Tumor viruses, oncogenes, and human cancer

The senile epidermis: environmental influences on skin ageing and cutaneous carcinogenesis

There is a wealth of new knowledge regarding mechanisms of carcinogenesis and their interaction with senescence and environmental insults, particularly on the effects of UV irradiation on the skin. Innovations and advances in tissue culture techniques now permit in vitro studies of keratinocytes and other benign and malignant skin-derived cells. The ageing processes and cutaneous neoplasia, therefore, can now be studied at the cellular level. New insights regarding the interrelationship of ageing, environment and cutaneous neoplasia are close at hand. Depletion in the number of Langerhans cells and suppression of their function in ageing and UV-exposed skin may allow tumour cells to overcome the host's defence system. The potential increase in UV irradiation due to depletion of the ozone layer may increase the incidence of skin tumours. Carcinogenesis involves three distinct steps: initiation, promotion, and malignant conversion. The mechanism has been studied in mice, where it is suggested the c-ras oncogene may play an important role.

Lymphoma-specific T- and B-cell responses suggest the involvement of HTLV-I in virus-non-productive lymphomas of a married couple

In a married couple, a T-cell and a B-cell lymphoma occurred at the same time in the husband (FR) and wife (FE), respectively. Serum antibodies of patient FE with less advanced tumor progression specifically recognized HTLV-I-related envelope precursor molecules of 66-68 kDa molecular mass on HTLV-I-infected T- and B-cell lines, but not on HTLV-II or HIV-infected cells. In addition, in vivo-activated CD8+ T-cell lines (TCL) from this patient specifically lysed autologous B-lymphoma cells, T-lymphoma cells from the husband (FR), as well as the HTLV-I-transformed MT2 T-cell line. All positive target cells shared an HLA-class-I cross-reactive determinant identified by the alloantiserum WER127. On a clonal level, the specificity of the cytotoxic T-cell response was unequivocally distinguishable from classical natural-killer-like cytotoxicity. Results imply the involvement of a common inductive agent in the manifestation of malignant lymphoma in both patients (FR and FE). Since antibodies from cases with classical HTLV-I-induced adult T-cell leukemias (ATLL) did not bind antigens on cells of either lymphoma (FR or FE) and active virus production was not demonstrable under various different conditions, these results argue against HTLV-1 itself being the transforming agent. However, humoral and cellular immune responses of one patient (FE), in addition to de novo HLA-class-1 antigen expression of both patients, are nonetheless consistent with the involvement of viral infections(s). These were responsble for the expression of HTLV-1-characteristic envelope determinants of the malignant progeny of respective T- and B-cell origin.

Cutaneous chemical carcinogenesis

This review is designed to inform the clinician of current concepts regarding the pathogenesis of chemically induced skin cancer. Chemicals induce cutaneous cancers in a wide variety of experimental animals and in humans. The most common benign experimental tumors are papillomas and keratoacanthomas, whereas common malignancies are squamous cell carcinomas and melanomas. Carcinoma development is a multistage process that involves at least three mechanistically distinct steps. Initiation is the earliest change in an epidermal cell exposed to carcinogens such as polycyclic aromatic hydrocarbons, alkylating agents, or nitrosamines. This stage appears to result from carcinogen-induced deoxyribonucleic acid damage leading to a mutation-like genetic change. Only a limited number of epidermal genes may be changed to yield the initiated cell, and one has been identified as the Harvey ras gene, a gene involved in epidermal proliferation. Initiated epidermal cells are not malignant but are insensitive to the normal signals for terminal differentiation in the epidermis. The second stage, tumor promotion, results from repeated exposure of initiated skin to one of a variety of noncarcinogenic promoting agents such as phorbol esters, benzoyl peroxide, anthralin, or certain halogenated aromatic hydrocarbons. Some promoters require specific cellular receptors and produce transient changes in the growth or differentiation of the epidermis. Collectively these agents produce a tissue environment that is conducive to the selective clonal outgrowth of the initiated cell population, resulting in a clinically apparent premalignant tumor. During the third stage of carcinogenesis, premalignant cells are converted to malignancy. This step may occur spontaneously, but the frequency is greatly enhanced by exposure to mutagens, including several initiating agents. Thus malignant conversion is likely due to additional mutations in a benign tumor cell. The Harvey ras gene may also be a potential target in the conversion step. Several agents, such as corticosteroids and retinoids, have been identified as anticarcinogens for skin. They appear to be primarily antipromoting agents and could important clinical applications. Melanomas can be induced in several species by repeated exposure to initiators or by exposure to an initiator and a tumor promoter. the experimental pathogenesis of this tumor is unclear. It is proposed that intermediates in the synthesis of melanin pigment could act as endogenous carcinogens or promoters in melanoma development. Increased awareness of the mechanisms of chemical carcinogenesis in skin will enhance cancer prevention in this tissue. Furthermore, astute

Monoclonal antibodies and cutaneous T cell lymphoma. Theoretical and practical considerations

The T cell nature of mycosis fungoides and Sézary syndrome was established a decade ago. The recent advent of monoclonal antibodies to T cells and other lymphoid subpopulations has resulted in an explosion of knowledge on the biology of this group of disorders. These reagents have increased our knowledge on thymic differentiation status, pathogenesis, the phenotype of premalignant vs malignant lymphocytic infiltrates, the identification of other previously unrecognized cells within lymphomas, and the phenotype of circulating vs skin lymphocytes. Therapeutic applications may result. These new developments are discussed.