3.1 SLAMF7 mRNA expression level and prognostic value in OV
We investigated the mRNA expression levels of SLAM family members in 424 cases of OV samples from the TCGA and 88 cases of normal ovarian tissues from the GTEX database. The results revealed significantly higher expression of SLAMF2 and SLAMF7 (Figure 1A, P <0.05) in tumor tissue compared to normal tissue, while the other members showed no statistically significant difference (Supplementary Figure 1A). The Log-rank test revealed that lower mRNA expression of SLAMF2 was significantly correlated with shorter overall survival (OS) (Figure 1B, P = 0.016), and lower mRNA expression of SLAMF7 was significantly correlated with shorter disease-free survival (DFS) and OS (Figure 1C, P<0.05). No statistically significant differences were observed for the other members (Supplementary Figures 2 and 3). We further analyzed the mRNA expression level of SLAMF7 in relation to other clinicopathological features. Patients with early-stage I or II cancer had significantly higher SLAMF7 mRNA expression in the tumor than those with advanced-stage (FIGO III or IV) cancer (Figure 1D). However, there was no correlation between SLAMF7 expression and tumor grade. Further analysis of the GEO database (GSE9891) confirmed higher expression of SLAMF7 in tumor tissue (Figure 1E), and high SLAMF7 expression (GSE18521, and GSE32062) indicated a favorable OS of OV patients (Figure 1F). A multivariable Cox proportional hazards model was performed, adjusting for prespecified variables, including age, FIGO stage (I-II vs. III-IV), lymph node invasion, neoplasm location (Unilateral vs. Bilateral), histological grade (G1-2 vs. G3-4), tumor residual (No vs. Yes), and primary therapy outcome (PR&CR vs. RD&SD). The results indicated that high SLAMF7 expression was an independent prognostic marker for DFS (HR = 0.691, 95% CI 0.527-0.906, P = 0.007) and OS (HR = 0.616, 95% CI 0.449-0.845, P = 0.003) in OV (Supplementary Tables 1 and 2). These findings demonstrate that SLAMF7 is a potentially favorable prognostic biomarker involved in the progression of OV.
3.2 Evaluation of SLAMF7 protein in OV samples
IHC analysis of tissue array slides showed a positive signal for SLAMF7 in the interstitial components of the tumor tissue. Among the analyzed samples, 68 patients showed negative to weak staining (low expression), while 32 patients showed moderate to strong staining (high expression) in tumor tissues (Figures 2A and 2B). Table 1 provides the basic features of patients. Further analysis demonstrated that patients with high SLAMF7 expression had higher rates of lymph node invasion compared to those with low SLAMF7 expression (Table 2). The median follow-up time after surgery was 53.0 months (3-86 months), and during the follow-up period, 48 patients died. The Log-rank test showed that patients with low SLAMF7 expression had a shorter median OS (47.0 months, 95% CI 27.6-66.1 months) compared to patients with high SLAMF7 expression (not reached) (Figure 2C). Cox regression analysis adjusted for related clinical factors indicated that high SLAMF7 expression was an independent protective factor for patients’ OS (HR = 0.421, P = 0.031, Table 3). These findings suggest that SLAMF7 is expressed in the interstitial components of OV tissue and that higher SLAMF7 expression is associated with a better patient prognosis.
3.3 The relationship between SLAMF7 and immune cell infiltration in OV
Studies have shown that SLAMF7 can directly regulate immune cells and the immune environment[19], so we speculate that the SLAMF7 could modulate tumor progression through immune-related pathways in OV. We discovered the genes that differed between low and high expression groups of SLAMF7 mRNA in OV. GSEA analysis revealed that the SLAMF7 is involved in the T cytotoxic pathway, Fceri-mediated Nf Kb activation, and immunoregulatory interactions between a lymphoid and a non-lymphoid cell (Figure 3A). Furthermore, immune infiltration analysis indicated that SLAMF7 mRNA expression was positively associated with infiltrating T cells, Th1 cells, B cells, T Reg, DC, NK CD56dim cell, cytotoxic cells, macrophages, iDC, T helper cells, Tem, neutrophils, aDC, CD8 T cells, and TFH (Figure 3B, P <0.05). These results suggested that SLAMF7 was significantly associated with immune infiltration in OV. To investigate the potential relationship between SLAMF7 and interstitial lymphocytes, we further analyzed the correlation between SLAMF7 and specific lymphocyte biomarkers.
The results revealed a strong correlation between SLAMF7 and T cell markers, including CD3D (P <0.05, r = 0.66), CD3E (P <0.05, r = 0.66), and CD3G (P <0.05, r = 0.68), as shown in Figure 3C. However, a weak correlation was observed between SLAMF7 and marker genes of B cells and NK cells (Figures 3D and 3E). To further investigate the relation between SLAMF7 and T cells, an IHC analysis of T cell-specific marker CD3 was performed for a tissue array of OV. The results indicated that the expression location of CD3 was identical to SLAMF7 (Figure 4A), and a significantly positive correlation existed between CD3 and SLAMF7 expression (Figure 4B). In summary, these findings suggested that SLAMF7 modulates T-cell immune infiltration and affects the prognosis of OV.