Abstract 4534: A therapeutic humanized anti-carcinoma monoclonal antibody (mAb) can enhance NK activity and target immunosuppressive regulatory T cells
Authors: Fantini Massimo , Morelli Maria Pia , Annunziata Christina M. , Arlen Philip M. , Tsang Kwong Y. 
Published: September 2020

Abstract
Background: NEO-201 is a therapeutic IgG1 humanized mAb reactive against many different carcinomas, but not reactive against most normal tissues. No reactivity was observed with NEO-201 in subsets of hematopoietic cells except CD15+ granulocytes. Functional analysis revealed that NEO-201 is capable of engaging in ADCC and CDC to kill tumor cells. Previous studies showed that NEO-201 attenuates growth of human tumor xenografts in mice and demonstrates safety/tolerability in non-human primates with a transient decrease in neutrophils being the only adverse effect observed. A first in human clinical trial evaluating NEO-201 in adults with chemo-resistant solid tumors is ongoing at the NIH clinical Center. NEO-201 recognizes tumor-associated variants of CEACAM5 and 6. CEACAM1 is a potent inhibitor of natural killer (NK) cell function; binding between CEACAM1 on NK cells and CEACAM1 or CEACAM5 on tumor cells inhibits activation signaling by NKG2D, which prevents NK cell cytolysis and permits tumor cells to evade NK killing. Preclinical evaluation showed that NEO-201 reacts against human regulatory T cells (Tregs). This study was designed to assess NK enhancing pathway and further investigated the phenotypic and functional effects of NEO-201 on human Tregs in vitro.
Materials & Methods: Various human tumor cell lines were used as target cells and NK-92 cells (CEACAM1+/CD16-) were used as effectors to assess the ability of NEO-201 to block the interaction between CEACAM5 on tumor cells and CEACAM1 on NK cells in order to enhance the in vitro killing of tumor cells. Phenotypic analysis was conducted by flow cytometry for Treg markers: CD4, CD25, CD127, FoxP3, CD15s, CD45RA, CCR4, NEO-201 antigen, CEACAM5 and CEACAM6.
Results: Functional analysis revealed that NEO-201 is capable of engaging enhancing NK-92 activity to kill tumor cells. Expression profiling revealed that various tumor cell lines expressed different levels of CEACAM5+ and NEO-201+ cells. Addition of NEO-201 significantly enhanced NK-92 cell cytotoxicity against highly CEACAM5+/NEO-201+ cells, suggesting that its activity is correlated with the level of CEACAM5+/NEO-201+ tumor cells. Furthermore, the % of NEO-201+ cells in the population of CD4+CD25highCD127negFoxP3+CD15s+CCR4+Tregs ranged from 60%-80%. NEO-201 mAb mediated CDC activity against Tregs.
Conclusions: This study demonstrates NEO-201 can block the interaction between tumor cell CEACAM5 and NK cell CEACAM1 to reverse CEACAM1-dependent inhibition of NK killing. NEO-201 can also target and eliminate human immunosuppressive regulatory T cells (Tregs).
Citation Format: Massimo Fantini, Maria Pia Morelli, Christina M. Annunziata, Philip M. Arlen, Kwong Y. Tsang. A therapeutic humanized anti-carcinoma monoclonal antibody (mAb) can enhance NK activity and target immunosuppressive regulatory T cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4534.