TIGIT Expression on Activated NK Cells Correlates with Greater Anti-Tumor Activity but Promotes Functional Decline upon Lung Cancer Exposure: Implications for Adoptive Cell Therapy and TIGIT-Targeted Therapies

Treatments targeting TIGIT have gained a lot of attention due to strong preclinical and early clinical results, particularly with anti-PD-(L)1 therapeutics. However, this combination has failed to meet progression-free survival endpoints in phase III trials. Most of our understanding of TIGIT comes from studies of T cell function. Yet, this inhibitory receptor is often upregulated to the same, or higher, extent on NK cells in cancers. Studies in murine models have demonstrated that TIGIT inhibits NK cells and promotes exhaustion, with its effects on tumor control also being dependent on NK cells. However, there are limited studies assessing the role of TIGIT on the function of human NK cells (hNK), particularly in lung cancer. Most studies used NK cell lines or tested TIGIT blockade to reactivate exhausted cells obtained from cancer patients. For therapeutic advancement, a better understanding of TIGIT in the context of activated hNK cells is crucial, which is different than exhausted NK cells, and critical in the context of adoptive NK cell therapeutics that may be combined with TIGIT blockade. In this study, the effect of TIGIT blockade on the anti-tumor activities of human ex vivo-expanded NK cells was evaluated in vitro in the context of lung cancer. TIGIT expression was higher on activated and/or expanded NK cells compared to resting NK cells. More TIGIT⁺ NK cells expressed major activating receptors and exerted anti-tumor response as compared to TIGIT^- cells, indicating that NK cells with greater anti-tumor function express more TIGIT. However, long-term TIGIT engagement upon exposure to PVR⁺ tumors downregulated the cytotoxic function of expanded NK cells while the inclusion of TIGIT blockade increased cytotoxicity, restored the effector functions against PVR-positive targets, and upregulated immune inflammation-related gene sets. These combined results indicate that TIGIT blockade can preserve the activation state of NK cells during exposure to PVR⁺ tumors. These results support the notion that a functional NK cell compartment is critical for anti-tumor response and anti-TIGIT/adoptive NK cell combinations have the potential to improve outcomes.

Low-dose immunogenic chemotherapeutics promotes immune checkpoint blockade in microsatellite stability colon cancer

More than 85% of colorectal cancer (CRC) patients, who are with microsatellite stability (MSS), are resistant to immune checkpoint blockade (ICB) treatment. To overcome this resistance, combination therapy with chemotherapy is the most common choice. However, many CRC patients do not benefit more from combination therapy than chemotherapy alone. We hypothesize that severe immunosuppression, caused by chemotherapy administered at the maximum tolerated dose, antagonizes the ICB treatment. In this study, we found that low-dose oxaliplatin (OX), an immunogenic cell death (ICD)-induced drug, increased the antitumor response of TIGIT blockade against CT26 tumor, which is regarded as a MSS tumor. Combined treatment with OX and TIGIT blockade fostered CD8+ T-cell infiltration into tumors and delayed tumor progression. Importantly, only low-dose immunogenic chemotherapeutics successfully sensitized CT26 tumors to TIGIT blockade. In contrast, full-dose OX induces severe immunosuppression and impaired the efficacy of combination therapy. Further, we also found that lack of synergy between nonimmunogenic chemotherapeutics and TIGIT blockade. Consequently, this study suggests that the strategies of combination treatment of chemotherapy and ICB should be re-evaluated. The chemotherapeutics should be chosen for the potential to ICD and the dosage and regimen should be also optimized.

An engineered IL-21 with half-life extension enhances anti-tumor immunity as a monotherapy or in combination with PD-1 or TIGIT blockade

Interleukin-21 (IL-21) has exhibited anti-tumor activity in preclinical and clinical studies; however, its modest efficacy and short half-time has limited its therapeutic utility as a monotherapy. Therefore, we engineered a fusion protein (IL-21-αHSA) in which a nanobody targeting human serum albumin (HSA) was fused to the C-terminus of rhIL-21. The αHSA nanobody displayed broad species cross-reactivity and bound to a HSA epitope that does not overlap with the FcRn binding site, thus providing a strategic design for half-life extension. The IL-21-αHSA fusion protein showed increased stability compared to rhIL-21, while retaining its bioactivity in a liquid solution for at least 6 months. Moreover, IL-21-αHSA showed a dramatically extended half-life and prolonged exposure in cynomolgus monkeys, with the t_1/2 and AUC nearly 10 and 50 times greater than that of rhIL-21, respectively. Furthermore, IL-21-αHSA displayed enhanced anti-tumor efficacy in two syngeneic mouse models. Notably, IL-21-αHSA increased the anti-tumor effect of programmed cell death protein 1 (PD-1) and T cell immunoglobulin and ITIM domain (TIGIT) blockades when used in combination, with a protection against tumor rechallenge, suggesting the formation of long-term anti-tumor memory response. KEGG analysis identified significantly enriched pathways associated with anti-tumor immune response, with increased expression of genes associated with CD8⁺ T and NK cell cytotoxicity. Overall, these data support further clinical evaluation of IL-21-αHSA as a monotherapy or in combination with immune checkpoint blockades.