Table 1.
Pre-treatment virus-specific B and T cell reactivities in 17 patients with MCPyV-positive MCC receiving pembrolizumab
| Patient no. | Antibodies to small T-antigena | MCPyV tetramer analysisb | MCPyV intracellular cytokine reactivityc | Response assessed by RECIST 1.1d |
|---|---|---|---|---|
| 3 | + | + | – | CR |
| 7 | + | + | – | CR |
| 8 | + | + | + | PR |
| 6 | + | + | – | PR |
| 9 | + | + | – | PD |
| 16 | + | + | – | PR |
| 12 | + | – | – | PR |
| 21 | + | – | – | CR |
| 19 | + | – | + | PD |
| 4 | + | N/A | – | PR |
| 13 | + | N/A | – | PR |
| 26 | + | N/A | – | PR |
| 23 | + | N/A | – | PD |
| 15 | + | N/A | – | PD |
| 25 | + | N/A | – | PR |
| 14 | – | N/A | – | CR |
| 10 | – | – | + | PR |
a Baseline serum samples from all patients were used to measure MCPyV small T-antigen oncoprotein antibody titers at Laboratory Medicine (University of Washington, Seattle, WA) as described [6]. Titers above 74 STU were considered positive as negative control sera titers fall below 74 STU [7]
b All patients were low-resolution HLA class I genotyped to determine eligibility for CD8 T cell specific MCPyV peptide-HLA class I tetramer screening (Bloodworks Northwest, Seattle, WA). Pre- and post-treatment peripheral blood mononuclear cells (PBMCs) collected from patients with HLA class I types that corresponded to available MCPyV-specific tetramers (A*02:01, A*24:02, B*07:02, B*35:02, or B*37:01; n = 17 patients) were stained with appropriate tetramers and analyzed by flow cytometry. Samples with > 0.01% of CD8+ T cells co-staining with tetramers were considered positive. N/A (Not Available): nine patients, regardless of tumor viral status, had HLA class I types not amenable to tetramer staining and could thus not be evaluated for the presence of T cells recognizing MCPyV
c PBMCs pre-treatment and post-treatment blood collections (week 12 or 21) were stimulated with pools of MCPyV-specific peptides in a flow cytometry-based intracellular cytokine secretion assay (HIV Vaccine Trials Network, Seattle, WA). PBMCs that secreted interferon-gamma and/or IL-2 robustly (≥0.1% of CD8 T cells after background subtraction) were considered reactive to MCPyV
d Abbreviations for RECIST 1.1 response criteria are as follows: CR complete response, PR partial response, PD progressive disease