Patrick E. Duffy, M.D.
Chief, Vaccine Development Unit, LMIV
LMIV Vaccine Development Unit develops and performs clinical evaluation of prototype malaria vaccines. Each candidate vaccine has to undergo a rigorous development process that requires the input of many highly skilled scientists with specific areas of expertise. These include creation of expression systems, fermentation optimization, scale-up of purification technology, clinical good manufacturing practices (cGMP) production, formulation, quality control, preclinical testing, and clinical trials.
This product-oriented research is different from the investigator-initiated research conducted in most laboratories. The need for multiple, highly technical inputs makes it impractical to have a single person knowledgeable in all aspects of a specific product.
For these reasons, the unit has adopted an organizational structure used almost universally by biotechnology companies to conduct this development process. This model best practices from both the public and private sectors to rapidly advance vaccine products into Phase II clinical trials. Our organizational approach is coupled with creative management practices, allowing us to operate and fund the program within the framework of the federal government.
The Vaccine Development Unit has focused research to eradicate malaria through development of a vaccine to interrupt malaria transmission (VIMT), including transmission blocking components and pre-erythrocytic components.
The objective of this program is to develop a transmission-blocking vaccine (TBV) that would eliminate malaria transmission in low-endemic areas and reduce disease burden in moderate- and high-transmission areas. Unlike asexual blood-stage antigens that are primarily designed as anti-disease vaccines, TBVs prevent transmission by blocking infection of mosquitoes with antibodies taken up in the blood meal.
Conceptually, the use of these vaccines will parallel conventional malaria control programs, such as residual insecticide spraying and insecticide-treated bed nets. TBVs are likely to have similar broad strengths and weaknesses: They are likely to have their greatest impact in areas of relatively low epidemic transmission but are unlikely to reduce the prevalence of parasitized humans in areas of high transmission. However, even in areas of high transmission, data from insecticide-treated bed net trials and other trials show that the frequency of severe malaria is reduced when transmission is reduced, even if most children remain infected.
P25 is synthesized after fertilization of gametes and is composed of the dominant surface proteins of the free living parasites (ookinetes) in the mosquito midgut. Orthologs, found in all malarial parasites, are closely related proteins consisting of 4 EGF-like domains. Antibodies to these orthologs kill parasites in the midgut through mechanisms that are not fully understood.
These proteins are expressed in gametocytes and exposed on the surface of gametes following their release from the red cell after ingestion by the mosquito. Gene knockout experiments show that these proteins are critical to fertilization of the released gametes. Monoclonal antibodies against these proteins, especially in the presence of complement, are highly effective in killing parasites. Experiments with avian malaria in chickens and with primate malaria in monkeys show that natural infection, even with high levels of gametocytes, fails to induce appreciable antibodies to these proteins. However, vaccination induces antibodies that are boosted by natural infection.
These antigens have high priority as vaccine candidates. However, no group has yet succeeded in developing a method of satisfactorily expressing these proteins in their native conformation.
Pre-erythrocytic-stage vaccines are designed to induce immunity against antigens on sporozoites inoculated by mosquitoes to prevent invasion of human hepatocytes by sporozoites or to prevent the development of a single sporozoite into thousands of individual merozoites in human hepatocytes. An effective pre-erythrocytic vaccine will thus prevent the clinical disease and also disrupt malaria transmission. Even a partially effective vaccine will significantly reduce the initial sporozoite and liver-stage parasite burden, thus leading to a substantial reduction in frequency and severity of clinical malaria.
LMIV added a CS protein (CSP) vaccine to its product development plan in October 2006. The approach is to produce a recombinant protein encompassing the full-length CSP excluding the N-terminal signal and C-terminal GPI anchor signal sequences. The rationale for this approach is that the N-terminal segment of the CSP, including the conserved Region I, may also provide protective immunity. RTS,S contains half of the natural CS repeats without NVDP sequences, whereas our recombinant CSP (rCSP) will include a complete repeat region. Moreover, the rCSP will be chemically conjugated to a recombinant Plasmodium aeruginosa rEPA to enhance the immunogenicity of the rCSP. This carrier has been used as the polysaccharide vaccine Vi against Salmonella typhi, to improve the immunogenicity of the polysaccharide, and the conjugate vaccine is safe in humans and has been licensed in 94 countries. In the past few years, we have developed expertise in chemically conjugating malaria antigens, including AMA1, MSP1, MSP3, Pfs25H, Pvs25H, and Pvs25, to this carrier. Conjugation significantly enhanced immunogenicity of these malaria antigens in animal studies. In addition, the Pfs25H-OMPC and Pfs25H-Pfs25H, conjugates that we have developed were capable of inducing sustained high immune responses in animals. We will investigate whether the rEPA as the carrier will also induce sustained immune responses to malaria antigens including rCSP.
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Patrick E. Duffy is chief of the Laboratory of Malaria Immunology and Vaccinology. Before taking this position in November 2009, he served as malaria program director at Seattle Biomedical Research Institute (SBRI) and affiliate professor of global health at the University of Washington. His research is focused on understanding the pathogenesis and immunology of malaria in humans. He leads the Pregnancy Malaria Initiative to develop a malaria vaccine for pregnant women, a Grand Challenges in Global Health consortium project to understand immunity to severe malaria in African children, and a consortium of laboratories identifying novel vaccine targets against liver stage malaria parasites. He recently established the Malaria Clinical Trials Center for experimental malaria infections of humans in Seattle and for several years led the SBRI-Tanzania Malaria Research Training Program for young African scientists. He received his medical degree from Duke University, his internal medicine training at Walter Reed, and his postdoctoral training in molecular vaccine development at the National Institutes of Health.
Animal StudiesLynn Lambert, L.A.T.G., Team LeadKatie ZeleskiSachy Orr-Gonzalez
Clinical TrialsRuth Ellis, M.D., M.P.H., Team LeadAlemush ImeruRegina White
Formulation UnitKelly Rausch, M.Sc., Team LeadEmma Barnafo
Conjugation DevelopmentDavid Jones, Ph.D., Team LeadChris Rowe, M.S.Beth Chen
Quality ControlDaming Zhu, M.Sc., Team LeadHolly McClellanMark Decotiis
ImmunologyCharles Anderson, Ph.D., Team LeadJoan AebigOlga MuratovaAndrew OrcuttSarah BrockleyPavel TishchenkoGuan-Hong SongJama Hersi
Zhu D, McClellan H, Dai W, Gebregeorgis E, Kidwell MA, Aebig J, Rausch KM, Martin LB, Ellis RD, Miller L, Wu Y. Long term stability of a recombinant Plasmodium falciparum AMA1 malaria vaccine adjuvanted with Montanide(®) ISA 720 and stabilized with glycine. Vaccine. 2011 May 9;29(20):3640-5.
Ellis RD, Martin LB, Shaffer D, Long CA, Miura K, Fay MP, Narum DL, Zhu D, Mullen GE, Mahanty S, Miller LH, Durbin AP. Phase 1 trial of the Plasmodium falciparum blood stage vaccine MSP1(42)-C1/Alhydrogel with and without CPG 7909 in malaria naïve adults. PLoS One. 2010 Jan 22;5(1):e8787.
Ellis RD, Mullen GE, Pierce M, Martin LB, Miura K, Fay MP, Long CA, Shaffer D, Saul A, Miller LH, Durbin AP. A Phase 1 study of the blood-stage malaria vaccine candidate AMA1-C1/Alhydrogel with CPG 7909, using two different formulations and dosing intervals. Vaccine. 2009 Jun 24;27(31):4104-9.
Wu Y, Ellis RD, Shaffer D, Fontes E, Malkin EM, Mahanty S, Fay MP, Narum D, Rausch K, Miles AP, Aebig J, Orcutt A, Muratova O, Song G, Lambert L, Zhu D, Miura K, Long C, Saul A, Miller LH, Durbin AP. Phase 1 trial of malaria transmission blocking vaccine candidates Pfs25 and Pvs25 formulated with montanide ISA 51. PLoS One. 2008 Jul 9;3(7):e2636.
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Last Updated October 30, 2012