Safety Study of Ibalizumab Subcutaneous Injection in Healthy Volunteers

The study is a phase 1, randomized, double-blinded, placebo-controlled, sequential
dose-escalation and safety study of ibalizumab in at-risk HIV-negative volunteers. The study
involves the administration of four total injections of ibalizumab or matching placebo in
each volunteer, given once every week, in one of three groups as defined below:

Group 1: 120 mg sc weekly x 4 weeks, randomized 6:2 with placebo Group 2: 240 mg sc weekly
x 4 weeks, randomized 6:2 with placebo Group 3: 480 mg sc weekly x 4 weeks, randomized 6:2
with placebo

Volunteers will be screened up to 42 days prior to enrollment and first drug administration,
and will be followed for 26 weeks after the final injection.

All subjects will be expected to participate in two (2) intense PK sampling periods with a
duration of 7 days for the first period and 14 days for the second period. During these
periods (following Day 0 and following Week 3) subjects will have daily serum concentration
and other investigational pharmacokinetic assessments.

All volunteers will be encouraged to participate in an optional collection of genital
secretions (semen or vaginal wash) at Week 4.

An independent data safety monitoring board (DSMB) will review study data after four out of
eight at-risk HIV-negative volunteers in Group 1 (120 mg dose) have received all study drug
injections and completed 6 weeks of follow-up before approving escalation to Group 2 (240 mg
dose). The DSMB will also review all available study data from Groups 1, and 2 after four
out of eight volunteers in Group 2 have received all study drug injections and completed 6
weeks of follow-up before approving escalation to Group 3 (480 mg dose).