Central Memory CD4+ T Cells Are Responsible for the Recombinant Bacillus Calmette-Guérin ΔureC::hly Vaccine's Superior Protection Against Tuberculosis

Abstract

Bacillus Calmette-Guérin (BCG) has been used for vaccination against tuberculosis for nearly a century. Here, we analyze immunity induced by a live tuberculosis vaccine candidate, recombinant BCG ΔureC::hly vaccine (rBCG), with proven preclinical and clinical safety and immunogenicity. We pursue in-depth analysis of the endogenous mycobacteria-specific CD4+ T-cell population, comparing the more efficacious rBCG with canonical BCG to determine which T-cell memory responses are prerequisites for superior protection against tuberculosis. rBCG induced higher numbers and proportions of antigen-specific memory CD4+ T cells than BCG, with a CXCR5+CCR7+ phenotype and low expression of the effector transcription factors T-bet and Bcl-6. We found that the superior protection of rBCG, compared with BCG, correlated with higher proportions and numbers of these central memory T cells and of T follicular helper cells associated with specific antibody responses. Adoptive transfer of mycobacteria-specific central memory T cells validated their critical role in protection against pulmonary tuberculosis.

Persistent BCG bacilli perpetuate CD4 T effector memory and optimal protection against tuberculosis

“…At present, few reports directly identify an antigen-specific CD4 T CM cells induced in mice by BCG alone [19,22]; some describe T CM -like cells after clonal expansion induced by prime-boost vaccination, challenge or reinfection [14,21,53]. In humans, T CM may only appear after contraction of the BCG-specific T EM response [20].…”

“…The background responses of most assays in naïve mice (<0.05% CD4 T cells) may obscure such populations [57]. Indeed, recent studies have had to employ enrichment of tetramer + cells [58], to allow detection of rare T CM cells in BCG vaccinates [19,22]. Other in vitro expansion approaches, such as cultured ELISPOT [59] may also help to resolve this population.…”

“…Given its variable efficacy, it is of critical importance to understand the mechanisms underlying its protective capacity, if improved vaccines or vaccination strategies are to be progressed. The majority of these studies report BCG to induce a predominant CD4 T EM response, defined by CD62L lo expression, often associated with cytokine multifunctionality [9,16,18]; but few identify BCG-specific CD62L hi or CCR7 hi CD4 T CM responses [19][20][21][22]. We recently reported CD4 T EM cells to persist 18 months following BCG immunization [9], and consistently, observe no defined contraction of immune responses following immunization.…”

A novel multivalent tuberculosis vaccine confers protection in a mouse model of tuberculosis

“…Indeed, even protection conferred by the recombinant BCG ΔureChly + vaccine, initially designed to induce CD8 + T cells, 20 was later thought to be mediated by CD4 + T cells. 21,22 The molecular adjuvant IL-33 has previously been shown to boost cytokine responses by both CD8 + and CD4 + T cells in a pVax1-based immunization regimen using Mtb, LCMV and HIV antigens. 11,14 Although administering RSQ-15 with mtrIL-33 alone had no significant effect on vaccine immunogenicity, co-administration of RSQ-15 + mtrIL-33 along with a plasmid expressing Ag85B greatly enhanced cytokine production in the lungs.…”

Estudo comparativo de promotores de micobactérias utilizando GFP como gene repórter para o desenvolvimento de vacinas de BCG recombinante.

“…Funcionando como um 'sistema de entrega' de produtos gênicos heterólogos, este seria capaz de induzir respostas imunológicas de longa duração, e muitas vezes protetoras . Desde que esta proposta foi lançada, vários antígenos já foram clonados com sucesso em BCG, tais como antígenos virais, como em pesquisas contra o HIV (ALDOVINI, YOUNG, 1991;LAGRANDERIE et al, 1998;VENKATASWAMY et al, 2014); bacterianos, como por exemplo contra a Bordetella pertusis (NASCIMENTO et al, 2000), e parasitários, como contra a Leishmania major (ABDELHAK et al (1995) e o Shistosoma mansoni (VARALDO et al, 2004), ou até mesmo em vacinas melhoradas de BCG contra a tuberculose (DA COSTA et al, 2014;HOFT et al, 2008;VOGELZANG et al; Uma abordagem interessante é clonar uma série de promotores diferentes num mesmo vetor de expressão, e relacionar sua atividade com a resposta imunológica produzida (DHAR et al, 2000(DHAR et al, , 2003. Desse modo, a escolha do promotor é fundamentada em sua aplicação funcional, variando de acordo com a patologia e o sistema de defesa do hospedeiro.…”