Given sex differences in viral reservoir dynamics, the role of oestrogen in maintaining viral latency and subtle immunological differences between women and men, biological sex is likely to be a crucial factor affecting the success of strategies working towards the remission or cure of HIV, Dr Eileen Scully of the Johns Hopkins University School of Medicine said in a plenary presentation to the recent Conference on Retroviruses and Opportunistic Infections (CROI 2020).
Although half of all new HIV infections occur in women and girls, enrolment of both cisgender and transgender women in clinical trials and basic research studies has been limited. If an HIV cure is going to work for all people living with HIV, it is crucial that more women are involved in research studies towards a cure.
A range of factors contribute to sex-based differences in immune response, including anatomical differences, the microbiome, genetics, immune cell phenotypes and epigenetics. Data show that HIV transcription and residual viraemia (the viral load on fully suppressive treatment) are lower in women; that women have lower levels of replication-competent virus; and that viral rebound (the rise of the viral load to above the level where standard tests can detect it) takes longer in women on average when treatment is interrupted in a research study.
Scully stressed that such differences are not a problem for research, but can be a source of discovery. Just as the identification and study of unique individuals who can control HIV without medication has advanced our knowledge, understanding sex differences may generate new insights that contribute to the development of a cure.
Moreover, some curative strategies are focused on host factors (characteristics of the person who has HIV), rather than viral factors. They may involve activating the cell’s own mechanisms, using agents such as toll-like receptor agonists and immune checkpoint inhibitors, and directing immune responses against them, in so-called 'kick and kill’ approaches.
“To optimise these interventions we have to work to understand the underlying drivers of individual variation, including sex,” she said. For Scully, assessing the impact of sex is “simply a matter of scientific rigour.”
Scully also presented results of the first ever HIV cure-related study to be conducted exclusively in women (see A study exclusively in women below).
Women’s participation in cure studies
The participation of women in cure-related studies remains limited. A session at a pre-conference Community Cure Workshop highlighted women’s motivations and concerns about taking part in cure studies. Dr Liz Barr, a community representative to the AIDS Clinical Trials Group (ACTG), reported on a survey of cure-related trials and observational studies she ran in 2019. Of 133 research groups that were approached, 65 responded, but only 31 shared data on enrolment by sex.
Just 17% of cure-study participants were female. As most studies are at an early stage (phase I) with a limited number of participants (median 12), the number of female participants in each individual study is minuscule (median one participant, meaning that half of studies have no female participants). This makes it impossible for most investigators to meaningfully analyse sex differences amongst their own participants, and suggests the need for research groups to pool data.
Barr found that three-quarters of studies had no target – formal or informal – for recruitment by sex, with just 6% of studies surveyed (four studies) having a formal target.
In relation to other under-served groups, the participation of transgender people and those over the age of 50 was also poor (1.4% and 6.7% respectively), whereas black and Latino people were better represented (32% and 12% respectively).
Women may have different priorities and concerns about taking part in cure-related studies, according to another survey presented at the community workshop. Dr Karine Dubé of the University of North Carolina surveyed 272 people living with HIV in the United States, 35% of whom were cisgender women.
Participants were asked about factors that would increase their willingness to take part in an HIV cure-related study. For women, the top two were “feeling good about helping other people with HIV” and “feeling good about contributing to HIV cure research”, with the first of these altruistic motivations more frequently cited by women than men.
Other important motivators included “hoping that my HIV disease will improve”, “getting special knowledge about HIV and my health”, “having regular access to a study nurse” and “being compensated for taking part”. Each of these was cited by seven in ten women or more, and significantly more frequently than by men.
"Many potential participants greatly appreciated having a study that was focused on women."
Asked to consider strategies that might achieve remission of HIV, but which would have various inconveniences or disadvantages, women appeared less willing than men to accept clinical risks for the sake of no longer needing to take daily pills. Women were more concerned about strategies that involved pain, changes in appearance (such as a rash or weight gain), a temporary increase in side effects, a small long-term risk of cancer, no improvement in quality of life, or no increase in life expectancy. They were less willing to stop their antiretroviral therapy (ART) in order to find out whether the remission strategy was effective. On the other hand, women were more ready than men to accept medical visits every two weeks.
Offered a choice between different therapeutic options, relatively few people chose continuing with daily ART (11% of women and 8% of men), with many preferring a long-acting injectable/implant that delivers the HIV medication we already have (61% of women and 54% of men), while men were more ready to try an experimental, long-lasting remission strategy (16% of women and 29% of men).
A study exclusively in women
At the main conference, Dr Scully presented results from the first-ever HIV cure study to be exclusively conducted in women. Key to the rationale of the Moxie study (also known as ACTG A5366) are data suggesting that oestrogen (the primary female sex hormone) may contribute to lower levels of HIV transcription in women. For example, as women progress through the menopause, reduced levels of oestrogen are associated with increased HIV transcription activity. An estrogen receptor (ESR1) has been identified as a key cellular factor that regulates maintenance (or reversal) of the latent viral reservoir.
"Understanding sex differences may generate new insights that contribute to the development of a cure."
This poses a problem for ‘kick and kill’ approaches to cure in which latency reversal agents reactivate latent HIV within CD4 cells, in order to allow other drugs and the immune system to attack the virally infected minority of cells. The effectiveness of these latency reversal agents may be limited in women by the presence of oestrogen.
The hypothesis of the study was that treatment with the selective oestrogen receptor modulator tamoxifen (often used against breast cancer) would enhance the ability of the latency reversal agent vorinostat to reactivate HIV in the reservoir and induce HIV transcription (genetic activity). Study participants were post-menopausal women who were virally suppressed on ART. They were randomised to take vorinostat with or without a preceding course of tamoxifen. The study did not involve an analytical treatment interruption.
While the study did not show tamoxifen to enhance vorinostat, there were no safety issues, and perhaps the study’s greatest lesson is that women can be recruited to cure-related studies. The 31 participants were recruited quickly, and without difficulty, from study sites across the United States. They had a median age of 57, were 58% black and had been on ART for a median of 7.5 years.
The fact that the study was specifically for women made recruitment easier, Scully told aidsmap.com. Firstly, many potential participants greatly appreciated having a study that was focused on women. Secondly, staff at study sites were obliged to focus their recruitment efforts on a new group of potential participants, instead of relying on established recruitment approaches and existing pools of potential volunteers (who are overwhelmingly male). Scully believes that investigators should set targets for enrolment for both sex and gender, with incentives for study sites to meet those targets.
“The number one reason listed for participating in this study was altruistic,” Kate Starr, community representative on the study, told us. “That speaks volumes as to what these women value. They want to feel a part of a community and to help others.”
Illustrating this were responses to a survey that Dr Karine Dubé conducted as women ended the nine-week study. All but one respondent said they would recommend participation to other women:
“Be part of something greater than self.”
“The only way we can find a cure is for us to participate in studies and this was very easy.”
“Because when you join you learn so many things that can help with having HIV."
Four in five women said they had personally benefitted from taking part, citing the satisfaction of “helping science move along”, increased knowledge, close clinical monitoring and financial compensation.
Basic science and social support
Moxie is unlikely to be the last women-only study. At the pre-conference workshop, Dr Krista Dong of the Ragon Institute outlined plans for a study with young women who seroconverted whilst in the FRESH cohort in the hyper-endemic region of KwaZulu-Natal, South Africa. FRESH is already a remarkable study that provides a model for how basic science research can be combined with a social support programme.
The FRESH (Females Rising through Education, Support, and Health) cohort is made up of young, socioeconomically disadvantaged women at high risk of HIV. The scientific aim is to diagnose acute (very early) HIV infection in young women, allowing the investigation of the earliest immunological and virological events after HIV infection in order to inform vaccine and cure research.
"The aim is to diagnose acute HIV infection in young women, allowing the investigation of the earliest immunological and virological events after infection."
So as to identify women as soon after HIV infection as possible, the participants are asked to attend twice weekly and be tested for HIV RNA. So as to make this attendance valuable for the women themselves, Dong and colleagues developed a social programme focused on life-skills and job-skills needed to enter and succeed in the workforce, with training delivered at the time of the study visit. Topics covered include women's health, HIV prevention, gender-based violence, relationships, stress management, self-esteem, and communication.
In the past seven years, 2168 women have taken part in FRESH, of whom 89 were diagnosed with acute HIV (mostly diagnosed in Fiebig stage 1, a median of four days after their previous negative test). Since 2015, those with acute infection have been immediately offered four-drug ART, with the aim of reducing the size of the reservoir.
Now women who seroconverted in FRESH will be invited to take part in a clinical trial that combines a latency reversal agent, vesatolimod, with two broadly neutralising antibodies (bNAbs). Previous analysis suggests that the two bNAbs selected (CAP256 and VRC07) are likely to be especially potent in this population.
Eligible participants will have started ART in acute infection and will have been virally suppressed for at least a year. For the first ten weeks, participants will continue to take their ART alongside vesatolimod and two bNAbs. They will then stop their ART and continue the new agents for a further ten weeks, before stopping all interventions at week 20. The study’s primary endpoints are safety and tolerability, but time to viral rebound (and restart of ART) will also be assessed.
Scully EP. Sex differences in HIV. Conference on Retroviruses and Opportunistic Infections, abstract 63, March 2020.
Barr L. Sex Differences in HIV Cure Research & Status of Women’s Participation in Current Cure-Related Studies. Pre-CROI Community HIV Cure Research Workshop, March 2020.
Dubé K et al. Women’s Involvement in HIV Cure-Related Research – Empirical Data, Unresolved Challenges and Opportunities for the Future. Pre-CROI Community HIV Cure Research Workshop, March 2020.
Scully EP et al. Effect of Tamoxifen on Vorinostat-induced HIV RNA Expression in Women on ART (ACTG A5366): The MOXIE Trial. Conference on Retroviruses and Opportunistic Infections, abstract 333, March 2020.
Dong K. The FRESH Cohort, South Africa. Pre-CROI Community HIV Cure Research Workshop, March 2020.