An immunohistological study of testicular germ cell tumours using two different monoclonal antibodies against placental alkaline phosphatase

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.

Molecular-Docking-Guided Design, Synthesis, and Biologic Evaluation of Radioiodinated Quinazolinone Prodrugs

Enzyme-mediated cancer imaging and therapy (EMCIT) is a novel approach in which radioactive water-soluble molecules are precipitated in vivo following their hydrolysis by extracellular enzymes overexpressed by cancer cells. AutoDock 3.0 was used to model the interaction-binding between a series of iodinated quinazolinone derivatives and human placental alkaline phosphatase (PLAP, crystal structure in the Protein Data Bank) and to assess the effects of structural modification of the derivatives. Ammonium 2-(2',4'-diphosphoryloxyphenyl)-6-iodo-4-(3H)-quinazolinone (IQ2-P,4-P), having the most favorable calculated inhibition constant, was synthesized and characterized. Concentration-dependent, PLAP-mediated conversion of IQ2-P,4-P (4)/125IQ2-P,4-P (6) to water-insoluble 2-(2',4'-dihydroxyphenyl)-6-[127I/125I]iodo-4-(3H)-quinazolinone (127IQ2-OH,4-OH (2)/125IQ2-OH,4-OH (7)) was observed in solution. Autoradiography indicated that 6 is hydrolyzed by human cancer cells and the resulting 7 precipitates on exterior cell surfaces. Biodistribution studies in mice demonstrated that 6 is minimally retained by normal tissues. The findings support the validity of the EMCIT approach.

Establishing a germ cell origin for metastatic tumors using OCT4 immunohistochemistry

BACKGROUND

There are diverse morphologic manifestations of metastatic tumors. The determination of tumor origin is critical for patient management, and it is especially important when the differential diagnosis includes metastatic germ cell tumor, which is a highly treatable condition. OCT4 is a nuclear transcription factor that is expressed in pluripotent embryonic germ cells. In this study, the author sought to determine the usefulness of OCT4 immunohistochemistry in the diagnosis of metastatic germ cell tumors.

METHODS

Sixty-two retroperitoneal lymph node dissection specimens from patients with histories of testicular germ cell tumors were stained using the antibodies against OCT4. In addition, 84 metastatic, nongerm cell lesions from men with known primary tumors were studied in parallel for OCT4 immunohistochemistry.

RESULTS

All embryonal carcinoma components (n = 29 specimens) and seminoma components (n = 18 specimens) from retroperitoneal lymph node dissection specimens showed strong, intense, diffuse nuclear staining for OCT4. Yolk sac tumors (n = 12 tumors), choriocarcinomas (n = 4 tumors), mature teratomas (n = 16 tumors), and primitive neuroectodermal tumors (n = 5 tumors) were negative for OCT4 staining. Metastatic, nonsmall cell carcinomas from the lung (n = 14 tumors), colon (n = 12 tumors), stomach (n = 5 tumors), pancreas (n = 7 tumors), prostate (n = 12 tumors), kidney (n = 3 tumors), and urinary bladder (n = 15 tumors) all were found to be negative immunohistochemically for OCT4, as were metastatic small cell carcinomas (n = 4 tumors) and metastatic melanomas (n = 7 tumors). In addition, malignant lymphomas (n = 5 tumors) also were negative for OCT4.

CONCLUSIONS

Immunohistochemical detection of OCT4 is highly sensitive and specific for the diagnosis of seminoma and embryonal carcinoma metastatic from the testis. Establishing germ cell origin for metastatic tumors has important implications for assessing patient prognosis and treatment options.

A phase I trial of idiotypic vaccination with HMFG1 in ovarian cancer

INTRODUCTION

An extended phase I trial was conducted in a total of 26 patients with ovarian cancer. The objectives were to assess the safety and tolerability of idiotypic vaccination using the murine monoclonal antibody HMFG1 (anti-MUC1), and to develop robust assays to monitor humoral immune responses generated against either the antibody or MUC1.

MATERIAL AND METHODS

All patients had undergone standard debulking surgery (where appropriate) and at least one regimen of platinum-based chemotherapy. Eligibility criteria included: (a) residual disease at the end of chemotherapy, (b) relapsed disease, and (c) pathologically confirmed second complete remission following salvage chemotherapy. Patients received a priming dose of 25 mg of HMFG1 either intravenously or intraperitoneally, followed by up to six intradermal doses of HMFG1 in 10% Alhydrogel at intervals of 1 month. The three dose levels were 0.5 mg, 1 mg and 5 mg. We devised modifications of published protocols for the measurement of anti-idiotypic and anti-MUC1 antibody responses and also extended the use of the IAsys resonant mirror biosensor to measure the kinetics of the idiotypic network response in these patients.

RESULTS

There were no serious adverse events at any dose level. The trial confirmed that all doses could be administered safely with minimal toxicity. No clinical responses were seen in patients with evaluable disease. ELISA for anti-idiotypic antibodies (Ab2) showed significant levels in patients who completed the protocol. There were no significant differences in the levels of Ab2 generated by the different doses of antibody. These results were confirmed by biosensor assays for Ab2, which also showed affinity maturation of the Ab2 response as patients progressed through the vaccination protocol. Biosensor assays also demonstrated no difference in the affinity of Ab2 generated by different booster doses of HMFG1. ELISA for anti-MUC1 antibodies showed less consistent results, with very small but statistically significant rises in anti-MUC1 signals seen in 38% of patients who completed the vaccination regimen.

DISCUSSION

The clinical endpoints of safety and tolerability were met. The assays developed for this project have shown reproducibility and may provide surrogate endpoints to assess vaccination for future trials. The use of similar biosensors may be of particular relevance for monitoring of humoral immune responses in other vaccine trials. The low levels of anti-MUC1 antibodies generated may correspond with the lack of clinical efficacy in the few patients with evaluable disease.

Ribonucleases and their antitumor activity

The antitumor effect of ribonucleases was studied with animal ribonucleolytic enzymes, bovine pancreatic RNase A, bovine seminal RNase (BS-RNase), onconase and angiogenin. While bovine pancreatic RNase A exerts a minor antitumor effect, BS-RNase and onconase exert significant effects. Angiogenin, as RNase, works in an opposite way, it initiates vascularization of tumors and subsequent tumor growth. Ribonunclease inhibitors are not able to inhibit the antitumor effectiveness of BS-RNase or onconase. However, they do so in the case of pancreatic RNases. Conjugation of BS-RNase with antibodies against tumor antigens (preparation of immunotoxins) like the conjugation of the enzyme with polymers enhances the antitumor activity of the ribonuclease. After conjugation with polymers, the half-life of BS-RNase in blood is extended and its immunogenicity reduced. Recombinant RNases have the same functional activity as the native enzymes. The synthetic genes have also been modified, some of them with gene sequences typical for the BS-RNase parts. Recent experimental efforts are directed to the preparation of 'humanized antitumor ribonuclease' that would be structurally similar to human enzyme with minimal immunogenicity and side effects. The angiogenesis of tumors is attempted to be minimized by specific antibodies or anti-angiogenic substances.

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.

Testicular yolk sac carcinoma in a calf

A testicular yolk sac carcinoma (YSCA) was diagnosed in a 28-day-old male Japanese black calf. Macroscopically, the abdominal cavity was filled with reddish gelatinous masses of various sizes. There were no testes in the scrotum or pelvic cavity. Histologically, the masses consisted of the tissues showing a variety of patterns; loose reticular network, pseudopapillary arrangement, festoon, solid nest, and labyrinthine pattern. Tumor cells were round to oval, with single central or polar nuclei with sharply defined nuclear borders and deeply basophilic chromatin. Tumor cells sometimes had glycogen granules, periodic acid-Schiff (PAS)-positive inclusions, or sudanophilic droplets in their cytoplasm. Hyaline matrices were found in extracellular areas and were intensely PAS positive. Immunohistochemically, most of the tumor cells and hyaline matrices had positive reactivity to anti-alpha-fetoprotein and anti-placental-alkaline-phosphatase antibodies. Positive reaction to anti-laminin antibody appeared only in hyaline matrices. This is the first case of a tumor in a domestic animal with histologic and immunohistochemical features analogous to those of human YSCA, endodermal sinus type.

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.

Targeting phosphodiesterases as a strategy for killing tumor cells

Ribonucleases (RNases) are being employed as alternative cytotoxic proteins to the conventionally used ones such as ricin and Pseudomonas exotoxin. Mammalian RNases are attractive enzymes because of their comparable cytotoxicity when suitably directed and the likelihood of lower immunogenicity compared to plant and bacterial toxins. Bovine seminal RNase (BSRNase) is a member of the RNase superfamily, but differs in many interesting ways. Unlike the rest of the family it is dimeric, and possesses antitumor and immunosuppressive properties. These features make it a choice candidate for a single-chain antibody (scFv) based immunotoxin. This work describes preliminary data on the construction, expression in Escherichia coli and characterization of a tumor-specific scFv (directed against human placental alkaline phosphatase)-BSRNase chimeric molecule. It is shown that the created molecule has RNA degrading activity and antigen-binding activity when refolded from bacterial inclusion bodies.

Deoxyribonuclease I (DNAse I). A novel approach for targeted cancer therapy

A number of phosphodiesterases, some of which possess additional biological activities (e.g., antitumor, immunosuppressive, and so on), have been considered for use in targeted tumor therapy. We propose Deoxyribonuclease I (DNase I), a compact, monomeric enzyme, as a very attractive candidate for targeting to tumor cells. Only a small amount of enzyme targeted to a cell needs to enter the nucleus in order to degrade the chromosomal DNA, making a cell incapable of further replication. We describe preliminary data on the construction of a potent single-chain antibody (scFv) immunotoxin based on bovine pancreatic DNAse I. The use of a mammalian enzyme should be much less toxic and less immunogenic than current immunotoxins and may expand the current limits of immunotoxin therapy.

Antibody-directed enzyme prodrug therapy (ADEPT). A three-phase study in ovarian tumor xenografts

Antibody-directed enzyme prodrug therapy (ADEPT) has been studied in a human ovarian carcinoma xenograft grown subcutaneously in nude mice. Radioimmunoassay of supernatants obtained from tumor homogenates showed these to contain carcinoembryonic antigen (CEA). Biodistribution studies with 125I-labeled monoclonal anti-CEA antibody, A5B7, and its F(ab')2 fragment showed localization in these xenografts. The AB57-F(ab')2 fragment conjugated to a bacterial enzyme, carboxypeptidase G2 (CPG2), and, radiolabeled with 125iodine, also localized in the xenografts. The radiolabeled conjugate cleared from blood faster than the antibody alone. The percentage of injected dose per gram in tumor at 24 h postinjection was about fivefold lower than antibody alone. Tumor-to-blood ratio at 72 h after injection of the radiolabeled conjugate was 7 and the tumor-to-normal tissue ratios at this time point ranged from 20 (liver) to 75 (colon). A three-phase ADEPT antitumor study was carried out in which A5B7-F(ab')2-CPG2 was allowed to localize and was followed by accelerated inactivation/clearance of blood CPG2 by a galactosylated anti-CPG2 antibody (SB43gal). A benzoic acid mustard-derived prodrug was injected 24 h after the conjugate, which led to growth delay in this tumor compared to the control untreated group. Further antitumor studies in this model are in progress.

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.

Langerhans' cell histiocytosis (histiocytosis X): immunophenotype and growth fraction

The immunophenotype and proliferation fraction have been investigated in 26 cases of Langerhans' cell histiocytosis (LCH). In all cases LCH cells were positive for S-100 protein, CD1a, or both. In most cases LCH cells expressed the macrophage-associated marker CD68 and in two cases they contained lysozyme. Expression of both cytoplasmic CD2 and CD3 was observed in cryostat sections. An unexpected finding was the presence of placental alkaline phosphatase in LCH cells. Langerhans' cells in normal skin were negative for both CD2 and CD3, but a proportion contained placental alkaline phosphatase. In four cases of Rosai-Dorfman disease the histiocytic cells, which share certain immunophenotypic properties with Langerhans' cells, also were positive for placental alkaline phosphatase. A significant proportion of LCH cells stained positively with the antibody to proliferating cell nuclear antigen and also with the proliferation marker Ki-S1. A good correlation between the percentage of Ki-67-positive and proliferating cell nuclear antigen- and Ki-S1-positive cells, respectively, was observed. Thus, in comparison with their putative precursors, LCH cells have an aberrant phenotype and are proliferating locally. This might suggest that LCH is a neoplastic rather than a reactive process.

Isoenzymes of alkaline phosphatases in seminomas. An immunohistochemical and biochemical study

Placental alkaline phosphatase (the PLAP-like isoenzyme) and liver alkaline phosphatase (LAP) were demonstrated immunohistochemically by use of monoclonal antibodies in the tumor cells of twelve seminomas and one seminoma metastasis. Intestinal alkaline phosphatase (IAP) was not found. The PLAP-like and LAP enzymes showed high catalytic activities compared to normal testis. This is the first occasion that LAP has been demonstrated by immunochemistry in seminoma cells. The results suggest that demonstration of these tumor enzymes may be useful markers for seminomas in histopathological specimens.

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.

Immunoscintigraphy with 131I-labelled H17E2 monoclonal antibody compared with conventional lymphangiography and computed tomography in the detection of metastases in patients with testicular germ cell tumours

131I-labelled H17E2 monoclonal antibody (MAb) was administered to 16 patients with germ cell tumours of the testis (GCT). Eleven patients had non-seminomatous GCT and five seminoma. The MAb was administered into the webs between the second and third toes of both feet in 12 patients and intravenously in four patients at a dose of 1.5-2mCi. 131I-labelled 2-118 MAb (non-specific) was administered subcutaneously into the webs between the second and third toes of both feet in two patients and intravenously in one patient with non-seminomatous GCT. All three patients had only computed tomography (CT) scan. Patients were scanned immediately after until 7 days post-injection. For comparison all patients had CT scan and eight out of 16 patients had conventional lymphangiography (LG). When the radiolabelled MAb was given subcutaneously, the immunoscan (IS) was true positive in 9/12 (75%) patients and true negative in 2/12 (16.5%) and equivocal in 1/12 (8.5%). The LG gave true positive results in 6/8 (75%) patients and true negative results in 2/8 (25%) and the CT scan true positive results in 8/12 (66.6%) patients, true negative results in 2/12 (16.3%) and false negative results in 2/12 (16.3%). There was an excellent correlation of IS images with the LG results (true positivity 100%). When the radiolabelled MAb was given intravenously, both IS and CT scan gave true positive results in four cases. Our findings showed that the true positivity of IS reached 93.8%, whereas that of CT scan 87.5%. In all three patients who had the 131I-labelled 2-118 non-specific MAb, the IS was false negative, whereas the CT scan was true positive. Thus, this procedure may offer information complementary to that provided by existing conventional imaging methods.

Placental-like alkaline phosphatase in seminoma

Tumor marker identification in testicular cancer has contributed to early detection and monitoring of non-seminomatous disease. A placental alkaline phosphatase-like (PLAP-like) enzyme derived from seminomas has recently been focused upon as a possible marker for this disease. The biochemistry of the PLAP-like enzyme is reviewed, as well as its occurrence in tissue and sera from healthy persons and patients with testicular cancer.

Immunohistological distribution of 5T4 antigen in normal and malignant tissues

A trophoblast cell surface antigen has been characterised by a monoclonal antibody (mAb) 5T4, raised following immunisation with solubilised wheat germ agglutinin binding glycoproteins from human syncytiotrophoblast plasma membrane (StMPM). The expression of the 72 kDa glycoprotein was assessed on cryostat sections of a range of neoplastic and non-neoplastic tissues, using an avidin-biotin immunoperoxidase technique. In products of conception, intense reactions were noted with villous syncytiotrophoblast membrane in normal early and term placenta, with weaker positivity of placental site trophoblast. Most normal or non-neoplastic tissues were negative, including liver, kidney, spleen, small intestine, ovary and testis. Faint or moderate positive reactions were present in some specialised epithelia. Of 115 neoplasms examined, 76 showed reactions with tumour cells including carcinomas of the bladder, breast, cervix, endometrium, lung, oesophagus, ovary, pancreas, stomach and testicular non-seminomatous germ cell tumours. Choriocarcinomas and placental site trophoblastic tumours were also positive. Most adenocarcinomas of colon and seminomas were negative as were all malignant melanomas and malignant lymphomas. A radioimmunoassay did not detect the antigen in either normal or pregnancy serum. The relatively low level of expression in normal tissues and reactivity with a wide range of carcinomas suggested that the antibody may be useful in diagnostic or targeting studies.

Metastatic spermatocytic seminoma. A case report with light microscopic, ultrastructural, and immunohistochemical findings

A case of metastatic spermatocytic seminoma with metastases to homolateral retroperitoneal paraaortic lymph nodes in a 50-year-old man is described. The metastases were detected 18 months after orchiectomy. A retroperitoneal biopsy with cytoreductive lymphadenectomy was performed followed by radiotherapy and consecutively by combination chemotherapy. The patient died 25 months after orchiectomy of complications arising after a second course of chemotherapy. No signs of further tumor spread were observed. Autopsy was not performed. The tissue of the metastases fulfilled the light microscopic criteria for spermatocytic seminoma and ultrastructurally showed intercellular communications with typical intercellular bridges. The absence of placental alkaline phosphatase in tumor cells is also consistent with this diagnosis. The metastases differed from the primary tumor in the presence of focal lymphocytic infiltration and granulomatous reaction. This patient represents the first fully documented case of a metastasizing spermatocytic seminoma.

Use of anti-seminoma monoclonal antibody to confirm the diagnosis of mediastinal seminoma. A case report

Chest x-ray in a 20-year-old man showed a large anterior mediastinal mass and a needle aspirate was diagnosed by light microscopy (LM) as non-Hodgkin's lymphoma. Treatment with CHOP (cyclophosphamide, adriamycin, vincristine and prednisone) was ineffective and a tissue biopsy was performed. LM showed large, non-cohesive cells with abundant cytoplasm and rounded nuclei. Differential diagnoses included malignant lymphoma, seminoma, thymoma, anaplastic carcinoma, malignant melanoma and paraganglioma. Electron microscopy was not conclusive and immunoperoxidase staining was carried out. The malignant cells were negative for common leukocyte antigen, Leu M1, alpha-fetoprotein, chorionic gonadotrophin, cytokeratin, epithelial membrane antigen, carcinoembryonic antigen, S-100 protein and neuron-specific enolase but positive for placental alkaline phosphatase. In addition, there was strong positivity with a monoclonal antibody (mAb) which was recently shown to react with testicular seminomas. This case illustrates the value of this mAb in confirming the diagnosis of mediastinal seminoma.

What's new in tumor markers and their measurements?

Clinical interest and usefulness of the various marker determinations in staging, detection, prognosis, and monitoring of therapy in patients with tumors of different organ systems is discussed. It is stated that there is an urgent need for markers that can be used in early stage cancers, since neither the classical nor the new markers are sensitive or specific enough to be used for screening purposes or the detection of incipient malignancies. Despite having experienced frustrating limitations with the circulating markers these substances became of great interest as target antigens in histopathology and immunescintigraphy. These new applications of the tumor markers are also reviewed.

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.

Placental-like alkaline phosphatase reactivity in human tumors: an immunohistochemical study of 520 cases

Placental-like alkaline phosphatase (PLAP) activity has been reported in various human neoplasms of both somatic and germ cell types. The expression of PLAP was examined with a polyclonal antibody and the immunoperoxidase technique in formalin-fixed, paraffin-embedded sections of 37 germ cell neoplasms and 483 somatic tumors. The expression of keratin and epithelial membrane antigen (EMA) was concurrently assessed to determine whether these stains were helpful in distinguishing germ cell neoplasms from somatic tumors that might mimic them microscopically. All germ cell lesions were reactive for PLAP, but so were 62 somatic carcinomas, usually in female müllerian, intestinal, and lung cancers and less often in carcinomas of the breast and kidney. PLAP-reactive somatic tumors exhibited EMA and keratin positivity in the absence of prior protease digestion, whereas germ cell neoplasms failed to do so. Malignant mesotheliomas were nonreactive for PLAP, as were carcinomas of the nasopharynx, adrenals, liver, pancreas, stomach, prostate, and urinary bladder. PLAP is a highly sensitive but nonspecific immunohistologic marker of germ cell differentiation. However, non-protease-enhanced stains for keratin and EMA allow separation of germ cell and somatic carcinomas, despite their shared capacity for PLAP expression. In somatic neoplasms, PLAP immunoreactivity might be of potential use in predicting possible primary sources for metastatic tumors of unknown origin.

Monoclonal antibodies to human trophoblast and sperm antigens: report of two WHO-sponsored workshops, June 30, 1986--Toronto, Canada

Two WHO-sponsored workshops were recently held to obtain a consensus view from researchers active in the field of reproductive immunology on the current status of the application of monoclonal antibodies to studies of molecular events underlying reproduction and to determine the feasibility of using this approach to identify trophoblast- or sperm-specific antigens that might represent suitable candidates for the development of antifertility vaccines. A total of 66 mouse monoclonal antibodies reacting with human sperm and 45 monoclonal antibodies reacting with human trophoblast membrane components were submitted by 29 laboratories. These were evaluated in coded form by 42 laboratories with the appropriate expertise in biochemistry, immunohistology and tests of reproductive cell function. The majority of both anti-sperm and anti-trophoblast monoclonal antibodies cross-reacted with cellular elements in non-reproductive tissues. However, at least five monoclonal antibodies (two anti-trophoblast and three anti-sperm) appeared to demonstrate sufficient specificity to warrant further investigation as reagents for the identification of antifertility vaccine candidates.

Tumor markers in the human ovary and its neoplasms. A comparative immunohistochemical study

The incidence and histologic characteristics of the expression of placental alkaline phosphatase (PLAP) in ovarian tumors was compared with that of five other tumor antigens. Three monoclonal antibodies were used for the specific localization of PLAP. PLAP was present in some sex cord cells of the 13-16-week fetal ovary, probably germ cells. In normal ovaries, all antigens except carcinoembryonic antigen (CEA) were frequently found in inclusion cysts; the germinal epithelium was positive only for cancer antigen 125 (CA 125). The frequency and extent of PLAP expression in nonmucinous carcinomas was higher than observed for CA 19-9 and CEA, but was lower than for CA 125 and human milk fat globule antigen. Serous tumors had the highest PLAP expression, followed by endometrioid and poorly differentiated adenocarcinomas, and some other tumors. PLAP was predominantly membranous; its histologic distribution was in general heterogeneous. Different antibodies to PLAP gave different staining intensities in some tumors, but the staining patterns were always qualitatively identical.

Vasitis nodosa--a site of arrest of malignant germ cells

A 40-year-old man, with a history of vasectomy 11 years previously, presented with a tumour in his right testis. At orchidectomy a seminoma was found, together with a nodule on the vas deferens. Histological examination of this area in the vas identified the lesion of vasitis nodosa and also showed it to be the site of proliferating germ cells. The pathogenesis of this lesion is discussed.

Antibody-guided radiolocalisation of tumours in patients with testicular or ovarian cancer using two radioiodinated monoclonal antibodies to placental alkaline phosphatase

Monoclonal antibodies (H317 and H17E2) against placental-type alkaline phosphatase and testicular placental-like alkaline phosphatase were radiolabelled with 123I or 131I and used in a prospective study of patients with germ-cell neoplasms of the testis (13 studies) or epithelial-origin neoplasms of the ovary (13 studies). The presence of tumour was confirmed in the majority of patients with active disease by antibody scanning. The absence of tumour was confirmed in all cases in patients in complete remission. In two patients with positive antibody scans but no disease found by conventional radiological evaluation, further investigations subsequently revealed the presence of tumour. A positive antibody scan indicates the definite presence of a tumour, although a negative antibody scan does not always exclude the presence of disease. This method may be of clinical value in establishing disease status in patients with potentially curable diseases such as ovarian or testicular cancers.

Indium-111 labelled monoclonal antibody to placental alkaline phosphatase in in the detection of neoplasms of testis, ovary, and cervix

A monoclonal antibody (H17E2) against placental alkaline phosphatase (PLAP) and testicular placental-like alkaline phosphatase was labelled with indium-111 and used in radioimmunoscintigraphy of 15 patients known or suspected to have germ-cell carcinoma of the testis or carcinoma of the ovary or cervix. Good images of neoplastic lesions were obtained in most patients with active disease. In 1 patient with testicular teratoma and elevated human chorionic gonadotropin who had a normal computed tomography scan, the labelled antibody located microscopic disease in a lymph node, which was then removed. No false positive localisation was seen in patients with PLAP-negative tumours or sites of inflammation. This method may be helpful in the diagnosis, staging, and monitoring of PLAP-positive neoplasms of testicular, ovarian, and cervical origin.

Serum marker potential of placental alkaline phosphatase-like activity in testicular germ cell tumours evaluated by H17E2 monoclonal antibody assay

A monoclonal antibody (H17E2) was used in a solid-phase localisation of enzyme activity (ILEA) assay to evaluate placental-like alkaline phosphatase (PLAP) as a serum marker of testicular germ cell tumours. Single or repeated assays were performed on 213 normal blood donor and a smaller number of term pregnancy and testicular cancer sera. The detection limit of PLAP by this system was 0.14 O.D. units equivalent to 0.04iul-1. Of 50 patients with established metastatic disease tested before treatment, 88% of 16 with seminoma, 54% of 13 with mixed seminoma and malignant teratoma and 33% of 21 with malignant teratoma had serum PLAP greater than 0.2 O.D. units. This compared to an incidence of 2% in non-smokers and of 29% in smokers who had been free of disease for more than 12 months. In 15 of 22 successfully treated patients, pre-treatment serum PLAP exceeded 0.2 O.D. units (mean 0.69 O.D.) and varying (53-97%) reductions in the initial levels occurred with treatment. These results with monoclonal antibody ILEA assay suggest that measurement of PLAP levels will be useful in the management of patients with germ cell tumours, particularly seminoma.

Monoclonal antibody assay of serum placental alkaline phosphatase in the monitoring of testicular tumours

A monoclonal antibody (H17E2) recognising both placental alkaline phosphatase (PLAP) and testicular PLAP-like alkaline phosphatase was incorporated in a solid phase immunoassay. This was used to measure levels of PLAP in 257 sera from 148 patients with germ cell neoplasms of the testis. High levels of PLAP were found in all patients with active seminomas (mean 0.85 O.D.) compared to those in clinical remission (mean 0.20 O.D.) (P less than 0.0001). More importantly, changing levels of PLAP correlated with the course of disease in 79 samples from 33 patients with seminoma (P less than 0.0001). Elevated PLAP levels were also noted in patients in remission who were smokers (mean 0.32 O.D.) compared to non-smokers (mean 0.15 O.D.) (P less than 0.001). These data demonstrate that determination of PLAP levels using this sensitive immunoassay is an important new adjunct in the monitoring of the response to treatment in patients with seminoma.

Placental alkaline phosphatase as a tumour marker in seminoma using the H17 E2 monoclonal antibody assay

Serum samples from 62 patients with seminoma were assayed for placental alkaline phosphatase-like activity using the monoclonal antibody H17 E2, in order to evaluate its utility as a serum tumour marker. Fifteen of 16 patients (94%) with active seminoma had elevated serum PLAP levels. Sixteen of 46 (35%) of patients considered to be in remission had elevated PLAP levels (false positive rate 35%). Fifteen false positive results were considered attributable to concomitant smoking, and if these patients are excluded, only one false positive case was detected. In 7 out of 7 patients sequential PLAP assays reflected clinical response to treatment.

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

We have prepared monoclonal antibodies by immunizing BALB/c mice with purified human term placental plasma membranes. The antibodies were selected to show predominant specificity for trophoblast and trophoblast derivatives. Four of these antibodies have been found to recognize the placenta-specific isozyme of alkaline phosphatase (EC 3.1.3.1), and to cross-react with the closely related testis form of this enzyme. One antibody recognized transferrin, a serum protein with an abundant placental receptor. The specificities of the other antibodies, whose target antigens are unknown, are described. Their reactivity with some human tumour-derived epithelial cell lines suggests that they may provide useful markers of human trophectoderm differentiation, as well as for properties selected for during tumour progression.