CIITA or RFX coding region loss of function mutations occur rarely in diffuse large B-cell lymphoma cases and cell lines with low levels of major histocompatibility complex class II expression.

Loss of major histocompatibility complex class II (MHCII) gene expression was associated with poor outcome in diffuse large B-cell lymphoma (DLBCL) in several studies. The mechanism for lost expression is unknown. MHCII gene expression is controlled by several transcription factors, including RFX (composed of RFXB, RFX5, and RFXAP), CREB, and NF-Y. These transcription factors interact with a master transactivator protein class II transactivator (CIITA) to form an enhanceosome complex. In the Bare Lymphocyte Syndrome (BLS), MHCII gene expression is absent due to small deletions or point mutations in the coding or splicing regions of either CIITA or an RFX subunit. This study investigated whether DLBCL with low MHCII expression had mutations similar to BLS. DNA from 46 patient tumors, for which gene expression profiling was available, was obtained from the Lymphoma and Leukemia Molecular Profiling Project (LLMPP). These cases had been previously reviewed by a panel of expert hematopathologists and each contained a minimum of 70% tumor. Twenty-three were from de novo DLBCL in the lowest 10% of MHCII expression, 4 Letters to the Editor