430P - Single-cell spatial architecture of tumour microenvironment in patients with in-transit melanoma (ITM)

Background

ITM refers to the presence of metastases between a primary melanoma and the nearest regional lymph node field. The 5-year overall survival rates for patients with ITM varies from 83% to 32%. The role of immunotherapies in the management of patients with ITMs is evolving. The tumour microenvironment of ITM remains poorly defined, where distinct cellular constitution, intercellular interactions and molecular signals may influence tumour progression and therapy outcomes.

Methods

We performed 41-plex CODEX (co-detection by indexing) multiplexed imaging on whole-tissue slides from 10 untreated and 10 post-progression ITM samples. Deep spatial multiplex imaging was used to characterise the spatial architecture of cancer cells, non-immune and immune cells within the tissue using advanced bioinformatics analyses including deep learning classifier, spatial deconvolution, and expression profiling.

Results

ITMs that completely regressed following systemic checkpoint therapies harboured higher proportions of CD8⁺ T cells at the invasive margin, higher expression of PD-L1 on CD14⁺ macrophages and clusters of activated T and B lymphocytes including CD45RO⁺ memory T cells. ITMs with recurrent post treatment demonstrated high immune exclusion, where CD3⁺ T cells with an exhausted phenotype (PD1⁺LAG3⁺) were restricted to the periphery and around intratumoural blood vessels by high density collagen IV deposition. Expression of alternate immune checkpoint receptors (LAG3, TIM3, ICOS, VISTA) was heterogeneous in all resistant patients. Post-treatment tumours showed high infiltration with CD45RO⁺CD8⁺ T cells in the vicinity of HLA-A expressing melanoma cells, but a lack of B cells in the cellular neighbourhood suggestive of inadequate co-stimulation.

Conclusions

Our results demonstrate patterns of immune cell recruitment, functional phenotypes and cellular neighbourhoods associated with immunotherapy response and tumour progression/therapy resistance in ITM melanoma patients treated with immunotherapy.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

(1) Melanoma Research Alliance; (2) ClearBridge Foundation; (3) National Health and Medical Research Council; (4) Cancer Institute New South Wales.

Disclosure

All authors have declared no conflicts of interest.