Endothelial Rap1B mediates T-cell exclusion to promote tumor growth: a novel mechanism underlying vascular immunosuppression

Guru Prasad Sharma, Ramoji Kosuru, Sribalaji Lakshmikanthan, Shikan Zheng, Yao Chen, Robert Burns, Gang Xin, Weiguo Cui, Magdalena Chrzanowska*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Overcoming vascular immunosuppression: lack of endothelial cell (EC) responsiveness to inflammatory stimuli in the proangiogenic environment of tumors, is essential for successful cancer immunotherapy. The mechanisms through which Vascular Endothelial Growth Factor A(VEGF-A) modulates tumor EC response to exclude T-cells are not well understood. Here, we demonstrate that EC-specific deletion of small GTPase Rap1B, previously implicated in normal angiogenesis, restricts tumor growth in endothelial-specific Rap1B-knockout (Rap1BiΔEC) mice. EC-specific Rap1B deletion inhibits angiogenesis, but also leads to an altered tumor microenvironment with increased recruitment of leukocytes and increased activity of tumor CD8+ T-cells. Depletion of CD8+ T-cells restored tumor growth in Rap1BiΔEC mice. Mechanistically, global transcriptome and functional analyses indicated upregulation of signaling by a tumor cytokine, TNF-α, and increased NF-κB transcription in Rap1B-deficient ECs. Rap1B-deficiency led to elevated proinflammatory chemokine and Cell Adhesion Molecules (CAMs) expression in TNF-α stimulated ECs. Importantly, CAM expression was elevated in tumor ECs from Rap1BiΔEC mice. Significantly, Rap1B deletion prevented VEGF-A-induced immunosuppressive downregulation of CAM expression, demonstrating that Rap1B is essential for VEGF-A-suppressive signaling. Thus, our studies identify a novel endothelial-endogenous mechanism underlying VEGF-A-dependent desensitization of EC to proinflammatory stimuli. Significantly, they identify EC Rap1B as a potential novel vascular target in cancer immunotherapy.

Original languageEnglish (US)
Pages (from-to)265-278
Number of pages14
Issue number2
StatePublished - May 2023


  • Angiogenic signaling
  • Small GTPase Rap1
  • Tumor blood vessels
  • Tumor microenvironment
  • Vascular anergy

ASJC Scopus subject areas

  • Physiology
  • Cancer Research
  • Clinical Biochemistry


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