Phorbol 12-myristate 13-acetate induces resistance of human melanoma cells to natural-killer- and lymphokine-activated-killer-mediated cytotoxicity

A parathyroid-hormone-related-protein (PTH-rP)-specific cytotoxic T cell response induced by in vitro stimulation of tumour-infiltrating lymphocytes derived from prostate cancer metastases, with epitope peptide-loaded autologous dendritic cells and low-dose IL-2

Bone metastases are one of the most common events in patients with prostate carcinoma. PTH-rP, a protein produced by prostate carcinoma and other epithelial cancers, is a key agent for the development of bone metastases. A PTH-rP-derived peptide, designated PTR-4 was identified, which is capable to bind HLA-A2.1 molecules and to generate PTH-rP-specific cytotoxic T cell (CTL) lines from healthy HLA-A2.1(+) individual peripheral-blood-mononuclear-cells (PBMC). In this model, we investigated the in vitro possibility of generating an efficient PTH-rP specific CTL response by cyclical stimulations with IL-2 and PTR-4 peptide-pulsed autologous dendritic cells (DC), of HLA-A2.1(+) tumour infiltrating lymphocytes (TIL) derived from a patient with metastatic prostate carcinoma. A T cell line generated in this way (called TM-PTR-4) had a CD3(+), CD5(+), CD4(-), CD8(+), CD45(Ro+), CD56(-) immunophenotype and a HLA-A2.1 restricted cytotoxic activity to PTR-4-peptide pulsed CIR-A2 (HLA-A2.1(+)) target cells, PTH-rP(+)/HLA-A2.1(+) CIR-A2 transfected with PTH-rP gene, prostate carcinoma LNCaP cells, and autologous metastatic prostate cancer cells (M-CaP). These lymphocytes were not cytotoxic to HLA-A2.1(+) targets not producing PTH-rP, such as peptide-unpulsed CIR-A2 and colon carcinoma SW-1463, cell lines. Our results provide evidence that PTR-4 peptide-pulsed autologous DC may break the tolerance of human TIL against the autologous tumour by inducing a PTH-rP-specific CTL immune reaction. In conclusion PTR-4 peptide-pulsed autologous DC may be a promising approach for vaccine-therapy and antigen-specific CTL adoptive immunotherapy of hormone-resistant prostrate cancer.

Culture medium induced morphological changes of melanoma cells associated with change in sensitivity to lysis by lymphokine-activated killer cells

Three sublines (Clones 1, 2 and 7) of the human melanoma CaCL 73-36 cell line with different cellular morphology, growth patterns, melanin content and surface antigenic profile were maintained in RPMI-1640 medium plus 10% fetal bovine serum (abbreviated as RPMI). Each subline was divided into two groups: one grown in RPMI and the other in Dulbecco's modified Eagle's medium plus 10% fetal bovine serum (abbreviated as DMEM) for 96 h. Phenotypically, Clone 2 expressed Class I and II MHC and ICAM-1 on the surface and in the cytoplasm, while Clones 1 and 7 failed to express these antigens in both the cytoplasm and on the cell surface. Melanotic Clones 1 and 7 cells became even more pigmented, had slower growth rates, and exhibited lower saturation densities when incubated in DMEM than when they were incubated in RPMI. On the other hand, Clone 2 cells maintained in RPMI were grossly amelanotic, contained defective-like melanosomes detected ultrastructurally, and had distinct clusters of microvilli polarly located in most of the cells. Such specialized ultrastructures were not affected by medium conditions. Analysis of sensitivity of the clonal sublines to cytolysis by allogeneic effector cells revealed that in spite of low levels of natural killer (NK) cytotoxicity noted, DMEM produced a 2- to 14-fold increase in sensitivity to NK cells, irrespective of which medium was used. Different levels of lymphokine-activated killer (LAK) cytolytic activity were clearly observed in sublines maintained in RPMI, with Clone 2 being the most sensitive and both Clones 1 and 7 being less sensitive. Cells grown in DMEM exhibited significantly higher levels of sensitivity to LAK cytolysis than cells grown in RPMI as revealed by their differences in lytic units (p < 0.05). This was likely due to the high levels of surface ICAM-1 expression in cells incubated in DMEM vs little expression of this adhesion molecule by cells grown in RPMI. Taken together, these results demonstrate the presence of heterogeneous subpopulations within the CaCL 73-36 melanoma cell line regarding their pigmentary status, antigenic profile, growth pattern and responsiveness to NK/LAK cytolysis. The results also call attention to the importance of utilizing a same medium in short- and long-term cultures of melanomas for biological studies and response evaluations of therapeutic agents such as LAK cells, when multiple cell targets from different patients or multi-metastatic cell lines from individual patients are to be compared. Finally, these melanoma sublines may be valuable for further elucidation of the relationship between MHC expression, and increased sensitivity to LAK cytolysis, and the role of the components of DMEM in the mechanism for the observed induction of cell differentiation and enhanced LAK cytolysis.

Extracellular adenosine 5' triphosphate involvement in the death of LAK-engaged human tumor cells via P2X-receptor activation

This study reports that extracellular ATP is a critical factor involved in LAK cell-mediated cytotoxicity. Human colon carcinoma LoVo cells were resistant to LAK cells as well as to ATP, while their multidrug resistant (MDR-1+) derivative, LoVo-Dx cells, were sensitive to both LAK and ATP. LoVo-Dx cells, became resistant to LAK cells and ATP after 48 h pretreatment with Phorbol 12-Myristate-13-Acetate (PMA), while 48 h pretreatment with verapamil in parallel sensitized LoVo cells to LAK cells and to ATP as well. The sensitivity to ATP and LAK cells was not related to the expression of extracellular ecto-ATPase activity on cell targets membranes. Conversely, apyrase, an enzyme with powerful ecto-ATPase activity, abolished the LAK- and ATP-mediated cytotoxicity. Furthermore, ADP-beta-S, an antagonist of ATP, abolished both LAK and ATP-mediated cell killing. Purine binding sites have been detected by radioreceptor assays with ADP-beta[35S] on the cell surface of ATP and LAK-sensitive LoVo-Dx cells. By contrast, no nucleotide receptor was found on the ATP and LAK-resistant cells. Such a putative cytotoxic purinoreceptor has been categorized as P2x purinergic receptor by a panel of synthetic nucleotides. These results demonstrate that extracellular ATP is needed for an efficient LAK cell-mediated killing of tumor cells. We propose that ATP acts as a natural amplifier of physical, or immune cytotoxic damages since it may be released in large amounts from target cells injured by several cytotoxic mediators secreted by LAK effectors.

All-trans retinoic acid decreases susceptibility of a gastric cancer cell line to lymphokine-activated killer cytotoxicity

All-trans retinoic acid (RA) was previously shown to regulate the growth of gastric cancer cells derived from the cell line SC-M1. This study was designed to investigate the effect of RA on the sensitivity of SC-M1 cells to lymphokine-activated killer (LAK) activity. RA at the concentration range of 0.001-10 microM was shown to induce SC-M1 cells to exhibit resistance to LAK activity in a dose-dependent manner. A kinetics study indicated that a significantly increased resistance was detected after 2 days of co-culturing SC-M1 cells with RA and reached a maximum after 6 days of culture. Similar results were obtained from two other cancer cell lines: promyelocytic leukaemia HL-60 and hepatic cancer Hep 3B. A binding assay demonstrated that the binding efficacy between target SC-M1 cells and effector LAK cells was not altered by RA. Flow cytometric analyses revealed that RA exhibited no effect on the expression of cell surface molecules, including HLA class I and class II antigens, intercellular adhesion molecule-1 and -2, and lymphocyte function antigen-3. Cell cycle analysis revealed that culture of SC-M1 cells with RA resulted in an increase in G0/G1 phase and a decrease in S phase, accompanied by a decrease in cyclin A and cyclin B1 mRNA as determined by Northern blot analysis. Additionally, RA was shown to enhance the expression of retinoic acid receptor alpha (RAR alpha) in SC-M1 cells, and to have no effect on the expression of RARbeta or RARgamma. Taken together, these results indicate that RA can significantly increase gastric cancer cells SC-M1 to resist LAK cytotoxicity by means of a cytostatic effect through a mechanism relating to cell cycle regulation. The prevailing ideas, such as a decrease in effector to target cell binding, a reduced MHC class I antigen expression or an altered RARbeta expression, are not involved.

Prolactin increases the susceptibility of primary leukemia cells to NK and LAK effectors

Our previous studies have shown that prolactin (PRL), a pituitary and lymphocyte hormone and a ligand of the cytokine/hemopoietin receptors (R) superfamily, acts synergistically with interleukin (IL)-2 on the development of lymphokine activated killer (LAK) cells and enhances the effects of GM-CSF and IL-3 on myeloid progenitors' proliferation and differentiation. More recently, we have demonstrated that GM-CSF and IL-3 increase the sensitivity of acute myeloid leukemic (AML) cells to LAK activity. Together, these findings have prompted us to study the role of PRL on the target arm of the LAK response. We show here that CD33+ blasts from AML patients express membrane PRL-R and that the PRL/PRL-R interaction is followed by increased susceptibility to natural killer (NK) (p < 0.02) and LAK (p < 0.001) cells. As predicted from the dimerization model of PRL-R and in agreement with previous reports, the response of AML blasts to PRL was bell-shaped with a trend peak at 25 ng/ml. Although enhanced lysis occurred at the target recognition level, it was not accompanied by changes in the MHC class I, cellular adhesion molecules, or myeloid differentiation antigens. Cell cycle recruitment and lysis increased concurrently in three cases studied, suggesting a modulatory action of PRL on the expression of putative cycle-related NK/LAK-target structures. Together, these data strengthen the role of PRL in the LAK response.