The key proteins involved in functioning of Treg, including FoxP3, Granzyme A, XCL1 (lymphotactin), pSTAT5 (phosphorylated signal transducer and activation of transcription-5 protein), and GITR (glucocorticoid induced tumor necrosis factor receptor related protein) were found to be significantly reduced in patients with CVID with autoimmunity. The gene discussed is FOXP3; the disease is Autoimmunity.