OX40 Ligand Research Articles

Anti-OX40 Biological Therapies in the Treatment of Atopic Dermatitis: A Comprehensive Review.

Introduction. Atopic dermatitis (AD) is the most prevalent inflammatory dermatological disorder, affecting a significant percentage of the global population. This chronic disease has a multifactorial and intricate pathogenesis, influenced by genetic predisposition, skin barrier dysfunction, immune dysregulation, neuroimmune mechanisms, and alterations in the skin microbiome, among other factors. Methods. The treatment of AD has faced significant clinical challenges due to the ineffectiveness of conventional therapies. However, recent advances in understanding its pathophysiology have led to the introduction of new therapeutic options. Recently, the OX40 receptor has been identified as a key factor in the development of AD. Recent studies have demonstrated that blocking the OX40 ligand with monoclonal antibodies significantly and sustainably improves the signs and symptoms of moderate to severe AD. Results. A comprehensive review of the available literature on anti-OX40 treatments in atopic dermatitis that evaluates their mechanism of action, their clinical efficacy, and the prospects of this promising therapeutic option for improving AD management is provided. Conclusions. Anti-OX40 and anti-OX40L blockers are a promising therapeutic alternative for the management of moderate-severe atopic dermatitis. Prospective analytical studies are needed to determine whether this new therapeutic target represents a qualitative advance in modifying the progression of the disease.

EXTH-66. ONCOLYTIC ADENOVIRAL INFECTION SYNERGIZES WITH IMMUNE CHECKPOINT INHIBITION TO MEDIATE INTRACRANIAL TUMOR CONTROL IN DISPARATE MODELS OF MELANOMA BRAIN METASTASES

Abstract Amongst all solid cancers, melanoma brain metastases (MBM) have the highest likelihood of metastasizing to the brain. The emergence of immune checkpoint inhibitors (ICI) for metastatic melanoma have demonstrated increasingly promising results; however, intracranial progression remains a challenging obstacle. Oncolytic viral (OV) therapy leverages tumor cell replication machinery to selectively replicate and kill tumor cells and promote anti-tumor immunity. We propose this OV strategy can be applied to MBM through direct tumor infection that simultaneously sustains a distant antitumor immune response. To counteract immunosuppressive features of the tumor microenvironment (TME), a third-generation oncolytic adenovirus (Delta-24-RGDOX) has been developed which expresses the immune stimulatory OX40 ligand (OX40L). We quantified the cytotoxic capacity of Delta-24-RGDOX and its ability to achieve immunogenic cell death (ICD) in vitro along with cerebral organoid co-culture models. Additionally, we used a series of syngeneic murine melanoma models to explore local and systemic antitumor immunity following Delta-24-RGDOX infection. Delta-24-RGDOX inoculation achieved viral infection, OX40L cell surface expression, tumor cell cytotoxicity, and ICD in vitro. Viral oncolysis was recapitulated in a cerebral organoid melanoma co-culture model with concomitant alterations in microglia activation and detection of viral transcripts within microglia using single cell RNA sequencing, suggesting a viral-clearing role of microglia within the TME. Local tumor clearance was achieved in orthotopic intracranial models following direct intracranial viral inoculation alone, and in combination with ICI. Lastly, we demonstrated improvement in overall survival in a synchronous subcutaneous/intracranial B16F10 model where the subcutaneous tumor was treated with Delta-24-RGDOX in combination with ICI. In summary, Delta-24-RGDOX achieves viral infection, oncolysis, and ICD following infection of melanoma cell lines. These findings translated in multiple in vivo models including immune cell activation and systemic antitumor immunity against uninfected MBM. Future studies are needed to explore the role of immune cell trafficking, myeloid cell modulation, T cell priming, and clonal expansion withing locally infected and the distant melanoma TME.

EXTH-55. ANTI-TUMOR ACTIVITY OF A NEW ONCOLYTIC ADENOVIRUS DELTA-24-RGDOX-IL15 CO-EXPRESSING OX40L AND IL-15

Abstract Accumulating evidence show that the interaction between oncolytic viruses (OVs) and host immune system plays an essential role in cancer virotherapy. Compared to lytic potency of OVs, enhancement of OV-mediated anti-tumor immunity has become a more attractive strategy to improve OV efficacy. To this end, we have reported that the third-generation oncolytic adenovirus (OA), Delta-24-RGDOX, which expresses the immune co-stimulator OX40 ligand (OX40L), is more potent to elicit anti-tumor immunity than the second-generation OA Delta-24-RGD. Since IL-15 activates T and NK cells and promotes persistence of CD8+ memory T cells, we hypothesize that co-expression of OX40L and IL-15 by OAs will further potentiate their efficacy. For this purpose, we constructed the next generation OA Delta-24-RGDOX-IL15. In cultured human and murine tumor cell lines, this new virus effectively expressed the two molecules and displayed comparable potency in viral replication and oncolysis as OAs expressing either of the two (Delta-24-RGDOX, Delta-24-RGD-IL15). Then, we tested the anti-tumor activity of Delta-24-RGDOX-IL15 (two doses, intratumorally, one week interval) in two syngeneic tumor models in C57BL/6 mice: 1) intracranial (i.c.) gliomas from GL261-5 cells; 2) subcutaneous (s.c.)/i.c. melanomas from B16 cells (virus injected into s.c. tumors only). We found Delta-24-RGDOX-IL15 was more efficacious than the other two OAs to inhibit tumor growth of both treated tumor and the untreated i.c. tumors in the second model, leading to long-term survivors (p < 0.05). Different from adoptive cell therapies with cells engineered to express IL-15, we haven’t observed any obvious toxicity with this new virus when it was injected intratumorally into either the i.c. or s.c. tumors. Further studies are in progress to analyze the modifications of the tumor microenvironment induced by the addition of IL-15 to Delta-24-RGDOX. We expect this virus to be a good candidate to be combined with CAR T cell therapies.

Phase 2b randomized clinical trial of amlitelimab, an anti-OX40 ligand antibody, in patients with moderate-to-severe atopic dermatitis

Amlitelimab, a fully human nondepleting monoclonal antibody targeting OX40 ligand on antigen-presenting cells, could prevent T-cell-driven inflammation seen in atopic dermatitis (AD). This trial evaluated the efficacy and safety of amlitelimab in adults with AD. In this 2-part, phase 2b, randomized, double-blinded placebo-controlled trial (NCT05131477), patients received subcutaneous amlitelimab every 4 weeks at doses of 250 mg with 500-mg loading dose, 250 mg, 125 mg, or 62.5 mg, or placebo for 24 weeks in Part 1 (1:1:1:1:1 randomization). In Part 2, clinical responders were reallocated 3:1 to withdraw amlitelimab or continue the previous dose regimen for 28 weeks. The primary end point was percent change in Eczema Area and Severity Index (EASI) from baseline to Week 16. 390 and 190 patients enrolled in Part 1 and Part 2, respectively. Significant percent change decreases in EASI were observed with amlitelimab vs. placebo (P<.001). Clinical responses at Week 24 (Investigator Global Assessment 0/1 and/or EASI-75) were maintained at Week 52 in patients continuing or withdrawn from amlitelimab. In patients maintaining clinical response at Week 52 while off-treatment, >80% had serum amlitelimab concentrations below a 4-μg/mL threshold for several weeks prior to Week 52. Reductions in AD-related biomarkers during Part 1 were maintained through Part 2. Amlitelimab was well tolerated over 52 weeks. Amlitelimab treatment significantly reduced clinical and biomarker responses, and was well tolerated in adults with AD through Week 52. Sustained responses were observed in the majority of patients after amlitelimab withdrawal for 28 weeks.

Human OX40L-CAR-Tregs target activated antigen-presenting cells and control T cell alloreactivity.

Regulatory T cells (Tregs) make major contributions to immune homeostasis. Because Treg dysfunction can lead to both allo- and autoimmunity, there is interest in correcting these disorders through Treg adoptive transfer. Two of the central challenges in clinically deploying Treg cellular therapies are ensuring phenotypic stability and maximizing potency. Here, we describe an approach to address both issues through the creation of OX40 ligand (OX40L)-specific chimeric antigen receptor (CAR)-Tregs under the control of a synthetic forkhead box P3 (FOXP3) promoter. The creation of these CAR-Tregs enabled selective Treg stimulation by engagement of OX40L, a key activation antigen in alloimmunity, including both graft-versus-host disease and solid organ transplant rejection, and autoimmunity, including rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus. We demonstrated that OX40L-CAR-Tregs were robustly activated in the presence of OX40L-expressing cells, leading to up-regulation of Treg suppressive proteins without induction of proinflammatory cytokine production. Compared with control Tregs, OX40L-CAR-Tregs more potently suppressed alloreactive T cell proliferation in vitro and were directly inhibitory toward activated monocyte-derived dendritic cells (DCs). We identified trogocytosis as one of the central mechanisms by which these CAR-Tregs effectively decrease extracellular display of OX40L, resulting in decreased DC stimulatory capacity. OX40L-CAR-Tregs demonstrated an enhanced ability to control xenogeneic graft-versus-host disease compared with control Tregs without abolishing the graft-versus-leukemia effect. These results suggest that OX40L-CAR-Tregs may have wide applicability as a potent cellular therapy to control both allo- and autoimmune diseases.

Robust and Sustained STING Pathway Activation via Hydrogel-Based In Situ Vaccination for Cancer Immunotherapy.

The stimulator of interferon genes (STING) pathway is crucial for tumor immunity, leading to the exploration of STING agonists as potential immunotherapy adjuvants. However, their clinical application faces obstacles including poor pharmacokinetics, transient activation, and an immunosuppressive tumor microenvironment (TME). Addressing these limitations, our study aims to develop an injectable silk fibroin hydrogel-based in situ vaccine. It incorporates a nanoscale STING agonist, an immunogenic cell death (ICD) inducer, and an immunomodulator to ensure their controlled and sustained release. cGAMP nanoparticles (cGAMPnps) with a core-shell structure ensure optimal delivery of cGAMP to dendritic cells (DCs), thereby activating the STING pathway and fostering DC maturation. ICD-associated damage-associated molecular patterns amplify and prolong STING activation via enhanced type I IFN and other inflammatory pathways, along with delayed degradation of cGAMP and STING. Furthermore, the STING-driven vascular normalization by cGAMPnps and ICD, in conjunction with immunomodulators like antiprogrammed cell death protein 1 antibody (anti-PD-1 Ab) or OX40 ligand (OX40L), effectively remodels the immunosuppressive TME. This in situ gel vaccine, when used independently or with surgery as neoadjuvant/adjuvant immunotherapy, enhances DC and CD8+ T-cell activation, suppressing tumor progression and recurrence across various immunologically cold tumor models. It revolutionizes the application of STING agonists in cancer immunotherapy, offering substantial promise for improving outcomes across a broad spectrum of malignancies.

NK Cell Degranulation Triggered by Rituximab Identifies Potential Markers of Subpopulations with Enhanced Cytotoxicity toward Malignant B Cells.

A promising strategy in cancer immunotherapy is to restore or enhance the cytotoxicity of NK cells, among others, by activating the mechanism of antibody-dependent cellular cytotoxicity (ADCC). Monoclonal antibodies targeting tumor antigens, such as rituximab (targeting CD20), induce NK cell-mediated ADCC and have been used to treat B cell malignancies, such as non-Hodgkin lymphoma, but not always successfully. The aim of this study was to analyze the gene expression profile of the NK cells involved in the cytolytic response stimulated by rituximab. NK cells were co-cultured with rituximab-opsonized Raji cells. Sorting into responder and non-responder groups was based on the presence of CD107a, which is a degranulation marker. RNA-seq results showed that the KIT and TNFSF4 genes were strongly down-regulated in the degranulating population of NK cells (responders); this was further confirmed by qRT-PCR. Both genes encode surface proteins with cellular signaling abilities, namely c-KIT and the OX40 ligand. Consistent with our findings, c-KIT was previously reported to correlate inversely with cytokine production by activated NK cells. The significance of these findings for cancer immunotherapy seems essential, as the pharmacological inhibition of c-KIT and OX40L, or gene ablation, could be further tested for the enhancement of the anti-tumor activity of NK cells in response to rituximab.

An open-label single-center investigator-initiated exploratory clinical study in patients with refractory or recurrent solid tumors using SBRT as “in situ vaccination”: R-ISV-FOLactis trial.

44 Background: The immunotherapy of sarcomas remains a challenge. As a breakthrough tool for cancer immunotherapy, the therapeutic cancer vaccine is in rapid development. In situ vaccination can be realized by intratumoral immune injection and radiotherapy. We have developed a bifunctional engineered Lactococcus lactis (FOLactis) expressing an encoded fusion protein of fms-like tyrosine kinase 3 ligand (Flt3L) and OX40 ligand (OX40L). We hypothesized that intratumoral injection of "FOLactis" combined with SBRT will realize tumor control and the synergetic application of PD-1 mAb systematically will further improve the effect of immunotherapy. Methods: This exploratory clinical study is designed as an open-label trial aimed at treating patients with advanced solid tumors who are unresponsive or intolerable to standard treatment. Patients will be treated with SBRT, intratumoral injection of "FOLactis", and PD-1 blockade. The primary endpoint was the objective response rate (ORR) of target lesions after 3 months and 6 months. The secondary endpoint included the disease control rate (DCR) of target lesions, progression-free survival (PFS), overall survival (OS), etc. Results: From July 2022 to December 2023, 30 patients were eligible for this trial (63% were sarcomas). 53.3% and 33.3% had received radiotherapy or PD-1/PD-L1 mAb before respectively. The ORR and DCR of target lesions after 3 months were 27.6% and 93.1%, while these of systemic efficacy were 17.2% and 55.2%, respectively. In sarcomas, the ORR, DCR of target lesions were 11.1% and 88.9%, while these of systemic efficacy were 5.5% and 50%, respectively. Considering the deferred response in sarcomas, we also calculated the ORR after 6 months as the primary endpoint. The ORR, DCR of target lesions after 6 months were 56.3% and 100%, while these in sarcomas were 41.7% and 100%, respectively. Systemic median PFS were 2.87 months. Median PFS of target lesions and mOS has not reached. Among the evaluable target lesions, 6-month EFS was 50% in sarcomas (6/12) and 50% in all patients (8/16). Expression of CD4+, CD8+ T cells and dendritic cells was significantly increased between pre-treatment and post-treatment peripheral blood in responders. The most common treatment-related adverse events (TRAEs) were fever (83.3%), lymphocytopenia (53.3%), hypocalcemia (30%), neutrophilia (26.7%) and nausea (26.7%). Grade≥3 TRAE occurred in 11 patients, including lymphocytopenia (30%), fever (6.7%), leukopenia (3.3%), anemia (3.3%) and cardiac insufficiency (3.3%). Conclusions: In situ vaccination with“FOLactis", along with SBRT was tolerable and induced anti-tumor immunity, which would also augment systemic response when synergized with PD-1 mAb. This in situ vaccination is probably a promising option for advanced solid tumors. Clinical trial information: ChiCTR2200060660 .

Immune checkpoint reprogramming via sequential nucleic acid delivery strategy optimizes systemic immune responses for gastrointestinal cancer immunotherapy

Monoclonal antibodies targeting immune checkpoints have been widely applied in gastrointestinal cancer immunotherapy. However, systemic administration of various monoclonal antibodies does not often result in sustained effects in reversing the immunosuppressive tumor microenvironment (TME), which may be due to the spatiotemporal dynamic changes of immune checkpoints. Herein, we reported a novel immune checkpoint reprogramming strategy for gastrointestinal cancer immunotherapy. It was achieved by the sequential delivery of siPD-L1 (siRNA for programmed cell death ligand 1) and pOX40L (plasmid for OX40 ligand), which were complexed with two cationic polymer brush-grafted carbon nanotubes (dense short (DS) and dense long (DL)) designed based on the structural characteristics of nucleic acids and brush architectures. Upon administrating DL/pOX40L for the first three dosages, then followed by DS/siPD-L1 for the next three dosages to the TME, it upregulated the stimulatory checkpoint OX40L on dendritic cells (DCs) and downregulated inhibitory checkpoint PD-L1 on tumor cells and DCs in a sequential reprogramming manner. Compared with other combination treatments, this sequential strategy drastically boosted the DCs maturation, and CD8+ cytotoxic T lymphocytes infiltration in tumor site. Furthermore, it could augment the local antitumor response and improve the T cell infiltration in tumor-draining lymph nodes to reverse the peripheral immunosuppression. Our study demonstrated that sequential nucleic acid delivery strategy via personalized nanoplatforms effectively reversed the immunosuppression status in both tumor microenvironment and peripheral immune landscape, which significantly enhanced the systemic antitumor immune responses and established an optimal immunotherapy strategy against gastrointestinal cancer.

Non-viral-mediated gene transfer of OX40 ligand for tumor immunotherapy.

Immune checkpoint blockade (ICB) is rapidly becoming a standard of care in the treatment of many cancer types. However, the subset of patients who respond to this type of therapy is limited. Another way to promote antitumoral immunity is the use of immunostimulatory molecules, such as cytokines or T cell co-stimulators. The systemic administration of immunotherapeutics leads to significant immune-related adverse events (irAEs), therefore, the localized antitumoral action is needed. One way to achieve this is intratumoral non-viral gene-immune therapy, which allows for prolonged and localized gene expression, and multiple drug administration. In this study, we combined the previously described non-viral gene delivery system, PEG-PEI-TAT copolymer, PPT, with murine OX40L-encoding plasmid DNA. The resulting OX40L/PPT nanoparticles were characterized via gel mobility assay, dynamic light scattering analysis and in vitro transfection efficiency evaluation. The antitumoral efficacy of intratumorally (i.t.) administered nanoparticles was estimated using subcutaneously (s.c.) implanted CT26 (colon cancer), B16F0 (melanoma) and 4T1 (breast cancer) tumor models. The dynamics of stromal immune cell populations was analyzed using flow cytometry. Weight loss and cachexia were used as irAE indicators. The effect of combination of i.t. OX40L/PPT with intraperitoneal PD-1 ICB was estimated in s.c. CT26 tumor model. The obtained OX40L/PPT nanoparticles had properties applicable for cell transfection and provided OX40L protein expression in vitro in all three investigated cancer models. We observed that OX40L/PPT treatment successfully inhibited tumor growth in B16F0 and CT26 tumor models and showed a tendency to inhibit 4T1 tumor growth. In B16F0 tumor model, OX40L/PPT treatment led to the increase in antitumoral effector NK and T killer cells and to the decrease in pro-tumoral myeloid cells populations within tumor stroma. No irAE signs were observed in all 3 tumor models, which indicates good treatment tolerability in mice. Combining OX40L/PPT with PD-1 ICB significantly improved treatment efficacy in the CT26 subcutaneous colon cancer model, providing protective immunity against CT26 colon cancer cells. Overall, the anti-tumor efficacy observed with OX40L non-viral gene therapy, whether administered alone or in combination with ICB, highlights its potential to revolutionize cancer gene therapy, thus paving the way for unprecedented advancements in the cancer therapy field.

The role of OX40 ligand/OX40 axis signalling in atopic dermatitis.

Atopic dermatitis (AD) is a heterogeneous inflammatory condition involving multiple immune pathways mediated by pathogenic T cells. OX40 ligand (OX40L) and OX40 are costimulatory immune checkpoint molecules that regulate effector and memory T-cell activity and promote sustained immune responses in multiple immunological pathways, including T helper (Th)2, Th1, Th17 and Th22. As such, OX40L/OX40 signalling between antigen-presenting cells (APCs) and activated T cells postantigen recognition promotes pathogenic T-cell proliferation and survival. Under inflammatory conditions, OX40L is upregulated on APCs, enhancing the magnitude of antigen-specific T-cell responses and secretion of proinflammatory cytokines. In AD, OX40L/OX40 signalling contributes to the amplification and chronic persistence of T-cell-mediated inflammation. Recent therapeutic success in clinical trials has highlighted the importance of the OX40L/OX40 axis as a promising target for the treatment of AD. Here, we discuss the many factors that are involved in the expression of OX40L and OX40, including the cytokine milieu, antigen presentation, the inflammatory environment in AD, and the therapeutic direction influenced by this costimulatory pathway.

Blockade of OX40/OX40L signaling using anti-OX40L alleviates murine lupus nephritis.

Genetic variants of the OX40 ligand (OX40L) locus are associated with the risk of systemic lupus erythematosus (SLE), it is unclear how the OX40L blockade delays the lupus phenotype. Therefore, we examined the effects of an anti-OX40L antibody in MRL/Lpr mice. Next, we investigated the effect of anti-OX40L on immunosuppression in keyhole limpet hemocyanin-immunized C57BL/6J mice. In vitro treatment of anti-OX40L in CD4+ T and B220+ B cells was used to explore the role of OX40L in the pathogenesis of SLE. Anti-OX40L alleviated murine lupus nephritis, accompanied by decreased production of anti-dsDNA and proteinuria, as well as lower frequencies of splenic T helper (Th) 1 and T-follicular helper cells (Tfh). In keyhole limpet hemocyanin-immunized mice, decreased levels of immunoglobulins and plasmablasts were observed in the anti-OX40L group. Anti-OX40L reduced the number and area of germinal centers. Compared with the control IgG group, anti-OX40L downregulated CD4+ T-cell differentiation into Th1 and Tfh cells and upregulated CD4+ T-cell differentiation into regulatory T cells in vitro. Furthermore, anti-OX40L inhibited toll-like receptor 7-mediated differentiation of antibody-secreting cells and antibody production through the regulation of the SPIB-BLIMP1-XBP1 axis in B cells. These results suggest that OX40L is a promising therapeutic target for SLE.

Abstract 3736: Bridging the gaps: A cross-species approach to PD-1 and OX40 combination immunotherapy

Abstract Monoclonal antibodies (mAbs) targeting immune checkpoints, such as PD-1, PD-L1, and CTLA4, have provided unprecedented clinical benefits to human cancer patients. Novel strategies such as combination therapy with OX40 or 4-1BB agonists are currently under investigation in various pre-clinical studies to enhance the therapeutic benefits of immune checkpoint inhibitors. While syngeneic mouse tumor xenograft models offer valuable insights in pre-clinical testing, they fall short in capturing the nuanced heterogeneity within and between tumors and the dynamic tumor-immune interface. In contrast, canine patients with spontaneous neoplasms possess a closely analogous and intact immune system. These canine patients, who receive sophisticated and advanced medical therapy like their human counterparts, can serve as a vital intermediate pre-clinical model system between rodent studies and human clinical trials, potentially reducing clinical trial failures. In this study, we have developed a novel bispecific fusion protein, denoted BsOXPD, that combines OX40 agonism and PD-1 blockade into a single therapeutic. Our bispecific fusion protein employs an anti-PD-1 nanobody (Nb) to bind and block the PD1 pathway and the extracellular domain (ECD) of the OX40 ligand to stimulate the OX40 receptor. We have developed murinized, caninized, and humanized versions of this protein. All versions of the bispecific fusion protein retain their biochemical and functional properties following the murinization, caninization, and humanization processes. Importantly, all versions effectively disrupt the PD-1/PD-L1 axis in murine, canine, and human systems while concurrently acting as potent OX40 agonists. To further improve the humanized version of the BsOXPD, we partially humanized the anti-PD1 Nb by introducing amino acid substitutions in various framework regions. The humanized anti-PD1 Nb still completely inhibited the binding of human PD-L1 to the PD-1 receptor. The caninized version of BsOXPD exhibits no toxicities or immune-related adverse events (irAEs) following intravenous injection at doses of 1 mg/kg or 3 mg/kg body weight in healthy beagle dogs. In summary, we have designed a cross-species Nb-based fusion protein for PD1 blockade and OX40 agonism. Our next goal is to evaluate the therapeutic efficacy of caninized BsOXPD in pet dogs with oral melanoma in neoadjuvant settings. Therefore, our cross-species approach will offer comprehensive insights into the safety, pharmacokinetic (PK) profile, and clinical benefits associated with the concurrent application of PD1 blockade and OX40 agonism. Citation Format: Maninder Sandey, Damien Ruiz, Jonathan Marable, Deepa Bedi, Payal Agarwal. Bridging the gaps: A cross-species approach to PD-1 and OX40 combination immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3736.

Intra-bone marrow injection with engineered Lactococcus lactis for the treatment of metastatic tumors: Primary report

Bone marrow has the capacity to produce different types of immune cells, such as natural killer cells, macrophages, dendritic cells (DCs) and T cells. Improving the activation of immune cells in the bone marrow can enhance the therapy of bone metastases. Previously, we designed an engineered probiotic Lactococcus lactis, capable of expressing a fusion protein of Fms-like tyrosine kinase 3 ligand and co-stimulator OX40 ligand (FOLactis), and proved that it can induce the activation and differentiation of several immune cells. In this research, we successfully establish mouse models of bone metastasis, lung metastasis and intraperitoneal dissemination, and we are the first to directly inject the probiotics into the bone marrow to inhibit tumor growth. We observe that injecting FOLactis into the bone marrow of mice can better regulate the immune microenvironment of tumor-bearing mice, resulting in a tumor-suppressive effect. Compared to subcutaneous (s.c.) injection, intra-bone marrow (IBM) injection is more effective in increasing mature DCs and CD8+ T cells and prolonging the survival of tumor-bearing mice. Our results confirm that IBM injection of FOLactis reprograms the immune microenvironment of bone marrow and has remarkable effectiveness in various metastatic tumor models.

520 - Evaluating the expression of OX40 and OX40 ligand in lesional skin versus non-lesional skin in volunteers with atopic dermatitis and in healthy control skin

Abstract Introduction/Background Growing evidence suggests that blocking the OX40 ligand (OX40L)/OX40 costimulatory pathway could have therapeutic effects in inflammatory diseases such as atopic dermatitis (AD). Amlitelimab (SAR445229; KY1005) is a potential first-in-class, fully human, non-depleting anti-OX40L monoclonal antibody that blocks OX40L-OX40 interactions. We report OX40L and OX40 expression from skin biopsies collected in two studies: an amlitelimab Phase 2a (Ph2a) study in patients with moderate-to-severe AD, and a small-scale study of patients with mild AD and healthy volunteers. Objectives Assess OX40L and OX40 expression in AD skin (lesional and non-lesional) and healthy control skin. Methods As part of a Ph2a randomized, double-blind, placebo-controlled study (NCT03754309) of amlitelimab in moderate-to-severe AD, 174 baseline-paired lesional/non-lesional skin biopsies were collected from all patients (n=87). In a separate small-scale study, 24 skin biopsies were collected, including healthy control skin from healthy volunteers (n=6) and paired lesional/non-lesional skin from patients with mild AD (n=9). Each biopsy underwent immunohistochemical (IHC; formalin-fixed paraffin-embedded) analyses using various antibodies (OX40L: rabbit IgG antibody from Cell Signaling Technology for Ph2a biopsies, proprietary mouse IgG2a KY1005 for small-scale study biopsies; OX40: clone Ber-ACT35 from BioLegend for all biopsies). A trained pathologist assessed IHC staining in the dermis and/or epidermis using semi-quantitative scoring (0 [no stained cells] to 10 [all cells stained]) or quantitative methods (cells/mm2, Tissue Studio 4.0, and HALO link image analysis software). Wilcoxon matched-pairs signed-rank test was used to assess IHC staining of Ph2a biopsies. Ph2a biopsies also underwent transcriptomic analyses (stored in RNALater) for OX40L (TNFSF4) and OX40 (TNFRSF4) on sequenced RNA using a linear mixed model with Benjamini-Hochberg adjustment. Results In baseline Ph2a biopsies, IHC analysis revealed elevated OX40L and OX40 staining in lesional versus non-lesional AD skin (P &amp;lt;0.0001 for both markers). For OX40L, the median score was 3 (lesional) versus 1 (non-lesional) and the Wilcoxon matched-pairs signed-rank test found P&amp;lt;0.0001. For OX40+ cells, the median expression was 179.8 cells/mm2 in lesional AD skin versus 54.45 cells/mm2 in non-­lesional AD skin (P&amp;lt;0.0001 using the Wilcoxon matched-pairs signed-rank test). These findings were confirmed by RNA sequencing analysis, with TNFSF4 (OX40L) and TNFRSF4 (OX40) differentially expressed in lesional and non-lesional AD skin (P&amp;lt;0.01 and P&amp;lt;0.0001, respectively). A larger scale study is ongoing that may further support this finding. In the small-scale study including patients with mild AD and healthy volunteers, there was a trend for an increase of mean OX40L+ and OX40+ cells/mm2 in lesional skin versus non-lesional skin and healthy control skin in the dermis and epidermis (OX40L+ dermal lesional, non-lesional, healthy, respectively: 17.6, 11.2, 11.5; OX40L+ epidermal: 5.8, 2.1, 1.9; OX40+ dermal: 5.7, 2.1, 0.4; OX40+ epidermal: 10.9, 9.0, 1.8); the increase was significant for lesional versus healthy control skin for dermal OX40+ cells/mm2 (P&amp;lt;0.001). Conclusions We confirm with IHC and RNA sequencing that OX40L and OX40 expression is elevated in skin lesions of patients with moderate-to-severe AD. We also demonstrate a trend to elevated OX40L and elevated OX40 in mild AD skin versus healthy volunteers. A potential explanation for the lower levels of OX40L and OX40 in patients with mild AD in this study may be their lower disease severity versus Ph2a study patients. These findings support the OX40L/OX40 pathway as a relevant target in T cell immune dysregulation; its blockade may represent a novel treatment approach for moderate-to-severe AD.

523 - Efficacy and safety of amlitelimab (an anti-OX40 ligand antibody) in patients with moderate-to-severe atopic dermatitis: 24-week results from a phase 2b trial (STREAM-AD)

Abstract Introduction/Background Targeting and binding OX40 ligand (OX40L) expressed on antigen-presenting cells may inhibit the persistent immune response that drives atopic dermatitis (AD) pathophysiology. Amlitelimab (SAR445229; KY1005) is a potential first-in-class, fully human, non-depleting anti-OX40L monoclonal antibody that blocks OX40L-OX40 interactions and has shown efficacy and an acceptable safety profile in a Phase 2a trial in adults with moderate-to-severe AD. Here, we present 24-week efficacy and safety results (Part 1) from an ongoing dose-ranging Phase 2b trial. The study remains blinded to individual patient data (Part 2 ongoing). Objectives To evaluate the efficacy and safety of amlitelimab in adults with moderate-to-severe AD. Methods STREAM-AD (NCT05131477) is a 52-week, randomised, double-blinded, placebo-controlled Phase 2b monotherapy trial. This study is designed with 2 parts (double-blind throughout): a 24-week treatment period (Part 1, completed and presented here) and a 36-week maintenance/withdrawal period (Part 2, ongoing). Adults (18 to &amp;lt;75 years; n=390) with moderate-to-severe AD were randomised 1:1:1:1:1 to receive subcutaneous amlitelimab Q4W (250 mg with 500 mg loading dose [LD], n=77; 250 mg without LD, n=78; 125 mg without LD, n=77; or 62.5 mg without LD, n=79) or placebo Q4W (n=79). The primary endpoint was percentage change in Eczema Area and Severity Index (EASI) from baseline at Week 16. Key secondary endpoints included percentage change in EASI at Week 24 and percentage of patients with at least 75% reduction from baseline in EASI (EASI-75), percentage of patients with Investigator Global Assessment response of 0 (clear) or 1 (almost clear) and a reduction from baseline of ≥2 points (IGA 0/1), and proportion of patients with a weekly average reduction of Peak Pruritus Numerical Rating Scale (PP-NRS) ≥4 points from baseline. The primary efficacy analysis included all randomised patients who completed Week 24 or discontinued treatment or study prior to Week 24 visit (n=390), whereas the safety analysis included all treated patients (n=388). Results Treatment with amlitelimab resulted in statistically significant improvements in percentage change in EASI from baseline to Week 16 compared to placebo for all four doses studied. The 250 mg with LD group had the numerically highest response versus placebo at Week 16, with a least-squares mean change from baseline of –32.1% (95% CI: –43.9, –20.3; P&amp;lt;0.0001); the remaining groups without LD had the following responses versus placebo: 250 mg, –27.3 (95% CI: –39.1, –15.6; P&amp;lt;0.0001); 125 mg, –22.2 (95% CI: –34.0, –10.4; P=0.0002); and 62.5 mg, –30.2 (95% CI: –41.9, –18.5; P&amp;lt;0.0001). There were also clinically meaningful improvements in all key secondary efficacy outcome measures, with all amlitelimab dose groups demonstrating nominally significant (P&amp;lt;0.05) efficacy versus placebo for EASI-75, IGA 0/1, and PP-NRS ≥4, except 250 mg (no LD) in IGA 0/1 at Week 16 (P=0.0562). Continued improvements were generally observed through Week 24 in primary and key secondary efficacy outcomes. Amlitelimab was well tolerated across all dose groups, with no safety concerns identified. Conclusions In this dose-ranging Phase 2b trial of amlitelimab in adults with moderate-to-severe AD, amlitelimab demonstrated clinically meaningful efficacy over 24 weeks with an acceptable safety profile across all four dose groups.

P17.15.A THANK PHASE I TRIAL OF DNX-2440 ONCOLYTIC ADENOVIRUS IN PATIENTS WITH FIRST OR SECOND RECURRENCE OF GLIOBLASTOMA: PRELIMINARY RESULTS

Abstract BACKGROUND Oncolytic immunovirotherapy is emerging as a potential therapeutic approach in neuro-oncology. The oncolytic adenovirus DNX-2401, genetically engineered for selective replication and enhanced infectivity in tumor cells, has shown efficacy in adult patients with recurrent glioblastoma (GBM). In order to overcome the immunosuppressive brain-tumor microenvironment and thus enhance its antiglioma effect, DNX-2440 is a new armed virus which contains the same modifications but additionally incorporates OX40 ligand to induce the expression of such molecule in tumor cells and so increase the antitumor immune response. MATERIAL AND METHODS We are conducting a phase I open-label single-center study to investigate the safety and efficacy of a single intratumoral injection of DNX-2440 in patients with first or second recurrence of GBM. This is a dose escalation study, with a 3 + 3 design, evaluating an initial dose of 4x10e9 viral particles (vp) and a target dose of 4x10e10 vp. A single measurable lesion bigger than 10 mm in two perpendicular diameters and smaller than 25 cc is required for inclusion in the study. RESULTS To date 16 patients (6 [37.5%] female, 10 [62.5%] male) have been enrolled and treated with DNX-2401. Median age is 55 years (range, 39-80) and median KPS is 80 (range 70-90). As per protocol, surgery consisted of biopsy in all patients followed by intratumoral injection of DNX-2440. No dose limiting toxicity has been registered during the dose escalation phase (first cohort of 3 patients receiving 4x10e9 vp, and second cohort of 3 patients receiving 4x10e10 vp), and the remainder patients have received the target dose of 4x10e10 vp in the dose expansion cohort. Safety profile is acceptable with no serious adverse events related to DNX-2440 reported to date. Clinical benefit with tumor size reduction and prolonged survival have already been confirmed in 3 patients. Correlative analyses evaluating immune response in blood samples are ongoing. CONCLUSION Our current data suggest that intratumoral injection of DNX-2440 is feasible and safe, and seems to provide a clinical benefit in some patients with recurrent GBM. Furthermore, this trial illustrates the potential of oncolytic virus platforms to reshape the brain-tumor microenvironment and its interesting role in combination strategies with other immune-oncology agents for treating this disease.

392 Safety of amlitelimab in a Phase 2a clinical trial of patients with moderate-to-severe atopic dermatitis

Abstract Amlitelimab (SAR445229), a fully human, nondepleting, noncytotoxic, monoclonal antibody, binds to OX40Ligand (OX40L) on antigen-presenting cells to block OX40-OX40L interactions. Outcomes from a 36-week, double-blind, Phase 2a trial (NCT03754309) in patients with moderate-to-severe atopic dermatitis are described. This study aims to assess the safety of OX40-OX40L signaling blockade with amlitelimab in patients with moderate-to-severe atopic dermatitis. Eighty-nine patients were randomized to amlitelimab low-dose (LD; 200-mg loading/100-mg maintenance Q4W), high-dose (HD; 500 mg/250 mg Q4W) or placebo. The coprimary safety endpoint was treatment-emergent adverse event (TEAE) incidence to W16. Safety was assessed to W36. Amlitelimab was well tolerated. Related TEAE incidence was similar between amlitelimab [LD 35% (10/29); HD 20% (6/30)] and placebo [31% (9/29)] to W16 and W36 [LD 10% (2/20); HD 0 (0/22); placebo 0 (0/17)]. The TEAEs more common with amlitelimab vs. placebo (≥5% difference) to W16 included headache [LD 0; HD 3 (10%); placebo 1 (3.4%)], upper respiratory tract infection [3 (10.3%); 0; 1 (3.4%)], hyperhidrosis [0; 2 (6.7%); 0], pyrexia [2 (6.9%); 0; 0], aspartate aminotransferase increased [0; 2 (6.7%); 0] and iron-deficiency anemia [2 (6.9%); 0; 0]; and to W36, Herpes simplex [0; 2 (9.1%); 0]. Before W16, one severe adverse event (SAE) of infected dermal cyst was reported as possibly related; it resolved, and the patient completed the study. Post-W16, one unrelated SAE of sudden death occurred 87 days following the final amlitelimab dose. No hypersensitivity or tolerability events, or clinically meaningful changes in laboratory values, vital signs or electrocardiogram recordings were reported. Amlitelimab was well tolerated in a Phase 2a trial of patients with moderate-to-severe atopic dermatitis, confirming the unremarkable safety profile observed in Phase 1.

DIPG-10. DELTA-24-RGDOX PROMOTES ANTITUMOR IMMUNE RESPONSE IN DMG MODELS

Abstract Diffuse Midline Gliomas (DMG) are very aggressive brain tumors that arise in the brainstem of children. The prognosis of these patients is still dismal, with an overall survival of less than one year. DMG tumors are poorly infiltrated by the immune system, and therefore in this project, we propose the use of the oncolytic adenovirus Delta-24-RGDOX to enhance the antitumor immune response. Delta-24-RGDOX is based on the Delta-24-RGD platform and incorporates the OX40 ligand (OX40L). The binding of OX40 to OX40L leads to the co-stimulation of CD4 and CD8 cells, generating effector and memory T cells. Therefore, the aim of this project is to improve the antitumor effect of the virus, providing a greater co-stimulation in the tumor. In vitro, Delta-24-RGDOX was able to efficiently infect and express viral proteins in human and murine DMG cell lines, and to cause cell death in a dose-dependent manner. Moreover, the virus expressed OX40L on the membrane of infected cells, which was functional and capable of activating CD8 T cells. Once we confirmed that the viral administration into DMG in vivo models was safe, we evaluated the therapeutic effect of the virus. We observed a significant survival increase after Delta-24-RGDOX treatment of a DMG model at early tumor stage (P=0.0033, median OS PBS 9 vs 12 days for virus treated mice) and in already stablished tumors (P=0.018, median OS PBS 9 vs 12.5 days for virus treated mice). Importantly, tumors from treated mice (7 days after treatment) displayed a significant increase of immune infiltration compared to controls. Moreover, splenocytes from Delta-24-RGDOX treated mice were also more activated. These data demonstrated that Delta-24-RGDOX expresses OX40L on infected cells, promoting the modulation of the tumor microenvironment and leading to an improved survival outcome in DMG models.

A phase 1 study of the OX40 agonist, BGB-A445, with or without tislelizumab, an anti-PD-1 monoclonal antibody, in patients with advanced solid tumors.

2574 Background: OX40 is an immune costimulatory receptor, expressed on activated CD4+ and CD8+ T cells, which promotes T cell proliferation and survival in the tumor microenvironment. BGB-A445 is a novel monoclonal antibody (mAb) OX40 agonist that does not compete with endogenous OX40 ligand binding. BGB-A445 has demonstrated antitumor activity as a single agent and in combination with an anti-PD-1 mAb in preclinical studies. Here, we report data from the ongoing dose-escalation part of a multicenter, phase 1 dose escalation/expansion study (NCT04215978) of BGB-A445 alone or in combination with tislelizumab (TIS) in patients (pts) with advanced solid tumors. Methods: Eligible pts were enrolled into seven sequential dose escalation cohorts of BGB-A445 IV as monotherapy (Part A) or five increasing dose levels of BGB-A445 IV in combination with TIS 200 mg IV (Part B) on day 1 of 21-day cycles. Dose escalation was guided by a Bayesian (mTPI-2) approach. This study assessed safety, tolerability, pharmacokinetics (PK) profile, and preliminary antitumor activity (RECIST v1.1). Results: As of August 31, 2022, 59 pts were enrolled in Part A and 32 pts in Part B. Median (range) age was 59 years (28-80) and 61 years (37-75) in Parts A and B, respectively; 26 (44%) and 13 (41%) pts were male, respectively. ≥Grade 3 treatment-emergent AEs (TEAEs) were reported in 24 (41%) and 17 (53%) pts in Parts A and B, respectively; the most commonly reported (≥3 reported) ≥grade 3 TEAEs were gastrointestinal disorders (diarrhea, nausea, and abdominal pain). Serious TEAEs were reported in 23 (39%) pts in Part A and 16 (50%) in Part B. Treatment-related AEs leading to treatment discontinuation were reported in 1 (2%) pt in Part A and 0 (0%) pts in Part B. In Part A, all grade immune-mediated AEs (imAEs) were reported in 11 (19%) pts; no pts reported ≥grade 3 imAEs. In Part B, all grade imAEs were reported in 14 (44%) pts; ≥grade 3 imAEs were reported in 1 (3%) pt (one event each of rash maculopapular and diarrhea). There were no dose-limiting toxicities or concerning patterns of safety/tolerability observed. BGB-A445 PK (maximum concentration [Cmax] and area under the curve from day 0 to 21 [AUC0-21]) were linear and dose proportional in all tested dose ranges. In the efficacy-evaluable population of Parts A (n=50) and B (n=30), respectively, partial response was observed in 2 (4%) pts (unconfirmed) and 7 (23%) pts (confirmed); stable disease in 18 (36%) and 13 (43%) pts (confirmed), and progressive disease in 26 (52%) and 8 (27%) pts. Conclusions: In the dose escalation part of this study, BGB-A445 alone or in combination with TIS was generally well tolerated across all doses in pts with advanced solid tumors, and demonstrated preliminary antitumor activity as both a single and combination agent. The dose expansion part of the study is ongoing in pts with non-small cell lung cancer and head and neck squamous cell carcinoma. Clinical trial information: NCT04215978 .