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Measuring naturally acquired ex vivo IFN-γ responses to Plasmodium falciparum cell-traversal protein for ookinetes and sporozoites (CelTOS) in Ghanaian adults.

Anum D, Kusi KA, Ganeshan H, Hollingdale MR, Ofori MF, Koram KA, Gyan BA, Adu-Amankwah S, Badji E, Huang J, Belmonte M, Banania GJ, Kwofie TB, Villasante E, Dodoo D, Sedegah M - Malar. J. (2015)

Bottom Line: Identification of sporozoite/liver stage antigens is, therefore, crucial for the development of effective vaccines.A positive IFN-γ response for stimulants was defined by two criteria; a stimulation index of two or greater relative to the unstimulated control, and a difference of 10 or greater in spot forming cells between stimulant and the unstimulated control.These findings support the further evaluation of CelTOS as a pre-erythrocytic candidate antigen for inclusion in a potential multi-antigen vaccine.

View Article: PubMed Central - PubMed

Affiliation: Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana. akusi@noguchi.ug.edu.gh.

ABSTRACT

Background: A malaria vaccine that targets the sporozoite/liver stage parasites could potentially prevent blood stage infection and the associated clinical symptoms. Identification of sporozoite/liver stage antigens is, therefore, crucial for the development of effective vaccines. Cell-traversal protein for ookinetes and sporozoites (CelTOS) is a highly conserved antigen involved in sporozoite motility and hepatocyte invasion and has been shown to induce significant IFN-γ production in PBMCs from radiation-attenuated sporozoite-immunized malaria-naïve individuals. The aim of this study was to ascertain whether such CelTOS-specific recall responses are also induced in individuals with natural exposure to Plasmodium falciparum.

Methods: Ex vivo IFN-γ responses to 15mer overlapping peptide pools covering the entire sequence of CelTOS and five other candidate antigens, CSP, AMA1, MSP1, TRAP and LSA1, were characterized using PBMCs from 35 malaria exposed adults. Responses to four CelTOS peptide pools (CelTp1, CelTp2, CelTp3 and CelTp4), a pool containing peptides from the entire CelTOS antigen (CelTTp), and pools comprised of overlapping peptides from each of the other five malaria antigens were assessed by ex vivo ELISpot assay. A positive IFN-γ response for stimulants was defined by two criteria; a stimulation index of two or greater relative to the unstimulated control, and a difference of 10 or greater in spot forming cells between stimulant and the unstimulated control.

Results: Of the 35 volunteers tested, five had positive IFN-γ recall responses against the four different CelTOS pools while four volunteers made responses against the CelTTp pool; six volunteers were, therefore, positive with CelTOS. By contrast, six volunteers responded to AMA1, seven to LSA1, 15 to MSP1 and two volunteers responded against CSP and TRAP.

Conclusions: These results suggest natural malaria transmission induces CelTOS-specific ex vivo IFN-γ in Ghanaian adults and that the frequency of these responses was similar to those of other previously characterized malaria antigens. These findings support the further evaluation of CelTOS as a pre-erythrocytic candidate antigen for inclusion in a potential multi-antigen vaccine.

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Proportion of IFN-γ positive responders to the six malaria vaccine candidate antigens. The absolute number of responders for each pool has been expressed as a proportion of the total number of volunteers (35). *Proportions that were positive against CSPp and TRAPp were significantly different from that of MSP1p in pairwise comparisons.
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Fig4: Proportion of IFN-γ positive responders to the six malaria vaccine candidate antigens. The absolute number of responders for each pool has been expressed as a proportion of the total number of volunteers (35). *Proportions that were positive against CSPp and TRAPp were significantly different from that of MSP1p in pairwise comparisons.

Mentions: IFN-γ responses to peptide pools representing the six tested malaria antigens CelTOS, CSP, AMA1, LSA1, TRAP and MSP1 are shown in Figure 3. Responses differed among volunteers, probably due to their different HLA molecules. However, 17 of the 35 volunteers (49%) responded to at least one of the tested malaria antigen peptide pools. The frequency of positive volunteers to each antigen is shown in Figure 4. The most frequent positive response was to MSP1p (15/35 volunteers, 43%), followed by LSA1p (7/35, 20%), AMA1p (6/35, 17%), CelTTp (4/35, 11%), CSPp (2/35, 6%) and TRAPp (2/35, 6%). Three of the five volunteers that were positive against at least one of the four separate CelTOS pools (CelTp1, CelTp2, CelTp3 and CelTp4) were also positive against CelTTp (v1, v4, and v16), and in addition one volunteer (v32) who was negative against all four separate CelTOS pools was positive against CelTTp. Overall, among the 35 volunteers, four/35 (11%) were positive against one antigen (only MSP1p), 13/35 (29%) were positive against at least two different antigens, five/35 (14%) were positive against at least three antigens, and only v16 (3%) was positive against four antigens. Six of thirty five (6/35) volunteers (17%) had summed activities greater than 100 sfc/m, and LSA1p and/or MSP1p made the greatest contributions; TRAPp made the greatest contributions to the next two highest volunteers (6%). Eighteen volunteers (51%) did not respond to any of the malaria antigen pools although they responded to stimulation with Con A and CEF (Additional file 1).Figure 3


Measuring naturally acquired ex vivo IFN-γ responses to Plasmodium falciparum cell-traversal protein for ookinetes and sporozoites (CelTOS) in Ghanaian adults.

Anum D, Kusi KA, Ganeshan H, Hollingdale MR, Ofori MF, Koram KA, Gyan BA, Adu-Amankwah S, Badji E, Huang J, Belmonte M, Banania GJ, Kwofie TB, Villasante E, Dodoo D, Sedegah M - Malar. J. (2015)

Proportion of IFN-γ positive responders to the six malaria vaccine candidate antigens. The absolute number of responders for each pool has been expressed as a proportion of the total number of volunteers (35). *Proportions that were positive against CSPp and TRAPp were significantly different from that of MSP1p in pairwise comparisons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4308902&req=5

Fig4: Proportion of IFN-γ positive responders to the six malaria vaccine candidate antigens. The absolute number of responders for each pool has been expressed as a proportion of the total number of volunteers (35). *Proportions that were positive against CSPp and TRAPp were significantly different from that of MSP1p in pairwise comparisons.
Mentions: IFN-γ responses to peptide pools representing the six tested malaria antigens CelTOS, CSP, AMA1, LSA1, TRAP and MSP1 are shown in Figure 3. Responses differed among volunteers, probably due to their different HLA molecules. However, 17 of the 35 volunteers (49%) responded to at least one of the tested malaria antigen peptide pools. The frequency of positive volunteers to each antigen is shown in Figure 4. The most frequent positive response was to MSP1p (15/35 volunteers, 43%), followed by LSA1p (7/35, 20%), AMA1p (6/35, 17%), CelTTp (4/35, 11%), CSPp (2/35, 6%) and TRAPp (2/35, 6%). Three of the five volunteers that were positive against at least one of the four separate CelTOS pools (CelTp1, CelTp2, CelTp3 and CelTp4) were also positive against CelTTp (v1, v4, and v16), and in addition one volunteer (v32) who was negative against all four separate CelTOS pools was positive against CelTTp. Overall, among the 35 volunteers, four/35 (11%) were positive against one antigen (only MSP1p), 13/35 (29%) were positive against at least two different antigens, five/35 (14%) were positive against at least three antigens, and only v16 (3%) was positive against four antigens. Six of thirty five (6/35) volunteers (17%) had summed activities greater than 100 sfc/m, and LSA1p and/or MSP1p made the greatest contributions; TRAPp made the greatest contributions to the next two highest volunteers (6%). Eighteen volunteers (51%) did not respond to any of the malaria antigen pools although they responded to stimulation with Con A and CEF (Additional file 1).Figure 3

Bottom Line: Identification of sporozoite/liver stage antigens is, therefore, crucial for the development of effective vaccines.A positive IFN-γ response for stimulants was defined by two criteria; a stimulation index of two or greater relative to the unstimulated control, and a difference of 10 or greater in spot forming cells between stimulant and the unstimulated control.These findings support the further evaluation of CelTOS as a pre-erythrocytic candidate antigen for inclusion in a potential multi-antigen vaccine.

View Article: PubMed Central - PubMed

Affiliation: Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana. akusi@noguchi.ug.edu.gh.

ABSTRACT

Background: A malaria vaccine that targets the sporozoite/liver stage parasites could potentially prevent blood stage infection and the associated clinical symptoms. Identification of sporozoite/liver stage antigens is, therefore, crucial for the development of effective vaccines. Cell-traversal protein for ookinetes and sporozoites (CelTOS) is a highly conserved antigen involved in sporozoite motility and hepatocyte invasion and has been shown to induce significant IFN-γ production in PBMCs from radiation-attenuated sporozoite-immunized malaria-naïve individuals. The aim of this study was to ascertain whether such CelTOS-specific recall responses are also induced in individuals with natural exposure to Plasmodium falciparum.

Methods: Ex vivo IFN-γ responses to 15mer overlapping peptide pools covering the entire sequence of CelTOS and five other candidate antigens, CSP, AMA1, MSP1, TRAP and LSA1, were characterized using PBMCs from 35 malaria exposed adults. Responses to four CelTOS peptide pools (CelTp1, CelTp2, CelTp3 and CelTp4), a pool containing peptides from the entire CelTOS antigen (CelTTp), and pools comprised of overlapping peptides from each of the other five malaria antigens were assessed by ex vivo ELISpot assay. A positive IFN-γ response for stimulants was defined by two criteria; a stimulation index of two or greater relative to the unstimulated control, and a difference of 10 or greater in spot forming cells between stimulant and the unstimulated control.

Results: Of the 35 volunteers tested, five had positive IFN-γ recall responses against the four different CelTOS pools while four volunteers made responses against the CelTTp pool; six volunteers were, therefore, positive with CelTOS. By contrast, six volunteers responded to AMA1, seven to LSA1, 15 to MSP1 and two volunteers responded against CSP and TRAP.

Conclusions: These results suggest natural malaria transmission induces CelTOS-specific ex vivo IFN-γ in Ghanaian adults and that the frequency of these responses was similar to those of other previously characterized malaria antigens. These findings support the further evaluation of CelTOS as a pre-erythrocytic candidate antigen for inclusion in a potential multi-antigen vaccine.

Show MeSH
Related in: MedlinePlus