However, if once in contact with this envelope protein, the virus receptors (CD4 and CXCR4) induce intracellular signal leading to cell apoptosis, then questions must be asked about the advisability of using the HIV envelope glycoprotein without modifying it, because the risk would be to induce the very CD4+ lymphopenia that the vaccine is supposed to prevent [86,87]. The gene discussed is ERVW-1; the disease is lymphopenia.