How efficient is immunological surveillance against cancer and why does it fail?

Thyroid cancer and the immune system: a model for effective immune surveillance

Differentiated thyroid cancers, including papillary and follicular variants, are a useful model with which to examine interactions between cancer and the immune system. Differentiated thyroid cancers are detected in only 20,000 individuals annually in the USA, but thyroid microcarcinomas (< 1 cm in diameter) are far more common. This suggests that the immune system might restrain the growth of these microcarcinomas. On the clinical level, patients with lymphocytes that infiltrate into papillary thyroid cancer have improved survival, supporting the notion that immune system activation might improve this. Together, these observations suggest that the growth and distant spread of thyroid carcinoma are suppressed by mechanisms of immune surveillance, possibly involving lymphocytes, macrophages and their secreted products. In this review, we examine the general hypothesis of immune surveillance and the data pertaining to the roles of lymphocytes, dendritic cells and cytokines in the immune response against thyroid cancers.

Health risks associated with inhaled nasal toxicants

Health risks of inhaled nasal toxicants were reviewed with emphasis on chemically induced nasal lesions in humans, sensory irritation, olfactory and trigeminal nerve toxicity, nasal immunopathology and carcinogenesis, nasal responses to chemical mixtures, in vitro models, and nasal dosimetry- and metabolism-based extrapolation of nasal data in animals to humans. Conspicuous findings in humans are the effects of outdoor air pollution on the nasal mucosa, and tobacco smoking as a risk factor for sinonasal squamous cell carcinoma. Objective methods in humans to discriminate between sensory irritation and olfactory stimulation and between adaptation and habituation have been introduced successfully, providing more relevant information than sensory irritation studies in animals. Against the background of chemoperception as a dominant window of the brain on the outside world, nasal neurotoxicology is rapidly developing, focusing on olfactory and trigeminal nerve toxicity. Better insight in the processes underlying neurogenic inflammation may increase our knowledge of the causes of the various chemical sensitivity syndromes. Nasal immunotoxicology is extremely complex, which is mainly due to the pivotal role of nasal lymphoid tissue in the defense of the middle ear, eye, and oral cavity against antigenic substances, and the important function of the nasal passages in brain drainage in rats. The crucial role of tissue damage and reactive epithelial hyperproliferation in nasal carcinogenesis has become overwhelmingly clear as demonstrated by the recently developed biologically based model for predicting formaldehyde nasal cancer risk in humans. The evidence of carcinogenicity of inhaled complex mixtures in experimental animals is very limited, while there is ample evidence that occupational exposure to mixtures such as wood, leather, or textile dust or chromium- and nickel-containing materials is associated with increased risk of nasal cancer. It is remarkable that these mixtures are aerosols, suggesting that their "particulate nature" may be a major factor in their potential to induce nasal cancer. Studies in rats have been conducted with defined mixtures of nasal irritants such as aldehydes, using a model for competitive agonism to predict the outcome of such mixed exposures. When exposure levels in a mixture of nasal cytotoxicants were equal to or below the "No-Observed-Adverse-Effect-Levels" (NOAELs) of the individual chemicals, neither additivity nor potentiation was found, indicating that the NOAEL of the "most risky chemical" in the mixture would also be the NOAEL of the mixture. In vitro models are increasingly being used to study mechanisms of nasal toxicity. However, considering the complexity of the nasal cavity and the many factors that contribute to nasal toxicity, it is unlikely that in vitro experiments ever will be substitutes for in vivo inhalation studies. It is widely recognized that a strategic approach should be available for the interpretation of nasal effects in experimental animals with regard to potential human health risk. Mapping of nasal lesions combined with airflow-driven dosimetry and knowledge about local metabolism is a solid basis for extrapolation of animal data to humans. However, more research is needed to better understand factors that determine the susceptibility of human and animal tissues to nasal toxicants, in particular nasal carcinogens.

Restoration of the hamster tracheal wall following injury by electrocoagulation

The trachea of Syrian golden hamsters was injured by electrocoagulation. The lesions induced as well as the repair process were studied by light and scanning electron microscopy. The changes observed were considered to create the proper conditions for studying the significance of severe focal damage to the respiratory tract for the formation of tumors at the site of injury. Electrocoagulation caused deep crater-like injuries measuring 2 to 3 mm in diameter. Not only the mucosa, but also the submucosal tissues and cartilage rings were damaged. The repair process of the epithelium followed the pattern of covering the defect by squamous epithelium, hyperplasia, and stratified squamous metaplasia and finally differentiation into normal tracheal epithelium. The recovery of the epithelium was strikingly slow; even after a recovery period of 10 weeks regeneration of the epithelium was still incomplete in some animals. This relatively slow process of repair was ascribed to the depth and severity of the injuries involving a large mass of damaged tissues other than epithelium. Regeneration of the cartilage rings comprised three processes, viz removal of necrotic cartilage, growth of fibroblasts into the necrotic cartilage, and deposition of new cartilage along the necrotic rings.

Overview of some aspects of quantitative risk assessment

Use of animal data to estimate the human risk from long-term exposure to low doses of environmental carcinogens poses a number of biological, toxicological, and statistical problems. One of the problems is that of extrapolating animal dose-response relations from the high-dose range, where animal test data are available, to the low doses that humans might encounter. Different mathematical models for extrapolation are summarized, and the procedures for an problems of estimating human risk on the basis of animal studies are evaluated.

Clinical studies on cell-mediated immunity in patients with malignant disease. I. Effect of immunotherapy with OK-432 on lymphocyte subpopulation and phytomitogen responsiveness in vitro

Immunotherapy with daily intradermal injections of OK-432, penicillin- and heat-treated lyophilized powder of Su-strain of streptococcus pyogens A3, for over a period of four weeks resulted in quantitative and qualitative effectiveness on impaired cell-mediated immunity even in many patients with far advanced cancer of the stomach or lung. In vitro lymphocyte studies following immunotherapy with OK-432 demonstrated restoration of circulating lymphocyte counts to more than 1,500/microliters, a level associated with normalized subpopulation constitution and increases of phytomitogen blastogenesis. Furthermore, a delayed hypersensitivity skin reaction to PPD was boosted or converted into a positive reaction in some cases. There was, however, no detectable, definite effect on humoral immunity after the therapy. Survival rates at three and six months after the initiation of immunochemotherapy using OK-432 and another chemotherapeutic agent, 5-fluorouracil, in 40 patients with cancer were significantly longer than those of matched control patients given chemotherapy alone.

Non-linear pharmacokinetic parameters need to be considered in high dose/low dose extrapolation

It is impossible to prove that any chemical, natural or man-made, cannot cause cancer in man. However, it is possible to estimate the relative degrees of risk associated with various agents. The precision of these estimations increases as experimental procedures elucidate the basic type of mechanism associated with carcinogenesis, the role of absorption, metabolism and distribution, and excretion in increasing or decreasing activity, and the dose dependency of metabolic pathways. We must constantly strive to make the most accurate risk estimations possible so that the complex issues of risk/benefit may be properly considered.

Microsomal aspects of carcinogenesis and neoplasia

Neither immunologic nor genetic concepts of carcinogenesis have yet been decisively confirmed, and epigenetic theories, as formulated so far, are either non-predictive or insufficiently consistent with morphologic and experimental evidence. Computing data, concerned with carcinogenic mechanisms and neoplastic changes at the level of the endoplasmic reticulum, may lead to a new coherent understanding of tumor pathogenesis. Carcinogenic agents initiate biophysical perturbations, chemical alterations and conformational transitions in the membrane lattice of the endoplasmic reticulum. Foremost among the resulting neoplastic changes is an increased, irreversible separation of polyribosomes from membranes of the ergastoplasm. The carcinogenic process, apparently, deletes a protein required for polysome attachment. Since microsomal cytochromes can be synthesized by membrane-bound polysomes only, the translation of genetic information for their biosynthesis is irreversibly restricted. A similar, self-perpetuating deficiency may be postulated for the polysome attachment protein. Activities, depending on cytochromes P-450 and b5, are hampered, e.g. those of the monoxygenase system. Cholesterogenesis is derepressed. Ratios of phospholipids/cholesterol are decreased, and lipid-protein complexes, altered both in structure and function. Another distinct effect of the membrane-polysome separation is the unmasking of thiol-disulfide exchange enzymes which, in turn, stimulate the biosyntehsis of proteins and of deoxyribonucleotides involved in cell replication.

Premorbid psychological factors as related to cancer incidence

In planning for studies relating psychological factors and/or stress (PF&/oS) to cancer, one should be aware of epidemiological findings that might contribute to or even account wholly for any found relationships. Most studies have not examined the known biological causes of cancer, nor have they described a rationale for relationships sought. The two broad mechanisms leading to cancer, carcinogens and lowered resistance to it, include physical and chemical causes, viruses and chronic infection, medication, genetic predisposition, hormonal stimuli, and aging. Interfering variables may bias or dilute a real relationship. Validity and reliability of instruments measuring PF&/oS are so variable as to warrant considerable care in their use. The latent periods of different cancers are measured in years, not months, with consequent potent impact on possible inferences drawn from prebiopsy and short prospective studies. In these and in retrospective studies, cancer can have strong and biasing effects on apparently straightforward PF&/oS measurements, as can iatrogenic effects. Some theoretical issues are discussed. The known prospective studies are discussed and reasons are given for the view that they are less convincing then many seem to think. A sketch of a model relating PF&/oS to cancer appearance is outlined, with some theoretical implications, and issues in research design are addressed.

Non-organ specific autoantibodies in malignant diseases

A significant increase in non-organ specific autoantibodies is demonstrated in13 per cent of the sera from 202 patients with histologically proven malignancies, as compared with only 4 per cent of sera from 214 age and sex matched control patients. It appears that the incidence of autoantibodies is related to the histological type of the tumour but not to the presence or absence of tumour dissenmination. While the control group shows the expected increase in both incidence and titre of autoantibodies with increasing age, the malignant patients show no such pattern i.e. in cancer patients autoantibodies occur with equal frequency and at similar titres regardless of age. The absence of an age related increase in incidence and titre of non organ specific autoantibodies does not appear to have been reported previously. Our findings lend support to the hypothesis that cancer is associated with a breakdown of immunological surveillance, not only in old but also in young cancer patients. Thus the findings of non organ specific autoantibodies, especially to smooth muscle antigen, in an apparently healthy adult could be considered evidence of such a breakdown, carrying with it an increased risk of neoplasia.

Morphological observations of immunobiology of laryngeal cancer. Evaluation of the defensive activity of immunocompetent cells present in tumour stroma

A series of 104 patients with squamous cell carcinoma of the larynx was studied with regard to tumour-host interaction. Prognostic evaluation was based upon histologic grading and morphological evidence of host immune response, judged by the presence and degree of lymphocyte and plasma cell infiltration in tumour stroma. Histologic grade and lymphoplasma-cellular infiltration do correlate with the 5-year survival. The immune response, however, seems to be a favourable prognostic sign only for well differentiated tumours; in our series, all poorly differentiated neoplasms showed minimal or no cellular response. The survival rate increases with the increasing intensity of cellular response within each class of tumour cell differentiation. Small lymphocytes are the basic elements of cell-mediated immune response. After tumour antigenic stimulation they change into immunoblasts which in turn would produce "committed" lymphocytes which would recognize and destroy tumour cells.