Tumorigenicity and the expression of cell-surface carbohydrates

Intratumor immunologic heterogeneity

Tumor cells express a great variety of antigens including tumor specific transplantation antigens, tumor-associated antigens, differentiation antigens, histocompatibility antigens, lectin-binding sites and receptors for natural killer cells and natural antibodies. These antigens are distributed unevenly on tumor subpopulations and each subpopulation may induce different immune responses to the same determinant. Intratumor immunologic heterogeneity arises early in cancer, possibly during preneoplasia, and exists throughout the course of progression. Metastatic subpopulations are not generally less antigenic than subpopulations within primary tumors. Different arrays of antigenic determinants are displayed by subpopulations but variability in cell surface expression of a single determinant is also a fundamental type of immunologic heterogeneity. Antigenic specificity patterns commonly reveal one-way cross-reactions between tumor subpopulations. One-way cross-reactions might occur due to quantitative differences, cell-cycle variations, modulation, masking, H-2 expression and restriction phenomena, or alteration in the carbohydrate side-chains of glycoproteins. Interactions which occur when subpopulations co-exist may alter immune responses so that the response to the mixture is not the sum of the responses to the individual subpopulations. It is suggested that the exploitation of the mechanisms involved in immunologic heterogeneity may lead to new therapeutic approaches and that the great diversity of determinants expressed by tumor cells could lead to development of multivalent panel of monoclonal antisera which, acting synergistically, could preferentially lyse tumor cells.

The reversal immune surveillance hypothesis

The proposed reveral immune surveillance hypothesis is based on the identification primarily of self and secondarily of foreignness, unlike the original hypothesis that is based on the identification of foreignness per se. The proposed system is considered to have evolved from the invertebrates through to the vertebrates to become more complex in the mammals, and involves the identification of cell types by lymphocytes through the cell type surface pattern and major histocompatibility antigens. The identification of self and associated foreignness by the immune system is required for the regulation of cell differentiation and replication, and because of this design, the ability of the immune system to destroy foreignness can be regarded as a natural consequence. The reversal immune surveillance hypothesis explains why spontaneously occurring tumours may not be antigenic, in the sense of eliciting their own destruction, and is consistent with the destruction of tumour cells that display significant amounts of viral antigens or gross antigenic changes induced by carcinogenic agents. It is also able to explain the stimulation and inhibition of tumour development.

Isolation of high-rate DNA synthetic cells by con A chromatography

The separation of L1210 cells with columns of Con A-derivatized nylon was investigated. Most of the cells bound to the column irreversibly. The binding was lectin-specific. Cells were pulse labeled with 3H-thymidine and applied to Con A columns. Those cells not binding the columns were enriched in incorporated thymidine compared to the unseparated population. Data is presented which suggests that a small, synchronized fraction of cells synthesizing DNA at a high rate is reduced in Con A-nylon affinity. It is proposed that L1210 cell DNA synthesis is not uniform in rate and that changes in this rate are related to changes in the ability of cells to bind Con A-nylon.