Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-defi cient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8 + T-cell infi ltration and activation in vivo , and that CD8 + T-cell depletion severely compromises antitumor effi cacy. Olaparib-induced T-cell recruitment is mediated through activation of the cGAS/STING pathway in tumor cells with paracrine activation of dendritic cells and is more pronounced in HR-defi cient compared with HR-profi cient TNBC cells and in vivo models. CRISPR-mediated knockout of STING in cancer cells prevents proinfl ammatory signaling and is suffi cient to abolish olaparib-induced T-cell infi ltration in vivo. These fi ndings elucidate an additional mechanism of action of PARP inhibitors and provide a rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC. SIGNIFICANCE: This work demonstrates cross-talk between PARP inhibition and the tumor microenvironment related to STING/TBK1/IRF3 pathway activation in cancer cells that governs CD8 + T-cell recruitment and antitumor effi cacy. The data provide insight into the mechanism of action of PARP inhibitors in BRCA-associated breast cancer.

Although the main focus of immuno-oncology has been manipulating the adaptive immune system, harnessing both the innate and adaptive arms of the immune system might produce superior tumour reduction and elimination. Tumour-associated macrophages often have net pro-tumour effects, but their embedded location and their untapped potential provide impetus to discover strategies to turn them against tumours. Strategies that deplete (anti-CSF-1 antibodies and CSF-1R inhibition) or stimulate (agonistic anti-CD40 or inhibitory anti-CD47 antibodies) tumour-associated macrophages have had some success. We hypothesized that pharmacologic modulation of macrophage phenotype could produce an anti-tumour effect. We previously reported that a first-in-class selective class IIa histone deacetylase (HDAC) inhibitor, TMP195, influenced human monocyte responses to the colony-stimulating factors CSF-1 and CSF-2 in vitro. Here, we utilize a macrophage-dependent autochthonous mouse model of breast cancer to demonstrate that in vivo TMP195 treatment alters the tumour microenvironment and reduces tumour burden and pulmonary metastases by modulating macrophage phenotypes. TMP195 induces the recruitment and differentiation of highly phagocytic and stimulatory macrophages within tumours. Furthermore, combining TMP195 with chemotherapy regimens or T-cell checkpoint blockade in this model significantly enhances the durability of tumour reduction. These data introduce class IIa HDAC inhibition as a means to harness the anti-tumour potential of macrophages to enhance cancer therapy.

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Highlights d Distinct CD8 + T cell phenotypes are enriched after immune checkpoint blockade (ICB) d Immune checkpoint ligands are upregulated in macrophages and tumor cells after ICB d Two cancer cell subpopulations are conserved across heterogeneous RCC tumors d Cancer cell programs drive distinct immune interactions and predict patient outcomes

Macrophages are present in all vertebrate tissues and have emerged as multifarious cells with complex roles in development, tissue homeostasis, and disease. Macrophages are a major constituent of the tumor microenvironment, where they either promote or inhibit tumorigenesis and metastasis depending on their state. Successful preclinical strategies to target macrophages for anticancer therapy are now being evaluated in the clinic and provide proof of concept that targeting macrophages may enhance current therapies; however, clinical success has been limited. This review discusses the promise of targeting macrophages for anticancer therapy, yet highlights how much is unknown regarding their ontogeny, regulation, and tissue-specific diversity. Further work might identify subsets of macrophages within different tissues, which could reveal novel therapeutic opportunities for anticancer therapy.

Crucial transitions in cancer-including tumor initiation, local expansion, metastasis, and therapeutic resistance-involve complex interactions between cells within the dynamic tumor ecosystem. Transformative single-cell genomics technologies and spatial multiplex in situ methods now provide an opportunity to interrogate this complexity at unprecedented resolution. The Human Tumor Atlas Network (HTAN), part of the National Cancer Institute (NCI) Cancer Moonshot Initiative, will establish a clinical, experimental, computational, and organizational framework to generate informative and accessible three-dimensional atlases of cancer transitions for a diverse set of tumor types. This effort complements both ongoing efforts to map healthy organs and previous largescale cancer genomics approaches focused on bulk sequencing at a single point in time. Generating single-cell, multiparametric, longitudinal atlases and integrating them with clinical outcomes should help identify novel predictive biomarkers and features as well as therapeutically relevant cell types, cell states, and cellular interactions across transitions. The resulting tumor atlases should have a profound impact on our understanding of cancer biology and have the potential to improve cancer detection, prevention, and therapeutic discovery for better precision-medicine treatments of cancer patients and those at risk for cancer.Cancer forms and progresses through a series of critical transitions-from pre-malignant to malignant states, from locally contained to metastatic disease, and from treatment-responsive to treatment-resistant tumors (Figure 1). Although specifics differ across tumor types and patients, all transitions involve complex dynamic interactions between diverse pre-malignant, malignant, and non-malignant cells (e.g., stroma cells and immune cells), often organized in specific patterns within the tumor

Germ-cell tumours (GCTs) are derived from germ cells and occur most frequently in the testes1,2. GCTs are histologically heterogeneous and distinctly curable with chemotherapy3. Gains of chromosome arm 12p and aneuploidy are nearly universal in GCTs4–6, but specific somatic genomic features driving tumour initiation, chemosensitivity and progression are incompletely characterized. Here, using clinical whole-exome and transcriptome sequencing of precursor, primary (testicular and mediastinal) and chemoresistant metastatic human GCTs, we show that the primary somatic feature of GCTs is highly recurrent chromosome arm level amplifications and reciprocal deletions (reciprocal loss of heterozygosity), variations that are significantly enriched in GCTs compared to 19 other cancer types. These tumours also acquire KRAS mutations during the development from precursor to primary disease, and primary testicular GCTs (TGCTs) are uniformly wild type for TP53. In addition, by functional measurement of apoptotic signalling (BH3 profiling) of fresh tumour and adjacent tissue7, we find that primary TGCTs have high mitochondrial priming that facilitates chemotherapy-induced apoptosis. Finally, by phylogenetic analysis of serial TGCTs that emerge with chemotherapy resistance, we show how TGCTs gain additional reciprocal loss of heterozygosity and that this is associated with loss of pluripotency markers (NANOG and POU5F1)8,9 in chemoresistant teratomas or transformed carcinomas. Our results demonstrate the distinct genomic features underlying the origins of this disease and associated with the chemosensitivity phenotype, as well as the rare progression to chemoresistance. These results identify the convergence of cancer genomics, mitochondrial priming and GCT evolution, and may provide insights into chemosensitivity and resistance in other cancers.

Precursor states of Multiple Myeloma (MM) and its native tumor microenvironment need in-depth molecular characterization to better stratify and treat patients at risk. Using single-cell RNA sequencing of bone marrow cells from precursor stages, MGUS and smoldering myeloma (SMM), to full-blown MM alongside healthy donors, we demonstrate early immune changes during patient