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Second, the anticipation of violence can lead to increased anxiety, fear, and depression. Given the sensationalized and speculative nature of many mass school shootings that has more recently fed the perception that schools are unsafe, arming teachers likely would heighten levels of anxiety and negatively affect a school's climate for teaching and learning.


Rather than arming school faculty or staff, NASRO recommends that sufficient federal, state and/or local funding be made available to place at least one carefully selected, specially trained school resource officer in every school in the nation. NASRO further recommends that large schools be provided more than one SRO.


Mucosa-associated invariant T (MAIT) cells represent a large innate-like evolutionarily conserved antimicrobial T-cell subset in humans. MAIT cells recognize microbial riboflavin metabolites from a range of microbes presented by MR1 molecules. MAIT cells are impaired in several chronic diseases including HIV-1 infection, where they show signs of exhaustion and decline numerically. Here, we examined the broader effector functions of MAIT cells in this context and strategies to rescue their functions. Residual MAIT cells from HIV-infected patients displayed aberrant baseline levels of cytolytic proteins, and failed to mobilize cytolytic molecules in response to bacterial antigen. In particular, the induction of granzyme B (GrzB) expression was profoundly defective. The functionally impaired MAIT cell population exhibited abnormal T-bet and Eomes expression patterns that correlated with the deficiency in cytotoxic capacity and cytokine production. Effective antiretroviral therapy (ART) did not fully restore these aberrations. Interestingly, IL-7 was capable of arming resting MAIT cells from healthy donors into cytotoxic GrzB+ effector T cells capable of killing bacteria-infected cells and producing high levels of pro-inflammatory cytokines in an MR1-dependent fashion. Furthermore, IL-7 treatment enhanced the sensitivity of MAIT cells to detect low levels of bacteria. In HIV-infected patients, plasma IL-7 levels were positively correlated with MAIT cell numbers and function, and IL-7 treatment in vitro significantly restored MAIT cell effector functions even in the absence of ART. These results indicate that the cytolytic capacity in MAIT cells is severely defective in HIV-1 infected patients, and that the broad-based functional defect in these cells is associated with deficiency in critical transcription factors. Furthermore, IL-7 induces the arming of effector functions and enhances the sensitivity of MAIT cells, and may be considered in immunotherapeutic approaches to restore MAIT cells.


The mucosa-associated invariant T (MAIT) cells recognize antigens that are byproducts of the riboflavin biosynthesis pathway shared by many microbes. These antigens are presented by the MHC class I-like MR1 molecules and trigger rapid activation of MAIT cells in an innate-like fashion with deployment of effector mechanisms including cytokine production and cytolysis. Here, we investigated the MAIT cell response to bacteria in humans infected with HIV-1, and possible means to restore functionality to these cells. MAIT cell dysfunction in HIV-infected patients included an inability to express components of the cytolytic effector machinery. Impairment of the MAIT cell population involved the loss of expression of the transcription factors T-bet and Eomes. Interestingly, IL-7 had strong effects on MAIT cells, including the antigen-independent arming of cytolytic function and enhanced sensitivity for low levels of bacteria. In HIV-infected patients, plasma IL-7 levels were positively associated with the size of the MAIT cell population, and IL-7 could rescue their function. These findings indicate that MAIT cell impairment in HIV-1 infection is broad-based, includes loss of critical transcription factors, and loss of cytolytic function. Furthermore, the data support the notion that IL-7 is a strong candidate for immunotherapy in diseases associated with MAIT cell loss.


IL-7 is a pleiotropic cytokine that has strong survival and homeostatic effects towards T cells, particularly the memory T cell populations with which MAIT cells show similarities (reviewed in [36]). IL-7 has attracted interest in the context of HIV-1 disease, and was proposed as a potential cytokine intervention therapy in treatment failure as well as in approaches to purge the viral reservoir (reviewed in [37]). Furthermore, IL-7 was recently shown by Tang et al. to enhance MAIT cell Th1/17 cytokine production in response to polyclonal stimulation [38]. In the present study, we investigate the cytolytic function of MAIT cells in the context of HIV-1 infection, the basis for dysfunction of MAIT cells in this disease, and possible approaches to rescue their function. Our findings indicate that arming of cytolytic capacity in MAIT cells is severely defective in HIV-1 infected patients, and that the broad-based functional defects in these cells are associated with deficiency in critical transcription factors. Furthermore, IL-7 induces the arming of effector functions and enhances the sensitivity of MAIT cells in healthy donors, and can partially reverse the functional and transcription factor defects in MAIT cells from HIV-1 infected patients. Thus, inclusion of IL-7 may be considered in immunotherapeutic approaches to restore MAIT cell numbers and function in conditions associated with loss and dysfunction of these cells.


IL-18 and IL-12 have been shown to stimulate MAIT cell effector function [19, 22, 23]. We therefore compared these cytokines with IL-7 in their capacity to arm MAIT cell effector function. In three HIV-uninfected donors, IL-7 was similar or superior to IL-18/IL-12 in arming and enhancing MAIT cell effector functions alone or following bacterial stimulation (S3A and S3B Fig). The exception to this pattern was IFNγ, as IL-12/IL-18 triggered direct activation of this effector function both alone and together with E. coli stimulus (S3A and S3B Fig). Furthermore and contrary to IL-7 treatment, IL-18/IL-12 seemed to enhance the decrease in MAIT cell numbers following bacterial stimulation (S3C Fig). This observation is in line with previous studies where IL-18 and IL-12 triggered direct effector responses and were implicated in MAIT cell loss [30, 39].


Next, we investigated the responses of MAIT cells in terms of GrzB arming and cytolytic potential following a 24 h bacterial stimulation (Fig 5B). All measured facets of MAIT cell cytotoxic potential examined were impaired in chronic HIV-1 infection, including reduction in the levels of MAIT cells expressing CD107a+GrzAlo (p = 0.0006), CD107a+GrzB+ (p


The potential of IL-7 treatment to restore MAIT cell functional defects in HIV-1 infected patients was evaluated in vitro. Interestingly, GrzA and Prf upregulation following IL-7 treatment in samples from healthy controls (n = 8) and HIV-1 infected patients (n = 6) was not significantly different (Fig 7A). However, whereas GrzB upregulation occurred in MAIT cells from both groups, it was weaker in HIV-1 infected patients suggesting that the cytotoxicity arming effect of IL-7 in these patients may be less distinct (p = 0.0293, Fig 7A). In a second round of experiments the ability of IL-7 to support the MAIT cell response in HIV-1 infected patients to a 24 h bacterial stimulation was evaluated. IL-7 treatment significantly improved all measured phenotypic aspects of MAIT cell cytotoxic potential including the generation of CD107a+GrzAlo, CD107a+GrzB+, and CD107a+Prf+ phenotypes, as well as the production of IFNγ by MAIT cells (n = 6) (Fig 7B). Next, we investigated whether the improvement of MAIT cell effector functions by IL-7 treatment might be linked with restoration of the abnormal MAIT cell transcription factor profile in nine ART-untreated HIV-1 infected patients. Importantly there was no difference in CD127 levels by T-betnegEomesneg and T-betdimEomeshi MAIT cells (S4A Fig). Next, PBMCs were cultured with IL-7 for a maximum of 48 h to minimize introducing potential confounders, including global cellular proliferation, activation-induced cell death, and HIV-1 replication that may result from a long-term IL-7 exposure. The frequency of T-betnegEomesneg MAIT cells showed a trend towards a decrease during this culture (n = 9, p = 0.0732; Fig 7C). Short-term IL-7 treatment also reduced the already low frequency of T-betnegEomesneg MAIT cells in seven HIV-uninfected healthy controls (p = 0.0156; S4B Fig).


IL-7 has strong effects on T cell homeostasis and supports the survival of T cells by upregulating Bcl-2. These characteristics have made IL-7 attractive for cytokine immunotherapy in humans. MAIT cells express high levels of the IL-7Rα (CD127) [12, 38], a finding that opened the possibility that IL-7 may have strong effects on MAIT cells. Interestingly, IL-7 alone in the absence of other stimuli was capable of arming resting MAIT cells from healthy donors into cytotoxic GrzB+ effector T cells. The induction of GrzB is profound, as resting MAIT cells essentially lack expression of this protein. Along with this effect, MAIT cells also further upregulated Prf and GrzA, without inducing any detectable spontaneous cytokine production. In the absence of bacterial antigen the effect of IL-7 is thus specifically to induce the cytotoxic arming of MAIT cells. Importantly, this in turn leads to a significantly increased cytolytic activity against MR1-expressing targets pulsed with bacteria. Perhaps an even more striking and potentially physiologically important effect is the radically enhanced sensitivity of MAIT cells to very low bacterial doses after IL-7 treatment. IL-7 supports strong cytokine production and cytolytic responses at antigen doses that are otherwise non-stimulatory for MAIT cells. These effects are consistent with the observations by Tang et al., where IL-7 enhanced expression of the TCR, CD8 chains and components of TCR signaling pathway [38]. Altogether, IL-7 may be suitable for immunotherapy approaches aimed at enhancing MAIT cell function in humans. 59ce067264






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