As evidenced by the extensive discussions following my biopsy from last Friday, a tumor is indeed a very complex structure. It comprises cancer cells and stromal cells, tumor infiltrating cells—both cells of the immune system and cells not by convention being of the immune system, as well as an extracellular matrix mainly of proteins and carbohydrates.
Following my recent CT scan, the hope from obtaining core biopsies from one of my lung nodules was to get a better sense of the cancer at a cellular level, which may help shed some light on whether or not treatment with M7824, a completely novel, first-in-class, bispecific fusion protein is working (see prior posts for more details).
In particular, the presence of immune system cells (T cells, or T lymphocytes) in tumor biopsies and their potential impact on prognosis have been studied for decades. T cells are a type of white blood cell that circulate around our bodies, scanning for cellular abnormalities and infections. Broadly speaking they can be divided into two different types, “killer” CD8-positive T-cells and “helper” CD4-positive T-cells. CD8-positive T cells are critical mediators of adaptive immunity. They include cytotoxic T cells, which are important for killing cancerous or virally infected cells, and CD8-positive suppressor T cells, which restrain certain types of immune response.
Despite contributions by other immune cell subsets, CD8-positive T cells have emerged as the predominant effector in most cancer immunotherapy settings¹. Accordingly, many immunotherapeutic strategies (including checkpoint inhibitors, such as anti-CTLA4, PD1, and PD-L1 antibodies) are dedicated to stimulating, enhancing and maintaining responses by tumor-reactive CD8-positive T-cells.
Favorable outcomes have been demonstrated in patients where high numbers of CD8-positive cells were found at the tumor site in patients with head and neck cancer, breast, colorectal cancer and also for others solid cancers. In one study, head and neck cancer patients whose tumors were densely infiltrated by CD3-positive and CD8-positive T cells had a significantly longer overall survival (OS) and progression-free survival (PFS) compared with patients whose tumors were poorly infiltrated².
While there seems to be a consensus that CD8 infiltration is a good prognostic marker in most malignancies analyzed, however, the impact of CD8-positive T cells on clinical outcome may differ and is difficult to quantify. Not only is the type of T cell important, but also its location, and moreover the specific phenotype and function of those cells in the particular environment.
Nonetheless, based on the preliminary results from my recent tumor biopsy and other factors, it appears that there is sufficient evidence of immune system activation in the vicinity of the tumor to indicate that the experimental agent M7824 may indeed be performing as we hoped. Accordingly, I am in 100% agreement with my doctor’s recommendation to continue on the therapy and will receive my next infusion this coming Tuesday at NIH. After a few more cycles of therapy, another CT scan will be taken in the future with the hope of demonstrating that the recent tumor growth was from treatment effect “pseudo-progression” rather than true disease progression, which has been previously described with immune checkpoint inhibitors like M7824.
¹ Targeting CD8+ T-cell tolerance for cancer immunotherapy. Stephanie R Jackson, Jinyun Yuan, and Ryan M Teague. Immunotherapy. 2014 Jul; 6(7): 833–852.
² Tumour-infiltrating lymphocytes predict response to definitive chemoradiotherapy in head and neck cancer. P Balermpas, Y Michel, J Wagenblast, O Seitz, C Weiss, F Rödel, C Rödel and E Fokas. British Journal of Cancer (2014) 110, 501–509. doi:10.1038/bjc.2013.640