Moreover, by incubating the infected cells at temperatures blocking fusion but not endocytosis, in the presence of fusion inhibitors, they showed that regardless of the viral strain and the envelope protein (Env or VSV-G), the virus present in the endosomes did not contribute to the infection in T lymphoblastic (Sup T1-R5) cells, CEM-ss cells, and in primary human CD4+ T lymphocytes. Here, CD4 is linked to infection.