BACKGROUND: The epidemiologic and clinical characteristics of heart transplant (HTx) recipients during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic remains unclear. We studied the characteristics of HTx recipients from December 20, 2019, to February 25, 2020, in an effort to understand their risk and outcomes. METHODS: All accessible HTx recipients were included in this single-center retrospective study. We collected information on the recipients using a web-based questionnaire as well as the hospital database. RESULTS: We followed 87 HTx recipients (72.4% were men, and the average age was 51 years). A total of 79 recipients resided in Hubei, and 57 recipients had a Wuhan-related history of travel or contact. Most took precautionary measures while in contact with suspicious crowds, and 96.6% of the families and communities undertook prevention and quarantine procedures. Four upper airway infections were reported, and 3 of them tested negative for SARS-CoV-2 (the fourth recovered and was not tested). All cases were mild and successfully recovered after proper treatment. Laboratory results of 47 HTx cases within the last 2 months were extracted. Of these, 21.3% of recipients had pre-existing lymphopenia, and 87.2% of recipients had a therapeutic concentration of tacrolimus (5−12 ng/ml). Liver and kidney insufficiency was seen in 5 and 6 recipients, respectively. CONCLUSION: HTx recipients who practiced appropriate prevention measures had a low rate of infection with SARS-CoV-2 and transition to the associated disease COVID-19. These early data will require confirmation as the pandemic establishes around the world.

High-mobility group box 1 (HMGB1) is a chromatin-binding nuclear molecule that has potent proinflammatory effects once released by damaged cells. In some disease models, carbon monoxide (CO) exhibits anti-inflammatory and protective properties. Here, we investigated whether the protective effect of CO on renal ischemia-reperfusion injury is associated with the inhibition of HMGB1 translocation and release. A renal ischemia-reperfusion injury model was established with a 100% mortality rate in untreated mice. Pretreatment with the CO-releasing molecule-2 (CORM-2) resulted in 100% survival, maximal preservation of renal function, a marked reduction in pathological damage, and blunted upregulation of TLR4, RAGE, TNF-α, IL-1β, IL-6, and MCP1 mRNA. Interestingly, CORM-2 pretreatment almost completely inhibited ischemia-induced HMGB1 nucleocytoplasmic shuttling and release. This inhibition was associated with a decrease in nuclear histone acetyltransferase activity. Indeed, CORM-2 pretreatment inhibited the acetylation and release of HMGB1 during hypoxic culture of primary mouse renal tubular epithelia cells in vitro. Using the same renal ischemia-reperfusion injury model, neutralization of HMGB1 was protective, and administration of exogenous HMGB1 largely reversed the protective effect of CORM-2 on kidney ischemia-reperfusion injury. Thus, CORM-2-delivered CO protects against lethal renal ischemia-reperfusion injury. This protection is correlated with the prevention of HMGB1 nuclear-cytoplasmic translocation and release.

Motivated by practical needs such as large-scale learning, we study the impact of adaptivity constraints to linear contextual bandits, a central problem in online active learning. We consider two popular limited adaptivity models in literature: batch learning and rare policy switches. We show that, when the context vectors are adversarially chosen in d-dimensional linear contextual bandits, the learner needs O(d log d log T ) policy switches to achieve the minimax-optimal regret, and this is optimal up to poly(log d, log log T ) factors; for stochastic context vectors, even in the more restricted batch learning model, only O(log log T ) batches are needed to achieve the optimal regret. Together with the known results in literature, our results present a complete picture about the adaptivity constraints in linear contextual bandits. Along the way, we propose the distributional optimal design, a natural extension of the optimal experiment design, and provide a both statistically and computationally efficient learning algorithm for the problem, which may be of independent interest.Author names are listed in alphabetical order.

Blockade of extracellular high mobility group box 1 (HMGB1) can significantly prolong murine cardiac allograft survival. Here, we determined the role of HMGB1 in xenotransplantation. Sprague‐Dawley rat hearts were transplanted heterotopically into BALB/c mice. Xenografts without any treatment developed predominant acute vascular rejection within 6 days. Both passively released HMGB1 from xenografts and actively secreted HMGB1 from infiltrated immune cells were significantly increased after xenotransplantation. HMGB1‐neutralizing antibody treatment significantly prolonged xenograft survival and attenuated pathologic damage, immune cell infiltration, and HMGB1 expression and release in the xenografts. Compared to control IgG treatment evaluated at study endpoint, treatment with HMGB1‐neutralizing antibody markedly suppressed xenoreactive B cell responses, as evidenced by the significant inhibition of anti‐rat antibody production and deposition in xenografts at Day 6 posttransplant. Furthermore, treatment with anti‐HMGB1 antibody suppressed B cell activation and reduced IFN‐γ and IL‐17A production after xenotransplantation. These results demonstrate for the first time that HMGB1 plays an important role in mediating acute xenograft rejection. Thus, we have shown that neutralization of extracellular HMGB1 can significantly inhibit xenoreactive B cell responses and delay xenograft rejection in a rat‐to‐mouse model of xenotransplantation, uncovering new insights in the role of HMGB1 in transplantation.

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These data suggest that xenogeneic Sertoli cells exert a global immune suppressive effect that extends across species barriers in a stringent model of alloimmune rejection. The combination of NPSCs with other immune modulatory regimes may yield novel approaches toward prevention of allo-islet transplant rejection.

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