Gilead's Biannual HIV Prevention Shot Succeeds, Trial Stopped Early

Gilead Sciences recently made a significant announcement regarding its HIV prevention efforts. The company disclosed that it has halted the Phase III PURPOSE 1 trial for its new HIV preventive treatment, lenacapavir, ahead of schedule due to its outstanding efficacy. The trial demonstrated that lenacapavir, administered as a biannual injection, was 100% effective in preventing HIV infection among women. This news led to a substantial rise in Gilead's stock price, adding $6.6 billion to its market value.

The PURPOSE 1 trial is part of Gilead's broader PURPOSE program, which includes five separate studies aimed at preventing HIV worldwide. This particular study involved over 5300 participants, specifically women and adolescent girls aged between 16 and 25, from South Africa and Uganda. Participants were divided into three groups: one receiving the biannual lenacapavir injection, another taking Gilead's daily oral drug Descovy, and a third group on daily Truvada tablets.

Lenacapavir's efficacy was contrasted with the rate of HIV infection in the study's background population and with Truvada, a well-known daily oral HIV prevention medication. The results were striking. Among the 2134 women who received lenacapavir, none contracted HIV. In contrast, 16 out of the 1068 women taking daily Truvada pills did become infected. The infection rate for lenacapavir was significantly lower than the background rate of 2.41 infections per 100 person-years and also surpassed Truvada’s rate of 1.69 infections per 100 person-years.

Moreover, Descovy, another Gilead product, did not perform as well as lenacapavir in the study. Of the 2136 women taking Descovy, 39 contracted HIV, which corresponds to an infection rate of 2.02 per 100 person-years. This rate was not substantially better than the background HIV infection rate and was similar to that of Truvada.

The decision to terminate the blinded phase of PURPOSE 1 was supported by the study's independent data monitoring committee (DMC). The DMC recommended offering open-label lenacapavir to all participants based on the interim analysis. The drug was generally well-tolerated with no significant new safety concerns identified, and detailed findings will be disclosed at a forthcoming conference.

Industry experts have expressed optimism about the market potential of lenacapavir. According to Brian Abrahams from RBC Capital Markets, there is a high level of interest in a twice-yearly injectable HIV prevention method among individuals at higher risk of infection. Abrahams projected that lenacapavir could significantly expand the market and generate sales exceeding $1.7 billion annually in the future.

Looking ahead, Gilead is anticipating results from PURPOSE 2, another crucial trial that assesses lenacapavir for PrEP in men who have sex with men, transgender individuals, and gender non-binary people. Participants for this study are being recruited from various countries, including Argentina, Brazil, Mexico, Peru, South Africa, Thailand, and the United States. The findings from PURPOSE 2 are expected by late 2024 or early 2025. Together with PURPOSE 1 results, they will be instrumental in Gilead's pursuit of regulatory approval for lenacapavir as a PrEP option.

In summary, Gilead Sciences' lenacapavir has shown extraordinary promise as a biannual injectable for HIV prevention, particularly among women, marking a significant milestone in global HIV prevention efforts.