Such striking findings seem unlikely to be only true for a single polymorphism, but probably reflect a general principle governing susceptibility to TB
July 15, 2021
Such striking findings seem unlikely to be only true for a single polymorphism, but probably reflect a general principle governing susceptibility to TB. shortly after contamination and confer protection before regulatory networks are allowed to develop. Early studies using vaccines that elicit lung resident T cells by targeting the lung mucosa have been encouraging, but many questions remain. Due to the fundamental nature of these questions, and the need to understand and manipulate the early events in the lung after aerosol contamination, only coordinated methods that utilize tractable animal models to inform human TB vaccine trials will move the field towards its goal. Bacille Calmette-Guerin (BCG), TB remains a massive international health emergency, with ~ 9 million new cases of active disease and over a million deaths annually . In response to the urgent need for a new and effective TB vaccine, at least 15 candidates have entered clinical trials . Although these candidates differ in their formulations, they share a systemic route of administration and a common goal of boosting the number of Pipequaline IFN–producing T cells realizing immunodominant Mtb antigens . The first of these candidates, a Modified Vaccinia Ankara vector expressing Mtb antigen 85A (MVA85A), recently completed an efficacy trial in which it was used to boost infants previously immunized with BCG . Despite the fact that MVA85A significantly amplified the Mtb-specific T cell response, it provided no protection beyond the very limited immunity conferred by BCG alone. These disappointing results, together with Pipequaline years of research in animal models in which vaccine candidates have conferred marginal levels of protection, have profoundly impacted the TB field. There is general consensus that devising an effective TB vaccine will require new methods. However, since the correlates of protective immunity are unknown, there is little agreement on the best path forward [3, 5-13]. TB is usually a complex contamination, unlike any for which an effective vaccine has been developed. (Mtb), the causative agent of TB, is usually a slow growing bacterium with a lung portal Pipequaline of access that manipulates the host response to delay the onset of adaptive immunity. This delay is usually widely thought to be Mtbs primary niche-establishing strategy, and represents a critical bottleneck to its control, and possibly to its eradication by adaptive immunity [14, 15]. In this review, we discuss recent work that provides insights into mechanisms that regulate adaptive immunity to Mtb. In particular, we discuss why the T cell response to Mtb is usually slow to develop, and possible reasons why late-arriving T cells may be restricted in their ability to mediate protection. We frame our conversation in the context of the ongoing argument regarding strategies for developing an effective TB vaccine, as some have suggested that T cell based approaches be replaced by other strategies [5, 8]. However, in light of new understanding of T cell regulation during TB, we contend that our best hope for an effective vaccine is usually to elicit Mtb-specific T cells that are long-lived and reside in, or rapidly home to, the airways and lung parenchyma. We outline gaps in current knowledge that restrict progress towards such a vaccine. Given the fundamental nature of these knowledge gaps and the central importance of local immune responses in the lung, we argue that only a coordinated approach that includes animal and human studies can move the field forward. 2. Regulation of adaptive immunity against Mst1 Mtb 2.1 Importance of T cell mediated immunity CD4 T cells, especially Th1 cells producing IFN-, are critical for adaptive immunity against TB in both mice and humans . Mice lacking CD4 T cells, IFN-, IL-12 signaling (a pathway required for Th1 development), or T-bet (a transcription factor requisite for Th1s) are profoundly susceptible to Mtb contamination . Likewise, humans with genetic deficiencies in IFN- or IL-12 signaling , as well as HIV-infected individuals depleted of CD4 T cells , are severely restricted in their ability to contain mycobacterial infections, including TB. CD8 T cells can help control Mtb by both perforin-mediated cytolysis of infected macrophages and direct killing of Mtb [18, 19], and have been shown to be critical for BCG-induced immunity in a nonhuman primate model of TB . 2.2 The delayed T cell response to Mtb infection Mtb control requires CD4 T cells to interact directly with infected cells presenting Mtb antigens , a requirement that also seems likely.