Understanding the correlation between in vitro and in vivo immunotoxicity tests for nanomedicines.

Preclinical characterization of novel nanotechnology-based formulations is often challenged by physicochemical characteristics, sterility/sterilization issues, safety and efficacy. Such challenges are not unique to nanomedicine, as they are common in the development of small and macromolecular drugs. However, due to the lack of a general consensus on critical characterization parameters, a shortage of harmonized protocols to support testing, and the vast variety of engineered nanomaterials, the translation of nanomedicines into clinic is particularly complex. Understanding the immune compatibility of nanoformulations has been identified as one of the important factors in (pre)clinical development and requires reliable in vitro and in vivo immunotoxicity tests. The generally low sensitivity of standard in vivo toxicity tests to immunotoxicities, inter-species variability in the structure and function of the immune system, high costs and relatively low throughput of in vivo tests, and ethical concerns about animal use underscore the need for trustworthy in vitro assays. Here, we consider the correlation (or lack thereof) between in vitro and in vivo immunotoxicity tests as a mean to identify useful in vitro assays. We review literature examples and case studies from the experience of the NCI Nanotechnology Characterization Lab, and highlight assays where predictability has been demonstrated for a variety of nanomaterials and assays with high potential for predictability in vivo.