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Elucidating the molecular basis of immunodeficiency diseases is a powerful approach to discovering new immunoregulatory pathways in humans. Here we report 10 affected individuals from 4 families with a new immunodeficiency disease comprising of severe progressive lymphopenia, autoimmunity, immunodeficiency, and liver disease due to recessive loss of function variants in “GTPase of immunity-associated proteins” protein 5 (GIMAP5). We show that the disease involves the progressive loss of naïve T lymphocytes and a corresponding increase in antigen-experienced, but poorly functional and replicatively senescent T cells. In vivo treatment of Gimap5-deficient mice with rapamycin (an inhibitor of mTORC1) significantly restores the fraction of naïve T lymphocytes. Furthermore, a GIMAP5-deficient human patient who was treated with rapamycin (sirolimus) showed a remarkable reduction in spleen/lymph node size. Together, these observations reveal that GIMAP5 plays a critical role in lymphocyte metabolism which is essential for senescence prevention and immune competence, suggesting that an inhibitor of mTORC1 could be a valuable clinical intervention in treating patients deficient for GIMAP5.

Interleukin-2, which conveys essential signals for effective immunity and immunological tolerance, operates through a heterotrimeric receptor comprised of α, β and γ chains. Genetic deficiency of the α or γ chain causes debilitating disease. Here we identify human interleukin-2 receptor (IL-2R) β chain (CD122) gene defects as a cause of life-threatening dysregulation of immunity and peripheral tolerance. We report homozygous mutations in the human IL-2Rβ gene from four consanguineous families, comprising either recessive missense mutations in five children or an early stop-gain mutation in two deceased fetuses and a premature neonate. All patients surviving to childhood presented with autoantibodies, hypergammaglobulinemia, bowel inflammation, and dermatological abnormalities, as well as cytomegalovirus disease in most cases. Patient T lymphocytes lacked surface expression of IL-2Rβ and were unable to normally respond to high-dose IL-2 stimulation. By contrast, patient natural killer (NK) cells retained partial IL-2Rβ expression and cytotoxic function. IL-2Rβ loss of function was recapitulated in a recombinant system, in which endoplasmic reticulum sequestration was revealed as the mechanism by which certain missense mutations cause disease. Hematopoietic stem cell transplant resulted in resolution of clinical symptoms in one patient. The hypomorphic nature of this disease highlights the significance of variable IL-2Rβ expression in different lymphocyte subsets as a means of modulating immune function. Insights from these patients can inform the development of IL-2-based therapeutics for immunological diseases and cancer.