Exploring immunological mechanisms and new therapeutic targets in Hodgkin lymphoma

Interplay between immune cells in anti-PD-1–treated cHL

Basic scientific research efforts are aimed at improving the understanding of the activity of immune checkpoint inhibitors in classical Hodgkin lymphoma (cHL). At ISHL 2022, Paczkowska et al. presented results regarding peripheral immune responses to PD-1 blockade that were generated using single-cell RNA sequencing [1]. Also, the researchers sought to define non-CD8-T-cell–dependent mechanisms of immune evasion. Peripheral blood mononuclear cells were obtained from 13 healthy donors, 11 patients with newly diagnosed cHL, and 20 patients with relapsed/refractory cHL who were receiving anti-PD-1 treatment. After negative selection of CD3-positive and CD3-negative cells, these separated populations were submitted to RNA sequencing.

Patients with the most favorable responses to PD-1 blockade had significantly higher CD4-positive T-cell receptor diversity at baseline and more abundant naïve/central memory T-cell subsets at day 1 of cycle 4. These data suggested that patients who responded most favorably to anti-PD-1 treatment had the continued capacity to mount new CD4-positive T-cell responses to tumor neoantigens. Compared to healthy donors, all patients with cHL had significantly reduced numbers of circulating B cells across all B-cell clusters. Patients with the most favorable responses to PD-1 blockade showed significantly higher numbers of circulating B cells, and increased B-cell receptor diversity at baseline and on treatment. This highlights the potentially important role of B-cell–mediated responses in cHL.

With regard to circulating monocytes, a new subset was identified that was primarily seen in patients with cHL in comparison to healthy donors. These cells had marked upregulation of multiple immunosuppressive and tumorigenic cytokines and chemokines, as well as increased expression of PD-L1 and SIRPα. RNAscope analysis of the intact cHL tumor microenvironment revealed the presence of tumor-infiltrating monocytes and macrophages with similar features in the immediate proximity of CD30-positive, PD-L1–positive Hodgkin Reed/Sternberg (HRS) cells. At the clinical level, the transcriptional signature of circulating Cluster 0 monocytes was associated with a lack of response to PD-1 blockade both at baseline and on treatment.

Overall, the study has demonstrated profound rewiring of the circulating immune signature in patients with cHL. CD4-positive T cells, B cells as well as cancer-associated monocyte abundance and function were associated with response to anti–PD-1 treatment.

cGAS-STING immune response pathway

The cyclic GMP-AMP (cGAMP) synthase (cGAS), a cytosolic DNA sensor, triggers innate immune responses through its function as a second messenger, which binds to and activates the adaptor protein STING. The latter subsequently induces the expression of interferons (IFNs), chemokines and cytokines involved in anti-tumor immune responses. STING expression was immunohistochemically assessed in a pilot study of 32 untreated cHL patients [2]. In addition, an in vitro system of cHL cell lines were treated with a STING agonist and the TBK1/IKKε inhibitor amlexanox, alone or in combination with other agents. Then cGAS-STING–associated anti-tumor immune responses were investigated based on the protein expression of the cGAS-STING components and the RNA levels of IFN-β, CXCL10 and IFN-γ.

Using an arbitrary 10 % cutoff, STING was positive in the HRS cells of 63 % of patients with a membranous and cytoplasmic pattern. Treatment with the STING agonist stimulated gene expression of IFN-β and/or CXCL10 depending on the cell line; this indicated the presence of a functional cGAS-STING anti-tumor immune response pathway. Silencing of the STING gene resulted in decreased CXCL10 and type 1 IFN gene expression by cHL cells. Moreover, amlexanox treatment led to downregulation of IFN-β or CXCL10 gene expression in vitro. As the authors concluded, modulation of gene expression of type 1 IFNs by STING agonists and amlexanox might have direct therapeutic implications in cHL.

Deregulated CK2 expression

Another potential future target is casein kinase II (CK2), a pleiotropic kinase consisting of 2 catalytic and 2 regulatory subunits. This kinase sustains cancer signaling cascades through the activation of the NF-kB, PI3K and STAT pathways that are key players in HL. The study by Visentin et al. was based on four HL cell lines all of which expressed higher levels of CK2a, but not CK2b compared to normal B lymphocytes (p < 0.001) [3]. Similarly, HRS cells in the lymph nodes of 35 patients highly expressed CK2a but not CK2b. Patients with lower levels of CK2b showed improved progression-free survival (p < 0.05).

Treatment of the cell lines with the CK2 inhibitor silmitasertib induced down-regulation of AKT, RelA and STAT3, and time- and dose-dependent apoptosis (p < 0.0001). Moreover, sil­mitasertib had a synergistic anti-apoptotic effect in combination with monomethyl auristatin E. Treatment with bortezomib gave rise to upregulation of CK2b. The authors concluded that CK2a is overexpressed and induces key pro-survival signals in HL, while its inhibition triggers apoptosis. CK2b was likely downregulated due to proteasome degradation.

REFERENCES

1. Paczkowska J et al., Single-cell RNA sequencing reveals the interplay between circulating CD4 T cells, B cells and cancer-associated monocytes in classic Hodgkin lymphoma treated with PD-1 blockade. ISHL 2022, T028
2. Xagoraris I et al., The cGAS-STING anti-tumor immune response pathway as a potential therapeutic target in classical Hodgkin lymphoma. ISHL 2022, P053
3. Visentin A et al., The kinase CK2 is deregulated and targetable in classical Hodgkin lymphoma. ISHL 2022, P054

© 2022 Springer-Verlag GmbH, Impressum

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