Correlative humoral and cellular immunity to genetically attenuated malaria parasites in humans

Abstract

Malaria caused by Plasmodium falciparum remains one of the major infectious diseases with a high burden in Sub-Saharan Africa. In spite of the advancements made in vaccine development and implementation in endemic countries, sterile and durable protection has not been achieved. Recently, we have shown the superior protective capacity of whole sporozoites attenuated to arrest late (GA2) but not early (GA1) during the liver stage development in a controlled human malaria infection study. Here we report the breadth of antigens targeted by hitherto understudied parasite liver stage immunity and convey the coherence between humoral and cellular immunity observed in our clinical study. Our findings uncover the underlying immunogenic differences between early- and late-liver stage arresting parasites and identify key liver stage antigens for future vaccine development focused on inducing sterile immunity to malaria.

Keywords: Immunity; Microbiology parasite.

Graphical abstract

Figure 1

Immunization with the late liver stage arresting parasite induces a stronger and broader humoral response compared to early-arresting parasite (A) A schematic overview of the clinical trial where participants were immunized three times with mosquito bites (MBs) infected with either early (GA1) or late (GA2) arresting Pf parasites, followed by a challenge with wild type (WT) Pf. (B) IgG binding values in plasma collected at (III) from microarray coated with 262 peptides covering 224 unique antigens. (C) The number of targeted antigens in GA1-MBs and GA2-MBs participants across three time points. Statistical analysis was performed by the Friedman test and the p values were indicated. (D) Predicted expression stage of antigens targeted upon GA1-MBs and GA2-MBs immunization. (E) Predicted presence of signal peptide (top), Pf-specific PEXEL motifs (middle), and the number of transmembrane domains (bottom) among the antigens targeted upon GA1-MBs and GA2-MBs immunization. (F) Predicted location of targeted antigens after GA1-MBs and GA2-MBs. (G) The MFI fold change compared to baseline (B) of Pf antigens with higher seroprevalence in GA2-MBs compared to GA1-MBs following three immunizations. (H) Pearson correlations between targeted antigen counts at the indicated immunization time point and α-PfCSP antibody titers following the previous immunization. See also Figure S2 and Tables S1, S2–S5, S6, and S7.

Figure 2

Pf-specific polyfunctional effector memory T cell response correlates with the humoral response (A) Experimental design of stimulating PBMCs with Pf-infected or uninfected erythrocytes to detect Pf-specific cellular responses in immunization groups. (B) Frequency of monofunctional (1 cytokine/cell) and polyfunctional (>1 cytokine/cell) CD4⁺ and Vδ2⁺ γδ T cells after three immunizations (III) compared to the baseline (B). (C and D) Frequencies of cellular responses defined as central (CCR7⁺CD45RA⁻, T_CM) and effector (CCR7⁻CD45RA⁻, T_EM) memory T cells as previously reported among CD4⁺ (C) and Vδ2⁺ γδ (D) T cells. (E) Principal component analysis of mono- and polyfunctional CD4⁺ and Vδ2⁺ γδ T_CM and T_EM frequencies at both baseline and following three immunizations. (F) Pearson correlation of polyfunctional CD4⁺ T_EM with the number of targeted antigens following three immunizations. (B–D) Statistical analysis was performed by non-parametric paired t test with p values indicated in the panels. Black horizontal lines indicate arithmetic mean. See also Figures S4A and S4B, and Tables S8, S9, and S10.