Histone deacetylase HDAC7 is required for early B cell development and governs the acquisition of B cell progenitors gene identity. Its role in mature B cell biology and associated malignancies is unknown. Here, by using a conditional mouse model for specific deletion in activated B cells, we demonstrate that HDAC7 is essential for the formation of germinal centers (GC). HDAC7 deficiency results in the generation of aberrant GCB cells, diminished class switch recombination (CSR) and plasma cell