CD4 and infection: Nevertheless, THP-1-CD4R cells were able to sustain HIV-1 replication and spread of infection in culture (Figure 7) comparable to levels in primary human MDMs [26], suggesting that post-entry blocks are comparable in both instances, although we cannot exclude the possibility that the high levels of CD4 presumably trapped intracellularly in the THP-1-CD4R cells might impair to some extent viral spread by altering Env incorporation into progeny virions.