Malaria causes almost half a million deaths each year. Existing interventions will almost certainly not be enough to tackle this enormous public health problem on their own. An effective vaccine is urgently needed. The leading malaria vaccine, RTS,S, confers suboptimal protective efficacy, and in addition targets only Plasmodium falciparum and not the other major species of human malaria, P. vivax. This thesis investigates the potential of combining pre-erythrocytic malaria vaccines as a means of enhancing protective efficacy. A novel mathematical model was developed which expresses probability of protection as a function of vaccine-induced humoural and cellular responses. The model predicts that combining partially effective vaccines should result in more than additive improvements in protective efficacy. This was supported by an experiment combining Rv21, a P. vivax circumsporozoite virus-like particle, with viral vectored P. vivax TRAP, the two leading pre-erythrocytic malaria vaccine antigens; this combination raised protective efficacy from 50% and 0%, respectively, to 100% sterile protection. It was also found that antigenic interference, a reduction in anti-CSP titres when Rv21 and PvTRAP are combined, occurred only in the presence of Matrix M adjuvant, and not when using alum, AddaVax or no adjuvant. With a view to creating a single-component multi-antigen vaccine, which would be more cost-effective than a multi-component vaccine, experiments were carried out to establish the virus-like particle Qβ as a platform capable of eliciting protective immunity via the display of short peptides derived from the CSP repeat region of both P. vivax and P. falciparum. For the first time, a tetramer peptide derived from the CSP repeat region of P. vivax VK210, AGDR, was shown capable of eliciting protective immunity alone. Finally, five novel linear B-cell epitopes were discovered, one from P. falciparum CSP, three from P. vivax TRAP and one from TRSP, each capable of conferring partial protection on mice. These epitopes were identified using novel screening methods, using sera from whole-protein vaccinated mice or by exploiting conservation within invasion protein sequences. Two of the protective epitopes, (NANP)6 and (ADGN long) were combined and found to enhance protective efficacy as predicted by the mathematical model. Thus this thesis lays the groundwork for the development of a single-component multi-epitope malaria vaccine with enhanced protective efficacy.

Apical membrane antigen 1 (AMA1) is a leading candidate vaccine antigen against blood stage malaria and several clinical trials using mostly protein-in-adjuvant vaccines have shown limited success. This thesis describes the development of recombinant adenoviral (AdHu5) and poxviral (MVA) vectors encoding AMA1 from Plasmodium chabaudi murine parasites. In this murine malaria model, AdHu5 and MVA encoding AMA1 when used in a heterologous prime boost regime showed excellent immunogenicity, both humoral and cellular. The vaccination regime was protective against blood stage challenge and both antibodies and CD4+ T cells found to be important for vaccine induced blood stage protection. In parallel to this novel P. falciparum vaccines encoding AMA1 were also developed and administered in a similar prime boost regime to mice and rabbits. The vaccination regime induced cellular immune response and high titre antibodies against AMA1 and these antibodies showed growth inhibitory activity against the homologous parasite strain. In an effort to overcome the issue of antigenic polymorphism and to circumvent pre-existing immunity to human adenovirus, biallelic simian and human adenoviral vectors and MVA encoding AMA1 vaccines were also developed and administered to mice and macaques. These vectors also induced high titre antibodies and the serum from macaques was found to have growth inhibitory activity. These vaccine candidates are now being taken forward to Phase I/II clinical trials in Oxford. This work also described the attempt to improve MVA as a antibody inducing vector to allow better antibody mediated immunity to blood stage malaria.

Introduction: Despite advances in prevention and treatment of vaccine-preventable diseases, diarrhoeal and pneumococcal diseases remain a major source of morbidity and mortality among children worldwide. The introduction of vaccines has led to dramatic reductions in the burden of infectious diseases and mortality among children. South Africa was the first country in Africa to introduce rotavirus vaccine (RV) and pneumococcal conjugate vaccine (PCV) in 2008 as part of its national immunisation programme. Performance of immunization programmes is commonly measured by the coverage and uptake of vaccines, hence ensuring that every child is immunized at the earliest or appropriate age is an important public health goal. We therefore assessed proportions and factors associated with uptake of RV and PCV among infants who were followed during the routine demographic surveillance system of the Africa Centre Demographic Surveillance Area (DSA) in a rural South Africa setting. Methods: An open cohort of children resident in the DSA aged 12 months or below was prospectively followed between January 2008 and December 2011. Trained interviewers visited households and administered a standardised questionnaire. Mothers and caregivers were asked to show the interviewers the South African Road-To-Health (RTH) card for all children aged 12-23 months at the time of the visit or through maternal recall for children whose RTH card was not available. The RTH card includes dates of all routine vaccinations a child has received. Rotavirus vaccine doses are given at 6 and 14 weeks of age and PCV doses at 6 and 14 weeks and 9 months. Complete uptake was defined as “complete” if a child received all recommended doses of either RV or PCV and incomplete if a child did not receive any dose or received one dose of RV or PCV. Logistic regression models were used to assess factors associated with uptake of RV and PCV separately. Results: A total of 6,263 children were included in the analysis, of which 3,082 (49%) were females. At birth, 3,823 (61%) children were living in rural areas and about one-sixth of the children were living in households located far from a health facility (≥5km). The overall uptake of RV and PCV vaccines among children aged 12 months or below was 50% and 37% respectively. Infants who ever migrated outside the DSA had reduced odds of complete RV and PCV vaccination compared to infants who did not out migrate (adjusted OR=0.49, 95% CI 0.41-0.57) and (adjusted OR=0.52, 95% CI 0.43-0.63) respectively. Complete uptake of RV was associated with the increase in education levels of mothers compared secondary education (adjusted OR=1.70, 95 % CI 1.02-2.34) or tertiary education (adjusted OR=1.80, 95 % CI 0.97-2.44). Infants whose mothers were employed were less likely than infants whose mothers were not employed to have complete vaccination for RV or PCV (adjusted OR=0.71, 95 % CI 0.60-0.84) and (adjusted OR=0.81, 95% CI 0.68-0.96) respectively. Similarly, infants whose mothers were resident in the DSA were more likely than infants whose mothers were not resident to have complete vaccination for RV or PCV (adjusted OR=1.97, 95 % CI 1.49-2.60) and (adjusted OR=1.55, 95% CI 1.16-2.08) respectively. Conclusion and recommendation: The uptake of complete RV and PCV were generally low among children in rural South Africa within our study period. Child outmigration, maternal employment, maternal education and maternal residency in the DSA at child birth were associated with complete uptake of RV and PCV vaccines. Programmes targeting mothers of lower socio-economic status are required. Such programmes may include vaccine awareness and immunization campaigns at the community level to improve vaccine uptake and more targeted interventions in areas with low RV and PCV uptake.

Chapter I Introduction Salmonellae are facultative Gram-negative intracellular pathogens. Different serovars of it causes a variety of diseases in multiple hosts with different disease outcomes. Salmonella enterica serovar Enteritidis and Typhimurium (STM) can infect domestic animals causing gastroenteritis or typhoid like fever. Typhoid fever in humans which is actually caused by Salmonella enterica serovar Typhi still remains a significant health problem in many parts of the world with an estimated annual incidence of nearly 16 million cases and about 600,000 deaths. The infection begins via the orofecal route following which it invades the intestinal mucosa through several ways, namely by antigen sampling M cells, CD18 macrophages present in the intestinal lumen or via a forced entry in the non-phagocytic enterocytes. Upon entry, Salmonella resides in an intracellular phagosomal compartment called Salmonella containing vacuole (SCV) and has several strategies to counteract the host defense mechanisms. Following phagocytosis and its compartmentalization into Salmonella containing vacuole (SCV), a series of defense mechanisms are initiated. These include toxic reactive oxygen species or super oxide production, nitric oxide production, phagosomal acidification and release of hydrolases and defensins through fusion of phagosome with lysosomes generating highly bactericidal environment. The SCV transiently acquires endocytic markers like TfnR, EEA1, Rab4, Rab5, Rab11 and Rab7 and resist killing by avoiding phagosomal maturation and vesicular trafficking of iNOS and NADPH oxidase vesicles. Moreover, Salmonella also uses acidic pH of the SCV (~ pH 4.5) to assemble the Salmonella Pathogenecity Island 2 (SPI-2) type three secretion system (TTSS) which is essential for survival inside the macrophages. Salmonella uses these hostile conditions inside the host as cues for regulating their virulence factors using global regulatory factors. Hfq is one such global regulator playing an important role in many physiological processes and stress responses. Understanding the importance of Hfq regulated genes which impart Salmonella survival advantage under hostile conditions for successful infection will be of particular significance. The host too recognizes pathogen using innate immune receptors present either on the cell surface like TLRs (Toll Like Receptors) or inside the cells like NLRs (Nod Like Receptors). Innate immune receptors recognize pathogen associated molecular patterns (PAMPs) such as Lipopolysacharide (LPS), peptidoglycon (PGN), or hypomethylated DNA or RNA. Recognition of PAMPs by innate receptors leads, via activation of transcription factors (NF-κB and IRF3), to the generation of pro and anti-inflammatory cytokines, chemokines. Vaccination has been practiced for many years and it is one of the most effective methods of controlling infectious diseases like typhoid. At present two licensed vaccines against Salmonella are in use globally namely, Vi polysaccharide subunit vaccine (Typhim Vi™) and live attenuated typhoid vaccine (Vivotif Berma™). Lack of immunological memory, low efficacy (55-75 % protection) and requirement of higher number of doses are the important practical shortcomings associated with the currently used vaccines. So there is a need for a safer and immunogenic vaccine to combat Salmonella infection. Chapter II Salmonella Typhimurium lacking hfq gene induces long term memory response and confers protective immunity Currently available vaccines for typhoid have less-than-desired efficacy and certain unacceptable side effects, making it pertinent to search for new improved ones. Of the various strategies used for the generation of vaccine strains, focus is on manipulation of virulence regulator genes for bacterial attenuation. Hfq is a RNA chaperon which mediates the binding of small RNA to the mRNA and assists in post-transcriptional gene regulation in bacteria. Salmonella hfq deletion mutant is highly attenuated in vitro as well as in vivo implying its role in bacterial virulence. In this study, we have evaluated the efficacy of the Salmonella Typhimurium hfq deletion mutant as a candidate for live oral vaccine against Salmonella infection in murine salmonellosis model. The hfq deletion mutant is not only able to confer protection when administered orally to the mice against oral challenge with serovar Typhimurium virulent strain, but also elicits cross protective immune responses to other Salmonella serovars. The vaccine candidate appears to be safe for use in pregnant mice. This protection is partially mediated by the increase in the number of CD4+ T lymphocytes upon vaccination. STM hfq deletion mutant further exhibited significant increase in the lipopolysaccharide as well as outer membrane protein specific IgG in the serum as well as secretory S-IgA in the intestinal washes. In addition, vaccination led to an increased serum IFN-γ and IL-6. Taken together, our results suggest that the Salmonella Typhimurium hfq deletion mutant can be an excellent live oral vaccine candidate. Chapter III Acidic pH induced STM1485 gene governs intracellular replication and pathogenesis in Salmonella During the course of infection, Salmonella has to face several potentially lethal environmental conditions such as low pH both inside and outside the host. The ability to sense and respond to the acidic pH is crucial for survival and replication of Salmonella. Exposure to acidic pH results in the expression of large pool of virulence genes. One such gene highly up regulated inside the macrophage is STM 1485. In order to understand physiological role of STM 1485 in Salmonella pathogenesis, STM 1485 gene was deleted chromosomally and characterized in vitro and in vivo. In vitro the mutant did not show any growth defects at pH 4.5 and no difference in acid tolerance response. The 1485 deletion mutant was compromised in its capacity to proliferate inside the cells and is further lowered inside activated macrophages. We further showed that surface translocation of SPI-2 encoded translocon protein SseB was reduced at low pH in vitro in STM 1485 mutant and the mutant was found to colocalize with lysosomes higher than the wild type. In addition, the STM 1485 deletion mutant displayed decreased virulence in murine typhoid model when infected intragastrically. Based on our results, we hypothesize that the acid shock protein encoded by the STM 1485 might be involved in the formation of SPI-2 translocon at low pH and there by contributing to the virulence of Salmonella. Chapter IV Role of Nod1 in sensing vacuolar pathogen Salmonella in epithelial cells Nod1 and Nod2 are the archetypal members of the Nod like receptor family (NLR) and they recognize distinct peptidoglycan motifs of Gram-negative and Gram-positive bacteria respectively. Role of Nod1 and Nod2 in sensing bacterial pathogens have been elucidated. However, the role of Nod1 in sensing vacuolar pathogen Salmonella in epithelial cells is not understood. So in this study we investiged the role of Nod1 in the innate immune response against Salmonella in epithelial cells. We demonstrate that the recognition of Salmonella by Nod1 leads to NF-κB activation and this activation is diminished in epithelial cells expressing a dominant-negative Nod1 construct or Nod1 shRNA. Using a set of Salmonella mutants we show that the availability of ligand is higher when the bacteria were in cytosol rather than in vacuole. Further we also observed that the Nod1 mediated killing of Salmonella is mediated through the defensins. Based on our results we hypothesize that Salmonella uses its vacuolar niche to evade Nod1 mediated innate immune response.

INTRODUÇÃO: A infecção pelo vírus da hepatite B (VHB) é responsável por grande parte das doenças hepáticas crônicas em todo o mundo. Em pessoas vivendo com HIV/Aids (PVHA) a infecção pelo VHB tem maior risco de evolução para cirrose e carcinoma hepatocelular. A vacina da hepatite B é importante na prevenção de doença potencialmente grave, particularmente em PVHA, já que ambos os vírus têm as mesmas vias de transmissão e a coinfecção tem uma alta morbidade. Indivíduos imunocompetentes têm uma boa resposta humoral após uma primeira série de vacina da hepatite B e não há recomendações de rotina para doses de reforço. PVHA podem ter uma pior resposta à vacina da hepatite B, quando comparada à resposta em indivíduos imunocompetentes e a duração da imunidade nesses pacientes é desconhecida. OBJETIVOS: Geral: Avaliar os marcadores sorológicos de proteção e infecção pelo VHB em pacientes adultos vivendo com HIV/Aids, vacinados previamente para hepatite B. Específicos: Avaliar a persistência dos anticorpos anti-HBs em PVHA vacinadas previamente para hepatite B e que apresentaram resposta humoral protetora inicial; avaliar a resposta sorológica à revacinação para hepatite B nos pacientes vacinados previamente e que não apresentaram resposta humoral protetora inicial; investigar a presença de marcadores sorológicos de infecção pelo VHB em PVHA vacinadas previamente para hepatite B. MÉTODOS: Estudo observacional de coorte retrospectiva de PVHA vacinadas primariamente para hepatite B entre 2001 e 2002. Marcadores sorológicos de infecção e proteção para o vírus da hepatite B foram investigados nesses pacientes que ainda estavam em acompanhamento no Serviço de Extensão ao Atendimento de Pacientes HIV/Aids (SEAP), da divisão de Clínica de Moléstias Infecciosas e Parasitárias do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo entre 2012 e 2014. RESULTADOS: Uma coorte de 121 PVHA foi analisada quanto à soroconversão e persistência do anti-HBs. A maioria era do sexo feminino (54,5%) com média de idade de 50,1 anos. Destes pacientes, 58 (grupo 1) eram inicialmente respondedores à primeira série da vacina (anti- HBs >=10 mUI/mL) e 63 (grupo 2) eram não respondedores. Após um período mediano de avaliação de 11 anos, nenhum dos pacientes teve evidência sorológica de infecção pelo VHB e 41/58 (70.7%) dos inicialmente respondedores mantinham anti-HBs >= 10 mUI/mL. Maior contagem de células T CD4+ e anti-HBs >= 100 mUI/mL, no momento da primeira série vacinal, estiveram associados à persistência de anti-HBs. Durante o período avaliado, 35/63 (55.6%) dos pacientes inicialmente não respondedores (grupo 2) soroconverteram com sucesso (anti-HBs >= 10 mUI/mL) em resposta a uma ou mais doses de reforço vacinal. Foi associado à soroconversão do anti-HBs o número de doses de reforço recebidas. A partir do momento da soroconversão (anti-HBs >=10 mUI/mL), 70 pacientes não receberam nenhuma dose adicional de vacina de hepatite B (grupo 3). Após um período mediano de 10 anos, 54/70 (77,1%) destes indivíduos mantinham anti- HBs >= 10 mUI/mL. CONCLUSÕES: A avaliação dos marcadores sorológicos para VHB em PVHA vacinadas previamente para hepatite B evidenciou: alta persistência de anti-HBs após um período de 10 a 11 anos; doses adicionais de vacina foram capazes de induzir resposta humoral em indivíduos inicialmente não respondedores; não foram detectados marcadores sorológicos de infecção (HbsAg ou Anti-HBc) após 11 anos da vacinação inicial / BACKGROUND: Hepatitis B Virus (HBV) infection is responsible for great part of chronic hepatic diseases worldwide. In people living with HIV (PLHIV), HBV infection has more risk of progressing to cirrhosis and hepatocarcinoma. Hepatitis B vaccine is important in the prevention of a potentially severe disease, particularly in PLHIV, since both viruses have the same routes of transmission and co-infection has greater morbidity. Immunocompetent individuals have a good humoral response after the first hepatitis B vaccine series and no recommendation is made regarding booster doses. PLHIV may have a poor hepatitis B vaccine response, when compared to immunocompetent and the duration of immunity in these patients is unknown. OBJECTIVES: General: Evaluate serological markers of infection and protection from HBV in PLHIV previously vaccinated for hepatitis B. Specific: Evaluate anti-HBs persistence in PLHIV previously vaccinated for HBV who responded to a primary vaccine series; evaluate response to revaccination for hepatitis B in patients who did not respond to first vaccine series; investigate serological markers of infection from HBV in PLHIV previously vaccinated for hepatitis B. METHODS: Observational retrospective study of a PLHIV cohort primarily vaccinated between 2001 and 2002 for hepatitis B. Serological markers of infection and protection from HBV were investigated in those patients who were still attending the HIV/AIDS Patient Care Extension Service at the Clinical Division of Infectious and Parasitic Diseases attached to Hospital das Clínicas at Faculdade de Medicina at Universidade de São Paulo between 2012 and 2014. RESULTS: A cohort of 121 PLHIV was analyzed for seroconversion and persistence of anti-HBs. The majority were female (54.5%) and mean age 50.1 years. From these patients, 58 (group 1) were initially responders to the first vaccine series (anti- HBs >=10 mIU/mL) and 63 (group 2) were non- responders. After a median period of 11 years, none of the patients had serologic evidence of HBV infection and 41/58 (70.7%) of the initially responders had maintained anti-HBs >=10 mIU/mL. Greater CD4+ cell counts and anti- HBs>= 100mIU/mL at the time of first vaccine series were associated with persistence of anti-HBs. During evaluation period, 35/63 (55.6%) of the initially non-responders (group 2) successfully seroconverted (anti-HBs >=10 mIU/mL) in response to one or more booster doses. Booster doses may be effective in PLHIV. Number of booster doses were associated to seroconversion. Seventy of the 121 patients did not receive any further booster doses of hepatitis B vaccine from the time of their seroconversion (anti-HBs >=10 mIU/mL) (group 3). After 10 years of the seroconversion, 54/70 (77,1%) of these individuals has maintained anti- HBs >= 10 mIU/mL. CONCLUSIONS: Evaluation of serological markers for HBV in PLHIV previously vaccinated for hepatitis B showed: strong persistence of anti-HBs after a period of 10 to 11 years; additional vaccine doses elicited humoral response in initially non-responders; there was no serologic evidence of HBV infection (HbsAg ou Anti-HBc) about 11 years after initial vaccination

INTRODUÇÃO: A infecção pelo vírus da hepatite B (VHB) é responsável por grande parte das doenças hepáticas crônicas em todo o mundo. Em pessoas vivendo com HIV/Aids (PVHA) a infecção pelo VHB tem maior risco de evolução para cirrose e carcinoma hepatocelular. A vacina da hepatite B é importante na prevenção de doença potencialmente grave, particularmente em PVHA, já que ambos os vírus têm as mesmas vias de transmissão e a coinfecção tem uma alta morbidade. Indivíduos imunocompetentes têm uma boa resposta humoral após uma primeira série de vacina da hepatite B e não há recomendações de rotina para doses de reforço. PVHA podem ter uma pior resposta à vacina da hepatite B, quando comparada à resposta em indivíduos imunocompetentes e a duração da imunidade nesses pacientes é desconhecida. OBJETIVOS: Geral: Avaliar os marcadores sorológicos de proteção e infecção pelo VHB em pacientes adultos vivendo com HIV/Aids, vacinados previamente para hepatite B. Específicos: Avaliar a persistência dos anticorpos anti-HBs em PVHA vacinadas previamente para hepatite B e que apresentaram resposta humoral protetora inicial; avaliar a resposta sorológica à revacinação para hepatite B nos pacientes vacinados previamente e que não apresentaram resposta humoral protetora inicial; investigar a presença de marcadores sorológicos de infecção pelo VHB em PVHA vacinadas previamente para hepatite B. MÉTODOS: Estudo observacional de coorte retrospectiva de PVHA vacinadas primariamente para hepatite B entre 2001 e 2002. Marcadores sorológicos de infecção e proteção para o vírus da hepatite B foram investigados nesses pacientes que ainda estavam em acompanhamento no Serviço de Extensão ao Atendimento de Pacientes HIV/Aids (SEAP), da divisão de Clínica de Moléstias Infecciosas e Parasitárias do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo entre 2012 e 2014. RESULTADOS: Uma coorte de 121 PVHA foi analisada quanto à soroconversão e persistência do anti-HBs. A maioria era do sexo feminino (54,5%) com média de idade de 50,1 anos. Destes pacientes, 58 (grupo 1) eram inicialmente respondedores à primeira série da vacina (anti- HBs >=10 mUI/mL) e 63 (grupo 2) eram não respondedores. Após um período mediano de avaliação de 11 anos, nenhum dos pacientes teve evidência sorológica de infecção pelo VHB e 41/58 (70.7%) dos inicialmente respondedores mantinham anti-HBs >= 10 mUI/mL. Maior contagem de células T CD4+ e anti-HBs >= 100 mUI/mL, no momento da primeira série vacinal, estiveram associados à persistência de anti-HBs. Durante o período avaliado, 35/63 (55.6%) dos pacientes inicialmente não respondedores (grupo 2) soroconverteram com sucesso (anti-HBs >= 10 mUI/mL) em resposta a uma ou mais doses de reforço vacinal. Foi associado à soroconversão do anti-HBs o número de doses de reforço recebidas. A partir do momento da soroconversão (anti-HBs >=10 mUI/mL), 70 pacientes não receberam nenhuma dose adicional de vacina de hepatite B (grupo 3). Após um período mediano de 10 anos, 54/70 (77,1%) destes indivíduos mantinham anti- HBs >= 10 mUI/mL. CONCLUSÕES: A avaliação dos marcadores sorológicos para VHB em PVHA vacinadas previamente para hepatite B evidenciou: alta persistência de anti-HBs após um período de 10 a 11 anos; doses adicionais de vacina foram capazes de induzir resposta humoral em indivíduos inicialmente não respondedores; não foram detectados marcadores sorológicos de infecção (HbsAg ou Anti-HBc) após 11 anos da vacinação inicial / BACKGROUND: Hepatitis B Virus (HBV) infection is responsible for great part of chronic hepatic diseases worldwide. In people living with HIV (PLHIV), HBV infection has more risk of progressing to cirrhosis and hepatocarcinoma. Hepatitis B vaccine is important in the prevention of a potentially severe disease, particularly in PLHIV, since both viruses have the same routes of transmission and co-infection has greater morbidity. Immunocompetent individuals have a good humoral response after the first hepatitis B vaccine series and no recommendation is made regarding booster doses. PLHIV may have a poor hepatitis B vaccine response, when compared to immunocompetent and the duration of immunity in these patients is unknown. OBJECTIVES: General: Evaluate serological markers of infection and protection from HBV in PLHIV previously vaccinated for hepatitis B. Specific: Evaluate anti-HBs persistence in PLHIV previously vaccinated for HBV who responded to a primary vaccine series; evaluate response to revaccination for hepatitis B in patients who did not respond to first vaccine series; investigate serological markers of infection from HBV in PLHIV previously vaccinated for hepatitis B. METHODS: Observational retrospective study of a PLHIV cohort primarily vaccinated between 2001 and 2002 for hepatitis B. Serological markers of infection and protection from HBV were investigated in those patients who were still attending the HIV/AIDS Patient Care Extension Service at the Clinical Division of Infectious and Parasitic Diseases attached to Hospital das Clínicas at Faculdade de Medicina at Universidade de São Paulo between 2012 and 2014. RESULTS: A cohort of 121 PLHIV was analyzed for seroconversion and persistence of anti-HBs. The majority were female (54.5%) and mean age 50.1 years. From these patients, 58 (group 1) were initially responders to the first vaccine series (anti- HBs >=10 mIU/mL) and 63 (group 2) were non- responders. After a median period of 11 years, none of the patients had serologic evidence of HBV infection and 41/58 (70.7%) of the initially responders had maintained anti-HBs >=10 mIU/mL. Greater CD4+ cell counts and anti- HBs>= 100mIU/mL at the time of first vaccine series were associated with persistence of anti-HBs. During evaluation period, 35/63 (55.6%) of the initially non-responders (group 2) successfully seroconverted (anti-HBs >=10 mIU/mL) in response to one or more booster doses. Booster doses may be effective in PLHIV. Number of booster doses were associated to seroconversion. Seventy of the 121 patients did not receive any further booster doses of hepatitis B vaccine from the time of their seroconversion (anti-HBs >=10 mIU/mL) (group 3). After 10 years of the seroconversion, 54/70 (77,1%) of these individuals has maintained anti- HBs >= 10 mIU/mL. CONCLUSIONS: Evaluation of serological markers for HBV in PLHIV previously vaccinated for hepatitis B showed: strong persistence of anti-HBs after a period of 10 to 11 years; additional vaccine doses elicited humoral response in initially non-responders; there was no serologic evidence of HBV infection (HbsAg ou Anti-HBc) about 11 years after initial vaccination