Abstract A031: Cancer vaccine formulation dictates synergy with CTLA-4 and PD-L1 checkpoint blockade therapy
Authors: Hailemichael Yared , Fu Tihui , Woods Amber , Roszik Jason , Schluns Kimberly S. , Engelhard Victor H. , Sharma Padmanee , Overwijk Willem W. 
Published: November 2016

Introduction: Therapeutic blockade of the T cell checkpoint receptors, CTLA-4 and PD-1, can cure some patients with metastatic cancer. Primary resistance to checkpoint blockade therapy is likely due to insufficient spontaneous anti-tumor immunity, and might be overcome by tumor-specific vaccination. However, the same 676-patient landmark study1 that led to FDA approval of anti-CTLA-4 for patients with melanoma showed no added benefit to anti-CTLA-4 monotherapy of concurrent vaccination with gp100 peptide in Incomplete Freund's Adjuvant (IFA), which instead significantly decreased overall response rate and disease control rate through an unknown mechanism1.

Experimental Procedure: To understand the parameters that control synergy between checkpoint blockade and anti-cancer vaccination, we modelled vaccination with gp100 peptide in IFA and anti-CTLA-4 therapy in the standard treatment model of established subcutaneous B16 melanoma2. To correct for the fact that B16 melanoma progresses so rapidly that there is no time for multiple cycles of gp100 vaccination as was given to the melanoma patients, we adoptively transferred naive TCR-transgenic pmel-1 CD8+ T cells that specifically recognize the hgp10025-33 epitope.

Results: Paralleling what was observed in patients1, gp100/IFA vaccination did not enhance, but significantly decreased, the therapeutic efficacy of anti-CTLA-4 therapy, even though we found high levels of gp100-specific pmel-1 T cells in the circulation. Anti-CTLA-4 monotherapy increased intratumoral localization of Tyrosinase-related protein-2 (TRP-2), p15E and gp100 melanoma antigen-specific CD8+ effector T cells (Teff), while gp100/IFA vaccination-induced, gp100-specific CD8+ Teff accumulated at the inflamed vaccination site. Combination of gp100/IFA vaccination and anti-CTLA-4 therapy caused TRP-2, p15E and gp100-specific Teff to similarly redistribute to the gp100/IFA vaccination site and away from the tumor site. This T cell redistribution was accompanied by reduced tumor control and was mediated by IFN-γ, CXCR3 and ICAM-1. At vaccination sites, ICAM-1 and VCAM-1 expression lacked clear association with the vasculature, and instead was abundant on SSChiCD11bhiLy6GloLy6ChiF4-80+CCR2+ (inflammatory) monocytes. Inflammatory monocytes infiltrating were accompanied by CD8+ Teff recruitment; and, conversely, when CD8+ Teff level were low so were inflammatory monocytes, indicating CCR2/CXCR3 positive feedback loop between CD8+ Teff and inflammatory monocytes resulting in their accumulation at the vaccination site, and consequent local skin inflammation. Non-persistent vaccine formulations do not induce these undesirable effects and potently synergize with anti-CTLA-4 and anti-PD-L1 checkpoint blockade, resulting in markedly increased anti-tumor activity. In a challenging setting of 7-day established tumors where dual checkpoint blockade cured only 10% of the mice, addition of non-persistent Vesicular Stomatitis Virus encoding gp100 (VSV.gp100) resulted in 67% cure (p &lt; 0.0001, &gt;200d). Correspondently, dual checkpoint blockade with gp100/IFA vaccination did not cure any mice.

Conclusions: Overall, our results indicate persistent vaccine formulations can fail to increase, or even diminish, the efficacy of CTLA-4 and PD-L1 checkpoint-based cancer therapy through divergent trafficking of checkpoint blockade-induced Teff to the vaccination site. Non-persistent vaccine formulations do not induce these undesirable effects and potently synergize with anti-CTLA-4 and anti-PD-L1 checkpoint blockade, resulting in markedly increased anti-tumor activity.

1. Hodi, F.S., et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 363, 711-723 (2010).

2. Fu, T., He, Q. & Sharma, P. The ICOS/ICOSL pathway is required for optimal antitumor responses mediated by anti-CTLA-4 therapy. Cancer Res 71, 5445-5454 (2011).

Citation Format: Yared Hailemichael, Tihui Fu, Amber Woods, Jason Roszik, Kimberly S. Schluns, Victor H. Engelhard, Padmanee Sharma, Willem W. Overwijk. Cancer vaccine formulation dictates synergy with CTLA-4 and PD-L1 checkpoint blockade therapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A031.