ANPEP and neuroblastoma: In agreement with the above experiments, optimal recovery of cell surface MHC-I expression could only be observed in double p65/IRF1 transfectants (Fig. 4B), conclusively showing critical dependence of MHC-I/APM reactivation on NF-kB/IRF1 synergy, particularly in certain NB cells with hard-to-rescue APM defects.