Yuanqing Liu

Nitric Oxide-Independent CTL Suppression during Tumor Progression: Association with Arginase-Producing (M2) Myeloid Cells

Most of the mice bearing a s.c. BW-Sp3 lymphoma tumor mount a CD8+ T cell-mediated response resulting in tumor regression. Nonetheless, tumor progression occurs in some of the recipients and is associated with CTL inactivity. We demonstrated that T cell-activating APC were induced in regressors whereas T cell suppressive myeloid cells predominated in the spleen of progressors. Indeed, in vitro depletion of either the adherent or the CD11b+ populations restored T cell cytotoxicity and proliferation in these mice. This CTL inhibition was cell-to-cell contact-dependent but not mediated by NO. However, the same progressor suppressive cells prevented the activity of in vitro-restimulated CTLs derived from regressors in a cell-to-cell contact and NO-dependent fashion. Thus, either the NO-dependent or -independent suppressive pathway prevailed, depending on the target CTL population. In addition, the suppressive population expressed a high arginase activity, suggesting an association of the suppressive phenotype with alternatively activated (M2) myeloid cells. However, the high arginase activity is not directly involved in the suppressive process. Our results provide new insights for myeloid cell-mediated CTL inhibition during cancer progression.

B7-1, IFNγ and anti-CTLA-4 co-operate to prevent T-cell tolerization during immunotherapy against a murine T-lymphoma†

We previously reported on a murine T lymphoma cell line, BW‐Sp3, with inherent immunogenicity. BW‐Sp3 tumors can elicit an anti‐tumor CD8+ CTL response capable of mediating a regression of subcutaneous tumors. However, this immune response is inadequate to eliminate cancer cells completely in a significant percentage of the recipients, resulting in progressing tumors. In this tumor model, tumor progression correlated with a tolerization of tumor‐reactive T cells and cellular immunotherapy of tumor bearing animals, with or without B7‐mediated costimulation, even increased tumor progression (Raes et al, 1998 ). In the present study, we investigated whether the co‐expression of IFNγ, together with B7‐1, could have beneficial effects on immunotherapy. Although immunotherapy with IFNγ and B7‐1 single transfectants tended to tolerize anti‐tumor T‐cells and consequently increased tumor growth, the B7‐1/IFNγ double transfectants resulted in a more beneficial outcome. This phenomenon correlated with an increased CTL‐inducing potential of the double transfectants. Secondly, we wondered whether CTLA‐4 signalling was involved in the down‐regulation of the anti‐tumor response. Indeed, when immunotherapy was provided along with anti‐CTLA‐4, the protection by B71/IFNγ double transfectants was further improved and the tumor‐promoting effect of BW‐Sp3(B7‐1) was compensated for. Our results indicate that B7‐1, IFNγ and the blockade of CTLA‐4 cooperate to tilt the balance in favour of tumor elimination, while either factor alone fails to do so or even promotes tumor growth. Int. J. Cancer 87:539–547, 2000.

Ablation of NK Cell Function During Tumor Growth Favors Type 2-Associated Macrophages, Leading to Suppressed CTL Generation

Several reports describe regulatory interactions between NK cells and CTLs. We addressed the issue of NK participation in the early anti-tumor defense by inoculating α-ASGM-1 treated mice with BW-Sp3 T lymphoma. Rejection of BW-Sp3 depends on strong CTL responses. Our results demonstrated that (i) NK cells are a prerequisite for efficient CTL generation and (ii) the absence of NK cells favors the outgrowth of alternatively activated macrophages that can suppress CTL restimulation. In vitro studies demonstrate that in splenic cultures from NK-deficient, tumor-bearing mice, the presence of alternatively activated macrophages correlates with a lack of Type 1 cytokines, while the production of Type 2 cytokines is promoted. Provision of the Type 1 cytokine, IFN-γ can boost overall CTL activity but does not revert the dominance of arginase producing adherent cells in the NK-deficient CTL cultures. The role of NK effector functions in the efficient switch of the immune system towards Type 1 activation was evaluated in cytotoxicity assays. The results indicate that the accessory function of NK can depend at least partially on their ability to preferentially engage arginase-producing cells, suggesting that NK/macrophage lytic interactions might be involved in the switch from Type 2 to Type 1-dependent immune responses.

Classical and alternative activation of macrophages: different pathways of macrophage-mediated tumor promotion

Macrophages often function as control switches of the immune system, securing the balance between pro- and anti-inflammatory reactions. For this purpose and depending on the activating stimuli, macrophages can develop into different subsets: classically (M1) or alternatively (M2) activated macrophages, the characterization of which is a current topic of investigation. Accumulating evidence suggests that both populations, using their own specific mechanisms, may influence the behaviour of cancer cells, shape the tumor microenvironment and subverte anti-tumor immunity, thereby contributing to tumor growth and progression.

Functional and Molecular Characterization of Myeloid Suppressor Cells Expanded During Lymphoma Tumour Progression

We previously reported that in mice with large progressing T‐cell lymphoma tumours, dysfunctions in the antitumour CTL activity occur, associated with an accumulation of splenic arginase‐producing myeloid suppressor cells (MSCs). In this study, we first demonstrate that both the presence and the activation state of these MSC depends on tumour evolution. While in tumour regressors hardly any arginase‐producing MSC can be found, both the amount and the arginase activity of this population expands from early over late progressors. This gradual induction of MSCs is paralleled by an increasing suppression of CTL activity and Th1, but not Th2, cytokine production. Upon analysing the molecular repertoire of MSC in vitro, we found, besides arginase1, a well‐established marker for alternatively activated myeloid cells or M2, a strong upregulation of FIZZ1 and Ym, two additional recently identified markers for M2. Further evaluation of molecular markers by microarray analysis in MSC yielded genes involved in wound healing (e.g. coagulation factor XIIIa), anti‐inflammation (e.g. selenoprotein P), immunomodulation (e.g. PD‐L2) and fat and sugar metabolism (e.g. leptin receptor). Of note, many of these genes are regulated by type 2 cytokines (IL‐4, IL‐13 and IL‐10) and are therefore rather M2 associated. Overall, our data provide new markers for MSC in cancer and further establish their M2 activation state.