CLN-978, a novel half-life extended CD19/CD3/HSA-specific T cell-engaging antibody construct with potent activity against B-cell malignancies with low CD19 expression.

BACKGROUND: Despite significant progress in the development of T cell-engaging therapies for various B-cell malignancies, a high medical need remains for the refractory disease setting, often characterized by suboptimal target levels. METHODS: To address this issue, we have developed a 65-kDa multispecific antibody construct, CLN-978, with affinities tuned to optimize the killing of low-CD19 expressing tumor cells. CLN-978 bound to CD19 on B cells with picomolar affinity, and to CD3ε on T cells with nanomolar affinity. A serum albumin binding domain was incorporated to extend serum half-life. In this setting, we biophysically characterize and report the activities of CLN-978 in cell co-culture assays, multiple mouse models and non-human primates. RESULTS: Human T cells redirected by CLN-978 could eliminate target cells expressing less than 300 copies of CD19 on their surface. The half-life extension and high affinity for CD19 led to significant antitumor activity in murine lymphoma models at very low doses of CLN-978. In primates, we observed a long serum half-life, deep and sustained depletion of normal B cells, and remarkable tolerability, in particular, reduced cytokine release when CLN-978 was administered subcutaneously. CONCLUSIONS: CLN-978 warrants further exploration. An ongoing clinical phase 1 trial is investigating safety, pharmacokinetics, pharmacodynamics, and the initial therapeutic potential of subcutaneously administered CLN-978 in patients with non-Hodgkin's lymphoma.

Engaging natural killer cells for cancer therapy via NKG2D, CD16A and other receptors.

The field of immuno-oncology has revolutionized cancer patient care and improved survival and quality of life for patients. Much of the focus in the field has been on exploiting the power of the adaptive immune response through therapeutic targeting of T cells. While these approaches have markedly advanced the field, some challenges remain, and the clinical benefit of T cell therapies does not extend to all patients or tumor indications. Alternative strategies, such as engaging the innate immune system, have become an intense area of focus in the field. In particular, the engagement of natural killer (NK) cells as potent effectors of the innate immune response has emerged as a promising modality in immunotherapy. Here, we review therapeutic approaches for selective engagement of NK cells for cancer therapy, with a particular focus on targeting the key activating receptors NK Group 2D (NKG2D) and cluster of differentiation 16A (CD16A).

Co-Anchoring of Engineered Immunogen and Immunostimulatory Cytokines to Alum Promotes Enhanced-Humoral Immunity.

Protein antigens are often combined with aluminum hydroxide (alum), the most commonly used adjuvant in licensed vaccines; yet the immunogenicity of alum-adjuvanted vaccines leaves much room for improvement. Here, the authors demonstrate a strategy for codelivering an immunostimulatory cytokine, the interleukin IL-21, with an engineered outer domain (eOD) human immunodeficiency virus gp120 Env immunogen eOD, bound together to alum to bolster the humoral immune response. In this approach, the immunogen and cytokine are co-anchored to alum particles via a short phosphoserine (pSer) peptide linker, promoting stable binding to alum and sustained bioavailability following injection. pSer-modified eOD and IL-21 promote enhanced lymphatic drainage and lead to accumulation of the vaccine in B cell follicles in the draining lymph nodes. This in turn promotes enhanced T follicular helper cell priming and robust germinal center responses as well as increased antigen-specific serum IgG titers. This is a general strategy for codelivery of immunostimulatory cytokine with immunogens providing a facile approach to modulate T cell priming and GC reactions toward enhanced protective immunity using the most common clinical vaccine adjuvant.

Cell-penetrating peptides enhance peptide vaccine accumulation and persistence in lymph nodes to drive immunogenicity.

Peptide-based cancer vaccines are widely investigated in the clinic but exhibit modest immunogenicity. One approach that has been explored to enhance peptide vaccine potency is covalent conjugation of antigens with cell-penetrating peptides (CPPs), linear cationic and amphiphilic peptide sequences designed to promote intracellular delivery of associated cargos. Antigen-CPPs have been reported to exhibit enhanced immunogenicity compared to free peptides, but their mechanisms of action in vivo are poorly understood. We tested eight previously described CPPs conjugated to antigens from multiple syngeneic murine tumor models and found that linkage to CPPs enhanced peptide vaccine potency in vivo by as much as 25-fold. Linkage of antigens to CPPs did not impact dendritic cell activation but did promote uptake of linked antigens by dendritic cells both in vitro and in vivo. However, T cell priming in vivo required Batf3-dependent dendritic cells, suggesting that antigens delivered by CPP peptides were predominantly presented via the process of cross-presentation and not through CPP-mediated cytosolic delivery of peptide to the classical MHC class I antigen processing pathway. Unexpectedly, we observed that many CPPs significantly enhanced antigen accumulation in draining lymph nodes. This effect was associated with the ability of CPPs to bind to lymph-trafficking lipoproteins and protection of CPP-antigens from proteolytic degradation in serum. These two effects resulted in prolonged presentation of CPP-peptides in draining lymph nodes, leading to robust T cell priming and expansion. Thus, CPPs can act through multiple unappreciated mechanisms to enhance T cell priming that can be exploited for cancer vaccines with enhanced potency.

A novel IgG-based FLT3xCD3 bispecific antibody for the treatment of AML and B-ALL.

BACKGROUND: In lymphoid malignancies, the introduction of chimeric antigen receptor T (CAR-T) cells and bispecific antibodies (bsAbs) has achieved remarkable clinical success. However, such immunotherapeutic strategies are not yet established for acute myeloid leukemia (AML), the most common form of acute leukemia in adults. Common targets in AML such as CD33, CD123, and CLEC12A are highly expressed on both AML blasts and on normal myeloid cells and hematopoietic stem cells (HSCs), thereby raising toxicity concerns. In B-cell acute lymphoblastic leukemia (B-ALL), bsAbs and CAR-T therapy targeting CD19 and CD22 have demonstrated clinical success, but resistance via antigen loss is common, motivating the development of agents focused on alternative targets. An attractive emerging target is FLT3, a proto-oncogene expressed in both AML and B-ALL, with low and limited expression on myeloid dendritic cells and HSCs. METHODS: We developed and characterized CLN-049, a T cell-activating bsAb targeting CD3 and FLT3, constructed as an IgG heavy chain/scFv fusion. CLN-049 binds the membrane proximal extracellular domain of the FLT3 protein tyrosine kinase, which facilitates the targeting of leukemic blasts regardless of FLT3 mutational status. CLN-049 was evaluated for preclinical safety and efficacy in vitro and in vivo. RESULTS: CLN-049 induced target-restricted activation of CD4+ and CD8+ T cells. AML cell lines expressing a broad range of surface levels of FLT3 were efficiently lysed on treatment with subnanomolar concentrations of CLN-049, whereas FLT3-expressing hematopoietic progenitor cells and dendritic cells were not sensitive to CLN-049 killing. Treatment with CLN-049 also induced lysis of AML and B-ALL patient blasts by autologous T cells at the low effector-to-target ratios typically observed in patients with overt disease. Lysis of leukemic cells was not affected by supraphysiological levels of soluble FLT3 or FLT3 ligand. In mouse xenograft models, CLN-049 was highly active against human leukemic cell lines and patient-derived AML and B-ALL blasts. CONCLUSIONS: CLN-049 has a favorable efficacy and safety profile in preclinical models, warranting evaluation of its antileukemic activity in the clinic.

Pharmacokinetic tuning of protein-antigen fusions enhances the immunogenicity of T-cell vaccines.

The formulations of peptide-based antitumour vaccines being tested in clinical studies are generally associated with weak potency. Here, we show that pharmacokinetically tuning the responses of peptide vaccines by fusing the peptide epitopes to carrier proteins optimizes vaccine immunogenicity in mice. In particular, we show in immunized mice that the carrier protein transthyretin simultaneously optimizes three factors: efficient antigen uptake in draining lymphatics from the site of injection, protection of antigen payloads from proteolytic degradation and reduction of antigen presentation in uninflamed distal lymphoid organs. Optimizing these factors increases vaccine immunogenicity by up to 90-fold and maximizes the responses to viral antigens, tumour-associated antigens, oncofetal antigens and shared neoantigens. Protein-peptide epitope fusions represent a facile and generalizable strategy for enhancing the T-cell responses elicited by subunit vaccines.

TCR sequencing paired with massively parallel 3' RNA-seq reveals clonotypic T cell signatures.

High-throughput 3' single-cell RNA-sequencing (scRNA-seq) allows cost-effective, detailed characterization of individual immune cells from tissues. Current techniques, however, are limited in their ability to elucidate essential immune cell features, including variable sequences of T cell antigen receptors (TCRs) that confer antigen specificity. Here, we present a strategy that enables simultaneous analysis of TCR sequences and corresponding full transcriptomes from 3'-barcoded scRNA-seq samples. This approach is compatible with common 3' scRNA-seq methods, and adaptable to processed samples post hoc. We applied the technique to identify transcriptional signatures associated with T cells sharing common TCRs from immunized mice and from patients with food allergy. We observed preferential phenotypes among subsets of expanded clonotypes, including type 2 helper CD4+ T cell (TH2) states associated with food allergy. These results demonstrate the utility of our method when studying diseases in which clonotype-driven responses are critical to understanding the underlying biology.

Enhanced CAR-T cell activity against solid tumors by vaccine boosting through the chimeric receptor.

Chimeric antigen receptor-T cell (CAR-T) therapy has been effective in the treatment of hematologic malignancies, but it has shown limited efficacy against solid tumors. Here we demonstrate an approach to enhancing CAR-T function in solid tumors by directly vaccine-boosting donor cells through their chimeric receptor in vivo. We designed amphiphile CAR-T ligands (amph-ligands) that, upon injection, trafficked to lymph nodes and decorated the surfaces of antigen-presenting cells, thereby priming CAR-Ts in the native lymph node microenvironment. Amph-ligand boosting triggered massive CAR-T expansion, increased donor cell polyfunctionality, and enhanced antitumor efficacy in multiple immunocompetent mouse tumor models. We demonstrate two approaches to generalizing this strategy to any chimeric antigen receptor, enabling this simple non-human leukocyte antigen-restricted approach to enhanced CAR-T functionality to be applied to existing CAR-T designs.

Anchoring of intratumorally administered cytokines to collagen safely potentiates systemic cancer immunotherapy.

The clinical application of cytokine therapies for cancer treatment remains limited due to severe adverse reactions and insufficient therapeutic effects. Although cytokine localization by intratumoral administration could address both issues, the rapid escape of soluble cytokines from the tumor invariably subverts this effort. We find that intratumoral administration of a cytokine fused to the collagen-binding protein lumican prolongs local retention and markedly reduces systemic exposure. Combining local administration of lumican-cytokine fusions with systemic immunotherapies (tumor-targeting antibody, checkpoint blockade, cancer vaccine, or T cell therapy) improves efficacy without exacerbating toxicity in syngeneic tumor models and the BrafV600E /Ptenfl/fl genetically engineered melanoma model. Curative abscopal effects on noncytokine-injected tumors were also observed as a result of a protective and systemic CD8+ T cell response primed by local therapy. Cytokine collagen-anchoring constitutes a facile, tumor-agnostic strategy to safely potentiate otherwise marginally effective systemic immunotherapies.

Order of administration of combination cytokine therapies can decouple toxicity from efficacy in syngeneic mouse tumor models.

In combination cancer immunotherapies, consideration should be given to designing treatment schedules that harmonize with the immune system's natural timing. An efficacious temporally programmed combination therapy of extended half-life interleukin 2 (eIL2), tumor targeting antibody, and interferon (IFN) α was recently reported; however, tumor-ablative efficacy was associated with significant toxicity. In the current work, altering the order and timing of the three agents is shown to decouple toxicity from efficacy. Delaying the administration of eIL2 to be concurrent with or after IFNα eliminates toxicity without affecting efficacy in multiple syngeneic tumor models and mouse strains. The toxicity resulting from eIL2 administration before IFNα is dependent on multiple systemic inflammatory cytokines including IL6, IL10, IFNγ, and tumor necrosis factor α. Natural killer (NK) cells are the main cellular contributor to toxicity, but are not essential for tumor control in this system. When pre-conditioned with eIL2, splenic NK cells became hyper-activated and upregulate IFNα signaling proteins that cause an excessive, toxic response to subsequent IFNα exposure. This work illustrates an example where accounting for the temporal dynamics of the immune system in combination therapy treatment schedule can favorably decouple efficacy and toxicity.

Enhancement of Peptide Vaccine Immunogenicity by Increasing Lymphatic Drainage and Boosting Serum Stability.

Antitumor T-cell responses have the potential to be curative in cancer patients, but the induction of potent T-cell immunity through vaccination remains a largely unmet goal of immunotherapy. We previously reported that the immunogenicity of peptide vaccines could be increased by maximizing delivery to lymph nodes (LNs), where T-cell responses are generated. This was achieved by conjugating the peptide to 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-PEG (DSPE-PEG) to promote albumin binding, which resulted in enhanced lymphatic drainage and improved T-cell responses. Here, we expanded upon these findings and mechanistically dissected the properties that contribute to the potency of this amphiphile-vaccine (amph-vaccine). We found that multiple linkage chemistries could be used to link peptides with DSPE-PEG, and further, that multiple albumin-binding moieties conjugated to peptide antigens enhanced LN accumulation and subsequent T-cell priming. In addition to enhancing lymphatic trafficking, DSPE-PEG conjugation increased the stability of peptides in serum. DSPE-PEG peptides trafficked beyond immediate draining LNs to reach distal nodes, with antigen presented for at least a week in vivo, whereas soluble peptide presentation quickly decayed. Responses to amph-vaccines were not altered in mice deficient in the albumin-binding neonatal Fc receptor (FcRn), but required Batf3-dependent dendritic cells (DCs). Amph-peptides were processed by human DCs equivalently to unmodified peptides. These data define design criteria for enhancing the immunogenicity of molecular vaccines to guide the design of next-generation peptide vaccines. Cancer Immunol Res; 6(9); 1025-38. ©2018 AACR.

Integrin-targeted cancer immunotherapy elicits protective adaptive immune responses.

Certain RGD-binding integrins are required for cell adhesion, migration, and proliferation and are overexpressed in most tumors, making them attractive therapeutic targets. However, multiple integrin antagonist drug candidates have failed to show efficacy in cancer clinical trials. In this work, we instead exploit these integrins as a target for antibody Fc effector functions in the context of cancer immunotherapy. By combining administration of an engineered mouse serum albumin/IL-2 fusion with an Fc fusion to an integrin-binding peptide (2.5F-Fc), significant survival improvements are achieved in three syngeneic mouse tumor models, including complete responses with protective immunity. Functional integrin antagonism does not contribute significantly to efficacy; rather, this therapy recruits both an innate and adaptive immune response, as deficiencies in either arm result in reduced tumor control. Administration of this integrin-targeted immunotherapy together with an anti-PD-1 antibody further improves responses and predominantly results in cures. Overall, this well-tolerated therapy achieves tumor specificity by redirecting inflammation to a functional target fundamental to tumorigenic processes but expressed at significantly lower levels in healthy tissues, and it shows promise for translation.

Eradication of large established tumors in mice by combination immunotherapy that engages innate and adaptive immune responses.

Checkpoint blockade with antibodies specific for cytotoxic T lymphocyte-associated protein (CTLA)-4 or programmed cell death 1 (PDCD1; also known as PD-1) elicits durable tumor regression in metastatic cancer, but these dramatic responses are confined to a minority of patients. This suboptimal outcome is probably due in part to the complex network of immunosuppressive pathways present in advanced tumors, which are unlikely to be overcome by intervention at a single signaling checkpoint. Here we describe a combination immunotherapy that recruits a variety of innate and adaptive immune cells to eliminate large tumor burdens in syngeneic tumor models and a genetically engineered mouse model of melanoma; to our knowledge tumors of this size have not previously been curable by treatments relying on endogenous immunity. Maximal antitumor efficacy required four components: a tumor-antigen-targeting antibody, a recombinant interleukin-2 with an extended half-life, anti-PD-1 and a powerful T cell vaccine. Depletion experiments revealed that CD8+ T cells, cross-presenting dendritic cells and several other innate immune cell subsets were required for tumor regression. Effective treatment induced infiltration of immune cells and production of inflammatory cytokines in the tumor, enhanced antibody-mediated tumor antigen uptake and promoted antigen spreading. These results demonstrate the capacity of an elicited endogenous immune response to destroy large, established tumors and elucidate essential characteristics of combination immunotherapies that are capable of curing a majority of tumors in experimental settings typically viewed as intractable.

Strong Enrichment of Aromatic Residues in Binding Sites from a Charge-neutralized Hyperthermostable Sso7d Scaffold Library.

The Sso7d protein from the hyperthermophilic archaeon Sulfolobus solfataricus is an attractive binding scaffold because of its small size (7 kDa), high thermal stability (Tm of 98 °C), and absence of cysteines and glycosylation sites. However, as a DNA-binding protein, Sso7d is highly positively charged, introducing a strong specificity constraint for binding epitopes and leading to nonspecific interaction with mammalian cell membranes. In the present study, we report charge-neutralized variants of Sso7d that maintain high thermal stability. Yeast-displayed libraries that were based on this reduced charge Sso7d (rcSso7d) scaffold yielded binders with low nanomolar affinities against mouse serum albumin and several epitopes on human epidermal growth factor receptor. Importantly, starting from a charge-neutralized scaffold facilitated evolutionary adaptation of binders to differentially charged epitopes on mouse serum albumin and human epidermal growth factor receptor, respectively. Interestingly, the distribution of amino acids in the small and rigid binding surface of enriched rcSso7d-based binders is very different from that generally found in more flexible antibody complementarity-determining region loops but resembles the composition of antibody-binding energetic hot spots. Particularly striking was a strong enrichment of the aromatic residues Trp, Tyr, and Phe in rcSso7d-based binders. This suggests that the rigidity and small size of this scaffold determines the unusual amino acid composition of its binding sites, mimicking the energetic core of antibody paratopes. Despite the high frequency of aromatic residues, these rcSso7d-based binders are highly expressed, thermostable, and monomeric, suggesting that the hyperstability of the starting scaffold and the rigidness of the binding surface confer a high tolerance to mutation.

Engineering New Approaches to Cancer Vaccines.

Recently, a number of promising approaches have been developed using synthetic chemistry, materials science, and bioengineering-based strategies to address challenges in the design of more effective cancer vaccines. At the stage of initial priming, potency can be improved by maximizing vaccine delivery to lymph nodes. Because lymphatic uptake from peripheral tissues is strongly size dependent, antigens and adjuvants packaged into optimally sized nanoparticles access the lymph node with much greater efficiency than unformulated vaccines. Once primed, T cells must home to the tumor site. Because T cells acquire the necessary surface receptors in the local lymph node draining the tissue of interest, vaccines must be engineered that reach organs, such as the lung and gut, which are common sites of tumor lesions but inaccessible by traditional vaccination routes. Particulate vaccine carriers can improve antigen exposure in these organs, resulting in greater lymphocyte priming. Immunomodulatory agents can also be injected directly into the tumor site to stimulate a systemic response capable of clearing even distal lesions; materials have been designed that entrap or slowly release immunomodulators at the tumor site, reducing systemic exposure and improving therapeutic efficacy. Finally, lessons learned from the design of biomaterial-based scaffolds in regenerative medicine have led to the development of implantable vaccines that recruit and activate antigen-presenting cells to drive antitumor immunity. Overall, these engineering strategies represent an expanding toolkit to create safe and effective cancer vaccines.