Follow-up of Gambian children recruited to a pilot safety and immunogenicity study of the malaria vaccine SPf66

A pilot safety and immunogenicity trial of the malaria vaccine SPf66 was undertaken in The Gambia in 1993. One hundred and fifty infants aged 6–11 months were immunized with either 0.5 mg or 1.0 mg of SPf66 produced either in Colombia or in the USA or with a control vaccine. Children who received SPf66 experienced more clinical attacks of malaria than did children in the control group during the first period of surveillance and the difference in incidence between children who had received high dose Colombian vaccine and the control children was statistically significant at the 5% level. During the 1995 malaria transmission season, 127 children from the original cohort of 150 were observed. During 18 weeks of intensive surveillance, the incidence of clinical malaria was again higher among children who had received SPf66 than among children who had received inactivated polio vaccine (6.23 vs 4.89 clinical attacks per 1000 days at risk), the effect being most marked among children who were in the high dose groups, but differences between groups were now no longer statistically significant .     

Serological responses of Gambian children to immunization with the malaria vaccine SPf66

Antibody responses to the malaria vaccine SPf66 and to its constituent peptides were measured over a period of 2 years in Gambian children who had been immunized with SPf66 or with a control vaccine (inactivated polio vaccine). Three hundred and six of 308 children (99%) who had received three doses of SPf66 vaccine had antibodies to SPf66 at a level above that found in European controls who had not been exposed to malaria. Responses to the constituent peptides derived from 35.1, 55.1 and 83.1-kDa proteins were found in 88%, 97% and 97% of children, respectively; 26% had an antibody response to the NANP repeat peptide of circumsporozoite protein which is also included in the SPf66 vaccine. A response to SPf66 was found in 22% of children who had received the control vaccine. Antibody responses to NANP, 35.1, 55.1 and 83.1-kDa peptide were found in 3%, 33%, 49% and 33% of these children. Overall, no significant correlation was found between the level of anti-SPf66 antibody at the beginning of the malaria transmission season following vaccination and the subsequent risk of malaria. However, further analysis showed that among the control children who had acquired antibodies to SPf66 as a result of natural exposure to malaria, those with high levels of anti-SPf66 were less at risk of malaria, perhaps reflecting their greater previous exposure and thus immunity. In contrast, among children who had received three doses of SPf66, those with high antibody levels were at greater risk of have malaria during the subsequent malaria transmission season.     

Evaluation of the SPf66 vaccine for malaria control when delivered through the EPI scheme in Tanzania

BACKGROUND: Malaria control programmes need to protect young children, who bear the brunt of malaria disease and death in Africa. The development of a vaccine is a priority if improved and sustained malaria control is to be achieved. The best use of a vaccine in Africa will be achieved if it can be delivered through the expanded programme of immunization (EPI). We conducted a trial designed to evaluate the efficacy of SPf66 vaccine for malaria control when delivered through the EPI scheme in Tanzania. METHODS: The study was a two-arm, double blind, individually randomized placebo controlled trial involving 1207 infants. The primary objective of the trial was to estimate the efficacy of three doses of SPf66 given at 1, 2 and 7 months of age in preventing clinical episodes of malaria. These were documented through a health facility-based passive case detection system. RESULTS: Among 1207 randomized children, overall compliance for third dose was 91%. SPf66 was safe, immunogenic and did not interfere with the humoral immune responses to EPI vaccines. There were 294 children among SPf66 recipients and 288 among placebo recipients with at least one malaria episode, yielding a vaccine efficacy estimate of 2% (95% CI: -16, 16; P = 0.84). CONCLUSION: This has been the first trial of a malaria vaccine among very young infants. It provides information on the safety of peptide vaccines administered at this early age as well as their capacity to induce immune responses without negatively interacting with EPI vaccines. Given the modest protection previously documented in older age groups and the lack of efficacy in younger infants, this vaccine in its current alum-based formulation does not appear to have a role in malaria control in sub-Saharan Africa. The lack of efficacy found in this trial also raises concerns about potential difficulties of inducing protective immune responses against malaria through immunization in infants.     

Safety in infants of SPf66, a synthetic malaria vaccine, delivered alongside the EPI

The most likely mechanism to deliver a malaria vaccine in African countries is through the Expanded Program of Immunization (EPI). So far only SPf66, a multistage synthetic peptide, has shown any evidence of protection in Phase III field trials. In Tanzania, SPf66 reduced the risk of clinical malaria by 31% in children aged 1-5 years. In order to progress in the critical path of vaccine development and testing towards the implementation of a new vaccine in malaria control programs, we carried out a randomized double-blind placebo controlled efficacy trial of SPf66 when given alongside the EPI scheme. Monitoring of safety and reactogenicity during this trial included detailed clinical and laboratory assessments on 98 infants and assessment of adverse effects within 1 h of vaccination for all 1207 children vaccinated. Surveillance systems monitored attendances as outpatients, admissions to hospital and fatal events in the community. No serious adverse effects were detected more frequently amongst SPf66 recipients compared to placebo. This first assessment in very young infants of a synthetic vaccine provides evidence of a good safety profile.     

Determination of the immunization schedule for field trials with the synthetic malaria vaccine SPf 66

The synthetic malaria vaccine SPf 66 has been shown to be safe, immunogenic and effective in trials performed with controlled groups naturally and experimentally exposed to the disease. In order to continue the trials in open populations, it was necessary to standardize the vaccination characteristics. We have performed four field trials with soldier volunteers with the aim, among others, of defining the number of doses required, the intervals between applications, the protein concentration, and the adjuvant to be used. In these trials, the vaccinated individuals' immune responses were evaluated by assaying anti-SPf 66 antibody titres, in vitro growth inhibition of the P. falciparum parasite, and the vaccinees' capacity to recognize P. falciparum native proteins. From these results we conclude that the best vaccination schedule, for adults, is three doses administered subcutaneously on days 0, 30 and 180, each containing 2 mg of the synthetic polymerized petide SPf 66 adsorbed to alum hydroxide.     

Humoral immune responses during a malaria vaccine trial in Tanzanian infants

The development of a malaria vaccine is a priority for improved and sustained malaria control. Optimal use of a vaccine in Africa will only be achieved if it can be delivered through the Expanded Programme of Immunization (EPI). We have completed a trial of the peptide vaccine SPf66 in Tanzanian infants, given alongside the EPI vaccines. This paper describes the humoral responses to SPf66 and the EPI vaccines. A total of 1207 infants were recruited into a two-arm, double-blind, individually randomized placebo-controlled trial of SPf66. The objectives of the trial were to determine the safety, immunogenicity and efficacy of SPf66 and to assess interactions with EPI vaccines when three doses of SPf66 were delivered alongside the EPI vaccines. Cross-sectional surveys were carried out to asses seroconversion rates to the EPI vaccines and the antibody response to SPf66 (NANP)50 and Plasmodium falciparum lysates. Seroconversion rates to EPI vaccines were high and no statistically significant differences in prevalence or titres were found between SPf66 and placebo recipients. IgG antibodies against SPf66 (NANP)50 and whole P. falciparum lysate were present in high titres in mothers of recruited children at the time of birth. Vaccination with SPf66 stimulated a good anti-SPf66 IgG response which declined to preimmunization levels by 2 years of age and which was not associated with protection against clinical malaria. The vaccine induced no IgG antibodies against (NANP)50 or P. falciparum lysates. SPf66 stimulated a humoral immune response when given to very young infants and did not interfere with seroconversion to EPI vaccines. The response to SPf66 was qualitatively different from that seen in older children, in whom SPf66 has been shown to be moderately efficacious. This difference raises concerns about the difficulties of immunizing very young infants who need to be targeted by antimalarial vaccination programs.     

In human malaria protective antibodies are directed mainly against the Lys-Glu ion pair within the Lys-Glu-Lys motif of the synthetic vaccine SPf 66

The KEK (Lysine-Glutamic acid-Lysine) motif is frequently found in the primary structure of certain malaria proteins involved in invasion, and plays an important role in the interaction of these proteins with the erythrocyte. This motif is contained in a peptide which forms part of the polymeric synthetic malaria vaccine SPf 66, currently undergoing extensive human trials. Analysis of the antibody titres against the subunit peptides that comprise this vaccine has shown that protection is associated with high titres to the KEK-containing peptide. In this paper we examine the fine recognition of this motif by polyclonal sera from protected vaccinated individuals, demonstrating the critical role played by the interacting ion pair formed between the amino terminal lysine (K) and glutamic acid (E), which act as contact residues for an important proportion of the antibody population directed against this vaccine. This ion pair in the KEK motif constitutes perhaps one of the most important malaria epitopes involved in protection, and could explain the mechanism through which protective immunity is acquired.     

Assessment of the role of the humoral response to Plasmodium falciparum MSP2 compared to RESA and SPf66 in protecting Papua New Guinean children from clinical malaria

The prevalence and concentration of naturally acquired humoral response (IgG) to merozoite surface protein 2 (MSP2), RESA, SPf66 and crude schizont extract were measured in a population living in a malaria highly endemic area of Papua New Guinea. A prospective longitudinal study in 0–5–15 year old children was conducted for one year in order to examine the relationship between the humoral response to these antigens and subsequent susceptibility to clinical malaria using a series of clinical definitions. The prevalence and concentration of antibodies to all antigens increased with age. Such correlation with age was most marked for MSP2 recombinant proteins. When age and previous exposure were controlled for, only antibody levels to MSP2 recombinant proteins (3D7 andd3D7) and to RESA predicted a reduction in incidence rate of episodes of clinical malaria. Our results support the inclusion of the recombinant proteins of the 3D7 allelic family of merozoite surface antigen 2 and RESA into a subunit vaccine against malaria.,     

Renal involvement in Gambian children with cerebral or mild malaria

Kidney function was studied in 80 Gambian children with cerebral malaria, 73 children with mild malaria, and in 19 children with other febrile illnesses. Serum creatinine was measured, and the excretion in urine of immunoglobulin G, transferrin, albumin and alpha 1 microglobulin was determined. Twenty-five percent of children with cerebral malaria, and 4% of children with mild malaria had an elevated serum creatinine above 62 mumol/l. Increased urinary protein excretion was frequent: 53% of children with cerebral malaria had a glomerulo-tubular pattern of protein excretion, and 46% a tubular pattern. Median albuminuria was 68 mg/l in children with cerebral malaria, 18 mg/l in children with mild malaria, and 9 mg/l in febrile children with other diseases (P < 0.0001). There was no significant association between the proteinuria and height of fever or the degree of parasitaemia, and there was no significant association between death and signs of renal impairment. Renal involvement is common in children with malaria in The Gambia, with prerenal, glomerular, and tubulo-interstitial factors contributing. It is more pronounced in children with cerebral malaria than in those with mild malaria. However, renal dysfunction is relatively mild and does not indicate a worse prognosis.     

Immunogenicity of malaria transmission-blocking vaccine candidate, y230.CA14 following crosslinking in the presence of tetanus toxoid

Proteolytically processed 310 kDa form of Plasmodium falciparum gamete surface antigen, Pfs230, is the target of malaria transmission-blocking monoclonal antibodies. To design a recombinant malaria transmission-blocking subunit vaccine, the amino terminus of the 310 kDa surface-exposed form of Pfs230 was mapped to amino acids (aa) 522 and 584 using a series of peptides and recombinant proteins encoding distinct regions of Pfs230. Antiserum generated against an Escherichia coli-produced recombinant protein, spanning the Pfs230 processing site and extending into the cysteine domains, r230/MBP.C (aa 443-1132), reduced parasite infectivity by 71.2-89.8%. To determine if the region spanning the cleavage site blocked malaria transmission when produced as a secreted protein by Saccharomyces cerevisiae, y230.CA14 (aa 467-584) was generated, purified, emulsified in adjuvant and used to vaccinate mice. In contrast to E. coli-produced r230/MBP.C, the immune response generated against y230. CA14 was very weak. To enhance the response, y230.CA14 was mixed with tetanus toxoid, chemically crosslinked, repurifed, and its immunogenicty compared with unconjugated y230.CA14. Conjugated-y230. CA14/TT required fewer booster injections to induce an immune response against Pfs230 and the antibodies generated reacted with the surface of intact gametes and immunoprecipitated radiolabelled Pfs230 extracted from 125I surface-labelled gametes to a greater extent. After seven injections, all y230.CA14 vaccinated mice developed anti-Pfs230 antibodies and the isotype profile was the same. In addition to enhancing the initial immune response generated against y230.CA14, conjugation focuses the immune response toward epitopes within the region of Pfs230 present on the surface of the gamete.     

恶性疟原虫DNA疫苗在小鼠体内组织分布和安全性的初步研究

目的　探讨疟疾DNA疫苗在小鼠体内的组织分布 ,并对其安全性进行观察。方法　将重组质粒pBK -CSP经肌肉途径免疫BALB/c小鼠 ,分别在 4周和 8周后剖杀动物并摘取各种组织 ,抽提全组织DNA进行PCR扩增后经琼脂糖凝胶电泳分析 ,并对DNA疫苗的安全性进行观察。结果　免疫 4周和 8周后 ,仅有DNA疫苗接种位点的肌肉组织检测到CSP基因 ,而 10 0 μg的质粒DNA并未产生明显的毒副作用。 结论　疟疾DNA疫苗接种 4周后 ,质粒DNA仅分布于接种部位 ,并可持续至 8周以上 ,而未发现毒副作用。     

恶性疟原虫裂殖子表面蛋白2融合HBS基因重组质粒的免疫原性研究

目的　构建恶性疟原虫海南分离株 (FCC1/HN)裂殖子表面蛋白 2 (MSP2 )融合HBsAg基因片断真核重组表达质粒 pVXORF1-PfMSP2 -HBS ,观察该DNA疫苗的免疫特性。方法　 (1)以恶性疟原虫海南分离株 (FCC1/HN)基因组为模板 ,扩增出pfMSP2 DNA片断 ,将该片段克隆入质粒pVXORF1-HBS中HBS的上游并与之紧密相连 ,构建质粒 pVXORF1-PfMSP2 -HBS ;构建真核重组表达质粒 pVXORF1-PfMSP2 以作为对照。 (2 )用上述构建的质粒及空质粒 pVXORF1免疫KM小鼠 ,以ELISA检测血清IgG抗体。 结果　 (1)筛选出的重组子为编码FCC1/HNMSP2 基因片断的重组质粒 pVXORF1-PfMSP2 -HBS及 pVXORF1-PfMSP2 。 (2 )裸DNA尾根多点注射KM小鼠 ,显示 pVXORF1-PfMSP2 -HBS组小鼠较pVXORF1-PfMSP2 组小鼠产生抗PfMSP2 蛋白的抗体效价明显增高 ,二者比较 ,差异有非常显著意义 (P <0 0 1)。结论　PfMSP2 融合HBsAg基因片段激发机体产生抗PfMSP2 抗体的能力显著增强 ,提示PfMSP2 融合HBsAg基因有可能作为高效抗红内期恶性疟原虫复合多价基因疫苗的有效组成部分     

Safety and immunogenicity of the RTS,S/AS02A candidate malaria vaccine in children aged 1-4 in Mozambique

BACKGROUND: The development of a malaria vaccine remains a public health priority for sub-Saharan Africa. RTS,S/AS02A candidate malaria vaccine has been shown to be safe and immunogenic in previous studies in adults and staggered dose-escalation studies in children in The Gambia. However, genetic features and the intensity of malaria transmission may modify the safety and immune response of a vaccine. OBJECTIVE: We carried out a phase I, double-blind randomized controlled trial in 60 children aged 1-4 in Mozambique to evaluate the safety, reactogenicity and immunogenicity of the paediatric vaccine dose (fixed 25 microg RTS,S in 0.25 ml) of RTS,S/AS02A, prior to undertaking a planned larger phase IIb proof-of-concept of efficacy study in the same population. METHOD: Children were randomized to receive either RTS,S/AS02A or Engerix-B vaccine. Monitoring of safety and reactogenicity included detailed clinical and laboratory analyses and assessment of adverse events (AEs). RESULTS: The RTS,S/AS02A was found to be safe and well tolerated. Serious adverse events were balanced between both groups and none was related to vaccination. The frequency of adverse events reported with RTS, S/AS02A was comparable to previous studies in children. Grade 3 AEs were infrequent (one case of pain, one of fever in each group and some swelling greater than 20 mm in diameter), transient and resolved without sequelae. RTS,S/AS02A was highly immunogenic for anti-circumsporozoite protein antibody response and induced a strong anti-hepatitis-B surface antigen response.     

Genetic diversity and malaria vaccine design, testing and efficacy: preventing and overcoming 'vaccine resistant malaria'

The development of effective malaria vaccines may be hindered by extensive genetic diversity in the surface proteins being employed as vaccine antigens. Understanding of the extent and dynamics of genetic diversity in vaccine antigens is needed to guide rational vaccine design and to interpret the results of vaccine efficacy trials conducted in malaria endemic areas. Molecular epidemiological, population genetic, and structural approaches are being employed to try to identify immunologically relevant polymorphism in vaccine antigens. The results of these studies will inform choices of which alleles to include in multivalent or chimeric vaccines; however, additional molecular and immuno-epidemiological studies in a variety of geographic locations will be necessary for these approaches to succeed. Alternative means of overcoming antigenic diversity are also being explored, including boosting responses to critical conserved regions of current vaccine antigens, identifying new, more conserved and less immunodominant antigens, and developing whole-organism vaccines. Continued creative application and integration of tools from multiple disciplines, including epidemiology, immunology, molecular biology, and evolutionary genetics and genomics, will likely be required to develop broadly protective vaccines against Plasmodium and other antigenically complex pathogens.     

Down‐selecting circumsporozoite protein‐based malaria vaccine: A comparison of malaria sporozoite challenge model

Plasmodium falciparum circumsporozoite protein (PfCSP) is the main target antigen in development of pre‐erythrocytic malaria vaccines. To evaluate PfCSP vaccines in animal models, challenge by intravenous sporozoite injection is preferentially used. However, in clinical trials, vaccinated human volunteers are exposed to the bites of malaria‐infected mosquitoes. In this study, we down‐selected Escherichia coli‐produced full‐length PfCSP (PfCSP‐F) and its three truncated PfCSPs based on their abilities to elicit immune response and protection in mice against two challenge models. We showed that immunization with three doses of PfCSP‐F elicited high anti‐PfCSP antibody titres and 100% protection against the bites of infected mosquitoes. Meanwhile, three‐dose truncated PfCSP induced 60%‐70% protection after immunization with each truncated PfCSP. Heterologous prime‐boost immunization regimen with adenovirus‐PfCSP‐F and R32LR greatly induced complete protection against intravenous sporozoite injection. Our results suggest that Abs to both anti‐repeat and anti‐nonrepeat regions induced by PfCSP‐F are required to confer complete protection against challenge by the bites of infected mosquitoes, whereas anti‐repeat Abs play an important role in protection against intravenous sporozoite injection. Our findings provide a potential clinical application that PfCSP‐F vaccine induces potent Abs capable of neutralizing sporozoites in the dermis inoculated by infected mosquitoes and subsequently sporozoites in the blood circulation.     

A study to assess the immunogenicity, reactogenicity and safety of hepatitis A vaccine administered subcutaneously to patients with congenital coagulation disorders

Summary. The objective was to compare the immunogenicity, reactogenicity and safety of an inactivated hepatitis A vaccine administered subcutaneously to patients with congenital coagulation disorders. Subjects, 97 patients with congenital coagulation disorders (67 men aged > 16 and 30 children aged ≤ 16 years), received hepatitis A vaccine administered at 1440 ELISA (enzyme linked immunosorbent assay) units (ELU) to the adult group and at 720 ELU to the child group at 0 and 6 months by the subcutaneous route. The vaccine was well tolerated, with the incidence of adverse events decreasing with subsequent administration of vaccine. Overall, 90% of subjects seroconverted 1 month after the booster (95% confidence interval 76–97%), with 100% seroconversion occurring in the child group compared with 85% in the adult group. There was a corresponding progressive rise in geometric mean titres in each group and no significant difference in the geometric mean titres was found between the two groups. Of the subjects, 29% were HIV positive, 3% of children compared with 40% of adults. A lower rate of seroconversion was observed in subjects with low CD4 counts. Administration of two doses of an inactivated hepatitis A vaccine at 1440 ELU in adults and 720 ELU in children is safe and highly immunogenic when given by the subcutaneous route.     

Safety and immunogenicity of the synthetic malaria vaccine SPf66 in a large field trial.

In the first field trial with synthetic malaria vaccine SPf66 in a large population naturally exposed to malaria, 9957 persons greater than 1 year old and residing on the Colombian Pacific coast received three doses of the vaccine. To evaluate vaccine safety, clinical observations were made 30 min and 48 h after each immunization. There were no adverse reactions in 95.7% of cases. In the 4.3% of cases with adverse reactions, local induration and erythema were the most frequent. In a randomly selected group of vaccinees, anti-SPf66 antibody titers were measured after the third dose: 93% of the vaccinees raised antibodies to SPf66. Among these, 55% had titers greater than 1:1600. These results demonstrate the safety and immunogenicity of the SPf66 vaccine in a large field trial.     

Effectiveness of chemoprophylaxis and other determinants of malaria in travellers to Kenya

Summary objective  To investigate the effectiveness of chemoprophylaxis and the determinants of malaria importation from Kenya.
method  In a population-based case-control study, 51 travellers from Bavaria diagnosed with falciparum malaria imported from Kenya (cases) and a sample of 383 healthy Bavarian travellers returning from Kenya (controls) were interviewed. Data were analysed by multiple logistic regression.
results  Mefloquine (OR = 0.055; 95% Cl 0.019-0.16) and chloroquine combined with proguanil (OR = 0.128; 95% CI 0.039-0.419) were highly protective against P. falciparum malaria, whereas other drugs were ineffective (OR = 1.225; 95% CI 0.536-2.803). Ineffective prophylaxis (10.4%) and non-prophylaxis (11.2%) were the main reasons for malaria importation. Travelling alone or with friends, male sex, and travel duration over 4 weeks could be identified as additional risk factors. The main reason for inadequate chemoprophylaxis was inappropriate medical advice (87.5%). Prophylaxis refusal occurred frequently despite correct advice (58.1%). Diagnosis was often delayed unnecessarily (27.5%).
conclusion  Malaria importation from Kenya could be reduced substantially (34%) by eliminating inappropriate medical advice.     

A quantitative ultrastructural study of renal pathology in fatal Plasmodium falciparum malaria

OBJECTIVE: To use electron microscopy to examine the role of parasitized red blood cell (PRBC) sequestration in the pathogenesis of acute renal failure in severe falciparum malaria. METHODS: Ultrastructural pathological examination of renal tissues from Southeast Asian adults (n = 63) who died from severe falciparum malaria. Qualitative and quantitative determination of the major pathological features of disease, including PRBC and leukocyte sequestration. Clinico-pathological correlation with the pre-mortem clinical picture and peripheral parasite count. RESULTS: There was a high incidence of malaria-associated renal failure in this population (> 40%) and a correlation between this incidence, severe malarial anaemia and shock. Pathological features included PRBC sequestration in glomerular and tubulo-interstitial vessels, acute tubular damage and mild glomerular hypercellularity resulting from the accumulation of host monocytes within glomerular capillaries. No evidence for an immune complex mediated glomerulonephritis was found. There was a correlation between parasite sequestration in the kidney and pre-mortem renal failure, although overall levels of sequestration were relatively low. Levels of sequestration (Knob+ PRBC) were significantly higher in malaria-associated renal failure than in fatal cases without renal failure (P = 0.005). CONCLUSION: Malaria-associated renal failure is a common and serious complication of severe Plasmodium falciparum malaria in this population, associated with acute tubular injury rather than glomerulonephritis, and linked to localization of host monocytes in the kidney as well as sequestration of PRBCs.