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Biomedical subjects

D C Kaslow

Publications and source records attributed to D C Kaslow.

At least 37 records · Page 2Linked to original sources
PubMed1999

Partial protection against Plasmodium vivax blood-stage infection in Saimiri monkeys by immunization with a recombinant C-terminal fragment of merozoite surface protein 1 in block copolymer adjuvant.

Merozoite surface protein 1 is a candidate for blood-stage vaccines against malaria parasites. We report here an immunization study of Saimiri monkeys with a yeast-expressed recombinant protein containing the C terminus of Plasmodium vivax merozoite surface protein 1 and two T-helper epitopes of tetanus toxin (yP2P30Pv20019), formulated in aluminum hydroxide (alum) and block copolymer P1005. Monkeys immunized three times with yP2P30Pv20019 in block copolymer P1005 had significantly higher prechallenge titers of immunoglobulin G (IgG) antibodies against the immunogen and asexual blood-stage parasites than those immunized with yP2P30Pv20019 in alum, antigen alone, or phosphate-buffered saline (PBS) (P < 0.05). Their peripheral blood mononuclear cell proliferative responses to immunogen stimulation 4 weeks after the second immunization were also significantly higher than those from the PBS control group (P < 0.05). Upon challenge with 100,000 asexual blood-stage parasites 5 weeks after the last immunization, monkeys immunized with yP2P30Pv20019 in block copolymer P1005 had prepatent periods longer than those for the control alone group (P > 0.05). Three of the five animals in this group also had low parasitemia (peak parasitemia, </=20 parasites/microliter of blood). Partially protected monkeys had significantly higher levels of prechallenge antibodies against the immunogen than those unprotected (P < 0.05). There was also a positive correlation between the prepatent period and titers of IgG antibodies against the immunogen and asexual blood-stage parasites and a negative correlation between accumulated parasitemia and titers of IgG antibodies against the immunogen (P < 0.05). These results indicate that when combined with block copolymer and potent T-helper epitopes, the yeast-expressed P2P30Pv20019 recombinant protein may offer some protection against malaria.

Adjuvants, Immunologic↗
PubMed1999

Testing the efficacy of a recombinant merozoite surface protein (MSP-1(19) of Plasmodium vivax in Saimiri boliviensis monkeys.

Saimiri boliviensis monkeys were immunized with the yeast-expressed recombinant protein yP2P30Pv200(19). The antigen consisted of the C-terminus (amino acid Asn1622-Ser1729) of the merozoite surface protein 1 of the Plasmodium vivax Salvador I strain. Two universal T helper cell epitopes (P2 and P30) of tetanus toxin and six histidine residues for purification purposes were attached to the N- and C-termini, respectively. Four groups of five monkeys were given three immunizations at four-week intervals with either 250 microg of yP2P30Pv200(19) formulated with nonionic block copolymer P1005, 250 microg of antigen adsorbed to alum, 250 microg of antigen in phosphate-buffered saline (PBS), or PBS alone. Five weeks after the last immunization, each animal was inoculated with 100,000 parasitized erythrocytes of the Salvador I strain of P. vivax. Animals were splenectomized one week after challenge to increase parasite densities; after seven weeks of infection, animals were treated. Eighteen weeks later, the animals were rechallenged with the homologous parasite. Following the first challenge, three monkeys immunized with the antigen with P1005 were protected; no animals were protected from rechallenge. One monkey immunized with yP2P30Pv200(19) with alum was protected; no protection was seen after rechallenge. Two monkeys immunized with antigen alone were protected; none were protected from rechallenge. One control animal had a low parasite count following primary infection; none were protected against rechallenge. Adverse reactions were only observed with animals receiving P1005. It is proposed that splenectomy of the monkeys prevented adequate assessment of the efficacy of this antigen. Identification of a monkey host that supports high density parasitemia without splenectomy appears needed before further testing of blood-stage vaccines against P. vivax.

Adjuvants, Immunologic↗
PubMed1998

Adherence of erythrocytes during exflagellation of Plasmodium falciparum microgametes is dependent on erythrocyte surface sialic acid and glycophorins.

Malaria male gametocytes within a newly ingested infected blood meal in the mosquito midgut emerge from erythrocytes and extrude approximately eight flagellar microgametes in a process termed exflagellation. In culture, and in blood removed from infected patients, emerging microgametes avidly adhere to neighboring uninfected and infected erythrocytes, as well as to emerged female macrogametes, creating "exflagellation centers". The mechanism of erythrocyte adherence is not known nor has it been determined for what purpose microgametes may bind to erythrocytes. The proposition of a function underlying erythrocyte adherence is supported by the observation of species-specificity in adhesion: microgametes of the human malaria Plasmodium falciparum can bind human erythrocytes but not chicken erythrocytes, whereas avian host Plasmodium gallinaceum microgametes bind chicken but not human erythrocytes. In this study we developed a binding assay in which normal, enzyme-treated, variant or null erythrocytes are identified by a cell surface fluorescent label and assayed for adherence to exflagellating microgametes. Neuraminidase, trypsin or ficin treatment of human erythrocytes eliminated their ability to adhere to Plasmodium falciparum microgametes, suggesting a role of sialic acid and one or more glycophorins in the binding to a putative gamete receptor. Using nulls lacking glycophorin A [En(a-)], glycophorin B (S-s-U-) or a combination of glycophorin A and B (Mk/Mk) we showed that erythrocytes lacking glycophorin B retain the ability to bind but a lack of glycophorin A reduced adherence by exflagellating microgametes. We propose that either the sialic acid moiety of glycophorins, predominantly glycophorin A, or a more complex interaction involving the glycophorin peptide backbone, is the erythrocyte receptor for adhesion to microgametes.

Animals↗
PubMed1998

Definition of T cell epitopes within the 19 kDa carboxylterminal fragment of Plasmodium yoelii merozoite surface protein 1 (MSP1(19)) and their role in immunity to malaria.

MSP1(19) is one of the leading malaria vaccine candidates. However, the mechanism of protection is not clear. To determine whether MSP1(19)-specific effector T cells can control parasitaemia, we analysed the specificity of T cells induced following immunization with recombinant forms of P. yoelii MSP1(19) and asked whether they could protect mice. There was no evidence that effector T cells were capable of protecting since: (1) immunization of mice with yMSP1(19), but not defined epitopes, was able to induce protection; and (2) long term MSP1(19)-specific CD4+ T cell lines were incapable of adoptively transferring protection. In contrast, priming mice with the T cell epitopes resulted in a rapid anamnestic antibody response to MSP1(19) after either challenge with MSP1(19) or parasite. Thus, MSP1(19) contains multiple T cell epitopes but such epitopes are the targets of helper T cells for antibody response but not of identified effector T cells capable of controlling parasitaemia.

Adoptive Transfer↗
PubMed1998

Intranasal immunization with yeast-expressed 19 kD carboxyl-terminal fragment of Plasmodium yoelii merozoite surface protein-1 (yMSP119) induces protective immunity to blood stage malaria infection in mice.

Variable protection against malaria blood-stage infection has been demonstrated in mice following parenteral immunization with the highly conserved 19 kD carboxylterminal fragment of the merozoite surface protein-1 (MSP119) using CFA/IFA and other adjuvants. Here we show that intranasal immunization of BALB/C mice with yeast expressed Plasmodium yoelii MSP119 plus a mixture of native and recombinant cholera toxin B subunit, could induce serum MSP119-specific antibodies at titres ranging from 20 000 to 2 560 000. The Ig subclass responses were predominantly G1 and G2b. Intranasal immunization led to protection following challenge (peak parasitaemia < 1%) in mice with the highest MSP119-specific titre (>/= 640 000). In two of the three protected mice, a peak parasitaemia of 0.1%-1% was followed by a boost of the antibody response whereas one of the three protected mice did not boost its antibody response after a peak parasitaemia of 0.02%. In unprotected mice, antibody levels rose, then fell, following the detection of parasites in the peripheral blood. CD4+ T cell-depletion abrogated the ability of the mice to boost their antibody response following challenge. These data demonstrate the potential for intranasal immunization with MSP119 to protect against malaria.

Adjuvants, Immunologic↗
PubMed1998

Phase I/IIa safety, immunogenicity, and efficacy trial of NYVAC-Pf7, a pox-vectored, multiantigen, multistage vaccine candidate for Plasmodium falciparum malaria.

Candidate malaria vaccines have failed to elicit consistently protective immune responses against challenge with Plasmodium falciparum. NYVAC-Pf7, a highly attenuated vaccinia virus with 7 P. falciparum genes inserted into its genome, was tested in a phase I/IIa safety, immunogenicity, and efficacy vaccine trial in human volunteers. Malaria genes inserted into the NYVAC genome encoded proteins from all stages of the parasite's life cycle. Volunteers received three immunizations of two different dosages of NYVAC-Pf7. The vaccine was safe and well tolerated but variably immunogenic. While antibody responses were generally poor, cellular immune responses were detected in >90% of the volunteers. Of the 35 volunteers challenged with the bite of 5 P. falciparum-infected Anopheles mosquitoes, 1 was completely protected, and there was a significant delay in time to parasite patency in the groups of volunteers who received either the low or high dose of vaccine compared with control volunteers.

Adolescent↗
PubMed1998

Saccharomyces cerevisiae-secreted fusion proteins Pfs25 and Pfs28 elicit potent Plasmodium falciparum transmission-blocking antibodies in mice.

Transmission-blocking vaccines based on sexual-stage surface antigens of Plasmodium falciparum may assist in the control of this lethal form of human malaria. Two vaccine candidates, Pfs25 and Pfs28, were produced as single recombinant fusion proteins. The 39-kDa chimeric proteins, having a C-terminal His6 tag, were secreted by Saccharomyces cerevisiae, using the prepro-alpha-factor leader sequence. Pfs25-28 fusion proteins were significantly more potent than either Pfs25 or Pfs28 alone in eliciting antibodies in mice that blocked oocyst development in Anopheles freeborni mosquitoes: complete inhibition of oocyst development in the mosquito midgut was achieved with fewer vaccinations, at a lower dose, and for a longer duration than with either Pfs25 or Pfs28 alone. Increased antigen-specific immunoglobulin G titers and highly significant lymphoproliferative stimulation by Pfs28-containing antigens suggest the presence of an immunodominant helper T-cell epitope in the Pfs28 portion of the fusion proteins. This epitope may be responsible for the enhanced humoral response to both Pfs25 and Pfs28 antigens. Protein production of the fusion protein was improved 12-fold by converting Pfs28 codons to yeast-preferred codons (TBV28), using a modified ADH2 promoter and incorporating a (Glu-Ala)2 repeat after the Kex2 cleavage site.

Animals↗
PubMed1998

Enhanced protective antibody responses to PspA after intranasal or subcutaneous injections of PspA genetically fused to granulocyte-macrophage colony-stimulating factor or interleukin-2.

Antibody to pneumococcal surface protein A (PspA) has been shown to be protective for Streptococcus pneumoniae infections in mice. In an attempt to define a model for inducing protective antibody to PspA in the absence of adjuvant, we designed two genetic fusions, PspA-interleukin-2 [IL-2]) and PspA-granulocyte-macrophage colony-stimulating factor (GM-CSF). These constructs maintained high cytokine function in vitro, as tested by their activity on IL-2 or GM-CSF-dependent cell lines. While intranasal immunization with PspA induced no detectable anti-PspA response, both PspA-IL-2 and PspA-GM-CSF stimulated high immunoglobulin G1 (IgG1) antibody responses. Interestingly, only the PspA-IL-2, not the PspA-GM-CSF, construct stimulated IgG2a antibody responses, suggesting that this construct directed the response along a TH1-dependent pathway. Comparable enhancement of the anti-PspA response with similar isotype profiles was observed after subcutaneous immunization as well. The enhancement observed with PspA-IL-2 was dependent on IL-2 activity in that it was not seen in IL-2 receptor knockout mice, while PspA in alum induced high-titer antibody in these mice. The antibody was tested for its protective activity in a mouse lethality model using S. pneumoniae WU-R2. Passive transfer of 1:90 dilutions of sera from mice immunized with PspA-IL-2 and PspA-GM-CSF elicited protection of CBA/N mice against intravenous challenge with over 170 50% lethal doses of capsular type 3 strain WU2. Only 0.17 microg or less of IgG antibody to PspA was able to provide passive protection against otherwise fatal challenge with S. pneumoniae. The data demonstrate that designing protein-cytokine fusions may be a useful approach for mucosal immunization and can induce high-titer systemic protective antibody responses.

Administration, Intranasal↗
PubMed1998

Pathways and strategies for developing a malaria blood-stage vaccine.

In the past 10 years, our knowledge of the malaria parasite has increased enormously: identification and analysis of parasite antigens, demonstration of protection of monkeys and mice following immunization with these antigens, and better understanding of the mechanisms of immunity to malaria and the pathogenesis of disease in malaria. Powerful new adjuvants have been developed, some of which--it is hoped--will be suitable for human use. Recently, a successful human trial of a vaccine aimed at sporozoites (the stage inoculated by mosquitoes) was completed. However, it is the red blood cell stage of the parasite that causes disease, and it is against this stage--in which the parasite grows at an exponential rate--that it has proven very difficult to induce a protective immune response by vaccination. This review focuses on recent exciting developments toward a blood-stage vaccine. We analyze the major obstacles to vaccine development and outline a strategy involving public- and industry-funded research that should result in development of a vaccine.

Animals↗
PubMed1998

A longitudinal investigation of IgG and IgM antibody responses to the merozoite surface protein-1 19-kiloDalton domain of Plasmodium falciparum in pregnant women and infants: associations with febrile illness, parasitemia, and anemia.

This study was aimed at delineating characteristics of naturally acquired immunity against the merozoite surface antigen-1 (MSP-1) of Plasmodium falciparum, a candidate malaria vaccine antigen. A case/control study was performed on 75 case/control pairs of infants with febrile illness at the time of the first detected infection indicating a clinical case. The presence and level of antibodies at one month prior to the first infection and at the time of the first infection in the afebrile group was significantly higher than in the febrile group. Decreased parasite density and decreased infection-related loss of hemoglobin was seen in infants with anti-MSP-1(19kD) IgG antibodies. In addition, mothers who were positive for the presence of these antibodies conferred protection against placental infection and infection in their infants. In this study, development of anti-MSP-1(19kD) antibody responses in 24 infants were studied longitudinally using monthly serum samples collected from birth until approximately one year of age. In addition, umbilical cord blood sera and respective mothers' sera were analyzed. Longitudinal studies of antibody responses revealed several short-lived IgG and IgM peaks throughout an infant's first year that correlated with detection of parasitemia. The protection against parasitemia and febrile illness was observed in infants when anti-MSP-1(19kD) antibodies were present; when infants were negative for IgG, they had a 10-times greater risk of becoming parasitemic. These data from a longitudinal and prospective study of malaria suggest a protective role for anti-MSP-1(19kD) antibodies in infants and pregnant women.

Anemia↗
PubMed1998

Gametocyte infectivity by direct mosquito feeds in an area of seasonal malaria transmission: implications for Bancoumana, Mali as a transmission-blocking vaccine site.

Infectivity of gametocytemic volunteers living in Bancoumana, a village 60 km from Bamako, Mali, was determined by direct feeds of laboratory-reared Anopheles gambiae s. l. Gametocytemic adolescents (10-18 years old) were as infectious to mosquitoes as younger volunteers and appear to be a more suitable population for testing transmission-blocking efficacy as compared with adults (> 18 years old). To begin to validate the membrane-feeding assay, sera collected from these same volunteers were subjected to a standard membrane-feeding assay. The data suggest that areas with intense but seasonal transmission might be feasible sites for testing transmission-blocking vaccines because of the high gametocytemic rates, high mosquito infectivity rates, and lack of pre-existing humoral-mediated transmission-blocking activity. The differences observed between field-based direct mosquito feeds and laboratory-based membrane feeding assays suggests that caution be used in interpreting Phase I study results in which laboratory-based membrane-feeding assays are used as a surrogate for vaccine efficacy.

Adolescent↗
PubMed1998

Passive transfer of growth-inhibitory antibodies raised against yeast-expressed recombinant Plasmodium falciparum merozoite surface protein-1(19).

Purified rabbit immunoglobulin raised against yeast-expressed recombinant FVO or 3D7 Plasmodium falciparum merozoite surface protein-1 (MSP-1) 19k-D C terminal fragment (MSP-1(19)) was transfused into malaria-naive Aotus nancymai monkeys that were immediately challenged with FVO asexual stage malaria parasites. Control monkeys received rabbit immunoglobulin raised against the sexual stage antigen Pfs25 or Aotus hyperimmune serum obtained from monkeys immunized by P. falciparum infection and drug cure. Passive transfer of rabbit anti-MSP-1(19) failed to protect against homologous or heterologous challenge and, when compared with negative controls, there were no differences in prepatent periods or time to treatment. Interestingly, rabbit anti-MSP-1(19), but not anti-Pfs25, immunoglobulin, and immune monkey serum prevented the development of antibodies directed against MSP-1(19) fragment by infected monkeys, indicating that the antibodies were reactive with native MSP-1(19) antigen in vivo. The prepatent period and time to treatment was greatly delayed in the two monkeys that received Aotus immune serum, both of which developed a chronic intermittent low level infection. In vitro parasite growth inhibition assays (GIAs) confirmed the presence of inhibitory activity (40% maximum inhibition) in concentrated anti-MSP-1(19) immunoglobulin (4.8 mg/ml), but the peak concentrations we achieved in vivo (1 mg/ml) were not inhibitory in vitro. Subinhibitory levels of anti-MSP-1(19) antibodies achieved by passive transfer were not protective against P. falciparum challenge.

Animals↗
PubMed1998

Humoral immune responses against Plasmodium vivax MSP1 in humans living in a malaria endemic area in Flores, Indonesia.

The aim of this study was to evaluate the relationship among age, parasitemia status, spleen size, hematocrit, and antibody levels to Plasmodium vivax merozoite surface protein 1 (MSP1) in individuals chronically exposed to P. vivax. Subjects were recruited from the population of three adjacent villages on the Island of Flores in Indonesia where malaria transmission is hyperendemic and tropical splenomegaly syndrome is highly prevalent. Subjects were evaluated for spleen size, hematocrit, presence of parasitemia, and presence of antibodies to a recombinant peptide consisting of 90 amino acids from the carboxy terminus of MSP1. Fifty-seven percent of 2-4 year olds, 45% of 5-9 years old, and 7% of > or = 15 years old were parasitemic; 99% of the > or = 15 years old had splenomegaly, and 31% of them had Hackett 4 or 5 spleens. The frequency of antibody positivity to MSP1 antigen in ELISA increased with age reaching a maximum of 89% in > or = 20 years old. The frequency of antibody positivity to MSPI also increased with spleen size, and with a decline in the prevalence of parasitemia.

Adolescent↗
PubMed1998

Sequence polymorphism in two novel Plasmodium vivax ookinete surface proteins, Pvs25 and Pvs28, that are malaria transmission-blocking vaccine candidates.

BACKGROUND: For many malarious regions outside of Africa, development of effective transmission-blocking vaccines will require coverage against both Plasmodium falciparum and P. vivax. Work on P. vivax transmission-blocking vaccines has been hampered by the inability to clone the vaccine candidate genes from this parasite. MATERIALS AND METHODS: To search for genes encoding the ookinete surface proteins from P. vivax, the DNA sequences of the eight known proteins in the P25 subfamily (Pfs25, Pgs25, Pys25, Pbs25) and in the P21/28 subfamily (Pfs28, Pgs28, Pys21, Pbs21) of zygote/ookinete surface proteins were aligned. Regions of highest identity were used to design degenerate PCR oligonucleotides. Genomic DNA from the Sal I strain of P. vivax and genomic and splinkerette DNA libraries were used as PCR templates. To characterize the polymorphisms of Pvs25 and Pvs28, these two genes were PCR amplified and the DNA sequences were determined from genomic DNA extracted from patients infected with P. vivax. RESULTS: Analysis of the deduced amino acid sequence of Pvs28 revealed a secretory signal sequence, four epidermal growth factor (EGF)-like domains, six copies of the heptad amino acid repeat (GSGGE/D), and a short hydrophobic region. Because the fourth EGF-like domain has four rather than six cysteines, the gene designated Pvs28 is the presumed homologue of P21/28 subfamily members. Analysis of the deduced amino acid sequence of Pvs25 revealed a similar structure to that of Pvs28. The presence of six rather than four cysteines in the fourth EGF-like domain suggested that Pvs25 is the homologue of P25 subfamily members. Several regions of genetic polymorphisms in Pvs25 and Pvs28 were identified in field isolates of P. vivax. CONCLUSIONS: The genes encoding two ookinete surface proteins, Pvs28 and Pvs25, from P. vivax have been isolated and sequenced. Comparison of the primary structures of Pvs25, Pvs28, Pfs25, and Pfs28 suggest that there are regions of genetic polymorphism in the P25 and P21/28 subfamilies.

Amino Acid Sequence↗