Clinical and molecular characteristics associated with response to therapeutic PD-1/PD-L1 inhibition in advanced Merkel cell carcinoma

Abstract

Background: Based on its viral-associated or UV-associated carcinogenesis, Merkel cell carcinoma (MCC) is a highly immunogenic skin cancer. Thus, clinically evident MCC occurs either in immuno-compromised patients or based on tumor-intrinsic immune escape mechanisms. This notion may explain that although advanced MCC can be effectively restrained by treatment with PD-1/PD-L1 immune checkpoint inhibitors (ICIs), a considerable percentage of patients does not benefit from ICI therapy. Biomarkers predicting ICI treatment response are currently not available.

Methods: The present multicenter retrospective study investigated clinical and molecular characteristics in 114 patients with unresectable MCC at baseline before treatment with ICI for their association with therapy response (best overall response, BOR). In a subset of 21 patients, pretreatment tumor tissue was analyzed for activation, differentiation and spatial distribution of tumor infiltrating lymphocytes (TIL).

Results: Of the 114 patients, n=74 (65%) achieved disease control (BOR=complete response/partial response/stable disease) on ICI. A Bayesian cumulative ordinal regression model revealed absence of immunosuppression and a limited number of tumor-involved organ systems was highly associated with a favorable therapy response. Unimpaired overall performance status, high age, normal serum lactate dehydrogenase and normal serum C reactive protein were moderately associated with disease control. While neither tumor Merkel cell polyomavirus nor tumor PD-L1 status showed a correlation with therapy response, treatment with anti-PD-1 antibodies was associated with a higher probability of disease control than treatment with anti-PD-L1 antibodies. Multiplexed immunohistochemistry demonstrated the predominance of CD8⁺ effector and central memory T cells (T_CM) in close proximity to tumor cells in patients with a favorable therapy response.

Conclusions: Our findings indicate the absence of immunosuppression, a limited number of tumor-affected organs, and a predominance of CD8⁺ T_CM among TIL, as baseline parameters associated with a favorable response to PD-1/PD-L1 ICI therapy of advanced MCC. These factors should be considered when making treatment decisions in MCC patients.

Keywords: costimulatory and inhibitory T-cell receptors; immunotherapy; lymphocytes; skin neoplasms; translational medical research; tumor-Infiltrating.

Figure 1

Response of n=114 advanced MCC patients on PD-1/PD-L1 immune checkpoint inhibition therapy. Waterfall plot depicting the best overall response (BOR) as change in the sum of the longest diameters of target lesions from baseline to BOR. Each bar, color coded by therapeutic antibody, represents an individual patient. The pointed vertical line discriminates patients with disease control (BOR=CR/PR/SD) from patients with disease progression (BOR=PD). CR, complete response; MCC, Merkel cell carcinoma; PD, progressive disease; PR, partial response; SD, stable disease.

Figure 2

Best overall response (BOR) to anti-PD-1/PD-L1 therapy in correlation to baseline clinical patient and tumor characteristics. The correlations are visualized by average predictive comparisons calculated by a Bayesian cumulative ordinal regression model. While the presented data refer to the full model using four categories of response: CR, PR, SD, and PD, to ease interpretation we mapped the obtained results by average predictive comparisons on a single probability scale for disease control (BOR=CR/PR/SD) and disease progression (BOR=PD) as a probability distribution, given as the percentage of average predictive comparison. The 95% credibility intervals are colored in light blue. Distinct parameters are marked as reference (Ref), described as vertical blue lines set at 0% average predictive comparison. CR, complete response; CRP, C reactive protein; ECOG, Eastern Cooperative Oncology Group; LDH, lactate dehydrogenase; MCPyV, Merkel cell polyomavirus; NLR, neutrophil to lymphocyte ratio; PD, progressive disease; PR, partial response; SD, stable disease.

Figure 3

High density of tumor-infiltrating CD8⁺ central memory T cells in close proximity to tumor cells in MCC patients showing disease control (CR/PR/SD) on PD-1/PD-L1 ICI phenotyping of the cellular immune infiltrate present in MCC tumor lesions obtained at baseline of ICI therapy of a representative patient responding with disease control (A) and disease progression (B) was done by multiplexed immunohistochemistry-based staining using antibodies against CD4 (green), CD8 (yellow), CD20 (red), FOXP3 (orange), CD68 (magenta), and the MCC marker synaptophysin (SYN) (cyan); nuclei are stained with DAPI (blue). depicted are merged images at ×20 magnification. (C) Percentage of CD8⁺ T cells in pretreatment tumor tissue from patients showing disease control and those showing disease progression in the juxtatumoral and intratumoral area. P values were determined using beta regression. (D) Measurement of the distance between CD8⁺ T cells and tumor cells. (E) Mean value of the distance between CD8⁺ T cells and tumor cells for patients showing disease control and those showing disease progression. P values were determined using unpaired, two-tailed Student’s t-test. CR, complete response; ICI, immune checkpoint inhibitor; MCC, Merkel cell carcinoma; PR, partial response; SD, stable disease.

Figure 4

Predominance of central memory T cells (T_CM) among tumor-infiltrating lymphocytes of patients showing disease control (CR/PR/SD) on PD-1/PD-L1 ICI therapy. Multiplexed immunofluorescence staining of pretreatment tumor tissue from a representative patient showing disease control (A) and disease progression (B) using antibodies against CD27 (green), GZMB (yellow), TCF1 (red), CD45RA (orange), CD45RO (magenta), and the MCC marker synaptophysin (SYN) (cyan); nuclei are stained with DAPI (blue). Depicted are merged images at ×20 magnification. To visualize the colocalization of CD27, TCF1 and CD45RO, an enlarged image view is shown. CR, complete response; ICI, immune checkpoint inhibitor; MCC, Merkel cell carcinoma; PR, partial response; SD, stable disease.

Figure 5

Schematic overview on relevant clinical and molecular parameters determined before treatment and their predictive value on PD-1/PD-L1 ICI therapy response. CRP, C reactive protein; ECOG, Eastern Cooperative Oncology Group; ICI, immune checkpoint inhibitor; LDH, lactate dehydrogenase.