Innate immunity in HIV, helminth and malaria co-infections : effects on experimental TB vaccination and clinical malaria presentation

Abstract

Tuberculosis(TB), malaria and helminthiasis are a major challenge for the global public health in the 21st century. The HIV-associated TB epidemic, occurrence of drug resistant strains of Mycobacterium tuberculosis (M.tb) and the limited efficacy of the Bacille Calmette Guerin (BCG) vaccine are important obstacles of reducing TB morbidity and mortality. An estimated 1.5 million people died from TB in 2013, of these approximately one quarter were HIV positive. A new TB vaccine should be safe and efficacious in all populations, including HIV positives. In Sub-Saharan Africa, there is substantial geographical overlap of malaria tropica and soil-transmitted helminth infections and co-infections are common. Intervention strategies mostly neglect co-morbidity, although there is evidence that helminths impact on clinical malaria. The human gut microbiota has an extensive role in nutrition and host health. Gastrointestinal helminths and the gut microbiota share the same niche and close interactions are likely. Chapter 2 documents the clinical trial testing the safety and immunogenicity of the TB vaccine H1/IC31 in HIV infected volunteers. The trial was designed as a phase II, multi-centre, double-blind, placebo-controlled trial and volunteers with a CD4+ lymphocyte count above 350/mm3 and no evidence of active TB were included. H1/IC31 consists of a fusion protein of Ag85B and ESAT-6, both secreted, immuno-dominant proteins isolated from M.tb culture supernatants. Safety was assessed based on medical history, clinical examinations, and blood and urine testing. Immunogenicity was tested using whole blood stimulation followed by intracellular cytokine staining and flow cytometry. The vaccine was safe and well tolerated in HIV infected individuals and CD4+ lymphocyte counts and viral loads remained constant. H1/IC31 was observed to be immunogenic and induced specific Th1 responses with bi-functional CD4+ T cells expressing IL-2 and TNF-a and polyfunctional CD4+T cells expressing IFN-g ,IL-2 and TNF-a. The ancillary study in chapter 3 investigates the induction and maintenance of CD4+ memory T cells following vaccination with H1/IC31. Induction of vaccine specific central (TCM) and effector (TEM) memory CD4+ T cells was detected. The magnitude was highly heterogeneous and the volunteers were grouped into non-, intermediate and high responder based on maintenance of vaccine specific TCM or TEM until 6 months after initial vaccination. Amplicon based transcript quantification of peripheral whole blood using next generation sequencing was performed to identify differentially expressed genes either induced by vaccination or present at baseline. Higher expression of genes implicated in resolution of inflammation were detected in high responder three days after the first vaccination. At baseline, high expression of genes involved in antiviral innate immunity was observed in non-responders and correlated with impaired vaccine specific maintenance of TCM and TEM. A functional variant of TLR-8 was present in a subgroup of TEM high responder, that was previously reported to result in slower disease progression in HIV infected individuals. Summarizing, HIV infected individuals with high expression levels of genes involved in antiviral innate immunity were found to have an affected long-term maintenance of H1/IC31 induced cellular memory response. In chapter 4 co-infections of Plasmodium falciparum (P.falciparum) and soil-transmitted helminths and the effect on clinical presentation of malaria are investigated in children aged 2 months to 9 years from the coastal region of Tanzania. Opposite to Hookworm infections, children co-infected with P. falciparum and Enterobius vermicularis (E. vermicularis) showed a significant reduction of clinical malaria cases. Expression of IL-6 and TNF-a by monocytes and conventional dendritic cells from peripheral blood after stimulation of toll-like receptors with known agonists was reduced in children infected with E. vermicularis. Transcriptome analysis of whole blood revealed lower expression of genes implicated in Th1 responses, pro-inflammation and IFN inducible genes in children with E. vermicularis. The gut microbiome from children with E. vermicularis showed a higher diversity and a function towards an anti-inflammatory enterotype. For the first time it was demonstrated, that E. vermicularis reduces the risk of clinical malaria by suppression of pro-inflammatory cytokine expression at the level of the systemic innate immune system.