Nitric oxide (NO) is a neurotransmitter involved in memory processes. Currently, the only recognized physiological signalling pathway controlled by NO is the activation of guanylyl cyclase. In this thesis, we propose an alternative NO-signalling pathway that involves the Heme-regulated eukaryotic initiation factor-2a kinase (HRI) and eIF2a phosphorylation. We have found that the enzyme BACE1, a key protein in Alzheimer’s disease (AD), is controlled by this novel pathway. This pathway would be involved in the physiology of memory formation and learning processes. We have also studied how an external stress factor, the Herpes Simplex Virus 1, can disrupt this cascade leading to a pathological increase in BACE1 and amyloid ß-peptide (Aß) production. Aß aggregates forming fibrils that generate free radicals. These react with NO producing peroxynitrite, which contribute to AD progression. Since NO turns toxic when produced in a pro-oxidant environment we have also studied the effect of peroxynitrite in Stroke. / L’òxid nítric (NO) és un neurotransmissor involucrat en processos de memòria. Actualment, l’única cascada de senyalització fisiològica controlada per NO consisteix en l’activació de la guanilat ciclasa. En aquesta tesi, en proposem una d’alternativa que inclou la fosforilació de eIF2a per la Heme-regulated eukaryotic initiation factor-2a kinase (HRI). Hem mostrat com l’enzim BACE1, una proteïna clau en la malaltia d’Alzheimer (AD), és controlat per aquesta nova cascada de senyalització, que podria estar involucrada en la fisiologia de l’aprenentatge i la memòria. També hem estudiat com un factor d’estrès extern, l’ Herpes Simplex Virus 1, pot pertorbar aquesta cascada donant lloc a increments patològics en BACE1 i pèptid ß-amiloide (Aß). L’Aß agrega formant fibril·les que generen radicals lliures. Aquests reaccionen químicament amb NO produint peroxinitrit, que contribueix a la progressió de l’AD. Pel fet que l’NO esdevé tòxic quan és produït en un entorn pro-oxidant, hem estudiat també l’impacte que el peroxinitrit té en l’ictus.

A proteína quinase dependente de RNA (PKR) é uma molécula sentinela ativada em situações de estresse celular, incluindo infecções virais. A ativação de PKR por meio de sua fosforilação aciona cascatas de sinalização intracelular envolvidas em respostas inflamatórias e inibição da síntese protéica. Dados prévios do nosso laboratório sugerem que PKR está envolvida na hiperalgesia térmica de origem inflamatória. No presente estudo, foi investigado o papel da PKR na hiperalgesia térmica induzida pelo vírus da herpes simples tipo 1 (HSV1), durante as fases herpética e pós-herpética, combinando métodos comportamentais, genéticos, farmacológicos e moleculares. Camundongos C57bl/6, PKR+/+ e PKR-/- machos foram inoculados com HSV1. Os grupos controle foram inoculados com HSV1 inativo. Alodínia mecânica e hiperalgesia térmica foram monitoradas antes da inoculação do vírus e 8, 14, 21 e 28 dias após a inoculação. A curva dose e temporesposta e o teste da capsaicina foram realizados no 8º e 21º dias após a inoculação do vírus. Também nos períodos herpético e pós-herpético, foi investigado o perfil de expressão de proteínas envolvidas nas vias de sinalização de PKR (PKR, eIF2?, PACT, IKK e PP2A?), assim como o efeito da inibição de PKR pelo monitoramento da fosforilação de PKR, IKK?/?, P38, JNK, ERK1,2 e STAT3, e expressão de CaMKII? e TRPV1 nos GRD (L3-L6) ipsilateralmente à pata inoculada. Alodínia mecânica e hiperalgesia térmica ficaram evidentes até 28 dias após a inoculação. Camundongos PKR-/- desenvolveram alodínia mecânica, mas não hiperalgesia térmica, quando comparados com animais PKR+/+. A inibição sistêmica de PKR reverteu a hiperalgesia térmica de modo tempo- e dose-dependente e preveniu o comportamento nocifensivo induzido por capsaicina, enquanto PKR-/- apresentaram resposta nocifensiva praticamente ausente em ambas as fases herpética e pósherpética. Houve aumento da expressão de PP2A? e da fosforilação de PKR, IKK?/? e eIF2?, durante os períodos herpético e pós-herpético, e de PACT na fase pósherpética. A inibição de PKR promoveu o aumento da fosforilação de P38 em ambas as fases, e redução da fosforilação de PLC?1 acompanhada do retorno da fosforilação de Akt e STAT3 ao nível do grupo controle e o aumento da expressão de Ca-MKII? na fase herpética. Já na fase pós-herpética, reduziu a fosforilação de JNK e Akt e a expressão de Ca-MKII?, retornou a fosforilação de ERK1,2, PLC?1 e STAT3 ao nível do grupo controle e aumentou a expressão de TRPV1. Nossos resultados indicam que a atividade de PKR desempenha papel essencial na hiperalgesia térmica induzida por infecção pelo HSV1 / Double stranded RNA-activated protein kinase (PKR) is a sentinel molecule activated by cellular stress conditions, including viral infections. PKR activation by phosphorylation triggers cascades involved in inflammatory response and protein synthesis suppression. Our previous data suggest that PKR is involved in the inflammatory thermal hyperalgesia. Here we investigated the role played by PKR on thermal hyperalgesia induced by herpes simplex virus type-1 (HSV-1), during herpetic and post-herpetic phases, by combining behavioral, genetic, pharmacological, and molecular methods. Adult male C57bl/6, PKR+/+ and PKR-/- mice were inoculated with HSV-1. Control groups were inoculated with inactive (mock) HSV1. Mechanical allodynia and thermal hyperalgesia were monitored before virus inoculation and 8, 14, 21, and 28 days post-inoculation. The dose- and timeresponse curve and the capsaicin test were performed at 8th and 21st days post virus inoculation. Also in the herpetic and post-herpetic periods, was investigated the expression profile of proteins involved in the PKR signaling pathways (PKR, eIF2?, PACT, IKK and PP2A?), and the effect of PKR inhibition by monitoring PKR, IKK?/?, P38, JNK, ERK1,2, and STAT3 phosphorylation, and Ca-MKII? and TRPV1 expression in the dorsal root ganglia (L3-L6) ipsilaterally to the inoculated paw. Mechanical allodynia and thermal hyperalgesia became evident until 28 days postinnoculation. PKR-/- mice developed mechanical allodynia but not thermal hyperalgesia, when compared with PKR+/+ mice. Systemic PKR inhibition reversed thermal hyperalgesia in a dose and time-dependent manner, and prevented the capsaicin-induced nocifensive behavior, whereas PKR-/- showed no nocifensive behavior almost absent in both herpetic and post-herpetic phases. There was increased expression of PP2A? and the phosphorylation of PKR, IKK?/?, and eIF2?, during herpetic and post-herpetic periods, and PACT in the post-herpetic phase. PKR inhibition increased P38 phosphorylation in both phases, and reduction of PLC?1 phosphorylation together with the return of the Akt and STAT3 phosphorylation to the control group level, and enhanced Ca-MKII? expression in the herpetic phase. At the post-herpetic phase, suppressed JNK and Akt, and Ca-MKII? expression returned ERK1,2, PLC?1 and STAT3 phosphorylation to control group level and increased TRPV1 expression. The data indicate that PKR activity plays an essential role in the HSV-1 infection-induced thermal hyperalgesia

Le virus de l'herpès simplex de type 1 (VHS-1) est l'un des agents pathogènes humains les plus anciens et les plus efficaces. On estime que 3.7 milliards de personnes dans le monde vivent avec le VHS-1. Le virus persiste à l'état latent dans les neurones sensoriels, réapparaissant occasionnellement sous la forme d'une infection lytique qui endommage l'épithélium. Même si le VHS-1 provoque une maladie bénigne connue sous le nom de feu sauvage dans la majorité des cas, l'infection peut entraîner des conséquences catastrophiques telles que l'encéphalite et la kératite chez les personnes immunodéprimées les nouveau-nés. Compte tenu de la présence généralisée des infections à VHS-1, le virus représente une menace potentielle pour le système de santé. Le génome à ADN du VHS-1 est protégé par une cage protéique appelée capside. Bien que l'assemblage de la capside du VHS-1 et l'encapsidation du génome aient lieu à l'intérieur du noyau de l'hôte, les étapes finales de la maturation doivent être achevées dans le cytoplasme. Ainsi, pour la sortie du noyau, le virus a développé un mécanisme connu sous le nom d’enveloppement-déenveloppement-réenveloppement. La première étape de ce processus est principalement régulée par le complexe de sortie nucléaire (pUL31 et pUL34) et entraîne le bourgeonnement de la capside alors enveloppée dans l'espace périnucléaire. Par la suite, le déenveloppement de ces capsides périnucléaires et leur libération dans le cytoplasme seraient largement modulés par la kinase virale pUs3. Ce processus est sélectif, car les capsides remplies d'ADN (capsides C) sortent préférentiellement du noyau au détriment des intermédiaires viraux sans génome (capsides A et B). Cependant, nous ne savons pas pourquoi les capsides C sont favorisées lors de ce processus. En aval, le virus mûrit, recrute de nombreuses protéines puis acquiert une enveloppe à partir d'un compartiment cytoplasmique. Il sort ensuite de la cellule sous forme de virions enveloppés matures. Outre les facteurs viraux mentionnés et quelques protéines hôtes, l'implication de nombreuses autres protéines virales et cellulaires dans cette voie n'a pas été entièrement caractérisée. Pour élucider davantage ce processus de sélection de la capside C, nous avons profité de l'analyse MS/MS des capsides nucléaires du VHS-1 pour définir les facteurs hôtes et viraux spécifiques à chaque intermédiaire de capside nucléaire (Chapitre 2; Article 1). Nous avons trouvé deux protéines virales (pUL42 et pUL46) et sept facteurs de l'hôte (glycogène synthase, quatre protéines différentes liées à la kératine, fibronectine 1 et PCBP1) qui étaient spécifiques des capsides C matures. Fait intéressant, toutes ces protéines semblent posséder des fonctions qui ont le potentiel de médier la sortie nucléaire préférentielle des capsides C. Par conséquent, l'analyse fonctionnelle future de ces protéines pourrait nous fournir des informations inestimables sur la sortie nucléaire actuellement énigmatique des capsides du VHS-1. Les travaux en cours d'un collègue de laboratoire avec lequel je collabore impliquent PCBP1 en tant que modulateur de la sortie nucléaire (mémoire de Mackenzie Thornbury). Nous nous sommes ensuite concentrés sur un ensemble de données protéomiques déjà existantes des virions extracellulaires matures, qui a identifié jusqu'à 49 protéines hôtes incorporées dans le virus, y compris une hélicase à ARN humaine appelée DDX3X qui s'est avérée être un modulateur actif de la propagation virale (Chapitre 2; Article 2). Nous avons remarqué que cette protéine se déplace vers le noyau tard lors de l'infection, coïncidant avec la majeure partie de la sortie nucléaire virale. Par conséquent, nous avons émis l'hypothèse que DDX3X serait impliqué dans la sortie nucléaire virale. Nous avons découvert que, tardivement au cours de l'infection, pUL31 interagit avec DDX3X au niveau du noyau. Nous avons également constaté que DDX3X stimule de grandes agrégations de capsides virales matures dans la périphérie nucléaire. Fait intéressant, la redirection de DDX3X vers le bord nucléaire dépend de la présence de la machinerie de sortie nucléaire virale (pUL31, pUL34 et pUs3) et de capsides matures. Enfin, nos données ont montré qu'en l'absence de DDX3X, les capsides C s'accumulent entre les deux membranes nucléaires, probablement à la suite d'une incorporation inefficace de pUs3 au site de sortie. Ces résultats ont élucidé une nouvelle fonction de DDX3X et pourraient ouvrir de nouvelles voies passionnantes de recherche pour développement d’antiviraux en ciblant cette hélicase à ARN cellulaire. / Herpes simplex virus type 1 (HSV-1) is one of the oldest and most successful human pathogens. It is estimated that 3.7 billion people worldwide are living with HSV-1. The virus latently persists in sensory neurons, occasionally recurring as a lytic infection which damages the connected epithelium. Even though HSV-1 causes a mild disease known as the cold sore in majority of cases, the infection can have catastrophic consequences such as encephalitis and keratitis in immunocompromised individuals, newborns and, more rarely, in immune competent adults. Considering the widespread presence of HSV-1 infections, the virus poses a potential threat to the healthcare system. The DNA genome of HSV-1 is protected by a protein cage called a capsid. Although HSV-1 capsid assembly and genome packaging take place inside the host nucleus, the final steps of maturation must be completed inside the cytoplasm. Since the large diameter of these viral capsids (~125 nm) far exceeds the 30 nm cut-off of the nuclear pore complex, the virus has evolved a mechanism known as envelopment-deenvelopmentreenvelopment. The first step of this complex process is mainly regulated by the components of the nuclear egress complex (pUL31 and pUL34) and results in the budding of enveloped capsid into the perinuclear space. Subsequently, deenvelopment of these perinuclear capsids and their release into the cytoplasm is thought to be largely modulated by the viral kinase pUs3. This process is selective as DNA-filled capsids (C-capsids) preferentially exit the nucleus compared to genome-free viral intermediates (A- and Bcapsids). However, it is unclear how C-capsids are preferentially selected for the nuclear egress. Further downstream, the virus matures and recruit numerous proteins onto the viral capsids and acquire an envelope from a cytoplasmic compartment. It then exits the cell as mature enveloped virions. Apart from the mentioned viral factors and a handful of host proteins, implication of many other viral and cellular proteins in this pathway have not been fully characterized. To further resolve this process of C-capsid selection, we took advantage of MS/MS analysis of HSV-1 nuclear capsids to define host and viral factors specific to each nuclear capsid intermediate (Chapter 2; Article 1). We found two viral proteins (pUL42 and pUL46) and seven host factors (glycogen synthase, four different keratin-related proteins, fibronectin 1, and PCBP1) that were specific to mature C-capsids. Interestingly, all these proteins seem to possess functions that have the potential to mediate the preferential nuclear exit of C-capsids. Therefore, future functional analysis of these proteins might provide us with invaluable insights into the currently enigmatic nuclear egress of HSV-1 capsids. Ongoing work by a lab colleague with which I collaborate implicates PCBP1 as a modulator of nuclear egress (memoir of Mackenzie Thornbury). We then focused on an existing proteomics data set of mature extracellular virions, which revealed 49 virus-incorporated host proteins, including a human RNA helicase called DDX3X that we found to be an active modulator of viral propagation (Chapter 2; Article 2). We observed that DDX3X relocates to the nuclear rim late during infection, coinciding with the bulk of viral nuclear egress, and leading us to hypothesize that DDX3X is involved in the process. We discovered that, late during the infection, pUL31 interacts with DDX3X at the nuclear rim. We also found that DDX3X stimulates large aggregations of mature viral capsids in the nuclear periphery. Unexpectedly, redirection of DDX3X to the nuclear rim was dependent on the presence of the viral nuclear egress machinery (pUL31, pUL34 and pUs3) and mature capsids. Lastly, our data showed that in the absence of DDX3X, C-capsids accumulate in the perinuclear space, likely as the result of inefficient incorporation of pUs3 to the site of egress. These results have elucidated a novel function for DDX3X and may open new and exciting paths to produce antivirals by targeting this cellular RNA helicase.

L'établissement de latence du virus de l'Herpès simplex 1 (HSV1) est contrôlé par les corps nucléaires PML (PML-NBs) mais leur implication exacte reste encore confuse. Une des caractéristiques majeures de la latence du virus est l'interaction entre le génome viral et les PML-NBs formant des structures nommées viral DNA-containing PML-NBs (vDCP-NBs). L'utilisation d'un modèle d'infection de fibroblastes primaires humains, qui reproduit la formation des vDCP-NBs, combinée à une approche par immuno-FISH, a permis de montrer que les vDCP-NBs contiennent l'histone H3.3 et ses chaperons, les complexes DAXX-ATRX et HIRA. La protéine HIRA a été également observé au sein des vDCP-NBs dans les neurones des ganglions trijumeaux de souris infectées par HSV1. Des expériences de ChIP-qPCR dans des cellules exprimant H3.3 ou H3.1 tagguées, nous a permis de déterminer que le génome viral est spécifiquement chromatinisé avec l'histone H3.3. La déplétion d'une seule protéine des complexes chaperons de H3.3 affecte légèrement l'incorporation de H3.3 dans les génomes viraux latents. Au contraire, l'absence de PML diminue significativement la chromatinisation H3.3 du génome HSV-1 latent sans remplacement par H3.1. Cette étude démontre une régulation épigénétique du génomes HSV1 latent par une chromatinisation dépendante de H3.3 impliquant les complexes chaperons DAXX-ATRX et HIRA. De plus, cette étude révèle un rôle majeur des PML-NBs dans la chromatinisation H3.3 des génomes HSV1 latent / Herpes simplex virus 1 (HSV-1) latency establishment is tightly controlled by PML nuclear bodies (PML-NBs) although their exact implication is still elusive. A hallmark of HSV-1 latency is the interaction between latent viral genomes and PML-NBs leading to the formation of viral DNA-containing PML-NBs (vDCP-NBs). Using a replication defective HSV-1 infected human primary fibroblast model reproducing the formation of vDCP-NBs, combined with an IF-FISH approach developed to detect latent HSV-1, we show that vDCP-NBs contain both histone H3.3 and its chaperone complexes, i.e. the DAXX/ATRX and the HIRA complex. HIRA was also detected co-localizing with vDCP-NBs present in trigeminal ganglia neurons from HSV-1 infected WT mice. ChIP-qPCR performed on fibroblasts stably expressing tagged H3.3 or H3.1 show that latent HSV1 genomes are chromatinized almost exclusively with H3.3. Depletion of single proteins from the H3.3 chaperone complexes only mildly affects H3.3 deposition on the latent HSV1 genome. In contrast, absence of PML significantly impacts on the chromatinization of the latent genomes with H3.3 without replacement with H3.1. Consequently, the study demonstrates a specific epigenetic regulation of latent HSV-1 through an H3.3-dependent HSV-1 chromatinization involving both H3.3 chaperones DAXX/ATRX and HIRA complexes. Additionally, the study reveals that PML-NBs are major actors of the latent HSV-1 H3.3 chromatinization through a PML-NBs/histone H3.3/H3.3 chaperones axis

No description available.

Department of Microbiology / PhD (Microbiology) / Human herpes virus type 8 (HHV-8), also known as Kaposi’s sarcoma associated herpes virus (KSHV), is the etiologic agent of Kaposi’s sarcoma (KS), and AIDS related Kaposi’s sarcoma (AIDS-KS). HHV-8 which is a member of the Herpesviridae family, exhibits extensive genetic diversity globally. In endemic regions, infection with HHV-8 occurs very early on in life, which is an indication of both environmental and vertical routes of transmission. The advent of HIV leads to the classification of an AIDS-KS defining condition in HIV infections. This suggests that in regions where HIV and HHV-8 are endemic, KS may become common in a mature HIV epidemic. Just like the prevalence of HIV in Northern South Africa is generally high as in most regions of the country, as the HIV epidemic matures in South Africa, it is important to understand the burden and distribution of HHV-8 infection, and the likely genotypes infecting the population. The main objective of the thesis was to establish the epidemiology and infecting genotypes of HHV-8 in Northern South Africa (Limpopo Province), where no data exists. First, a systematic review of the literature was carried out for the entire African continent to determine the seroprevalence and genotype distribution of HHV-8 in all African countries (n=53). In this review, Sudan and South Sudan were considered as one country. Articles were searched using the PRISMA guideline and exported using an article grid. More than two-thirds (64%) of the studies reported on seroprevalence, 29.3% on genotypes; and 9.5% were on both seroprevalence and genotypes. About 45% (24/53) of the African countries had data on HHV-8 seroprevalence exclusively, and more than half (53%) had data on either seroprevalence or genotypes. Almost half (47%) of the countries had no data on HHV-8 infection. There was high heterogeneity in the types of tests and interpretation algorithms used in determining HHV-8 seropositivity across the different studies. Generally, seroprevalence ranged from 2.0% in a group of young children in Eritrea to 100% in a small group of individuals with KS in the Central Africa Republic and a larger group of KS in individuals in Morocco. Approximately, 16% of all the studies reported on children. The difference in seroprevalence across the African region was not significant (95% CI, X2 =0.86; p =0.35), although specifically, a relatively significant ETTA MASHU ELIZABETH, PHD IN MICROBIOLOGY|UNIVERSITY OF VENDA, 2019|VIII level of infection was observed in HIV-infected children. About 38% of the countries had data on K1 genotypes A, A5, B, C, F and Z which occurred at frequencies of 5.3%, 26.3%, 42.1%, 18.4%, 5.3% and 2.6% respectively. Twenty-three percent of the countries had data for K15 genotypes, whereas genotypes P, M and N occurred at frequencies of 52.2%, 39.1% and 8.7% respectively. Data on HHV-8 inter-genotype recombinant is scanty. Our finding suggests that HHV-8 is endemic on the entire African continent, and in HIV endemic regions, but there is need for a harmonized testing protocol for better understanding of HHV-8 seropositivity. HHV-8 genotype A5 and B for K1 gene and genotype P and M for K15 gene are the most predominant genotypes in Africa. The review, for the first time, has provided information on HHV-8 burden on the entire African continent, and suggests that vaccine development efforts for Africa should focus on genotypes B and P. The second component of the investigation focused on the burden of HHV-8 in an HIV population in Northern South Africa (Limpopo Province). Plasma from 3501 HIV infected individuals from 5 districts in Limpopo Province were assessed for antibodies to both the lytic antigen (ORFK8.1) and the latent antigen (ORF73). The distribution of infection was analyzed based on demographic, socioeconomic, and immunological parameters. Statistical inferences for significant differences were determined by Chisquare at a confidence interval of 95%. P-values less than 0.05 were considered significant. About 19.0% of the study population was positive for antibodies to either the lytic or latent antigens or both. Prevalence of antibodies to the lytic antigen was significantly higher than prevalence of antibodies to the latent antigen (17.3% vs 4.1%; p=0.0001). Significant differences were observed for age groups, racial population groups, districts and year of sample collection (p=<0.0001, p=<0.0001, p=<0.0001 and p=0.0385) respectively. Associations were found between both antigens in comparison to the different variables such as age group, racial population groups and districts (R2 value ranging between 0.886 and 1.0). The burden of HHV-8 has now been established for the first time in Northern South Africa. The third aspect of the investigation was a meta-analysis of HHV-8 seroprevalence in Southern Africa in order to understand the impact of geographical location (urban vs rural) on infection. The analysis revealed a significant association between urban settings and HHV-8 infection (p=0.0001). ETTA MASHU ELIZABETH, PHD IN MICROBIOLOGY|UNIVERSITY OF VENDA, 2019|IX The fourth component of the thesis examined the detection of HHV-8 antigen through polymerase chain reaction (PCR) in 534 participants in HIV infected and HIV noninfected populations. A selection of mouthwash DNA samples were subjected to Next Generation Sequencing (NGS) for subsequent genotype inference. Mouth wash samples were obtained from each consenting individual before eating or smoking, and their DNA was purified. A 233bp fragment of the ORF26 gene of HHV-8 was amplified by PCR. HHV-8 was detected in 150 of the 534 participants (28.1%). A significant difference in detection was observed for gender, HIV status, district and the level of education (p=0,0003; p=0.0094; p=0.0002 and p=0.0095) respectively. Consensus sequences were derived from NGS reads for 13 samples. The genotyping results revealed that genotype Q, B, E and N are the genotypes predominant in the study population. As such no mixed infections were detected. Therefore, from the investigations foregoing have demonstrated for the first time the following: (1) HHV-8 is endemic in the entire African continent, which suggest a coendemicity in regions already endemic for HIV; (2) HHV-8 is endemic in Northern South Africa; (3) Urban settings in Southern Africa are associated with high HHV-8 infection; (4) HHV-8 genotypes Q, B, E and N may be predominant in Northern South Africa, with B and P common on the entire African continent. Hence, studies should focus on the generation of full length HHV-8 genomes of the common genotypes to support the selection of genes for vaccine design and development. / NRF

Les infections virales en particulier celles dues aux virus de la famille des Herpesviridae pendant la période d’aplasie et de lymphopénie à la suite d’une greffe de cellules souches hématopoïétiques (GCSH) peuvent occasionner des complications très graves, souvent associées à une morbidité et mortalité élevées. Les recommandations cliniques actuelles préconisent l’utilisation des antiviraux pour la prévention de certaines de ces infections. L’efficacité du famciclovir et de l’acyclovir contre les virus de l’herpès simplex (HSV), le virus varicella-zoster (VZV) et l’herpésvirus humain de type 6 (HHV-6) est bien reconnue, cependant il nous manque des données quant à leur effet contre le virus Epstein-Barr (EBV) et le cytomégalovirus (CMV) dans la population pédiatrique. L’objectif principal de ce projet de maitrise a été de mesurer l’incidence de l’infection aux virus HSV, VZV, EBV, CMV et HHV-6 et de mesurer l’association entre l’utilisation de la prophylaxie antivirale (acyclovir et famciclovir) et l’infection (virémie asymptomatique et maladie) avec le CMV et l’EBV dans une cohorte pédiatrique de GCSH allogéniques. Les données d'une cohorte de sujets ayant subis pour la première fois une GCSH enrôlés dans quatre centres de greffes pédiatriques au Canada entre juillet 2013 et mars 2017 (Étude TREASuRE) ont été utilisées. Le recrutement a été effectué au : CHU Sainte-Justine (Montréal) (n=86), British Columbia Children’s Hospital (Vancouver) (n=31), Winnipeg Children's Hospital and CancerCare Manitoba (n=28) et Alberta Children’s Hospital (n=11). Le suivi des patients avait débuté 1 mois avant la greffe et avait duré 13 mois. L’âge médian des patients au recrutement était de 6,3 ans. Les courbes de Kaplan-Meier ont permis d’estimer l'incidence cumulée des infections CMV et EBV avec intervalle de confiance (IC) à 95% à 100 jours post-greffe en fonction de la prophylaxie antivirale (acyclovir ou famciclovir). Les modèles multivariés de régression de Cox à risques proportionnels ont permis de mesurer l'association entre la prise d’antiviraux (acyclovir ou famciclovir) et le développement de ces infections. L’étude a inclus 156 sujets âgés de 0 à 21 ans. Les incidences cumulées de la virémie des virus de HSV, VZV, EBV, CMV et HHV-6 à 100 jours de suivi ont été respectivement de 2.5% (IC 95% : 0.8–7.6), 0.8% (IC 95% : 0.1–6.1), 34.5% (IC 95% : 27.6–42.6), 19.9% (IC 95% : 14.5-27.1) et 3.4% (IC 95% : 1.2–9.1). Les incidences cumulées pour CMV et EBV n’ont pas montré de différence statistiquement significative entre les groupes ayant reçu la prophylaxie antivirale (acyclovir ou famciclovir) et ceux qui ne l’ont pas reçu. Les analyses de Cox n’ont montré aucun effet significatif des antiviraux sur le CMV avec un HR ajusté de 0.55 (IC 95% : 0.24–1.26) pour l’acyclovir et de 0.82 (IC 95% : 0.30–2.29) pour le famciclovir. Il en était de même pour l’EBV avec un HR ajusté de 1.41 (IC 95% : 0.63–3.14) pour l’acyclovir et de 0.79 (IC 95% : 0.36–1.72) pour le famciclovir. Notre étude n’a montré aucune preuve d’effet de la prophylaxie antivirale avec le famciclovir et l’acyclovir contre l’EBV et le CMV. Très peu de cas de HSV et de VZV ont été diagnostiqués dans cette cohorte ce qui est conforme avec l’idée selon laquelle l’acyclovir et le famciclovir sont efficaces pour ces virus. / Viral infections, especially those involving members of the Herpesviridae during the period of aplasia and lymphopenia following allogeneic hematopoietic stem cell transplantation (HSCT), cause very serious complications, often associated with high morbidity and mortality. Current clinical guidelines recommend prophylactic use of antivirals, which has proven to be effective against certain viruses. The efficacy of famciclovir and acyclovir against herpes simplex viruses (HSV), varicella zoster virus (VZV) and human herpesvirus type 6 (HHV-6) is well-recognized, however, we lack data on their effects against Epstein-Barr virus (EBV) and cytomegalovirus (CMV) in the pediatric population. The main objective of this master's project was to measure the incidence of herpes virus infection, specifically by HSV, VZV, EBV, CMV and HHV-6, and to measure the association between the use of antiviral prophylaxis (acyclovir and famciclovir) and infection (including both asymptomatic viremia and disease) by CMV and EBV in a pediatric cohort of allogeneic HSCT. We used data from the TREASuRE cohort, which includes patients enrolled for a first allogeneic HSCT in four pediatric centers in Canada between July 2013 and March 2017. Recruitment was carried out at: CHU Sainte-Justine (Montreal) (n = 86), British Columbia Children's Hospital (Vancouver) (n = 31), Winnipeg Children's Hospital and CancerCare Manitoba (n = 28) and Alberta Children's Hospital (n = 11). Patient follow-up began 1 month before transplant and lasted 13 months. Median patient age at recruitment was 6.3 years. Kaplan-Meier curves were used to estimate the cumulative incidence of CMV and EBV infections with 95% confidence interval (CI) at 100 days post-transplant according to antiviral prophylaxis (acyclovir or famciclovir). Multivariate proportional hazards Cox regression models were used to measure the association between antiviral use (acyclovir or famciclovir) and the detection of these infections. The study included 156 subjects aged 0 to 21 years. The cumulative incidences of viremia due to HSV, VZV, EBV, CMV and HHV-6 at day 100 of follow-up were respectively 2.5% (CI 95%: 0.8–7.6), 0.8% (CI 95%: 0.1-6.1), 34.5% (CI 95%: 27.6-42.6), 19.9% (CI 95%: 14.5-27.1) and 3.4% (95% CI: 1.2-9.1). The cumulative incidences for CMV and EBV did not show a statistically significant difference between the groups who received antiviral prophylaxis (acyclovir or famciclovir) and those who did not. Cox analyses showed no significant effect of antivirals on CMV with an adjusted HR of 0.55 (95% CI: 0.24–1.26) for acyclovir and 0.82 (95% CI: 0.30–2.29) for famciclovir. The same was true for EBV with an adjusted HR of 1.41 (95% CI: 0.63–3.14) for acyclovir and 0.79 (95% CI: 0.36–1.72) for famciclovir. Our study showed no evidence of an effect with use of famciclovir or acyclovir prophylaxis on EBV and CMV infections. Very few cases of HSV and VZV infections were diagnosed in this cohort, which is consistent with the idea that acyclovir and famciclovir are effective against the latter viruses.