Immunohistochemistry Analyses Of Lag-3 Expression Across Different Tumor Types And Co-Expression With Pd-1.

e15086 Background: Concomitant blockade of LAG-3 and PD-1 has been shown to restore T-cell activation and enhance anti-tumor immunity in preclinical models. Clinical trials evaluating anti-LAG-3/anti-PD-1 mAb combinations or bispecific molecules are ongoing. Establishing the tumor expression profile of LAG-3 and its relationship to PD-1 will aid in patient selection and interpretation of clinical responses to combined inhibition. Methods: LAG-3 Ab clone EPR4392(2) (Abcam) and PD-1 Ab clone NAT105 (Ventana) were developed as individual or combined dual IHC assays on the Ventana Discovery Ultra platform. LAG-3 IHC was performed on panels of commercially available tissues: 33 normal human tissues (2 each) and various tumor types including anal (n = 39), cervical cancer (40), cholangiocarcinoma (11), DLBCL (40), gastric cancer (34), HCC (18), SCCHN (39), HER2-positive breast cancer (48), mesothelioma (40), NSCLC (39), ovarian cancer (47), SCLC (48), and TNBC (40). LAG-3 IHC expression was confirmed by in situ hybridization (ACD RNAScope). Positivity was defined as at least one LAG-3+ve or PD-1+ve tumor-infiltrating lymphocyte (TIL) per 40x magnification hot spot field (HSF); high LAG-3 expression was defined as > 15 LAG-3+ve TILs per HSF. Results: LAG-3-specific staining in normal tissues was limited to mononuclear cells in lymphoid organs and GALT, with no staining observed in normal parenchyma. Across various tumor types, the frequency of LAG-3+ve tumor samples and high expression, respectively (%, %), were as follows: cervical (100; 57.5), anal (97.4; 30.8), DLBCL (95; 75), NSCLC (92.3; 25.6), TNBC (90; 22.5), gastric (88.2; 44.1), SCCHN (87.2; 56.4), HER2-positive breast (85.4; 39.6), HCC (83.3; 22.2), cholangiocarcinoma (81.8; 9.1), ovarian (70.2; 21.3), SCLC (50; 14.6) and mesothelioma (25; 10). In addition to TILs, LAG-3 expression was observed on tumor cells in DLBCL and a fraction of anal, breast, cervical, gastric, hepatocellular, SCCHN, NSCLC and ovarian cancers. LAG-3/PD-1 double IHC staining revealed dual positivity across 92.3% of NSCLC samples, with approximately 60% demonstrating TIL co-expression of PD-1 and LAG-3. Conclusions: LAG-3 expression was detected on TILs across a broad range of solid tumors and DLBCL, with varying level of intensity or association with PD-1 expression. Correlative assessments of LAG-3/PD-1 expression with clinical responses to MGD013, an investigational bispecific DART(R) molecule targeting LAG-3/PD-1 (NCT03219268), will be undertaken.