RRM2B and plasma cell myeloma: Also included are more recently designed, genetically engineered mouse models (GEMMs) of myeloma, e.g., one that is based on the loss of Rrm2b (ribonucleotide reductase regulatory TP53 inducible subunit M2B) (Chang et al., 2013), a key enzyme in de novo deoxyribonucleotide synthesis important for DNA damage repair.