Mithunah Krishnamoorthy

Background Despite rigorous multimodal therapy, recurrence is common among high-risk neuroblastoma patients. Neuroblastoma is a poorly immunogenic tumor with low tumor mutational burden (TMB). Currently, immunotherapy with immune checkpoint inhibitors (ICIs) are not approved for neuroblastoma. Novel strategies to sensitize neuroblastoma to ICIs are urgently needed. We have induced mismatch repair (MMR) deficiency in mouse neuro-2a tumors and show that these tumors become highly immunogenic and responsive to anti-CTLA4 but not anti-PD1 therapy. Methods The MMR gene Mlh1 was knocked out of neuro-2a and B16F10 cells, and clones were selected. MMR-deficient (dMMR) and -proficient (pMMR) neuroblastoma tumors were grown in immunocompetent and immunodeficient animals. Tumors were harvested, and tumor-infiltrating lymphocytes (TILs) were analyzed by flow cytometry. Neuro-2a tumor-bearing mice were treated with anti-PD1, anti-CTLA4, or a combination of both antibodies. NK cells were depleted in mice treated with anti-CTLA4 using the anti-asialo GM1 antibody to examine their role in the efficacy of anti-CTLA4 treatment. dMMR B16F10 melanoma tumor-bearing mice were treated with anti-PD1 followed by the analysis of TILs. Publicly available TARGET and TCGA databases were mined to examine the effect of T-cell infiltration on neuroblastoma and melanoma patient‘s survival, respectively. Results We show that high-risk neuroblastoma and melanoma patients with tumors containing high levels of T-cell and memory T-cell-related genes have improved survival. Additionally, inducing MMR deficiency in neuro-2a cells renders these tumors immunogenic, with high T-cell infiltration, and inhibits tumor growth in mice in an immune-dependent manner. We also show that dMMR neuroblastoma tumors are highly sensitive to anti-CTLA4 but not anti-PD1 treatment. Anti-CTLA4 therapy cured most tumor-bearing mice, inducing immune memory, epitope spreading, and increased tumor-specific T-cells in cured animals. Notably, the effect of anti-CTLA4 therapy was independent of NK cells. In neuroblastoma tumors with induced MMR deficiency, anti-PD1 treatment antagonized anti-CTLA4 by upregulating inhibitory molecules on T-cells and increasing the level of dysfunctional TILs. Interestingly, anti-PD1 therapy was effective against high TMB-background melanoma tumors with induced MMR deficiency. Our data suggests that this effect relied on lowering T-cell inhibitory molecules rather than increasing T-cell infiltration into tumors. Conclusions Inducing MMR deficiency in low and high TMB-background tumors leads to distinct responses to anti-PD1 therapy, with low levels of T-cell exhaustion being a positive indicator of response. Anti-CTLA4 therapy in combination with induced MMR deficiency is a novel strategy for treating low TMB-background high-risk neuroblastoma. Ethics Approval This study was approved by the Animal Care Committee at Western University; approval number 2017-030.

The primary function of myeloid cells is to protect the host from infections. However, during cancer progression or states of chronic inflammation, these cells develop into myeloid-derived suppressor cells (MDSCs) that play a prominent role in suppressing anti-tumor immunity. Overcoming the suppressive effects of MDSCs is a major hurdle in cancer immunotherapy. Therefore, understanding the mechanisms by which MDSCs promote tumor growth is essential for improving current immunotherapies and developing new ones. This review explores mechanisms by which MDSCs suppress T-cell immunity and how this impacts the efficacy of commonly used immunotherapies.

Neoadjuvant immunotherapy involves administering immune checkpoint inhibitors before surgical resection in high-risk resectable disease. This strategy was shown to have a high pathological response rate and prolonged relapse-free survival in randomized trials in melanoma, glioblastoma, and colon cancer with small numbers of patients. In resectable cancers, immune checkpoint inhibitors such as anti-programmed cell death-1 (PD1) and anti-cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) can enhance antitumor immunity by activating antigen-specific T cells found in the primary tumor. These tumor-reactive T cells continue to exert antitumor effects on remaining neoplastic cells after the resection of the primary tumor, potentially preventing relapses from occurring. Based on the scientific rationale and early clinical observations with surrogate survival endpoints, neoadjuvant immunotherapy may provide an effective alternative to other therapeutic strategies such as adjuvant treatment. However, this can be determined only by conducting randomized controlled trials comparing neoadjuvant immunotherapy with the current standard of care for each tumor site. This review discusses the cellular mechanisms that occur during successful neoadjuvant immunotherapy and highlights the clinical data from the available human studies that support the preclinical mechanistic data. Here we also discuss strategies required for successful neoadjuvant immunotherapy, including combination treatment strategies and resistance mechanisms to neoadjuvant treatment.

Pancreatic cancer has a high mortality rate, and its incidence is increasing worldwide. The almost universal poor prognosis of pancreatic cancer is partly due to symptoms presenting only at late stages and limited effective treatments. Recently, immune checkpoint blockade inhibitors have drastically improved patient survival in metastatic and advanced settings in certain cancers. Unfortunately, these therapies are ineffective in pancreatic cancer. However, tumor biopsies from long-term survivors of pancreatic cancer are more likely to be infiltrated by cytotoxic T-cells and certain species of bacteria that activate T-cells. These observations suggest that T-cell activation is essential for anti-tumor immunity in pancreatic cancers. This review discusses the immunological mechanisms responsible for effective anti-tumor immunity and how immune-based strategies can be exploited to develop new pancreatic cancer treatments.

The transient receptor potential (TRP) family is a large family of widely expressed ion channels that regulate the intracellular concentration of ions and metals and respond to various chemical and physical stimuli. TRP subfamily M member 7 (TRPM7) is unusual in that it contains both an ion channel and a kinase domain. TRPM7 is a divalent cation channel with preference for Ca²⁺ and Mg²⁺. It is required for the survival of DT40 cells, a B cell line; however, deletion of TRPM7 in T cells does not impair their development. We found that expression of TRPM7 was required for B cell development in mice. Mice that lacked TRPM7 in B cells failed to generate peripheral B cells because of a developmental block at the pro-B cell stage. The loss of TRPM7 kinase activity alone did not affect the proportion of peripheral mature B cells or the development of B cells in the bone marrow. However, supplementation with a high concentration of extracellular Mg²⁺ partially rescued the development of TRPM7-deficient B cells in vitro. Thus, our findings identify a critical role for TRPM7 ion channel activity in B cell development.

B cell antigen uptake and presentation require the dual ion channel–kinase TRPM7.