Background: Previous data on the relationship between PD-L1 expression and activity of anti-PD-1 and anti-PD-L1 antibodies have been conflicting. MK-3475, a humanized monoclonal IgG4 antibody against PD-1, has demonstrated durable antitumor activity in MEL and NSCLC. We evaluated tumor PD-L1 expression and its relationship with outcomes in a phase I clinical trial of MK-3475. We also evaluated T cell activation as a pharmacodynamic marker of MK-3475 activity.

Methods: 135 MEL pts received MK-3475 10 mg/kg Q2W, 10 mg/kg Q3W, or 2 mg/kg Q3W. Tumor response was assessed by RECIST 1.1 per independent central review, including requirement for a confirmatory CT scan. Pretreatment biopsy was required. Serial blood samples were collected before infusion at the start of cycles 1-5 (Q2W dosing) or 1-4 (Q3W dosing). Tumor PD-L1 expression was assessed by IHC. A preliminary cutoff of 1% of stained cells was used to define PD-L1 positivity. Absolute CD4+ and CD8+ T cell counts and the percentage of activated (HLA-DR as marker) CD4+ and CD8+ T cells in peripheral blood were assessed by multiplex flow cytometry (n = 101).

Results: Median PFS was 36 weeks, 6-month overall survival (OS) rate was 89%, and 12-month OS rate was 81%. Median duration of response and OS were not reached. In the 116 pts with measurable disease, ORR was 41%. PFS and response rate were significantly associated with tumor PD-L1 expression (Table). At week 6, a statistically significant percent increase from baseline in the percentage of activated (HLA-DR+) CD4+ and CD8+ T cells was observed at all doses (pooled mean percent change [SE], +24.0% [4.7%] for HLA-DR+/CD8+, +17.5% [2.7%] for HLA-DR+/CD4+).

Conclusions: Tumor PD-L1 expression levels were associated with tumor response and PFS in MEL pts treated with MK-3475; activity was also observed in pts with low PD-L1 expression. As assessed by HLA-DR expression, post-treatment T cell activation in the circulating pool was increased at all doses tested.

 Patients WithMeasurable Disease and Interpretable PD-L1 IHC Results Patients With InterpretablePD-L1 IHC Results and PFS and OS Data 
PD-L1 TumorExpression ORR, n (%) PFS at 6 months, % (95% CI) Median PFS OS at 6 months, % (95% CI) Median OS 
Positive (membrane staining in ≥1% of cells) 55 29 (53) 60 58 (47-72) 10.6 mo 93(87-100) Not reached 
Negative (membrane staining in <1% of cells) 16 1* (6) 22 32 (16-64) 2.9 mo 75(58-97) Not reached 
HR (95% CI) for PD-L1-positive vs negative 0.54(0.28-1.05) 0.67(0.25-1.83) 
One-sidedP value(PD-L1 association test) <0.004 (logistic regression) 0.034(Cox regression) 0.220(Cox regression) 
 Patients WithMeasurable Disease and Interpretable PD-L1 IHC Results Patients With InterpretablePD-L1 IHC Results and PFS and OS Data 
PD-L1 TumorExpression ORR, n (%) PFS at 6 months, % (95% CI) Median PFS OS at 6 months, % (95% CI) Median OS 
Positive (membrane staining in ≥1% of cells) 55 29 (53) 60 58 (47-72) 10.6 mo 93(87-100) Not reached 
Negative (membrane staining in <1% of cells) 16 1* (6) 22 32 (16-64) 2.9 mo 75(58-97) Not reached 
HR (95% CI) for PD-L1-positive vs negative 0.54(0.28-1.05) 0.67(0.25-1.83) 
One-sidedP value(PD-L1 association test) <0.004 (logistic regression) 0.034(Cox regression) 0.220(Cox regression) 

*IPI-pretreated patient who received MK-3475 10 mg/kg Q2W.

Citation Format: Adil I. Daud, Omid Hamid, Antoni Ribas, F. Stephen Hodi, Wen-Jen Hwu, Richard Kefford, Jedd Wolchok, Peter Hersey, Jeffrey S. Weber, Richard Joseph, Tara C. Gangadhar, Roxana S. Dronca, Amita Patnaik, Hassane Zarour, Anthony M. Joshua, Kevin Gergich, Dianna Wu, Jared K. Lunceford, Kenneth Emancipator, Marisa Dolled-Filhart, Nicole Li, Scot Ebbinghaus, S. Peter Kang, Caroline Robert. Antitumor activity of the anti-PD-1 monoclonal antibody MK-3475 in melanoma(MEL): Correlation of tumor PD-L1 expression with outcome. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT104. doi:10.1158/1538-7445.AM2014-CT104