Staphylococcus aureus specific lung resident memory CD4 Th1 cells attenuate the severity of influenza virus induced secondary bacterial pneumonia.

Staphylococcus aureus is a major cause of severe pulmonary infections. The evolution of multi-drug resistant strains limits antibiotic treatment options. To date, all candidate vaccines tested have failed, highlighting the need for an increased understanding of the immunological requirements for effective S. aureus immunity. Using an S. aureus strain engineered to express a trackable CD4 T cell epitope and a murine model of S. aureus pneumonia, we show strategies that lodge Th1 polarised bacterium specific CD4 tissue resident memory T cells (Trm) in the lung can significantly attenuate the severity of S. aureus pneumonia. This contrasts natural infection of mice that fails to lodge CD4 Trm cells along the respiratory tract or provide protection against re-infection, despite initially generating Th17 bacterium specific CD4 T cell responses. Interestingly, lack of CD4 Trm formation after natural infection in mice appears to be reflected in humans, where the frequency of S. aureus reactive CD4 Trm cells in lung tissue is also low. Our findings reveal the protective capacity of S. aureus specific respiratory tract CD4 Th1 polarised Trm cells and highlight the potential for targeting these cells in vaccines that aim to prevent the development of S. aureus pneumonia.