Spleen-Dependent Immune Protection Elicited by CpG Adjuvanted Reticulocyte-Derived Exosomes from Malaria Infection Is Associated with Changes in T cell Subsets' Distribution

Abstract

Reticulocyte-derived exosomes (<i>rex</i>) are 30-100 nm membrane vesicles of endocytic origin released during the maturation of reticulocytes to erythrocytes upon fusion of multivesicular bodies with the plasma membrane. Combination of CpG-ODN with rex obtained from BALB/c mice infected with the reticulocyte-prone non-lethal <i>P. yoelii</i> 17X malaria strain (<i>rexPy</i>), had been shown to induce survival and long lasting protection. Here, we show that splenectomized mice are not protected upon <i>rexPy</i>+CpG inmunizations and that protection is restored upon passive transfer of splenocytes obtained from animals immunized with <i>rexPy</i>+CpG. Notably, <i>rexPy</i> immunization of mice induced changes in PD1^- memory T cells with effector phenotype. Proteomics analysis of <i>rexPy</i> confirmed their reticulocyte origin and demonstrated the presence of parasite antigens. Our studies thus prove, for what we believe is the first time, that <i>rex</i> from reticulocyte-prone malarial infections are associated with splenic long-lasting memory responses. To try extrapolating these data to human infections, <i>in vitro</i> experiments with spleen cells of human transplantation donors were performed. Plasma-derived exosomes from vivax malaria patients (<i>exPv</i>) were actively uptaken by human splenocytes and stimulated spleen cells leading to changes in T cell subsets.