Effects of recombinant interferon-gamma and interleukin-2 on the generation of lymphokine-activated killer cells in vitro

Proliferation of IL-2 activated lymphocytes preferably occurs in aggregates by cells expressing the CD57 antigen

Aggregates of lymphocytes were investigated in long-term cultures of IL-2 stimulated peripheral blood mononuclear cells. Cells in clusters formed broad contact areas where coated pits and vesicles were often detectable. Proliferating cells were preferably found in aggregates indicating that the cell clusters represent proliferation centres in which cell division may be promoted by accessory signal transduction mediated by the close cell-to-cell contact. In bulk cultures CD57+ cells yielded increased proliferation capacity compared to CD57- cells. In addition, CD57+ cells were preferably localized in aggregates where they occupied the same position at the periphery of the clusters than the proliferating cells, suggesting that both cell types may be identical. It is discussed that the CD57 antigen represents a differentiation marker which is upregulated when CD57- cells start to proliferate assisted in cell aggregates.

Development of four donor-specific phenotypes in human long-term lymphokine-activated killer cell cultures

A series of 62 lymphokine-activated killer cell (LAK) cultures from 44 different donors was investigated for the distribution of various CD markers during a cultivation period of 3 weeks. Great differences in the phenotypic pattern were found between different donors, but similar changes of the subset pattern of various donors allowed a classification of the LAK cultures into four distinct LAK types. LAK type 1 was characterised by low numbers of CD3+ cells and high values for CD56+ cells. In LAK type 2 cultures gamma/delta TCR+ cells extensively proliferated, whereas in LAK type 3 cultures the CD57 and CD8 values increased considerably. LAK type 4 cultures did not show any of these characteristics. The resulting phenotype of a LAK culture was donor-specific, as LAK cultures established from the same peripheral blood mononuclear cells (PBMC), fresh or after cryopreservation, or from PBMC obtained from the same donor at different venous punctures, always developed the same phenotype. A clear correlation between phenotype and killing activity could only be found for LAK type 1 cultures, which always developed high lytic activity. Long-term IL-2 stimulation induced high levels of perforin-positive cells in LAK cultures but the perforin content did not correlate with the cytotoxicity. The transcription pattern for various cytokines only varied slightly between the cultures. Messenger RNA for granulocyte/macrophage- colony-stimulating factor, interferon gamma, tumour necrosis factor alpha, interleukin-4 (IL-4) and IL-5 were found in almost all cultures during the entire cultivation period, whereas mRNA for IL-2 was never detected. Most variations in the transcription pattern were observed for IL-6 and IL-7. However, no correlation could be found between the endogenous cytokine production and the phenotype or lytic activity of the LAK cultures. Further studies are required to determine the factors that cause lymphocyte subsets from a specific donor to proliferate preferentially under long-term IL-2 stimulation.

On the mode of action of intravesical bacillus Calmette-Guérin: in vitro characterization of BCG-activated killer cells

Previously we had shown that, upon activation with viable bacillus Calmette-Guérin (BCG), peripheral blood mononuclear cells (PBMNC) could be rendered cytotoxic against otherwise insensitive natural killer (NK)-resistant bladder cancer cell lines. This phenomenon had been termed the BCG-activated killer (BAK) cell phenomenon. By means of depletion and enrichment procedures of mononuclear cell subpopulations derived from BCG-activated PBMNC we further characterized the cytolytic BAK effector cells functionally in an in vitro cytotoxicity assay against the bladder carcinoma cell line BT-A and phenotypically in their pathway of activation. Neither macrophages nor CD4+ T-helper/inducer cells exerted cytotoxic BAK activity. This cytotoxicity was restricted to the CD8+CD56+ subpopulation of T-cytotoxic/NK cells. Furthermore, activation of BAK cells via interferon gamma (IFN-gamma) was evidenced by the complete inhibition of BAK cell generation with an IFN-gamma antibody.

Induction of bacillus-Calmette-Guérin-activated killer cells from human peripheral blood mononuclear cells against human bladder carcinoma cell lines in vitro

Cytotoxicity against two human bladder carcinoma cell lines (BT-A and BT-B) was investigated using human peripheral blood mononuclear cells (PBMC) stimulated with viable bacillus Calmette-Guérin (BCG) or sonicated BCG (s-BCG). We applied a cytotoxicity assay based on radioactive labelling of tumour cells by incorporation of L[3H]methionine. The results were compared with the cytotoxicity exerted by lymphokine-activated killer (LAK) cells generated by interleukin-2 (IL-2) and interferon gamma (IFN gamma). BCG-stimulated PBMC showed a cytotoxic potential against BT-A and BT-B comparable to that of IFN gamma-generated LAK cells, but this did not reach the level of IL-2-generated LAK cells. We termed these cytotoxic effectors BCG-activated killer (BAK) cells. In contrast to their cytotoxicity against bladder tumour cells, BAK cells did not differ from unstimulated PBMC in the killing of K562 cells. Only viable but not sonicated BCG was able to induce cytotoxicity against BT-A and BT-B. We could demonstrate the presence of the cytokines IFN gamma, IL-2, tumour necrosis factor alpha (TNF alpha) and TNF beta in the supernatants harvested during the generation of BAK cells. Monoclonal antibodies neutralizing IFN gamma were able to inhibit BCG-mediated cytotoxicity, giving evidence of the involvement of IFN gamma in the induction of BAK cells. Furthermore, we performed experiments to investigate the cytotoxic potential of distinct cell populations. The cells effective in BCG-activated killing of bladder tumour cells could be localized within the CD8+/CD56+ lymphocyte subset. CD4+ cells and macrophages did not exhibit cytolytic activity. Our findings imply that the activation by BCG of CD8+/CD56+ killer cells might be an important antitumoral mechanism during BCG therapy against superficial urothelial bladder cancer.