7820 Immune system adaptation during gender-affirming testosterone treatment

Abstract Disclosure: T. Lakshmikanth: None. C. Consiglio: None. F. Sardh: None. R. Forlin: None. J. Wang: None. Z. Tan: None. H. Barencilla: None. L. Rodriguez: None. J. Sugrue: None. P. Noori: None. M. Ivanchenko: None. L. Piñero Páez: None. L. Gonzalez: None. C. Habimana Mugabo: None. A. Johnsson: None. H. Ryberg: None. Å. Hallgren: None. C. Pou: None. Y. Chen: None. J. Mikeš: None. A. James: None. P.M. Dahlqvist: None. J. Wahlberg Hughes: None. A. Hagelin: None. M. Holmberg: None. M. Degerblad: None. M. Isaksson: None. D. Duffy: None. O. Kampe: None. N. Landegren: None. P. Brodin: None. Infectious, inflammatory and autoimmune conditions present differently in males and females. Following SARS-CoV-2 infection, male sex is associated with increased risk of death, while female sex is associated with increased risk of the postinfectious disorder, long COVID. Similar trends are seen in other infections. Female immune responses to vaccines are typically stronger, and adverse reactions are more frequent, like most autoimmune diseases. Immunological sex-differences stem from genetic, hormonal and behavioural factors but their relative importance is poorly understood. To understand the consequences of changing sex-hormones in vivo, we performed longitudinal, systems-level analyses in 22 adults, assigned female at birth, and undergoing gender-affirming testosterone treatment (trans-men). We find that sex hormones modulate a cross-regulation axis of type-I interferon (IFN-I) and TNFα in humans. This is mediated by a reduced frequency of plasmacytoid dendritic cells (pDC), and functional attenuation of IFN-I responses in both pDCs and monocytes. Conversely, testosterone potentiates monocyte responses to lipopolysaccharide (LPS) leading to increased TNFα, IL-6 and IL-15 production and downstream epigenetic opening of NFκB regulated genes and potentiation of IFNγ responses, primarily by NK cells. IFNγ in turn feeds back onto monocytes leading to upregulation of SLAMF7 and further enhanced TNFα responses by myeloid cells. These results are corroborated by sex-divergent responses in multiple public datasets and collectively illustrate the dynamic recalibration of human immune systems by sex hormones with implications for individuals undergoing gender-affirming hormone therapy, but also better understanding of divergent responses to infection, vaccines and self-antigens in cisgender individuals. Presentation: 6/2/2024