256 The TIGIT/CD226/CD155 axis and the effects of combining PD-1/PD-L1 blockade with TIGIT-targeting antibody therapy in syngeneic murine glioblastoma models

Background

Recently, TIGIT+PD1 blockade was shown to confer additive survival benefits in orthotopic glioblastoma and colon cancer mouse models^{1 2}—notably, this included experiments³ that used the 1G9 TIGIT monoclonal antibody (mAb) that has potentially agonistic effects.¹ Herein we investigated the TIGIT/CD226/CD155 axis and effects of combining clinically analogous PD-1/PD-L1 mAbs with TIGIT-targeting 1G9 mAb in murine glioblastoma models.

Methods

The overall survival (OS) associated with TIGIT (non-depleting IG9; 200μg every 3days for 4 doses),¹ PD-1 (8H3; initial 500μg followed by 250μg every 3days for 7 doses), PD-L1 (6A2; initial 500μg followed by 250μg every 3days for 7 doses), and/or IgG mAbs was assessed in immunocompetent C57BL/6 albino mice intracranially implanted with syngeneic GL261-luc2 or CT2A-luc.^{4 5} The roles of T cells and NK cells were examined using depletion with CD8a, CD4, or NK1.1 mAbs. Expression of TIGIT/CD226/CD155 and PD-1/PD-L1/PD-L2 by tumor and tumor-infiltrating immune cells was evaluated using flow cytometry and RT-qPCR.

Results

In vitro, GL261-luc2 and CT2A-luc tumor cells moderately expressed PD-L1, PD-1, and TIGIT; but strongly expressed TIGIT’s inhibitory ligand CD155.(Figure1A-B) Ex vivo, >83% of CD8+ and CD4+TILs in GL261-luc2 co-expressed TIGIT+/CD226+: ≥2x the proportions in CT2A-luc.(Figure 2A) CD155 and PD-L1 were highly co-expressed on tumor-infiltrating macrophages: greater in GL261-luc2 than CT2A-luc tumors.(Figure 2B)In GL261-luc2 mice, anti-TIGIT monotherapy displayed minimal OS improvement; whereas anti-PD-1 and anti-PD-L1 monotherapies demonstrated robust OS responses.(Figure 3A) Adding anti-TIGIT to PD-1/PD-L1 blockade demonstrated synergism with anti-PD-1. Anti-TIGIT plus anti-PD-1 displayed nominally improved OS in CT2A-luc compared to anti-PD-1 monotherapy (p=0.11).(Figure 3B).Given robust T-cell expression of TIGIT and PD-1, we examined how CD4+ or CD8+ depletion affected responses in GL261-luc2 mice: depletion completely abrogated anti-PD-1’s benefits.(Figure 4) Although CD4/CD8 depletion also reduced anti-TIGIT+anti-PD1’s efficacy, the resulting OS matched that of non-depleted anti-PD-1 monotherapy. Additionally, NK cell depletion had no effect on anti-TIGIT+anti-PD1’s efficacy.

Conclusions

Our results recapitulate published findings regarding the synergistic benefits of combining TIGIT 1G9 mAb with anti-PD-1 using the clinically-relevant 8H3 mAb in syngeneic mouse glioblastoma, and extend those findings to anti-TIGIT+anti-PDL1 combinations. TIGIT/CD226 was highly co-expressed by immuno-responsive GL261-luc2’s tumor-infiltrating lymphocytes (TILs); wheres CD155/PD-L1 expression predominated in tumor-infiltrating myeloid cells. Depletion of CD8+ or CD4+ TILs modestly reduced anti-TIGIT+anti-PD1’s efficacy—suggesting a mechanism that is at least partially independent of T (and NK) cells. Our preliminary results suggest a complex interplay between TIGIT/CD226/CD155 and PD-1/PD-L1/PD-L2 axes in tumors and their microenvironmental constituents that warrants further investigation; plus, careful consideration of antibody clones’ functionality is necessary for designing immunotherapy combinations.

Acknowledgements

We gratefully acknowledge the support of the The Jennifer Oppenheimer Cancer Research Initiative; The Ben and Catherine Ivy Foundation; Hope It’s A Beach Thing; and the Pan Mass Challenge (Erica’s Entourage and CRUS11TOUR), and the NCI (P01CA236749; K12CA090354).

References

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