IL7R and severe combined immunodeficiency: In addition, the vast majority (~97.5%) of the patient’s CD3+ T cells did not express IL-7Rα whereas only ~2.5% expressed IL-7Rα, suggesting that they might be maternal cells transferred to the patient in utero, as transplacentally-acquired maternal cells have been previously detected in the periphery of up to 40% of SCID patients (26).