AK2 deficiency compromises the mitochondrial energy metabolism required for differentiation of human neutrophil and lymphoid lineages.

Reticular dysgenesis is a human severe combined immunodeficiency that is primarily characterized by profound neutropenia and lymphopenia. The condition is caused by mutations in the adenylate kinase 2 (AK2) gene, resulting in the loss of mitochondrial AK2 protein expression. AK2 regulates the homeostasis of mitochondrial adenine nucleotides (ADP, ATP and AMP) by catalyzing the transfer of high-energy phosphate. Our present results demonstrate that AK2-knocked-down progenitor cells have poor proliferative and survival capacities and are blocked in their differentiation toward lymphoid and granulocyte lineages. We also observed that AK2 deficiency impaired mitochondrial function in general and oxidative phosphorylation in particular - showing that AK2 is critical in the control of energy metabolism. Loss of AK2 disrupts this regulation and leads to a profound block in lymphoid and myeloid cell differentiation.

Correction of murine Rag1 deficiency by self-inactivating lentiviral vector-mediated gene transfer.

Severe combined immunodeficiency (SCID) patients with an inactivating mutation in recombination activation gene 1 (RAG1) lack B and T cells due to the inability to rearrange immunoglobulin (Ig) and T-cell receptor (TCR) genes. Gene therapy is a valid treatment option for RAG-SCID patients, especially for patients lacking a suitable bone marrow donor, but developing such therapy has proven challenging. As a preclinical model for RAG-SCID, we used Rag1-/- mice and lentiviral self-inactivating (SIN) vectors harboring different internal elements to deliver native or codon-optimized human RAG1 sequences. Treatment resulted in the appearance of B and T cells in peripheral blood and developing B and T cells were detected in central lymphoid organs. Serum Ig levels and Ig and TCR Vß gene segment usage was comparable to wild-type (WT) controls, indicating that RAG-mediated rearrangement took place. Remarkably, relatively low frequencies of B cells produced WT levels of serum immunoglobulins. Upon stimulation of the TCR, corrected spleen cells proliferated and produced cytokines. In vivo challenge resulted in production of antigen-specific antibodies. No leukemia development as consequence of insertional mutagenesis was observed. The functional reconstitution of the B- as well as the T-cell compartment provides proof-of-principle for therapeutic RAG1 gene transfer in Rag1-/- mice using lentiviral SIN vectors.