Identification of mycobacterial ribosomal proteins as targets for CD4+ T cells that enhance protective immunity in tuberculosis

Mycobacterium tuberculosis remains a threat to global health, and a more efficacious vaccine is needed to prevent disease caused by Mtb. We previously reported that the mycobacterial ribosome is a major target of CD4 + T cells in mice immunized with a genetically modified M. smegmatis strain (IKEPLUS), but not in mice immunized with M bovis BCG. Two specific ribosomal proteins, RplJ and RpsA, were identified as cross-reactive targets of Mtb, but the breadth of the CD4 + T cell response to Mtb ribosomes was not determined. In the current study, a library of Mtb ribosomal proteins and in silico predicted peptide libraries were used to screen CD4 + T cell responses in IKEPLUS immunized mice. This identified 24 out of 57 Mtb ribosomal proteins distributed over both large and small ribosome subunits as specific CD4 + T cell targets. Although BCG did not induce detectable responses against ribosomal proteins or peptide epitopes, the Mtb ribosomal protein RplJ produced a robust and multifunctional Th1-like CD4 + T cell population when administered as a booster vaccine to previously BCG primed mice. Boosting of BCG primed immunity with Mtb RplJ protein led to significantly reduced lung pathology as compared to BCG immunized animals, and reductions in the bacterial burden of mediastinal lymph node compared to naive and standard BCG vaccinated mice. These results identify the mycobacterial ribosome as a potential source of cryptic or subdominant antigenic targets of protective CD4 + T cell responses, and suggest that supplementing BCG with ribosomal antigens may enhance protective vaccination against Mtb.