Cellular senescence enhances adaptive anticancer immunosurveillance

METTL3-mediated HSPA9 m6A modification promotes malignant transformation and inhibits cellular senescence by regulating exosomal mortalin protein in cervical cancer

The role of RNA methyltransferase 3 (METTL3) in tumor progression when tethered to aberrantly expressed oncogenes remains unknown. In especial, the correlation between cervical cancer (CCa)-derived exosomes and m6A methylation in malignant traits of cervical epithelium is currently elusive. Mortalin expression was found to be up-regulated in plasma exosomes isolated from CCa patients. Furthermore, mortalin gained increased mRNA stability and enhanced translation efficiency via the m6A methylation in the HSPA9 mRNA 3'UTR, which was catalysed by METTL3 in CCa cells. Exosomal mortalin overexpression significantly promoted the proliferation, migration and invasion of CCa both in vitro and in vivo. Additionally, exosome-encapsulated mortalin suppressed cellular senescence and facilitated malignant transformation by blocking nuclear transport of p53, thereby preventing the p53-Gadd45A interaction and resulting in inactivation of p53. Our studies demonstrated the significant role of METTL3 mediated exosomal mortalin in malignant transformation and cellular senescence suppression of CCa. Exosomal mortalin could clinically serve as a potential early-diagnosis biomarker and therapeutic target for CCa given its abundance and propensity to be found.

Therapy-Induced Senescence Contributes to the Efficacy of Abemaciclib in Patients with Dedifferentiated Liposarcoma

PURPOSE

We conducted research on CDK4/6 inhibitors (CDK4/6i) simultaneously in the preclinical and clinical spaces to gain a deeper understanding of how senescence influences tumor growth in humans.

PATIENTS AND METHODS

We coordinated a first-in-kind phase II clinical trial of the CDK4/6i abemaciclib for patients with progressive dedifferentiated liposarcoma (DDLS) with cellular studies interrogating the molecular basis of geroconversion.

RESULTS

Thirty patients with progressing DDLS enrolled and were treated with 200 mg of abemaciclib twice daily. The median progression-free survival was 33 weeks at the time of the data lock, with 23 of 30 progression-free at 12 weeks (76.7%, two-sided 95% CI, 57.7%-90.1%). No new safety signals were identified. Concurrent preclinical work in liposarcoma cell lines identified ANGPTL4 as a necessary late regulator of geroconversion, the pathway from reversible cell-cycle exit to a stably arrested inflammation-provoking senescent cell. Using this insight, we were able to identify patients in which abemaciclib induced tumor cell senescence. Senescence correlated with increased leukocyte infiltration, primarily CD4-positive cells, within a month of therapy. However, those individuals with both senescence and increased TILs were also more likely to acquire resistance later in therapy. These suggest that combining senolytics with abemaciclib in a subset of patients may improve the duration of response.

CONCLUSIONS

Abemaciclib was well tolerated and showed promising activity in DDLS. The discovery of ANGPTL4 as a late regulator of geroconversion helped to define how CDK4/6i-induced cellular senescence modulates the immune tumor microenvironment and contributes to both positive and negative clinical outcomes. See related commentary by Weiss et al., p. 649.

What do cancer-specific CD8+ T cells see? The contribution of immunopeptidomics

Immunopeptidomics is the survey of all peptides displayed on a cell or tissue when bound to human leukocyte antigen (HLA) molecules using tandem mass spectrometry. When attempting to determine the targets of tumour-specific CD8+ T cells, a survey of the potential ligands in tumour tissues is invaluable, and, in comparison with in-silico predictions, provides greater certainty of the existence of individual epitopes, as immunopeptidomics-confirmed CD8+ T-cell epitopes are known to be immunogenic, and direct observation should avoid the risk of autoreactivity which could arise following immunisation with structural homologues. The canonical sources of CD8+ T-cell tumour specific epitopes, such as tumour associated antigens, may be well conserved between patients and tumour types, but are often only weakly immunogenic. Direct observation of tumour-specific neoantigens by immunopeptidomics is rare, although valuable. Thus, there has been increasing interest in the non-canonical origins of tumour-reactive CD8+ T-cell epitopes, such as those arising from proteasomal splicing events, translational/turnover defects and alternative open reading frame reads. Such epitopes can be identified in silico, although validation is more challenging. Non-self CD8+ T-cell epitopes such as viral epitopes may be useful in certain cancer types with known viral origins, however these have been relatively unexplored with immunopeptidomics to date, possibly due to the paucity of source viral proteins in tumour tissues. This review examines the latest evidence for canonical, non-canonical and non-human CD8+ T-cell epitopes identified by immunopeptidomics, and concludes that the relative contribution for each of these sources to anti-tumour CD8+ T-cell reactivity is currently uncertain.