Another breakthrough in HIV research was announced in early 1996 at a Keystone Symposium by Edward Berger from the National Institute of Health in Bethesda who reported unpublished findings about a novel cell fusion coreceptor allowing the infection by T cell line-tropic (TCL-tropic or T-tropic) but not macrophage-tropic (M-tropic) HIV-1 isolates when co-expressed on CD4+ target cells. This evidence concerns the gene CD4 and infection.