VC TILs may have higher stem-like property than CC TILs
A recent study found that tumor-infiltrating CD8+ T cells can be divided into two functionally distinct subgroups: a terminally differentiated group marked by high expression of immune-checkpoint molecules such as PD-1 and TIM-3, and a stem-like group with low checkpoints but high TCF1 and CD28 expression(19). PD-1 (programmed death receptor 1, also known as CD279) is a co-inhibitory receptor restraining T cell function and anti-tumor response, thus considered as a marker of T cell exhaustion(20). TCF1 is a key transcription factor in stem cell-like T cells, and it plays a critical role in sustaining immune response to tumor and chronic virus infection(21, 22). To better characterize the functional profile of TILs after the REP process, we analyzed the expression of PD-1 and TCF1 in VC and CC TILs. The percentage of PD-1 positive CD4+ and CD8+ T cells in CC TILs is only around 10%, but it is even lower in VC TILs (Figure 4A). Almost 100% of CD8+ VC TILs is TCF1+, which is significantly higher than that in CC TILs (Figure 4B), indicating that VC TILs may possess a stronger stem-like property and, thus, a better potential to amplify and survive in vivo than CC TILs. We further examined the memory phenotype of VC and CC TILs by CD45RA and CCR7 staining and found that VC TILs have a higher percentage of naïve and central memory T cells (Tcm) (Figure 4C) and a lower percentage of effector memory and effector memory RA T cells (Tem and TemRA) (Figure 4D) than CC TILs, especially in CD4+ T cells, which is consistent with the higher stem-like phenotype of VC TILs.
In addition, we profiled our TIL samples by CD103 and CD39 staining as CD103+CD39+ tumor-infiltrating CD8+ T cells that may represent tumor-reactive cells in solid tumors and are associated with better overall survival(23). We observed that 6/10 of CC TIL samples and 2/4 of VC TIL samples have more than 20% CD8+ T cells showing CD103 and CD39 double positivity, but this ratio is low in CD4+ T cells (Figure 4E).