Experimental immunotherapy with NK-like cells. A preliminary report

Poly(I:C) potentiates Bacillus Calmette-Guérin immunotherapy for bladder cancer

Non-specific immunotherapy consisting of intravesical instillation of Bacillus Calmette-Guérin (BCG) is currently the best available treatment to prevent non-muscle-invasive bladder tumor recurrence and progression. This treatment however is suboptimal, and more effective immunotherapeutic approaches are needed. Toll-like receptors (TLRs) play a major role in the activation of the immune system in response to pathogens and danger signals but also in anti-tumor responses. We previously showed that human urothelial cells express functional TLRs and respond to TLR2 and TLR3 agonists. In this study, we analyzed the potential of polyinosinic:polycytidylic acid [poly(I:C)], a TLR3 agonist, to replace or complement BCG in the treatment of non-muscle-invasive bladder cancer. We observed that poly(I:C) had an anti-proliferative, cytotoxic, and apoptotic effect in vitro on two low-grade human bladder cancer cell lines, MGH-U3 and RT4. In MGH-U3 cells, poly(I:C) induced growth arrest at the G1-S transition. Poly(I:C) also increased the immunogenicity of MGH-U3 and RT4 cells, inducing the secretion of MHC class I molecules and of pro-inflammatory cytokines. By comparison, poly(I:C) had less in vitro impact on two high-grade human bladder cancer cell lines, 5637 and T24, and on MBT-2 murine high-grade bladder cancer cells. The latter can be used as an immunocompetent model of bladder cancer. The combination poly(I:C)/BCG was much more effective in reducing MBT-2 tumor growth in mice than either treatment alone. It completely cured 29% of mice and also induced an immunological memory response. In conclusion, our study suggests that adding poly(I:C) to BCG may enhance the therapeutic effect of BCG.

Combination immunotherapy of murine transitional cell cancer using BCG and an interferon-inducing pyrimidinone

The immunomodulator ABPP (2-amino-5-iodo-6-phenyl-4(3H) pyrimidinone) is an interferon inducer and has been shown to have in vivo activity against the murine bladder tumor MBT-2. Two experiments were performed to determine if ABPP might enhance the in vivo anti-tumor activity of Bacillus Calmette-Guerin (BCG). First, in vivo stimulation of cell-mediated cytotoxicity by BCG and ABPP was measured in C3H mice using a chromium-release assay. An earlier, greater, and longer-lasting increase in cytotoxicity was caused by ABPP than by BCG. Based on the differing times to peak cytotoxic stimulation, groups of 15 mice each were pretreated intraperitoneally at different times prior to inoculation with MBT-2. Compared to saline, ABPP alone did not increase survival, while BCG alone did increase survival (p less than 0.01), and the combination of BCG and ABPP yielded the highest survival (p less than 0.001). These results indicate that 1) ABPP affects the immune system differently than BCG, and 2) while ABPP may have less single-agent activity against MBT-2 than BCG, ABPP may serve to potentiate the activity of BCG.

Surface Ly-5 glycoprotein in murine natural killer (NK) cell development, target binding and cytotoxicity

The role of surface Ly-5 glycoprotein expression in the binding and lysis of susceptible tumor targets by natural killer cells was studied using NK cell-enriched splenocytes from 6-8 week old C57BL/6 mice which were reacted with anti-Ly-5 serum in the presence or absence of a source of complement. A conjugate assay was used to demonstrate that abrogation of tumor cell lysis by anti-Ly-5 serum involved the inhibition of NK cell binding to susceptible YAC-1 targets. Additionally, reconstituted membrane vesicles from NK cell-enriched splenocyte populations blocked binding of effector cells to YAC-1 lymphoma targets, a phenomenon which was abrogated by pretreatment of vesicles with anti-Ly-5 serum. Indirect immunofluorescent labeling and cell sorting were used in the physical separation of Ly-5+ and Ly-5- cells to examine the effect of interferon and interleukin preparations on Ly-5 expression and Nk activity. Three hour treatment of sorted Ly-5- cells with murine alpha + beta interferon resulted in conversion of 22% of the cells to an Ly-5+ phenotype, as well as a significant increase in the percent specific lysis of NK-susceptible YAC-1 targets when compared to freshly sorted Ly-5- cells (29.5 +/- 1.9 vs 2.6 +/- 4.0; p less than .001). In vitro proliferation of sorted Ly-5- cells was induced by three week culture in an interferon- and interleukin-containing supernatant from ConA stimulated BALB/c splenocytes (CM), followed by repeat analysis of Ly-5 expression and cytotoxic activity. Cell sorter purified Ly-5- cells cultured in CM acquired substantial surface Ly-5 with concomitant high levels of cytotoxic activity that remained partially susceptible to inhibition by anti-Ly-5 serum. The data presented suggest that surface Ly-5 glycoprotein expression is important for binding of freshly isolated NK cells to YAC-1 targets. In addition, Ly-5- precursors of NK cells are present in murine splenic tissues and can be induced by CM to become highly active effector cells with increased surface Ly-5 expression. The persistent susceptibility of a subset of these cells to inhibition of cytotoxic activity by anti-Ly-5 serum provides additional evidence of an important role for the Ly-5 glycoprotein in the natural killer cell cytolytic mechanism against certain targets.