Tertiary lymphoid structures in colorectal cancer - organization and immune cell interactions.

Am J Clin Exp Immunol 2024;13(6):236-245 www.ajcei.us /ISSN:2164-7712/AJCEI0155486 Review Article Tertiary lymphoid structures in colorectal cancer - organization and immune cell interactions Maya Vladova Gulubova1,2, Stefan P Valkanov3,4, Maria Magdalena K Ignatova6, Georgi A Minkov4,5 Clinics of Pathology, University Hospital “Prof. Dr. Stoyan Kirkovich”, Stara Zagora, Bulgria; 2Department of Anatomy, Histology, Embryology and Pathology, Medical Faculty, “Asen Zlatarov University Bourgas”, Bourgas, Bulgaria; 3Clinics of Neurosurgery, University Hospital “Prof. Dr. Stoyan Kirkovich”, Stara Zagora, Bulgria; 4 Department of Surgery, Medical Faculty, Trakia University, Stara Zagora, Bulgria; 5Clinics of Surgery, University Hospital “Prof. Dr. Stoyan Kirkovich”, Stara Zagora, Bulgria; 6Complex Oncology Centre, Stara Zagora, Bulgria 1 Received January 17, 2024; Accepted March 12, 2024; Epub December 25, 2024; Published December 30, 2024 Abstract: Tertiary lymphoid structures (TLS), formerly recognized as Crohn’s-like structures, serve as crucial biomarkers for evaluating the progression of colorectal cancer (CRC). Understanding their spatial distribution, cellular composition, and interactions within CRC is paramount for comprehending the immune response in the tumor microenvironment (TME). TLS are comprised of a T-cellular compartment and a B-cellular compartment, the latter encompassing follicular dendritic cells (FDCs), high endothelial venules (HEVs), and lymphatic vessels. While T helper cells predominate in cancer TLS, the specific functions of their subpopulations remain inadequately understood. Notably, T follicular helper (Tfh) cells play a central role in the activation of CD8+ T cells, and both Tfh cells and Tfhassociated genes have been linked to enhanced CRC survival. In stage II CRC TLS, an escalation in the number of FoxP3+ T regulatory cells (Tregs) is regarded as a negative prognostic factor. Moreover, within TLS, T lymphocytes shield B lymphocytes from the immunosuppressive effects of the TME. B lymphocyte activation is succeeded by class recombination (CSR) and somatic hypermutation (SHM). Dendritic cells (DCs) constitute a vital cellular component of the TLS T compartment. During steady state and early stages of CRC, specialized antigen-presenting cells such as DCs migrate to regional lymph nodes through afferent lymphatics. They deliver MHC antigen-derived peptide complexes (tumor antigens) to naïve CD4+ and CD8+ T cells, which subsequently infiltrate the tumor site as antigen-specific T cells. Key DC markers studied in TLS include CD83 and DC-LAMP. Research has indicated that the DC-LAMP gene signature in tumor TLS reflects Th1 cell targeting, cytotoxicity, and T cell activation. This review comprehensively outlines the functions performed by distinct cell subsets within tertiary lymphoid structures (TLS) in tumors. Keywords: Tertiary lymphoid structures (TLS), T helpers, B cell activation, dendritic cells, colorectal cancer Introduction Tumors develop a specific microenvironment consisting in immune cells, endothelial cells, cancer-associated stromal cells and recently found lymphocyte aggregations called tertiary lymphoid structures (TLS), that release tumorpromoting or tumor-suppressing factors in the tumor microenvironment (TME), that govern tumor development [1-3]. An immunoscore assessing different lymphocytes has been created, that together with conventional TNM staging AJCC/UICC TNM classification can lead to better determination of tumor prognosis [4, 5] and the outcome of chemotherapy, radiotherapy and immunotherapy [6, 7]. Colorectal cancer (CRC) and immune biomarkers CRC is one of the most often diagnosed worldwide [8]. The majority of patients with CRC are usually diagnosed in stage II and III of the disease. Several authors have proposed the use of new immunologic biomarkers that can give information about disease recurrence and the use of adjuvant radio- and chemotherapy [9, 10]. The immune cell infiltration has been evaluated mainly in tumor stroma (TS) and the tumor invasive front (IF) [4, 11]. In CRC the evaluation of the immune infiltrate has been associated with cancer development and prognosis [11-14]. Tumors usually establish an immunohttps://doi.org/10.62347/GRYY2849 Tertiary lymphoid structures in colorectal cancer suppressive microenvironment that inhibits effective immune responses. Classically, it has been accepted that tumor-associated antigens (TAAs) are captured and processed by dendritic cells (DCs) that migrate to regional secondary lymphoid organs (SLO) and to TLS and present them to naïve T cells in paracortex and some TAA are accepted by B cell receptor (BCR) of B cells in the cortex [6, 15, 16]. Tertiary lymphoid structures and CRC development One important immune biomarker of CRC development and prognosis is TLS formation [9, 17], previously known as Crohn’s-like structures appeared in the vicinity of the tumor [1719]. According to me and others TLS present in 78.6% of CRC and are positive prognostic factor for stage II CRC [20]. The peritumoral location of TLS in CRC has been associated with worse prognosis and cancer progression [21, 22]. In a study of large cohort of CRC patients (n=195) authors have found that higher numbers of TLS present in less advanced tumors (TNM - I+II) [23]. Increased TLS in the IF of CRC in node-negative patients are associated with better prognosis [20]. Therefore, we decided to examine the precise cellular composition of TLS, possible immune cell collaboration in TLS and to delineate the axis of DCs Ag presentation to naïve CD4 and CD8 T cells in T-zone, T follicular helper cells (Tfh) in the T zone and at the border of germinal centers (GC), and B cell activation. We try to represent in schemas the complex efforts of DCs, Tfh cells and B cells to activate CD8+ T cells and send them to the tumor area. TLS origin and formation In the recent 20 years, a new lymphoid structure has been investigated in some tumors such as bronchial cancer, CRC, gastric cancer, etc. [9] and has been called tertiary lymphoid structure. TLS has been situated closer to the tumor and mirror SLO organization and function. TLS are formed mainly at the tumor margin or in the tumor stroma [2]. Moreover, TLS are detected at sites of chronic inflammation [20] or autoimmunity [24]. The term TLS has been mentioned first in 1992 by Louis Picker and Eugene Butcher [25]. Authors call these structures extra-lymphoid sites, where lymphocyte precursors (or memory lymphocytes) are re237 stimulated by antigen. TLS are structures that arise in non-immune tissues and initiate adaptive immune response [24]. TLS contains immune cells organized as SLOs [26]. The development of SLOs is a genetically programmed process that takes place during embryogenesis. SLOs are lymph nodes (LN), white pulp of the spleen, human appendix, mucosal-associated lymphoid tissue (MALT) that includes also Payer’s patches (PP) and tonsils [27-29] (...truncated)