Since the non-replicating PV constructs could not be assessed in the primary target cells the recent development of molecularly cloned constructs in a Renilla replication competent backbone is certainly a step forward in the development of a standardized PBMC based neutralization assay to assess neutralization in primary cells [31, 32] . It remains elusive whether the HJ16, HGN194 and HK20 mAbs would have been obtained from other patients. HK20 like Abs have been detected through ELISA and although the neutralizing capacity of this fraction was not shown it still provides proof that a significant number of HIV-1 infected patients have responded to the gp41-HR1 region which is only briefly exposed [2, 3] .