Meral Esen

Vaccination of malaria-naive volunteers with a high dose of Plasmodium falciparum sporozoites chemoattenuated by chloroquine (CQ) (PfSPZ-CVac [CQ]) has previously demonstrated full protection against controlled human malaria infection (CHMI). However, lower doses of PfSPZ-CVac [CQ] resulted in incomplete protection. This provides the opportunity to understand the immune mechanisms needed for better vaccine-induced protection by comparing individuals who were protected with those not protected. Using mass cytometry, we characterized immune cell composition and responses of malaria-naive European volunteers who received either lower doses of PfSPZ-CVac [CQ], resulting in 50% protection irrespective of the dose, or a placebo vaccination, with everyone becoming infected following CHMI. Clusters of CD4 ⁺ and γδ T cells associated with protection were identified, consistent with their known role in malaria immunity. Additionally, EMRA CD8 ⁺ T cells and CD56 ⁺ CD8 ⁺ T cell clusters were associated with protection. In a cohort from a malaria-endemic area in Gabon, these CD8 ⁺ T cell clusters were also associated with parasitemia control in individuals with lifelong exposure to malaria. Upon stimulation with P . falciparum –infected erythrocytes, CD4 ⁺ , γδ, and EMRA CD8 ⁺ T cells produced IFN-γ and/or TNF, indicating their ability to mediate responses that eliminate malaria parasites.

The SARS-CoV-2 spike (S) glycoprotein is synthesized as a large precursor protein and must be activated by proteolytic cleavage into S1 and S2. A recombinant modified vaccinia virus Ankara (MVA) expressing native, full-length S protein (MVA-SARS-2-S) is currently under investigation as a candidate vaccine in phase I clinical studies. Initial results from immunogenicity monitoring revealed induction of S-specific antibodies binding to S2, but low-level antibody responses to the S1 domain. Follow-up investigations of native S antigen synthesis in MVA-SARS-2-S–infected cells revealed limited levels of S1 protein on the cell surface. In contrast, we found superior S1 cell surface presentation upon infection with a recombinant MVA expressing a stabilized version of SARS-CoV-2 S protein with an inactivated S1/S2 cleavage site and K986P and V987P mutations (MVA-SARS-2-ST). When comparing immunogenicity of MVA vector vaccines, mice vaccinated with MVA-SARS-2-ST mounted substantial levels of broadly reactive anti-S antibodies that effectively neutralized different SARS-CoV-2 variants. Importantly, intramuscular MVA-SARS-2-ST immunization of hamsters and mice resulted in potent immune responses upon challenge infection and protected from disease and severe lung pathology. Our results suggest that MVA-SARS-2-ST represents an improved clinical candidate vaccine and that the presence of plasma membrane–bound S1 is highly beneficial to induce protective antibody levels.

Potent protection against malaria can be induced by attenuated live-immunization with Plasmodium falciparum (Pf) sporozoites (SPZ). However, a better understanding of the critical processes involved in the establishment of protective immunity is needed. We explored the safety and vaccine efficacy of early chemo-attenuation of PfSPZ under atovaquone-proguanil (AP). AP caused early arrest of P. berghei liver stages. Despite the absence of replication, robust protection in mice correlated with parasite-specific effector-memory CD8 ⁺ T-cell responses. In a phase I clinical trial a single dose of AP prevented Pf infections in the liver of adult, human subjects who received three doses of 5.12x10 ⁴ or 1.5x10 ⁵ PfSPZ by direct venous inoculation combined with oral AP. However, only 2 of 8 (25%) and 2 of 10 (20%), respectively, were protected against controlled human malaria infection (CHMI) 10 weeks after the last vaccine dose, despite levels of IgG antibodies to the Pf circumsporozoite protein (PfCSP) comparable to those achieved in fully protected volunteers after immunization with 5.12x10 ⁴ PfSPZ with chloroquine chemoprophylaxis active only against subsequent blood stages. We identify lower IgG recognition of the secreted liver stage-specific antigens LISP2 and LSA1 and the multi-stage antigen MSP5 as immune signatures of inferior vaccine efficacy compared to PfSPZ with chloroquine chemoprophylaxis. In conclusion, we show that immune signatures of liver stage antigens, but neither an established rodent malaria model nor concentrations of antibodies against the major surface protein of sporozoites, permit prediction of vaccine efficacy. Thus, this study provides a clear rationale for the development of live sporozoite vaccination protocols that boost exposure to Pf liver stage antigens. Significance Statement: Our research demonstrates that attenuation of liver infection of high doses of Plasmodium falciparum sporozoites by concomitant single-dose administration of atovaquone-proguanil is safe in humans. However, vaccine efficacy was modest when compared to an identical protocol using chloroquine that acts only on the subsequent blood infection. Immune signatures of secreted P. falciparum liver stage antigens, but neither an established rodent malaria model nor concentrations of sporozoite antibodies, permit prediction of vaccine efficacy.

Helminth infections are common in sub-Saharan Africa. Besides direct clinical effects, a bias towards a T helper type 2 (Th2) cell immune response is observed. The consequences of parasite infection during pregnancy for the mother and particularly for the fetus and the newborn can be severe and may include impaired immune response during acute infection and vaccination. Here, we present data of immune responses to vaccines given within the expanded program on immunization (EPI) of infants born to helminth infected or non-infected mothers. The study was conducted in Lambaréné and surroundings, Gabon. Maternal helminth infection was diagnosed microscopically using the Kato-Katz method for soil-transmitted helminths (STH), urine filtration for Schistosoma haematobium infections and the saponin-based method for filarial infections. Plasma antibody levels to different vaccine antigens were measured in mothers and their offspring by enzyme-linked immunosorbent assay (ELISA) at different timepoints. We found 42.3% of the mothers to be infected with at least one helminth species. Significantly lower anti-tetanus toxoid immunoglobulin (Ig) G was detected in the cord blood of infants born to helminth infected mothers. Following vaccination, immune responses of the infants to EPI vaccines were similar between the two groups at nine and 12 months. Even though infection with helminths is still common in pregnant women in Gabon, in our setting, there was no evidence seen for a substantial effect on infants’ immune responses to vaccines given as part of the EPI.

Soil-transmitted helminth (STH) infections are common in the tropical and subtropical countries. The burden of disease is highest in endemic areas with limited access to good quality water supply and poor sanitary conditions. Major approaches to control and reduce morbidity caused by worm infections include the periodic deworming of pre-school and school-aged children with anthelminthic drugs. Population-based studies and individual patient management including interventional studies can only be successful when accurate diagnostic techniques are used. The lack of appropriate diagnostic tools providing accurate results concerning both infectious status and intensity of infection—as these two factors vary in regions of low infection intensities—is a major challenge. Currently, available techniques show limited sensitivity and specificity and as such, a combination of several techniques is usually used to diagnose the large variety of parasite species. The objective of this review was to describe the advantages and disadvantages of the different available techniques for the diagnosis of STH infections and to highlight their use in control programs.

Controlled human malaria infection (CHMI) by direct venous inoculation (DVI) with 3,200 cryopreserved Plasmodium falciparum sporozoites (PfSPZ) consistently leads to parasitemia and malaria symptoms in malaria-naive adults. We used CHMI by DVI to investigate infection rates, parasite kinetics, and malaria symptoms in lifelong malaria–exposed (semi-immune) Gabonese adults with and without sickle cell trait. Eleven semi-immune Gabonese with normal hemoglobin (IA), nine with sickle cell trait (IS), and five nonimmune European controls with normal hemoglobin (NI) received 3,200 PfSPZ by DVI and were followed 28 days for parasitemia by thick blood smear (TBS) and quantitative polymerase chain reaction (qPCR) and for malaria symptoms. End points were time to parasitemia and parasitemia plus symptoms. PfSPZ Challenge was well tolerated and safe. Five of the five (100%) NI, 7/11 (64%) IA, and 5/9 (56%) IS volunteers developed parasitemia by TBS, and 5/5 (100%) NI, 9/11 (82%) IA, and 7/9 (78%) IS by qPCR, respectively. The time to parasitemia by TBS was longer in IA (geometric mean 16.9 days) and IS (19.1 days) than in NA (12.6 days) volunteers (P = 0.016, 0.021, respectively). Five of the five, 6/9, and 1/7 volunteers with parasitemia developed symptoms (P = 0.003, NI versus IS). Naturally adaptive immunity (NAI) to malaria significantly prolonged the time to parasitemia. Sickle cell trait seemed to prolong it further. NAI plus sickle cell trait, but not NAI alone, significantly reduced symptom rate. Twenty percent (4/20) semi-immunes demonstrated sterile protective immunity. Standardized CHMI with PfSPZ Challenge is a powerful tool for dissecting the impact of innate and naturally acquired adaptive immunity on malaria.