The malaria blood stage antigen PfCyRPA formulated with the TLR-4 agonist adjuvant GLA-SE elicits parasite growth inhibitory antibodies in experimental animals

Table 2 Humoral immune responses elicited in NMRI mice with adjuvanted formulations of recombinant PfCyRPA

Adjuvant	Dose of adjuvant	Dose of PfCyRPA (µg)	Mean ELISA endpoint titer and ELISA sero-conversion rates						Avidity index	IFA sero-conversion rate	GIA IC₅₀ [mg/mL]
Adjuvant	Dose of adjuvant	Dose of PfCyRPA (µg)	1. imm.		2. imm.		3. imm.		3. imm.	3. imm.	3. imm.
GLA-LSQ	5 µg GLA; 2 µg QS-21	20	35,200	6/6	819,200	6/6	1,433,600	6/6	1.0 ± 0.2	5/6	1.1
GLA-SE	5 µg GLA; 2% squalene	20	35,200	6/6	1,024,000	6/6	819,200	6/6	1.3 ± 0.4	5/6	1.1
GLA-Alum	5 µg GLA; 100 µg Alum	20	192,000	6/6	1,024,000	6/6	1,024,000	6/6	1.4 ± 0.2	5/6	0.9
Nanoalum	100 µg Nanoalum	20	10,800	3/6	166,400	6/6	972,800	6/6	1.1 ± 0.3	1/6	2.0
No adjuvant	–	20	13,600	2/6	36,160	5/6	332,800	5/6	1.1 ± 0.1	3/6	1.8

Mean ELISA IgG endpoint titers of responders and the proportion of animals that seroconverted are shown. The avidity index of the anti-PfCyRPA IgG collected after the third immunization are provided. The avidity index is defined as the NH₄SCN concentration (M) where 50% of the bound antibodies in ELISA are eluted. Shown are mean values ± standard deviation of six mice per group. The proportion of animals that had developed blood stage parasite cross-reactive IgG after the third vaccination in IFA at a serum dilution of 1:500 is shown. GIA values: The concentrations of purified total IgG from pooled sera giving 50% growth inhibition in GIA (IC₅₀) are shown. They were determined in a standardized in vitro [³H]-hypoxanthine incorporation assay. Shown are mean values of two independent assays (Fig. 1p–t)

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