Media release

From: Springer Nature

1.  Immunology: Immune adaptations in female-to-male gender-affirming hormone treatment (N&V)

Immune responses in trans men (assigned female at birth) during gender-affirming hormone therapy become more like those of cisgender male individuals, reports a study in Nature this week. The analysis, which involves 23 trans men, highlights the role of sex hormones in the regulation of immunity. The findings have implications for the health of individuals undergoing gender-affirming hormone therapy as well as for improving understanding of differences in immune responses between cisgender individuals.

Immune responses differ between male and female individuals, owing to genetic, hormonal and behavioural factors, but the relative importance of these factors remains to be determined. The immunological consequences of marked changes in hormone levels experienced during female-to-male gender-affirming testosterone therapy are also poorly understood. Studying the effect of gender-affirming hormone therapy on immune responses offers an opportunity to establish the roles of sex hormones on immunity and improve care of this historically excluded and underserved patient population.

By profiling the immune system of 23 trans men, assigned female at birth, before and during gender-affirming testosterone treatment, Petter Brodin and colleagues uncover insights about the contribution of sex hormones to immune responses. Individuals were monitored just before starting treatment, then again at 3 months and 12 months following testosterone injections, administered once every 12 weeks. The authors observed a shift in the immune response to more closely resemble the responses of cisgender male individuals within 3 months of starting treatment.

The authors note that the study is limited by sample size. However, they propose that the findings could help to improve the health and wellbeing of trans men and avoid long-term adverse outcomes such as severe infections and inflammatory disorders, which are typical of individuals assigned male at birth and of individuals receiving testosterone therapy for clinical reasons. In addition, the findings may also help to explain differences in immune responses between cisgender male and female individuals, as well as changes in immune responses regulated by changes in sex hormones as humans age, such as during the menopause.