Mycobacterium tuberculosis (Mtb) infects one-third of the global population. A more efficacious vaccine is urgently needed for control and prevention of disease. We recently reported a genetically modified strain of M. smegmatis, IKEPLUS, which is a promising vaccine candidate due to its ability to generate an unprecedented level of bactericidal immunity against Mtb in mice. Since protective immunity induced by IKEPLUS is dependent on antigen-specific CD4+ T cell memory, we hypothesized that specificity of the CD4+ T cell response was critical for protection. To determine CD4+ T cell specificity directly, we generated MHC class II (I-Ab) restricted T cell hybridomas from IKEPLUS-immunized mice. Screening of T cell hybridomas against anion exchange-fractionated IKEPLUS and Mtb proteins provided evidence for multiple specific targets, one of which was identified as the AtpA protein, a product of the Mtb Rv1308 gene. In a complementary approach, using in vitro assays of IFNγ production by splenocytes from IKEPLUS-immunized mice, we identified an immunogenic peptide within the Mtb RplJ protein encoded by the Rv0651 gene. Our results demonstrate the CD4+ T cell response in IKEPLUS-immunized mice has multiple targets, among which AtpA and RplJ represent novel specificities for protective responses against Mtb. Further studies to more fully define the range of specificities of CD4+ T cells in IKEPLUS-immunized mice should help to inform the design of effective vaccines against Mtb.
- Copyright © 2013 by The American Association of Immunologists, Inc.