YY1 and disease arising from reactivation of latent virus: However, the importance of YY1 in regulating the MIEP in the context of latent infection was unclear, at least in the NT2D1 cell line (22), and attempts to generate YY1 knockout NT2D1 cells to directly determine if YY1 is required for latency in these cells were thwarted by cell death as a result of YY1 knockdown (23).