Publisher Summary Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Biology of natural killer cells.

Publisher Summary The recognition of the existence of natural cell-mediated immunity, particularly natural cell-mediated cytotoxicity, has significantly altered the concepts concerning the potential mechanisms for in vivo resistance against tumor growth and for in vitro cell-mediated immune reactions. When cytotoxic reactions are measured, the evaluation of the role of natural killer (NK) cells and other more well-known mechanisms of cytotoxicity must be done carefully. This chapter focuses on natural cell-mediated cytotoxicity. It summarizes the known information on the expression of natural cytotoxicity in rodents and in man, its specificity, the nature of the effector cells and their relationship to other immune mechanisms, and the possible in vivo relevance of natural cytotoxicity, particularly in regard to resistance against tumor growth. The basic observation that initiated the studies of natural cell mediated cytotoxicity includes that lymphoid cells from some normal mice, rats, and human donors, which are not inoculated with tumor cells or other sources of antigen, exhibit significant levels of cytotoxic reactivity against certain syngeneic or allogeneic tumor cells.

Natural Cell-Mediated Immunity

Recent evidence, has demonstrated an association between a subpopulation of peripheral blood mononuclear cells, morphologically identified as large granular lymphocytes (LGL), and natural killer (NK) activity. We have now evaluated more directly the role of LGL in both NK activity and antibody- dependent cellular cytotoxicity (ADCC), by using highly enriched populations of LGL, obtained by centrifugation of peripheral blood mononuclear cells on Percoll discontinuous density gradients. Both spontaneous and interferon- augmented NK and ADCC activities were exclusively associated with the LGL- enriched, low density fractions. The majority of LGL formed conjugates with NK-susceptible and antibody-coated target cells. Approximately 20 percent of small conventional lymphocytes also formed conjugates with the target cells for NK, but this was not associated with cytotoxic activity. Virtually all LGL were found to have receptors for the Fc portion of IgG (FcγR). The frequency of LGL among blood leukocytes was 2-6 percent. LGL could be enriched to an average purity of 95 percent by combining discontinuous density gradient centrifugation with subsequent adsorptions of the low density fractions on monolayers of immobilized immune complexes. About 50 percent of LGL were found to be FcγR-bearing T cells (T(G)), forming low affinity rosettes with sheep erythrocytes at 4 degrees C. Only 10-20 percent of LGL formed high affinity rosettes with sheep erythrocytes at 29 degrees C. LGL could be enriched to a purity of more than 90 percent by depleting high affinity rosette-forming cells from low density Percoll fractions. LGL were only a subpopulation of T(G) cells, because some lymphocytes with conventional morphology also adhered to the immobilized immune complex monolayers and formed high affinity rosettes with sheep erythrocytes. Separation of these cells from LGL by discontinuous density gradient centrifugation indicated that they are not cytotoxic, suggesting a morphological and functional subdivision of T(G) cells. The verification in this study that virtually all human NK and K cells have a characteristic morphology adds a useful parameter to the monitoring of human lymphocytes, and the ability to purify these cells by simple physical procedures should be invaluable in their further characterization.

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Characteristics of human large granular lymphocytes and relationship to natural killer and K cells

On analysis ofin vitro assays of human natural killer (NK) cell function the inadequacy of commonly used methods of expressing lytic activity was apparent. A comparison was made of the data obtained using modifications of two equations—the simple exponential fit and the von Krogh equations. Both of these equations were found to satisfy the following essential criteria for use in these assays. First, the majority of the results obtained in the chromium-release assay could be used in data reduction; second, the resultant “dose-response” curve was reduced to linearity; and third, a single numerical expression was obtained which was directly proportional to the cytotoxic activity. Of the two methods the more conventional exponential fit was found to be the simpler to use. The closeness of fit of the experimentally derived data to the ideal curves did not support the possibility that normal lymphocyte preparations contain suppressor cells capable of inhibiting NK activity. Data have also been presented showing that NK-sensitive targets could be categorized with respect to their susceptibility by comparing the slopes of the target cell survival curves obtained using the exponential fit equation. These observations are relevant to the accurate assessment of NK activity in patient populations and to the determination of the effects of disease and its treatment on this activity.

Spontaneous human lymphocyte-mediated cytotoxicity against tumor target cells. IX. The quantitation of natural killer cell activity

In children, cancer probably arises from a combination of inherited genetic mutations and genetic alterations that are acquired during the rapid cellular expansion that occurs during embryogenesis, and it is rarely associated with immune cell infiltrates. Conversely, in adults, cancer is frequently preceded by a long period of subclinical inflammatory disease and micronecrosis that provides a setting in which the epigenetic regulation of genes, cell death, cell proliferation and mutagenesis occurs. Here, we provocatively suggest that adult cancer results from rounds of disordered and unscheduled necrotic cell death, subsequent epithelial proliferation and the resulting suppressed immunity, rather than from a process that is dictated solely by cell growth. This paradigm shift regarding the development of cancer and this 'sixth sense' of the immune system indicates new strategies for cancer prevention and therapy.

Inflammation and necrosis promote tumour growth

Inhibition of Leukocyte Migration by Tumor-Associated Antigens in Soluble Extracts of Human Breast Carcinoma

To elucidate the in vivo role of natural killer (NK) cells, the growth of several murine and human tumors was studied in four variants of athymic, nude mice with different levels of NK activity.

Beige-nude mice, homozygous for both the beige and the nude genes, had very low levels of NK activity, and their response to the B-cell mitogen, bacterial lipopolysaccharide, was lower than that of high-NK, adult NIH nude mice. Young and adult NIH nudes had different NK levels and showed different response in assays for K-cell, T-cell, and B-cell activity. The B-cell-defective NIH-II mice had slightly lower NK levels than adult NIH animals, but much lower response in the antibody-dependent cell-mediated cytotoxicity assay.

No correlation was found between host NK activity and the s.c. growth of various human (LOX, CEM, K562) and murine (YAC-1) tumor cells. Low NK activity was not associated with increased lung colony formation in a metastasis model using i.v.-injected human (LOX) and murine (B16F10) melanoma cells. No relationship was found between host NK activity and the rate of elimination of i.v.-injected 5-iodo-2′-deoxyuridine-labeled LOX, B16F10, and YAC-1 cells from lungs, liver, or spleen.

The results fail to support the view that NK cells exert significant direct effects on tumor cells in vivo .

https://cancerres.aacrjournals.org/content/canres/44/10/4403.full.pdf

Lack of Correlation between Natural Killer Activity and Tumor Growth Control in Nude Mice with Different Immune Defects

One hundred and seven patients with carcinoma of the lung underwent immunologic testing, and 62 of these patients were randomized to an immunotherapy protocol comparing the effects of Pasteur strain BCG, either alone or combined with allogeneic tumor cells, to the effects of no immunotherapy. Patients with residual disease left at the time of surgery or with metastatic disease at the time of diagnosis showed no increase in survival as a result of this form of immunotherapy. An insufficient number of patients with less advanced disease, in whom we would expect the most beneficial effect, have been entered in this study. In general, we were unable to document substantial effects of immunotherapy on the immunologic parameters tested. Only in recall antigen skin testing was there a statistically significant increase in reactivity in the immunotherapy groups. Tests of general immune status appeared to have a predictive value in monitoring lung cancer patients. Anergic patients had a poorer prognosis than did patients who demonstrated skin test reactivity. Patients with normal percentages of lymphocytes (T cells) forming rosettes with sheep erythrocytes at 29 degrees C were generally normal in other tests of immune competence. In serial studies of rosette formation, all patients who developed recurrent disease had a pattern of depressed or falling rosette values, and these abnormalities occurred an average of 3.1 months prior to clinical detection of recurrence. Patients with large-cell anaplastic carcinoma were found to have a significantly higher incidence of depressed rosette levels than the other histologic types. Both large and small-cell anaplastic patients had significantly depressed lymphocyte proliferation by mitogens and allogeneic cells. Although lung cancer patients have been described as immunologically depressed, they are capable of recognizing tumor-associated antigens. When tested in leukocyte migration inhibition assays with tumor-associated antigens, the majority of the patients in our study were found to be reactive. The use of a 3 M KCl extract of pleural effusion cells from a patient with pulmonary adenocarcinoma has given good reactivity and specificity in lung cancer patients of all histologic types. In addition, these patients have been shown to respond in a mixed lymphocyte/tumor interaction to tumor-associated antigens (Dean, 1976b).

Immunological monitoring and immunotherapy in carcinoma of the lung.

Methods are described by which cryopreserved cells can be utilized in a number of in vitro assays. On a per cell basis, nearly total recovery of function can be demonstrated for lymphocyte transformation (mitogens, antigens and MLC) and rosette-forming cells. Excellent recovery of mononuclear cell production of leukocyte migration inhibitory factor was also observed. Highly reproducible activity was recovered on a per lymphocyte basis in lymphocyte cytotoxicity but with a definite decrement in the percentage recovery. Both for longitudinal studies of immune function and for standardization of these assays in one or more laboratories such cryopreserved cells are ofimmense value and should be widely utilized.

G. B. Cannon

Papers

Inhibition of Leukocyte Migration by Tumor-Associated Antigens in Soluble Extracts of Human Breast Carcinoma

Lack of Correlation between Natural Killer Activity and Tumor Growth Control in Nude Mice with Different Immune Defects

Immunological monitoring and immunotherapy in carcinoma of the lung.

Cryopreservation of human lymphocyte function as measured by in vitro assays.

Cytostasis of tumor cell lines by human granulocytes.