Macrophages within solid tumors and metastatic sites are heterogenous populations with different developmental origins and substantially contribute to tumor progression. A number of tumor-promoting phenotypes associated with both tumor- and metastasis-associated macrophages are similar to innate programs of embryonic-derived tissue-resident macrophages. In contrast to recruited macrophages originating from marrow precursors, tissue-resident macrophages are seeded before birth and function to coordinate tissue remodeling and maintain tissue integrity and homeostasis. Both recruited and tissue-resident macrophage populations contribute to tumor growth and metastasis and are important mediators of resistance to chemotherapy, radiation therapy, and immune checkpoint blockade. Thus, targeting various macrophage populations and their tumor-promoting phenotypes holds therapeutic promise. Here, we discuss various macrophage populations as regulators of tumor progression, immunity, and immunotherapy. We provide an overview of macrophage targeting strategies, including therapeutics designed to induce macrophage depletion, impair recruitment, and induce repolarization. We also provide a perspective on the therapeutic potential for macrophage-specific acquisition of trained immunity as an anti-cancer agent and discuss the therapeutic potential of exploiting macrophages and their traits to reduce tumor burden.

Obesity is characterized by chronic systemic inflammation and enhances cancer metastasis and mortality. Obesity promotes breast cancer metastasis to lung in a neutrophil-dependent manner; however, the upstream regulatory mechanisms of this process remain unknown. Here, we show that obesity-induced monocytes underlie neutrophil activation and breast cancer lung metastasis. Using mass cytometry, obesity favors the expansion of myeloid lineages while restricting lymphoid cells within the peripheral blood. RNA sequencing and flow cytometry revealed that obesity-associated monocytes resemble professional antigen-presenting cells due to a shift in their development and exhibit enhanced MHCII expression and CXCL2 production. Monocyte induction of the CXCL2–CXCR2 axis underlies neutrophil activation and release of neutrophil extracellular traps to promote metastasis, and enhancement of this signaling axis is observed in lung metastases from obese cancer patients. Our findings provide mechanistic insight into the relationship between obesity and cancer by broadening our understanding of the interactive role that myeloid cells play in this process.

Children of women with pre-eclampsia have increased risk of cardiovascular (CV) and metabolic disease in adult life. Furthermore, the risk of pregnancy complications is higher in daughters born to women affected by pre-eclampsia than in daughters born after uncomplicated pregnancies. While aberrant inflammation contributes to the pathophysiology of pregnancy complications, including pre-eclampsia, the contribution of maternal inflammation to subsequent risk of CV and metabolic disease as well as pregnancy complications in the offspring remains unclear. Here, we demonstrate that 24-week-old female rats (F1) born to dams (F0) exposed to lipopolysaccharide (LPS) during pregnancy (to induce inflammation) exhibited mild systolic dysfunction, increased cardiac growth-related gene expression, altered glucose tolerance, and coagulopathy; whereas male F1 offspring exhibited altered glucose tolerance and increased visceral fat accumulation compared with F1 sex-matched offspring born to saline-treated dams. Both male and female F1 offspring born to LPS-treated dams had evidence of anemia. Fetuses (F2) from F1 females born to LPS-treated dams were growth restricted, and this reduction in fetal growth was associated with increased CD68 positivity (indicative of macrophage presence) and decreased expression of glucose transporter-1 in their utero-placental units. These results indicate that abnormal maternal inflammation can contribute to increased risk of CV and metabolic disease in the offspring, and that the effects of inflammation may cross generations. Our findings provide evidence in support of early screening for CV and metabolic disease, as well as pregnancy complications in offspring affected by pre-eclampsia or other pregnancy complications associated with aberrant inflammation.

Pregnancy complications can have long-term negative effects on the health of the affected mothers and their children. In this review, we highlight the underlying inflammatory etiologies of common pregnancy complications and discuss how aberrant inflammation may lead to the acquisition of innate immune memory. The latter can be described as a functional epigenetic reprogramming of innate immune cells following an initial exposure to an inflammatory stimulus, ultimately resulting in an altered response following re-exposure to a similar inflammatory stimulus. We propose that aberrant maternal inflammation associated with complications of pregnancy increases the cross-generational risk of developing noncommunicable diseases (i.e., pregnancy complications, cardiovascular disease, and metabolic disease) through a process mediated by innate immune memory. Elucidating a role for innate immune memory in the cross-generational health consequences of pregnancy complications may lead to the development of novel strategies aimed at reducing the long-term risk of disease.

Background: Bladder cancer is the fifth most common cancer in North America. The standard of care for high-risk non-muscle invasive bladder cancer (NMIBC) involves intravesical immunotherapy with Bacillus Calmette Guérin (BCG). However, it is possible that the efficacy of this modality of BCG administration is suboptimal, as most patients do not respond fully to this immunotherapy. Furthermore, our current understanding of the immunotherapeutic effect of BCG is incomplete. Using a mouse model of NMIBC, we compared the tumor immune microenvironment (TiME) following intravesical versus intravenous administration of BCG, as well as changes in tumor volume and mice survival. Methods: Female C57Bl/6 mice (6-8 weeks old) were catheterized and instilled with 2.5x105 MB49 bladder cancer cells after poly-L-lysine treatment. Beginning on day 7, mice were treated with intravenous (IV) or intravesical BCG (8 mg/ml) or saline once weekly for three weeks. Ultrasound was performed weekly to monitor tumor growth. Similarly, a cohort of non-tumor bearing mice was treated with poly-L-lysine on day one followed by three weekly intravesical instillations of BCG. In both cohorts, mice were sacrificed on day 23 and bladders were harvested, enzymatically dispersed to generate single-cell suspensions for analysis by flow cytometry, or snap frozen for transcriptomic analysis using NanoString nCounter Platform. Results: Mice receiving IV BCG had better survival and their bladder tumors were significantly smaller compared with mice receiving intravesical BCG. This reduction in tumor size was associated with a significantly increased proportion of CD8+ T cells and a significantly reduced proportion of inflammatory monocytes in bladder tumors from mice treated with IV BCG compared with intravesical BCG. Whole tumor transcriptome analysis revealed alterations in various signalling pathways associated with route of BCG administration. Our results demonstrate similar trends in the distribution of immune populations in the TiME following intravesical saline and IV BCG treatment, as well as following IV saline and intravesical BCG treatment. We also found that the TiME after intravesical BCG treatment has more immune cells which are predominantly immature myeloid cells. Moreover, our results indicate that intravesical BCG treatment leads to a significant population of immature myeloid cells in the bladders of non-tumor bearing mice. Conclusion/Significance: These results provide evidence that the route of BCG administration is an important determinant of the TiME composition and may influence anti-tumor responses. Understanding the link between the TiME and BCG therapy may facilitate the development of new approaches to improve outcomes and reduce recurrence rates in patients with NMIBC. Citation Format: Aline Atallah, Arielle Grossman, Jean-Francois Pare, Robert Siemens, Tiziana Cotechini, Charles H. Graham. Effect of route of Bacillus Calmette Guerin administration on the immune microenvironment and growth of bladder tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3540.