Enhancement of antibody-dependent cellular cytotoxicity of cetuximab by a chimeric protein encompassing interleukin-15

ABSTRACT

Enhancement of antibody-dependent cellular cytotoxicity (ADCC) may potentiate the antitumor efficacy of tumor-targeted monoclonal antibodies. Increasing the numbers and antitumor activity of NK cells is a promising strategy to maximize the ADCC of standard-of-care tumor-targeted antibodies. For this purpose, we have preclinically tested a recombinant chimeric protein encompassing the sushi domain of the IL15Rα, IL-15, and apolipoprotein A-I (Sushi-IL15-Apo) as produced in CHO cells. The size-exclusion purified monomeric fraction of this chimeric protein was stable and retained the IL-15 and the sushi domain bioactivity as measured by CTLL-2 and Mo-7e cell proliferation and STAT5 phosphorylation in freshly isolated human NK and CD8⁺ T cells. On cell cultures, Sushi-IL15-Apo increases NK cell proliferation and survival as well as spontaneous and antibody-mediated cytotoxicity. Scavenger receptor class B type I (SR-B1) is the receptor for ApoA-I and is expressed on the surface of tumor cells. SR-B1 can adsorb the chimeric protein on tumor cells and can transpresent IL-15 to NK and CD8⁺ T cells. A transient NK-humanized murine model was developed to test the increase of ADCC attained by the chimeric protein in vivo. The EGFR⁺ human colon cancer cell line HT-29 was intraperitoneally inoculated in immune-deficient Rag2^−/−γc^−/− mice that were reconstituted with freshly isolated PBMCs and treated with the anti-EGFR mAb cetuximab. The combination of the Sushi-IL15-Apo protein and cetuximab reduced the number of remaining tumor cells in the peritoneal cavity and delayed tumor engraftment in the peritoneum. Furthermore, Sushi-IL15-Apo increased the anti-tumor effect of a murine anti-EGFR mAb in Rag1^−/− mice bearing subcutaneous MC38 colon cancer transfected to express EGFR. Thus, Sushi-IL15-Apo is a potent tool to increase the number and the activation of NK cells to promote the ADCC activity of antibodies targeting tumor antigens.

KEYWORDS:

• interleukin 15
• apolipoprotein A-I
• scavenger receptor class B type I
• antibody-dependent cellular cytotoxicity
• NK cell
• cetuximab

Conflict of interest

I.M. has participated in advisory boards serving Roche-Genentech, Bristol-Myers Squibb, Incyte, Medimmune, Novartis, Alligator Biosciences, Bioncotech, Lilly, MSD, and LeadArtis. J.P.M and P.W. are former U3 Pharma employees. The rest of the authors have no conflict of interest to declare.

Acknowledgments

This work was supported by Worldwide Cancer Research Grant under Grant 15–1146, Asociación Española Contra el Cancer (AECC) Foundation under Grant GCB15152947MELE, Red Temática de Investigacion Cooperativa en Cancer under Grants RD12/0036/0040 and RD12/0036/0062, Fondo de Investigación Sanitaria-Fondo Europeo de Desarrollo Regional (FEDER) under Grants PI14/01686, PI13/00207, PI16/00668, and H2020 PROCROP project under Grant 635122. P.B. is supported by Miguel Servet II (CPII15/00004) contract from Instituto de Salud Carlos III. EP-R is supported by the Carmen Lavigne training program of Asociación Española contra el Cancer and by Consejeria de Salud de la Junta de Andalucía. We thank Dr. Pablo Umaña for providing EGFR⁺-MC38 cells.