Elimination of carcinoma cells from human bone marrow

Resistance of ovarian teratocarcinoma cell spheroids to complement-mediated lysis

We have shown previously that it is possible to target complement-mediated killing against cultured ovarian tumour cells in vitro. As malignant ovarian cells usually grow in solid nodules in vivo, we have in the present study examined the effectiveness of complement killing against ovarian teratocarcinoma cells (PA-1) growing in three-dimensional tumour microspheroids (TMSs). Our study shows that PA-1 cells growing in TMSs are less susceptible to complement-mediated killing than cells growing in monolayer cultures, even after neutralization of protectin (CD59), the main inhibitor of complement lysis. Cells in suspension and cells growing in TMSs showed a similar expression of membrane co-factor protein (MCP, CD46) and CD59. Decay-accelerating factor (DAF, CD55) was not detected on the surface of cells in suspension, but appeared focally on the outermost cell layers of the TMSs. Complement-activating antibodies bound to all PA-1 cells in suspension but only to the most peripherally located cells in TMSs, even though the target antigens were similarly expressed in the two systems. Antibody-induced complement activation on PA-1 cells in suspension led to C3 and C5b-9 deposition on most cells, while C3 and C5b-9 were only found on the outermost layers of the TMSs. The increased complement resistance of tumour cells growing in three-dimensional spheroids is partly because of an insufficient penetration of antibodies and complement into the TMSs. TMSs are a useful model for the development of more efficient ways to kill malignant cells in micrometastases with monoclonal antibodies and complement.

Toxicity of ribosome-inactivating proteins-containing immunotoxins to a human bladder carcinoma cell line

Immunotoxins were prepared by linking the type 1 ribosome-inactivating proteins (RIP) momordin I, pokeweed antiviral protein from seeds (PAP-S) and saporin-S6 to the 48-127 monoclonal antibody (MAb) recognising a glycoprotein (gp54) expressed on all human bladder tumours tested and on human bladder carcinoma cell lines, in particular on the T24 cell line. T24 cells required a 2 hr contact with immunotoxins to ensure binding and endocytosis. A time course of exposure, followed by further incubation without the immunotoxins, showed that maximum inhibition of protein synthesis by T24 cells was reached after 2 hr of contact followed by 3 days without the immunotoxins. Under optimal conditions, 48-127/RIP immunotoxins at nanomolar concentrations inhibited by 50% protein synthesis of target T24 cells. No toxicity was observed if (i) target cells were treated with non-conjugated RIP, (ii) target cells were treated with momordin I- or PAP-S-containing immunotoxins made with an irrelevant antibody and (iii) a non-target cell line was treated with the same 2 RIP conjugated to 48-127 antibody. The in vitro selective toxicity of these immunotoxins encourages further studies in view of a possible use in clinical trials for the local therapy of human bladder carcinomas.

The effect of ricin B chain on the intracellular trafficking of an A chain immunotoxin

Covalent linkage of the A chain of ricin to the LICR-LOND-Fib75 monoclonal antibody produced an immunotoxin, Fib75-SS-ricin A, which demonstrated immunospecific toxicity to human bladder carcinoma cells in tissue culture (Forrester et al., 1984). The present studies have shown that ricin B chain potentiates the toxicity of the immunotoxin by two orders of magnitude and also significantly increases the rate of protein synthesis inhibition. Using immunoelectron microscopy, the receptor-mediated endocytosis and intracellular routing of the immunotoxin was studied with and without ricin B chain treatment after immunolocalisation of the conjugate. Fib75-SS-ricin A was internalised by the EJ cells predominantly in uncoated pits and vesicles and directed to the endosomes. Some degradation of the complex appeared to take place in multivesicular endosomes at early timepoints and 24 h after internalisation, most of the immunotoxin was found in lysosomes. Some ricin A chain epitopes were detected in Golgi vesicles. Cells treated with immunotoxin and ricin B chain endocytosed the complex predominantly in coated pits and coated vesicles. Using pre-embedding immunoperoxidase techniques, ricin chains were found in the whole Golgi complex and most of the conjugate escaped lysosomal degradation. Internalised immunotoxin was recycled back to the plasma membrane in an active form associated with vesicles which appeared to be derived predominantly from multivesicular endosomes. A similar mode of recycling has recently been reported (McIntosh et al., 1990) for ricin holotoxin in the same cell line. These observations may explain the potentiating effect of toxin B chains in the antibody-directed targeting of toxin A chains.

Comparative activities of rabbit complements of different ages using an in-vitro marrow purging model

In order to determine the best time to obtain complement for use in marrow purging in vitro, we have used 51Cr-release and limiting dilution assays (LDA) to evaluate the ability of serum from rabbits 20-30 (25d), 30-40 (35d) and 40-50 (45d) days old to lyse a series of neoplastic target cells in the presence of complement activating antibodies. Utilizing a limiting dilution assay (LDA) to measure log depletion of tumor cells in a 20-fold excess of normal bone marrow, treatment with monoclonal antibody and 25d complement depleted at least 4 logs of leukemia or lymphoma cells. 35d and 45d complements were approximately one log less effective. When normal bone marrow alone was treated with either J5 (CD10) antibody alone, each complement alone or a combination of J5 antibody with each complement, there was no significant depletion of hematopoietic progenitors in any subgroup. These results suggest that complement from 20-30 day old rabbits should be used for the purpose of ex-vivo purging due to its highly sensitive and specific activity.

Late intensification with high-dose melphalan and autologous bone marrow support in breast cancer patients responding to conventional chemotherapy

Fifteen patients with advanced breast cancer who had achieved either a good partial or a complete response to conventional chemotherapy were selected to receive intensification treatment with high-dose melphalan 140-200 mg/m2 (HDM). All patients received autologous bone marrow rescue. All patients experienced marked haematological toxicity, and most experienced moderate or mild gastrointestinal side effects. There were three treatment-related deaths. Of twelve assessable patients eleven have relapsed; median time to relapse after HDM is 7 months. Nine of these eleven have died from recurrent breast cancer. Of the three patients remaining alive, only one is disease-free, at 18 months after HDM. Analysis of the pattern of metastatic relapse suggests that recurrence was due to failure of HDM to eradicate residual disease in the patient, rather than reinfusion of viable tumour cells. Treatment intensification with HDM has not succeeded in prolonging survival in patients already in good remission.

Antibody-mediated targeting in the treatment and diagnosis of cancer: an overview

Enhancing the discrimination between tumour and host has been an underlying goal of efforts to improve the diagnosis and treatment of cancer. Over the past 15 years considerable interest has focussed upon targeting systems designed to permit selective delivery of a variety of agents, including drugs, radioisotopes and toxins, to tumours, for both diagnosis and therapy. A vast body of information has accumulated on this subject, and considerable emphasis has been placed on the use of antibodies as carriers, as at present they offer the greatest clinical potential. Many targeting systems have been evaluated in vitro and in pre-clinical models, but few, with the exception of antibody-radioisotope conjugates, have been evaluated in patients. However, systematic evaluation of the therapeutic potential of immunoconjugates in the clinic is planned or already under way. While reviews of some individual aspects of antibody targeting do exist, there are none that encompass this entire field. Our objective is to fill this gap with a concise overview of antibody-mediated targeting for diagnostic and therapeutic applications.

Monoclonal antibodies in oncology

Monoclonal antibodies (MCAs) can be used to differentiate between normal and neoplastic cells and thus exploited for diagnostic and, ultimately, therapeutic gain. The evidence for the existence of human tumour antigens is reviewed. Several areas of diagnosis are already benefiting from the application of the monoclonal technology. Immunohistology can help the pathologist with difficult diagnostic problems. New classifications of lymphoma and leukaemia can be based on specific surface molecules. Similarly, the detection of shed tumour antigens is already established as part of the routine assessment of many patients with common solid tumours. Isotopically labelled monoclonal antibodies have been used to localise primary and metastatic tumours. The use of antibodies in this way is not only a promising diagnostic tool but also the first step in studying the possibility of arming antibodies to provide therapeutic agents. Such trials are currently in progress.

Concentration of hematopoietic progenitor cells from human bone marrow by a new type of blood component separator

A new type of blood component separator (BCS) was used for the isolation of hematopoietic progenitor cells from human bone marrow aspirates. The BCS was filled with 100-150 ml bone marrow and centrifuged to prepare a buffy coat. This buffy coat was isolated in 10-15% of the original bone marrow volume and contained 64 +/- 8% of the nucleated cells (NC). Morphological examination revealed that the buffy coat was highly enriched for myeloblasts, promyelocytes, lymphocytes and monocytes, whereas the contamination with granulocytes was reduced to 46 +/- 8% of the granulocytes initially present in the bone marrow suspension. In addition the contamination with red blood cells (RBC) was very low; the buffy coat contained only 6 +/- 2% of the RBC. Furthermore it was demonstrated by means of colony assays that the buffy coat was highly enriched for hematopoietic progenitor cells. It contained 91 +/- 6% of the granulocyte/monocyte progenitor cells (CFU-GM) and 87 +/- 9% of the erythroid progenitor cells (BFU-E). These results are comparable to those obtained with continuous or semicontinuous blood cell processors. The advantages of the BCS is that it is a simple and inexpensive apparatus which fits in a normal blood bank centrifuge. It permits efficient preparation and isolation of a buffy coat from human bone marrow without substantial loss of hematopoietic progenitor cells.

Removal of tumour cells from bone marrow: an evaluation of the available techniques

Autologous bone marrow transplantation has offered a way of increasing the dose of drugs and radiotherapy which can be used to treat patients with malignant disease in an attempt to eradicate tumour. Bone marrow is taken prior to treatment and returned to the patient to 'rescue' haemopoietic function after ablative therapy is completed. Bone marrow removed for autograft may be contaminated with tumour cells at the time of harvest, and it is undesirable to return these to patients even though there are little data available concerning the number of tumour cells necessary to reseed various malignancies. This review considers the various methods available for removing tumour cells from bone marrow destined for autologous transplantation, and evaluates their advantages and disadvantages.

Detection of micrometastases in patients with primary breast cancer

An immunocytochemical method was used to screen smears obtained at primary surgery from multiple bone-marrow sites in 110 patients with breast cancer; at this time other techniques did not reveal metastases. Tumour cells were detected in the bone-marrow of 31 (28%) patients. The number of cells detected ranged from 1 to greater than 500; none was detected in conventionally stained smears. Patients in whom conventional criteria indicated a very poor prognosis seemed more likely to have such micrometastases. A further follow-up period is required to determine whether patients with micrometastases relapse earlier than those in whom no tumour cells are demonstrable.