The gut microbiota of brain tumor patients can impact immunotherapy efficacy in a preclinical model of glioma

Combination immune checkpoint inhibitors (ICI) can affect durable response in melanoma brain metastases (MBM) but have largely been ineffective for the treatment of glioblastoma (GBM), a primary brain tumor. Recent studies in animal models and humans have suggested that the microbe composition of the gut can influence the effectiveness of ICI in melanoma and other cancers. Our central hypothesis is that the gut microbiome can influence immunotherapy responsiveness for GBM patients. We obtained microbiome (stool) samples from GBM and MBM patients prior to beginning any treatment or surgical interventions. We then transplanted these microbiome samples into gnotobiotic mice to create humanized microbiome mice. We transplanted two GBM patients and two MBM patients microbiome samples to create 4 unique patient-derived humanized microbiome mouse lines (GBM1, GBM2, MBM1, and MBM2). Using 16s ribosomal RNA microbiome sequencing, we found that each patient-derived microbiome mouse line had a unique microbiome composition as measured by relative abundance and diversity of species. Mice from each line were then intracranially injected with GL261 murine glioma cells and treated with the ICI anti-PD-1 or isotype control. We found that MBM1 and GBM2 mice were resistant to anti-PD-1 and did not display prolonged survival with anti-PD-1 treatment. However, GBM1 and MBM2 mice were positive responders to anti-PD-1 and displayed significantly prolonged survival compared to isotype control. Additional microbiome sequencing analyses are ongoing that will reveal positive microbiome profiles among these patient-derived lines, and additional GBM and MBM patient-derived microbiome lines are being created and tested for immunotherapy efficacy. Ultimately, understanding how certain microbial communities can enhance the effectiveness of immunotherapy may lead to the development of new approaches that include modification or transplantation of microbe communities in GBM patients for increased therapeutic impact.