INFECTION AND IMMUNITY, OCt. 1994, p. 4488-4494 0019-9567/94/$04.00+0 Copyright X 1994, American Society for Microbiology Naturally Acquired Human Antibodies Which Recognize the First Epidermal Growth Factor-Like Module in the Plasmodium falciparum Merozoite Surface Protein 1 Do Not Inhibit Parasite Growth In Vitro JONATHAN A. CHAPPEL,'t ANDREA F. EGAN,2 ELEANOR M. RILEY,2 PIERRE DRUILHE,3 AND ANTHONY A. HOLDER'* Division of Parasitology, National Institute for Medical Research, Mill Hill, London,' and Institute of Cell, Animal and Population Biology, Division of Biological Sciences, University of Edinburgh, Edinburgh,2 United Kingdom, and Parasitologie Biomedicale, Institut Pasteur, Paris, France3 Received 22 April 1994/Returned for modification 6 June 1994/Accepted 2 August 1994 Merozoite surface protein 1, one of the major surface proteins of the invasive blood stage of the malaria parasite, is a prime candidate for the development of a vaccine against the human disease. Previously, monoclonal antibodies which both inhibited the growth of Plasmodiumfalciparum in vitro and bound to the first of two epidermal growth factor-like modules located near the carboxy terminus of the protein had been identified. In this study, we have used affinity chromatography on a recombinant fusion protein corresponding to the first epidermal growth factor-like module in P. falkiparum merozoite surface protein 1 to prepare antibody induced by natural infection. The antibody was purified from the total immunoglobulin G fraction of adult West African donors, shown to passively confer immunity against falciparum malaria. Such affinity- purified antibodies were shown to recognize the native protein by a number of separate criteria and to block the binding of an inhibitory monoclonal antibody, but they failed to inhibit parasite invasion in an in vitro growth assay. These results indicate that antibody alone is not sufficient to interfere with erythrocyte invasion. There is an urgent need to develop a more effective vaccine against malaria. Much work on vaccine development has been focused on merozoite surface protein 1 (MSP-1), a high- molecular-mass protein synthesized by the intracellular schi- zont of the asexual blood and liver stages and expressed on the surface of merozoites released from the ruptured schizont (18, 24). MSP-1 preparations purified from a number of malaria parasites have, by immunization, induced significant levels of protection against challenge with blood-stage parasites in both rodent (26) and simian (20, 21, 41, 46) experimental model systems. Investigators have used parts of MSP-1, either ex- pressed in Escherichia coli (17, 20, 23, 28, 33) or as synthetic peptides (13, 40), to induce complete or partial protection or to delay the progress of infection. A synthetic peptide polymer, which includes a sequence from the N terminus of Plasmodium falciparum MSP-1, produced encouraging results in a recent clinical trial (49). MSP-1 is modified by proteolysis leading to shedding of the molecule except for a small C-terminal fragment, which can be detected on the surface of the parasite in a newly infected erythrocyte. Prior to the release of merozoites from the mature schizont, P. falciparum MSP-1 is processed by protease(s) to at least four major polypeptides, held together in a noncovalent complex on the merozoite surface (35). One of these, a 42-kDa membrane-bound fragment from the C terminus (designated MSP-142), undergoes a second proteolytic cleavage to produce MSP-133 and MSP-119 (1, 6). The membrane-bound MSP-119 * Corresponding author. Mailing address: Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, U.K. Phone: (44) 81-959-3666. Fax: (44) 81-913-8593. Electronic mail address: a-holder@nimr.mrc.ac.uk. t Present address: The Scripps Research Institute, La Jolla, CA 92037. polypeptide, comprising two cysteine-rich epidermal growth factor (EGF)-like modules (4), is carried into the new eryth- rocyte on the surface of the invading merozoite (2). The EGF-like modules are found in MSP-1 in all species of malaria parasite examined (16, 25), and there is evidence to suggest that they are an important target of protective immu- nity. In studies using the rodent malaria models Plasmodium yoelii and Plasmodium chabaudi, MSP-1-specific monoclonal antibodies (MAbs) passively protected mice against challenge infection with homologous blood-stage parasites (8, 32, 34). Two of these antibodies bind to discontinuous disulfide- constrained epitopes within the EGF-like modules (10, 37). Mice immunized with the cysteine-rich region of P. yoelii MSP-1, expressed as a fusion protein in E. coli, were partially or completely protected against challenge infection with P. yoelii parasites (17, 33). A number of investigators have reported P. falciparum MSP1-specific MAbs which inhibit the in vitro growth of the parasite (2, 15, 42), and these antibodies react with MSP-119. The EGF-like modules have been ex- pressed in a correctly folded form in insect cells (11, 39), yeast cells (30), and E. coli cells (9, 12). Serum from rabbits immunized with a correctly folded insect cell product repre- senting MSP-142, but not with an identical but incorrectly folded yeast cell product, completely inhibited P. falciparum growth in vitro (11). We have reproduced the individual EGF-like modules of the P. falciparum MSP-1 by expression as fusion proteins in E. coli and have shown that a number of MSP-1-specific MAbs, including the invasion-inhibitory anti- bodies 5B1 (42) and 12.8 (2), bound to disulfide-constrained epitopes in the first of the EGF-like modules (MSP-1-EGF1) (12). We show here that, in contrast to results obtained with MSP-1-specific MAbs, immunoglobulin G (IgG) affinity se- lected on MSP-1-EGF1 from the naturally acquired repertoire 4488 Vol. 62, No. 10 on July 23, 2020 by guest http://iai.asm.org/ Downloaded from