Combination of NKG2A and PD-1 Blockade Improves Radiotherapy Response in Radioresistant Tumors

Abstract

Radiotherapy (RT) is commonly employed to treat solid tumors. Immune checkpoint blockade of programmed cell death protein 1 (PD-1) and CTLA-4 improves survival in RT patients, yet many fail to respond to combination therapy. Natural killer group 2 (NKG2) family receptors, particularly inhibitory NKG2A and activating NKG2D, have emerged as promising therapeutic targets to improve antitumor T cell responses; thus, we examined how these receptors and their ligands (Qa-1b and retinoic acid early inducible 1 [Rae-1], respectively) regulate the RT response in C57BL/6 mice bearing syngeneic B16F10 melanoma and MC38 colorectal adenocarcinoma tumors. RT (15 Gy) transiently reduced B16F10 tumor burden, whereas MC38 tumors exhibited durable response to RT. Intratumoral NK and CD8 T cells expressed NKG2A and NKG2D in both models, which was unaltered by RT. In vitro/in vivo RT increased tumor/stromal cell Qa-1b and Rae-1 expression in both models, especially B16F10 tumors, but IFN-γ stimulation induced both Qa-1b and Rae-1 only in B16F10 tumors. NKG2A/Qa-1b inhibition alone did not improve RT response in either model, but combined RT and NKG2A/PD-1 blockade improved survival in the B16F10 model. Depletion experiments indicate that the triple therapy efficacy is CD8 T cell–dependent with negligible NK cell contribution. RNA sequencing of CD8 T cells from triple therapy–treated B16F10 tumors showed increased proliferative capacity compared with RT and PD-1 blockade alone. Our work demonstrates that RT modulates NKG2A ligand expression, which inhibits RT-induced T cell responses in tumors that fail to respond to combined RT and PD-1 blockade. These results provide a rationale for combining NKG2A blockade with immune checkpoint blockade therapies and RT to improve clinical response.

Sculpting the tumour microenvironment by combining radiotherapy and ATR inhibition for curative-intent anti-PD-L1- and anti-NKG2A-based adjuvant immunotherapy

“…We found that addition of anti-NKG2A antibody to the combination was essential to shifting the cell cycle towards the G2/M phase in T cells, which was in line with previous data showing repeated cell division in NKG2A + CD8 T cells 33 . These results are also consistent with findings of elevated proliferative capacity of CD8 T cells in response to combined RT and dual NKG2A/PD-1 blockade 34 .…”

Radiation-induced tumor immune microenvironments and potential targets for combination therapy

“…Only a triplet regimen comprising RT+NKG2A blockade+anti-PD−1 therapy improved the survival rate of B16F10 mice, although the improvement was related to T cells rather than NK cells. 199 , 202 Treating irradiated B16F10 tumors with α-CD16/α-4-1BB NPs, designed to simultaneously activate two costimulatory receptors, was shown to lead to greater tumor volume reduction than treatment with a mixture of α-CD16 NPs and α-4-1BB NPs. 201 The combination of RT and an ATR inhibitor (ATRi) increased NK cell activation and TIGIT expression in NK cells in HNSCC patients.…”

Disruption of the NKG2A:HLA-E Immune Checkpoint Axis to Enhance NK Cell Activation against Cancer

“…Ionising radiation downregulated surface HLA-E expression on melanoma cells [142], however the effect of radiation on HLA-E expression appears to be dependent on tumour type and the model investigated. For example radiation increases HLA-E surface expression in glioblastoma [44] and also Qa-1b expression in murine models of melanoma and colorectal cancer [143]. Accordingly, NKG2A blockade improves survival in combination with radiotherapy in murine models of melanoma [143].…”

“…For example radiation increases HLA-E surface expression in glioblastoma [44] and also Qa-1b expression in murine models of melanoma and colorectal cancer [143]. Accordingly, NKG2A blockade improves survival in combination with radiotherapy in murine models of melanoma [143]. In contrast, radiotherapy has also been reported to reduce the sensitivity of cancer cells to NK cell mediated lysis [144] and it is therefore important to take this into account when considering strategies which combine radiotherapy and immunotherapy in patients.…”