31P - Characterization of pre-exhausted / exhausted state of CD8+ T cells in HRAS mutant head and neck carcinomas (HNSCCs). Implications for response to immune checkpoint blockade (ICB).

Background

HRAS mutations have been found in 6% of HNSCCs. T cell exhaustion, defined as dysfunctional T cells stimulated by continuous antigen exposure. To guide immunotherapeutic approaches, we sought to assess the immune landscape of HRAS-mutant tumors by investigating the subpopulations of pre-exhausted and exhausted T cells.

Methods

We found 10 cases of HRAS mutant tumors and 39 cases of HRAS wild-type (WT) tumors. We sought to characterize exhausted CD8+ T cell subpopulations by measuring the expression of T-cell Factor-1 (TCF-1) and Programmed Cell Death-1 (PD-1) in the tumor's center (C) and periphery (P). Multiplex immunohistochemistry (IHC) was performed in FFPE tissue sections using three primary antibodies (PD1-CD8-TCF1/7), followed by analysis of a manually trained algorithm in Qupath software.

Results

HRAS mutant tumors present numerically higher numbers of total immune cells both in the C and the P than HRAS-WT tumors, that reached statistical significance only in the P (5123.17/mm²vs. 3527.93/mm², p=0.002). In addition, the density of CD8+ T Cells was increased in both the C (694.10/mm² vs. 356.02/mm²) and the P (851.10/mm² vs. 333.30/mm2) in HRAS mutant tumors. Importantly, the percentage of pre-exhausted CD8 (+) T Cells was elevated in the P of HRAS mutant tumors (384.67/mm²vs. 51.18/mm², p=0.040), indicating a possible association of response to ICB, since pre-exhausted T cells mediate the proliferative response to immunotherapy. On the contrary, exhausted T cells, defined as PD-1(+)TCF-1 (-) were more abundant in the C of HRAS mutant tumors compared to WT (13.77% vs. 2.67% of total CD8+ cells, p=0.022). Moreover, increased area occupied by CD11c+ dendritic cells and numbers of CD8+ T cells were found in regional lymph nodes from HRAS mutant patients (79.25% vs 38.80%, p=0.036 and 10160.43 vs 4438.28/mm², p=0.036, respectively), consistent with data showing that maintenance of TCF1 by intratumoral T cells requires continuous migration from draining lymph nodes.

Conclusions

Pre-exhausted PD-1(+)TCF-1(+) T cells are significantly increased at the periphery of HRAS mutant tumors, suggesting a potential sensitivity of these tumors to ICB.

Legal entity responsible for the study

The authors.

Funding

Kura Oncology.

Disclosure

All authors have declared no conflicts of interest.