“…In an effort to understand the increasing prevalence of CRFs in particular regions of the world, many researchers initiated the study of the in vitro activity of isolated proteins (Nef, Vpu, Tat) or genomic regions (LTR) derived from CRFs, in comparison to the activity of the proteins/regions derived from the parental subtypes ( Woollard et al, 2014 , De Candia et al, 2013 , Turk et al, 2006 , Turk et al, 2009 ). Others went one step further and analyzed the ex vivo replicative fitness of CRFs ( Rubio et al, 2014 , Njai et al, 2006 ).…”