A novel TM4SF4-targeting therapeutic antibody candidate with antitumor activity by blocking IGF1R and CD44 signaling and downregulating PD-L1 and B7-H4

<b>Rationale:</b> Transmembrane 4 superfamily member 4 (TM4SF4) has been identified as a key regulator of epithelial-mesenchymal transition (EMT)-associated stemness in non-small cell lung cancer (NSCLC) cells through autocrine signaling involving insulin-like growth factor 1 (IGF1) and osteopontin (OPN). Given its pivotal role in tumor progression and therapy resistance, TM4SF4 represents a promising therapeutic target. <b>Methods:</b> To develop a therapeutic antibody against TM4SF4, we generated anti-TM4SF4 monoclonal antibodies in mice by targeting the large extracellular loop (LEL) of human TM4SF4 using a 15-mer peptide, hTM4SF4 (T126-E140). Among the generated clones, the 2B7 antibody exhibited high specificity and reactivity to TM4SF4. Mechanistic studies were conducted to evaluate the effects of 2B7 on key signaling pathways, EMT-associated stemness, immune checkpoint ligand (ICL) expression, and immune responses. To facilitate clinical translation, 2B7 was humanized, generating the Hz2B7-1.1 antibody, which underwent affinity maturation to select the lead candidate, Hz2B7-1.2. Functional assays, including antibody-dependent cellular cytotoxicity (ADCC) and preclinical evaluations in xenograft models, were performed to assess its therapeutic potential. <b>Results:</b> The 2B7 antibody demonstrated significant antitumor efficacy in both A549 xenograft and patient-derived xenograft (PDX) models. Mechanistically, 2B7 inhibited key signaling pathways, including PI3K/AKT/GSK3β/β-catenin and JAK2/STAT3, leading to a reduction in EMT-associated stemness and therapy resistance. Additionally, 2B7 downregulated the expression of ICLs, such as PD-L1 and B7-H4, promoting T-cell activation and mitigating immune evasion. Furthermore, 2B7 reduced the secretion of exosomal ICLs by tumor cells and enhanced antitumor immune responses. The humanized antibody Hz2B7-1.2 retained binding properties and antitumor activity comparable to the parental 2B7 antibody and effectively induced ADCC as an IgG1-type antibody. <b>Conclusions:</b> The humanized anti-TM4SF4 antibody, Hz2B7-1.2, exhibits strong antitumor activity through multiple mechanisms, including inhibition of oncogenic signaling pathways, reduction of EMT-associated stemness, and modulation of immune responses. These findings support Hz2B7-1.2 as a promising therapeutic candidate for TM4SF4-positive cancers, warranting further clinical investigation.