key: cord-0767068-ptkjx340 authors: Kaufmann, Eva; Khan, Nargis; Tran, Kim A.; Ulndreaj, Antigona; Pernet, Erwan; Fontes, Ghislaine; Lupien, Andréanne; Desmeules, Patrice; McIntosh, Fiona; Abow, Amina; Moorlag, Simone J.C.F.M.; Debisarun, Priya; Mossman, Karen; Banerjee, Arinjay; Karo-Atar, Danielle; Sadeghi, Mina; Mubareka, Samira; Vinh, Donald C.; King, Irah L.; Robbins, Clinton S.; Behr, Marcel A.; Netea, Mihai G.; Joubert, Philippe; Divangahi, Maziar title: BCG vaccination provides protection against IAV but not SARS-CoV-2 date: 2022-02-21 journal: Cell Rep DOI: 10.1016/j.celrep.2022.110502 sha: fef1e8891739d9c7cfdeaa34c1c6bfae8302e78d doc_id: 767068 cord_uid: ptkjx340 Since the vast majority of species solely rely on innate immunity for host defense, it stands to reason that a critical evolutionary trait like immunological memory evolved in this primitive branch of our immune system. There is ample evidence that vaccines such as Bacillus Calmette-Guerin (BCG) induce protective innate immune memory responses (trained immunity) against heterologous pathogens. Here we show that while BCG vaccination significantly reduces morbidity and mortality against influenza A virus (IAV), it fails to provide protection against SARS-CoV-2. In contrast to IAV, SARS-CoV-2 infection leads to unique pulmonary vasculature damage facilitating viral dissemination to other organs, including the bone marrow (BM), a central site for BCG-mediated trained immunity. Finally, monocytes from BCG-vaccinated individuals mount an efficient cytokine response to IAV infection, while this response is minimal following SARS-CoV-2. Collectively, our data suggest that the protective capacity of BCG vaccination is contingent on viral pathogenesis and tissue tropism. While the concept of the innate memory response (termed trained immunity) is "young", 58 the evidence of innate memory in host defense against diverse infectious diseases is "old" 59 (Divangahi et al., 2021) . A growing body of literature indicates that live attenuated 60 vaccines (LAVs) such as BCG, measles-containing vaccines, smallpox and Oral 61 Poliovirus Vaccines (OPV) induce cross-protection against other infectious diseases 62 8 reprogramming that modifies the chromatin accessibility and thereby the readable gene 217 information. In the context of LAVs, there are three known factors that can impact the 218 epigenetic programming of an immune cell: (1) direct infection; (2) pathogen-associated 219 molecular patterns (PAMPs) from the microorganisms; and (3) endogenous cytokines 220 released during the induction of the host response. The impact of these key factors occurs 221 centrally, at the level of HSCs in the bone marrow (BM) , and peripherally at the tissue-222 specific level. Recently, it has been demonstrated in pre-clinical (Kaufmann et al., 2018) 223 and clinical (Cirovic et al., 2020) studies that BCG reprograms BM-HSCs towards 224 myelopoiesis to generate trained immunity, while the access of virulent M. tuberculosis to 225 the BM prevents trained immunity (Khan et al., 2020) . These studies provide a logical 226 explanation of why short-lived innate immune cells can acquire memory and how trained 227 immunity induced by LAVs (e.g., BCG) can provide cross-protection against other 228 infectious diseases. Our data suggests that compared to IAV infection, the unique 229 pulmonary vascular damage induced during SARS-CoV-2 infection may allow for viral 230 dissemination to the BM, effectively preventing the ability of BCG to generate trained 231 immunity. Furthermore, our results from monocytes of BCG-vaccinated humans suggest 232 that in contrast to IAV infection, potential virulence factors from SARS-CoV-2 can 233 substantially suppress the inflammatory programming of trained immune cells. Thus, 234 identifying these virulence factors can lead us closer to uncover how SARS-CoV-2 hijacks 235 our immune responses. 236 Our data contrasts with a recent study demonstrating that BCG-iv vaccination increases 237 survival of K18-hACE2 transgenic mice following SARS-CoV-2 challenge (Hilligan et al., 238 2022) . Intranasal SARS-CoV-2 infection, the approach used by Hilligan et al., has been 239 observed by us and reported by others (Kumari et al., 2021) to result in pulmonary and 240 neurological pathology, whereas we did not observe neurological symptoms following 241 intratracheal challenge. However, in our K18-hACE2 transgenic mouse model, BCG-iv 242 vaccination did not provide significant protection after either intranasal or intratracheal 243 infection with SARS-CoV-2. Our results from the BCG vaccination in murine models of 244 COVID-19 are furthermore supported by two physiological hamster models of SARS-245 CoV-2 infection, demonstrating that BCG vaccination has no significant impact on 246 J o u r n a l P r e -p r o o f 9 protection against mild or severe forms of COVID-19. One possible explanation for this 247 discrepancy is the strains of BCG (Tice vs. Pasteur) used between our two groups that 248 may have different protective capacities. 249 250 These studies are currently being validated in humans, with several large, ongoing clinical 251 trials of both BCG vaccination given for the first time or following revaccination. Using 252 three animal models of SARS-CoV-2 infection, our results strongly argue for the 253 vaccination of all individuals enrolled in BCG clinical trials with currently available, SARS-254 CoV-2-specific effective vaccines. Our observations are also supported by published data 255 on the efficacy of BCG vaccination against COVID-19 in human cohorts (Pépin et al., 256 2021 , Hensel et al., 2020 . Considering dysregulated immunity is the major cause of 257 morbidity and mortality during SARS-CoV-2 and variants of SARS-CoV-2 infection, 258 understanding the pathogenesis of COVID-19 is essential for developing novel host-259 targeted therapies. 260 261 Limitations of the study: In this study, we show that the protection of BCG to pulmonary 262 viral pathogens is mainly determined by pathogenesis of infections. In contrast to IAV 263 infection, the distinct tropism of SARS-CoV-2 to infect pulmonary endothelial cells can be 264 a major cause of lung hemorrhage and dissemination of the virus to other organs including 265 bone marrow. Given our recent studies showing that a pulmonary pathogen (M. 266 tuberculosis) can access the bone marrow to reprogram Hematopoietic stem and 267 progenitor cells (HSPCs) and prevent trained immunity (Khan et al., 2020) The authors declare no competing interests. Table S1 . Table S2 . Table S1 . Heatmap data are displayed as mean. See also Fig. S4 and Table S1 . (Table S1) All animals were clinically examined and tested for pathogens upon arrival. All animal studies were conducted in accordance with the guidelines of and approved by the Animal Crystal violet (0.1% w/v in 10% EtOH). TCID50/mL was calculated using the method by Reed and Muench. TRIzol-chloroform method (Genezol TriRNA Pure Kit) was used for viral and total RNA isolation from 454 VeroE6 cell culture supernatants or mouse and hamster bone marrow and lung tissues, respectively. cDNA The viral SARS-CoV-2-N2 primers were purchased from IdT as commercial 2019-nCoV_N2 Combined Samples were fixed with 1% PFA and acquired on BD Fortessa-X20 within 3 days. Data were analyzed 552 using FlowJo v10. Human Randomized trial of BCG vaccination at birth to low-birth-weight children: 590 beneficial nonspecific effects in the neonatal period? 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