Glioblastoma multiforme (GBM) is the most common and aggressive form of primary brain cancer, for which effective therapies are urgently needed. Chimeric antigen receptor (CAR)-based immunotherapy represents a promising therapeutic approach, but it is often impeded by highly immunosuppressive tumor microenvironments (TME). Here, in an immunocompetent, orthotopic GBM mouse model, we show that CAR-T cells targeting tumor-specific epidermal growth factor receptor variant III (EGFRvIII) alone fail to control fully established tumors but, when combined with a single, locally delivered dose of IL-12, achieve durable anti-tumor responses. IL-12 not only boosts cytotoxicity of CAR-T cells, but also reshapes the TME, driving increased infiltration of proinflammatory CD4+ T cells, decreased numbers of regulatory T cells (Treg), and activation of the myeloid compartment. Importantly, the immunotherapy-enabling benefits of IL-12 are achieved with minimal systemic effects. Our findings thus show that local delivery of IL-12 may be an effective adjuvant for CAR-T cell therapy for GBM.

Invasive fungal disease (IFD) is a major cause of infectious mortality in hemato-oncology patients due to their underlying disease and its treatment, which lead to periods of prolonged immunosuppression (1). Invasive pulmonary aspergillosis (IPA) is the most common cause of mortality due to mold disease (2, 3), and early diagnosis and treatment are vital for improving outcomes (4). However, early diagnosis is hampered by the limitations of current biomarker tests and a lack of consensus on the best samples to be tested (i.e., blood, bronchoalveolar [BAL] fluid, or tissue biopsy specimens) in terms of both test sensitivity and practicability. Direct examination or culture of pulmonary tissue remains the "gold standard" for the diagnosis of IPA (5, 6). However, lung biopsy in this acute care setting is rarely performed due to the associated risks. Consequently, in view of the diagnostic challenges and worse outcomes with late treatment, an empirical strategy has been-and remains-the standard of care in many hematology units (7). This approach leads to overtreatment with antifungal drugs, which have significant side effects and drugdrug interactions. Furthermore, health care systems are exposed to spiraling drug costs (8). Improving the means of diagnosis of IPA is an urgent clinical need.Attempts have been made to optimize and standardize existing tests (5,6,(9)(10)(11)

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CAR-T cell therapy against CD19 has changed the treatment landscape in relapsed/refractory (r/r) B-ALL. R/r T-ALL has a dismal prognosis, with an unmet need for effective targeted therapies. Several unique challenges mean that CAR-T cell therapy has yet to be successfully translated to T-ALL. Most strategies have targeted pan-T cell antigens (CD7, CD5) but these are limited by T cell aplasia and fratricide, requiring elimination of CAR-T antigen surface expression during manufacture. An ideal target would be exclusively or largely confined to the malignant T cell component but published examples of these (CD1a and TRBC1) are expressed in only minor T-ALL subsets. We previously showed that CD21 is expressed in a NOTCH-dependent manner in T-ALL (Leukemia. 2013, 27:650) and have developed it as a potential immunotherapy target, being primarily expressed on normal B cells, with minimal expression on mature T cells. 70% of human T-ALL cell lines (9/16) expressed surface CD21 by flow cytometry (FACS), with a median antigen density in positive lines of 2545/cell. In primary T-ALL, 57% of presentation samples (n=58) expressed CD21 (median antigen density 1168/cell). 45% of relapse (n=11) and 20% of primary refractory cases (n=30) expressed CD21, with a similar antigen density to presentation samples. CD21 positivity varied by maturational stage, with highest expression in cortical T-ALL (80% of cases) followed by pre-T (72%), mature (67%), ETP (25%) and pro-T (17%). Healthy donor blood (n=14) showed CD21 expression limited to B cells and a low proportion (11%) of T cells (10-fold lower intensity v B cells, 316 antigens/cell). T cell CD21 expression was not up-regulated upon activation with CD3/CD28 antibodies (n=6) and was not associated with markers of differentiation/exhaustion. To target CD21, DNA gene-gun vaccination of rats with a plasmid encoding full-length CD21, followed by phage display was performed and multiple anti-CD21 scFvs isolated. These were cloned into 4-1BBζ CARs and expressed in primary T cells but failed to kill or secrete cytokines in response to CD21+ SupT1 cells. CD21 is a bulky molecule, with 15/16 sushi repeats in the extracellular domain. All isolated scFvs were found to bind membrane-distal domains. We hypothesized that ineffective signalling due to inadequate synapse formation was responsible for poor performance of anti-CD21 CAR-T, and that binders to membrane-proximal epitopes would signal more efficiently. We re-vaccinated rats with the first 5 sushi repeats of CD21 and generated a library of binders which bound CD21 at this membrane-proximal region. Multiple candidate binders expressed as CARs were functional, with cytotoxicity and interferon-γ secretion in response to CD21+ target cells. However, non-specific background cytokine secretion was seen against CD21 negative cells, and no IL-2 secretion was seen. Re-cloning binders into a fragment antigen binding (Fab)-CAR architecture yielded constructs capable of specific cytotoxicity, IFN-γ and IL2 secretion against a CD21+ cell line but not its CD21 negative counterpart (n=6). Our lead anti-CD21 candidate CAR specifically proliferated in vitro, without fratricide or premature exhaustion/ differentiation, and was active against low-density CD21-positive cell lines (n=3) and primary cells from 2 T-ALL patients. Improved functionality of Fab v scFv-based CAR was not driven by higher affinity binding or CAR surface expression. We tested anti-CD21 CAR in murine models of T-ALL. NSG mice were injected with SupT1-luciferase cells and treated with aCD19 or aCD21 CAR-T on day +5. At 2 weeks post treatment, markedly lower disease burden was seen in CD21 CAR-T v CD19 recipients by bioluminescence imaging (median radiance 71700 v 790000 p=0.0079). Further, we injected primary T-ALL blasts in another cohort, treating with aCD19 or aCD21 CAR-T on D+20. Serial bleeds from day 27 post CAR-T showed tumour control in aCD21 CAR treated mice (p=0.024) with an overall survival advantage (median OS 44 days vs undefined, HR = 19.8, p = 0.0069, n=4/group). In summary, we propose CD21 as a novel target for CAR-T cell therapy in T-ALL. Its expression is largely restricted to the malignant T cell compartment, overcoming issues with fratricide and on-target off-tumour effects seen in many T-ALL CAR-T strategies to date. Despite the complexity of the target, we have successfully generated an aCD21 CAR that is functional both in vitro and in vivo. Disclosures Maciocia: Autolus: Current equity holder in publicly-traded company. Onuoha: Autolus: Ended employment in the past 24 months. Khwaja: Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Maciocia: Autolus: Current equity holder in publicly-traded company, Research Funding. Pule: Autolus: Current Employment, Current equity holder in publicly-traded company.

Antibody phage display is a powerful platform for discovery of clinically applicable high affinity monoclonal antibodies against a broad range of targets. Libraries generated from immunized animals offer the advantage of in vivo affinity-maturation of V regions prior to library generation. Despite advantages, few studies have described isolation of antibodies from rats using immune phage display. In our study, we describe a novel primer set, covering the full rat heavy chain variable and kappa light chain variable regions repertoire for the generation of an unbiased immune libraries. Since the immune repertoire of rats is poorly understood, we first performed a deep sequencing analysis of the V(D)J regions of VH and VLK genes, demonstrating the high abundance of IGVH2 and IGVH5 families for VH and IGVLK12 and IGVLK22 for VLK. The comparison of gene’s family usage in naïve rats have been used to validate the frequency’s distribution of the primer set, confirming the absence of PCR-based biases. The primers were used to generate and assemble a phage display library from human CD160-vaccinated rats. CD160 represents a valid therapeutic target as it has been shown to be expressed on chronic lymphocytic leukaemia cells and on the surface of newly formed vessels. We utilised a novel phage display panning strategy to isolate a high affinity pool (KD range: 0.399–233 nM) of CD160 targeting monoclonal antibodies. Subsequently, identified binders were tested for function as third generation Chimeric Antigen Receptors (CAR) T cells demonstrating specific cytolytic activity. Our novel primer set coupled with a streamlined strategy for phage display panning enable the rapid isolation and identification of high affinity antibodies from immunised rats. The therapeutic utility of these antibodies was demonstrated in CAR format.

Treatment with T-cells redirected to tumour specificity with a chimeric antigen receptor (CAR) may be well suited to treat intracranial tumours due to the ability of T-cells to access the central nervous system and migrate to infiltrative sites of disease. In adult glioblastoma, a case report of local and distant eradication of intracranial and spinal tumour deposits following intraventricular infusion of IL13Ra2-CAR T-cells indicates the potential of this approach. However, in contrast to the sustained complete remissions observed in haematological malignancies, in the majority of patients with glioblastoma CAR T-cell therapy has not resulted in clinical benefit. Tumour heterogeneity and the highly immune inhibitory tumour microenvironment (TME) are likely key barriers to achieving durable anti-tumour immunity. Here use intra-tumoural administration of IL-12 to enable CAR T-cell immunity. We employed CAR-T cells targeting the tumour-specific epidermal growth factor variant III (EGFRvIII). In an immunocompetent orthotopic mouse model of high-grade glioma, we show that CAR-T cells alone failed to control fully established tumour, but when combined with a single, locally delivered dose of IL-12, durable antitumor responses were achieved. IL-12 not only boosted cytotoxicity of CAR T-cells, but also reshaped the TME driving increased infiltration of proinflammatory CD4+ T-cells, decreased numbers of regulatory T-cells (Tregs) and activation of the myeloid compartment. Critically, immunotherapy enabling benefits of IL-12 were achieved with minimal systemic effects. Our findings show that local delivery of IL-12 is an effective adjuvant for CAR-T cell therapy for high-grade glioma. Assessment of application in high-risk childhood brain tumours is ongoing.

Adoptive T-cell therapy aims to achieve lasting tumor clearance, requiring enhanced engraftment and survival of the immune cells. Cytokines are paramount modulators of T-cell survival and proliferation. Cytokine receptors signal via ligand-induced dimerization, and this principle has been hijacked utilizing non-native dimerization domains. A major limitation of current technologies resides in the absence of a module that recapitulates the natural cytokine receptor heterodimeric pairing. To circumvent this, we created a new engineered cytokine receptor able to constitutively recreate receptor-heterodimer utilizing the heterodimerization domain derived from the IgG1 antibody (dFab_CCR). We found that the signal delivered by the dFab_CCR-IL2 proficiently mimicked the cytokine receptor heterodimerization, with transcriptomic signatures like those obtained by activation of the native IL2 receptor. Moreover, we found that this dimerization structure was agnostic, efficiently activating signaling through four cytokine receptor families. Using a combination of in vivo and in vitro screening approaches, we characterized a library of 18 dFab_CCRs co-expressed with a clinically relevant solid tumor–specific GD2-specific CAR. Based on this characterization, we suggest that the co-expression of either the common β-chain GMCSF or the IL18 dFab_CCRs is optimal to improve CAR T-cell expansion, engraftment, and efficacy. Our results demonstrate how Fab dimerization is efficient and versatile in recapitulating a cytokine receptor heterodimerization signal. This module could be applied for the enhancement of adoptive T-cell therapies, as well as therapies based on other immune cell types. Furthermore, these results provide a choice of cytokine signal to incorporate with adoptive T-cell therapies.

Adoptive T cell therapy aims to achieve lasting tumour clearance, requiring enhanced engraftment and survival of the immune cells. Cytokines are paramount modulators of T cell survival and proliferation. Cytokine receptors signal via ligand-induced dimerization, and this principle has been hijacked utilising non-native dimerization domains. A major limitation of current technologies resides in the absence of a module that recapitulates the natural cytokine receptor heterodimeric pairing. To circumvent this, we created a new engineered cytokine receptor able to constitutively recreate receptor-heterodimer utilising the heterodimerization domain derived from the IgG1 antibody (dFab_CCR). We found that the signal delivered by the dFab_CCR-IL2 proficiently mimics the cytokine receptor heterodimerization, with transcriptomic signatures similar to that obtained by the activation of IL2 native receptor. Importantly, we found that this dimerization structure is agnostic, efficiently activating signaling through four cytokine receptor families. Using a combination of in vivo and in vitro screening approaches, we characterized a library of 18 dFab_CCRs co-expressed with a clinically relevant solid tumor-specific GD2 CAR. Based on this characterization we suggest that the co-expression of either the common beta-chain GMCSF or the IL18 dFab_CCRs is optimal to improve CAR T cell expansion, engraftment, and efficacy. Our results demonstrate how the Fab dimerization is efficient and versatile in recapitulating a cytokine receptor heterodimerization signal. This module could be applied for the enhancement of adoptive T cell therapies, and therapies based on other immune cell types. Furthermore, these results provide a choice of cytokine signal to incorporate with adoptive T cells therapies.