Retroviral CRISPR/Cas9-Mediated Gene Targeting for the Study of Th17 Differentiation in Vitro.

T helper cells that produce IL-17A, known as Th17 cells, play a critical role in immune defense and are implicated in autoimmune disorders. CD4 T cells can be stimulated with antigens and well-defined cytokine cocktails in vitro to mimic Th17 cell differentiation in vivo. Research has been conducted extensively on the Th17 differentiation regulation mechanisms using the in vitro Th17 polarization assay. Conventional Th17 polarization methods typically involve obtaining naïve CD4 T cells from genetically modified mice to study the effects of specific genes on Th17 differentiation and function. These methods can be time-consuming and costly and may be influenced by cell-extrinsic factors from the knockout animals. Thus, a protocol using retroviral transduction of guide RNA to introduce gene knockout in CRISPR/Cas9 knockin primary mouse T cells serves as a very useful alternative approach. This paper presents a protocol to differentiate naïve primary T cells into Th17 cells following retroviral-mediated gene targeting, as well as the subsequent flow cytometry analysis methods for assaying infection and differentiation efficiency.