CD40L association with protection from severe malaria

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Abstract

CD40 ligand (CD40L), a glycoprotein involved in B cell proliferation, antigen presenting cell activation, and Ig class switching, is important in the immune response to infection. Rare coding mutations in CD40L can lead to life-threatening immunodeficiency but the potential for common variants to alter disease susceptibility remains to be explored. To identify polymorphisms in CD40L, we sequenced 2.3 kb of the 5′ flanking region and the first exon of the gene in DNA samples from 36 Gambian females and one chimpanzee. Diversity was lower than the average reported for other areas of the X chromosome, and only two polymorphisms were identified. The polymorphisms were genotyped in DNA samples from 957 Gambian individuals, cases and controls from a study of severe malaria. A significant reduction in risk for severe malaria (OR = 0.52, P = 0.002) was associated with males hemizygous for the CD40L−726C. Analysis by transmission disequilibrium test of 371 cases, for whom DNA from both parents was also available, confirmed the result was not due to stratification (P = 0.04). A similar but non-significant trend was found in females. This preliminary association of a common variant in CD40L with a malaria resistance phenotype encourages further genetic characterization of the role of CD40L in infectious disease.

Introduction

CD40L is a type II membrane glycoprotein expressed by activated CD4+ T cells, and plays a pivotal role in the immune response. CD40L is involved in B cell proliferation, antigen presenting cell activation, Ig class switching, and is involved in the formation of germinal centres and preventing B-cells from undergoing apoptosis.1 The importance of CD40L in immune regulation was first demonstrated in humans in the genetic disease X-linked hyperimmunoglobulin M syndrome, in which the absence of CD40L on activated T cells diminishes the cell-mediated immune response and prevents B cells from undergoing Ig class switching. The disease phenotype includes low levels of IgG and IgA, normal or elevated serum levels of IgM, and susceptibility to opportunistic infections.2,3

CD40L expression has been reported on basophils, eosinophils, activated B cells and blood dendritic cells.4,5,6 It has been implicated as a critical player in HIV infection, contributing to the immune control of viral replication and possibly promoting the replication of HIV in lymphocytes.7 CD40L has also been shown to help activate T cell mediated immune response by activating antigen-presenting cells, which in turn express higher levels of B7 proteins. More generally, it is becoming clear that CD40L is important in the immune response to infectious agents. However, the extent of CD40L’s control of immune regulation is still far from being understood.

We set out to study the role of CD40L variants in the human response to Plasmodium falciparum malaria infection. Common variants in genes expressed in erythrocytes, including G6PD, β-globin, and Duffy, have already been demonstrated to induce malaria resistance.8 More recently genes involved in the immune response, such as HLA-B53, which induce malaria resistance or susceptibility phenotypes, have been identified9,10,11 and CD40L is an important candidate locus to screen for disease association.

The CD40L gene spans roughly 12 kb, and codes for a 39-kDa cell surface protein that is a member of the tumour necrosis factor superfamily.12 Its genomic location, Xq26.2, lies near a region of low nucleotide diversity, a SNP ‘desert’, postulated to be due to recent coalescence of the human X chromosome.13 Sequence for the gene has recently been obtained; the gene contains five exons, the first of which codes for intracellular and transmembrane regions while the rest of the exons code for extracellular sequence.14,15 CD40L expression on T cells is transient, with the ligand being present on activated mature T cells but not on resting T cells. The sensitive regulation of CD40L expression suggests that polymorphisms in the 5′ regulatory region may be important for the immune response, prompting our strategy of screening for polymorphisms not only in the first exon but also in the 5′ regulatory region.16

Results

We sequenced 2195 bases of the CD40L 5′ promoter region, exon 1, and part of intron 1, in DNA obtained from 36 healthy Gambian females and one chimpanzee (Figure 1). The region sequenced spanned from −1866 nt to +457 nt in relation to the transcription start site. The sequence did not include the nucleotides from −211 nt to −88 nt, which surround a polyA repeat region. Two human polymorphisms were identified at −726 nt (C/T) and +220 nt (C/T). CD40L+220 is a synonymous mutation in exon 1. CD40L−726 is in the promoter region; however, MatInspector17 was unable to identify specific regulatory sites at the locus.

Figure 1
figure1

Annotated sequence of CD40L promoter region. Sequencing started 1866 bases upstream of the start of transcription. Exon 1 begins at +73; intron 1 begins at 229. Seven fixed differences between human and chimpanzees are underlined and labelled ‘X in chimps’. Discrepancies with previously published sequence(14) are underlined and labelled ‘X found’. Three single nucleotide polymorphisms are underlined and labelled ‘X/Y polymorphism’. The CD40L-726T/C and CD40L+220T/C polymorphisms were identified by sequencing; while the CD40L+50T/C polymorphism is noted in the literature but not found in our sample.

Seven fixed differences between humans and chimpanzees were identified at −1798, −1534, −1050, −532/−536, −458, +94 and +313 nt. Discrepancies were found between the Gambians and the published sequence at −940, −733, −735, −600, −594, +357, +371 and +427 nt.14 DNA from three Caucasian males was sequenced to see if these were Gambian-specific differences; however, they showed the same discrepancy with the published data.

Sequence data were used to quantify the level of nucleotide diversity in the region. One in every 1098 nucleotides was polymorphic (one in 2039 non-coding and one in 156 coding sequence). Nucleotide diversity was calculated by θ, the number of variant sites normalized for a given sequence length and sample size.18 For two polymorphisms in 2195 bases in 72 chromosomes, θ = 2.6 × 10−6, as compared with θ = 1.3 × 10−5 found elsewhere on the X chromosome and θ = 5.3 × 10−4 for a range of candidate genes distributed throughout the genome.19,20 Linkage disequilibrium (LD) between CD40L−726 and CD40L+220 was calculated using hemizygous males, because phase can be calculated unambiguously in these individuals (Methods). Significant LD was found in controls (D′ = 0.75, P = 0.028).

Having observed low nucleotide diversity in humans, we sequenced one chimpanzee for the entire 5′ region, to examine the mutation rate. Seven in 2195 bases varied between humans and chimpanzees, a 99.7% sequence identity between species. This value is somewhat higher than previous X chromosome reports of 99.3%.19 The chimpanzee sequence was also used to determine the ancestral alleles for the two human polymorphisms. From chimpanzee data, both CD40L−726 and CD40L+220 were likely thymine residues in their ancestral state, and subsequently mutated to produce the derived cytosine residues.

Samples from 676 severe malaria cases and 281 controls recruited in the Gambia were compared for the CD40L−726 and CD40L+220 polymorphisms to test for association of CD40L with malaria. Samples included individuals from the Mandinka, Wollof, Fulani, Jola, Serehule, Serere, and Manjago ethnic groups. Samples were initially divided by gender for an overall case and control comparison, and then analysed by Mantel-Haenszel stratified by ethnic group. The CD40L−726C and CD40L+220C alleles were each compared in controls with severe malaria cases, cerebral malaria cases, and severe malarial anaemia cases (Table 1). In Gambian males, CD40L−726C demonstrated significant association with severe malaria, cerebral malaria, and severe malarial anaemia, with odds ratios of 0.52 (P = 0.006), 0.55 (P = 0.007), and 0.49 (P = 0.010), respectively. The results remained significant when ethnic differences were accounted for using the Mantel-Haenszel weighted odds ratio,21 with values of 0.54 (P = 0.006), 0.58 (P = 0.022), and 0.51 (P = 0.030), respectively. Use of haplotypic data (Table 2) did not further break down the association with the CD40L−726C allele in males.

Table 1 Results of case and control comparisons in Gambia for the CD40L−726C and CD40L+220C alleles. The first four columns give the frequencies of individuals who have a copy of the CD40L−726C allele. For females this includes ct heterozygotes and cc homozygotes. The odds ratios for comparison of cases and controls are given with the 95% confidence intervals. The Mantel-Haenszel weighted odds ratio for stratified samples was used to calculate odds ratios for combined males and females
Table 2 CD40L−726/+220 haplotype frequencies in Gambian male cases and controls. Gambian males were used to get an unambiguous estimate of haplotype frequency in hemizygous samples

Comparison of females heterozygous or homozygous for CD40L−726C to those homozygous for CD40L−726T, in cases and controls gave non-significant results. The trend however was similar to that found in males with severe malaria, cerebral malaria, and severe malarial anaemia, producing odds ratios of 0.74 (P = 0.160), 0.68 (P = 0.082), and 0.80 (P = 0.461), respectively. When analysed by the Mantel-Haenszel weighted odds ratio, the values were 0.74 (P = 0.190), 0.68 (P = 0.117), and 0.83 (P = 0.683). To explore a recessive model, females homozygous for CD40L−726C were compared with individuals who were either heterozygous or homozygous for CD40L−726T; the resulting odds ratios were 0.87 (P = 0.627), 0.84 (P = 0.572), and 1.17 (P = 0.692).

To ensure that population stratification was not a confounder in our study, we confirmed our results using a transmission disequilibrium test (TDT). The TDT assesses the association of alleles to disease state within families by identifying which allele from a heterozygous parent is transmitted to an infected child.22,23 DNA from both parents was available for 371 cerebral malaria cases. The relationship of CD40L−726C to malaria was investigated for males and females separately in a family-based study of cerebral malaria, by typing the 742 parents.

In families in which the affected male child had cerebral malaria without severe anaemia, 22 heterozygous mothers transmitted CD40L−726C and 38 transmitted CD40L−726T, a significant difference (P = 0.038). In families in which the affected male child had cerebral malaria with or without severe anaemia, 32 mothers transmitted CD40L−726C and 45 transmitted CD40L−726T (P = 0.068). The family study supports the findings in Gambian cases and controls, indicating that the CD40L−726C association is not due to stratification. In females TDT, like the case-control study, did not show significant results. In families where the female child had cerebral malaria without severe anaemia, 24 mothers transmitted CD40L−726C and 24 transmitted CD40L−726T. In families where the female child had cerebral malaria with or without severe anaemia, 30 mothers transmitted CD40L−726C and 27 transmitted CD40L−726T.

Discussion

These data suggest that CD40L is relatively conserved both in terms of sequence identity between chimpanzees and humans, and in the level of nucleotide diversity seen in a human study population, which is five-fold lower than previous reports on the X chromosome average.19 A previous study has noted regions of low diversity elsewhere on Xq,13 and it has been proposed that these so-called ‘SNP deserts’ are due to a recent coalescence of the X chromosome. Two noteworthy features of the present study are that we observe low diversity at this locus in an African population, and that the low species divergence between human and chimpanzee included the 5′ flanking region of CD40L. This raises the possibility that the locus has been subject to a low mutation rate and/or selective pressure, and more data are needed to examine this question.

In males, the CD40L−726C allele was associated with protection against both cerebral malaria and severe malarial anaemia. Differences in ethnic make up between cases and controls can generate false-positive signals of genetic association when both allele frequency and disease frequency differ in the populations being compared. We addressed this issue in two ways: (1) by stratifying for ethnic group in the case-control analysis; and (2) by re-analysing those cases for which parental DNA was available using the TDT statistic, which is not subject to the confounding effect of population stratification that can compromise classic case-control studies.24 By both criteria, the CD40L−726C was associated with protection against cerebral malaria in males. Females possessing this allele showed a non-significant trend towards protection by case-control analysis, but not in the family-based TDT test. These observations suggest that the association, if real, follows an inheritance model with a more limited power of detection in females. Alternatively there could be a real difference between males and females in the biological effect of the allele.

Taken together these data indicate that CD40L is an important locus for further investigation in relation to malaria susceptibility. Further exploration of this effect will involve identification and genotyping of larger numbers of polymorphic markers in both coding and non-coding regions of CD40L to form haplotypes, and study of these marker sets in additional populations in malaria-endemic areas. Additionally markers at greater distances from CD40L−726 would be needed to test for factors in neighbouring genes such as Rac/Cdc42 guanine exchange factor 6 (ARHGEF6). At only 5.6 kb away, ARHGEF6 is likely to be in LD with CD40L; however its known functions in regulation of gene expression and cytoskeletal architecture, do not suggest involvement in malaria pathogenesis.25 Other nearby genes whose association must be excluded include Tondu, RNA binding motif X, HIV Tat specific factor 1, and bombesin subtype-3, at distances of 91 kb, 102 kb, 115 kb, and 120 kb away, respectively.

Our finding of an association of a CD40L variant with resistance to severe malaria provides evidence to implicate CD40L as a factor in immunity or pathogenesis of this common infectious disease. The next step is to find out whether the same association is seen in other populations, and further genetic characterization of the region is needed to determine whether CD40L−726 itself, or a neighbouring marker that is in linkage disequilibrium with this polymorphism, is the true functional determinant.

Materials and methods

Study population

The CD40L promoter region was sequenced in 36 Gambian females. Children with severe malaria and their parents were recruited, after obtaining informed parental consent, at the Royal Victoria Hospital, Banjul, The Gambia, as described elsewhere.9 Severe malaria fell into two major categories, cerebral malaria and severe malarial anaemia. Cerebral malaria was defined as a Blantyre coma score of <3, persisting after appropriate treatment for hypoglycaemia or convulsions if these were also present, in a child with asexual P. falciparum parasitaemia and no other evident cause of coma. Severe malaria anaemia was defined as Hb 5 g/dl accompanied by asexual P. falciparum parasitaemia. Samples from the umbilical cord of healthy Gambian newborns were used as a control for population allele frequency. The study was approved by the Gambian Government/MRC Joint Ethical Committee.

DNA was extracted using a Nucleon kit and concentration was determined by the PICO-Green assay. Samples were then diluted to 1 ng/μL in TE. Samples for allele-specific genotyping were enriched by whole genome amplification, using GENPAK N15 primers. Five ng of genomic DNA was added to a 50 μL reaction mix including 2 mM MgCl2, 20 μM each dNTP, 16 mM (NH4)2 SO4 , 67 mM Tris-HCl (pH 8.8 at 25°C), and 0.01% Tween-20. The cycling conditions are 94°C 3 min, 50 cycles of 94°C 1 min, 37°C 2 min ramping up 1°C/sec to 55°C, 55°C 4 min, followed by 71°C 5 min.

Sequencing of CD40L promoter and 1st exon

We sequenced from −1857 nt to +415 nt relative to the transcription start site of the CD40L gene in 36 Gambian females and in one chimpanzee. Samples were first amplified for a 2319 nt region (−1861 nt to +458 nt), consisting of the 5′ flanking region of CD40L, exon 1 and the first 100 nt of intron 1, using the primers, 5′-CACTGGGGAGAGCATTCAGG-3′ and 5′-CAGAGAT GGTATGGGCAGAG-3′. Ten ng of genomic DNA was added to a 20 μL reaction mix including 10 pmol each forward and reverse primer, 16 mM (NH4)2 SO4 , 67 mM Tris-HCl (pH 8.8 at 25°C), 0.01% Tween-20, 1.5 mM MgCl2, 200 μM each dNTP and 1.5U Taq DNA polymerase. The cycling conditions were 94°C 12 min, 36 cycles of 94°C 30 sec, 60°C 45 sec, and 72°C 2 min, followed by 72°C 10 min. The first round PCR product was diluted 1:30 in H2O. Second round PCR forward and reverse primers were designed to have an M13 tail complementary to the M13 sequencing primers for dye primer cycle sequencing (forward: 5′-TGT AAAACGACGGCCAGT-3′ and reverse 5′-CAGGAAA CAGCTATGACC-3′). Six overlapping sequences were amplified in second round PCR using nested primers. Primers for −1861 nt to −1395 nt: 5′-CACTGGGGA GAGCATTCAGG-3′ and: 5′-AGCTTTTCACTACAT CTGCC-3′, for −1487 nt to −1019 nt: 5′-TTC CTTCAGTGGAACTAAGG-3′ and 5′-TGCCAACTC CTTACATGTTG-3′, for −1137 nt to −625 nt: 5′-GCC CTTCAGAAATGTGTAATC-3′ and 5′-AAATCAGGCCA AGACTCTGG-3′, for −712 nt to −211 nt: 5′-TGG ATTGGAACAGTGTACAC-3′ and 5′-CATTCTTGCC TTGAAATGTC-3′, for −88 nt to +242 nt: 5′-GCT GGGAGAGAAGACTACG-3′ and 5′-GTGGTTCAT CTTACCTTGTC-3′, and for +11 nt to +458 nt: 5′-TCT TCTCATGCTGCCTCTGC-3′ and 5′-CAGAGATGGT ATGGGCAGAG-3′. The fifth sequencing segment does not include all of the nucleotides in the region and was designed to circumvent a polyA region that interfered with sequencing. Second round amplification used the same reagents. Cycling conditions for second round amplification were 94°C 12 min, 36 cycles of 94°C 30 sec, 54°C 45 sec, and 72°C 2 min, followed by 72°C 10 min. Second round products were diluted 1:6 in H2O and sequenced using the Perkin Elmer (Foster City, CA, USA) Big-Dye Primer kit and protocol.

Genotyping

Gambian samples were typed for CD40L−726 (C/T) and CD40L+220 (C/T) polymorphisms using allele specific PCR amplification. Allele-specific primers and one consensus complementary primer were designed to amplify a 276 bp and 466 bp segment respectively. Primers for CD40L−726 are 5′-CTGAACTGTTACATCAGCAT-3′ for CD40L−726T, 5′-CTGAACTGTTACATCAGCAC-3′ for CD40L−726C and 5′-CTAAACTCAATGAAAGCCTG-3′ for the reverse consensus primer. Primers for CD40L+220 are 5′-GACATTTCAAGGCAAGAATG-3′ for the forward consensus primer, 5′-GTTCATCTTACCTTGTCCAG-3′ for CD40L+220C and 5′-GTTCATCTTACCTTGTCCAA-3′ for CD40L+220T. Twenty-five ng whole genome amplified DNA was added into a 15 μL reaction with 15 pmol each forward and reverse primer, 16 mM (NH4)2 SO4, 67 mM Tris-HCl (pH 8.8 at 25°C), 0.01% Tween-20, 1.9 mM MgCl2, 0.6 μM each dNTP, and 0.25 U Taq DNA polymerase (Bioline Biotaq). Cycling conditions were 96°C 1 min, 5 cycles of 96°C 35 sec, 70°C 45 sec, and 72°C 35 sec, then 21 cycles of 96°C 25 sec, 65°C 50 sec, and 72°C 40 sec, then 6 cycles of 96°C 35 sec and 55°C 1min, followed by 72°C 90 sec.

Nucleotide diversity

Nucleotide diversity (θ) was calculated by normalizing the observed number of variant sites (k), by the number of chromosomes studied (n) and the total sequence length (L):

Linkage disequilibrium analysis (LD)

LD between loci was calculated using the classical LD coefficient D, which measures the deviation from random association between alleles at different loci.27 For two loci, one with alleles A and a and one with alleles B and b, D = PABpApB where PAB is the frequency of the haplotype having allele A at the first locus and allele B at the second locus, and pA and pB are the frequencies of alleles A and B respectively.18 The D′ statistic was calculated as D divided by its maximum possible value, min{pApb, papB} if D > 0 and max{pApB, papb if D < 0.27 The significance of disequilibrium is calculated using the χ2 statistic.

Association analysis

Cases and controls were analysed for differences in allele and haplotype frequencies using Epi Info Version 5.01A. Fisher’s exact test was used to calculate the significance of the difference in frequencies. The relative risk in a case-control study was estimated by calculating the ratio of the odds of having the allele among the cases compared to that among the controls. The Mantel-Haenszel weighted odds ratio for stratified samples was performed to calculate odds ratios for combined males and females and for grouped ethnic data.21

Transmission disequilibrium test (TDT)

The TDT statistic was calculated for 371 families, cases with cerebral malaria for which a mother/father pair was available. The TDT statistic is , where a is the number of times in an informative family a heterozygous parent transmits the marker allele and b is the number of times the heterozygous parent transmits the other allele.22,23 The TDT was calculated as a two-sided test, in which a null hypothesis of no association is rejected if either allele is transmitted significantly more often than the other.

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Acknowledgements

We thank David Reich, Shiv Pillai and Joel Hirschorn for many thoughtful discussions and comments and Nick Mundy for the chimpanzee DNA sample. This study would not have been possible without the kind cooperation of the families studied, and the doctors and nurses of RVH, Banjul, The Gambia.

Author information

Correspondence to D Kwiatkowski.

Additional information

This study was funded by the Medical Research Council and the Rhodes Scholarship Trust.

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Sabeti, P., Usen, S., Farhadian, S. et al. CD40L association with protection from severe malaria. Genes Immun 3, 286–291 (2002) doi:10.1038/sj.gene.6363877

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Keywords

  • CD40L
  • severe malaria

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    • , Sarah Joseph
    • , Dushyanth Jyothi
    • , David Kachala
    • , Dorcas Kamuya
    • , Haddy Kanyi
    • , Harin Karunajeewa
    • , Nadira Karunaweera
    • , Momodou Keita
    • , Angeliki Kerasidou
    • , Aja Khan
    • , Katja Kivinen
    • , Gilbert Kokwaro
    • , Amadou Konate
    • , Salimata Konate
    • , Kwadwo Koram
    • , Dominic Kwiatkowski
    • , Moses Laman
    • , Si Le
    • , Ellen Leffler
    • , Martha Lemnge
    • , Enmoore Lin
    • , Alioune Ly
    • , Alexander Macharia
    • , Bronwyn MacInnis
    • , Nguyen Mai
    • , Julie Makani
    • , Cinzia Malangone
    • , Valentina Mangano
    • , Alphaxard Manjurano
    • , Lamin Manneh
    • , Laurens Manning
    • , Magnus Manske
    • , Kevin Marsh
    • , Vicki Marsh
    • , Gareth Maslen
    • , Caroline Maxwell
    • , Eric Mbunwe
    • , Marilyn McCreight
    • , Daniel Mead
    • , Alieu Mendy
    • , Anthony Mendy
    • , Nathan Mensah
    • , Pascal Michon
    • , Alistair Miles
    • , Olivo Miotto
    • , David Modiano
    • , Hiba Mohamed
    • , Sile Molloy
    • , Malcolm Molyneux
    • , Sassy Molyneux
    • , Mike Moore
    • , Catherine Moyes
    • , Frank Mtei
    • , George Mtove
    • , Ivo Mueller
    • , Regina Mugri
    • , Annie Munthali
    • , Theonest Mutabingwa
    • , Behzad Nadjm
    • , Andre Ndi
    • , Carolyne Ndila
    • , Charles Newton
    • , Amadou Niangaly
    • , Haddy Njie
    • , Jalimory Njie
    • , Madi Njie
    • , Malick Njie
    • , Sophie Njie
    • , Labes Njiragoma
    • , Francis Nkrumah
    • , Neema Ntunthama
    • , Aceme Nyika
    • , Vysaul Nyirongo
    • , John O'Brien
    • , Herbert Obu
    • , Abraham Oduro
    • , Alex Ofori
    • , Subulade Olaniyan
    • , Rasaq Olaosebikan
    • , Tom Oluoch
    • , Olayemi Omotade
    • , Olajumoke Oni
    • , Emmanuel Onykwelu
    • , Daniel Opi
    • , Adebola Orimadegun
    • , Sean O'Riordan
    • , Issa Ouedraogo
    • , Samuel Oyola
    • , Michael Parker
    • , Richard Pearson
    • , Paul Pensulo
    • , Norbert Peshu
    • , Ajib Phiri
    • , Nguyen Phu
    • , Margaret Pinder
    • , Matti Pirinen
    • , Chris Plowe
    • , Claire Potter
    • , Belco Poudiougou
    • , Odile Puijalon
    • , Nguyen Quyen
    • , Ioannis Ragoussis
    • , Jiannis Ragoussis
    • , Oba Rasheed
    • , John Reeder
    • , Hugh Reyburn
    • , Eleanor Riley
    • , Paul Risley
    • , Kirk Rockett
    • , Joanne Rodford
    • , Jane Rogers
    • , William Rogers
    • , Kate Rowlands
    • , Valentín Ruano-Rubio
    • , Kumba Sabally-Ceesay
    • , Abubacar Sadiq
    • , Momodou Saidy-Khan
    • , Horeja Saine
    • , Anavaj Sakuntabhai
    • , Abdourahmane Sall
    • , David Sambian
    • , Idrissa Sambou
    • , Miguel SanJoaquin
    • , Nuno Sepúlveda
    • , Shivang Shah
    • , Jennifer Shelton
    • , Peter Siba
    • , Nilupa Silva
    • , Cameron Simmons
    • , Jaques Simpore
    • , Pratap Singhasivanon
    • , Dinh Sinh
    • , Sodiomon Sirima
    • , Giorgio Sirugo
    • , Fatoumatta Sisay-Joof
    • , Sibiry Sissoko
    • , Kerrin Small
    • , Elilan Somaskantharajah
    • , Chris Spencer
    • , Jim Stalker
    • , Marryat Stevens
    • , Prapat Suriyaphol
    • , Justice Sylverken
    • , Bintou Taal
    • , Adama Tall
    • , Terrie Taylor
    • , Yik Teo
    • , Cao Thai
    • , Mahamadou Thera
    • , Vincent Titanji
    • , Ousmane Toure
    • , Marita Troye-Blomberg
    • , Stanley Usen
    • , Sophie Uyoga
    • , Aaron Vanderwal
    • , Hannah Wangai
    • , Renee Watson
    • , Thomas Williams
    • , Michael Wilson
    • , Rebecca Wrigley
    • , Clarisse Yafi
    •  & Lawrence Yamoah

    The Lancet Haematology (2018)