CD155 blockade enhances allogeneic natural killer cell-mediated antitumor response against osteosarcoma.

BACKGROUND: Osteosarcoma (OS) patients that present with metastatic disease have a poor prognosis and no curative options. Allogeneic bone marrow transplant (alloBMT) is curative for hematologic malignancies through the graft-versus-tumor (GVT) effect, but to date has been ineffective for solid tumors like OS. CD155 is expressed on OS and interacts strongly with the inhibitory receptors TIGIT and CD96 but also binds to the activating receptor DNAM-1 on natural killer (NK) cells but has never been targeted after alloBMT. Combining adoptive transfer of allogeneic NK (alloNK) cells with CD155 checkpoint blockade after alloBMT may enhance a GVT effect against OS but could enhance toxicities like graft-versus-host-disease (GVHD).

METHODS: Ex vivo activated and expanded murine NK cells were generated with soluble IL-15/IL-15Rα. AlloNK and syngeneic NK (synNK) cell phenotype, cytotoxicity, cytokine production, and degranulation against the CD155-expressing murine OS cell line K7M2 were assessed in vitro. Mice bearing pulmonary OS metastases underwent alloBMT followed by infusion of alloNK cells with combinations of anti-CD155 and anti-DNAM-1 blockade. Tumor growth, GVHD and survival were monitored and differential gene expression of lung tissue was assessed by RNA microarray.

RESULTS: AlloNK cells exhibited superior cytotoxicity against CD155-expressing OS compared to synNK cells, and this activity was further enhanced by CD155 blockade. CD155 blockade increased alloNK cell degranulation and interferon gamma production through DNAM-1, as these functions were abrogated during DNAM-1 blockade. In vivo, CD155 blockade after alloBMT increased survival and decreased OS disease burden with no exacerbation of GVHD. Treatment with combination CD155 and DNAM-1 blockade ameliorated survival and tumor control benefits seen with CD155 blockade alone. In mice treated with CD155 blockade, genes related to NK cell cytotoxicity were upregulated. DNAM-1 blockade resulted in upregulation of NK cell inhibition and T cell function gene expression.

CONCLUSIONS: These results demonstrate the safety and efficacy of infusing alloNK cells with CD155 blockade to mount a GVT effect against OS and show benefits are in part through DNAM-1. Defining the hierarchy of receptors that govern alloNK responses will be critical to translating combination adoptive NK cell and immune checkpoint inhibition for patients with solid tumors treated with alloBMT.

WHAT IS ALREADY KNOWN ON THIS TOPIC: Allogeneic bone marrow transplant (alloBMT) has yet to show efficacy in treating solid tumors, such as osteosarcoma (OS). CD155 is expressed on OS and interacts with natural killer (NK) cell receptors, such as activating receptor DNAM-1 and inhibitory receptors TIGIT and CD96 and has a dominant inhibitory effect on NK cell activity. Targeting CD155 interactions on allogeneic NK cells could enhance anti-OS responses, but this has not been tested after alloBMT.

WHAT THIS STUDY ADDS: CD155 blockade enhances allogeneic natural killer cell-mediated cytotoxicity against osteosarcoma and improved overall survival and decreased tumor growth after alloBMT in an in vivo mouse model of metastatic pulmonary OS. Addition of DNAM-1 blockade abrogated CD155 blockade-enhanced allogeneic NK cell antitumor responses.

HOW THIS STUDY MIGHT AFFECT RESEARCH PRACTICE OR POLICY: These results demonstrate efficacy of allogeneic NK cells combined with CD155 blockade to mount an antitumor response against CD155-expressing OS. Translation of combination adoptive NK cell and CD155 axis modulation offers a platform for alloBMT treatment approaches for pediatric patients with relapsed and refractory solid tumors.