Immune Cells in Cerebrospinal Fluid Predict Response to Immunotherapy

Immune checkpoint inhibitors including anti-PD1, anti-PD-L1, and anti-CTLA4, have shown significant clinical benefits in patients with progressive or metastatic solid tumors, including some brain metastasis. Notably, these immune-based therapies have improved outcomes for some of those suffering from lung cancer and melanoma.

Some patients with brain metastasis benefit from treatment with immune checkpoint inhibitors (ICI) and the degree and phenotype of the immune cell infiltration has been used to predict response to ICI. However, the anatomical location of brain lesions limits access to tumor material to characterize the immune phenotype. Cerebrospinal fluid (CSF) can provide fundamental information about the genomic characteristics of brain tumors and hence be used as a relatively non-invasive liquid biopsy.

A large team of Oncologists and their colleagues at the Vall d’Hebron University Hospital, Barcelona, Spain) analyzed samples from 48 patients with brain metastasis. The scientists assessed the immune cells present in the brain metastases, and in parallel, performed immune cell profiling of the CSF. They sought to identify which cell types were present in the CSF and compare them with those obtained from the metastatic lesions. A total of ten CSF samples were analyzed.

The team loaded samples into the 10× Genomics Chromium Controller for droplet-encapsulation (Pleasanton, CA, USA). Single-cell gene expression and T cell receptor T clonotypes (TCR) were produced using the Chromium Single-Cell 5′ Library, and sequenced on a NovaSeq 6000 (Illumina, San Diego, CA, USA). Immune cell populations were determined after processing by flow cytometry using BD FACSCELESTA (immune cell characterization panel) or BD LSRFortessa cell analyzer (BD Biosciences, San Jose, CA, USA). Other methods used by the team included Immunohistochemistry, Targeted RNA profiling, and Whole exome sequencing.

The team reported that tumor immune infiltration and specifically CD8+ T cell infiltration can be discerned through the analysis of the CSF. Consistently, identical T cell receptor clonotypes were detected in brain lesions and CSF, confirming cell exchange between these compartments. The analysis of immune cells of the CSF can provide a non-invasive alternative to predict the response to ICI, as well as identify the T cell receptor clonotypes present in brain metastasis.

Holger Heyn, PhD, a Genomic Scientist and co-corresponding author of the study, said, “Single cell transcriptome sequencing provides the highest resolution for the detection and monitoring of several different diseases. The identification of clonal T-cells in both metastasis and liquid biopsy is of particular interest. We have shown that the sequencing of T-cell receptors provides a cellular barcode that can be assessed outside of the tumor. Importantly, this approach opens up new avenues for the detection of systemic disease.” The study was published on March 8, 2021 in the journal Nature Communications.

Related Links:
Vall d’Hebron University Hospital
10× Genomics
Illumina
BD Biosciences