Predictors of program interest in a digital health pilot study for heart health

Digital health programs can play a key role in supporting lifestyle changes to prevent and reduce cardiovascular disease (CVD) risk. A key concern for new programs is understanding who is interested in participating. Thus, the primary objective of this study was to utilize electronic health records (EHR) to predict interest in a digital health app called Lark Heart Health. Because prior studies indicate that males are less likely to utilize prevention-focused digital health programs, secondary analyses assessed sex differences in recruitment and enrollment. Data were drawn from an ongoing pilot study of the Heart Health program, which provides digital health behavior coaching and surveys for CVD prevention. EHR data were used to predict whether potential program participants who received a study recruitment email showed interest in the program by "clicking through" on the email to learn more. Primary objective analyses used backward elimination regression and eXtreme Gradient Boost modeling. Recruitment emails were sent to 8,649 patients with available EHR data; 1,092 showed interest (i.e., clicked through) and 345 chose to participate in the study. EHR variables that predicted higher odds of showing interest were higher body mass index (BMI), fewer elevated lab values, lower HbA1c, non-smoking status, and identifying as White. Secondary objective analyses showed that, males and females showed similar program interest and were equally represented throughout recruitment and enrollment. In summary, BMI, elevated lab values, HbA1c, smoking status, and race emerged as key predictors of program interest; conversely, sex, age, CVD history, history of chronic health issues, and medication use did not predict program interest. We also found no sex differences in the recruitment and enrollment process for this program. These insights can aid in refining digital health tools to best serve those interested, as well as highlight groups who may benefit from behavioral intervention tools promoted by additional recruitment efforts tailored to their interest.

Weight Loss in a Digital Diabetes Prevention Program for People in Health Professional Shortage and Rural Areas

Individuals with prediabetes living in hard-to-reach and underserved areas experience barriers to accessing traditional in-person preventive health services. The National Diabetes Prevention Program (DPP) is a preventive health care program designed to reduce the risk of developing type 2 diabetes. Although there have been increasing numbers of remote DPPs accessible, there are little data on the clinical outcomes of digital DPPs for members living in hard-to-reach and underserved areas. This study assessed whether living in a designated Health Professional Shortage Area (HPSA) and a rural versus urban area impacted the weight loss of N = 7266 members of a fully digital program called Lark DPP. Secondary analyses included between-group comparisons of program retention and member characteristics, demographics, and socioeconomics. Percent weight loss did not differ by HPSA (P = 0.16) or rural/urban status (P = 0.15), despite greater potential barriers for members residing in HPSAs (eg, highest starting body mass index, lowest income, lowest education). Mean percent weight loss for members residing in an HPSA and rural area was mean (M) = 4.75%, standard error (SE) = 0.09; for members in a non-HPSA, rural area M = 4.96%, SE = 0.16; for members in an HPSA, urban area M = 4.55%, SE = 0.13; and for members in a non-HPSA, urban area M = 4.77%, SE = 0.13. Members of a fully digital DPP achieved weight loss that did not differ by HPSA or urban/rural designation. Fully digital programs offer a solution to reduce the risk of type 2 diabetes in areas where residents may not otherwise have access to diabetes prevention services.

Weight Loss and Modeled Cost Savings in a Digital Diabetes Prevention Program

Background

Participation in the National Diabetes Prevention Program (DPP) can improve individual health through reduced risk of type 2 diabetes and save the healthcare system substantial medical costs associated with a diagnosis of type 2 diabetes and its associated complications. There is less evidence of outcomes and cost savings associated with a fully digital delivery of the DPP.

Methods

This study assessed 13,593 members who provided an initial digital weight and subsequently achieved various weight loss and engagement outcomes during their participation in a digital DPP. Analyzed data included both complete observations and missing observations imputed using maximum likelihood estimation. Findings include members' behavioral correlates of weight loss and a literature-based cost-savings estimate associated with achieving three mutually exclusive weight loss or engagement benchmarks: ≥5% weight loss, >2% but <5% weight loss, and completion of ≥4 educational lessons.

Results

11,976 members (88%) provided a weight after 2 months of participation, enabling calculation of their weight nadir. Considering complete data, 97% of members maintained or lost weight. Using the imputed data for these calculations, 32.0% of members achieved ≥5%, 32.4% achieved >2% but <5%, 32.0% maintained ±2%, and 3.6% gained weight. Members who lost the most weight achieved their weight nadir furthest into the program (mean day = 189, SE = 1.4) and had the longest active engagement (mean days = 268, SE = 1.4), particularly compared to members who gained weight (mean nadir day = 119, SE = 3.7; active engagement mean days = 199, SE = 4.9) (both p ≤ 0.0001). Modeled 1-year cost-savings estimates ranged from $11,229,160 to $12,960,875.

Conclusions

Members of a fully digital DPP achieved clinical and engagement outcomes during their participation in the program that confer important health benefits and cost savings.

The Effects of Providing a Connected Scale in an App-Based Digital Health Program: Cross-sectional Examination

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Relationships Between Blood Pressure Reduction, Weight Loss, and Engagement in a Digital App–Based Hypertension Care Program: Observational Study

Background

Home blood pressure (BP) monitoring is recommended for people with hypertension; however, meta-analyses have demonstrated that BP improvements are related to additional coaching support in combination with self-monitoring, with little or no effect of self-monitoring alone. High-contact coaching requires substantial resources and may be difficult to deliver via human coaching models.

Objective

This observational study assessed changes in BP and body weight following participation in a fully digital program called Lark Hypertension Care with coaching powered by artificial intelligence (AI).

Methods

Participants (N=864) had a baseline systolic BP (SBP) ≥120 mm Hg, provided their baseline body weight, and had reached at least their third month in the program. The primary outcome was the change in SBP at 3 and 6 months, with secondary outcomes of change in body weight and associations of changes in SBP and body weight with participant demographics, characteristics, and program engagement.

Results

By month 3, there was a significant drop of –5.4 mm Hg (95% CI –6.5 to –4.3; P<.001) in mean SBP from baseline. BP did not change significantly (ie, the SBP drop maintained) from 3 to 6 months for participants who provided readings at both time points (P=.49). Half of the participants achieved a clinically meaningful drop of ≥5 mm Hg by month 3 (178/349, 51.0%) and month 6 (98/199, 49.2%). The magnitude of the drop depended on starting SBP. Participants classified as hypertension stage 2 had the largest mean drop in SBP of –12.4 mm Hg (SE 1.2 mm Hg) by month 3 and –13.0 mm Hg (SE 1.6 mm Hg) by month 6; participants classified as hypertension stage 1 lowered by –5.2 mm Hg (SE 0.8) mm Hg by month 3 and –7.3 mm Hg (SE 1.3 mm Hg) by month 6; participants classified as elevated lowered by –1.1 mm Hg (SE 0.7 mm Hg) by month 3 but did not drop by month 6. Starting SBP (β=.11; P<.001), percent weight change (β=–.36; P=.02), and initial BMI (β=–.56; P<.001) were significantly associated with the likelihood of lowering SBP ≥5 mm Hg by month 3. Percent weight change acted as a mediator of the relationship between program engagement and drop in SBP. The bootstrapped unstandardized indirect effect was –0.0024 (95% CI –0.0052 to 0; P=.002).

Conclusions

A hypertension care program with coaching powered by AI was associated with a clinically meaningful reduction in SBP following 3 and 6 months of program participation. Percent weight change was significantly associated with the likelihood of achieving a ≥5 mm Hg drop in SBP. An AI-powered solution may offer a scalable approach to helping individuals with hypertension achieve clinically meaningful reductions in their BP and associated risk of cardiovascular disease and other serious adverse outcomes via healthy lifestyle changes such as weight loss.

Weight loss in a digital app-based diabetes prevention program powered by artificial intelligence

Objective

The National Diabetes Prevention Program (DPP) reduces diabetes incidence and associated medical costs but is typically staffing-intensive, limiting scalability. We evaluated an alternative delivery method with 3933 members of a program powered by conversational Artificial Intelligence (AI) called Lark DPP that has full recognition from the Centers for Disease Control and Prevention (CDC).

Methods

We compared weight loss maintenance at 12 months between two groups: 1) CDC qualifiers who completed ≥4 educational lessons over 9 months (n  =  191) and 2) non-qualifiers who did not complete the required CDC lessons but provided weigh-ins at 12 months (n  =  223). For a secondary aim, we removed the requirement for a 12-month weight and used logistic regression to investigate predictors of weight nadir in 3148 members.

Results

CDC qualifiers maintained greater weight loss at 12 months than non-qualifiers (M  =  5.3%, SE  =  .8 vs. M  =  3.3%, SE  =  .8; p  =  .015), with 40% achieving ≥5%. The weight nadir of 3148 members was 4.2% (SE  =  .1), with 35% achieving ≥5%. Male sex (β = .11; P  =  .009), weeks with ≥2 weigh-ins (β = .68; P < .0001), and days with an AI-powered coaching exchange (β = .43; P < .0001) were associated with a greater likelihood of achieving ≥5% weight loss.

Conclusions

An AI-powered DPP facilitated weight loss and maintenance commensurate with outcomes of other digital and in-person programs not powered by AI. Beyond CDC lesson completion, engaging with AI coaching and frequent weighing increased the likelihood of achieving ≥5% weight loss. An AI-powered program is an effective method to deliver the DPP in a scalable, resource-efficient manner to keep pace with the prediabetes epidemic.

Discovering Engagement Personas in a Digital Diabetes Prevention Program

Digital health technologies are shaping the future of preventive health care. We present a quantitative approach for discovering and characterizing engagement personas: longitudinal engagement patterns in a fully digital diabetes prevention program. We used a two-step approach to discovering engagement personas among n = 1613 users: (1) A univariate clustering method using two unsupervised k-means clustering algorithms on app- and program-feature use separately and (2) A bivariate clustering method that involved comparing cluster labels for each member across app- and program-feature univariate clusters. The univariate analyses revealed five app-feature clusters and four program-feature clusters. The bivariate analysis revealed five unique combinations of these clusters, called engagement personas, which represented 76% of users. These engagement personas differed in both member demographics and weight loss. Exploring engagement personas is beneficial to inform strategies for personalizing the program experience and optimizing engagement in a variety of digital health interventions.

Engagement in Digital Health App-Based Prevention Programs Is Associated With Weight Loss Among Adults Age 65+

Background

Digital health programs have been shown to be feasible and effective for the prevention of chronic diseases such as diabetes. Contrary to expectations, findings also suggest that older adults have higher levels of engagement with digital health programs than younger adults. However, there is a paucity of research examining outcomes among older adults in digital health programs and whether higher engagement is related to better outcomes.

Methods

We examined weight loss outcomes for 538 users aged 65 and older participating in one of two app-based prevention programs called the Diabetes Prevention Program and the Prevention Program, respectively. Both programs were available on a single artificial intelligence (AI)-powered digital health platform and shared a common goal of weight loss. We also examined the relationship between key engagement metrics (i.e., conversing with the AI-powered coach, weigh-ins, and initiating educational lessons early in the program) and weight loss outcomes.

Results

The average weight loss of all enrollees having a weight measurement after after the 9th week was 4.51%, and the average weight loss of the Diabetes Prevention Program enrollees meeting a minimum engagement level was 8.56%. Greater weight loss was associated with a greater number of days with AI-powered coaching conversations (p = 0.03), more weigh-ins (p = 0.00), and early educational lesson initiation (p = 0.02).

Conclusions

Digital health programs powered by AI offer a promising solution for health management among older adults. The results show positive health outcomes using app-based prevention programs, and all three engagement metrics were independently associated with weight loss.

Reach of a Fully Digital Diabetes Prevention Program in Health Professional Shortage Areas

The National Diabetes Prevention Program (NDPP) offers lifestyle change education to adults at risk for diabetes across the United States, but its reach is curbed due, in part, to limitations of traditional in-person programs. Diabetes Prevention Programs (DPPs) that are fully digital may increase reach by overcoming these barriers. The aim of this research was to examine the reach of Lark's DPP, a fully digital artificial-intelligence-powered DPP. This study assessed geographic features and demographic characteristics of a sample of Lark DPP commercial health plan members with complete data (N = 16,327) and compared several demographic features with a large composite sample of members from DPPs across the nation (NDPP; N = 143,489) and a National Health Interview Survey (NHIS) sample of prediabetic adults in the United States (NHIS; N = 2118). Examination of the Lark DPP sample revealed that 24.4% of members lived in rural areas, 30.8% lived in whole county health professional shortage areas, and only 7.6% of members lived in a zip code with an in-person DPP. When comparing the Lark sample with the NDPP and NHIS samples, Lark DPP enrollees tended to be younger and have a higher body mass index (BMI) (p's < 0.001). Lark provides convenient access to a DPP for individuals living in hard-to-reach areas who may face barriers to participating in in-person or telephonic DPPs or who prefer a digital program. Compared with the NDPP sample, Lark is also reaching younger and higher BMI users, who are traditionally difficult to enroll and have a high need for intervention.

Older Adults Engage With Personalized Digital Coaching Programs at Rates That Exceed Those of Younger Adults

Background: The US population is aging and has an expanding set of healthcare needs for the prevention and management of chronic conditions. Older adults contribute disproportionately to US healthcare costs, accounting for 34% of total healthcare expenditures in 2014 but only 15% of the population. Fully automated, digital health programs offer a scalable and cost-effective option to help manage chronic conditions. However, the literature on technology use suggests that older adults face barriers to the use of digital technologies that could limit their engagement with digital health programs. The objective of this study was to characterize the engagement of adults 65 years and older with a fully automated digital health platform called Lark Health and compare their engagement to that of adults aged 35-64 years. Methods: We analyzed data from 2,169 Lark platform users across four different coaching programs (diabetes prevention, diabetes care, hypertension care, and prevention) over a 12-month period. We characterized user engagement as participation in digital coaching conversations, meals logged, and device measurements. We compared engagement metrics between older and younger adults using nonparametric bivariate analyses. Main Results: Aggregate engagement across all users during the 12-month period included 1,623,178 coaching conversations, 588,436 meals logged, and 203,693 device measurements. We found that older adults were significantly more engaged with the digital platform than younger adults, evidenced by older adults participating in a larger median number of coaching conversations (514 vs. 428) and logging more meals (174 vs. 89) and device measurements (39 vs. 28) all p ≤ 0.01. Conclusions: Older adult users of a commercially available, fully digital health platform exhibited greater engagement than younger adults. These findings suggest that despite potential barriers, older adults readily adopted digital health technologies. Fully digital health programs may present a widely scalable and cost-effective alternative to traditional telehealth models that still require costly touchpoints with human care providers.

Evolutionary analyses of the major variant surface antigen-encoding genes reveal population structure of Plasmodium falciparum within and between continents

Malaria remains a major public health problem in many countries. Unlike influenza and HIV, where diversity in immunodominant surface antigens is understood geographically to inform disease surveillance, relatively little is known about the global population structure of PfEMP1, the major variant surface antigen of the malaria parasite Plasmodium falciparum. The complexity of the var multigene family that encodes PfEMP1 and that diversifies by recombination, has so far precluded its use in malaria surveillance. Recent studies have demonstrated that cost-effective deep sequencing of the region of var genes encoding the PfEMP1 DBLα domain and subsequent classification of within host sequences at 96% identity to define unique DBLα types, can reveal structure and strain dynamics within countries. However, to date there has not been a comprehensive comparison of these DBLα types between countries. By leveraging a bioinformatic approach (jumping hidden Markov model) designed specifically for the analysis of recombination within var genes and applying it to a dataset of DBLα types from 10 countries, we are able to describe population structure of DBLα types at the global scale. The sensitivity of the approach allows for the comparison of the global dataset to ape samples of Plasmodium Laverania species. Our analyses show that the evolution of the parasite population emerging out of Africa underlies current patterns of DBLα type diversity. Most importantly, we can distinguish geographic population structure within Africa between Gabon and Ghana in West Africa and Uganda in East Africa. Our evolutionary findings have translational implications in the context of globalization. Firstly, DBLα type diversity can provide a simple diagnostic framework for geographic surveillance of the rapidly evolving transmission dynamics of P. falciparum. It can also inform efforts to understand the presence or absence of global, regional and local population immunity to major surface antigen variants. Additionally, we identify a number of highly conserved DBLα types that are present globally that may be of biological significance and warrant further characterization.

Genetic diversity in merozoite surface protein-1 and 2 among Plasmodium falciparum isolates from malarious districts of tribal dominant state of Jharkhand, India

INTRODUCTION

The genetic make-up of malaria parasite is potent for understanding the parasite virulence, designing antimalarial vaccine and evaluating the impact of malaria control measures. There is a paucity of information on genetic structure of Plasmodium falciparum in Jharkhand, India where malaria is rampant and this study aimed to establish molecular characterization of P. falciparum field isolates from Jharkhand measured with two highly polymorphic genetic markers, i.e. the merozoite surface proteins (MSPs) 1 and 2.

METHODS

The genetic diversity of P. falciparum population from low transmission area, Ranchi, Bokaro and Hazaribagh and highly malarious area, Latehar and Palamau districts of Jharkhand were evaluated by polymerase chain reaction-sequencing analyzing msp-1 and msp-2 genes to explore the genetic structure of parasite from this understudied region.

RESULTS

A total of 134 P. falciparum isolates were analyzed by polymorphic regions of msp-1 and msp-2 and classified according to prevalence of allelic families. The majority of patients from all the five sites had mean monoclonal infections of 67·1 and 60·4% of P. falciparum for msp-1 and msp-2, respectively, whereas, mean multiple genotypes of 32·8 and 39·5% for msp-1 and msp-2, respectively. Interestingly, we observed higher multiclonal infection in low transmission area as compared to highly malarious area in the case of msp-1 genotypes, whereas in msp-2 higher multiclonal infection was observed in highly malarious area compared to low transmission area. The overall multiplicities of infection of msp-1 and msp-2 were 1·38 and 1·39, respectively.

CONCLUSION

This is the first report on molecular characterization of P. falciparum field isolates from Jharkhand. The genetic diversity and allelic distribution found in this study is somewhat similar to other reports from India and Southeast Asian countries. However, P. falciparum infection can be highly complex and diverse in these disease-endemic regions of Jharkhand, suggesting continual genetic mixing that could have significant implications for the use of antimalarial drugs and vaccines.

Antibodies directed against merozoite surface protein-6 are induced by natural exposure to Plasmodium falciparum in a low transmission environment

Malaria caused by Plasmodium falciparum is a major cause of global infant mortality, and there is currently no licensed vaccine that provides protection against infection or disease. Several P. falciparum vaccine targets have undergone early testing, but many more candidates remain with little data to support their development. Plasmodium falciparum Merozoite Surface Protein 6 (PfMSP6) is a candidate of particular interest because it is a member of the PfMSP3 multi-gene family, raising the possibility that vaccine-induced immune responses could cross-react across multiple family members. However, few immunoepidemiological studies of PfMSP6 have been carried out to measure domain-specific anti-PfMSP6 responses. This study investigated anti-PfMSP6 responses in P. falciparum-infected individuals from the Peruvian Amazon, using two different PfMSP6 N-terminal allele antigens and a single C-terminal domain antigen, and compared the responses with both PfMSP6 genotyping data and anti-PfMSP3 response data that had been previously generated for the same samples. Anti-PfMSP6 responses were detected despite the low transmission setting, but were less frequent and of considerably lower intensity than anti-PfMSP3 responses. There was a positive correlation between anti-PfMSP3 and PfMSP6 responses, suggesting that the possibility that PfMSP3 family antigens could induce cross-reactive responses requires further detailed investigation.

The Plasmodium falciparum merozoite surface protein-1 19 KD antibody response in the Peruvian Amazon predominantly targets the non-allele specific, shared sites of this antigen

Background

Plasmodium falciparum re-emerged in Iquitos, Peru in 1994 and is now hypoendemic (< 0.5 infections/person/year). Purportedly non-immune individuals with discrete (non-overlapping) P. falciparum infections can be followed using this population dynamic. Previous work demonstrated a strong association between this population's antibody response to PfMSP1-19KD and protection against febrile illness and parasitaemia. Therefore, some selection for PfMSP1-19KD allelic diversity would be expected if the protection is to allele-specific sites of PfMSP1-19KD. Here, the potential for allele-specific polymorphisms in this population is investigated, and the allele-specificity of antibody responses to PfMSP1-19KD are determined.

Methods

The 42KD region in PfMSP1 was genotyped from 160 individual infections collected between 2003 and 2007. Additionally, the polymorphic block 2 region of Pfmsp1 (Pfmsp1-B2) was genotyped in 781 infection-months to provide a baseline for population-level diversity. To test whether PfMSP1-19KD genetic diversity had any impact on antibody responses, ELISAs testing IgG antibody response were performed on individuals using all four allele-types of PfMSP1-19KD. An antibody depletion ELISA was used to test the ability of antibodies to cross-react between allele-types.

Results

Despite increased diversity in Pfmsp1-B2, limited diversity within Pfmsp1-42KD was observed. All 160 infections genotyped were Mad20-like at the Pfmsp1-33KD locus. In the Pfmsp1-19KD locus, 159 (99.4%) were the Q-KSNG-F haplotype and 1 (0.6%) was the E-KSNG-L haplotype. Antibody responses in 105 individuals showed that Q-KNG and Q-TSR alleles generated the strongest immune responses, while Q-KNG and E-KNG responses were more concordant with each other than with those from Q-TSR and E-TSR, and vice versa. The immuno-depletion ELISAs showed all samples responded to the antigenic sites shared amongst all allelic forms of PfMSP1-19KD.

Conclusions

A non-allele specific antibody response in PfMSP1-19KD may explain why other allelic forms have not been maintained or evolved in this population. This has important implications for the use of PfMSP1-19KD as a vaccine candidate. It is possible that Peruvians have increased antibody responses to the shared sites of PfMSP1-19KD, either due to exposure/parasite characteristics or due to a human-genetic predisposition. Alternatively, these allelic polymorphisms are not immune-specific even in other geographic regions, implying these polymorphisms may be less important in immune evasion that previous studies suggest.

Genetic diversity of the malaria vaccine candidate Plasmodium falciparum merozoite surface protein-3 in a hypoendemic transmission environment

The N-terminal domain of Plasmodium falciparum merozoite surface protein-3 (PfMSP3) has been excluded from malaria vaccine development largely because of genetic diversity concerns. However, no study to date has followed N-terminal diversity over time. This study describes PfMSP3 variation in a hypoendemic longitudinal cohort in the Peruvian Amazon over the 2003-2006 transmission seasons. Polymerase chain reaction was used to amplify the N-terminal domain in 630 distinct P. falciparum infections, which were allele-typed by size and also screened for sequence variation using a new high-throughput technique, denaturing high performance liquid chromatography. PfMSP3 allele frequencies fluctuated significantly over the 4-year period, but sequence variation was very limited, with only 10 mutations being identified of 630 infections screened. The sequence of the PfMSP3 N-terminal domain is relatively stable over time in this setting, and further studies of its status as a vaccine candidate are therefore warranted.

Antibody response dynamics to the Plasmodium falciparum conserved vaccine candidate antigen, merozoite surface protein-1 C-terminal 19kD (MSP1-19kD), in Peruvians exposed to hypoendemic malaria transmission

Background

In high-transmission areas, developing immunity to symptomatic Plasmodium falciparum infections requires 2–10 years of uninterrupted exposure. Delayed malaria-immunity has been attributed to difficult-to-develop and then short-lived antibody responses.

Methods

In a study area with <0.5 P. falciparum infections/person/year, antibody responses to the MSP1-19kD antigen were evaluated and associations with P. falciparum infections in children and adults. In months surrounding and during the malaria seasons of 2003–2004, 1,772 participants received ≥6 active visits in one study-year. Community-wide surveys were conducted at the beginning and end of each malaria season, and weekly active visits were completed for randomly-selected individuals each month. There were 79 P. falciparum infections with serum samples collected during and approximately one month before and after infection. Anti-MSP1-19kD IgG levels were measured by ELISA.

Results

The infection prevalence during February-July was similar in children (0.02–0.12 infections/person/month) and adults (0.03–0.14 infections/person/month) and was negligible in the four-month dry season. In children and adults, the seroprevalence was maintained in the beginning (children = 28.9%, adults = 61.8%) versus ending malaria-season community survey (children = 26.7%, adults = 64.6%). Despite the four-month non-transmission season, the IgG levels in Plasmodium-negative adults were similar to P. falciparum-positive adults. Although children frequently responded upon infection, the transition from a negative/low level before infection to a high level during/after infection was slower in children. Adults and children IgG-positive before infection had reduced symptoms and parasite density.

Conclusion

Individuals in low transmission areas can rapidly develop and maintain αMSP1-19kD IgG responses for >4 months, unlike responses reported in high transmission study areas. A greater immune capacity might contribute to the frequent asymptomatic P. falciparum infections in this Peruvian population.

Genetic diversity of vaccine candidate antigens in Plasmodium falciparum isolates from the Amazon basin of Peru

Background

Several of the intended Plasmodium falciparum vaccine candidate antigens are highly polymorphic and could render a vaccine ineffective if their antigenic sites were not represented in the vaccine. In this study, characterization of genetic variability was performed in major B and T-cell epitopes within vaccine candidate antigens in isolates of P. falciparum from Peru.

Methods

DNA sequencing analysis was completed on 139 isolates of P. falciparum collected from endemic areas of the Amazon basin in Loreto, Peru from years 1998 to 2006. Genetic diversity was determined in immunological important regions in circumsporozoite protein (CSP), merozoite surface protein-1 (MSP-1), apical membrane antigen-1 (AMA-1), liver stage antigen-1 (LSA-1) and thrombospondin-related anonymous protein (TRAP). Alleles identified by DNA sequencing were aligned with the vaccine strain 3D7 and DNA polymorphism analysis and FST study-year pairwise comparisons were done using the DnaSP software. Multilocus analysis (MLA) was performed and average of expected heterozygosity was calculated for each loci and haplotype over time.

Results

Three different alleles for CSP, seven for MSP-1 Block 2, one for MSP-1 Block 17, three for AMA-1 and for LSA-1 each and one for TRAP were identified. There were 24 different haplotypes in 125 infections with complete locus typing for each gene.

Conclusion

Characterization of the genetic diversity in Plasmodium isolates from the Amazon Region of Peru showed that P. falciparum T and B cell epitopes in these antigens have polymorphisms more similar to India than to Africa. These findings are helpful in the formulation of a vaccine considering restricted repertoire populations.

Genetic diversity in the Block 2 region of the merozoite surface protein 1 (MSP-1) of Plasmodium falciparum: additional complexity and selection and convergence in fragment size polymorphism

Fragment size in the Block 2 repetitive region of merozoite surface protein 1 (MSP1) has commonly been used as a molecular marker in studies of malaria transmission dynamics and host immunity in Plasmodium falciparum malaria. In this study, we further explore the genetic variation in MSP-1 Block 2 underlying potential problems faced while studying the immune responses elicited by this vaccine target and while using it as a molecular marker in epidemiologic investigations. We describe the distribution of a new Block 2 recombinant allele family in samples collected from western Kenya and other malarious regions of the world and provide evidence that this allele family is found worldwide and that all MR alleles most likely originated from a single recombination event. We test whether the number of tandem repeats (i.e. fragment size) can be considered neutral in an area of high transmission in western Kenya. In addition, we investigate the validity of the assumption that Block 2 alleles of the same size and allele family are identical by examining MSP1 Block 2 amino acid sequences obtained from full-length MSP-1 clones generated from infected Kenyan children and find that this assumption does not hold. We conclude that the worldwide presence of a new allele family, the effect of positive natural selection, and the lack of conserved amino acid motifs within alleles of the same size suggest a higher level of complexity that may hamper our ability to elucidate allele family specific immune responses elicited by this vaccine target and its overall use as genetic marker in other types of epidemiologic investigations.

The effects of varying exposure to malaria transmission on development of antimalarial antibody responses in preschool children. XVI. Asembo Bay Cohort Project

In areas of intense malaria transmission, malaria morbidity and mortality is highest in children 3-18 months old. Interventions that reduce malaria exposure early in life reduce morbidity but may also delay development of clinical immunity. We assessed the relationship between intensity of malaria exposure and development of antibody responses. Thirty-nine children were monitored monthly, from birth to > or =2.5 years old (1238 observations), and were divided into 3 exposure categories, on the basis of parasitemic episodes or entomological data. Children with low exposure during the first 2 years of life had higher subsequent levels of antibody to merozoite surface protein-1(19-kDa) (a marker of blood-stage responses) by months 24-35 (P<.05). This inverse relationship decreased as children aged. There was no consistent relationship between exposure early in life and subsequent levels of antibody to circumsporozoite protein (a marker of sporozoite-stage responses). These data suggest that, in areas of intense malaria transmission, during the first 3 years of life, interventions that either reduce the number of asexual parasitemic episodes or lower entomological exposure do not delay the development of antibody responses to blood-stage malarial antigens.

Does infection with Human Immunodeficiency Virus affect the antibody responses to Plasmodium falciparum antigenic determinants in asymptomatic pregnant women?

OBJECTIVES

HIV-seropositive pregnant women are more susceptible to malaria than HIV-seronegative women. We assessed whether HIV infection alters maternal and cord plasma malarial antibody responses and the mother-to-infant transfer of malaria antibodies.

METHODS

We determined plasma levels of maternal and cord antibodies [Immunoglobulin (IgG)] to recombinant malarial proteins [merozoite surface protein 1 (MSP-1(19kD)), the erythrocyte binding antigen (EBA-175)], the synthetic peptides [MSP-2, MSP-3, rhoptry associated protein 1 (RAP-1), and the pre-erythrocytic stage, circumsporozoite protein (NANP)(5)] antigenic determinants of Plasmodium falciparum; and tetanus toxoid (TT) by ELISA among samples of 99 HIV-seropositive mothers, 69 of their infants, 102 HIV-seronegative mothers and 62 of their infants.

RESULTS

The prevalence of maternal antibodies to the malarial antigenic determinants ranged from 18% on MSP3 to 91% on EBA-175; in cord plasma it ranged from 13% to 91%, respectively. More than 97% of maternal and cord samples had antibodies to TT. In multivariate analysis, HIV infection was only associated with reduced antibodies to (NANP)(5) in maternal (P=0.001) and cord plasma (P=0.001); and reduced mother-to-infant antibody transfer to (NANP)(5) (P=0.012). This effect of HIV was independent of maternal age, gravidity and placental malaria. No consistent HIV-associated differences were observed for other antigenic determinants.

CONCLUSION

An effect of HIV infection was only observed on one malarial antigenic determinant, suggesting that the increased susceptibility to malaria among HIV-infected pregnant women may not be explained on the basis of their reduced antibody response to malaria antigens.

Antibody responses to repetitive epitopes of the circumsporozoite protein, liver stage antigen-1, and merozoite surface protein-2 in infants residing in a Plasmodium falciparum-hyperendemic area of western Kenya. XIII. Asembo Bay Cohort Project

The present study was initiated to characterize antibody responses to repetitive epitopes of the circumsporozoite protein (CSP), liver stage antigen-1 (LSA-1), and merozoite surface protein-2 (MSP-2) of Plasmodium falciparum in infants residing in a P. falciparum-hyperendemic area of western Kenya. In this study, development and maintenance of these antibody responses in 28 infants were studied longitudinally by use of monthly serum samples collected from birth to age 1 year. Mother plasma and infant umbilical cord plasma were also tested to assess the transplacental transfer of maternal antibodies. Results showed that antibodies passively transferred from mothers were detectable for CSP, LSA-1, and MSP-2 repeat epitopes. Infants were able to mount and maintain a strong antibody response against LSA-1 in their first year of life. Infants often responded to CSP repeats, but with a much lower antibody titer. Antibody responses in infants against Fc27 and 3D7 repeats of MSP-2 were low throughout their first year. In addition, 51 infants whose first detected infection occurred at > 4 months of age were selected to determine antibody responses to the antigens tested upon their first and second detected infections. Antibody responses to LSA-1 and, to a lesser degree, CSP increased in positivity rates and titer upon second infection. Antibody responses to Fc27-type and 3D7-type repeats of MSP-2 were low upon both infections. There was no association between maternally transferred anti-LSA-1, anti-CSP, or anti-MSP-2 antibodies and an infant's first detected infection. No significant correlation was found between an infant's antibody responses to the 4 antigen repetitive epitopes and protection against malarial parasitemia during the first year of life.

Plasmodium falciparum genotypes, low complexity of infection, and resistance to subsequent malaria in participants in the Asembo Bay Cohort Project

To assess the relationship between the within-host diversity of malaria infections and the susceptibility of the host to subsequent infection, we genotyped 60 children's successive infections from birth through 3 years of life. MSP-1 Block2 genotypes were used to estimate the complexity of infection (COI). Malaria transmission and age were positively associated with the number of K1 and Mad20 alleles detected (COI(KM)) (P < 0.003). Controlling for previous parasitemia, transmission, drug treatment, parasite density, sickle cell, and age, COI(KM) was negatively correlated with resistance to parasitemia of > 500/microl (P < 0.0001). Parasitemias with the RO-genotype were more resistant than those without this genotype (P < 0.0000). The resistance in low COI(KM) infections was not genotype specific. We discuss the impact of genotype-transcending immunity to conserved antigenic determinants. We also propose a diversity-driven immunomodulation hypothesis that may explain the delayed development of natural immunity in the first few years of life and suggest that interventions that decrease the COI(KM) could facilitate the development of protective immunity.

Glycosylphosphatidylinositol anchors of Plasmodium falciparum: molecular characterization and naturally elicited antibody response that may provide immunity to malaria pathogenesis

Induction of proinflammatory cytokine responses by glycosylphosphatidylinositols (GPIs) of intraerythrocytic Plasmodium falciparum is believed to contribute to malaria pathogenesis. In this study, we purified the GPIs of P. falciparum to homogeneity and determined their structures by biochemical degradations and mass spectrometry. The parasite GPIs differ from those of the host in that they contain palmitic (major) and myristic (minor) acids at C-2 of inositol, predominantly C18:0 and C18:1 at sn-1 and sn-2, respectively, and do not contain additional phosphoethanolamine substitution in their core glycan structures. The purified parasite GPIs can induce tumor necrosis factor alpha release from macrophages. We also report a new finding that adults who have resistance to clinical malaria contain high levels of persistent anti-GPI antibodies, whereas susceptible children lack or have low levels of short-lived antibody response. Individuals who were not exposed to the malaria parasite completely lack anti-GPI antibodies. Absence of a persistent anti-GPI antibody response correlated with malaria-specific anemia and fever, suggesting that anti-GPI antibodies provide protection against clinical malaria. The antibodies are mainly directed against the acylated phosphoinositol portion of GPIs. These results are likely to be valuable in studies aimed at the evaluation of chemically defined structures for toxicity versus immunogenicity with implications for the development of GPI-based therapies or vaccines.

Anti-merozoite surface protein-1 19-kDa IgG in mother-infant pairs naturally exposed to Plasmodium falciparum: subclass analysis with age, exposure to asexual parasitemia, and protection against malaria. V. The Asembo Bay Cohort Project

The anti-merozoite surface protein-1 19-kDa IgG (anti-MSP119KD) IgG responses of 33 parasitemic infants, aged 6-14 months, were compared with those of their mothers at the time of the infant's delivery and at the time the infants were sampled; the antimalaria protection associated with these responses was also compared. IgG1 and IgG3 were the predominant subclasses. Infants <300 days old and pregnant mothers had the lowest cytophilic-to-noncytophilic IgG ratio. By 300 days of age, the infants had IgG subclass compositions and levels similar to those of their mothers at the same date. Among infants, older infants with only 1 or 2 detected asexual parasitemias had the highest cytophilic-to-noncytophilic IgG ratio and IgG1 levels. IgG1 level was negatively correlated with protection. The findings suggest that the MSP119KD antibody response develops with age, not with multiple experiences with parasitemia, and, thus, that an antimalaria vaccine strategy for pregnant mothers could delay infants' first parasitemias until they are more capable of mounting a favorable anti-MSP119KD response.

A longitudinal investigation of IgG and IgM antibody responses to the merozoite surface protein-1 19-kiloDalton domain of Plasmodium falciparum in pregnant women and infants: associations with febrile illness, parasitemia, and anemia

This study was aimed at delineating characteristics of naturally acquired immunity against the merozoite surface antigen-1 (MSP-1) of Plasmodium falciparum, a candidate malaria vaccine antigen. A case/control study was performed on 75 case/control pairs of infants with febrile illness at the time of the first detected infection indicating a clinical case. The presence and level of antibodies at one month prior to the first infection and at the time of the first infection in the afebrile group was significantly higher than in the febrile group. Decreased parasite density and decreased infection-related loss of hemoglobin was seen in infants with anti-MSP-1(19kD) IgG antibodies. In addition, mothers who were positive for the presence of these antibodies conferred protection against placental infection and infection in their infants. In this study, development of anti-MSP-1(19kD) antibody responses in 24 infants were studied longitudinally using monthly serum samples collected from birth until approximately one year of age. In addition, umbilical cord blood sera and respective mothers' sera were analyzed. Longitudinal studies of antibody responses revealed several short-lived IgG and IgM peaks throughout an infant's first year that correlated with detection of parasitemia. The protection against parasitemia and febrile illness was observed in infants when anti-MSP-1(19kD) antibodies were present; when infants were negative for IgG, they had a 10-times greater risk of becoming parasitemic. These data from a longitudinal and prospective study of malaria suggest a protective role for anti-MSP-1(19kD) antibodies in infants and pregnant women.

Identification of T and B cell epitopes recognized by humans in the C-terminal 42-kDa domain of the Plasmodium falciparum merozoite surface protein (MSP)-1

The 42-kDa, C-terminal region of the merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a putative malaria vaccine candidate Ag. Nine synthetic peptides corresponding to predicted T cell sites of MSP-1 in blocks 15 and 16 and eight overlapping peptides representing the conserved block 17 were used to identify naturally immunogenic epitopes. These peptides were tested for their ability to induce proliferation of PBMC from residents in western Kenya, where malaria transmission is holoendemic. Six peptides (PL145, PL146, PL147, PL148, PL149, and PL150) from blocks 15 and 16 induced a positive proliferative response in &gt; 30% of the individuals tested, and three peptides (PL151, PL152, and PL153) induced a proliferative response in &lt; 25% of the donors. Among these peptides, PL146 was from the highly conserved region, PL150 was from a polymorphic region, and all other peptides were from a dimorphic region of blocks 15 and 16. In block 17, only three peptides, PL99, PL100, and PL103, induced proliferation in 30 to 37% of the volunteers. The rest of the peptides induced a proliferative response in approximately 13 to 25% of the donors. The plasma from these donors widely reacted with different allelic forms of 19-kDa recombinant proteins representing block 17 and recognized at least two linear B epitopes, PL104 and PL97. In summary, this study revealed that a majority of immunodominant T and B epitopes are localized in the conserved or dimorphic regions that are nonpolymorphic in the 42-kDa protein of MSP-1. This study suggests that incorporation of T epitopes from the dimorphic blocks 15 and 16 in a vaccine construct may be useful to ensure Ag-specific memory responses.

Identification of T and B cell epitopes recognized by humans in the C-terminal 42-kDa domain of the Plasmodium falciparum merozoite surface protein (MSP)-1

The 42-kDa, C-terminal region of the merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a putative malaria vaccine candidate Ag. Nine synthetic peptides corresponding to predicted T cell sites of MSP-1 in blocks 15 and 16 and eight overlapping peptides representing the conserved block 17 were used to identify naturally immunogenic epitopes. These peptides were tested for their ability to induce proliferation of PBMC from residents in western Kenya, where malaria transmission is holoendemic. Six peptides (PL145, PL146, PL147, PL148, PL149, and PL150) from blocks 15 and 16 induced a positive proliferative response in > 30% of the individuals tested, and three peptides (PL151, PL152, and PL153) induced a proliferative response in < 25% of the donors. Among these peptides, PL146 was from the highly conserved region, PL150 was from a polymorphic region, and all other peptides were from a dimorphic region of blocks 15 and 16. In block 17, only three peptides, PL99, PL100, and PL103, induced proliferation in 30 to 37% of the volunteers. The rest of the peptides induced a proliferative response in approximately 13 to 25% of the donors. The plasma from these donors widely reacted with different allelic forms of 19-kDa recombinant proteins representing block 17 and recognized at least two linear B epitopes, PL104 and PL97. In summary, this study revealed that a majority of immunodominant T and B epitopes are localized in the conserved or dimorphic regions that are nonpolymorphic in the 42-kDa protein of MSP-1. This study suggests that incorporation of T epitopes from the dimorphic blocks 15 and 16 in a vaccine construct may be useful to ensure Ag-specific memory responses.