√“¬ß“π‚§√ß°“√«‘®—¬ª√–®”ªï 2546 Annual Progress Report 2003

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this model will allow the investigation of basic liver stage biology and the screening of new drugs and vaccines that target the pre erythrocytic stages of malaria.

52nd Annual Meeting of the American Society of Tropical Medicine and Hygiene. Philadelphia, Pensylvania, USA. 3-7 December 2003.

PRE-CLINICAL EVALUATION OF VACCINE CANDIDATE P.FALCIPARUM MSP-L(42) FORMULATED WITH NOVEL ADJUVANTS IN COMPARISON WITH CLINICALLY APPROVED ALUM

Pichyangkul S, Miller RS, Tongtawe P, Gettayacamin M, Colgin L, Ruble D,Heppner DG, Kester KE, Lyon J, Angov E, Christian F, Ockenhouse CF, Ballou RW, Diggs CL, Voss SG, Cohen J and Walsh DS

Using the standardized rhesus monkey malaria vaccine model, we compared the safety and immunogenicity of the recombinant Plasmodium falciparum merozoite surface protein (MSP-l(42))antigen formulated with 4 novel adjuvant systems to alum. A five dose regimen (week 0, 4, 13, 21 and 30) of 50 ug of MSP-l(42) was administered by intramuscular injection with clinically approved alum or one of the four proprietary GlaxoSmithKline adjuvants (ASOI, AS02, AS05 and AS08). All five formulations of MSP-l(42) were safe and well tolerated. AS02 and ASOI formulations elicited significantly higher levels of anti-MSP-l(42) antibody than the alum formulation. All MSP-l(42) formulations tested generated high stimulation indices, including the alum adjuvanted vaccine. ELlS POT assays showed that the two formulations of MSP-l(42) vaccine which induced the highest titers of antibody, AS02 and AS01, demonstrated different cytokine response profiles. Both AS02 and ASOI formulations induced comparable levels of lFN-γ after the 3rd dose; however, the IL-5 response was greatly diminished in animals receiving ASOI adjuvanted vaccine. Using a IFN-γ/IL-5 ratio, the ASOI formulation clearly induced a strong Thl response. The AS02 formulation induced a balanced Thl/Th2 response. The lFN-γresponse generated by AS02 and ASOl formulations persisted at least 24 weeks after vaccination. Due to the induction of balanced Thl/Th2 response, MSP-l(42)/ASO2 formulation was then selected for Phase 1 trails, and the field trails of this vaccine are now underway in western Kenya.

International Conference on Malaria: Current Status and Future Trends. Chulabhorn Research Institute, Bangkok, Thailand. 16-19 February 2003.

QUANTITATIVE KINETICS OF PLASMODIUM VIVAX OOKINETE FORMATION IN THREE ANOPHELINE SPECIES

Zollner GE, Ponsa N, Coleman RE, Sattabongkot J, Jones JW and Vaughan JA

The ookinete is a crucial and vulnerable stage in plasmodial development within the mosquito vector. Following gamete formation and fertilization, spherical zygotes mature into motile, banana-shaped ookinetes within 12-18 h. The mature ookinetes actively move through the coagulated blood, peritrophic matrix and pass through the epithelium of the mosquito midgut

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√“¬ß“π‚§√ß°“√«‘®—¬ª√–®”ªï 2546 Annual Progress Report 2003

to form the propogative oocyst stage. Despite its importance, there is a paucity of data regarding the natural population densities of P. vivax ookinetes and subsequent conversion to oocysts. Studies were undertaken to quantify the in vivo kinetics of P. vivax ookinete formation in mosquito midguts. Laboratory-reared Anopheles dirus, An. minimus, and An. sawadwongpornimosquitoes were fed on gametocytemic blood drawn from patients at malaria clinics in Mae Sot District, Tak Province, Thailand. Twelve mosquito feeds of variable P. vivax infectivity were conducted. At 12, 18, 20, 22, 24, 26, 36 and 48 h after blood feeding, mosquitoes were dissected, and blood meals were examined for zygotes, retorts and mature ookinetes using an immunofluorescent assay based on a FITC-labeled anti-25-kDa monoclonal antibody (Pvs25). On days 7, 8 or 9 after feeding, midguts were examined for oocysts. Parasite densities varied greatly between patients and Anopheles . Densities of zygotes and ookinetes peaked at 20-26 h (mean 22 h) after feeding. The presence of relatively high densities of zygotes throughout ookinete development suggested that ookinete formation is dynamic and asynchronous. Variation in the transitional efficiencies of ookinetes to oocysts might be due to host (human) serum factors or the condition of ingested gametocytes. This study provides more information on the kinetics of in vivo formation of P. vivax ookinetes in three laboratory-adapted anopheline species. Studies are currently underway to assess the sporogonic development of P. vivax in wild-caught (F1) anopheline malaria vectors. These studies are crucial to understanding the population dynamics of sporogony, and hence malaria transmission, in the wild.

52nd Annual Meeting of the American Society of Tropical Medicine and Hygiene. Philadelphia, Pensylvania, USA. 3-7 December 2003.

QUANTITATIVE KINETICS OF PLASMODIUM VIVAX SPOROZOITE INVASION INTO MOSQUITO SALIVARY GLANDS

Vaughan JA, Zollner GE, Ponsa N, Sattabongkot J, Coleman RE and Jones JW

Detailed studies were undertaken to quantify the in vivo kinetics of Plasmodium vivax (VK210 strain) sporozoite release from the oocyst and invasion into the salivary glands. Blood from two separate patients were used; one was highly infectious and produced heavy parasite loads, the other was moderately infectious and produced much lighter parasite loads. Two mosquito species were used: A. dirus and A. minimus. Individual mosquitoes were sampled every other day for oocysts, hemolymph sporozoites and salivary gland sporozoites from day 10 to 18 after feeding. Parasite densities were 3 to 4 times higher in A. dirus than in A. minimus. There was no difference in the extrinsic incubation period between the 2 mosquito species. Interestingly, sporozoite production per oocyst in both A. dirus and A. minimus were higher with heavier oocyst burdens. From a population biology standpoint, this argues against the concept of a carrying capacity or intra-oocyst competition for nutrients within the mosquito hemocoel (at least under laboratory conditions). However, the efficiencies of P. vivax sporozoite invasion into the salivary glands were higher under conditions of lower sporozoite intensity. This suggests that there may be an inverse relationship between sporozite density and invasion efficiency into the salivary glands.

52nd Annual Meeting of the American Society of Tropical Medicine and Hygiene. Philadelphia, Pensylvania, USA. 3-7 December 2003.