CD4 and infection: Even though PBMCs are more relevant in generating recombinants similar in HIV patients, based on our previous experience, the infection efficiency of HIV in PBMCs is much lower than in U87.CD4.CCR5 cell line resulting in very low levels of recombinant genomes, and the sites of intersubtype recombination was similar in U87 cells and PBMCs [1, 2, 30, 31].