Spatial mapping of Ethiopian cutaneous leishmaniasis lesions reveals distinct tissue level immune programs

Human cutaneous leishmaniasis (CL) is a prevalent but neglected tropical disease characterised by inflammatory lesions that are either restricted to the site of the infected sand fly bite or disseminate to mucosae or within the skin. Compared to well-studied pre-clinical models, the nature and diversity of the tissue response in humans remains to be fully appreciated.

We conducted an exploratory study using spatial transcriptomics on paired lesional and non-lesional skin punch biopsies from five Ethiopian CL patients (two infected with L. aethiopica, one with L. tropica, and two with species unconfirmed). We used reference-free deconvolution, morphology-guided regional analyses, and immunohistochemistry-based validation to characterise the tissue responses.

We identified spatially distinct immunopathological tissue responses including: i) epithelial hyperplasia with interferon-stimulated keratinocytes, ii) cytotoxicity with tertiary lymphoid structures, iii) granulomatous inflammation with proinflammatory response, iv) granulomatous inflammation with M2-polarised myeloid cell responses, and v) fibrotic remodelling with active collagen synthesis. Each patient in this case series exemplified one of these tissue responses, but immunopathological features were not mutually exclusive. This study extends our understanding of Ethiopian CL immunopathology and provides a molecular and cellular context that can be applied in larger clinical cohorts for testing hypotheses regarding the host and/or parasite determinants of CL disease diversity.