JITC Digest February 2021

JITC Editor Picks

Deletion of Cbl-b inhibits CD8⁺ T-cell exhaustion and promotes CAR T-cell function

Jitendra Kumar, Ritesh Kumar, Amir Kumar Singh, Elviche L Tsakem, Mahesh Kathania, Matthew J Riese, Arianne L Theiss, Marco L Davila, K Venuprasad
Journal for ImmunoTherapy of Cancer 2021;9:e001688 (18 January 2021)
Research

Summary:

Functional exhaustion of T cells in the tumor microenvironment is a major barrier to translating the clinical success of chimeric antigen receptor (CAR) T cell therapies for hematologic malignancies into effective treatments for solid cancers. Reanalysis of published RNA-sequencing datasets by Jitendra Kumar and colleagues identified the E3 ubiquitin ligase Cbl-b as upregulated in exhausted PD-1⁺Tim3⁺ T cells and validated this expression in the MC38 mouse model of colon cancer. CRISPR-Cas9 deletion of Cbl-b in PD-1⁺Tim3⁺ tumor-infiltrating lymphocytes (TILs) isolated from MC38 tumors restored expression of interferon gamma, tumor necrosis factor alpha, granzyme B and IL-2; tumor growth was also delayed in homozygous Cbl-b knockout mice. Infusion of Cbl-b-knockout T cells transduced with a CD28-based CAR containing an scFv against human carcinoembryonic antigen (hCEA, a protein expressed on colon cancers) into MC38 tumor-bearing Rag-deficient mice led to delayed tumor growth and improved survival. The 21-day survival rate for treatment with Cbl-b-deficient anti-CEA CAR T cells was 75%, whereas all of the untreated mice and the mice that received Cbl-b wild type CAR T cells succumbed. PD-1 and Tim3 expressing TILs were found at a much lower frequency after infusion with CAR T cells lacking Cbl-b compared to those with the locus intact. In coculture experiments, CAR T cells lacking Cbl-b displayed enhanced cancer cell killing, and unlike the parental PD-1⁺Tim3⁺ CAR T cells, expression of effectors such as interferon gamma and granzyme B was maintained. Importantly, no signs of systemic toxicity were observed in spleens, lungs, livers, or colons of mice treated with the Cbl-b-deficient CAR T cells. Although further mechanistic characterization of the effects of Cbl-b on T cell exhaustion is needed, the study provides rationale for a strategy to enhance efficacy of CAR T cells in solid tumors.

A systemically deliverable Vaccinia virus with increased capacity for intertumoral and intratumoral spread effectively treats pancreatic cancer

Research

Summary:

Despite the potential for oncolytic viral therapy to synergize with other immunotherapies through direct killing of cancer cells, induction of immunogenic cell death, and modulation of the tumor microenvironment, poor viral spread within and between tumors limits the efficacy of these approaches. By arming a novel thymidine kinase (TK)-deleted, N1L gene-deleted oncolytic vaccinia virus with IL-21 and adding further modifications to enhance viral spread, Giulia Marelli and colleagues demonstrate enhanced antitumor efficacy in multiple models of pancreatic cancer, including orthotropic and disseminated tumors. Vaccinia virus produces two infectious forms, and the extracellular enveloped virion (EEV) is central for systemic distribution to multiple tumor sites. In both murine and Syrian hamster models of pancreatic cancer, an engineered virus with enhanced EEV production and enforced IL-21 expression, VVL-21, slowed tumor growth and prolonged survival when given after transient inhibition of PI3K (to prevent uptake of the vector by macrophages). Viral treatment led to significantly increased levels of circulating and intratumoral CD8⁺ T cells, with a reduction in splenic counts. VVL-21 treatment also led to increased numbers of circulating natural killer cells and a transient increase in intratumoral dendritic cells. M1 macrophage populations in the tumors increased 9 days after treatment, and co-culture experiments showed that VVL-21-infected cells enhanced expression of M1-associated cytokines in macrophages. While virus and PI3K inhibition alone led to tumor escape after day 15 in mouse models, the addition of anti-PD-1 antibody prolonged survival past the 50-day time point, with increased levels of CD8⁺ T cells appearing in the blood at day 17 and persisting over time. The study shows the potential for rationally designed oncolytic viral therapy combination regimens to enhance anti-tumor responses, with effects on both innate and adaptive immunity.

Skin dendritic cells in melanoma are key for successful checkpoint blockade therapy

Anastasia Prokopi, Christoph H Tripp, Bart Tummers, Florian Hornsteiner, Sarah Spoeck, Jeremy Chase Crawford, Derek R Clements, Mirjana Efremova, Katharina Hutter, Lydia Bellmann, Giuseppe Cappellano, Bruno L Cadilha, Sebastian Kobold, Louis Boon, Daniela Ortner, Zlatko Trajanoski, Suzie Chen, Tanja D de Gruijl, Juliana Idoyaga, Douglas R Green, Patrizia Stoitzner
Journal for ImmunoTherapy of Cancer 2020;9:e000832 (6 January 2021)
Research

Summary:

Current immunotherapeutic approaches for solid malignancies are largely aimed at enhancing the activity of tumor-infiltrating lymphocytes, yet emerging evidence highlights a central role for dendritic cells (DC) in the anti-tumor response. Using a murine model of spontaneous melanoma, Anastasia Prokopi and colleagues demonstrated that a decline in intratumoral DCs is associated with disease progression and that a “DC-boosting” strategy enhances the efficacy of checkpoint blockade. Specifically, the numbers of conventional type 2 dendritic cells (cDC2s) gradually declined with tumor growth, accompanied by a strong upregulation of transcripts for PD-1 and TIM-3. DC-boosting therapy (comprised of systemic flt3L, polyI:C, and a CD40 agonist antibody) combined with PD-L1/TIM-3 blockade significantly impaired tumor growth and prolonged survival. Tumors treated with the DC boost regimen upregulated expression of the chemokines Cxcl9 and Cxcl10, with accompanying significant changes in the immune cell infiltrates in the tumors, including persistent increases in total CD45⁺ cells, more conventional type 1 DCs (cDC1s) and cDC2s, as well as CD4⁺ and CD8⁺ T cells along with CD4⁺ Tregs and myeloid-derived suppressor cells (MDSCs). Notably, however, the high ratio of CD4⁺ T cells to Tregs indicated that T helper cells predominated over immunosuppressive cells. Both cDC1 and migratory skin cDC2s from the tumor-draining lymph node showed enhanced cross-presentation of tumor antigens in vitro after the DC boost therapy. Additionally, lymph node cDC2s after treatment induced expression of PD-1 and TIM-3 on CD8⁺ T cells. The combination of DC boosting and checkpoint blockade with anti-PD-L1 and anti-TIM3 mediated lasting anti-tumor immunity after cessation of treatment and led to enhanced T cell expression of several genes involved in cytotoxicity, including of Ifn, Gzmb and Tnf. This study further established the importance of DC in immunotherapy, pointing toward strategies to enhance responsiveness to checkpoint blockade.

Rethinking immune checkpoint blockade: ‘Beyond the T cell’

Summary:

The general paradigm that checkpoint blockade unleashes anti-tumor immunity by relieving T cell suppression has persisted for several decades. Emerging evidence, described by Xiuting Liu, Graham D Hogg, and David G DeNardo, reveals heretofore unappreciated and central roles of cell types beyond the lymphocytic compartment in the anti-cancer effects of checkpoint inhibition. The timely and persuasive review provides an overview of the direct and indirect mechanisms by which anti-PD-(L)1 and anti-CTLA-4 shape innate anti-tumor responses. Many of these phenomena, such as the myeloid-specific effects of checkpoint inhibition, have only come to light in recent years thanks to novel technologies such as lineage-specific deletion models. Additionally, the effects of checkpoint inhibition on the innate immune system are often context-dependent or otherwise complex, such as PD-(L)1 expression in dendritic cells, or the “double-edged” sword of myeloid-derived suppressor cells that simultaneously induce immunity and promote tolerance. The review not only concisely and clearly summarizes available evidence on the “classical” immune checkpoints (ie, PD-(L)1 and CTLA-4), but also provides intriguing insights on how emerging targets such as LAG3, TIGIT, and others may modulate innate immunity. The authors make a compelling case for moving beyond the “T cell-centric” view of immunotherapy, which may ultimately allow more patients to benefit.

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