CD4 and AIDS: While the population of peripheral CD4 T lymphocytes in the peripheral blood of JR-CSF mice remained stable over time, the peripheral CD4 T cells population in the JR-CSF/hu-cycT1 mice became gradually depleted so that by one year of age the CD4 to CD8 T cell ratio in the peripheral blood of the JR-CSF/hu-cycT1 mice had reversed to less than one, similar to the temporal course in HIV infected individuals that develop AIDS.