GUT MICROBIOTA AND OTHER FACTORS ASSOCIATED WITH INCREASED T CELL REGULATION IN HIV-EXPOSED UNINFECTED INFANTS

Michael Johnson ¹ Sarah Lazarus ^1,2 Ashlynn Bennett ¹ Adriana Tovar-Salazar ^1,3 Charles E Robertson ⁴ Jennifer Kofonow ⁴ Shaobing Li ¹ Bruce Mccollister ^4,5 Marta C Nunes ^6,7 Shabir Madhi ^6,8 Daniel Frank ⁴ Adriana Weinberg ^1,4,8*

• ¹ Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
• ² University of Wisconsin School of Medicine, Madison, United States
• ³ Bristol Myers Squibb (United States), New York, New York, United States
• ⁴ Department of Medicine University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
• ⁵ Department of Pathology, University of Colorado Anschutz Medical Campus, Aurora, United States
• ⁶ South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit and Department of Science and Technology/National Research Foundation South African Research Chair Initiative in Vaccine Preventable Diseases, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
• ⁷ Center of Excellence in Respiratory Pathogens (CERP), Hospices Civils de Lyon and Centre International de Recherche en Infectiologie (CIRI), Équipe Santé publique, épidémiologie et écologie évolutive des maladies infectieuses (PHE3ID), Inserm U1111, CNRS UMR5308, ENS de Lyon, Université Claude Bernard Lyon 1, Lyon, Rhône-Alpes, France
• ⁸ African Leadership in Vaccinology Expertise, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa

Infants exposed to HIV and uninfected (HEUs) are at higher risk of infectious morbidity than HIV-unexposed uninfected infants (HUUs). Multiple immune defects of unknown origin were observed in HEUs. We hypothesized that HEUs have more regulatory and inhibitory checkpointexpressing T cells (Treg, Tici) than HUUs, which may dampen their immune defenses against pathogens. To address the first part of this hypothesis, we compared 25 Treg/Tici subsets between HEUs and HUUs during the first 62 weeks of life and investigated the factors that may affect their frequencies. At birth, 3 Treg subsets, including the prototypic CD4+FOXP3+ and CD4+FOXP3+CD25+, had higher frequencies in 123 HEUs than in 117 HUUs, and 3 subsets had higher frequencies in HUUs. At 28 and 62 weeks of age, 5 Treg/Tici subsets had higher proportions in HEUs than HUUs. The frequencies of the Treg/Tici subsets that diverged between HEUs and HUUs at birth correlated with differential relative abundances of bacterial taxa in the maternal gut microbiome. The Treg/Tici subsets with significantly different frequencies at subsequent visits correlated with the concurrent composition of the infant gut microbiome. In vitro, treatment of HUU peripheral blood mononuclear cells (PBMC) with bacterial taxa most abundant in HEUs expanded Treg/Tici subsets with higher frequencies in HEUs than HUUs, recapitulating the in vivo correlations. Conversely, in vitro treatment of HEU PBMC did not increase Treg/Tici frequencies. Other factors that correlated with increased Treg/Tici frequencies were low maternal CD4+ T cells in HEUs at birth and male sex in the HUUs at 28 weeks of life. We conclude that maternal and infant gut dysbiosis are central to the increase in Treg/Tici in HEUs and may be targeted by mitigating interventions.