Tumor mutation burden for predicting immune checkpoint blockade response: the more, the better

Low-Salt Diet Reduces Anti-CTLA4 Mediated Systemic Immune-Related Adverse Events while Retaining Therapeutic Efficacy against Breast Cancer

Immune checkpoint inhibitor (ICI) therapy has revolutionized the breast cancer treatment landscape. However, ICI-induced systemic inflammatory immune-related adverse events (irAE) remain a major clinical challenge. Previous studies in our laboratory and others have demonstrated that a high-salt (HS) diet induces inflammatory activation of CD4+T cells leading to anti-tumor responses. In our current communication, we analyzed the impact of dietary salt modification on therapeutic and systemic outcomes in breast-tumor-bearing mice following anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4) monoclonal antibody (mAb) based ICI therapy. As HS diet and anti-CTLA4 mAb both exert pro-inflammatory activation of CD4+T cells, we hypothesized that a combination of these would lead to enhanced irAE response, while low-salt (LS) diet through blunting peripheral inflammatory action of CD4+T cells would reduce irAE response. We utilized an orthotopic murine breast tumor model by injecting Py230 murine breast cancer cells into syngeneic C57Bl/6 mice. In an LS diet cohort, anti-CTLA4 mAb treatment significantly reduced tumor progression (day 35, 339 ± 121 mm3), as compared to isotype mAb (639 ± 163 mm3, p < 0.05). In an HS diet cohort, treatment with anti-CTLA4 reduced the survival rate (day 80, 2/15) compared to respective normal/regular salt (NS) diet cohort (8/15, p < 0.05). Further, HS plus anti-CTLA4 mAb caused an increased expression of inflammatory cytokines (IFNγ and IL-1β) in lung infiltrating and peripheral circulating CD4+T cells. This inflammatory activation of CD4+T cells in the HS plus anti-CTLA4 cohort was associated with the upregulation of inflammasome complex activity. However, an LS diet did not induce any significant irAE response in breast-tumor-bearing mice upon treatment with anti-CTLA4 mAb, thus suggesting the role of high-salt diet in irAE response. Importantly, CD4-specific knock out of osmosensitive transcription factor NFAT5 using CD4cre/creNFAT5flox/flox transgenic mice caused a downregulation of high-salt-mediated inflammatory activation of CD4+T cells and irAE response. Taken together, our data suggest that LS diet inhibits the anti-CTLA4 mAb-induced irAE response while retaining its anti-tumor efficacy.

Urothelial Bladder Carcinomas with High Tumor Mutation Burden Have a Better Prognosis and Targetable Molecular Defects beyond Immunotherapies

Background: Urothelial bladder carcinomas had traditionally been difficult to treat cancers, with high morbidity and mortality rates when invasive and metastatic. In recent years, immunotherapy with immune checkpoint inhibitors has improved outcomes in several cancers, including bladder carcinomas. Despite positive overall results, many bladder cancer patients do not respond to immunotherapies. Validated predictive biomarkers of response would advance the selection of patients for these treatments. Tumor mutation burden (TMB) has been suggested as an immunotherapy biomarker and thus delineation of attributes of tumors with a high TMB is clinically relevant. Methods: Publicly available genomic and clinical data from the urothelial bladder carcinoma cohort of The Cancer Genome Atlas (TCGA) project are used to analyze characteristics and molecular alterations of the subset of cancers with an increased tumor mutation number compared with those with lower number of mutations. The cut-off for the high mutation burden in the analysis was set at 10 mutations per Megabase (MB). Results: In addition to their sensitivity to immune checkpoint inhibitors, urothelial carcinomas with high TMB possess several molecular defects that could be exploited for combinatorial treatments. Compared with bladder carcinomas with low TMB, carcinomas with high TMB display higher prevalence of mutations in tumor suppressor TP53, PIK3CA, in FAT4 cadherin and in genes encoding for several epigenetic modifier enzymes. The frequency of mutations in mismatch repair and DNA damage response genes is higher in cancers with high TMB. The group of urothelial carcinomas with high TMB has a better prognosis than the group with low TMB. This improved Overall Survival (OS) stems from improved survival of stage III cancers with high TMB compared with stage III cancers with low TMB, while stage II and stage IV cancers have similar OS, independently of their TMB. Conclusion: Differences of the landscape of high and low TMB urothelial cancers provides leads for further pathogenesis investigations and may prove useful for development of combination therapies including immunotherapies with targeted inhibitors.