An Extension of Protocol PRO 140_CD01 Study

Inclusion Criteria: 1. Subjects who have completed 12 weeks of treatment in PRO 140\_CD01 study without experiencing virologic failure. 2. Both male and female patients and their partners of childbearing potential must agree to use appropriate birth control methods (birth control pills, barriers, or abstinence) throughout the study duration (excluding women who are not of childbearing potential and men who have been sterilized). Females of childbearing potential must have a negative urine pregnancy test prior to receiving the first dose of study drug. 3. Willing and able to participate in all aspects of the study, including use of SC medication, completion of subjective evaluations, attendance at scheduled clinic visits, and compliance with all protocol requirements as evidenced by providing written informed consent. Exclusion Criteria: 1. Not currently enrolled in PRO140\_CD01 Treatment Substitution Study 2. Any acquired immune deficiency syndrome (AIDS)-defining illness according to the 1993 Centers for Disease Control and Prevention (CDC) AIDS surveillance definition 3. Laboratory test values ≥ grade 4 DAIDS laboratory abnormality. 4. Females who are pregnant, lactating, or breastfeeding, or who plan to become pregnant during the study 5. Unexplained temperature \>38.5C (101.3F) for seven consecutive days within 14 days prior to the first study dose 6. Diagnosed with either substance dependence or substance abuse or any history of a concomitant condition (e.g., medical, psychologic, or psychiatric) that in the opinion of the primary care provider and/or site investigator would interfere with the subject's successful completion of the study requirements 7. Any other clinical condition that, in the Investigator's judgment, would potentially compromise study compliance or the ability to evaluate safety/efficacy