# IL-27 producers in a neonatal BCG vaccination model are a heterogenous population of myeloid cells that are diverse in phenotype and function

## TL;DR

This study explores how different types of myeloid cells produce IL-27 after neonatal BCG vaccination and how this affects immune responses.

## Contribution

The study identifies a heterogeneous group of myeloid cells that produce IL-27 following BCG vaccination and reveals their diverse roles in immune responses.

## Key findings

- BCG vaccination increases IL-27 production over time in neonatal mice.
- CD11b+ F4/80+ myeloid cells increase MHC class II expression in spleen and lung after vaccination.
- Subpopulations of IL-27 producers include macrophages with immunosuppressive traits like increased Mrc1 expression.

## Abstract

Tuberculosis (TB) is a serious public health concern in many regions of the world and the only approved vaccine to prevent TB is the live-attenuated BCG vaccine. Despite being widely used, the BCG vaccine fails to prevent pulmonary TB in adults. The BCG vaccine is administered during the neonatal period when levels of the immunosuppressive cytokine interleukin (IL)-27 are elevated, and previous studies have demonstrated that the source of IL-27 can impact downstream immune responses. We therefore sought to characterize the specific subpopulations of myeloid cells that produce IL-27 following BCG vaccination. To investigate this, we administered the BCG vaccine to neonatal IL-27p28eGFP mice that report IL-27 production. Our studies demonstrated that BCG vaccination steadily increased IL-27 production throughout the weeks post-vaccination. We also showed that a predominantly CD11b+ F4/80+ population of IL-27 producers increased MHC class II expression following BCG vaccination in both the spleen and the lung. However, producers of IL-27 in these tissues differ, with a population of CD11c+ MHC II+ cells emerging in the spleen and a subset of Ly6G/C+ MHC II+ emerging in the lung. 10x scMultiome analysis further validated the increase in MHC class II expression and demonstrated improved antigen presentation functionality following vaccination. The sequencing analysis also revealed subpopulations of IL-27 producers with immunosuppressive functions such as a population of macrophages with increased Mrc1 expression post-vaccination. Our findings suggest that IL-27 producers are a heterogenous population of myeloid cells that impact the development of protective immune responses induced by the BCG vaccine.