People infected with HIV who are taking cART and have low viral load levels may still have reservoirs of HIV remaining in their body. BMS-936559 is a drug that has been studied in previous clinical trials to treat various types of cancer. The purpose of this study is to evaluate the safety, PK, and immunotherapeutic activity of a single dose of BMS-936559 (administered by an IV infusion) in HIV-infected people who are receiving cART and who have viral loads below the limit of detection. Researchers will also evaluate whether BMS-936559 can reduce hidden reservoirs of HIV.