PLA2G2D in tumour-draining lymph nodes regulates anti-tumour immunity.
Systemic anti-tumour immunity results from T cell priming in tumour-draining lymph nodes (TDLNs)1-4. Although the suppression of T cells in tumours is well characterized5-8, whether this occurs in TDLNs-and if so, through which mechanisms-remains poorly understood. Here, using imaging mass cytometry of TDLNs from patients with melanoma, we identify a spatial neighbourhood in the TDLN paracortex that is linked to the development of distant metastases. Targeted spatial transcriptomics of cells inside this neighbourhood revealed activated CD8+ T cells engaging with myeloid cells that expressed high levels of the immunosuppressive secretory phospholipase PLA2G2D. PLA2G2D+ myeloid cells were substantially more abundant in TDLNs than they were in primary tumours or metastases. Genetic loss-of-function or antibody-mediated inhibition of PLA2G2D reduced tumour growth markedly, and single-cell transcriptomics in melanoma-bearing mice revealed that expression of Pla2g2d is confined to lymph-node macrophages. Mechanistically, PLA2G2D directly suppressed the early proliferation of T cells in vitro, and inhibiting PLA2G2D resulted in an expansion of tumour-specific T cells in TDLNs, leading to an increase in these T cells in the circulation and subsequently in tumours. Notably, PLA2G2D and PD-1 act as non-redundant immune checkpoints, with combination treatment showing additive or synergistic efficacy in humanized mice treated with human-specific antibodies. Collectively, our in-depth spatial profiling identifies PLA2G2D as a TDLN-centred targetable immune checkpoint for cancer immunotherapy.