The V(D)J recombination/DNA repair factor artemis belongs to the metallo-β-lactamase family and constitutes a critical developmental checkpoint of the lymphoid system

V(D)J recombination constitutes a critical checkpoint in the development of the immune system as shown in several animal models as well as severe combined immune deficiency (SCID) condition in humans. We recently cloned the Artemis gene, whose mutations are responsible for RS-SCID, a condition characterized by an absence of both B and T lymphocytes and associated with increased sensitivity to ionizing radiations. Artemis is ubiquitously expressed and is localized in the nucleus. Artemis belongs to the metallo-beta-lactamase superfamily and defines a new group, beta-CASP, within this family. beta-CASP proteins are beta-lactamases acting on nucleic acids. While RS-SCID patients harbor Artemis loss-of-function mutations, we identified four patients with a combined immunodeficiency characterized by a low but detectable number of both B and T lymphocytes caused by hypomorphic mutations in the Artemis gene. Two of these patients developed aggressive B cell lymphomas, a condition that suggests Artemis may be considered a "caretaker" factor, similarly to the other V(D)J recombination/DNA repair actors.