Malaria immunology

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

A search for therapies for cerebral malaria in African children Plasmodium falciparum malaria is a potentially fatal infectious disease caused by mosquito-transmitted parasites. Last year P. falciparum infections caused over 219 million cases of malaria and 435 thousand deaths, the vast majority of which were young African children. The deadliest complication of infection is cerebral malaria (CM), causing greater than 90% of malarial fatalities. The mortality for CM is high, estimated to be 15-25%, despite treatment with highly effective anti-malarial drugs. Tragically, many children that survive CM suffer from life-long sequelae, including debilitating cognitive, hearing, and vision impairments. Critically, there are currently no adjunctive CM therapies to combine with rapid-acting antimalarial drugs. Given the global burden of severe malaria, the development of a CM therapy is a public health and humanitarian priority. At present our knowledge of the cellular and molecular mechanisms that underlie CM disease pathology is incomplete. Heavy iRBC sequestration in the cerebrovasculature of children who died of CM is often accompanied by intra- and perivascular pathology, including ring hemorrhages. These observations led to the generally accepted hypothesis that iRBC sequestration in the cerebrovasculature and the resulting sequelae including mechanical obstruction, inflammation, impaired vasoregulation, and BBB dysregulation may cause this clinical syndrome . Unfortunately, various therapies attempting to target this mechanism (at least 17 clinical trials of 11 therapies) have not shown efficacy. An existing mouse model for CM, experimental CM (ECM) shares many features with the human disease. Indeed, several studies including our own using MRI provided evidence of vasogenic brain swelling, blood-brain barrier dysfunction, and fatal brainstem herniation in ECM, similar to that observed in children with CM by MRI. However, the mouse model suggests an alternative mechanism of pathology. ECM requires cross-presentation of parasite antigens on MHC-I by the brain vasculature and targeting of this vasculature by CD3+CD8+ T cells. However, the presence or nature of immune cell infiltrates into the brains of children who dies of CM has not been rigorously determined. Thus, a critical gap in our knowledge of CM in children is whether a pattern of CD3+CD8+ T cell accumulation, which resembles that observed in the murine model of CM, exists in the brains of children who died of CM. We recently provided definitive evidence that CD3+CD8+ T cells are present in the brains of children who died of CM. CD3+CD8+ T cells were present in both the lumen of the venous vasculature in close association with the endothelium as well as on the abluminal side of vessels in the perivascular spaces. The number of CD3+CD8+ T cells is even greater in HIV-infected children with CM, suggesting that HIV coinfection can influence this disease. These observations open new avenues for adjunctive treatment for CM that involve modulating CD3+CD8+ T cells with a wealth of available T cell targeting therapeutics. Using the ECM mouse model to search for therapies to treat CM in African children Our goal over the last year was to better understand the similarities and differences in the pathology associated with CM in African children and ECM in mice to allow us to better evaluate DON as an adjunctive therapy in CM. To this end we established a collaboration with Dr. Terrie Taylor (Michigan State University), an expert in CM in children who heads a pediatric clinic in Malawi that treats children with CM. We described the immune infiltrates into the brains of children who died of CM using multiplex immunohistochemistry analysis of brain sections. We established for the first time that CD8+ T cells sequester along the abluminal face of blood vessels in the brains of children with CM. This finding opens up a new world of possible adjunctive therapies and validates the use of DON as a CM therapy. Based on these findings, in 2019, we initiated plans to carry out a phase I/IIa clinical trial of DON as an adjunctive therapy for African children with CM. To date we have: identified collaborators and a well-equipped site in Malawi to carry out the trial; written a clinical protocol that will soon be submitted for IRB approval in the U.S. and in Malawi; obtained a sufficient quantity of cGMP DON for our studies; submitted a pre-IND to the FDA for approval of the use of DON in our protocol and received FDA confirmation that no additional pre-clinical studies were required and obtained funding to support the clinical trial from DMID, NIAID. The impact of parasite biology on the induction of cerebral malaria (CM) Recent genomic analyses revealed that the coding regions of PbANKA that causes experimental CM (ECM) and the closely related Plasmodium berghei NK65 (PbNK65) that does not cause ECM differs in only 21 single nucleotide polymorphisms (SNPs). Thus, the SNP-containing genes might contribute to the pathogenesis of ECM. We first showed that a SNP resulting in a single amino acid change (S to F) in an ApiAP2 transcription factor in PbNK65 allowed infected mice to mount a T helper cell 1 (TH1)-type immune response that controlled subsequent infections. As compared to PbNK65S, PbNK65F parasites differentially expressed 46 genes, most of which are predicted to play roles in immune evasion. PbNK65F infections resulted in an early interferon-gamma response and a later expansion of germinal centers, resulted in high levels of infected red blood cell-specific TH1-type immunoglobulin G2b (IgG2b) and IgG2c antibodies. Thus, the Pb ApiAP2 transcription factor functions as a critical parasite virulence factor in malaria infections. We subsequently investigated the impact of this S to F SNP in ApiAP2 on the development of ECM. Using CRISPR-Cas9 engineered parasites, we showed that despite its immune modulatory role of this SNP the single amino acid change S to F in ApiAP2 is neither necessary nor sufficient to induce ECM and thus cannot account for parasite strain-specific differences in the ability to induce ECM.