Increased T Cell Differentiation and Cytolytic Function in Bangladeshi Compared to American Children

Immunological factors linked to geographical variation in vaccine responses

Vaccination is one of medicine's greatest achievements; however, its full potential is hampered by considerable variation in efficacy across populations and geographical regions. For example, attenuated malaria vaccines in high-income countries confer almost 100% protection, whereas in low-income regions these same vaccines achieve only 20-50% protection. This trend is also observed for other vaccines, such as bacillus Calmette-Guérin (BCG), rotavirus and yellow fever vaccines, in terms of either immunogenicity or efficacy. Multiple environmental factors affect vaccine responses, including pathogen exposure, microbiota composition and dietary nutrients. However, there has been variable success with interventions that target these individual factors, highlighting the need for a better understanding of their downstream immunological mechanisms to develop new ways of modulating vaccine responses. Here, we review the immunological factors that underlie geographical variation in vaccine responses. Through the identification of causal pathways that link environmental influences to vaccine responsiveness, it might become possible to devise modulatory compounds that can complement vaccines for better outcomes in regions where they are needed most.

Systems vaccinology studies - achievements and future potential

Human immune responses to vaccination are variable both within and between populations. Systems vaccinology, which is the application of multi-omics technologies to vaccine studies, seeks to understand such variation and predict responses to optimise vaccine strategies. Here, we outline new approaches to systems vaccinology, focusing on the incorporation of additional cohorts, endpoints and technologies.

Immune modulation by nutritional intervention in malnourished children: Identifying the phenotypic distribution and functional responses of peripheral blood mononuclear cells

Malnourished children are susceptible to an increased risk of mortality owing to impaired immune functions. However, the underlying mechanism of altered immune functions and its interaction with malnutrition is poorly understood. This study investigates the immune function and evaluates the effect of a particular nutritional intervention on the immune cells of undernourished children. Stunted (LAZ <-2) and at-risk of being stunted (length-for-age Z-scores, LAZ <-1 to -2) children aged between 12 and 18 months were enrolled and were provided with the daily nutritional intervention of one egg and 150 mL cow's milk for 90 days. Peripheral blood mononuclear cells (PBMCs) were isolated at enrolment and upon completion of the intervention. Phenotypic profiles for CD3+ cells, CD4+ cells, CD8+ cells, NKT cells, and B cells were similar in both cohorts, both before and after the intervention. However, activated B cells (CD25+) were increased after nutritional intervention in the at-risk of being stunted cohort. Several pro-inflammatory cytokines, IL-6, IFN-γ, and TNF-α, were elevated in the stunted children following the nutritional intervention. The results of the study indicate that nutritional intervention may have a role on activated B cells (CD25+) s in children who are at-risk of being stunted and may alter the capacity of PBMC to produce inflammatory cytokines in stunted children.

Small centers of defense

Deciphering immune responses to viruses and vaccines using human tonsil organoids.

Systems analysis and controlled malaria infection in Europeans and Africans elucidate naturally acquired immunity

Controlled human infections provide opportunities to study the interaction between the immune system and malaria parasites, which is essential for vaccine development. Here, we compared immune signatures of malaria-naive Europeans and of Africans with lifelong malaria exposure using mass cytometry, RNA sequencing and data integration, before and 5 and 11 days after venous inoculation with Plasmodium falciparum sporozoites. We observed differences in immune cell populations, antigen-specific responses and gene expression profiles between Europeans and Africans and among Africans with differing degrees of immunity. Before inoculation, an activated/differentiated state of both innate and adaptive cells, including elevated CD161⁺CD4⁺ T cells and interferon-γ production, predicted Africans capable of controlling parasitemia. After inoculation, the rapidity of the transcriptional response and clusters of CD4⁺ T cells, plasmacytoid dendritic cells and innate T cells were among the features distinguishing Africans capable of controlling parasitemia from susceptible individuals. These findings can guide the development of a vaccine effective in malaria-endemic regions.

Identification of Common CD8+ T Cell Epitopes from Lassa Fever Survivors in Nigeria and Sierra Leone

The high morbidity and mortality associated with clinical cases of Lassa fever, together with the lack of licensed vaccines and limited and partially effective interventions, make Lassa virus (LASV) an important health concern in its regions of endemicity in West Africa. Previous infection with LASV protects from disease after subsequent exposure, providing a framework for designing vaccines to elicit similar protective immunity. Multiple major lineages of LASV circulate in West Africa, and therefore, ideal vaccine candidates should elicit immunity to all lineages. We therefore sought to identify common T cell epitopes between Lassa fever survivors from Sierra Leone and Nigeria, where distinct lineages circulate. We identified three such epitopes derived from highly conserved regions within LASV proteins. In this process, we also identified nine other T cell epitopes. These data should help in the design of an effective pan-LASV vaccine.

Early and robust T cell responses have been associated with survival from Lassa fever (LF), but the Lassa virus-specific memory responses have not been well characterized. Regions within the virus surface glycoprotein (GPC) and nucleoprotein (NP) are the main targets of the Lassa virus-specific T cell responses, but, to date, only a few T cell epitopes within these proteins have been identified. We identified GPC and NP regions containing T cell epitopes and HLA haplotypes from LF survivors and used predictive HLA-binding algorithms to identify putative epitopes, which were then experimentally tested using autologous survivor samples. We identified 12 CD8-positive (CD8⁺) T cell epitopes, including epitopes common to both Nigerian and Sierra Leonean survivors. These data should be useful for the identification of dominant Lassa virus-specific T cell responses in Lassa fever survivors and vaccinated individuals as well as for designing vaccines that elicit cell-mediated immunity.

IMPORTANCE The high morbidity and mortality associated with clinical cases of Lassa fever, together with the lack of licensed vaccines and limited and partially effective interventions, make Lassa virus (LASV) an important health concern in its regions of endemicity in West Africa. Previous infection with LASV protects from disease after subsequent exposure, providing a framework for designing vaccines to elicit similar protective immunity. Multiple major lineages of LASV circulate in West Africa, and therefore, ideal vaccine candidates should elicit immunity to all lineages. We therefore sought to identify common T cell epitopes between Lassa fever survivors from Sierra Leone and Nigeria, where distinct lineages circulate. We identified three such epitopes derived from highly conserved regions within LASV proteins. In this process, we also identified nine other T cell epitopes. These data should help in the design of an effective pan-LASV vaccine.

Differential IL-18 Dependence of Canonical and Adaptive NK Cells for Antibody Dependent Responses to P. falciparum

Human adaptive natural killer (NK) cells have diminished reliance on accessory cytokines for their activation whilst being efficiently activated by infected host cells in conjunction with pathogen specific antibodies. Here, we show that potent antibody-dependent NK cell responses are induced by Plasmodium falciparum infected erythrocytes (iRBC) in peripheral blood mononuclear cells (PBMC) from malaria-exposed Gambian individuals in the presence of autologous sera, which are absent in those from malaria-naïve UK individuals. However, malaria hyper-immune serum promotes rapid NK cell responses to iRBC in cells from both Gambian and UK individuals. Among Gambians, highly differentiated, adaptive (CD56dimFcεR1γ-CD57+) NK cells dominate both antibody-dependent NK cell IFN-γ responses and degranulation responses, whereas among UK individuals these responses are predominantly found within canonical, highly differentiated CD56dimFcεR1γ+CD57+ NK cells. Indeed, overall frequencies of adaptive, FcεR1γ-CD57+ NK cells are significantly higher among Gambian donors compared to HCMV-infected and HCMV-uninfected UK adults. Among UK individuals, antibody-dependent NK cell IFN-γ responses to iRBC were dependent on IL-18 whereas among Gambians, the predominant adaptive FcεR1γ- NK cell response was IL-18 (and accessory cell) independent (although the lower frequency response of canonical FcεR1γ NK cells did rely on this cytokine).

High crossreactivity of human T cell responses between Lassa virus lineages

Lassa virus infects hundreds of thousands of people each year across rural West Africa, resulting in a high number of cases of Lassa fever (LF), a febrile disease associated with high morbidity and significant mortality. The lack of approved treatments or interventions underscores the need for an effective vaccine. At least four viral lineages circulate in defined regions throughout West Africa with substantial interlineage nucleotide and amino acid diversity. An effective vaccine should be designed to elicit Lassa virus specific humoral and cell mediated immunity across all lineages. Most current vaccine candidates use only lineage IV antigens encoded by Lassa viruses circulating around Sierra Leone, Liberia, and Guinea but not Nigeria where lineages I-III are found. As previous infection is known to protect against disease from subsequent exposure, we sought to determine whether LF survivors from Nigeria and Sierra Leone harbor memory T cells that respond to lineage IV antigens. Our results indicate a high degree of cross-reactivity of CD8+ T cells from Nigerian LF survivors to lineage IV antigens. In addition, we identified regions within the Lassa virus glycoprotein complex and nucleoprotein that contributed to these responses while T cell epitopes were not widely conserved across our study group. These data are important for current efforts to design effective and efficient vaccine candidates that can elicit protective immunity across all Lassa virus lineages.

Lassa virus (LASV), the causative agent of the hemorrhagic illness Lassa fever (LF), is found throughout West Africa. Humans are usually infected after contact with infected rodent excreta or aerosolized virus. The mortality rate among hospitalized LF cases is high and no effective treatments or vaccines exist. A vaccine effective against the four main lineages of LASV is needed to protect susceptible individuals across West Africa. To understand how this protection could occur, we examined the immune responses of LF survivors from two different regions of West Africa. As previous infection with Lassa virus protects from disease after subsequent exposure, the immune response of LF survivors provides a model of protective immunity that could be induced after vaccination. We found that LASV strains from lineages different from those that infected the LF survivors efficiently activated memory CD8+ T cell responses. We identified regions within LASV proteins that elicit memory responses in the majority of individuals. From these data, we propose that an effective vaccine that protects against lineages across West Africa should be designed to elicit memory CD8+ T cell responses in addition to antibody responses.