The following reagents were obtained through the AIDS Research and Reference Reagent Program, Division of AIDS, NIAID, NIH: TZM-bl (Cat.#8129) from Dr. John C. Kappes and Dr. Xiaoyun Wu, CEM.NKR-CCR5-Luc from Drs. John Moore and Catherine Splenlehauer (Cat.#5198), MAb α4β7 (Cat.#11718) from Dr. A.A. Ansari, MAb PG9 (Cat.#12149) from Dr. Larry Walker, MAb VRC01 (Cat.#12033) from Dr. John Mascola and bi-specific MAb CD3.8 (Cat.#12277) from Drs. Johnson Wong and Galit Alter. Here, CCR5 is linked to AIDS.