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IgM and IgG). Plasma samples were obtained from patients duringthe acute phase of their illness. Data on demographiccharacteristics, pre-morbid conditions, clinical features, androutine haematological and biochemical laboratory test findingswere collected and analysed

RESULTS

Migrant workers were younger, median age 31 years (range 19 to 37years), had no comorbidities and worked in heavy industry. Incomparison, the four Singaporean citizens were older with medianage 56 years (range 52 to 64 years). Two had comorbidities(hypertension and ischemic heart disease).All cases had complained of fever with median duration of 3 days.Other common symptoms included myalgia (89%), arthralgia and rash(78%), gastrointestinal symptoms (67%) and headache (44%).

Laboratory results showed lymphopenia with mean nadir of0.76� 109/L, occurring on mean day 4 of illness and mildthrombocytopenia with mean nadir of 153� 109/L.

CONCLUSIONS

Since January 2008, locally transmitted CHIKF has been reported inSingapore. From this small pilot study, patients with acute CHIKFpresenting to National University Hospital, Singapore from July toAugust 2008 could be divided into two distinct populations, one ofyounger migrant workers living in dormitories and one of olderSingaporean citizens with higher economic income living in nearbyhomes with gardens. Common presenting symptoms were fever,myalgia, arthralgia, rash, gastrointestinal symptoms and headache.Further study of CHIKF in Singapore would be valuable to characterizethe demographics, symptoms and laboratory results of affectedpatients

0005

MODELING HOW NOSOCOMIAL INFECTIONS SPREAD: DEPENDENCE AND INDEPENDENCE ASSUMPTIONS

Joc Cing TAY1, Hardiyanto WIBISONO1 and Paul Ananth TAMBYAH2

1ROSS Scientific Pte Ltd, Singapore, Singapore, 2National University Hospital, Singapore, Singapore

In most compartmental models of disease spread, spatial-temporalinteractions among individuals are homogenous and instantaneous.These assumptions have been gradually replaced by network-based, time and space-explicit constructs of the environment inindividual-based models that are more accurate and mechanistic.The time-series data needed are however, prohibitively large andexpensive to collect. In this feasibility study, the authors presenta similar attempt based on more easily collected, relative visitationfrequencies in staff movement patterns (collected over 2 weeks ata Surgical ICU (SICU) of an academic hospital). We hypothesize thatunder assumptions of continuity and periodicity of shifts, the time-dependent movement patterns are well estimated by relativefrequencies. Movement patterns of the SICU staff were collectedusing the TrackME system from ROSS Scientific. Each individualwears a receiver that logs the places visited and durations of eachvisit. If he/she visits a location (say A) n times out of a total of mvisits to all tracked locations, then the likelihood of he/she visitingA will be n/m among other choices. We do this for modelingmiscellaneous activities only.

METHOD

Figure 1 represents the average movement patterns of 5 Staff Nursesfor 9 tracked locations out of 20 possible locations within the ward.

The edges represent transitions from one location to another,labelled with probabilities. The transition matrix is given in Figure 2where the transition from location j to location i at time t, is given byXij where i, j are the row and column indices. A comparison ofrelative frequencies versus the Markovian steady state vector of thismatrix is given in Table 1

RESULTS

the error is surprisingly small (RMS error¼ 0.02) despite the fact thatdata collected contained discontinuities as they were taken frommultiple samples

CONCLUSIONS

The preliminary results suggest that under assumptions ofa continuous and periodic work pattern, characteristic of staff in theSICU ward, such relative frequencies well approximates theMarkovian steady state that was under the more stringentassumption of non-independent activity patterns. If so, they havesignificant implications on how data can be collected economicallyand yet providing accurate models of disease carriage.

0006

EVALUATION OF SIMIAN ADENOVIRAL VECTOR ADCH63 EXPRESSING MSP-1 AS A CANDIDATE BLOOD-STAGE MALARIAVACCINE

Anna GOODMAN1, Sarah GILBERT1, Stefano COLLOCA2, Matthew DICKS1, Adrian HILL1 and Simon DRAPER1

1University of Oxford, oxford, United Kingdom, 2Okairos AG, Rome, Italy

Complete protection against Plasmodium yoelii malaria has beendemonstrated using a heterologous prime-boost regime with viralvectors encoding the 42 kDa region of merozoite surface protein-1

(MSP-1) in a mouse model. This successful regime incorporateda human adenovirus serotype 5 (AdHu5) prime, boosted eight weekslater with a modified vaccinia virus Ankara (MVA) vector. Adenoviral

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vectors have generated great scientific interest in recent years andappear to be superior viral vectors with great potential in vaccineregimes. Their potential use in humans, however, is limited bynatural anti-vector immunity to human adenoviruses, but thisproblem could be largely circumvented by the use of simianadenoviral vaccine vectors. Recent clinical trials have suggested thatthe simian adenoviral vector AdCh63 is a promising clinicalcandidate.We have developed vectors (of human and simian origin) and MVAencoding a novel construct based on P. falciparum MSP-1 and haveundertaken comparative immunogenicity studies in mice. Theantigen, termed ‘PfM128, is based on the five highly conservedblocks from P. falciparum MSP-1, plus both dimorphic alleles of the42 kDa region. We have used these vectors to map novel murine Tcellepitopes within PfMSP-1. We compare antibody titres andpolyfunctional T cell responses when simian adenoviral vectorAdCh63 is used to replace AdHu5 in a heterologous prime-boostregime. These data suggest that simian adenoviral vectors havegreat potential for use in future blood-stage malaria vaccinationregimes in humans.

METHOD

The antigen, termed ‘PfM128’, was inserted into adenoviralvectors AdHu5, AdCh63 (Okairos) and Modified Vaccinia Ankaravirus (MVA). BALB/c mice (n¼ 6/ group) were immunised asfollows: AdHu5 PfM128 or AdCh63 PfM128 (1010 vp id) wasadministered at week 0. MVA PfM128 (107pfu id) was administeredat week 8. Sera was taken at weeks 2 and 8 post-prime and week2 post-boost. Total IgG were measured using ELISA to ETSR andQKNG GST-MSP119. The quantity and quality of the T cell response

to PfM128 was determined using ICS. Spleens were taken at 2weeks following the final immunisation.

RESULTS

Total IgG responses to both allelic forms of MSP-119 weredetermined by ELISA. No significant differences were foundbetween mice immunised with AdHu5 or AdCh63 PfM118. ACD8 + T cell epitope was identified using overlapping peptidepools. ICS was then used to determine CD8 + IFNg, IL-2 and TNFa

responses to peptide stimulation. Both immunisation regimeswere found to induce strong CD8 + T cell responses. Theseresponses were polyfunctional, with the majority of CD8 + T cellssecreting both IFNg and TNFa and a small proportion of cellssecreting IL-2. These cytokine responses did not differ betweengroups.

CONCLUSIONS

Viral vectored vaccines are shown to induce strong cellular andhumoural immune responses against an antigen construct basedon the blood-stage malaria candidate antigen, P. falciparumMSP-1. We demonstrate that human adenovirus 5 vector can beeffectively substituted for a simian adenoviral vector withouta reduction in immunogenicity. This work provides evidencea vaccine regime based on simian adenoviral vectors and theblood-stage antigen MSP-1 is likely to be of use in clinicalpractice. Funding has been obtained to take this work into phaseI clinical study of a simian adenoviral vector AdCh63 PfM128,boosted with MVA PfM128.

0008

HLA FOOTPRINTING REVEALS A NOVEL PROTECTIVE CD8 + T CELL RESPONSE IN HEPATITIS C VIRUS INFECTION

Karen FITZMAURICE1,2, Danijela PETROVIC1, Silvana GAUDIERI3, Elizabeth FREITAS3, Stuart SIMS2, Aideen LONG1,Dermot KELLEHER1 and Paul KLENERMAN2

1Trinity College, Dublin, Ireland, 2University of Oxford, Oxford, United Kingdom, 3Murdoch University, Perth, Australia

The cellular immune response is thought to play a key role indetermining a successful outcome to HCV infection. CD8+ Tcells are central to this process although the key features ofa successful CD8+ T cell response remain to be defined. A cohortof Irish women infected by a single source and defined bycommon age, gender and ethnicity provides an ideal setting inwhich to examine the impact of specific HLA Class I restrictedCD8+ T cells on virologic outcome. In this cohort a strongassociation between viral clearance and the HLA Class I alleleA*03 is described. We proposed that the mechanismunderpinning the protective nature of HLA A*03 was thepresentation of key immunodominant epitope(s) to CD8 + T cells.In this study, we used a novel approach combining the use ofbio-informatic epitope prediction with a unique set of host andviral genetic data to identify a key protective HLA A*03restricted epitope.

METHOD

Selective immune pressures imposed by CD8 + T cell responses are wellknown to drive escape mutations within targeted T cell epitopes. Thereproducible hallmark of this, a ‘‘footprint’’ is visible at populationlevel and reflects viral adaptation to HLA Class I directed responses. Wefirst identified 26 putative A*03 restricted epitopes using different

epitope prediction programs. Viral sequences were then obtained from9 HLA A*03+ve patients and 19 HLA A*03-ve controls. Polymorphismswithin the predicted epitopes were observed and associations linkingthem to the presence of HLA A*03 were identified. Cellular assays wereused to confirm these findings.

RESULTS

We observed a strong ‘‘footprint’’ in a novel predicted NS3 epitope(TVYHGAGTK) in HLA A*03 positive patients. In this epitope, lysinewas substituted with arginine K1088R, a key anchor position, in 77%of HLA A*03 positive patients vs 5% (p¼ 0.0002). A second significantsubstitution of threonine to alanine T1087A was also noted (p¼ 0.02)and the double substitution TK1087/8AR was found to occur in 55% vs5% controls (p¼ 0.007). Peptide-specific CD8 + T cell responses wereobserved in 60% of patients despite the 3 decades since exposure andT cell recognition was significantly reduced in cells stimulated withthe escape mutants.

CONCLUSIONS

We propose that the protective effect of HLA A*03 can be attributedto the targeting of this key immunodominant epitope in a conserved