 This study aims to assess the safety, tolerability and pharmacokinetics of Ig NextGen 10 in patients with primary immune deficiency currently being treated with Intragam P. Eligible patients will switch from 3 to 4 weekly intravenous Intragam P therapy to receive seven cycles of Ig NextGen 10 treatment administered intravenously at three- to four-weekly intervals. Patients will be monitored on the study for up to 36 weeks. 