A Mathematical Model for Predicting Patient Responses to Combined Radiotherapy with CTLA-4 Immune Checkpoint Inhibitors
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The purpose of this study was to develop a cell–cell interaction model that could predict a tumor’s response to radiotherapy (RT) combined with CTLA-4 immune checkpoint inhibition (ICI) in patients with hepatocellular carcinoma (HCC). The previously developed model was extended by adding a new term representing tremelimumab, an inhibitor of CTLA-4. The distribution of the new immune activation term was derived from the results of a clinical trial for tremelimumab monotherapy (NCT01008358). The proposed model successfully reproduced longitudinal tumor diameter changes in HCC patients treated with tremelimumab (complete response = 0%, partial response = 17.6%, stable disease = 58.8%, and progressive disease = 23.6%). For the non-irradiated tumor control group, adding ICI to RT increased the clinical benefit rate from 8% to 32%. The simulation predicts that it is beneficial to start CTLA-4 blockade before RT in terms of treatment sequences. We developed a mathematical model that can predict the response of patients to the combined CTLA-4 blockade with radiation therapy. We anticipate that the developed model will be helpful for designing clinical trials with the ultimate aim of maximizing the efficacy of ICI-RT combination therapy.Keywords:
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Monoclonal antibody based immune checkpoint blockade therapies have achieved clinical successes in management of malignant tumors. As the first monoclonal antibody targeting immune checkpoint molecules entered into clinics, the molecular basis of ipilimumab-based anti-CTLA-4 blockade has not yet been fully understood. In the present study, we report the complex structure of ipilimumab and CTLA-4. The complex structure showed similar contributions from VH and VL of ipilimumab in binding to CTLA-4 front β-sheet strands. The blockade mechanism of ipilimumab is that the strands of CTLA-4 contributing to the binding to B7-1 or B7-2 were occupied by ipilimumab and thereafter prevents the binding of B7-1 or B7-2 to CTLA-4. Though ipilimumab binds to the same epitope with tremelimumab on CTLA-4 with similar binding affinity, the higher dissociation rate of ipilimumab may indicate the dynamic binding to CTLA-4, which may affect its pharmacokinetics. The molecular basis of ipilimumab-based anti-CTLA-4 blockade and comparative study of the binding characteristics of ipilimumab and tremelimumab would shed light for the discovery of small molecular inhibitors and structure-based monoclonal antibody optimization or new biologics.
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To prevent damage from an immune response against autoantigens and toxins originating from the gut, the liver promotes an immune-tolerant milieu providing fertile ground for immune escape of cancer cells. Therefore, the use and evaluation of immune checkpoint inhibitors (ICIs) in hepatocellular carcinoma (HCC) is a treatment rationale.In this article, we discuss the role of the dual ICIs blockade in advanced HCC, covering the biological basis for their combination, their mechanism of action, and the results of the early-phase studies testing nivolumab plus ipilimumab and durvalumab plus tremelimumab. Furthermore, we provide the results of the phase III HIMALAYA trial and an overview of the ongoing trials investigating the dual ICIs in different disease stages.The potential approval of the dual ICIs blockade strategies for advanced HCC will set the entry of antiangiogenic-free options, expanding the proportion of patients eligible for a first-line treatment. However, it will pose a series of clinical challenges with a sizable proportion of patients, namely Child-Pugh B, elderly, and immunocompromised patients, still marginalized. Also, given the rate of disease progression, identifying reliable predictive biomarkers is crucial to inform treatment choice and sequences. Finally, the compelling response rate of such combinations is paving the way for their evaluation in earlier stages.
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Immune checkpoint inhibitors are effective cancer treatments, but molecular determinants of clinical benefit are unknown. Ipilimumab and tremelimumab are antibodies against cytotoxic T-lymphocyte antigen 4 (CTLA-4). Anti-CTLA-4 treatment prolongs overall survival in patients with melanoma. CTLA-4 blockade activates T cells and enables them to destroy tumor cells.We obtained tumor tissue from patients with melanoma who were treated with ipilimumab or tremelimumab. Whole-exome sequencing was performed on tumors and matched blood samples. Somatic mutations and candidate neoantigens generated from these mutations were characterized. Neoantigen peptides were tested for the ability to activate lymphocytes from ipilimumab-treated patients.Malignant melanoma exomes from 64 patients treated with CTLA-4 blockade were characterized with the use of massively parallel sequencing. A discovery set consisted of 11 patients who derived a long-term clinical benefit and 14 patients who derived a minimal benefit or no benefit. Mutational load was associated with the degree of clinical benefit (P=0.01) but alone was not sufficient to predict benefit. Using genomewide somatic neoepitope analysis and patient-specific HLA typing, we identified candidate tumor neoantigens for each patient. We elucidated a neoantigen landscape that is specifically present in tumors with a strong response to CTLA-4 blockade. We validated this signature in a second set of 39 patients with melanoma who were treated with anti-CTLA-4 antibodies. Predicted neoantigens activated T cells from the patients treated with ipilimumab.These findings define a genetic basis for benefit from CTLA-4 blockade in melanoma and provide a rationale for examining exomes of patients for whom anti-CTLA-4 agents are being considered. (Funded by the Frederick Adler Fund and others.).
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Abstract: Enhancing or prolonging T-cell activation by monoclonal antibodies (mAbs) blocking negative signaling receptors such as CTLA4 is one approach to overcoming tumor-induced immune tolerance. Ipilimumab and tremelimumab inhibit CTLA4, prolonging antitumor immune responses and leading to durable anti-tumor effects. Treatment with these mAbs has demonstrated clinically important and durable tumor responses and disease control rates in patients with unresectable advanced melanoma. Durable objective responses have been reported across a spectrum of doses and schedules, with relative safety in this patient population. Although the phase III tremelimumab melanoma study was closed for “futility”, the 1-year survival rate of >50% for tremelimumab and the median survival of 11.7 months (compared with 10.7 months for chemotherapy) are notable. Results of the phase III studies testing CTLA4-blockade with ipilimumab are eagerly anticipated. The further development of these agents includes testing in the neoadjuvant melanoma setting (ipilimumab) as well the adjuvant high-risk melanoma setting (ipilimumab). Future progress with CTLA-4 blockade therapy will also likely come from the use of combinations of agents that target several critical regulatory pathways of the immune system and modulate the immune response in the host in a synergistic and controlled fashion. Keywords: cancer treatment, ipilimumab, tremelimumab, monoclonal antibodies
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Immune checkpoint inhibitors (ICIs) are a new way of immunotherapy, not simply refers to the improvement of immunity to the body, but by improving the immune microenvironment around the tumor, thereby activating immune cell activity in vivo to achieve anti-tumor purposes. Now, CTLA‐4 and PD‐1 or PD‐L1 monoclonal antibody are mainly developed relatively successfully for immune checkpoints, in addition to other new immune checkpoints that have been discovered and clinically tested. However, while immune checkpoint inhibitors have been developed successively, some vague problems still need to be solved, such as the large gap between the immunotherapy effects of different patients. These issues are critical to the selection of immune checkpoint inhibitors. In this review, based on the study of the immunosuppressive mechanism of CTLA-4 and PD-1/PD-L1, the application of related immune checkpoint inhibitors in cancer treatment is discussed starting from three representative types of cancer. At the same time, according to the existing problems, some common immune-related adverse events and newly discovered immune checkpoints are summarized, and the future research direction of ICIs is further explored.
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Presurgical immune checkpoint blockade Checkpoint blockade immunotherapy using antibodies that inhibit the programmed cell death 1 (PD-1) or cytotoxic T lymphocyte–associated protein 4 (CTLA-4) pathways has resulted in unprecedented clinical outcomes for certain cancers such as melanoma. Topalian et al. review advances in neoadjuvant (presurgical) immunotherapy as an important next step for enhancing the response of early-stage tumors to immune checkpoint blockade. They highlight the mechanistic rationale for neoadjuvant immunotherapy and recent neoadjuvant clinical trials based on anti–PD-1 or anti–PD-1 ligand 1 (anti–PD-L1) therapy. Pathological assessment criteria that may provide early on-treatment biomarkers to predict patient response are also discussed. Science , this issue p. eaax0182
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Checkpoint blockade immunotherapy using antibodies that inhibit the programmed cell death 1 (PD-1) or cytotoxic T lymphocyte–associated protein 4 (CTLA-4) pathways has resulted in unprecedented clinical outcomes for certain cancers such as melanoma. Topalian et al. review advances in neoadjuvant (presurgical) immunotherapy as an important next step for enhancing the response of early-stage tumors to immune checkpoint blockade. They highlight the mechanistic rationale for neoadjuvant immunotherapy and recent neoadjuvant clinical trials based on anti–PD-1 or anti–PD-1 ligand 1 (anti–PD-L1) therapy. Pathological assessment criteria that may provide early on-treatment biomarkers to predict patient response are also discussed.
Science , this issue p. [eaax0182][1]
[1]: /lookup/doi/10.1126/science.aax0182
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Targeting CTLA-4, the patriarch of immune checkpoint modulators, is currently the only immunotherapeutic approach that has achieved significant clinical benefit in melanoma phase III trials. In this review, recent new ideas about the mechanism of action of anti-CTLA antibodies, other new molecules to target, and rationales for combination therapies will be discussed.Although the clinical efficacy of the anti-CTLA-4 monoclonal antibody (mAb) ipilimumab is meanwhile without doubt, its mechanism of action is still not fully understood. Recent data indicate that, besides modulation of the TCR signal, CTLA-4 mAbs can mediate regulatory T-cell depletion in an Fc gamma receptor dependent manner.Blockade of the molecules PD-1 and PD-L1 has given promising clinical responses (and this beyond melanoma), whereas their complex expression and interaction pattern makes a clear statement about the mechanism of action challenging.Additional other co-inhibitory and co-stimulatory molecules have been identified recently. Combinations of immune checkpoint modulators themselves or with other therapies, such as adoptive cell therapy, targeted therapy or radiotherapy, will improve the outcomes further.Immune checkpoint blockade is currently the most promising systemic therapeutic approach to achieve long-lasting responses or even cure in melanoma and other malignancies.
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