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432 Evaluation of novel anti-TIGIT antibody M6223 as a single agent and in combination with avelumab on human natural killer (NK) cell cytotoxicity
  1. Anton Titov,
  2. Nancy Sun,
  3. Christie Kelton,
  4. Mirek Jurzak,
  5. Hong Ma and
  6. Chunxiao Xu
  1. EMD Serono, Billerica, MA, United States


Background M6223 is a fully human antagonistic anti-TIGIT immunoglobulin (Ig) G1 antibody with fragment crystallizable (Fc)-mediated effector function. Preclinical studies demonstrated that M6223 could induce an anti-tumor immune response through several mechanisms, including direct blockade of the TIGIT pathway, stimulation of CD226 dimerization/activation, and depletion of TIGIT+ immune subsets by Fc-mediated effector function. Avelumab is a human IgG1 anti–PD-L1 antibody with a wild-type Fc region that has been shown to induce antitumor activity in vitro via both adaptive effector cells (T cells) and innate immune effector cells (antibody-dependent cell-mediated cytotoxicity [ADCC] via NK cells). It is approved for urothelial carcinoma (UC), renal cell carcinoma, and Merkel cell carcinoma. We report an evaluation of the effects of M6223 as a single agent and in combination with avelumab on human NK cell cytotoxicity.

Methods NK cell anti-tumor cytotoxicity was measured against the cancer line MDA-MB-231 with beta-2 microglobulin (B2M) knockout using fluorescent live cell imaging. NK cells were treated with M6223 or its Fc effector null version PPB1791. Avelumab was also tested alone or at a single dose combination with M6223 to evaluate additive potential of these antibodies. A variety of CD155 (poliovirus receptor [PVR]) knockout and partial knockouts were generated to assess the dependence of anti-tumor cytotoxicity on expression of this ligand.

Results M6223 induced significant NK cell anti-tumor cytotoxicity in 4 different NK donors at doses above 0.3 mcg/mL (t-test: p<0.05) with an EC50 value of approximately 100 ng/mL. There was limited in vitro NK fratricide. An Fc-mutant version of M6223 had reduced anti-tumor cytotoxicity (at 0.3 mcg/mL: p=0.28). M6223 in combination with avelumab was more effective than either antibody alone, indicating that CD16-mediated ADCC is likely additive with TIGIT blockade. Anti-tumor cytotoxicity was retained with PVR (CD155) expression on target MDA-MB-231 cells at a wild-type level of 30–50% and was almost completely eliminated in CD155-/- cells. CD112 alone did not facilitate significant M6223-induced anti-tumor cytotoxicity, consistent with a weaker role of DNAX accessory molecule 1 (DNAM-1)-mediated recognition of this receptor.

Conclusions This study confirmed that NK cell cytotoxicity plays an important role in the anti-tumor activity of M6223 and demonstrated the additive effect of avelumab and M6223 in enhancing NK cell activation, especially in CD155+ human leukocyte antigen (HLA) class I-deficient target tumors. Currently, M6223 plus avelumab is being studied as first-line maintenance therapy for advanced UC in the phase 2 JAVELIN Bladder Medley umbrella trial (NCT05327530).

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