6P - Combined single-cell and spatially resolved mapping of the human lymph node ecosystem reveals fundamental principles of lymphoma tissue organization

Background

Lymph nodes (LN) act as central hubs for the orchestration of adaptive immune responses. A network of lymph node stromal cells (LNSC), including mesenchymal and endothelial cells, build a 3D network for immune cells to migrate and home to distinct niches in the LN. Within B cell non-Hodgkin lymphomas, indolent follicular lymphomas (FL) are characterized by subtle structural changes while the compartmentalization of the tissue remains present. In contrast, aggressive diffuse large B cell lymphomas (DLBCL) are defined by a complete loss of tissue organization indicating a potential role of LNSCs in tumorigenesis. While the morphological differences are well-known, the underlying molecular and cellular mechanisms remain poorly understood.

Methods

Here, we dissect the mechanisms underlying loss of structure in lymphomagenesis using combined single-cell transcriptome and spatially-resolved mapping approaches of LNSCs and immune cells.

Results

Using ultra-high plex immunofluorescence imaging, we characterized how lymph node cells organize into spatially distinct cellular neighborhoods, the disruption of which was congruent with lymphoma-induced remodeling. Using single-cell transcriptome data, we investigated the molecular programs driving this loss of organization. In DLBCL, chemokines relevant for immune cell organization were downregulated, while chemokines contributing to inflammation were upregulated, suggesting a phenotypic switch from a structural organized to an inflammatory and fibrotic state. In silico cell-cell interaction analysis indicated that besides the loss of mesenchyme-derived chemokine gradients, inflammatory immune cells outside of follicles turn into ectopic sources of these chemokines, an effect which likely contributes to the diffuse growth pattern of aggressive lymphomas. High expression of organizing chemokines was associated with better overall survival, this association being significant in FL and a trend in DLBCL.

Conclusions

Collectively, these data suggest that a reprogramming of the LN microenvironment triggers an imbalance in chemokine gradients, which underlies loss of tissue organization in aggressive lymphomas.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.