Antibody-peptide epitope conjugate (APEC), another disguise for ADC

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Antibody-peptide epitope conjugate (APEC), another disguise for ADC


Tumor immunotherapies compose immune checkpoint inhibitors, therapeutic antibodies, tumor vaccines, cellular therapies, and so on. However, each has its own set of issues, such as the fact that CAR-T therapy is an individual therapy that is costly; immune checkpoint inhibitors are highly effective, but only in some patients.


The researchers expose us to a radically different way of thinking in this article: instead of working on T cells, they focus on changing cancer cell antigens. They employed antibodies to deliver viral antigens to the tumor location and trigger virus-specific T lymphocytes to target cancer cells, destroying them.


The corresponding author of this article is Harvard Medical School Investigator Mark Cobbold, whose team focuses on the development of new immunotherapies, having previously investigated the combination of anti-PD-1 and anti-vascular endothelial growth factor receptor 2 inhibitors in liver cancer, among other things.



Classical antibodies that target specific cancer cell targets (e.g., cetuximab targeting EGFR, rituximab targeting CD20) are connected to the peptide via a peptide substrate segment that can be recognized by proteases. Classical antibodies that target specific cancer cell targets (e.g., cetuximab targeting EGFR, rituximab targeting CD20) are connected to the peptide via a peptide substrate segment that can be recognized by proteases. The peptide can be specifically cleaved by metalloproteinases (MMP) and released at the site of the tumor lesion, enabling greater precision of antigenic peptide epitope delivery based on the antibody's directedness. In this paper, CMV antigenic peptide epitopes are employed, with peptides that have been proven to be functional and more generic for CMV-CTL.



Cytomegalovirus (CMV), a herpesvirus group DNA virus with a 229-kb double-stranded DNA chromosome, is a very widespread infection in the population, usually recessive and without clinical symptoms. However, under certain conditions (e.g., long-term immunosuppression), it can attack multiple organs and systems and cause severe disease. The incidence of  CMV infection tends to increase with age.


In fact, not all tumor-infiltrating T cells are specific for tumor antigens, partly due to the heterogeneity of the immune component, resulting in a largely unknown antigen specificity, and the CMV-specific CD8+ TILS mentioned in the text are present in the tumor as bystander CD8+ T cells and have no substantial effect on the tumor.



The researcher developed five types of antigenic peptide-antibody attachments: free peptide, antibody, antibody bound to CMV all-protein antigen (pp65), and antibody bound to CMV peptide epitope (NLV) (with or without the insertion of an MMP2 cleavable site. The results showed that none of the three intermediate forms reprogrammed tumor cell surface antigenicity, but peptides with cancer-associated metalloproteinase 2 (MMP2) cleavable sites were able to activate CMV-CTL, implying that antibodies conjugated to engineered peptide antigens can effectively reprogram tumor cell surface antigenicity.


To confirm the mechanism of APEC-induced antigen reprogramming, protease inhibitors and recombinant proteases were used to verify the dependence on protease activity. As seen from the results, protease inhibitors significantly reduced T cell activation upon addition of APEC to tumor cells, but had no effect on free peptide incubation.


Anti-CD20 therapeutic rituximab-based APECs were developed to validate the therapeutic efficacy of APECs in lymphoma. rAPEC was found to be effective for antigenic reprogramming of the malignant B cell line JY but not for healthy B cell reprogramming. Exogenous MMP2 protease, on the other hand, was able to sensitize healthy B cells to antigenic reprogramming. APEC-treated tumor cells activated only peptide antigen-specific T-cell populations inside PBMC, with no other T-cell populations showing signs of stimulation, according to flow analysis.


Animal experiments

Is it possible to reprogram the antigenicity of tumors in vivo after demonstrating the efficiency of APEC in vitro? First, APEC was demonstrated to be effective by penetrating tumor entities. The production of the CD107a/b marker represents T cell lysis of target cells, and high CD107a/b expression implies that MMP14-APEC can significantly activate CMV-CTLs in vivo.


MMP14-APEC was subsequently examined in three PDX tumor models (mammary gland, liver, and lung), all of which suppressed tumor growth and prolonged mouse survival.


The combination of MMP14-APEC with anti-VEGF antibody and immune checkpoint inhibitors dramatically reduced tumor growth and extended survival in the PDX model of colorectal cancer in mice (80% vs 0).