Functional, Antigen-Specific Stem Cell Memory (TSCM) CD4+ T Cells Are Induced by Human Mycobacterium tuberculosis Infection

Cheleka A. M. Mpande, One B. Dintwe, Munyaradzi Musvosvi, Simbarashe Mabwe, Nicole Bilek, Mark Hatherill, Elisa Nemes, Thomas J. Scriba, The SATVI Clinical Immunology Team, Cynthia Ontong, Elizabeth Filander, Fadia Alexander, Hadn Africa, Janelle Botes, Lebohang Makhethe, Lungisa Jaxa, Marcia Steyn, Noncedo Xoyana, Rachel Oelfose, Sindile Matiwane

Maintenance of long-lasting immunity is thought to depend on stem cell memory T cells (TSCM), which have superior self-renewing capacity, longevity and proliferative potential compared with central memory (TCM) or effector (TEFF) T cells. Our knowledge of TSCMderives primarily from studies of virus-specific CD8+TSCM. We aimed to determine if infection withMycobacterium tuberculosis(M. tb), the etiological agent of tuberculosis, generates antigen-specific CD4+TSCMand to characterize their functional ontology. We studied T cell responses to naturalM. tbinfection in a longitudinal adolescent cohort of recent QuantiFERON-TB Gold (QFT) converters and three cross-sectional QFT+adult cohorts; and to bacillus Calmette-Guerin (BCG) vaccination in infants.M. tband/or BCG-specific CD4 T cells were detected by flow cytometry using major histocompatibility complex class II tetramers bearing Ag85, CFP-10, or ESAT-6 peptides, or by intracellular cytokine staining. Transcriptomic analyses ofM. tb-specific tetramer+CD4+TSCM(CD45RA+CCR7+CD27+) were performed by microfluidic qRT-PCR, and functional and phenotypic characteristics were confirmed by measuring expression of chemokine receptors, cytotoxic molecules and cytokines using flow cytometry. M. tb -specific TSCMwere not detected in QFT-negative persons. After QFT conversion frequencies of TSCMincreased to measurable levels and remained detectable thereafter, suggesting that primaryM. tbinfection induces TSCMcells. Gene expression (GE) profiling of tetramer+TSCMshowed that these cells were distinct from bulk CD4+naïve T cells (TN) and shared features of bulk TSCMandM. tb-specific tetramer+TCMand TEFFcells. These TSCMwere predominantly CD95+and CXCR3+, markers typical of CD8+TSCM. Tetramer+TSCMexpressed significantly higher protein levels of CCR5, CCR6, CXCR3, granzyme A, granzyme K, and granulysin than bulk TNand TSCMcells.M. tb-specific TSCMwere also functional, producing IL-2, IFN-γ, and TNF-α upon antigen stimulation, and their frequencies correlated positively with long-term BCG-specific CD4+T cell proliferative potential after infant vaccination. Human infection withM. tbinduced distinct, antigen-specific CD4+TSCMcells endowed with effector functions, including expression of cytotoxic molecules and Th1 cytokines, and displayed chemokine receptor profiles consistent with memory Th1/17 cells. Induction of CD4+TSCMshould be considered for vaccination approaches that aim to generate long-lived memory T cells againstM. tb.