The following articles have been recommended for further reading in the field of cancer immunotherapy by JITC's Oncolytic and Local Immunotherapy Section Editor, Howard Kaufman, MD, FACS
“Intratumoral IL-12 delivery empowers CAR-T cell immunotherapy in a pre-clinical model of glioblastoma” by Giulia Agliardi et al
Glioblastoma multiforme (GBM) is a highly aggressive tumor with minimal options for treatment, motivating the investigation of combination immunotherapy strategies to overcome the highly immunosuppressive brain tumor microenvironment. Giulia Agliardi and colleagues report tumor control in pre-clinical models with the combination of intratumoral interleukin (IL)-12 therapy and systemically delivered chimeric antigen receptor (CAR) T cells targeting epidermal growth factor receptor variant III (EGFRvIII). Anti-EGFRvIII-CAR T cell monotherapy led to reduced malignant mass for early/small tumors in an immunocompetent orthotopic GL261 glioma mouse model, but larger tumors escaped. The addition of intratumoral IL-12, however, reduced tumor size and improved overall survival in mice with large gliomas. By flow-cytometry, the addition of IL-12 did not affect the quantity of CAR T cells infiltrating the tumors, however significant differences emerged in the CAR T cell phenotypes. Specifically, CAR T cells in tumors treated with IL-12 showed lower expression of PD-1, lymphocyte-activation gene 3 (LAG3), and exhaustion markers and increased expression of interferon gamma and tumor necrosis factor (TNF). This phenotype was also seen in endogenous CD4+ and CD8+ T cell infiltrates, induced by IL-12 independent of CAR T therapy. Overall, gliomas treated with IL-12 demonstrated higher CD4+ T cell infiltration, decreased Treg infiltration, and increased activation/anti-tumor phenotypes in myeloid-derived cells. Importantly, unlike the expected toxic effects of systemic IL-12 seen clinically, intratumoral IL-12 led to minimal toxicity. The findings set the stage for further studies of intratumoral IL-12 to potentially augment CAR T cell effector function and improve endogenous immune cell responses.
Why I like this paper: CAR T cell therapy for solid tumors has remained challenging and this paper demonstrates how local immunotherapy may allow more effective CAR T cell treatment of solid tumors without adding additional toxicity.
“Ki-67 regulates global gene expression and promotes sequential stages of carcinogenesis” by Karim Mrouj et al
The proliferation marker Ki-67 has been validated as a prognostic marker for malignancy and is an important regulator of heterochromatin, but its potential role in tumorigenesis is largely unknown. Karim Mrouj and colleagues identify Ki-67 as a global transcriptional regulator implicated in many tumorigenic factors, including initiation, growth, metastasis, and immune recognition. Mki67 knockout mice had reduced tumor burden in gastrointestinal cancer models, and colony formation assays confirmed that the basis of this observation was due to changes in tumorigenesis initiation rather than proliferation defects. RNAseq analysis of several different mouse and human Ki-67 knockout breast cancer cell lines revealed a role for the protein in regulation of global gene expression, consistent with its known role in chromatin regulation. In the knockouts, many tumorigenic pathways were altered, as well as a noted downregulation in polycomb-repression complex 2 (PRC2) and many of its targets, which mediates histone methylation and epithelial-to-mesenchymal transition (EMT). However, the broad changes in gene expression could not be fully attributed to PRC2-mediated repression. Functionally, Ki-67 deficiency reduced expression of mesenchymal markers and stem-like characteristics in mammary carcinoma cells, confirming a role in EMT. Upon orthotopic implantation into mice, Ki-67 deficient cells consistently formed smaller tumors with reduced metastatic seeding and sensitivity to drugs. With no change in proliferation to account for the decreased tumor burden, the group assessed other factors such as apoptosis, necrosis, and angiogenesis, but results were inconsistent across models. While most of these factors implicate Ki-67 in promoting tumorigenesis and malignancy, Ki-67-expressing cells did elicit an improved anti-tumor immune response in immunocompetent mice. Future studies will be needed to disentangle the context-dependent mechanisms of Ki-67-dependent regulation of tumorigenesis.
Why I like this paper: Ki-67 is a well-known marker of malignant cells and this paper confirms a role for Ki-67 expression in promoting specific aspects of tumor growth and progression, but also identified an unexpected role in enhancing anti-tumor immunity. The data presented adds further insight into how dysregulated gene expression in cancer cells influences the host anti-tumor immune response.
“Mutations in the IFNy-JAK-STAT pathway causing resistance to immune checkpoint inhibitors in melanoma increase sensitivity to oncolytic virus treatment” by Tan-Trieu Nguyen et al
Based on the observation that loss of function (LoF) mutations in Janus kinase 2 (JAK2) have been reported in patients with immune checkpoint inhibitor (ICI)-resistant melanoma, Tan-Trieu Nguyen and colleagues investigated whether aberrant interferon gamma (IFNy) signaling rendered tumors more sensitive to oncolytic virus therapy. Patient-derived cell lines from a baseline biopsy (wild-type JAK2; M420) and an anti-PD-1-resistant matched lesion from the same patient after anti-PD-1 treatment (LoF JAK2; M464) were compared in cytotoxicity assays for the oncolytic vesicular stomatitis virus, VSV-Δ51 (which contains a single-residue deletion to impair viral shutdown of interferon signaling). After IFNy pretreatment, a 22-fold decrease in the 50% tissue culture infective dose (TCID50) for VSV-Δ51 was seen in the M464 cell line compared to the M420 cell line. A similar effect was seen following infection with an oncolytic HSV-1 virus, although the decrease was only 7-fold. Complementation and knockdown of JAK2 recapitulated the importance of IFNy signaling. Interestingly, VSV-Δ51 consistently showed stronger cytotoxic effects compared to other oncolytic viruses. Pharmacologic inhibition of JAK1/2 with ruxolitinib also resulted in significantly increased VSV-Δ51 susceptibility and oncolysis. In a mouse model using B16-F10 cells, Jak2 knockout tumors had greater responses to VSV-Δ51 treatment compared to controls with Jak2 intact, more than doubling median survival. Finally, an estimated 11% of treatment-naïve melanomas in The Cancer Genome Atlas (TCGA) database harbor mutations disrupting IFNy signaling, thus making them potentially more sensitive to oncolytic virus treatment. This study provides strong evidence for leveraging IFNy/JAK2 signaling disruptions (endogenous or pharmacologic) to increase sensitivity to oncolytic virus treatment, which may be particularly beneficial for patients with ICI-resistant tumors and limited treatment options.
Why I like this paper: The data presented in this paper supports the concept that changes in the function of tumor cell innate sensing and anti-viral machinery elements may serve as predictive biomarkers for oncolytic virus anti-tumor activity.
“Oncolytic virotherapy-mediated anti-tumor response: a single-cell perspective” by Egle Ramelyte et al
Since its FDA approval for the treatment of melanoma in 2015, many groups have investigated Talimogene laherparepvec (T-VEC), a genetically modified strain of the herpes simplex virus type 1 (HSV-1), as a treatment option for other types of cutaneous cancers. Using the approved T-VEC melanoma treatment schedule, Egle Ramelyte and colleagues investigated immune responses, safety, and efficacy in 13 patients with various subtypes of primary cutaneous B cell lymphoma (pCBCL). Six patients (46.2%) experienced a clinical complete response, five a partial response, and two patients had disease progression. Two of three patients experienced a reduction in uninjected lesions, demonstrating both local and systemic anti-tumor efficacy of T-VEC, similar to what has been seen in melanoma. Contrary to what has been reported in melanoma, however, viral transcripts were present in both malignant and non-malignant cells. Serial fine needle aspirates (FNA) were taken post-injection in three patients and analyzed via single-cell RNA-sequencing, with immune cell profiles determined by reference-based annotation technology. Overall, the malignant B cell populations in both injected and uninjected lesions decreased as quickly as one day post-injection. Also, one day after injection, a 25-fold increase in NK cell-associated transcripts was seen, with cytotoxic and FASL gene expression pathways upregulated. An increase in dendritic cells, monocytes, CD8+ T cells (in injected lesions), CD4+ T cells (in uninjected lesion), and a decrease in Tregs was also observed. Additional noteworthy gene expression changes include an upregulation in interferon alpha/beta and a downregulation in PD-1 signaling. Altogether, this study demonstrates the anti-tumor activity and immunogenicity of T-VEC in pCBCLs, also showing a marked difference in the specificity of T-VEC infection compared to melanoma lesions, warranting additional clinical and mechanistic studies for the use of T-VEC in treating nonmelanoma skin cancers.
Why I like this paper: This paper utilized a serial biopsy of both injected and uninjected lesions, which resulted in a much better understanding of both the qualitative and quantitative impact of local T-VEC treatment. The data suggest that immune changes within the tumor microenvironment are especially rapid at the injection site and are somewhat different at uninjected tumors. The work also highlights that different tumors may elicit distinct immune responses and provides an example of how to integrate biomarker analyses into clinical trials of oncolytic virus therapy.
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