Lionel Tan

Advances in the Development of Vaccines against Neisseria meningitidis

Developments during the past decade have renewed hopes for solving this seemingly intractable problem. Knowledge of the meningococcal genome has led to the identification of novel antigens that have been incorporated into the NMB vaccines now being studied in clinical trials. However, it remains unclear whether these vaccines will provide sufficient immunogenicity in infants as well as wide-ranging coverage. This review highlights the evolution of meningococcal vaccines in general and discusses strategies being used to overcome the barriers to developing vaccines against NMB. Epidemiology of N. meningitidis Infection Meningococcal disease is a global health problem. The World Health Organization estimates that there are 1.2 million cases of invasive meningococcal disease and 135,000 related deaths annually. 3 Although the disease occurs sporadically in industrialized countries, with an incidence of 0.35 cases per 100,000 population in the United States and of 1.01 per 100,000 in Europe (ranging from 0.25 to 4.4 per 100,000 in Italy and Malta, respectively), 4 the major disease burden is in the nonindustrialized countries. A recent epidemic in Nigeria resulted in 4164 cases and 171 deaths in 1 week alone. 5 The meningococcus is pathogenic only in humans. It colonizes the nasopharynx asymptomatically in up to 40% of the adult population but occasionally causes invasive disease. When the infection is classified according to the polysaccharide capsule surrounding the bacterium, only six capsular groups (A, B, C, W-135, X, and Y) are associated with invasive disease. 6 The epidemiology of disease caused by these groups varies: group A is responsible for large epidemics in Africa, in which the incidence approaches 1000 cases per 100,000 population (and may involve environmental factors), whereas groups B and C cause disease predominantly in industrialized and newly industrialized countries. 2,6 Recently, groups W-135 and X (predominantly in Africa) and group Y (in the United States and other countries) have emerged as important disease-causing isolates.

Acute lung injury and other serious complications of Plasmodium vivax malaria.

Plasmodium vivax infection is classified among the so-called benign malarias, but it is increasingly recognised that serious and even life-threatening complications may occur. We present the case of a returning traveller with P vivax infection who developed acute lung injury 3 days into treatment, and discuss the serious complications of this infection. The case highlights the fact that P vivax infection is benign by name but not always by nature.

Characterization of Neisseria meningitidis isolates that do not express the virulence factor and vaccine antigen factor H binding protein.

ABSTRACT Neisseria meningitidis remains a leading cause of bacterial sepsis and meningitis. Complement is a key component of natural immunity against this important human pathogen, which has evolved multiple mechanisms to evade complement-mediated lysis. One approach adopted by the meningococcus is to recruit a human negative regulator of the complement system, factor H (fH), to its surface via a lipoprotein, factor H binding protein (fHbp). Additionally, fHbp is a key antigen in vaccines currently being evaluated in clinical trials. Here we characterize strains of N. meningitidis from several distinct clonal complexes which do not express fHbp; all strains were recovered from patients with disseminated meningococcal disease. We demonstrate that these strains have either a frameshift mutation in the fHbp open reading frame or have entirely lost fHbp and some flanking sequences. No fH binding was detected to other ligands among the fHbp-negative strains. The implications of these findings for meningococcal pathogenesis and prevention are discussed.

Design and Evaluation of Meningococcal Vaccines Through Structure-Based Modification of Host and Pathogen Molecules.

Neisseria meningitis remains a leading cause of sepsis and meningitis, and vaccines are required to prevent infections by this important human pathogen. Factor H binding protein (fHbp) is a key antigen that elicits protective immunity against the meningococcus and recruits the host complement regulator, fH. As the high affinity interaction between fHbp and fH could impair immune responses, we sought to identify non-functional fHbps that could act as effective immunogens. This was achieved by alanine substitution of fHbps from all three variant groups (V1, V2 and V3 fHbp) of the protein; while some residues affected fH binding in each variant group, the distribution of key amino underlying the interaction with fH differed between the V1, V2 and V3 proteins. The atomic structure of V3 fHbp in complex with fH and of the C-terminal barrel of V2 fHbp provide explanations to the differences in the precise nature of their interactions with fH, and the instability of the V2 protein. To develop transgenic models to assess the efficacy of non-functional fHbps, we determined the structural basis of the low level of interaction between fHbp and murine fH; in addition to changes in amino acids in the fHbp binding site, murine fH has a distinct conformation compared with the human protein that would sterically inhibit binding to fHbp. Non-functional V1 fHbps were further characterised by binding and structural studies, and shown in non-transgenic and transgenic mice (expressing chimeric fH that binds fHbp and precisely regulates complement system) to retain their immunogenicity. Our findings provide a catalogue of non-functional fHbps from all variant groups that can be included in new generation meningococcal vaccines, and establish proof-in-principle for clinical studies to compare their efficacy with wild-type fHbps.

Suppression of HBV by Tenofovir in HBV/HIV Coinfected Patients: A Systematic Review and Meta-Analysis

Background Hepatitis B coinfection is common in HIV-positive individuals and as antiretroviral therapy has made death due to AIDS less common, hepatitis has become increasingly important. Several drugs are available to treat hepatitis B. The most potent and the one with the lowest risk of resistance appears to be tenofovir (TDF). However there are several questions that remain unanswered regarding the use of TDF, including the proportion of patients that achieves suppression of HBV viral load and over what time, whether suppression is durable and whether prior treatment with other HBV-active drugs such as lamivudine, compromises the efficacy of TDF due to possible selection of resistant HBV strains. Methods A systematic review and meta-analysis following PRISMA guidelines and using multilevel mixed effects logistic regression, stratified by prior and/or concomitant use of lamivudine and/or emtricitabine. Results Data was available from 23 studies including 550 HBV/HIV coinfected patients treated with TDF. Follow up was for up to seven years but to ensure sufficient power the data analyses were limited to three years. The overall proportion achieving suppression of HBV replication was 57.4%, 79.0% and 85.6% at one, two and three years, respectively. No effect of prior or concomitant 3TC/FTC was shown. Virological rebound on TDF treatment was rare. Interpretation TDF suppresses HBV to undetectable levels in the majority of HBV/HIV coinfected patients with the proportion fully suppressed continuing to increase during continuous treatment. Prior treatment with 3TC/FTC does not compromise efficacy of TDF treatment. The use of combination treatment with 3TC/FTC offers no significant benefit over TDF alone.

Reduced glomerular filtration rate but sustained virologic response in HIV/hepatitis B co-infected individuals on long-term tenofovir

Summary.  Reports have described a decrease in glomerular filtration rate (eGFR) associated with tenofovir disoproxil fumarate (TDF) use in HIV positive individuals. However, no study has examined renal function over a prolonged period in HIV/hepatitis B virus (HBV) co‐infected patients. We assessed the long‐term durability and toxicity of TDF in a cohort of 39 e antigen (eAg) positive co‐infected patients commenced on TDF 245 mg daily either in addition to or as part of standard antiretroviral therapy. Immunological and virological parameters were followed to 260 weeks, with the median follow‐up period being 251 weeks (range 69–290 weeks). eGFR was calculated using the Modification in Diet in Renal Disease equation. On treatment at 260 weeks, 88% (14/16) had HIV viral load <50 copies/mL, median CD4 count rose from 318 to 532 cells/mm3, median alanine aminotransferase (ALT) fell from 61 IU/L to 42 IU/L, with 35% (7/20) having a normal ALT, median HBV DNA fell from 69 × 106 copies/mL to 500 copies/mL, with 75% (12/16) having an undetectable HBV DNA level and 55% (6/11) becoming eAg negative. Of those with detectable HBV DNA, none had TDF resistance mutations. The eGFR declined by 22.19 mL/min/1.73 mm2 from baseline (P = 0.023) over this period, which was unaffected by protease inhibitor use, baseline CD4 count, ALT or HBV DNA level. Three patients discontinued TDF therapy due to renal dysfunction. In conclusion, TDF has sustained efficacy but is associated with a significant decline in eGFR. Further larger studies are required to clarify this observation.

Current views of haemolytic streptococcal pathogenesis.

Purpose of review Increasing disease caused by beta-haemolytic streptococci indicates the need for improved understanding of pathogenesis. Recent findings Streptococcus pyogenes, or group A Streptococcus (GAS), causes significant disease worldwide. The closely related Streptococcus dysgalactiae subspecies equisimilis (SDSE) is increasingly recognized as causing a similar disease spectrum. Whole-genome sequencing applied to the study of outbreaks may reveal factors that contribute to pathogenesis and changes in epidemiology. The role of quorum sensing in biofilm formation, and interspecies communication with other streptococci, is discussed. GAS has evolved multiple mechanisms to evade the humoral arm of innate immunity, including complement, which is well known in protecting the host from bacteria, and the coagulation–fibrinolytic system, which is increasingly recognized as an innate immune effector. Summary Molecular biology has enhanced our understanding of the intricate balance of host–pathogen interactions that result in clearance or establishment of invasive streptococcal infection. Although the skin and oropharynx remain the usual ecological niche of GAS and SDSE, occasionally the bacteria find themselves within deeper tissues and blood. Recent research has armed us with better knowledge of bacterial adaptations to this alternative environment. However, the challenge is to translate this knowledge into clinical practice, through the development of novel therapeutic options and ultimately a vaccine against GAS.

Distinct Binding and Immunogenic Properties of the Gonococcal Homologue of Meningococcal Factor H Binding Protein

Neisseria meningitidis is a leading cause of sepsis and meningitis. The bacterium recruits factor H (fH), a negative regulator of the complement system, to its surface via fH binding protein (fHbp), providing a mechanism to avoid complement-mediated killing. fHbp is an important antigen that elicits protective immunity against the meningococcus and has been divided into three different variant groups, V1, V2 and V3, or families A and B. However, immunisation with fHbp V1 does not result in cross-protection against V2 and V3 and vice versa. Furthermore, high affinity binding of fH could impair immune responses against fHbp. Here, we investigate a homologue of fHbp in Neisseria gonorrhoeae, designated as Gonococcal homologue of fHbp (Ghfp) which we show is a promising vaccine candidate for N. meningitidis. We demonstrate that Gfhp is not expressed on the surface of the gonococcus and, despite its high level of identity with fHbp, does not bind fH. Substitution of only two amino acids in Ghfp is sufficient to confer fH binding, while the corresponding residues in V3 fHbp are essential for high affinity fH binding. Furthermore, immune responses against Ghfp recognise V1, V2 and V3 fHbps expressed by a range of clinical isolates, and have serum bactericidal activity against N. meningitidis expressing fHbps from all variant groups.

Bromine, bear-claw scratch fasciotomies, and the Eagle effect: management of group A streptococcal necrotising fasciitis and its association with trauma

Necrotising fasciitis is a rare, but potentially fatal, soft-tissue infection. Historical depictions of the disease have been described since classical times and were mainly recorded in wartime reports of battle injuries. Although several different species of bacteria can cause necrotising fasciitis, perhaps the most widely known is group A streptococcus (GAS). Infection control, early surgical debridement, and antibiotic therapy are now the central tenets of the clinical management of necrotising fasciitis; these treatment approaches all originate from those used in wars in the past 150 years. We review reports from the 19th century, early 20th century, and mid-20th century onwards to show how the management of necrotising fasciitis has progressed in parallel with prevailing scientific thought and medical practice. Historically, necrotising fasciitis has often, but not exclusively, been associated with penetrating trauma. However, along with a worldwide increase in invasive GAS disease, recent reports have cited cases of necrotising fasciitis following non-combat-related injuries or in the absence of antecedent events. We also investigate the specific association between GAS necrotising fasciitis and trauma. In the 21st century, molecular biology has improved our understanding of GAS pathogenesis, but has not yet affected attributable mortality.

Editorial Commentary: Step on the GAS: Are We Almost There for Clindamycin and Intravenous Immunoglobulin?

Recent outbreaks of scarlet fever [1], and increased maternal deaths due to invasive streptococcal disease [2] are poignant reminders that group A Streptococcus (GAS) remains a global threat to human health. Thankfully, GAS remains susceptible to penicillin, which is usually sufficient for the majority of patients infected with GAS. However, what to do in the minority of patients who develop severe invasive GAS (iGAS), typified by streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis, remains an enigma. The questions facing treating physicians are what adjunctive therapy should be administered, and at what point during the course of the illness? Two particular therapies for severe iGAS infection have been debated over the last 2 decades: clindamycin and intravenous immunoglobulin (IVIG). The other area of ambiguity is whether clinicians should provide antibiotics for close contacts of patients with iGAS. Sec