An investigation of factors influencing the in vitro induction of LAK activity against a variety of human bladder cancer cell lines

Th1 cytokine-secreting recombinant Mycobacterium bovis bacillus Calmette-Guérin and prospective use in immunotherapy of bladder cancer

Intravesical instillation of Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been used for treating bladder cancer for 3 decades. However, BCG therapy is ineffective in approximately 30–40% of cases. Since evidence supports the T helper type 1 (Th1) response to be essential in BCG-induced tumor destruction, studies have focused on enhancing BCG induction of Th1 immune responses. Although BCG in combination with Th1 cytokines (e.g., interferon-α) has demonstrated improved efficacy, combination therapy requires multiple applications and a large quantity of cytokines. On the other hand, genetic manipulation of BCG to secrete Th1 cytokines continues to be pursued with considerable interest. To date, a number of recombinant BCG (rBCG) strains capable of secreting functional Th1 cytokines have been developed and demonstrated to be superior to BCG. This paper discusses current rBCG research, concerns, and future directions with an intention to inspire the development of this very promising immunotherapeutic modality for bladder cancer.

Recent advances in bacillus Calmette–Guerin immunotherapy in bladder cancer

The concept of using Mycobacterium for cancer treatment goes back to the 19th Century. Today, bacillus Calmette–Guerin (BCG) vaccine is a well-established treatment for human bladder cancer that is arguably superior to intravesical chemotherapy for superficial disease and is commonly used as the first-line adjuvant treatment. Much has been learnt about the effects of BCG on bladder cancer and the immune system, but deeper understanding is required in order to improve its efficacy further, to be able to reliably predict responders and ultimately to adapt this most successful form of cancer immunotherapy for the treatment of other malignancies. This article summarizes the current understanding of BCG cancer immunotherapy mechanisms and discusses possible future developments.

Mechanisms of action of intravesical bacille Calmette-Guérin: local immune mechanisms

The local immune response to mycobacteria is complex, but mycobacterial antigen presentation by phagocytes to T helper cells is the pivotal interaction. Bacille Calmette-Guérin (BCG) vaccination is associated with the development of antituberculosis immunity but not necessarily with antitumor immunity. Animal studies have shown that an intact host immune system is required for the antitumor activity of BCG. Immunosuppressed and, particularly, T cell-depleted individuals fail to respond to BCG immunotherapy. Clinical and laboratory evidence suggest that the antitumor activity is concentrated at the site of BCG administration, which reinforces the view that local immune mechanisms are responsible for this phenomenon.

In vitro generation of bacillus Calmette-Guérin-activated killer cells

Tumor regression induced in cancer patients by local instillation of bacillus Calmette-Guérin (BCG) into the bladder is considered to be mediated by cellular immune and inflammatory reactions. In an attempt to elucidate which of these effects are relevant to tumoricidal activity, an in vitro system was employed in which the immunostimulatory effects of BCG could be studied. This report describes the induction of BCG-activated killer (BAK) cells, which effectively lyse bladder tumor cells. Human peripheral blood mononuclear cells (PBMC) were stimulated with viable and sonicated BCG (v-BCG and s-BCG, respectively) to generate BAK cells. Cytotoxicity of BAK cells was comparable with the cytotoxicity exerted by lymphokine-activated killer (LAK) cells generated by interferon (IFN)-gamma but did not reach the level of interleukin-2 (IL-2)-generated LAK cells. Induction of BAK cells was possible only with v-BCG and not with s-BCG. By depletion and enrichment of defined cell populations, the cytotoxic potential of BAK cells could be attributed to a population of CD8(+) and CD56(+) double-positive lymphocytes. Macrophages and CD4(+) cells were required for the induction of killing activity but had no such activity by themselves. Furthermore, the presence of IFN-gamma and IL-2 in the supernatants harvested during the generation of BAK cells was demonstrated. Monoclonal antibodies neutralizing these cytokines abolished BCG-mediated cytotoxicity. From these results, it is concluded that the known beneficial effect of local instillation of BCG on maintenance of the relapse-free state in superficial bladder cancer may be due to local generation of BAK cells.

Enhancing the immunotherapeutic potential of mycobacteria by transfection with tumour necrosis factor-alpha

In an attempt to enhance the anti-tumour properties of mycobacteria we have developed recombinant forms of Mycobacterium smegmatis which express and secrete biologically active human tumour necrosis factor-alpha (TNF-alpha). This was achieved by transfecting M. smegmatis using shuttle plasmids incorporating the cDNA sequence for the human TNF-alpha mature peptide. In vitro experiments on a panel of human bladder tumour cell lines (EJ18, MGH-U1, RT4, RT112) indicate that our genetically modified mycobacteria are more effective than wild-type at inducing or up-regulating the expression of intracellular adhesion molecule-1 and the secretion of an array of proinflammatory cytokines [interleukin-1 (IL-1), IL-6, IL-8, granulocyte-macrophage colony-stimulating factor]. We have also demonstrated increased adhesion molecule and cytokine expression in response to mycobacteria transfected with vector containing no gene insert. However, this was not as pronounced as that observed following tumour cell stimulation by the TNF-alpha-transfected strain. In contrast, in three out of four tumour cell lines all M. smegmatis strains were found to down-regulate the secretion of the anti-inflammatory cytokine transforming growth factor-beta1. Our studies have also confirmed that M. smegmatis is a powerful inhibitor of bladder tumour cell growth and revealed that its antiproliferative potency is enhanced by transfecting with human TNF-alpha and, to a lesser extent, with vector alone. All M. smegmatis strains were effective in the activation of peripheral blood leucocyte cultures. However, no differences were observed in the ability of the TNF-alpha-transfected, mock-transfected and wild-type mycobacteria to induce tumour cell killing activity. These results suggest that the immunomodulatory effects of M. smegmatis can be enhanced by transfection with vectors which allow the secretion of human TNF-alpha, thus increasing mycobacterial immunotherapeutic potential.

Superficial bladder cancer: the role of interferon-alpha

PURPOSE

We evaluate the clinical experience with recombinant interferon-alpha in superficial transitional cell carcinoma and discuss the most rational use of recombinant interferon-alpha in the context of current treatment options.

MATERIALS AND METHODS

The available data were reviewed and discussed at a consensus conference in August 1996. The conclusions and recommendations are those of the authors based on the consensus reached at that meeting.

RESULTS

While bacillus Calmette-Guerin (BCG) is recognized as the most efficacious intravesical agent in the prophylaxis and treatment of superficial transitional cell carcinoma, it is associated with significant toxicities and a 20 to 40% relapse rate. Interferons, particularly recombinant interferon-alpha, have demonstrated efficacy against primary and recurrent papillary transitional cell carcinoma and carcinoma in situ with minimal toxicity, although the response and relapse rates are inferior to BCG. Intravesical recombinant interferon-alpha therapy has also produced responses in patients who failed to respond or were refractory to BCG or chemotherapy.

CONCLUSIONS

The clinical experience suggests that recombinant interferon-alpha has an important role in the treatment of superficial transitional cell carcinoma, particularly as second line therapy following failure of BCG or chemotherapy, and it may have synergistic effects when combined with chemotherapy or BCG. We propose a prospective randomized study comparing the efficacy of recombinant interferon-alpha, BCG and BCG plus recombinant interferon-alpha as maintenance following complete response to primary BCG therapy. The proposed study would also investigate the efficacy of BCG plus recombinant interferon-alpha as second line therapy following BCG failure. This study will be important to determine the most effective strategy to integrate recombinant interferon-alpha into current treatment options for superficial bladder cancer.

In vitro effects of prostaglandin E2 or indomethacin on the proliferation of lymphokine-activated killer cells and their cytotoxicity against bladder tumor cells in patients with bladder cancer

PURPOSE

To investigate the combined effects of interleukin-2 (IL-2) with either prostaglandin E2 (PGE2) or indomethacin (IM) on the proliferation and cytolysis of bladder tumor cells by lymphokine-activated killer (LAK) cells in patients with bladder cancer.

METHODS

LAK cell proliferation was assayed in the presence of various concentrations of either PGE2 or IM by cell counting. Bladder cancer cell lines BIU-87, EJ and bladder tumor cells (BTC) from the patients were cultured as target cells, and the cytotoxicity of LAK cells was determined by 3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In addition, PGE2 in samples of conditioned medium from bladder cancer cells or peripheral blood mononuclear cells (PBMC) as well as plasma from 21 patients with bladder cancer and 20 healthy donors were determined by radioimmunoassay (RIA).

RESULTS

The proliferation of LAK cells induced by IL-2 was inhibited by PGE2 (0.05 to 5 ng/mL) in concentration-dependent manner. The enhanced growth of LAK cells was observed at certain concentrations of IM (100-400 ng/mL) from 48 to 96 h. Pretreatment of LAK cells with IM (200 ng/mL) significantly enhanced cytotoxicity against BIU-87, EJ cells, or BTC. More PGE2 was present in conditioned medium from BIU-87 cells than in the conditioned medium from PBMC.

CONCLUSIONS

These studies indicate that LAK cell proliferation induced by IL-2 in patients with bladder cancer is inhibited by PGE2 produced by PBMC and bladder cancer cells. This inhibition can be overcome by IM, which may be of use in immunotherapy of bladder cancer.

Bacillus Calmette-Guerin (BCG) enhances monocyte- and lymphocyte-mediated bladder tumour cell killing

A cytotoxicity assay was used to study the action of bacillus Calmette-Guerin (BCG) and cytokines on four human bladder cancer cell lines. Monocytes and lymphocytes from peripheral blood were incubated with or without BCG or cytokines for 24 h, after which [3H]thymidine-labelled target cells were added and the 72 h percentage specific release determined. BCG had a direct cytotoxic effect against tumour cells and significantly enhanced monocyte/macrophage and enhanced lymphocyte cytotoxicity against one cell line (UCRU-BL-17). Supernatants (SNs) from BCG-activated monocytes/macrophages and lymphocytes increased the percentage specific release of [3H]thymidine from UCRU-BL-17 cells. Interferon alpha (IFN-alpha) and interleukin 2 (IL-2) were cytotoxic towards UCRU-BL-17. No synergy occurred between BCG and cytokines at the concentrations tested. The results suggest that BCG is superior to IFN-alpha, interferon gamma (IFN-gamma) and IL-2 in enhancing cell-mediated cytotoxicity.

Specific binding of bacillus Calmette-Guérin to urothelial tumor cells in vitro

Intravesical immunotherapy with bacillus Calmette-Guérin (BCG) against recurrences of superficial bladder cancer and carcinoma in situ is a highly effective regimen in urology. Despite intensive efforts to clarify the immunological mechanisms of the most successful immunotherapy known today, the cellular mechanism of its antitumor activity remains unknown. In our approach to elucidate the way of action of intravesical BCG, we applied an in vitro adhesion assay to investigate the interaction of radiolabeled BCG with urothelial bladder-tumor cells. We demonstrated a BCG dose-dependent binding to bladder-tumor cell lines derived from tumors of different gradings. The binding of BCG is apparently specific, since competition experiments showed an inhibition by nonradioactive BCG but not by Escherichia coli. We also found that there was no difference between the binding of living or heat-killed mycobacteria. Control experiments showed only a low affinity of BCG for fibroblasts, smooth-muscle cells, and endothelial cells in comparison with the tumor cells. Furthermore, we investigated the role of fibronectin as an adhesion molecule that is also present in the bladder wall. We demonstrated that BCG was capable of binding to fibronectin-coated surfaces in a dose-dependent manner. However, competitive binding assays failed to reveal an inhibition of the binding of BCG to bladder-tumor cells by anti-fibronectin. Furthermore, binding was not influenced by soluble fibronectin. These data suggest that the in vitro attachment of BCG to bladder-tumor cells appears not to be mediated by fibronectin. In electron microscope studies an adhesion of BCG to bladder-tumor cells was observed after an incubation period of ony 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of lymphokine-activated killer activity in mice by prothymosin alpha

We have recently demonstrated that prothymosin alpha (ProT alpha) when administered intraperitoneally (i.p.) protects DBA/2 mice against the growth of syngeneic leukemic L1210 cells through the induction of tumoricidal peritoneal cells producing high levels of tumor necrosis factor alpha (TNF alpha) [Papanastasiou et al. (1992) Cancer Immunol Immunother 35: 145]. In this report we tested further immunological alterations that may be caused by the administration of ProT alpha in vivo. We demonstrate that i.p. injections of ProT alpha enhance natural killer (NK) cell activity and induce lymphokine-activated (LAK) activity in vivo. Thus, splenocytes from ProT alpha-treated DBA/2 animals exhibited significantly higher cytotoxic activity (up to threefold) against the NK-sensitive YAC cell line and the NK-resistant P815 and L1210 syngeneic tumor cells, as compared to splenocytes from syngeneic control mice. The enhancement of the cytotoxic profile of DBA/2 splenocytes was associated with increased percentages of CD8+ cells, NK cells and activated CD3+ cells. The ProT alpha-induced effect persisted for 30 days after the end of the ProT alpha treatment period and returned to normal levels 20 days later. Splenocytes from non-treated DBA/2 animals generated high NK and LAK activities in response to ProT alpha in vitro. The ProT alpha-induced NK and LAK activities reached 84% and 75% respectively of what was obtained with interleukin-2 (IL-2). High concentrations of TNF alpha and IL-2 were generated in response to ProT alpha in LAK cultures. These findings suggest that ProT alpha may provide an overall protective effect against tumor growth in vivo through induction of NK and LAK activities possibly indirectly via the production of IL-2 and TNF alpha in the spleen, peritoneal cavity and probably other lymphoid organs.

Induction of ICAM 1 expression on bladder tumours by BCG immunotherapy

AIMS

To determine the expression of intercellular adhesion molecule 1 and 2 (ICAM 1 and 2) in transitional cell carcinoma cells before and after immunotherapy with Calmette-Guérin bacillus (BCG).

METHODS

Frozen sections from 22 untreated bladder carcinomas were immunohistochemically examined with monoclonal antibodies to ICAM 1 and 2. Urinary cytospin slides were made for six patients for each of the six clinical instillations which constitute a therapeutic course. These slides were also stained for ICAM 1 and for leucocyte function associated antigen 1 (LFA 1).

RESULTS

Bladder cancer cells did not essentially express either ICAM 1 or 2, but cells in the stromal areas surrounding tumour expressed both these antigens. After repeated instillations of BCG organisms ICAM 1 positive normal and neoplastic epithelial cells were observed in the urine. Cells obtained from the first three instillations expressed lower densities of ICAM 1 than those from the later instillations. Many neutrophils expressing LFA-1 and some lymphocytes were also noted in the cytospin slides and some of these were conjugated to tumour cells expressing ICAM 1. Six months after treatment a single maintenance dose of BCG induced ICAM 1 expression.

CONCLUSION

Untreated superficial bladder carcinoma cells do not express ICAM 1 or 2, but these important immunological molecules were expressed in the stromal areas of tissue. Importantly, neoplastic cells in the urine expressed ICAM 1 after immunotherapy. This molecule can render bladder tumour cells vulnerable to non-antigen specific cytotoxicity mediated by activated lymphocytes.

The effect of recombinant cytokines on bladder cancer cells in vitro

We have studied the Major Histocompatibility Class II-modulating and antiproliferative actions of recombinant interferon-gamma, tumor necrosis factor-alpha, interleukin-1 alpha, interleukin-2 and granulocyte macrophage-colony stimulating factor on bladder cancer cells in vitro. Indirect immunofluorescent staining employing monoclonal antibody probes in conjunction with flow cytometric analysis and tritiated thymidine incorporation assays were used. Interferon-gamma was a strong inducer and enhancer of class II antigens. Tumor necrosis factor-alpha could not induce the expression of class II antigens on tumor cells, which were initially class II-negative, but enhanced the expression on cells which already demonstrated low levels of the antigen. Interleukin-1, interleukin-2 and granulocyte macrophage-colony stimulating factor did not affect the major histocompatibility class II expression. Interferon-gamma and tumor necrosis factor-alpha both demonstrated powerful anti-proliferative effects on the bladder cancer cells, particularly those derived from low grade tumors (G1 and G2). Interleukin-1 alpha had no effect on tumor cell proliferation. In contrast interleukin-2 and granulocyte macrophage-colony stimulating factor had significant stimulatory effects on the proliferation of the low grade tumor cells (G1).

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.