To confirm that CXCL12-resistant (RES) HIV variants are present at an advanced stage of infection, we next measured the effects of CXCL12 on CXCR4-using, recombinant viral populations generated from plasma of nine late diagnosed individuals with CD4TL count < 200/μl (Fig 1C and S3 Table). Here, CXCL12 is linked to infection.