PD1 blockade is effective in a subset of patients with B-cell lymphoma (e.g., classical-Hodgkin lymphomas); however, most patients do not respond to anti-PD1 therapy. To study PD1 resistance, we used an isoform-selective histone deacetylase inhibitor (HDACi; OKI-179), and a mouse mature B-cell lymphoma, G1XP lymphoma, immunosuppressive features of which resemble those of human B-cell lymphomas, including downregulation of MHC class I and II, exhaustion of CD8 þ and CD4 þ tumor-infiltrating lymphocytes (TIL), and PD1blockade resistance. Using two lymphoma models, we show that treatment of B-cell lymphomas refractory to PD1 blockade with both OKI-179 and anti-PD1 inhibited growth; furthermore , sensitivity to single or combined treatment required tumor-derived MHC class I, and positively correlated with MHC class II expression level. We conclude that OKI-179 sensitizes lymphomas to PD1-blockade by enhancing tumor immunogenicity. In addition, we found that different HDACis exhibited distinct effects on tumors and T cells, yet the same HDACi could differentially affect HLA expression on different human B-cell lymphomas. Our study highlights the immunologic effects of HDACis on antitumor responses and suggests that optimal treatment efficacy requires personalized design and rational combination based on prognostic biomarkers (e.g., MHCs) and the individual profiles of HDACi.

Immunotherapy has been applied successfully to treat B-cell lymphomas in preclinical models or clinical settings. However, immunotherapy resistance is a major challenge for B-cell lymphoma treatment. To overcome this issue, combinatorial therapeutic strategies have been pursued to achieve a better efficacy for treating B-cell lymphomas. One of such strategies is to combine immunotherapy with histone deacetylase (HDAC) inhibitors. HDAC inhibitors can potentially increase tumor immunogenicity, promote anti-tumor immune responses, or reverse immunosuppressive tumor environments. Thus, the combination of HDAC inhibitors and immunotherapy has drawn much attention in current cancer treatment. However, not all HDAC inhibitors are created equal and their net effects are highly dependent on the specific inhibitors used and the HDACs they target. Hence, we suggest that optimal treatment efficacy requires personalized design and rational combination based on prognostic biomarkers and unique profiles of HDAC inhibitors. Here, we discuss the possible mechanisms by which B-cell lymphomas acquire immunotherapy resistance and the effects of HDAC inhibitors on tumor cells and immune cells that could help overcome immunotherapy resistance.

BackgroundAntitumor immunity is highly heterogeneous between individuals; however, underlying mechanisms remain elusive, despite their potential to improve personalized cancer immunotherapy. Head and neck squamous cell carcinomas (HNSCCs) vary significantly in immune infiltration and therapeutic responses between patients, demanding a mouse model with appropriate heterogeneity to investigate mechanistic differences.MethodsWe developed a unique HNSCC mouse model to investigate underlying mechanisms of heterogeneous antitumor immunity. This model system may provide a better control for tumor-intrinsic and host-genetic variables, thereby uncovering the contribution of the adaptive immunity to tumor eradication. We employed single-cell T-cell receptor (TCR) sequencing coupled with single-cell RNA sequencing to identify the difference in TCR repertoire of CD8 tumor-infiltrating lymphocytes (TILs) and the unique activation states linked with different TCR clonotypes.ResultsWe discovered that genetically identical wild-type recipient mice responded heterogeneously to the same squamous cell carcinoma tumors orthotopically transplanted into the buccal mucosa. While tumors initially grew in 100% of recipients and most developed aggressive tumors, ~25% of recipients reproducibly eradicated tumors without intervention. Heterogeneous antitumor responses were dependent on CD8 T cells. Consistently, CD8 TILs in regressing tumors were significantly increased and more activated. Single-cell TCR-sequencing revealed that CD8 TILs from both growing and regressing tumors displayed evidence of clonal expansion compared with splenic controls. However, top TCR clonotypes and TCR specificity groups appear to be mutually exclusive between regressing and growing TILs. Furthermore, many TCRα/TCRβ sequences only occur in one recipient. By coupling single-cell transcriptomic analysis with unique TCR clonotypes, we found that top TCR clonotypes clustered in distinct activation states in regressing versus growing TILs. Intriguingly, the few TCR clonotypes shared between regressors and progressors differed greatly in their activation states, suggesting a more dominant influence from tumor microenvironment than TCR itself on T cell activation status.ConclusionsWe reveal that intrinsic differences in the TCR repertoire of TILs and their different transcriptional trajectories may underlie the heterogeneous antitumor immune responses in different hosts. We suggest that antitumor immune responses are highly individualized and different hosts employ different TCR specificities against the same tumors, which may have important implications for developing personalized cancer immunotherapy.

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PD1 blockade is effective in a subset of B-cell lymphoma patients (e.g., classical Hodgkin lymphomas); however, most patients do not respond to anti-PD1 therapy. To overcome PD1 resistance, we employ a newly developed isoform-selective histone-deacetylase-inhibitor (HDACi) (OKI-179) and a novel mouse mature B-cell lymphoma, G1XP lymphoma, that resembles immunosuppressive features of human B-cell lymphomas including downregulation of major histocompatibility complex (MHC) class I and II, exhaustion of CD8 and CD4 tumor-infiltrating lymphocytes (TILs), and PD1-blockade resistance. Using multiple lymphoma models, we show that combined treatment of OKI-179/anti-PD1 significantly inhibited growth of B-cell lymphomas refractory to PD1 blockade; furthermore, sensitivity to single or combined treatment required tumor-derived MHC class I, and positively correlated to MHC class II level. We conclude that OKI-179 sensitizes lymphomas to PD1 blockade by enhancing tumor immunogenicity. Additionally, we found that different HDACi exhibited distinct effects on tumors and T cells, yet the same HDACi could differentially affect HLA expression on different human B-cell lymphomas. Thus, our study highlights the importance of immunologic effects of HDACi on antitumor responses and suggests that optimal treatment efficacy requires personalized design and rational combination based on prognostic biomarkers (e.g., MHCs) and unique profiles of HDACi. Citation Format: Xiaoguang Wang, Brittany C. Waschke, Rachel A. Woolaver, Zhangguo Chen, Gan Zhang, Anthony D. Piscopio, Xuedong Liu, Jing H. Wang. Mechanistic consequences of histone-deacetylase inhibition towards sensitizing PD1 blockade-resistant B-cell lymphomas [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-54.