Problems and challenges in the development and validation of human cell-based assays to determine nanoparticle-induced immunomodulatory effects.

BACKGROUND: With the increasing use of nanomaterials, the need for methods and assays to examine their immunosafety is becoming urgent, in particular for nanomaterials that are deliberately administered to human subjects (as in the case of nanomedicines). To obtain reliable results, standardised in vitro immunotoxicological tests should be used to determine the effects of engineered nanoparticles on human immune responses. However, before assays can be standardised, it is important that suitable methods are established and validated. RESULTS: In a collaborative work between European laboratories, existing immunological and toxicological in vitro assays were tested and compared for their suitability to test effects of nanoparticles on immune responses. The prototypical nanoparticles used were metal (oxide) particles, either custom-generated by wet synthesis or commercially available as powders. Several problems and challenges were encountered during assay validation, ranging from particle agglomeration in biological media and optical interference with assay systems, to chemical immunotoxicity of solvents and contamination with endotoxin. CONCLUSION: The problems that were encountered in the immunological assay systems used in this study, such as chemical or endotoxin contamination and optical interference caused by the dense material, significantly affected the data obtained. These problems have to be solved to enable the development of reliable assays for the assessment of nano-immunosafety.

The suitability of different cellular in vitro immunotoxicity and genotoxicity methods for the analysis of nanoparticle-induced events.

Suitable assays and test strategies are needed to analyze potential genotoxic and immunotoxic health effects caused by nanoparticle exposure. The development and validation of such methods is challenging because nanoparticles may show unexpected behavior, like aggregation or interference with optical measurements, when routine in vitro assays are performed. In our interdisciplinary study, the effects of inorganic gold (4.5 nm) and iron oxide (7.3 nm) nanoparticles with a narrow size distribution were tested on human cells using different assay systems. The results show that cytotoxicity as well as immunotoxicity and genotoxicity induced by these two inorganic nanoparticles was low or absent when using a panel of cell-based tests in different laboratories. However, several technical issues had to be tackled that were specific for working with nanoparticles. The methods used, their suitability for nanotoxicity testing, and the technical problems encountered are carefully described and discussed in this paper.