CD4+ T cells are T lymphocyte subtypes that express the cell surface glycoprotein CD4. Mature T helper cells are an example, and the name is sometimes used interchangeably. CD4+ T cells develop in the thymus and populate in the spleen and lymph nodes, as well as in circulating blood. These cells are key players in the immune system especially in the case of HIV, in which they are the primary viral host. Ready-to-use kits are available for the rapid and reliable isolation of CD4+ T cells through magnetic-based positive or negative selection methods.