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Xin Zhao:
Exploration of Intratumor Heterogeneity and Tumoral Microenvironment in Non-small Cell Lung Cancer

Date: 01-11-2021    Supervisor: Karsten Kristiansen



Lung cancer has been a leading cause of all malignant tumour death around the world. The incidence of non-small cell lung cancer  (NSCLC), the major pathological subtype, has gradually increased in recent years. This spawned a series of new treatments and novel drugs. Targeted therapy and immunotherapy are progressively becoming the main approach to treatment or adjuvant therapy in the clinic of NSCLC patients. However, the drug responses are inadequate to a subset of patients. Although previous studies revealed that the  heterogeneity of tumour regions would be the pivotal reason for limited therapeutic effectiveness, the overall heterogeneous levels and interactive functional role of the tumour microenvironment are incompletely understood. It is critically needed to identify the heterogeneous patterns deeply and pervasively and elucidate the crucial features of the tumour immune environment related to the response of clinical treatment in NSCLC.

Therefore, this study focused on patients with early-stage NSCLC and used multiple omics techniques to explore the features of intratumor heterogeneity (ITH) and tumoral microenvironment (TME). It was divided into two sections. Section I focused on the ITH of genomic instability, differences of the intratumor immune microenvironment, and their variability in clinically relevant outcomes. Section II aimed at the similarities and differences of genomic instability between tumour and peritumoral tissues, the formation of TME, and their contribution to tumour evolution of pathogenic clone metastasis to lymph nodes. The findings corroborated that ITH extensively existed in lung  adenocarcinoma with or without EGFR mutations. The SNV-ITH level was higher in EGFRMT patients, and the two main subtypes of EGFR mutation exhibited a completely different spectrum of co-drivers and evolutionary trajectories. EGFR19DEL patients might have a relatively homogeneous origin in the early tumorigenesis. In addition, EGFRMT LUAD harboured significantly more M2 macrophage infiltration and fewer CD8+T cell infiltration, probably regulated via upregulating cytokines and chemokines for macrophages recruitment and polarization. The complex heterogeneity of the immunosuppressive microenvironment featured by the coexistence state of M2 macrophages and CD8+ T cells was most probably related to poor prognosis in EGFRMT patients. In section II, I did observe heterogeneity at the genomic level in the tumour and peritumoral region in NSCLC.

More tumour-related mutations were identified in the peritumoral region, which was associated with lymph node metastasis. The proportion of M2 macrophages in the tumour region was significantly lower than in the peritumoral and the adjacent normal region in NSCLC patients
who did not suffer lymph node metastasis.

This indicated that NSCLC patients without lymph node metastasis have higher immune cytotoxic activity in their tumour regions.  Spatial transcriptome evaluation highlighted the localization of M2 macrophage and tertiary lymphoidlike structure (TLS-like) in tumour regions. The location of M2 macrophage invasion may be closely related to lymph node metastasis. The TLS-like structures, located in the invasive margin area, were influenced by the nearby complex cellular environment promoting tumour lymph nodes metastasis in NSCLC.

Taken together, my study presents an essential line of tumour heterogeneity investigation moving forward to the predominant subtypes of NSCLC patients. These findings provide insights into intratumor heterogeneity and immune environments with implications for the
direction of EGFR-TKI therapy and immunotherapy in EGFRMT patients, also evaluation of lymph node metastases or not in NSCLC. It envisaged providing potential therapeutic targets and biomarkers of patients’ stratification for NSCLC precision treatment and prognosis prediction in the future.