Profiling the immune tumor microenvironment of pediatric brain tumors with cavitron ultrasonic surgical aspirator (CUSA)-derived tissue fragments

Background. Current treatment options for pediatric high-grade brain tumors are limited, with poor 5-year overall survival rates. While immunotherapy is promising for these patients, the composition of their tumor immune microenvironment (TIME) is still not fully understood, due to the limited availability of tumor material for research. Given the high abundance of tumor tissue fragments obtained using the cavitron ultrasonic surgical aspirator (CUSA), these samples could serve as a resource for research and diagnostic purposes. Methods. To evaluate CUSA tissue fragments as an alternative source for immune-landscape evaluation of brain tumors, we conducted immunological profiling on matched biopsy and CUSA-derived tissue fragments taken during resection from 11 pediatric brain tumor patients, using spectral flow cytometry and functional assays. Results. Cellular compositions were largely comparable between the two sources, both in freshly isolated and cryopreserved samples. Minor differences observed between biopsy and CUSA-derived tissue fragments from individual samples, likely reflect differences related with distinct tumor locations, caused by the small numbers of cells analyzed from one single biopsy versus multiple tumor sites collected with CUSA. Notably, expression of specific cellular immune subsets and their receptors indicating activation or regulation, were highly comparable between both materials, illustrating that CUSA can be used for detailed analyses of a multitude of immune cells and their functional markers. Moreover, CD8 + T-cells are enriched in tumor-infiltrating lymphocyte populations, maintaining their cytotoxic and proliferative capacity upon TCR (co)stimulation. Conclusions. Our findings demonstrate that CUSA-derived tissue fragments represent the TIME in pediatric brain tumors, offering a valuable sample resource for further research.