CXCR4 and infection: Our first report in RAG-hu mice showed a lack of CD4+ T cell loss in the blood through 24 weeks of infection with NLENG1-IRES, a reporter strain of HIV-1 that expresses GFP and places the nef gene under the control of an IRES element in the background of the CXCR4-tropic strain NL4-3 [87].