Immunoglobulins and serum proteins impair anti-tumor NK cell effector functions in malignant ascites

Introduction

Malignant ascites indicates ovarian cancer progression and predicts poor clinical outcome. Various ascites components induce an immunosuppressive crosstalk between tumor and immune cells, which is poorly understood. In our previous study, imbalanced electrolytes, particularly high sodium content in malignant ascites, have been identified as a main immunosuppressive mechanism that impaired NK and T-cell activity.

Methods

In the present study, we explored the role of high concentrations of ascites proteins and immunoglobulins on antitumoral NK effector functions. To this end, a coculture system consisting of healthy donor NK cells and ovarian cancer cells was used. The anti-EGFR antibody Cetuximab was added to induce antibody-dependent cellular cytotoxicity (ADCC). NK activity was assessed in the presence of different patient ascites samples and immunoglobulins that were isolated from ascites.

Results

Overall high protein concentration in ascites impaired NK cell degranulation, conjugation to tumor cells, and intracellular calcium signaling. Immunoglobulins isolated from ascites samples competitively interfered with NK ADCC and inhibited the conjugation to target cells. Furthermore, downregulation of regulatory surface markers CD16 and DNAM-1 on NK cells was prevented by ascites-derived immunoglobulins during NK cell activation.

Conclusion

Our data show that high protein concentrations in biological fluids are able to suppress antitumoral activity of NK cells independent from the mechanism mediated by imbalanced electrolytes. The competitive interference between immunoglobulins of ascites and specific therapeutic antibodies could diminish the efficacy of antibody-based therapies and should be considered in antibody-based immunotherapies.

Electrolyte imbalance causes suppression of NK and T cell effector function in malignant ascites

BACKGROUND

Malignant ascites commonly occurs in advanced or recurrent stages of epithelial ovarian cancer during peritoneal carcinomatosis and is correlated with poor prognosis. Due to its complex composition of cellular and acellular components malignant ascites creates a unique tumor microenvironment, which mediates immunosuppression and promotes progression of disease. However, the immunosuppressive mechanisms remain poorly understood.

METHODS

In the present study, we explored the antitumor activity of healthy donor NK and T cells directed against ovarian cancer cells in presence of malignant ascites derived from patients with advanced or recurrent peritoneal carcinomatosis. A wide range of methods was used to study the effect of ascites on NK and T cells (FACS, ELISA, EliSpot, qPCR, Live-cell and confocal microscopy, Western blot and electrolyte flux assays). The ascites components were assessed using quantitative analysis (nephelometry, potentiometry and clinical chemistry) and separation methods (dialysis, ultracentrifugal filtration and lipid depletion).

RESULTS

Ascites rapidly inhibited NK cell degranulation, tumor lysis, cytokine secretion and calcium signaling. Similarly, target independent NK and T cell activation was impaired in ascites environment. We identified imbalanced electrolytes in ascites as crucial factors causing extensive immunosuppression of NK and T cells. Specifically, high sodium, low chloride and low potassium content significantly suppressed NK-mediated cytotoxicity. Electrolyte imbalance led to changes in transcription and protein expression of electrolyte channels and impaired NK and T cell activation. Selected inhibitors of sodium electrolyte channels restored intracellular calcium flux, conjugation, degranulation and transcript expression of signaling molecules. The levels of ascites-mediated immunosuppression and sodium/chloride/potassium imbalance correlated with poor patient outcome and selected molecular alterations were confirmed in immune cells from ovarian cancer patients.

CONCLUSION

Our data suggest a novel electrolyte-based mechanism of immunosuppression in malignant ascites of patients with peritoneal carcinomatosis. We show for the first time that the immunosuppression of NK cytotoxicity in coculture assays is correlated to patient poor survival. Therapeutic application of sodium channel inhibitors may provide new means for restoring immune cell activity in ascites or similar electrolyte imbalanced environments.

Reactivity of NK Cells Against Ovarian Cancer Cells Is Maintained in the Presence of Calcium Phosphate Nanoparticles

Calcium phosphate nanoparticles (CaP-NPs) are biodegradable carriers that can be functionalized with biologically active molecules. As such, they are potential candidates for delivery of therapeutic molecules in cancer therapies. In this context, it is important to explore whether CaP-NPs impair the natural or therapy-induced immune cell activity against cancer cells. Therefore, in this study, we have investigated the effects of different CaP-NPs on the anti-tumor activity of natural killer (NK) cells using different ovarian cancer (OC) cell line models. We explored these interactions in coculture systems consisting of NK cells, OC cells, CaP-NPs, and therapeutic Cetuximab antibodies (anti-EGFR, ADCC-inducing antibody). Our experiments revealed that aggregated CaP-NPs can serve as artificial targets, which activate NK cell degranulation and impair ADCC directed against tumor targets. However, when CaP-NPs were properly dissolved by sonication, they did not cause substantial activation. CaP-NPs with SiO2-SH-shell induced some activation of NK cells that was not observed with polyethyleneimine-coated CaP-NPs. Addition of CaP-NPs to NK killing assays did not impair conjugation of NK with OC and subsequent tumor cytolytic NK degranulation. Therapeutic antibody coupled to functionalized CaP-NPs maintained substantial levels of antibody-dependent cellular cytotoxic activity. Our study provides a cell biological basis for the application of functionalized CaP-NPs in immunologic anti-cancer therapies.

A near-infrared emitting MOF: controlled encapsulation of a fluorescein sensitizer at the time of crystal growth

We report here a near-infrared (NIR) emitting lanthanide-based metal-organic framework (MOF) in which Yb³⁺ are sensitized by fluorescein (FL) as a low energy absorbing chromophore (FL@CD-MOF-161). The unique design of CD-MOF-161 allows for the entrapment of FL molecules in its pores during the synthesis and crystal growth, ensuring the efficient loading and spreading of chromophores within the crystal volume.