c-Rel is the cellular cognate of v-Rel, the avian reticuloendotheliosis virus strain T transforming gene. v-Rel encodes a phosphoprotein that is located in the cytoplasm of transformed spleen cells and in the nucleus of non-transformed fibroblasts, in contrast to the c-Rel protein, which is cytoplasmic. c-Rel has been shown to represent a constituent of the κB site binding transcription factor NFκB, which plays a crucial role in the expression of immunoglobulin κ light chain gene. c-Rel is a myeloid checkpoint protein that can be targeted for treating cancer. c-Rel has an important role in B-cell survival and proliferation. The REL gene is amplified or mutated in several human B-cell lymphomas, including diffuse large B-cell lymphoma and Hodgkin's lymphoma.