Harnessing B cells for TB vaccine development to improve therapy of TB and TB-HIV coinfection

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Abstract Current tuberculosis (TB) control in the presence or absence of human immunodeficiency virus (HIV) infection is suboptimal: Bacillus Calmette-Guérin (BCG), the sole TB vaccine in clinical use, provides only limited protection during childhood and multi-drug chemotherapy faces challenges due to the alarming spread of drug resistance. An integrated approach combining chemotherapy with a therapeutic vaccine given after exposure to Mycobacterium tuberculosis (Mtb) could be a way forward. TB vaccine research mostly focused on prophylactic candidates aiming to prevent infection. Therapeutic TB vaccines with novel mechanisms of action are needed (i) to complement existing chemotherapy and prevent relapse thereafter, and (ii) to cure latent TB infection (LTBI) or prevent reactivation. T lymphocytes are critical for the control of TB infection and the specific T cell response elicited by a vaccine has been used as a key correlate of immunogenicity. In contrast, B cells are understudied in all areas of TB research. Using a deep immunophenotyping approach, our preliminary data in mice suggest that TB infection leads to dramatic changes in the landscape of B cell subpopulations. We identified a novel B cell subset with marginal zone (MZ) phenotype that was activated, had a memory phenotype and expressed receptors recognizing the human cytokines A Proliferation-Inducing Ligand, APRIL, and B cell Activating Factor, BAFF, critical for B cell development and survival. Functional studies indicated that murine MZ B cells contributed to Mtb containment in mice. Surprisingly, these B cells expressed a panel of Th1 cytokines, well studied in T cells, suggesting a possible role in the first line of defense against TB infection. We found that MZ B cells were depleted in blood of TB patients and TB/HIV coinfected people. Our hypothesis is that MZ B cells can be restored by antitubercular therapy and harnessed for TB vaccine development. To test this, we genetically engineered BCG to express the human cytokines APRIL and BAFF that stimulate development and longevity of BAFF receptor- and APRIL receptor-expressing B cells, including MZ B cells. We will determine the safety, immunogenicity and prophylactic efficacy in mice. The therapeutic efficacy will be evaluated in two novel innovative mouse models that allow us to determine the capacity of cytokine expression in BCG strains to prevent relapse after drug treatment and to reduce the reactivation frequency of paucibacillary TB mimicking aspect of LTBI in humans. We will determine the frequency of MZ B cells in peripheral blood mononuclear cells (PBMC) from people having LTBI and TB, across HIV status, including antitubercular and antiretroviral therapy. We will stimulate PBMC of the same cohorts with cytokine-expressing BCG strains to study the immunological consequences and to demonstrate, in principle, the feasibility of these vaccines during therapy of TB, HIV and TB/HIV coinfection. We will monitor the global landscapes of T cells and B cells by high parameter flow cytometry to define immunological correlates of TB infection and vaccine protection. Our proposal will determine whether B cells can be harnessed by cytokine-secreting B cell-targeting BCG vaccines for TB vaccine development.