Immunogenomics of Colorectal Tumors: Facts and Hypotheses on an Evolving Saga

Computational Quantification of Cancer Immunoediting

The remarkable success of cancer immunotherapy has revolutionized cancer treatment, emphasizing the importance of tumor-immune interactions in cancer evolution and treatment. Cancer immunoediting describes the dual effect of tumor-immune interactions: inhibiting tumor growth by destroying tumor cells and facilitating tumor escape by shaping tumor immunogenicity. To better understand tumor-immune interactions, it is critical to develop computational methods to measure the extent of cancer immunoediting. In this review, we provide a comprehensive overview of the computational methods for quantifying cancer immunoediting. We focus on describing the basic ideas, computational processes, advantages, limitations, and influential factors. We also summarize recent advances in quantifying cancer immunoediting studies and highlight future research directions. As the methods for quantifying cancer immunoediting are continuously improved, future research will further help define the role of immunity in tumorigenesis and hopefully provide a basis for the design of new personalized cancer immunotherapy strategies.

Bypassing anti-PD-(L)1 therapy: Mechanisms and management strategies

Resistance to immune checkpoint inhibitors (ICIs) is a major issue of the current era in cancer immunotherapy. Immune evasion is a multi-factorial event, which occurs generally at a base of cold immunity. Despite advances in the field, there are still unsolved challenges about how to combat checkpoint hijacked by tumor cells and what are complementary treatment strategies to render durable anti-tumor outcomes. A point is that anti-programed death-1 receptor (PD-1)/anti-programmed death-ligand 1 (PD-L1) is not the solo path of immune escape, and responses in many types of solid tumors to the PD-1/PD-L1 inhibitors are not satisfactory. Thus, seeking mechanisms inter-connecting tumor with its immune ecosystem nearby unravel more about resistance mechanisms so as to develop methods for sustained reinvigoration of immune activity against cancer. In this review, we aimed to discuss about common and specific paths taken by tumor cells to evade immune surveillance, describing novel detection strategies, as well as suggesting some approaches to recover tumor sensitivity to the anti-PD-(L)1 therapy based on the current knowledge.

BAT26 Only Microsatellite Instability with High Tumor Mutation Burden—A Rare Entity Associated with PTEN Protein Loss and High PD-L1 Expression

Detecting microsatellite instability (MSI) in advanced cancers is crucial for clinical decision-making, as it helps in identifying patients with differential treatment responses and prognoses. BAT26 is a highly sensitive MSI marker that defines the mismatch repair (MMR) status with high sensitivity and specificity. However, isolated BAT26-only instability is rare and has not been previously reported. Of the 6476 cases tested using pentaplex MSI polymerase chain reaction, we identified two BAT26-only instability cases (0.03%) in this study. The case #1 patient was diagnosed with endometrial adenocarcinoma without MMR germline mutations. The endometrial tumor showed BAT26-only instability, partial loss of MLH1/PMS2 protein expression, and a high programmed cell death ligand 1 (PD-L1) combined positive score (CPS = 8). The tumor exhibited a somatic phosphatase and tensin homolog (PTEN) R303P missense mutation and loss of the PTEN protein. On a comprehensive cancer panel sequencing with ≥500 genes, the tumor showed an MSI score of 11.38% and high tumor mutation burden (TMB) (19.5 mt/mb). The case #2 patient was diagnosed with colorectal carcinoma with proficient MMR and PTEN protein loss without PTEN alteration, as well as a high PD-L1 CPS (CPS = 10). A pathogenic KRAS A146T mutation was detected with an MSI score of 3.36% and high TMB (13 mt/mb). In conclusion, BAT26-only instability is very rare and associated with PTEN protein loss, high TMB, and a high PD-L1 score. Our results suggest that patients with BAT26-only instability may show good responses to immunotherapy.

CSMD1 suppresses cancer progression by inhibiting proliferation, epithelial-mesenchymal transition, chemotherapy-resistance and inducing immunosuppression in esophageal squamous cell carcinoma

Human CUB and Sushi multiple domains (CSMD1) is considered a crucial role in cancer progression, but the specific function in esophageal squamous cell carcinoma (ESCC) is not clear. Understanding the role of CSMD1 in ESCC progression may lead to a novel strategy for ESCC treatment. Here, we found that both CSMD1 mRNA and protein levels were downregulated in ESCC tissues. Reduced CSMD1 expression was correlated with a poor prognosis in ESCC patients. CSMD1 expression inhibited proliferation, migration and invasion in ESCC cell lines in vitro. CSMD1 deficiency in established xenografted tumors increases tumor size and weight. We further found that CSMD1-overexpression cells are more sensitive to chemotherapy. Moreover, we addressed the role of CSMD1 in the CD8⁺ T cell immune response. An in vitro killing assay showed that the cytotoxicity of CD8⁺ T cells was inhibited in CSMD1-overexpression tumor cells. In vivo, in CSMD1 deficiency tumor-bearing mice activation and expansion of CD8⁺ T cells were increased. Further investigation showed that CSMD1 expression on tumor cells was positively correlated with CD8⁺ T cells infiltration and cytokines secretion. These findings highlight that CSMD1 is a tumor suppressor gene in ESCC patients and a positive regulator of CD8⁺ T cells expansion and activation, and could increase cytokines secretion, indicating that tumor cell-associated CSMD1 might be a target for ESCC.

PD-1/PD-L1 blockade, a novel strategy for targeting metastatic colorectal cancer: A systematic review and meta-analysis of randomized trials

Currently, standard treatment of patients with metastatic colorectal cancer (mCRC) comprises chemotherapy (CT) and/or biological therapy (BT) and/or best supportive care (BSC). The present study performed a meta-analysis on five phase II-III randomized clinical trials, which compared CT/BT/BSC as the control arm with the immune checkpoint inhibitors (ICIs) anti-programmed cell death protein 1 (PD-1) or its ligand (PD-L1) alone or in combination with cytotoxic T lymphocyte antigen 4 or mitogen activated protein kinase kinase inhibitors as the experimental arm, to evaluate whether a standard approach could be overcome using the novel target therapy strategy. Pooled hazard ratio (HR) for progression-free survival was 0.95 in favor of the experimental arm [95% confidence interval (CI), 0.74-1.22; P=0.68]. Heterogeneity was significant: Cochran's Q, 21.0; P=0.0082; I2 index, 76%. Pooled HR for overall survival was 0.88 in favor of the experimental arm (95% CI, 0.75-1.02; P=0.08). Heterogeneity was not significant (Cochran's Q, 6.0; P=0.31; I2 index, 16%). The present meta-analysis demonstrated a trend toward the improvement of survival by PD-1/PD-L1 blockade in mCRC. Further homogeneous studies are necessary to strengthen these results, beyond the known benefits of ICIs in deficient mismatch repair/high microsatellite instability tumors.

Tumor immune microenvironment is influenced by frameshift mutations and tumor mutational burden in gastric cancer

PURPOSE

Immunoscore can effectively predict prognosis in patients with colon cancer; however, its clinical application is limited. We modified the Immunoscore and created a tumor immune microenvironment (TIM) classification system for gastric carcinoma. Unlike previous studies that used small sample sizes or focused on particular immune-cell subtypes, our simplified system enables pathologists to classify gastric carcinomas intuitively using H&E-stained sections.

METHODS

Samples from 326 patients with advanced gastric carcinoma were reviewed and analyzed by pathologists using simple determination and digital image analysis. Comprehensive results of cancer-panel sequencing, Epstein-Barr‒virus (EBV) status, and PD-L1, HER2, ATM, PTEN, MET, FGFR2, and EGFR immunohistochemistry were evaluated with respect to the TIM class.

RESULTS

The TIM was classified as "hot" (n = 22), "immunosuppressed" (n = 178), "excluded" (n = 83), or "cold" (n = 43). TIM category was significantly associated with numbers of frameshift mutations (P < 0.001) and high tumor mutational burden (P < 0.004), and predicted overall survival. It was also significantly associated with age, histological type, degree of fibrosis, PD-L1 expression, loss of ATM and PTEN expression (P < 0.001), sex, EBV positivity, and HER2 overexpression (P < 0.04). "Hot" tumors were frequent in PD-L1 expressing and EBV-positive samples, and in those with ATM and PTEN loss. "Excluded" tumors were frequent in HER2-positive cases, whereas "cold" tumors were more frequent in younger patients with poorly cohesive histology and high fibrosis levels.

CONCLUSIONS

TIM classification system for gastric carcinoma has prognostic significance and results in classes that are associated with molecular characteristics.

Lynch Syndrome and MSI-H Cancers: From Mechanisms to "Off-The-Shelf" Cancer Vaccines

Defective DNA mismatch repair (dMMR) is associated with many cancer types including colon, gastric, endometrial, ovarian, hepatobiliary tract, urinary tract, brain and skin cancers. Lynch syndrome - a hereditary cause of dMMR - confers increased lifetime risk of malignancy in different organs and tissues. These Lynch syndrome pathogenic alleles are widely present in humans at a 1:320 population frequency of a single allele and associated with an up to 80% risk of developing microsatellite unstable cancer (microsatellite instability - high, or MSI-H). Advanced MSI-H tumors can be effectively treated with checkpoint inhibitors (CPI), however, that has led to response rates of only 30-60% despite their high tumor mutational burden and favorable immune gene signatures in the tumor microenvironment (TME). We and others have characterized a subset of MSI-H associated highly recurrent frameshift mutations that yield shared immunogenic neoantigens. These frameshifts might serve as targets for off-the-shelf cancer vaccine designs. In this review we discuss the current state of research around MSI-H cancer vaccine development, its application to MSI-H and Lynch syndrome cancer patients and the utility of MSI-H as a biomarker for CPI therapy. We also summarize the tumor intrinsic mechanisms underlying the high occurrence rates of certain frameshifts in MSI-H. Finally, we provide an overview of pivotal clinical trials investigating MSI-H as a biomarker for CPI therapy and MSI-H vaccines. Overall, this review aims to inform the development of novel research paradigms and therapeutics.

Caspase-cleavable peptide-doxorubicin conjugate in combination with CD47-antagonizing nanocage therapeutics for immune-mediated elimination of colorectal cancer

Here we report a novel combination of a caspase-cleavable peptide-doxorubicin conjugate (MPD-1) with CD47-antagonizing nanocage therapeutics for the treatment of microsatellite-stable (MSS) colorectal cancer (CRC). MPD-1 (i) upregulated markers of immunogenic cell death (ICD) in tumor, and increased co-stimulatory markers on dendritic cells (DCs), (ii) enhanced CD8⁺ T cell infiltration and antigen presenting cell (APC) activation, and (iii) showed negligible off-target immune-related toxicity compared to free dox. Then, the CD47 antagonist FS nanocage, a SIRPα-expressing ferritin nanocage, was co-administered with MPD-1 that resulted in 95.2% (p < 0.001) tumor growth inhibition in an established CRC model. T cell-mediated elimination of tumors was also confirmed by the tumor-specific activation of T cells detected by IFNγ and tumor-free mice were observed (95%) that bared a memory response when re-challenged. The strategically developed MPD-1 is an ideal adjuvant to immunotherapy and the combination with FS nanocage triggers potent immunity against MSS CRC. In summary, we present an approach to initiate and stimulate immune-mediated eradication of cancer cells using synergistic immunogenic agents targeting the MSS CRC.

The Ratio of Exhausted to Resident Infiltrating Lymphocytes Is Prognostic for Colorectal Cancer Patient Outcome

Immunotherapy success in colorectal cancer is mainly limited to patients whose tumors exhibit high microsatellite instability (MSI). However, there is variability in treatment outcomes within this group, which is in part driven by the frequency and characteristics of tumor-infiltrating immune cells. Indeed, the presence of specific infiltrating immune-cell subsets has been shown to correlate with immunotherapy response and is in many cases prognostic of treatment outcome. Tumor-infiltrating lymphocytes (TIL) can undergo distinct differentiation programs, acquiring features of tissue-residency or exhaustion, a process during which T cells upregulate inhibitory receptors, such as PD-1, and lose functionality. Although residency and exhaustion programs of CD8⁺ T cells are relatively well studied, these programs have only recently been appreciated in CD4⁺ T cells and remain largely unknown in tumor-infiltrating natural killer (NK) cells. In this study, we used single-cell RNA sequencing (RNA-seq) data to identify signatures of residency and exhaustion in colorectal cancer-infiltrating lymphocytes, including CD8⁺, CD4⁺, and NK cells. We then tested these signatures in independent single-cell data from tumor and normal tissue-infiltrating immune cells. Furthermore, we used versions of these signatures designed for bulk RNA-seq data to explore tumor-intrinsic mutations associated with residency and exhaustion from TCGA data. Finally, using two independent transcriptomic datasets from patients with colon adenocarcinoma, we showed that combinations of these signatures, in particular combinations of NK-cell activity signatures, together with tumor-associated signatures, such as TGFβ signaling, were associated with distinct survival outcomes in patients with colon adenocarcinoma.

ILT4 in Colorectal Cancer Cells Induces Suppressive T Cell Contexture and Disease Progression

Purpose

Immune checkpoint blockade (ICB) therapy shows little or no clinical benefit in most colorectal cancer (CRC) patients, due to the immunosuppressive T cell contexture in the tumor microenvironment (TME). Immunoglobulin-like transcript (ILT) 4 is an immunosuppressive molecule in myeloid cells. ILT4 is enriched in solid tumor cells, facilitating their proliferation, invasion, and metastasis. However, the regulatory role of ILT4 in T cell immunity of CRC is still undetermined. Here, we aimed to explore how tumor cell-derived ILT4 orchestrates T cell infiltration, subset distribution, and function in CRC.

Methods

A total of 145 paraffin-embedded cancer tissues and the corresponding clinicopathological information were collected from CRC patients. Immunohistochemical (IHC) staining and public database analyses determined the correlation of ILT4 expression with different T cell subset densities, IFN-γ levels, and patient outcomes. Paired Ig-like receptor B (PIR-B, ILT4 mouse ortholog)-overexpressing/-downregulated MC38 cells were subcutaneously injected into C57BL/6 mice as a CRC transplantation model. The frequencies, subsets, and IFN-γ levels of T cells in mouse blood and spleens were determined using flow cytometry and immunohistochemistry, respectively.

Results

High ILT4 expression in CRC cells was associated with decreased T cell infiltration, disease progression, and poor patient survival. T cell subset analyses indicated that ILT4-high patients showed reduced CD8⁺ T cell but elevated FOXP3⁺ regulatory T (Treg) cell frequencies in the TME. High ILT4 levels predicted lower IFN-γ production by tumor-infiltrating lymphocytes (TILs), especially by CD8⁺T cells in human CRC tissues. Moreover, PIR-B overexpression accelerated MC38 growth in mice, decreased CD3⁺/CD8⁺/IFN-γ⁺ T cell densities, and elevated Treg infiltration in the TME, blood, and spleens. PIR-B knockdown had the opposite effects.

Conclusion

ILT4 in CRC cells induced immunosuppressive T cell subset infiltration and impaired IFN-γ production in TILs, suggesting that ILT4 might be a potential immunotherapeutic target and prognostic biomarker.

Identification and Validation of a Four-Long Non-coding RNA Signature Associated With Immune Infiltration and Prognosis in Colon Cancer

The emerging evidence has demonstrated the critical roles of long non-coding RNAs (lncRNAs) as regulators in the tumor immune microenvironment (TIME). However, the tumor immune infiltration-associated lncRNAs and their clinical significance in colon cancer have not yet been thoroughly investigated. This study performed an integrative analysis of lncRNA expression profiles and immune cell infiltration profiles and identified 258 immune infiltration-associated lncRNAs. Of them, four lncRNAs (AC008494.3, LINC00926, AC022034.1, and SNHG26) were significantly and independently associated with the patient’s overall survival. Finally, we developed a tumor immune infiltration-associated lncRNA signature (TIILncSig) comprising of these four lncRNAs, which can divide colon cancer patients of The Cancer Genome Atlas (TCGA) into high-risk and low-risk groups with a significantly different outcome [Hazard ratio (HR) = 2.718, 95% CI = 1.955–3.779, p < 0.001]. Prognostic performance of the TIILncSig was further validated in another independent colon cancer cohort (HR = 1.832, 95% CI = 1.045–3.21, p = 0.034). Results of multivariate Cox regression and stratification analysis demonstrated that the TIILncSig is an independent predictive factor from other clinical features (HR = 2.687, 95% CI = 1.912–3.776, p < 0.001 for TCGA cohort and HR = 1.837, 95% CI = 1.047–3.223, p = 0.034 for GSE17538 cohort). Literature analysis provided experimental evidence supporting roles of the TIILncSig in cancer carcinogenesis and progression and immune regulation. Summary, our study will help to understand the mechanisms of lncRNAs in immune regulation in the tumor microenvironment and provide novel biomarkers or targets for prognosis prediction and therapy decision-making for patients with colon cancer.

Immunity-Related Gene Signature Identifies Subtypes Benefitting From Adjuvant Chemotherapy or Potentially Responding to PD1/PD-L1 Blockage in Pancreatic Cancer

Tumor microenvironment comprises of a variety of cell types, which is quite complex and involved in chemotherapy and immune checkpoint blockage resistance. In order to explore the mechanisms involved in tumor immune microenvironment in pancreatic ductal adenocarcinoma (PDAC), we first constructed an immunity-related 18-gene signature using The Cancer Genome Atlas (TCGA) PDAC project data. Then we applied the 18-gene signature to divide PDAC patients into low score and high score groups. Patients in high score group showed inferior prognosis, which was validated in another four independent cohorts, including Ruijin cohort. High score group showed significant enrichment of pathways involved in cell division and cell cycle especially in G1/S phase transition. In high score group, IHC analysis revealed higher levels of the proliferative indexes of Ki67 and PCNA than that in low score group. Prognostic analysis confirmed that patients in high score group could benefit from the gemcitabine-based adjuvant chemotherapy. In low score group, the programmed cell death 1 ligand 1(PD-L1) (+) cases showed worse prognosis but higher T cell infiltration than PD-L1(−) cases. Our immunity-related 18-gene signature could effectively predict PDAC prognosis, and it might be a practical predictive tool to identify PDAC subtype benefitting from gemcitabine-based adjuvant chemotherapy or potentially responding to PD1/PD-L1 blockade therapy.

The Emergence of Immune-checkpoint Inhibitors in Colorectal Cancer Therapy

Immunotherapy has revolutionized the treatment landscape in a number of solid tumors. In colorectal cancer, evidence suggests that microsatellite high (MSI-H) tumors are the most responsive to immune checkpoint blockade due to increased neo-antigen load and a favorable tumor microenvironment. Indeed, Pembrolizumab now represents a first-line option in such patients. However, MSI-H tumors represent the minority and a proportion of patients' progress despite initially responding. Trials are investigating different immunotherapy combinatorial strategies to enhance immune response in less immunogenic colorectal tumors. Such strategies include dual immune checkpoint blockade, combining immune checkpoint inhibitors with other treatment modalities such as radiotherapy, chemotherapy or other biological or targeted agents. Moreover, there is an increasing drive to identify biomarkers to better select patients most likely to respond to immunotherapy and understand intrinsic and acquired resistance mechanisms. Apart from MSI-H tumors, there is a strong rationale to suggest that tumors with alterations in DNA polymerase epsilon and DNA polymerase delta are also likely to respond to immunotherapy and trials in this subpopulation are underway. Other strategies such as priming O6-methylguanineDNA methyltransferase silenced tumors with alkylating agents to make them receptive to immune checkpoint blockade are also being investigated. Here we discuss different colorectal subpopulations together with their likelihood of response to immune checkpoint blockade and strategies to overcome barriers to a successful clinical outcome. We summarize evidence from published clinical trials and provide an overview of trials in progress whilst discussing newer immunotherapy strategies such as adoptive cell therapies and cancer vaccines.

Preclinical models as patients' avatars for precision medicine in colorectal cancer: past and future challenges

Colorectal cancer (CRC) is a complex and heterogeneous disease, characterized by dismal prognosis and low survival rate in the advanced (metastatic) stage. During the last decade, the establishment of novel preclinical models, leading to the generation of translational discovery and validation platforms, has opened up a new scenario for the clinical practice of CRC patients. To bridge the results developed at the bench with the medical decision process, the ideal model should be easily scalable, reliable to predict treatment responses, and flexibly adapted for various applications in the research. As such, the improved benefit of novel therapies being tested initially on valuable and reproducible preclinical models would lie in personalized treatment recommendations based on the biology and genomics of the patient's tumor with the overall aim to avoid overtreatment and unnecessary toxicity. In this review, we summarize different in vitro and in vivo models, which proved efficacy in detection of novel CRC culprits and shed light into the biology and therapy of this complex disease. Even though cell lines and patient-derived xenografts remain the mainstay of colorectal cancer research, the field has been confidently shifting to the use of organoids as the most relevant preclinical model. Prioritization of organoids is supported by increasing body of evidence that these represent excellent tools worth further therapeutic explorations. In addition, novel preclinical models such as zebrafish avatars are emerging as useful tools for pharmacological interrogation. Finally, all available models represent complementary tools that can be utilized for precision medicine applications.

Patient-derived tumor models: a more suitable tool for pre-clinical studies in colorectal cancer

Colorectal cancer (CRC), despite the advances in screening and surveillance, remains the second most common cause of cancer death worldwide. The biological inadequacy of pre-clinical models to fully recapitulate the multifactorial etiology and the complexity of tumor microenvironment and human CRC's genetic heterogeneity has limited cancer treatment development. This has led to the development of Patient-derived models able to phenocopy as much as possible the original inter- and intra-tumor heterogeneity of CRC, reflecting the tumor microenvironment's cellular interactions. Implantation of patient tissue into immunodeficient mice hosts and the culture of tumor organoids have allowed advances in cancer biology and metastasis. This review highlights the advantages and limits of Patient-derived models as innovative and valuable pre-clinical tools to study progression and metastasis of CRC, develop novel therapeutic strategies by creating a drug screening platform, and predict the efficacy of clinical response to therapy.

Angiogenesis as a hallmark of solid tumors - clinical perspectives

BACKGROUND

Angiogenesis is a key and early step in tumorigenesis, and is known as a hallmark of solid tumors and a key promoter of tumor recurrence. Unlike normal tissue vessels, the architecture of the tumor vasculature is abnormal, being leaky, tortuous, fragile and blind-ended. Perivascular cells are either detached or absent, causing reduction of vascular integrity, an increase in vessel immaturity, incoherent perfusion, defective functionality and enhanced tumor dissemination and metastasis. The abnormal tumor vasculature along with the defective tumor vessel functionality finally causes bouts of hypoxia and acidity in the tumor microenvironment (TME), further reinvigorating tumor aggression. Interstitial hypertension or high interstitial fluid pressure (IFP) is an outcome of tumor hyper-permeability. High IFP can be a barrier for either effective delivery of anti-cancer drugs toward the TME or accumulation of drugs within the tumor area, thus promoting tumor resistance to therapy. Some tumors do, however, not undergo angiogenesis but instead undergo vessel co-option or vascular mimicry, thereby adding another layer of complexity to cancer development and therapy.

CONCLUSIONS

Combination of anti-angiogenesis therapy with chemotherapy and particularly with immune checkpoint inhibitors (ICIs) is a promising strategy for a number of advanced cancers. Among the various approaches for targeting tumor angiogenesis, vascular normalization is considered as the most desired method, which allows effective penetration of chemotherapeutics into the tumor area, thus being an appropriate adjuvant to other cancer modalities.

Rational Treatment of Metastatic Colorectal Cancer: A Reverse Tale of Men, Mice, and Culture Dishes

Stratification of colorectal cancer into subgroups with different response to therapy was initially guided by descriptive associations between specific biomarkers and treatment outcome. Recently, preclinical models based on propagatable patient-derived tumor samples have yielded an improved understanding of disease biology, which has facilitated the functional validation of correlative information and the discovery of novel response determinants, therapeutic targets, and mechanisms of tumor adaptation and drug resistance. We review the contribution of patient-derived models to advancing colorectal cancer characterization, discuss their influence on clinical decision-making, and highlight emerging challenges in the interpretation and clinical transferability of results obtainable with such approaches. SIGNIFICANCE: Association studies in patients with colorectal cancer have led to the identification of response biomarkers, some of which have been implemented as companion diagnostics for therapeutic decisions. By enabling biological investigation in a clinically relevant experimental context, patient-derived colorectal cancer models have proved useful to examine the causal role of such biomarkers in dictating drug sensitivity and are providing fresh knowledge on new actionable targets, dynamics of tumor evolution and adaptation, and mechanisms of drug resistance.

Granzyme B PET Imaging of Immune Checkpoint Inhibitor Combinations in Colon Cancer Phenotypes

PURPOSE

Immune checkpoint inhibitor (ICI) monotherapy and combination regimens are being actively pursued as strategies to improve durable response rates in cancer patients. However, the biology surrounding combination therapies is not well understood and may increase the likelihood of immune-mediated adverse events. Accurate stratification of ICI response by non-invasive PET imaging may help ensure safe therapy management across a wide number of cancer phenotypes.

PROCEDURES

We have assessed the ability of a fluorine-labelled peptide, [18F]AlF-mNOTA-GZP, targeting granzyme B, to stratify ICI response in two syngeneic models of colon cancer, CT26 and MC38. In vivo tumour uptake of [18F]AlF-mNOTA-GZP following ICI monotherapy, or in combination with PD-1 was characterised and correlated with changes in tumour-associated immune cell populations.

RESULTS

[18F]AlF-mNOTA-GZP showed good predictive ability and correlated well with changes in tumour-associated T cells, especially CD8+ T cells; however, overall uptake and response to monotherapy or combination therapies was very different in the CT26 and MC38 tumours, likely due to the immunostimulatory environment imbued by the MSI-high phenotype in MC38 tumours.

CONCLUSIONS

[18F]AlF-mNOTA-GZP uptake correlates well with changes in CD8+ T cell populations and is able to stratify tumour response to a range of ICIs administered as monotherapies or in combination. However, tracer uptake can be significantly affected by preexisting phenotypic abnormalities potentially confusing data interpretation.

Immune escape: A critical hallmark in solid tumors

Incapacitated immune system is a characteristic hallmark of solid tumors. Immune system within a tumor undergoes an imbalance in cellular dispersion and functionality. Effector cells are precluded from the invasive margin of tumor; instead, immune suppressor cells are present at high fractions. Conditions in the tumor microenvironment (TME) like altered metabolism, chronic hypoxia and chronic inflammation are the known predisposing factors, implicated in the immune malfunctioning. Deficiency of innate immune sensing mediated by checkpoint receptors including programmed death-1 receptor (PD-1), CTL-associated antigen-4 (CTLA-4) hijacked by tumor cells takes a major part of the blame, requiring a need for appropriate strategies in order to bring back the balance in the immune system. Immune checkpoint inhibitor (ICI) therapy has been in the eye of the current research rendering promising results. The story is not, however, that easy in which it is not so effective for Cold tumors, it may cause severe adverse effects, and that patients may acquire resistance to such therapy; this requires for updating the current knowledge about the immune ecosystem, using tumor type dependent dose calculation and exploiting proper adjuvants in order for evolving desired responses.

Biology and Therapeutic Targets of Colorectal Serrated Adenocarcinoma; Clues for a Histologically Based Treatment against an Aggressive Tumor

Serrated adenocarcinoma (SAC) is a tumor recognized by the WHO as a histological subtype accounting for around 9% of colorectal carcinomas. Compared to conventional carcinomas, SACs are characterized by a worse prognosis, weak development of the immune response, an active invasive front and a frequent resistance to targeted therapy due to a high occurrence of KRAS or BRAF mutation. Nonetheless, several high-throughput studies have recently been carried out unveiling the biology of this cancer and identifying potential molecular targets, favoring a future histologically based treatment. This review revises the current evidence, aiming to propose potential molecular targets and specific treatments for this aggressive tumor.