Eleven HIV-1 subtype A, B and C viruses including five primary isolates (MW965, DJ263, SF162, JR-CSF and 92RW009) and six pseudotyped viruses (HIV-001428, ZM109F.PB4, ZM233M.PB6, Du156.12, JRFL and RHPA4259.7) were used for this study. All the primary viruses and envelope clones were obtained from the NIH, ARRRP. The HIV-1 isolates were expanded by only one cycle of growth on phytohemagglutinin (PHA) and interleukin-2 (IL-2)-stimulated PBMCs, as described previously [45] to avoid alterations in env sequences due to multiple rounds of expansion. Pseudotyped viruses were produced by co-transfection of the rev/env expression plasmid and an env-deficient HIV-1 backbone vector (pSG3ΔEnv) into exponentially dividing 293 T cells (ATCC; catalog no. 11268), in 6-well tissue culture plates (Corning Inc) using calcium phosphate (Promega Inc) method. Pseudovirus-containing culture supernatants were harvested 48 hours post transfection filtered (0.45 μm pore size) and stored at −80°C in 1 ml aliquots. The 50% tissue culture infectious dose (TCID50) was determined in TZM-bl cells.