# Hypoxia-induced immunosuppression in uveal melanoma is mediated by CD63+ exosomes delivering lactate to reprogram immune cells

## TL;DR

This study shows that hypoxia in uveal melanoma promotes immunosuppression through CD63+ exosomes that deliver lactate to reprogram immune cells.

## Contribution

The novel finding is that CD63+ exosomes mediate hypoxia-driven immunosuppression by transferring lactate to immune cells in uveal melanoma.

## Key findings

- Hypoxia increases CD63 expression and exosome secretion in uveal melanoma cells.
- Exosomal lactate promotes M2 macrophage polarization and CD8+ T cell exhaustion.
- CD63 knockdown abolishes exosome-mediated immunosuppressive effects.

## Abstract

Uveal melanoma (UM) is characterized by profound immunosuppression, resistance to immunotherapy, and significant hypoxia. This study investigates the role of hypoxia in mediating metabolic crosstalk with immune cells via CD63-enriched exosomes. Single-cell transcriptomic analysis identified a CD63-high tumor subpopulation in UM associated with lactate metabolism and vesicle transport. Under hypoxic conditions (1% O2 vs. 21% O2 normoxia), UMT2 cells exhibited upregulation of CD63 expression, increased exosome secretion, and elevated exosomal lactate levels. In co-culture assays, these hypoxic exosomes promoted macrophage M2 polarization, as indicated by increased CD206+ expression and elevated Extracellular Acidification Rate/Oxygen Consumption Rate (ECAR/OCR) ratios in macrophages and induced CD8+ T cell exhaustion, as evidenced by higher PD-1+TIM-3+ expression, and promoted the secretion of immunosuppressive cytokines such as TGF-β and IL-10. Importantly, these effects, which were driven by exosomal lactate transfer leading to macrophage metabolic reprogramming, were abolished upon CD63 knockdown using siRNA. Mechanistically, CD63 facilitates a hypoxia-induced exosomal lactate shuttle. We conclude that CD63-mediated transfer of hypoxic exosomal lactate establishes a critically immunosuppressive microenvironment in UM. Targeting the hypoxia/CD63/exosomal lactate axis may represent a promising novel therapeutic strategy to restore anti-tumor immunity in UM.

Schematic depicting hypoxic myeloma cells secrete CD63+ exosomes to deliver lactate and promote immunosuppression. Graphical Abstract was created by biorender and licensed to be published.Diagram illustrating the tumor microenvironment. It shows various cell types like cancer cells, T cells, macrophages, dendritic cells, and more. The image explains interactions such as hypoxia increasing CD63, exosomes, and lactic acid in cancer cells. T cell inhibition and exhaustion molecules like PD1 and TIM-3 are noted. Macrophage transformation into M2 macrophages is shown with an emphasis on immune suppressive factors TGF-beta and IL-10, and glycolysis. The left section provides a cell type legend.

Schematic depicting hypoxic myeloma cells secrete CD63+ exosomes to deliver lactate and promote immunosuppression. Graphical Abstract was created by biorender and licensed to be published.