In this example, targeting the disruption of the CCR5 protein appears to have not had any short term side effects on immune function (we still will hope to hear how this patient does over the next few years). This also worked because we had a good understanding of the important role CCR5 plays in HIV attachment and entry for many years.
In the case of HBV, the host proteins which have been identified to date are involved in housekeeping functions critical for maintaining human chromosomal organization and stability or are involved in regulating protein formation. It is uncertain how disruption of one or more of these proteins would affect normal human physiology. Also, replacement of the tissue reservoir for HIV (bone marrow) is much easier than for thie tissue reservoir for HBV (the liver).