High plasma levels of T-cell-derived CD3(+) sEVs and high levels of stimulatory and suppressive proteins on TEX-enriched CD3(−) sEVs were associated with better patient outcomes
by Karen O’Hanlon Cohrt, PhD
Recent research published in BJC Reports (a partner journal of the British Journal of Cancer) suggests that small extracellular vesicles (sEVs), also known as exosomes, may predict how cancer patients will respond to immunotherapies such as Keytruda and Opdivo. Theresa Whiteside’s (PhD) team at the University of Pittsburgh characterized sEVs from patients with recurrent or metastatic head and neck cancer before immunotherapy and found that higher levels of T-cell-derived sEVs were associated with better survival outcomes and lower risk of disease progression. The study highlights the potential for sEVs in identifying which patients will benefit from anti-PD1 therapy. The September 11, 2024, open-access BJC Reports article is titled “Small Extracellular Vesicles as Biomarkers of Response in Recurrent/Metastatic HNSCC Patients Treated with Immunotherapy.”
The Hunt for Head and Neck Cancer’s Hidden Signals
Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer globally, causing approximately 450,000 deaths per year (1). The approval of immune checkpoint inhibitors such as Keytruda and Opdivo – both of which are monoclonal antibodies developed to block the PD-1 checkpoint – has improved the overall treatment landscape, especially for patients with recurrent or metastatic disease.
However, only about 15-20% of patients respond to those therapies, highlighting the urgent need for new, non-invasive blood-borne biomarkers that can predict the response to therapy and potentially also serve as therapeutic targets. In recent years, small sEVs have emerged as potential predictive biomarkers in cancer and other diseases.
Tiny Messengers, Big Impact: How Cancer Hijacks Cellular Communication
sEVs are tiny vesicles, ranging from 30 to 150 nm in size, that originate from the endocytic compartment of parent cells. They function as an intercellular communication system, transporting diverse cargo such as receptors, enzymes, ligands, and nucleic acids to other cells, causing the recipient to change phenotype and function. This process, known as sEV-induced reprograming, can have stimulatory or inhibitory effects on immune cells.
Cancer cells exploit that system by producing an excess of tumor-derived sEVs (TEX), which carry immunosuppressive proteins that further reprogram immune cells, thereby suppressing anti-tumor immunity. This circulating TEX-mediated immune suppression is observed in HNSCC and has been shown to correlate with advanced disease and cancer progression.
Zooming in on Patients’ sEVs for Predictive Clues to Therapeutic Response
The current study probed the potential of sEVs as predictive biomarkers for the response to anti-PD1 monoclonal antibody therapy in HNSCC patients. To that end, the team accessed stored peripheral blood samples that had been collected from 24 patients with recurrent or metastatic HNSCC, before they had started anti-PD1 immunotherapy. Peripheral blood samples from five healthy donors served as controls in the study.
sEVs were isolated from the plasma fraction via centrifugation and ultrafiltration. The resulting eluates were characterized through video imaging, transmission scanning microscopy, and Western blotting. Total plasma sEVs were separated into T-cell-derived CD3(+) and tumor-enriched CD3(-) subsets using immune capture with an anti-CD3 antibody. Finally, the sEVs were stained for a panel of antigens previously shown to promote stimulatory or inhibitory effects on the immune system.
Higher Levels of T-Cell-Derived sEVs Correlate with Better Treatment Outcomes
The key finding of the present study is that high levels of T-cell-derived sEVs were associated with significantly lower risk of death and disease progression.
While the tumor-enriched CD3(-) subset was more abundant than the CD3(+) subset in patients, the number of tumor-derived sEVs did not appear to impact treatment outcome.
However, when the researchers measured the expression of suppressive (supp) and stimulatory (stim) proteins on the tumor-enriched sEV isolated from each patient, they made some interesting observations: “We calculated supp and stim scores for the CD3(−) sEVs of every patient and found that these scores were not significantly associated with best response. Surprisingly, the supp score was higher than the stim score in only a small majority of the patients (N = 13), and the supp/stim ratio in patients with PD (progressive disease) was significantly lower than in patients with PR (partial response) or SD (stable disease) after therapy.” The team notes that these results differ from what they previously saw in TEX from patients with other solid cancers (2, 3), and suggest that disease packaging of suppressive/stimulatory proteins into sEVs by parent cells may be altered in patients with HNSCC, resulting in a distinct sEV phenotype. They note that both high supp and stim scores of CD3(−) sEVs were significantly associated with better overall survival, and high supp score of CD3(−) sEVs was also associated with lower risk of disease progression. Based on their findings, it is possible that high expression levels of various immunoregulatory proteins on exosome surfaces may lead to better outcomes for patients treated with immunotherapy.
So, What Does All This Mean?
The researchers acknowledge certain study limitations including the small patient sample size, and the CD3+ sEV subset was not characterized phenotypically because of its scarcity. However, their findings suggest that evaluating sEV subsets may help to predict response to immunotherapy in patients with recurrent or metastatic HNSCC, and that larger, mechanistic studies are urgently needed to explore this.
References
- Barsouk A, Aluru JS, Rawla P, et al. Epidemiology, Risk Factors, and Prevention of Head and Neck Squamous Cell Carcinoma. Med Sci (Basel). 2023 Jun 13;11(2):42.
- Sharma P, Diergaarde B, Ferrone S, et al. Melanoma Cell-Derived Exosomes in Plasma of Melanoma Patients Suppress Functions of Immune Effector Cells. Sci Rep. 2020 Jan 9;10(1):92.
- Mondal SK, Haas D, Han J, Whiteside TL. Small EV in Plasma of Triple Negative Breast Cancer Patients Induce Intrinsic Apoptosis in Activated T Cells. Commun Biol. 2023 Aug 4;6(1):815.
About the Writer
Karen O’Hanlon Cohrt, PhD, is a science writer and editor based in Ireland.