Evidently, CD4 provides an attachment site on the cell surface for HIV. Fusin is then required for the virus's coat to fuse with the cell membrane and allow the virus to enter the cell. Interestingly, the fusin protein structure is similar to a receptor used by chemokines, chemicals which have recently been found to prevent HIV from reproducing. It is possible that chemokines attach to the fusin receptors and thus block infection by HIV.
The new discovery has many implications for future research. Scientists are attempting to produce animals with CD4 and fusin on their cells so that future research on HIV in live non-primate animals is possible. Testing for drugs and vaccines that act on HIV or fusion may be possible. Lastly, these findings shed some light on the mystery of how some people are able to resist infection by HIV or are able to carry the HIV virus without being harmed.
Source: "Scientists Fund Elusive Protein, HIV's Guide" by Warren E. Leary, New York Times, May 10, 1996