IL2RG and plasma cell myeloma: established a human MM model in NOD-RAG-1-null IL-2rg-null (NRG) mice and found that AKAP4 was not only highly expressed in myeloma cells, but also this protein, like CD138, could be used as a marker of myeloma cells to track the proliferation of malignant cells and to distinguish human myeloma cells from mouse cells (18).