Tumor-reactive Antibodies Research Articles

Increasing tumour immunogenicity by genetic modification

INTRODUCTION IT IS GENERALLY believed that tumour growth in most cases results from: (1) the accumulation of mutations in genes which alter cell differentiation and proliferation (e.g. oncogenes, tumour suppressor genes); and (2) the failure of the immune system to recognise and/or destroy those cells which are behaving abnormally. Although a large number of mutant cellular genes have been identified in tumour cells, it is apparently unpredictable when they occur and to detect them at early stages of tumour growth. Therefore, it is understandable that much interest has focused on developing new strategies in order to activate the host’s immune system against tumours. This concept has a long history and has been characterised by Oettgen and Old [l] as ‘a field that has gone through recurring cycles of enthusiasm and disillusionment’. In other words, none of the many approaches of cancer immunotherapy has fubilled the hopes raised by welldefined experimental animal systems once they were employed in patients. The subject is still highly relevant, however. Firstly, traditional forms of cancer therapy, such as surgery, radiation therapy and chemotherapy, although effective in many instances, often fail to provide long-term cure for cancer. Secondly, significant knowledge of regulation of immune responses and the mode of antigen presentation to T-cells allows the development of new strategies. Furthermore, many investigators involved in clinical trials report on individual but isolated cases of complete tumour regression, which appear to correlate with some form of immune intervention. However, the reasons for occasional tumour regression remain obscure. Broadly speaking, specific and non-specific strategies of cancer immunotherapy can be distinguished. The former mainly involved agents such as ‘Coleys toxin’ or adjuvants such as Bacillus Camette-Guerin (BCG) and Corynebacterium puruum. A large number of clinical trials have been carried out (reviewed in [l]), and they are mentioned here only because, at least in one clinical situation, significant therapeutic effects have been obtained in randomised trials. This was achieved by intravesical BCG instillation in superficial bladder cancer patients [2], although the underlying mechanism is not known. Specific cancer immunotherapy strategies can rely on tumour-reactive antibodies, adoptive transfer of immune cells (mainly LAK cells or T lymphocytes), tumour cells (modified or non-modified; autologous or allogeneic) as vaccines or tumour-specific antigens (peptides) as vaccines. The term vaccine usually refers to a therapeutic rather than a prophylactic modality. All approaches

The toxicity of chemically deglycosylated ricin A-chain in mice

Tumor-reactive antibodies coupled to ricin or its A-chain (immunotoxins) have been used in rodents and humans to treat a variety of neoplastic diseases. Side-effects of such treatment include hepatotoxicity, vascular leak syndrome, myalgia and low grade fever. At high doses, severe toxicities include liver damage, pulmonary edema, aphasia, rhabdomyolysis and kidney failure. There have been a limited number of toxicologic studies on uncoupled ricin or its A-chain and none on deglycosylated A-chain. Since the latter has been utilized in “second generation” immunotoxins, the current studies were carried out to evaluate the toxicities induced by deglycosylated ricin A-chain (dgA) in mice. The administration of dgA to normal BALB/c mice causes early (24 h) weight loss and late (10 day) accumumulation of ascites. These effects could be partially altered by changing the route of injection of dgA from i.v. to i.p. Thus, i.p. administration caused weight loss but not ascites, whereas i.v. administration caused both. Weight loss was associated with reduced fluid intake by the treated mice, and was not associated with increased levels of serum TNF-α. SCID mice injected with the same dose of dgA as normal BALB/c mice developed ascites, but it was of lesser severity, suggesting that a functional immune system, differences in microbial flora, or strain differences may be involved in the development of ascites.

Scanning tunneling microscopy imaging of the tumour associated antigenic 20 amino acid human polymorphic epithelial mucin core peptide fragment

Human polymorphic epithelial mucins (PEM) are high molecular weight glycoproteins that are associated with breast cancer. Recent structural studies have identified that the protein core of PEM contains a 20 amino acid tandem repeat that has elements of secondary structure which coincide with the epitopes for a number of tumour reactive antibodies. In our continuing structural studies we have now investigated the use of the scanning tunneling microscope (STM) to directly image the conformation of the twenty amino acid PEM core peptide. High resolution STM images reveal that the peptide has an overall topography similar to that predicted by molecular modelling. The images identify directly that the free peptide is conformationally non-restricted and can adopt a number of discrete conformations in the solid state.

Selective killing of leukaemia cells by antibody-toxin conjugates: implications for autologous bone marrow transplantation.

The recent development of tumour-reactive monoclonal antibodies has stimulated interest in their use in targeting toxic agents to tumour cells. One such approach involves the covalent coupling of tumour-reactive antibodies to the toxic peptide of the plant toxin, ricin. Such conjugates are highly effective in killing various tumour cells in vitro1–6. Here we have used the murine B-cell tumour, BCL1, in an adoptive transfer system capable of detecting 1–10 tumour cells, to demonstrate the effectiveness and specificity of an anti-immunoglobulin(Ig)–ricin A chain conjugate in deleting tumour cells from infiltrated murine bone marrow. We report that the transferred cells were able to repopulate the haematopoietic system of lethally irradiated mice and that in most mice the tumour did not recur. We discuss the implications of this approach for autologous bone marrow transplantation following supralethal tumour therapy.

Tumor directed antibody and carcinoembryonic antigen in the glomeruli of a patient with gastric carcinoma

A patient dying of gastric carcinoma was one of a group of cancer patients examined for the presence of glomerular immune complex deposits not associated with the nephrotic syndrome. The deposits were distributed in the mesangial and subendothelial regions. This distribution is found in experimental animals with neoplasia and glomerulopathy as well as in over 30 per cent of humans with cancer. Immunofluorescence showed IgG and C3 in the patient's glomeruli. Carcinoembryonic antigen was identified in the patient's glomeruli by the immunoperoxidase staining method. An IgG antibody was eluted from the kidney and found to be reactive with the patient's tumor, as well as another patient's colonic carcinoma. This reactivity was blocked by preincubation of the tumor substrate with anticarciboembryonic antigen. Thus, both a tumor associated antigen and a corresponding antibody were shown to be contained in the glomerular deposits. It is concluded that circulating immune complexes of high molecular weight containing carcinoembryonic antigen produced by the gastric carcinoma led to the formation of subendothelial deposits without significant renal damage. This is in contrast to the usual finding of membranous glomerulonephritis among cancer patients with the nephrotic syndrome and more closely resembles the animal models. Whereas tumor reactive antibodies can be found in the glomeruli of patients with cancer, a specific tumor associated antigen to which the antibody is reactive has only occasionally been demonstrated.

Naturally occurring cytotoxic tumour reactive antibodies directed against type C viral envelope antigens

TYPE C RNA viruses are frequently present in murine tumours, but the nature of the association between these viruses and malignancy is uncertain. The oncogene theory1,2 contends that type C viruses possess oncogenic information and that malignancy is the result of activation of this genetic information. Alternatively, the expression of type C viruses in a tumour may be a consequence, rather than a cause, of the neoplastic change and may be beneficial to the host by providing for potential immunological detection and eradication of neoplastic cells3. If type C viral antigens are targets for an immune surveillance mechanism, then normal animals would be expected to show evidence of immune sensitisation against viral antigens expressed on the surface of tumour cells. Here, we present evidence that naturally occurring antibodies (NOA) cytotoxic for a type C virus releasing teratoma-derived cell line are directed against viral antigens.

Anti-tumour antibodies in normal mouse sera.

Evidence for the involvement of the immune system in surveillance against nascent tumors was sought by testing whether normal mouse sera were cytotoxic in the presence of rabbit complement for a variety of lymphoid and non-lymphoid tumor-cell lines. Tumour-reactive antibodies were detected in all mouse sera tested, including sera from congenitally athymic (nude) mice. Considerable variation was noted, however, in the levels of naturally occurring antibodies against specific tumor antibodies were identified as being predominantly IgM. The possible relevance of natural anti-tumor antibodies to immune surveilance was discussed.