Reversal of tumor acidosis by systemic buffering reactivates NK cells to express IFN-γ and induces NK cell-dependent lymphoma control without other immunotherapies.

Like other immune cells, natural killer (NK) cells show impaired effector functions in the microenvironment of tumors, but little is known on the underlying mechanisms. Since lactate acidosis, a hallmark of malignant tissue, was shown to contribute to suppression of effective antitumor immune responses, we investigated the impact of tissue pH and lactate concentration on NK-cell functions in an aggressive model of endogenously arising B-cell lymphoma. The progressive loss of IFN-γ production by NK cells observed during development of this disease could be ascribed to decreased pH values and lactate accumulation in the microenvironment of growing tumors. Interestingly, IFN-γ expression by lymphoma-derived NK cells could be restored by transfer of these cells into a normal micromilieu. Likewise, systemic alkalization by oral delivery of bicarbonate to lymphoma-developing mice was capable of enhancing IFN-γ expression in NK cells and increasing the NK-cell numbers in the lymphoid organs where tumors were growing. By contrast, NK-cell cytotoxicity was dampened in vivo by tumor-dependent mechanisms that seemed to be different from lactate acidosis and could not be restored in a normal milieu. Most importantly, alkalization and the concomitant IFN-γ upregulation in NK cells were sufficient to significantly delay tumor growth without any other immunotherapy. This effect was strictly dependent on NK cells.

Recruitment of natural killer cells in advanced stages of endogenously arising B-cell lymphoma: implications for therapeutic cell transfer.

During inflammation and in transplantable tumor models, natural killer (NK) cells are recruited to pathologic tissues and activated to produce proinflammatory cytokines favoring adaptive immune responses of the T-helper type 1 (Th1) type. Interferon (IFN)-γ is needed to induce chemokines that attract NK cells in transplanted tumors. Nothing, however, is known on NK-cell migration in spontaneous tumors. As effective recruitment is a prerequisite for therapeutic NK-cell transfer, we investigated the cytokine milieu and the mechanisms that are instrumental for NK-cell accumulation in an endogenous tumor model. We make use of λ-myc transgenic mice that harbor the c-myc oncogene and develop spontaneous B-cell lymphoma. In contrast to lymphomas induced by tumor cell injection, virtually no IFN-γ produced by NK or by other cells was present in the tumor environment, particularly in advanced stages. Dendritic cells showed an impaired expression of interleukin-12, which is suggestive of deficient Th1 priming. The IFN-γ-dependent chemokines CXCL9 and CXCL10 were pivotal for NK-cell migration in the endogenous lymphoma model. Although IFN-γ was absent in late tumor stages, there was still expression of CXCL9 and CXCL10 with an ongoing influx of NK cells. The results demonstrate that transplantable tumor models do not reflect the situation as found in endogenously arising neoplasia, because in the latter, effective Th1 and cytotoxic T-lymphocyte responses are presumably not induced because of impaired IFN-γ production. The data also suggest that CXCL9 and CXCL10 production and NK-cell migration become independent of IFN-γ during tumor progression, and therefore support approaches of adoptive NK-cell transfer that hold promise for treatment of cancer.

Tracing functional antigen-specific CCR6 Th17 cells after vaccination.

BACKGROUND: The function of T helper cell subsets in vivo depends on their location, and one hallmark of T cell differentiation is the sequential regulation of migration-inducing chemokine receptor expression. CC-chemokine receptor 6 (CCR6) is a trait of tissue-homing effector T cells and has recently been described as a receptor on T helper type 17 (Th17) cells. Th17 cells are associated with autoimmunity and the defence against certain infections. Although, the polarization of Th cells into Th17 cells has been studied extensively in vitro, the development of those cells during the physiological immune response is still elusive. METHODOLOGY/PRINCIPAL FINDINGS: We analysed the development and functionality of Th17 cells in immune-competent mice during an ongoing immune response. In naïve and vaccinated animals CCR6(+) Th cells produce IL-17. The robust homeostatic proliferation and the presence of activation markers on CCR6(+) Th cells indicate their activated status. Vaccination induces antigen-specific CCR6(+) Th17 cells that respond to in vitro re-stimulation with cytokine production and proliferation. Furthermore, depletion of CCR6(+) Th cells from donor leukocytes prevents recipients from severe disease in experimental autoimmune encephalomyelitis, a model for multiple sclerosis in mice. CONCLUSIONS/SIGNIFICANCE: In conclusion, we defined CCR6 as a specific marker for functional antigen-specific Th17 cells during the immune response. Since IL-17 production reaches the highest levels during the immediate early phase of the immune response and the activation of Th17 cells precedes the Th1 cell differentiation we tent to speculate that this particular Th cell subset may represent a first line effector Th cell subpopulation. Interference with the activation of this Th cell subtype provides an interesting strategy to prevent autoimmunity as well as to establish protective immunity against infections.