INTERACTION MECHANISMS BETWEEN SMALL CELL LUNG CANCER CELLS AND T LYMPHOCYTES
KURŞUNEL, MUAMMER ALPER
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Tumors are capable of reshaping their microenvironment to escape from immune destruction. For this purpose, tumor cells initiate an immune regulatory program that is typically used by the normal cells to mitigate immunopathologies. Small cell lung cancer (SCLC) is associated with aggressive tumor growth together with a tendency to early dissemination and distant metastasis. Optimal drug responses are observed upon conventional chemotherapies; yet, inevitable therapy resistance develops shortly after. These facets of SCLC bring forward the cancer stem cell concept. Recent studies described the candidate stem cell populations of SCLC. Although mesenchymal or cancer stem cells are stated to be immune-tolerogenic, less is known how SCLC stem cells interact with immune cells. Thus, the aim of the study is to define the relationship between T cells and SCLC including its stem cell population and reveal their immunomodulatory capacities. SCLC cell lines (NCI-H82, NCI-H69, SCLC-21) which grow in suspension, stem cell-like adherent subclones isolated from NCI-H82 and NCI-H69, and CD44+CD90+ subpopulation from the adherent subclone of NCI-H69 were used. As an in vitro model, cancer stem cell (CSC) characteristics were confirmed by chondrocyte, osteocyte and adipocyte differentiation, tumor initiation and transcriptomics. PBMCs obtained from healthy volunteers were co-cultured with these subclones of SCLC cells in the presence of α-CD3 mAb and expression of activation markers, proliferation rate, cytokine production, and upregulation of co-inhibitory receptors were determined on T cells. PD-L1 and PD-L2 expression were measured on SCLC cells upon IFN-γ exposure or PBMC co-culture with or without IFN-γ blockade. The impact of PD-L1 expression on CD8+ T cell proliferation and T cell killing of SCLC cells were determined. Functional capacity of TIM-3+LAG3+ and TIM-3-LAG3- CD8+T cells upon SCLC co-culture was assessed in vitro. SCLC cells allowed or even supported T cell responses more prominently by stem-like SCLC cells. Furthermore, stem-like SCLC cells displayed adaptive resistance features by inducing PD-L1 and PD-L2 upon exposure to IFN-γ and activated PBMCs. However, the presence of PD-L1 on these cells was not leaded to decreased proliferation of CTLs and resistance against T cell-mediated killing. Alternatively, upregulation of co-inhibitory receptors indicated that T cells became prone to inhibitory signals; thus, more sensitive to immune suppression in the presence of SCLC cells. To summarize, the stem-like SCLC subclones possess significant immune regulatory capacities by upregulating co-inhibitory molecules in the microenvironment which could be important for immune modulation in SCLC tumors which have implications for future immunotherapeutic approaches.