The heterogeneity of tumor-infiltrating CD8+ T cells in metastatic melanoma distorts their quantification: how to manage heterogeneity?

Abstract

CD8 T-cell infiltration of metastatic melanoma may be a useful biomarker for prediction of prognosis and response to therapy. The heterogeneous distribution of CD8 T cells within a single tumor, and across different tumors within a single patient, may complicate quantification of infiltration. However, the impact of heterogeneity has not been quantified sufficiently. To address this, we have assessed intratumoral heterogeneity of CD8 T-cell counts, as well as intertumoral heterogeneity for synchronous and metachronous metastases. In a tissue microarray containing 189 melanoma metastases from 147 patients, the density of CD8 T cells per sample was determined by immunohistochemistry. The mean density and coefficient of variation were calculated for each tumor and the rates of discordant values were determined. CD8 counts varied widely among different core samples of the same tumors (average coefficient of variation=0.77, 95% confidence interval: 0.70-0.85), with discordance occurring in 40% of tumors. CD8 densities were similar among pairs of simultaneous tumors; however, significant changes in CD8 densities were observed among 35 pairs of metachronous tumors. CD8 T-cell density is not well represented by a single 1 mm diameter sample. Differences in CD8 T-cell counts, observed in clinical trials, from pretreatment to post-treatment specimens may be explained by the spatial and temporal heterogeneity of CD8 distribution, especially if the assessed samples are small (i.e. 1 mm). A sufficiently large biopsy of one of several synchronous tumors may be representative of CD8 T-cell infiltration of a patient's disease.

The COX2 Effector Microsomal PGE2 Synthase 1 is a Regulator of Immunosuppression in Cutaneous Melanoma

“…S6). The presence of CD8þ T cells in melanoma is correlated with a positive patient prognosis (32,33). Our current data provides the first evidence that mPGES1 is an important factor in regulating CD8 þ T-cell infiltration into these tumors.…”

The Link between the Multiverse of Immune Microenvironments in Metastases and the Survival of Colorectal Cancer Patients

“…Quantification of tumor-infiltrating lymphocytes in a small region of a randomly selected metastasis has previously been reported to be associated with survival (Halama et al, 2011;Katz et al, 2013;Kwak et al, 2016;Pugh et al, 2014;Tanis et al, 2015); however, the importance of analyzing the CT and IM regions of all resected metastases could be underlined by the fact that the tumor immune environment is heterogeneous. Several reports underlined the possible limitation of tumor sampling using single biopsies for patient treatment decision (Bettoni et al, 2017;Obeid et al, 2017). We show that a single biopsy accurately identifies low-infiltrated metastases, but the overall intra-metastatic immune infiltrate might be better estimated with multiple biopsies or sampling of larger tumor areas.…”

Gene expression analysis in formalin fixed paraffin embedded melanomas is associated with density of corresponding immune cells in those tissues

“…We have shown that a single core sample often misrepresents the CD8 + T cell density of the whole tumor, and that there can be significant differences in CD8 + T cell densities among pairs of metachronous tumors. However, a large biopsy of one tumor may be representative of multiple synchronous metastases 40 . Also by modeling different ways to sample a lung cancer, we found that different sampling strategies yield different densities of CD8 + infiltrate, but that the values most concordant with whole tumor counts were predicted by a random core sampling of the tumor or sampling of the tumor center 41 .…”

“…Most associations were stronger among tumors with greater than 50 immune cells per mm 2 (Immunotype B + C tumors) than among those without significant infiltrates within tumor nodules (Immunotype A tumors), which is likely explained in part by disproportionately high impact of peritumoral immune cells when tumor cell nests exclude immune cells, as is observed with Immunotype A tumors. Immune cell heterogeneity within tumors may contribute to decreased associations between gene expression analysis and IHC quantification 40 . In particular, collections of immune cells present not within the tumor itself but within tertiary lymphoid structures (TLS) on the peripheral margins of tumor 42 , 43 may have been represented by the gene expression analyses, but not by IHC of tumor cores taken from the center of tumor nodules.…”