Form and function in intratumoral immune organization: Understanding the cellular composition of TCF1+CD8+T cell niches in human cancer

Abstract Tumor infiltrating T cells are a positive prognosticator in many tumor types, and our prior work demonstrated that in renal cell carcinoma, patients with higher CD8 T cell infiltration have improved survival (Jansen Nature 2019). We described that this T cell response is supported by TCF1+ stem-like CD8 T cells, which reside within dense regions of closely clustered antigen presenting cells within the tumor. Interestingly, aggregations of immune cells have also been described in other settings and termed ‘tertiary lymphoid structures’ (TLS), raising an important question of whether the described immune niches are similar to these TLS or if they represent a distinct type of peripheral immune organization. In the work presented here, we use quantitative immunofluorescence image analysis to examine the cellular composition and organization of intratumoral immune niches, TLS, and secondary lymphoid tissue. The novel data presented here describes how immune niches are distinct from TLS and are more similar to the organization of T cell zones in secondary lymphoid tissue. Immune niches are T cell dominant structures, with T cell and antigen presenting cell compartments similar to T cell zones, whereas these niches profoundly lack the B cell presence seen in TLS and B cell zones of secondary lymphoid tissue. Immune niches are comparatively small in size (50-200um), while TLS are much larger (often >1mm), and, importantly, immune niches are found inside the tumor border, while TLS are located peripherally in tumor tissue. Notably, we find that immune niches have a marked presence of aSMA+ stromal cells, which are similar to those found in T cell zones but absent in B cell zones and TLS. When probed by flow cytometry and RNAseq, we find that aSMA+ stroma in immune niches are myofibroblast-like, similar those known to maintain the structure of secondary lymphoid tissues, and are distinct from those found in healthy kidney tissue. These data suggest these aSMA+ cells may play an important role in the organization of immune niches in tumor tissue. As we have shown that a robust T cell response is beneficial for patient outcomes, it is crucial to understand the mechanisms which support that response. Recently, our group defined that CD8 T cell activation in cancer is comprised of two phases, with an initial priming phase in the lymph node and a second phase of effector program acquisition in the tumor tissue (Prokhnevska Immunity 2023). We suggest that these immune niches represent an important hub for this development of T cell function, which is required for the robust, effective anti-tumor T cell response that supports improved patient outcomes and is the basis for the response to immunotherapy. Advancing our understanding of intratumoral immune organization will allow for enhanced biomarker discovery, improvement in existing therapies, and innovation in developing novel therapeutic strategies that will convert immunologically “cold” tumors to be immunologically “hot” and enhance anti-tumor immunity. Citation Format: Caroline S. Jansen, BaoHan Vo, Ewelina Sobierajska, Rachel Greenwald, Patrick Mullane, Nataliya Prokhnevska, Maria Cardenas, Mehmet Asim Bilen, Adeboye O. Osunkoya, Viraj A. Master, Haydn T. Kissick. Form and function in intratumoral immune organization: Understanding the cellular composition of TCF1+ CD8+ T cell niches in human cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr B030.