MECOM and severe combined immunodeficiency: This may explain the frequency by which RV integration induces activation of cell type-specific growth regulators such as LMO2 or MDS1/EVI1, and lymphoproliferative disorders in SCID patients [28], [29] or clonal expansion of hematopoietic progenitors in mice [30], [31], non-human primates [32], and man [33].