ERVW-1 and infection: Upon infection of PBMCs with R5-tropic HIV-1NL4-3, which is isogenic to its X4-tropic counterpart, except the 005pf135 V3 loop region in Env [58], neither wt nor 3xPTAPPA mutant revealed any differences in the replication capacity of HIV-1 or any response to insulin treatment (Fig 11C), indicating that multiplication of PTAPPA per se or insulin treatment has no unspecific negative impact on HIV-1, since it only occurs in X4-tropic virus replication.