Preclinical studies demonstrated that complement promotes tumor growth. Therefore, we sought to determine the best target for complement-based therapy among common human malignancies. High expression of 11 complement genes was linked to unfavorable prognosis in renal cell carcinoma. Complement protein expression or deposition was observed mainly in stroma, leukocytes, and tumor vasculature, corresponding to a role of complement in regulating the tumor microenvironment. Complement abundance in tumors correlated with a high nuclear grade. Complement genes clustered within an aggressive inflammatory subtype of renal cancer characterized by poor prognosis, markers of T cell dysfunction, and alternatively activated macrophages. Plasma levels of complement proteins correlated with response to immune checkpoint inhibitors. Corroborating human data, complement deficiencies and blockade reduced tumor growth by enhancing antitumor immunity and seemingly reducing angiogenesis in a mouse model of kidney cancer resistant to PD-1 blockade. Overall, this study implicates complement in the immune landscape of renal cell carcinoma, and notwithstanding cohort size and preclinical model limitations, the data suggest that tumors resistant to immune checkpoint inhibitors might be suitable targets for complement-based therapy.

In the metastasis-targeted organs, angiogenesis is essential for the progression of dormant micrometastases to rapidly growing and clinically overt lesions. However, we observed changes suggesting angiogenic switching in the mouse lungs prior to arrival of tumor cells (i.e., in the premetastatic niche) in the models of breast carcinoma. This angiogenic switching appears to be caused by myeloid-derived suppressor cells recruited to the premetastatic lungs through complement C5a receptor 1 signaling. These myeloid cells are known to secrete several proangiogenic factors in tumors, including IL-1β and matrix metalloproteinase-9, and we found upregulation of these genes in the premetastatic lungs. Blockade of C5a receptor 1 synergized with antiangiogenic Listeria monocytogenes–based vaccines to decrease the lung metastatic burden by reducing vascular density and improving antitumor immunity in the lungs. This was mediated even when growth of primary breast tumors was not affected by these treatments. This work provides initial evidence that angiogenesis contributes to the premetastatic niche in rapidly progressing cancers and that inhibiting this process through immunotherapy is beneficial for reducing or even preventing metastasis.

The link of the complement system to angiogenesis has remained circumstantial and speculative for several years. Perhaps the most clinically relevant example of possible involvement of complement in pathological neovascularization is age-related macular degeneration. Recent studies, however, provide more direct and experimental evidence that indeed the complement system regulates physiological and pathological angiogenesis in models of wound healing, retinal regeneration, age-related macular degeneration, and cancer. Interestingly, complement-dependent mechanisms involved in angiogenesis are very much context dependent, including anti- and proangiogenic functions. Here, we discuss these new developments that place complement among other important regulators of homeostatic and pathological angiogenesis, and we provide the perspective on how these newly discovered complement functions can be targeted for therapy.

The role of the most common TP53 single-nucleotide polymorphism (SNP) at codon 72, which encodes for proline (P72) or arginine (R72), in the regulation of the immune system has not yet been thoroughly explored. We found that this SNP contributes to aggravated inflammatory response in COVID-19 patients resulting from biased macrophage activation. R72-P53 inhibits mitochondrial manganese superoxide dismutase, leading to impaired reactive oxygen species scavenging, oxidation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), and, consequently, its inhibition. Reduced PTEN activity causes constitutive activation of the PI3K/Akt pathway, which restricts proinflammatory (M1) and promotes anti-inflammatory (M2) phenotypes through NF-κB and p53 inhibition. In contrast, PTEN-reduced PI3K/Akt activity, in P72 carrying cells, favors M1 phenotypes. LPS-stimulated R72 macrophages fail to reduce tumor growth in a mouse model of cancer, in contrast with P72 macrophages, which preserve M1 phenotype in vivo and reduce tumor growth by enhancing antitumor T cell responses, consistent with antitumor functions of M1 macrophages. In addition, P72 macrophages contributed to increased mortality in a mouse model of LPS-induced endotoxemia. Therefore, given the high frequency of P72 in African Americans, cell signaling alterations driven by codon 72 of TP53 SNP may potentially contribute to differences in clinical outcomes and health disparities in common diseases associated with dysregulated macrophage activation.