Table 2

Quantification of the cellular tumor infiltrate characterized by multiplex immunohistochemistry staining

Pretreatment MCC tumor tissue samples
Response to CPI		Total leucocyte no per observed area		T_CM in % of total lymphocyte no per observed area
Response to CPI		Juxtatumoral	Intratumoral	Juxtatumoral	Intratumoral
Disease control	PR	2121	731	4.7	2.2
	CR	1510	989	3.0	2.7
	CR	1813	3519	0.0	22.0
	SD	5436	9405	18.0	11.7
	PR	1902	2162	6.7	8.0
	PR	1451	97	13.0	26.7
	SD	115	283	23.0	33.0
	CR	1	14	0.0	0.0
	PR	1846	6030	0.0	11.0
	PR	1681	2080	13.0	11.7
	CR	2261	428	33.0	36.7
	Mean value	1831	2340	10.4	15.1
Disease progression	PD	NA	0	NA	0.0
	PD	44	54	0.0	0.0
	PD	1125	124	0.0	0.0
	PD	239	170	12.0	15.0
	PD	3831	2478	22.0	13.0
	PD	316	376	17.0	10.0
	PD	0	13	0.0	0.0
	PD	2438	287	3.7	0.5
	PD	403	62	2.0	1.7
	PD	159	66	0.0	0.0
	Mean value	950	363	6.3	4.0

Tumor tissue samples were obtained from MCC patients prior to the start of PD-1/PD-L1 immune checkpoint inhibitor therapy. Lymphocytes were identified based on CD45RA⁺ or CD45RO⁺ staining and the sum of both signals were used for the quantification of the total lymphocyte number per sample per observed area. T_CM were determined based on the triple CD27⁺TCF1⁺CD45RO⁺ staining.
CPI, checkpoint inhibition; CR, complete response; MCC, Merkel cell carcinoma; PD, progressive disease; PR, partial response; SD, stable disease; T_CM, central memory T-cells.