Dr Leo Carlin - Leukocyte Dynamics


Carlin head

Paradoxically, the immune system can both benefit and antagonise the growth of cancer. Therefore, understanding how the cells of the immune system interact with the cancer microenvironment is of crucial importance. In their updated seminal review 'Hallmarks of Cancer: The Next Generation', Hanahan and Weinberg underline the importance of 'Avoiding immune destruction' and 'Tumour-promoting inflammation' to cancer biology. The immune cell compartment of cancer is composed of tissue resident immune cells and leukocytes that infiltrate from the circulation. The development of the cancer immune environment is inherently dynamic and the processes that regulate immune cell recruitment and function are not well understood. In recent years, the field has discovered that immune cells play roles in initiation of primary tumours, tumour maintenance and growth, and in aiding cancer metastasis. Recent success in directing and strengthening the immune system's anti-cancer functions (e.g. Tumour Infiltrating Lymphocyte; TIL therapy and immune check-point inhibition) highlight the potential for new therapies that can come from better understanding of how leukocytes are (dys)regulated in inflammation and cancer. However, current tumour immunotherapy strategies do not work for all patients or cancers.

Left: 3D imaging of lung adenocarcinoma. Tumour (green), large blood vessels (red), bronchioles (magenta), perivascular space (yellow). Right: neutrophils in the vasculature of the lung

 Carlin image 2018 Neutrophils

We aim to better understand the immune system's role at the sites of primary tumour development and at the sites of cancer metastasis. All tumours have some influence on the local vasculature, either modifying it to meet their own needs or using it as a route to spread throughout the body. This has important consequences for our understanding of how the cells of the immune interact with the vasculature. Since it was first studied by microscopy more than 120 years ago, leukocyte extravasation has been refined in molecular detail in the post-capillary vessels, the major sites of immune cell infiltration in many (but, importantly, not all) anatomic sites. The way that leukocytes interact with the specialised vasculature of the lung, spleen, bone marrow, tumour co-opted vasculature and tumour neovasculature are relatively understudied often due to the technical difficulties of imaging some of these vascular beds. Due to the heterogeneity of the vasculature, these are exactly the areas that are least likely to fit the paradigms of leukocyte adhesion and transmigration established in the post-capillary venules. More recently, several innovative techniques have been developed to address these specialised sites by microscopy. This has helped to further investigate mechanisms of immune cell regulation, e.g. showing how immune cells interact with each other at sites of infection or injury to allow fine-tuning of the immune response and a greater portfolio of immune functions to be achieved. Therefore, a thorough examination of the localisation and regulation of leukocytes in situ is a clear unmet need to understand the fundamental mechanisms underlying onco-immunology.

We use advanced light microscopy in combination with other experimental approaches (flow cytometry, proteomics, transcriptomics) to better understand how the regulation of leukocyte dynamics contributes to the tumour environment in the context of both 'avoiding immune-destruction' and 'tumour-promoting inflammation'. Recent data point to multiple levels of immune regulation in cancer development and progression that parallel or redirect pathways that also mediate immune cell homeostasis and inflammation. Our overarching goal is to better understand how cancer evades and exploits the fundamental mechanisms of immune regulation and use this information to uncover new or better therapeutic strategies.

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