Background Immune checkpoint inhibitors provide limited clinical benefit in advanced hepatocellular carcinoma (HCC), highlighting the need to identify additional mechanisms of tumor immune evasion.Methods We performed genome-scale CRISPR-Cas9 knockout library screening to identify genes associated with T cell apoptosis and identified differentially expressed genes in tumor-infiltrating lymphocytes from HCC patients following high-dose interleukin 2 stimulation. Integrative analysis identified signal regulatory protein alpha (SIRPA) as a candidate regulator of T cell apoptosis. SIRPA was functionally validated in vivo and in vitro using Sirpα-/- mice and primary human T cells.Results In vitro, SIRPA deficiency significantly reduced apoptosis in both human and murine T cells, whereas SIRPA overexpression promoted apoptosis. In vivo, T cell-intrinsic loss of Sirpα markedly suppressed tumor growth, and even haploinsufficiency was sufficient to confer a notable antitumor effect. Following macrophage depletion, Sirpα-/- mice exhibited increased frequencies of functional CD8+ T cells in peripheral blood and tumor tissues, accompanied by elevated granzyme B expression, indicating that Sirpα deficiency confers resistance to apoptosis in T cells. Functionally, SIRPA overexpression impaired the cytotoxic activity of TCR-engineered T cells, whereas adoptive transfer of Sirpα-deficient T cells enhanced tumor control. Mechanistically, SIRPA overexpression activated SHP1, leading to inhibition of the PI3K/AKT/FOXO1 signaling pathway, and upregulation of EGR4. Elevated EGR4 interacted with FOXO1 to regulate the Bim/Bcl-2/Bax axis, thereby promoting T cell apoptosis and facilitating tumor immune evasion.Conclusions SIRPA functions as a previously unrecognized intrinsic regulator of T cell apoptosis in HCC. Targeting SIRPA may enhance anti-tumor immunity by preventing T cell apoptosis, representing a promising immunotherapeutic strategy.
Siglec-15 has recently emerged as an important regulator at the interface of glyco-immunology and cancer-immunology. The transmembrane immune receptor links cancer-associated glycosylation to immune suppression in the tumor microenvironment (TME). Siglec-15 signals through the adapter protein DAP12, using its immunoreceptor tyrosine-based activation motif to induce signaling. While typically expressed by osteoclasts, increased expression of Siglec-15 holds critical implications for tumor-associated macrophages (TAMs). Current evidence suggests that Siglec-15 modulates anti-tumor immunity via reprogramming of TAMs toward an M2-like, protumorigenic phenotype characterized by direct suppression of effector T cells through interleukin-10 and transforming growth factor-β production. Identification of its ligands is ongoing, but Siglec-15 has been shown to interact both with N-linked and O-linked sialoglycans and binding can be enhanced by glycan sulfation. In addition, ligand specificity appears to be determined by glycan presentation on specific glycoprotein scaffolds, among others found in CD44 and CD11b. Siglec-15 expression is detected in many solid and hematological cancers and has been shown to negatively correlate with programmed cell death protein 1/programmed death-ligand 1 expression in several studies, providing rationale for targeting this Siglec. Defining the physiological and cancer-associated ligands of Siglec-15 is critical for understanding its signaling and the functional consequences thereof. Blocking antibodies for Siglec-15 show promising effects in (pre)clinical studies. Here, we provide an overview of current insights into the glycan ligands of Siglec-15, discuss its role in controlling TAMs phenotypes, and functions in the TME. Moreover, we discuss current therapeutic strategies aimed at targeting Siglec-15 and its glycan ligands in cancer immunotherapy.
Background Immune checkpoint inhibitors (ICIs) have revolutionized the therapeutic paradigm for mismatch repair-deficient endometrial cancer (MMRd EC). However, a considerable subset of patients fails to achieve durable clinical benefit. This pronounced interpatient variability underscores the urgent unmet need for mechanistic predictive biomarkers beyond MMRd status alone to guide clinical decision-making.Methods We performed a multiproteomic mass spectrometry analysis on tumor specimens from an advanced or recurrent MMRd EC cohort stratified into ICI responders (ICI-R) and non-responders (ICI-NR). Proteomic signatures were validated spatially and structurally using whole-section Masson’s Trichrome digital imaging and polarization-resolved second-harmonic generation microscopy. Machine learning algorithms were constructed to integrate extracellular matrix (ECM) structural metrics with immune parameters to build a multiparametric predictive model of ICI resistance.Results ECM remodeling emerged as the dominant proteomic program characterizing ICI resistance. Quantitative spatial imaging revealed that increased intratumoral collagen density and peripheral fiber disorganization were significantly associated with impaired CD8+ T-cell infiltration and immunotherapy failure. Integrating collagen structural metrics with immune parameters yielded a predictive score that showed promising discrimination between ICI-Rs and ICI-NRs in our cohort, providing a framework for future validation in independent cohorts.Conclusions Our findings implicate ECM remodeling as a key determinant of immune exclusion and ICI resistance in MMRd EC. These findings support developing collagen-based spatial biomarkers and stromal-targeted approaches, though the clinical utility of this predictive score requires further validation in larger, independent cohorts.
