Regulatory programs that control the function of stem cells are active in cancer and confer properties that promote progression and therapy resistance. However, the impact of a stem cell-like tumor phenotype (“stemness”) on the immunological properties of cancer has not been systematically explored. Using gene-expression–based metrics, we evaluated the association of stemness with immune cell infiltration and genomic, transcriptomic, and clinical parameters across 21 solid cancers. We found pervasive negative associations between cancer stemness and anticancer immunity. This occurred despite high stemness cancers exhibiting increased mutation load, cancer-testis antigen expression, and intratumoral heterogeneity. Stemness was also strongly associated with cell-intrinsic suppression of endogenous retroviruses and type I IFN signaling, and increased expression of multiple therapeutically accessible immunosuppressive pathways. Thus, stemness is not only a fundamental process in cancer progression but may provide a mechanistic link between antigenicity, intratumoral heterogeneity, and immune suppression across cancers.

ABCB1 encodes Multidrug Resistance protein (MDR1), an ATP-binding cassette member involved in the cellular efflux of chemotherapeutic drugs. Here we report that ovarian and breast samples from chemotherapy treated patients are positive for multiple transcriptional fusions involving ABCB1, placing it under the control of a strong promoter while leaving its open reading frame intact. We identified 15 different transcriptional fusion partners involving ABCB1, as well as patients with multiple distinct fusion events. The partner gene selected depended on its structure, promoter strength, and chromosomal proximity to ABCB1. Fusion positivity was strongly associated with the number of lines of MDR1-substrate chemotherapy given. MDR1 inhibition in a fusion positive ovarian cancer cell line increased sensitivity to paclitaxel more than 50-fold. Convergent evolution of ABCB1 fusion is therefore frequent in chemotherapy resistant recurrent ovarian cancer. As most currently approved PARP inhibitors (PARPi) are MDR1 substrates, prior chemotherapy may precondition resistance to PARPi.

Purpose Germline BRCA1 or BRCA2 mutations in patients with high-grade serous ovarian cancer (HGSC) are associated with favorable responses to chemotherapy. However, secondary intragenic (reversion) mutations that restore protein function lead to clinically significant rates of acquired resistance. The goal of this study was to determine whether reversion mutations could be found in an unbiased manner in circulating cell-free DNA (cfDNA) to predict treatment response in HGSC. Patients and Methods Plasma and tumor samples were obtained from 30 patients with HGSC with either BRCA1 or BRCA2 germline mutation. Two cohorts were ascertained: patients with a malignancy before undergoing primary HGSC debulking surgery (n = 14) or patients at disease recurrence (n = 16). Paired tumor and plasma samples were available for most patients (24 of 30). Targeted amplicon, next-generation sequencing was performed using primers that flanked germline mutations, whose design did not rely on prior knowledge of reversion sequences. Results Five patients were identified with intragenic mutations predicted to restore BRCA1/2 open reading frames, including two patients with multiple independent reversion alleles. Reversion mutations were only detected in tumor samples from patients with recurrent disease (five of 16) and only in cfDNA from patients with a tumor-detected reversion (three of five). Findings from a rapid autopsy of a patient with multiple independent reversions indicated that reversion-allele frequency in metastatic sites is an important determinant of assay sensitivity. Abundance of tumor-derived DNA in total cell-free DNA, as measured by TP53 mutant allele frequency, also affected assay sensitivity. All patients with reversions detected in tumor-derived DNA were resistant to platin- or poly ADP ribose polymerase inhibitor-based chemotherapy. Conclusion Reversion mutations can be detected in an unbiased analysis of cfDNA, suggesting clinical utility for predicting chemotherapy response in recurrent HGSC.

We report an RNA molecule that exhibits activity analogous to that of alcohol dehydrogenase (ADH). Directed in vitro evolution was used to enrich nicotinamide adenine dinucleotide (NAD+)-dependent redox-active RNAs from a combinatorial pool. The most active ribozyme in the population forms a compact pseudoknotted structure and oxidizes an alcohol seven orders of magnitude faster than the estimated spontaneous rate. Moreover, this ADH RNA was coupled with a redox relay between NADH and flavin adenine dinucleotide to give a NAD+-regeneration system. Our demonstration of the redox ability of RNA adds support to an RNA-based metabolic system in ancient life.