Bispecific Antibodies Targeting CD3 and EGFRvIII

Introduction of CD3

CD3, a protein complex and co-receptor of T cells, plays a pivotal role in activating both cytotoxic T cells (CD8+ naive T cells) and helper T cells (CD4+ naive T cells). Comprising four distinct chains—CD3γ, CD3δ, and two CD3ε chains—it forms associations with the T cell receptor (TCR) and transmits signals to activate T cells upon antigen recognition by the TCR. CD3 is universally expressed on all T cells, influencing T cell development, differentiation, and function. Its involvement in various immune-related diseases, including autoimmune conditions, transplant rejection, and cancer, establishes CD3 as a valuable target for immunotherapy.

Introduction of EGFRvIII

EGFRvIII represents a mutant variant of EGFR prevalent in various tumor types, including glioblastoma multiforme (GBM), breast cancer, head and neck cancer, and ovarian cancer. Originating from an in-frame deletion of 801 base pairs spanning exons 2–7 of the EGFR gene, this mutation results in a truncated extracellular domain devoid of the ligand-binding region. Characterized by constitutive tyrosine kinase activity, EGFRvIII activates multiple signaling pathways that bolster tumor cell survival, growth, and resistance. Notably, EGFRvIII is exclusively expressed in tumor cells and is correlated with heightened tumor aggressiveness, recurrence, and an unfavorable prognosis. Consequently, EGFRvIII emerges as a highly specific and crucial target for effective tumor therapy.

Fig.1 Functional Domains of EGFR and EGFRvIII

Signaling Pathways Involved in Bispecific Antibodies Targeting CD3 and EGFRvIII

The primary mechanism of action for bispecific antibodies targeting CD3 and EGFRvIII lies in bridging T cells with EGFRvIII-expressing tumor cells, inducing T cell activation, and promoting cytotoxicity against the tumor cells. Through binding to CD3, these antibodies mimic TCR signaling, activating T cell proliferation and effector functions. Simultaneously, by binding to EGFRvIII, bispecific antibodies hinder EGFRvIII signaling, inhibiting the survival and resistance mechanisms of tumor cells. This triggers multiple signaling pathways in both T cells and tumor cells, including PI3K/AKT, MAPK, NF-κB, and JAK/STAT. These pathways play diverse roles in regulating the cell cycle, differentiation, apoptosis, migration, and other processes in both T cells and tumor cells. For instance, the PI3K/AKT pathway, activated by both TCR and EGFRvIII signaling, promotes T cell survival and proliferation, along with tumor cell growth and invasion. The MAPK pathway, activated by both TCR and EGFRvIII signaling, modulates T cell differentiation and cytokine production, as well as tumor cell proliferation and angiogenesis. The NF-κB pathway, primarily activated by TCR signaling, enhances T cell activation and cytokine secretion, alongside promoting tumor cell survival and inflammation. The JAK/STAT pathway, mainly activated by EGFRvIII signaling, mediates tumor cell proliferation, migration, and resistance to apoptosis.

Fig.2 Signaling Pathways Mediated by EGFR/EGFRvIII (An Z, 2018)

Clinic Status of Bispecific Antibodies Targeting CD3 and EGFRvIII

Currently, no bispecific antibodies specifically targeting CD3 and EGFRvIII have received marketing approval. However, multiple bispecific antibodies with this target are actively undergoing clinical trials, primarily focusing on treating glioblastoma multiforme (GBM) and other tumors expressing EGFRvIII.

Fig.3 Schematic Diagram of the Mechanism of BsAbs Targeting CD3 and EGFRvIII (Iurlaro R, 2022)

One promising candidate is AMG 596, a novel bispecific T-cell engager immuno-oncology therapy designed to target the tumor-specific antigen EGFRvIII and the T-cell co-receptor CD3. This innovative therapy aims to recruit and activate the patient's own T cells to eliminate tumor cells expressing EGFRvIII, a mutant form of EGFR prevalent in various tumors, including glioblastoma multiforme (GBM), the most common and aggressive primary brain tumor in adults. AMG 596 has demonstrated potent and specific anti-tumor activity in preclinical studies, leading to its advancement into phase I/II clinical trials for the treatment of EGFRvIII-expressing GBM. Distinguished as the first bispecific T-cell engager molecule specifically targeting EGFRvIII, AMG 596 holds promise as a groundbreaking immunotherapy for patients not only with GBM but also for those with other tumors expressing this antigen.

Table 1. Summary of AMG 596