Immunostaining of patient CD4 T cells and G22V-transfected CD4 T cells from a healthy donor showed accumulation of LCK in the RAB11 (see 605570)-positive endosomal compartment; the amount of LCK at the plasma membrane was reduced 2.7- and 2.8-fold in patient and mutant-transfected CD4 T cells, respectively, compared to controls. Proliferation of patient lymphocytes in response to activation with mitogen or antigen was profoundly reduced, with a 20-fold reduction on average compared to minimal normal values; proliferation of mutant-transfected CD4 T cells was also inhibited, with a 2.8- and 2.4-fold reduction in response to mitogen and antigen, respectively, compared to controls. Analysis of CD4 and CD8 T-cell subset proliferation after T-cell receptor (see TCR, 186880) stimulation demonstrated that patient cells divided up to 3 times whereas control cells divided up to 5 times. Gorska and Alam (2012) concluded that the UNC119 G22V mutation impairs LCK-dependent T-cell function.