specific antigens; amnion cells do not express transferrin receptors, placental alkaline phosphatase, or other antigens normally associated with trophoblasts following exposure to IFN-gamma and/or EGF. The results demonstrate independent modulation of expression of class I HLA, two amnion-specific antigens, and some trophoblast-associated antigens on amnion epithelial cells.