Tumor radiation therapy creates therapeutic vaccine responses to the colorectal cancer antigen GUCY2C

Immunological Assessment of Recent Immunotherapy for Colorectal Cancer

Colorectal cancer (CRC) is the third most prevalent malignancy with increased incidence and mortality rates worldwide. Traditional treatment approaches have attempted to efficiently target CRC; however, they have failed in most cases, owing to the cytotoxicity and non-specificity of these therapies. Therefore, it is essential to develop an effective alternative therapy to improve the clinical outcomes in heterogeneous CRC cases. Immunotherapy has transformed cancer treatment with remarkable efficacy and overcomes the limitations of traditional treatments. With an understanding of the cancer-immunity cycle and tumor microenvironment evolution, current immunotherapy approaches have elicited enhanced antitumor immune responses. In this comprehensive review, we outline the latest advances in immunotherapy targeting CRC and provide insights into antitumor immune responses reported in landmark clinical studies. We focused on highlighting the combination approaches that synergistically induce immune responses and eliminate immunosuppression. This review aimed to understand the limitations and potential of recent immunotherapy clinical studies conducted in the last five years (2019-2023) and to transform this knowledge into a rational design of clinical trials intended for effective antitumor immune responses in CRC.

Challenges to addressing the unmet medical needs for immunotherapy targeting cold colorectal cancer

With the establishment of the immune surveillance mechanism since the 1950s, attempts have been made to activate the immune system for cancer treatment through the discovery of various cytokines or the development of antibodies up to now. The fruits of these efforts have contributed to the recognition of the 3^rd generation of anticancer immunotherapy as the mainstream of cancer treatment. However, the limitations of cancer immunotherapy are also being recognized through the conceptual establishment of cold tumors recently, and colorectal cancer (CRC) has become a major issue from this therapeutic point of view. Here, it is emphasized that non-clinical strategies to overcome the immunosuppressive environment and clinical trials based on these basic investigations are being made on the journey to achieve better treatment outcomes for the treatment of cold CRC.

Radiotherapy/Chemotherapy-Immunotherapy for Cancer Management: From Mechanisms to Clinical Implications

Cancer immunotherapy has drawn much attention because it can restart the recognition and killing function of the immune system to normalize the antitumor immune response. However, the role of radiotherapy and chemotherapy in cancer treatment cannot be ignored. Due to cancer heterogeneity, combined therapy has become a new trend, and its efficacy has been confirmed in many studies. This review discussed the clinical implications and the underlying mechanisms of cancer immunotherapy in combination with radiotherapy or chemotherapy, offering an outline for clinicians as well as inspiration for future research.

Efficacy of radiotherapy combined with immune checkpoint inhibitors in patients with melanoma: a systemic review and meta-analysis

The purpose of this study is to review the efficacy of radiotherapy combined with immune checkpoint inhibitors (ICIs) in the treatment of melanoma and systematically evaluate the efficacy and safety of this combined treatment compared with ICIs alone. We searched a number of online databases up to 1 July 2021. Comprehensive Meta-Analysis 2.0 and RevMan 5.0 were used for summary analysis. The overall survival (OS), progression-free survival (PFS), overall response rate (ORR) and treatment adverse effects (AEs) were calculated. In total, 624 patients were included from 12 studies, including nine published studies and the results of three clinical trials. Radiotherapy combined with ICIs had a higher ORR compared with ICIs alone (35.00 vs. 20.39%). In terms of survival effect, radiotherapy combined with ICIs had no obvious advantage in OS. There was no statistically significant difference between 6-month and 12-month OS (P = 0.13; P = 0.69). There was no significant difference in PFS at 6 months (P = 0.08), but there was a significant difference in PFS at 12 months (P = 0.005). For patients with melanoma, radiotherapy combined with ICIs can improve the effective rate of treatment. Although there is no obvious OS advantage, it can improve PFS without serious adverse effects. Most of the studies included in this article are retrospective analyses, and there are few randomized controlled studies at present. Therefore, more prospective studies are still needed to explore the efficacy of radiotherapy combined with immunotherapy in melanoma.

Targeting gastrointestinal cancers with chimeric antigen receptor (CAR)-T cell therapy

The immune system is capable of remarkably potent and specific efficacy against infectious diseases. For decades, investigators sought to leverage those characteristics to create immune-based therapies (immunotherapy) that might be far more effective and less toxic than conventional chemotherapy and radiation therapy for cancer. Those studies revealed many factors and mechanisms underlying the success or failure of cancer immunotherapy, leading to synthetic biology approaches, including CAR-T cell therapy. In this approach, patient T cells are genetically modified to express a chimeric antigen receptor (CAR) that converts T cells of any specificity into tumor-specific T cells that can be expanded to large numbers and readministered to the patient to eliminate cancer cells, including bulky metastatic disease. This approach has been most successful against hematologic cancers, resulting in five FDA approvals to date. Here, we discuss some of the most promising attempts to apply this technology to cancers of the gastrointestinal tract.

Th balance related host genetic background affects the therapeutic effects of combining carbon-ion radiotherapy with dendritic cell immunotherapy

PURPOSE

The goal of this study is to clarify the underlying mechanisms of metastasis suppression by CiDC (carbon-ion radiotherapy (CIRT) combined with immature dendritic cell (iDC) immunotherapy), which was previously shown to significantly suppress pulmonary metastasis in a NR-S1-bearing C3H/He mouse model.

METHODS AND MATERIALS

Mouse carcinoma cell lines (LLC, LM8, Colon-26 and Colon-26MGS) were grafted into the right hind paw of syngeneic mice (C57BL/6J, C3H/He and BALB/c). Seven days later, the tumors on the mice were locally irradiated with carbon-ions (290 MeV/n, 6 cm SOBP, 1 or 2 Gy). At 1.5 days after irradiation, bone marrow-derived immature dendritic cells were administrated intravenously into a subset of the mice. The number of lung metastases was evaluated within three weeks after irradiation. In vitro cultured cancer cells were irradiated with carbon-ion (290 MeV/n, mono-energy, LET approximately 70 ∼ 80 keV/µm), and then co-cultured with iDCs for three days to determine the DC maturation.

RESULTS

CiDC effectively repressed distant lung metastases in cancer cell (LLC and LM8)-bearing C57BL/6J and C3H/He mouse models. However, Colon-26 and Colon-26MGS-bearing BALB/c models did not show enhancement of metastasis suppression by combination treatment. This was further evaluated by comparing LM8-bearing C3H/He and LLC-bearing C57BL/6J models with a Colon-26-bearing BALB/c model. In vitro co-culture assays demonstrated that all irradiated cell lines were able to activate C3H/He or C57BL/6J-derived iDCs into mature DCs, but not BALB/c-derived iDCs.

CONCLUSION

The genetic background of the host may have a strong impact on the potency of combination therapy. Future animal and clinical testing should evaluate host genetic factors when evaluating treatment efficacy.

A liposomal RNA vaccine inducing neoantigen-specific CD4+ T cells augments the antitumor activity of local radiotherapy in mice

Antigen-encoding, lipoplex-formulated RNA (RNA-LPX) enables systemic delivery to lymphoid compartments and selective expression in resident antigen-presenting cells. We report here that the rejection of CT26 tumors, mediated by local radiotherapy (LRT), is further augmented in a CD8⁺ T cell-dependent manner by an RNA-LPX vaccine that encodes CD4⁺ T cell-recognized neoantigens (CD4 neoantigen vaccine). Whereas CD8⁺ T cells induced by LRT alone were primarily directed against the immunodominant gp70 antigen, mice treated with LRT plus the CD4 neoantigen vaccine rejected gp70-negative tumors and were protected from rechallenge with these tumors, indicating a potent poly-antigenic CD8⁺ T cell response and T cell memory. In the spleens of CD4 neoantigen-vaccinated mice, we found a high number of activated, poly-functional, Th1-like CD4⁺ T cells against ME1, the immunodominant CD4 neoantigen within the poly-neoantigen vaccine. LRT itself strongly increased CD8⁺ T cell numbers and clonal expansion. However, tumor infiltrates of mice treated with CD4 neoantigen vaccine/LRT, as compared to LRT alone, displayed a higher fraction of activated gp70-specific CD8⁺ T cells, lower PD-1/LAG-3 expression and contained ME1-specific IFNγ⁺ CD4⁺ T cells capable of providing cognate help. CD4 neoantigen vaccine/LRT treatment followed by anti-CTLA-4 antibody therapy further enhanced the efficacy with complete remission of gp70-negative CT26 tumors and survival of all mice. Our data highlight the power of combining synergistic modes of action and warrants further exploration of the presented treatment schema.

Primary Tumor Site Specificity is Preserved in Patient-Derived Tumor Xenograft Models

Patient-derived tumor xenograft (PDX) mouse models are widely used for drug screening. The underlying assumption is that PDX tissue is very similar with the original patient tissue, and it has the same response to the drug treatment. To investigate whether the primary tumor site information is well preserved in PDX, we analyzed the gene expression profiles of PDX mouse models originated from different tissues, including breast, kidney, large intestine, lung, ovary, pancreas, skin, and soft tissues. The popular Monte Carlo feature selection method was employed to analyze the expression profile, yielding a feature list. From this list, incremental feature selection and support vector machine (SVM) were adopted to extract distinctively expressed genes in PDXs from different primary tumor sites and build an optimal SVM classifier. In addition, we also set up a group of quantitative rules to identify primary tumor sites. A total of 755 genes were extracted by the feature selection procedures, on which the SVM classifier can provide a high performance with MCC 0.986 on classifying primary tumor sites originated from different tissues. Furthermore, we obtained 16 classification rules, which gave a lower accuracy but clear classification procedures. Such results validated that the primary tumor site specificity was well preserved in PDX as the PDXs from different primary tumor sites were still very different and these PDX differences were similar with the differences observed in patients with tumor. For example, VIM and ABHD17C were highly expressed in the PDX from breast tissue and also highly expressed in breast cancer patients.

Split tolerance permits safe Ad5-GUCY2C-PADRE vaccine-induced T-cell responses in colon cancer patients

BACKGROUND

The colorectal cancer antigen GUCY2C exhibits unique split tolerance, evoking antigen-specific CD8⁺, but not CD4⁺, T-cell responses that deliver anti-tumor immunity without autoimmunity in mice. Here, the cancer vaccine Ad5-GUCY2C-PADRE was evaluated in a first-in-man phase I clinical study of patients with early-stage colorectal cancer to assess its safety and immunological efficacy.

METHODS

Ten patients with surgically-resected stage I or stage II (pN0) colon cancer received a single intramuscular injection of 10¹¹ viral particles (vp) of Ad5-GUCY2C-PADRE. Safety assessment and immunomonitoring were carried out for 6 months following immunization. This trial employed continual monitoring of both efficacy and toxicity of subjects as joint primary outcomes.

RESULTS

All patients receiving Ad5-GUCY2C-PADRE completed the study and none developed adverse events greater than grade 1. Antibody responses to GUCY2C were detected in 10% of patients, while 40% exhibited GUCY2C-specific T-cell responses. GUCY2C-specific responses were exclusively CD8⁺ cytotoxic T cells, mimicking pre-clinical studies in mice in which GUCY2C-specific CD4⁺ T cells are eliminated by self-tolerance, while CD8⁺ T cells escape tolerance and mediate antitumor immunity. Moreover, pre-existing neutralizing antibodies (NAbs) to the Ad5 vector were associated with poor vaccine-induced responses, suggesting that Ad5 NAbs oppose GUCY2C immune responses to the vaccine in patients and supported by mouse studies.

CONCLUSIONS

Split tolerance to GUCY2C in cancer patients can be exploited to safely generate antigen-specific cytotoxic CD8⁺, but not autoimmune CD4⁺, T cells by Ad5-GUCY2C-PADRE in the absence of pre-existing NAbs to the viral vector.

TRIAL REGISTRATION

This trial (NCT01972737) was registered at ClinicalTrials.gov on October 30th, 2013. https://clinicaltrials.gov/ct2/show/NCT01972737.

Non-thermal plasma induces immunogenic cell death in vivo in murine CT26 colorectal tumors

Immunogenic cell death is characterized by the emission of danger signals that facilitate activation of an adaptive immune response against dead-cell antigens. In the case of cancer therapy, tumor cells undergoing immunogenic death promote cancer-specific immunity. Identification, characterization, and optimization of stimuli that induce immunogenic cancer cell death has tremendous potential to improve the outcomes of cancer therapy. In this study, we show that non-thermal, atmospheric pressure plasma can be operated to induce immunogenic cell death in an animal model of colorectal cancer. In vitro, plasma treatment of CT26 colorectal cancer cells induced the release of classic danger signals. Treated cells were used to create a whole-cell vaccine which elicited protective immunity in the CT26 tumor mouse model. Moreover, plasma treatment of subcutaneous tumors elicited emission of danger signals and recruitment of antigen presenting cells into tumors. An increase in T cell responses targeting the colorectal cancer-specific antigen guanylyl cyclase C (GUCY2C) were also observed. This study provides the first evidence that non-thermal plasma is a bone fide inducer of immunogenic cell death and highlights its potential for clinical translation for cancer immunotherapy.

Mechanisms regulating T-cell infiltration and activity in solid tumors

T-lymphocytes play a critical role in cancer immunity as evidenced by their presence in resected tumor samples derived from long-surviving patients, and impressive clinical responses to various immunotherapies that reinvigorate them. Indeed, tumors can upregulate a wide array of defense mechanisms, both direct and indirect, to suppress the ability of Tcells to reach the tumor bed and mount curative responses upon infiltration. In addition, patient and tumor genetics, previous antigenic experience, and the microbiome, are all important factors in shaping the T-cell repertoire and sensitivity to immunotherapy. Here, we review the mechanisms that regulate T-cell homing, infiltration, and activity within the solid tumor bed. Finally, we summarize different immunotherapies and combinatorial treatment strategies that enable the immune system to overcome barriers for enhanced tumor control and improved patient outcome.

Immunotherapy Combined with Large Fractions of Radiotherapy: Stereotactic Radiosurgery for Brain Metastases-Implications for Intraoperative Radiotherapy after Resection

Brain metastases (BM) affect approximately a third of all cancer patients with systemic disease. Treatment options include surgery, whole-brain radiotherapy, or stereotactic radiosurgery (SRS) while chemotherapy has only limited activity. In cases where patients undergo resection before irradiation, intraoperative radiotherapy (IORT) to the tumor bed may be an alternative modality, which would eliminate the repopulation of residual tumor cells between surgery and postoperative radiotherapy. Accumulating evidence has shown that high single doses of ionizing radiation can be highly efficient in eliciting a broad spectrum of local, regional, and systemic tumor-directed immune reactions. Furthermore, immune checkpoint blockade (ICB) has proven effective in treating antigenic BM and, thus, combining IORT with ICB might be a promising approach. However, it is not known if a low number of residual tumor cells in the tumor bed after resection is sufficient to act as an immunizing event opening the gate for ICB therapies in the brain. Because immunological data on tumor bed irradiation after resection are lacking, a rationale for combining IORT with ICB must be based on mechanistic insight from experimental models and clinical studies on unresected tumors. The purpose of the present review is to examine the mechanisms by which large radiation doses as applied in SRS and IORT enhance antitumor immune activity. Clinical studies on IORT for brain tumors, and on combined treatment of SRS and ICB for unresected BM, are used to assess the safety, efficacy, and immunogenicity of IORT plus ICB and to suggest an optimal treatment sequence.

Prime-Boost Immunization Eliminates Metastatic Colorectal Cancer by Producing High-Avidity Effector CD8+ T Cells

Heterologous prime-boost immunization with plasmid DNA and viral vector vaccines is an emerging approach to elicit CD8+ T cell-mediated immunity targeting pathogens and tumor Ags that is superior to either monotherapy. Yet, the mechanisms underlying the synergy of prime-boost strategies remain incompletely defined. In this study, we examine a DNA and adenovirus (Ad5) combination regimen targeting guanylyl cyclase C (GUCY2C), a receptor expressed by intestinal mucosa and universally expressed by metastatic colorectal cancer. DNA immunization efficacy was optimized by i.m. delivery via electroporation, yet it remained modest compared with Ad5. Sequential immunization with DNA and Ad5 produced superior antitumor efficacy associated with increased TCR avidity, whereas targeted disruption of TCR avidity enhancement eliminated GUCY2C-specific antitumor efficacy, without affecting responding T cell number or cytokine profile. Indeed, functional TCR avidity of responding GUCY2C-specific CD8+ T cells induced by various prime or prime-boost regimens correlated with antitumor efficacy, whereas T cell number and cytokine profile were not. Importantly, although sequential immunization with DNA and Ad5 maximized antitumor efficacy through TCR avidity enhancement, it produced no autoimmunity, reflecting sequestration of GUCY2C to intestinal apical membranes and segregation of mucosal and systemic immunity. Together, TCR avidity enhancement may be leveraged by prime-boost immunization to improve GUCY2C-targeted colorectal cancer immunotherapeutic efficacy and patient outcomes without concomitant autoimmune toxicity.

The Immunoregulatory Potential of Particle Radiation in Cancer Therapy

Cancer treatment, today, consists of surgery, chemotherapy, radiation, and most recently immunotherapy. Combination immunotherapy-radiotherapy (CIR) has experienced a surge in public attention due to numerous clinical publications outlining the reduction or elimination of metastatic disease, following treatment with specifically ipilimumab and radiotherapy. The mechanism behind CIR, however, remains unclear, though it is hypothesized that radiation transforms the tumor into an in situ vaccine which immunotherapy modulates into a larger immune response. To date, the majority of attention has focused on rotating out immunotherapeutics with conventional radiation; however, the unique biological and physical benefits of particle irradiation may prove superior in generation of systemic effect. Here, we review recent advances in CIR, with a particular focus on the usage of charged particles to induce or enhance response to cancerous disease.

Immune-modulating properties of ionizing radiation: rationale for the treatment of cancer by combination radiotherapy and immune checkpoint inhibitors

Radiotherapy (RT) utilizes the DNA-damaging properties of ionizing radiation to control tumor growth and ultimately kill tumor cells. By modifying the tumor cell phenotype and the tumor microenvironment, it may also modulate the immune system. However, out-of-field reactions of RT mostly assume further immune activation. Here, the sequence of the applications of RT and immunotherapy is crucial, just as the dose and fractionation may be. Lower single doses may impact on tumor vascularization and immune cell infiltration in particular, while higher doses may impact on intratumoral induction and production of type I interferons. The induction of immunogenic cancer cell death seems in turn to be a common mechanism for most RT schemes. Dendritic cells (DCs) are activated by the released danger signals and by taking up tumor peptides derived from irradiated cells. DCs subsequently activate T cells, a process that has to be tightly controlled to ensure tolerance. Inhibitory pathways known as immune checkpoints exist for this purpose and are exploited by tumors to inhibit immune responses. Cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) on T cells are two major checkpoints. The biological concepts behind the findings that RT in combination with anti-CTLA-4 and/or anti-PD-L1 blockade stimulates CD8+ T cell-mediated anti-tumor immunity are reviewed in detail. On this basis, we suggest clinically significant combinations and sequences of RT and immune checkpoint inhibition. We conclude that RT and immune therapies complement one another.

Radiation meets immunotherapy - a perfect match in the era of combination therapy?

PURPOSE

This review focuses on recent advances in the field of combining radiation with immunotherapy for the treatment of malignant diseases, since various combinatorial cancer therapy approaches have lately proven highly successful.

RESULTS

With initial case reports and anecdotes progressively converting into solid clinical data, interest in cancer immunotherapy (CIT) has risen steeply. Especially immune checkpoint blockade therapies have recently celebrated tremendous successes in the treatment of severe malignancies resistant to conventional treatment strategies. Nevertheless, the high variability of patient responses to CIT remains a major hurdle, clearly indicating an urgent need for improvement. It has been suggested that successful cancer therapy most probably involves combinatorial treatment approaches. Radiotherapy (RT) has been proposed as a powerful partner for CIT due to its broad spectrum of immune modulatory characteristics. Several preclinical studies, supported by an increasing number of clinical observations, have demonstrated synergistic interactions between RT and CIT resulting in significantly improved therapy outcomes.

CONCLUSIONS

Numerous reports have shown that radiation is capable of tipping the scales from tumor immune evasion to elimination in different tumor types. The next puzzle to be solved is the question of logistics - including types, schedule and dosage of combinatorial RT and CIT strategies.

GUCY2C lysosomotropic endocytosis delivers immunotoxin therapy to metastatic colorectal cancer

The emergence of targeted cancer therapy has been limited by the paucity of determinants which are tumor-specific and generally associated with disease, and have cell dynamics which effectively deploy cytotoxic payloads. Guanylyl cyclase C (GUCY2C) may be ideal for targeting because it is normally expressed only in insulated barrier compartments, including intestine and brain, but over-expressed by systemic metastatic colorectal tumors. Here, we reveal that GUCY2C rapidly internalizes from the cell surface to lysosomes in intestinal and colorectal cancer cells. Endocytosis is independent of ligand binding and receptor activation, and is mediated by clathrin. This mechanism suggests a design for immunotoxins comprising a GUCY2C-directed monoclonal antibody conjugated through a reducible disulfide linkage to ricin A chain, which is activated to a potent cytotoxin in lysosomes. Indeed, this immunotoxin specifically killed GUCY2C-expressing colorectal cancer cells in a lysosomal- and clathrin-dependent fashion. Moreover, this immunotoxin reduced pulmonary tumors>80% (p<0.001), and improved survival 25% (p<0.001), in mice with established colorectal cancer metastases. Further, therapeutic efficacy was achieved without histologic evidence of toxicity in normal tissues. These observations support GUCY2C-targeted immunotoxins as novel therapeutics for metastatic tumors originating in the GI tract, including colorectum, stomach, esophagus, and pancreas.

Stereotactic ablative body radiotherapy combined with immunotherapy: present status and future perspectives

Radiotherapy is along with surgery and chemotherapy one of the prime treatment modalities in cancer. It is applied in the primary, neoadjuvant as well as the adjuvant setting. Radiation techniques have rapidly evolved during the past decade enabling the delivery of high radiation doses, reducing side-effects in tumour-adjacent normal tissues. While increasing local tumour control, current and future efforts ought to deal with microscopic disease at a distance of the primary tumour, ultimately responsible for disease-progression. This review explores the possibility of bimodal treatment combining radiotherapy with immunotherapy.