Targeting of Tumor-Associated Glycoforms of MUC1 with CAR T Cells.

We read with interest the manuscript by June and colleagues published recently in Immunity in which they describe targeting of aberrantly glycosylated tumor-associated cell membrane mucin MUC1 using chimeric antigen receptor-engineered human T cells (Posey et al., 2016). In that study, the authors used a second generation 4-1BB costimulatory-molecule-based chimeric antigen receptor (CAR) (Imai et al., 2004) in which targeting was achieved using a single-chain variable fragment (scFv) derived from the 5E5 antibody. This CAR selectively binds MUC1 that carries the Tn or sialyl (S)Tn glycan. Both of these truncated glycans are aberrantly expressed on the MUC1 glycoprotein in a spectrum of malignancies and consequently represent attractive targets for immunotherapeutic exploitation.

Binding to serine 65-phosphorylated ubiquitin primes Parkin for optimal PINK1-dependent phosphorylation and activation.

Mutations in the mitochondrial protein kinase PINK1 are associated with autosomal recessive Parkinson disease (PD). We and other groups have reported that PINK1 activates Parkin E3 ligase activity both directly via phosphorylation of Parkin serine 65 (Ser(65))--which lies within its ubiquitin-like domain (Ubl)--and indirectly through phosphorylation of ubiquitin at Ser(65). How Ser(65)-phosphorylated ubiquitin (ubiquitin(Phospho-Ser65)) contributes to Parkin activation is currently unknown. Here, we demonstrate that ubiquitin(Phospho-Ser65) binding to Parkin dramatically increases the rate and stoichiometry of Parkin phosphorylation at Ser(65) by PINK1 in vitro. Analysis of the Parkin structure, corroborated by site-directed mutagenesis, shows that the conserved His302 and Lys151 residues play a critical role in binding of ubiquitin(Phospho-Ser65), thereby promoting Parkin Ser(65) phosphorylation and activation of its E3 ligase activity in vitro. Mutation of His302 markedly inhibits Parkin Ser(65) phosphorylation at the mitochondria, which is associated with a marked reduction in its E3 ligase activity following mitochondrial depolarisation. We show that the binding of ubiquitin(Phospho-Ser65) to Parkin disrupts the interaction between the Ubl domain and C-terminal region, thereby increasing the accessibility of Parkin Ser(65). Finally, purified Parkin maximally phosphorylated at Ser(65) in vitro cannot be further activated by the addition of ubiquitin(Phospho-Ser65). Our results thus suggest that a major role of ubiquitin(Phospho-Ser65) is to promote PINK1-mediated phosphorylation of Parkin at Ser(65), leading to maximal activation of Parkin E3 ligase activity. His302 and Lys151 are likely to line a phospho-Ser(65)-binding pocket on the surface of Parkin that is critical for the ubiquitin(Phospho-Ser65) interaction. This study provides new mechanistic insights into Parkin activation by ubiquitin(Phospho-Ser65), which could aid in the development of Parkin activators that mimic the effect of ubiquitin(Phospho-Ser65).

Preclinical in vivo modeling of cytokine release syndrome induced by ErbB-retargeted human T cells: identifying a window of therapeutic opportunity?

The ErbB network is dysregulated in many solid tumors. To exploit this, we have developed a chimeric Ag receptor (CAR) named T1E28z that targets several pathogenetically relevant ErbB dimers. T1E28z is coexpressed with a chimeric cytokine receptor named 4αß (combination termed T4), enabling the selective expansion of engineered T cells using IL-4. Human T4(+) T cells exhibit antitumor activity against several ErbB(+) cancer types. However, ErbB receptors are also expressed in several healthy tissues, raising concerns about toxic potential. In this study, we have evaluated safety of T4 immunotherapy in vivo using a SCID beige mouse model. We show that the human T1E28z CAR efficiently recognizes mouse ErbB(+) cells, rendering this species suitable to evaluate preclinical toxicity. Administration of T4(+) T cells using the i.v. or intratumoral routes achieves partial tumor regression without clinical or histopathologic toxicity. In contrast, when delivered i.p., tumor reduction is accompanied by dose-dependent side effects. Toxicity mediated by T4(+) T cells results from target recognition in both tumor and healthy tissues, leading to release of both human (IL-2/IFN-γ) and murine (IL-6) cytokines. In extreme cases, outcome is lethal. Both toxicity and IL-6 release can be ameliorated by prior macrophage depletion, consistent with clinical data that implicate IL-6 in this pathogenic event. These data demonstrate that CAR-induced cytokine release syndrome can be modeled in mice that express target Ag in an appropriate distribution. Furthermore, our findings argue that ErbB-retargeted T cells can achieve therapeutic benefit in the absence of unacceptable toxicity, providing that route of administration and dose are carefully optimized.

Synergistic Chemoimmunotherapy of Epithelial Ovarian Cancer Using ErbB-Retargeted T Cells Combined with Carboplatin.

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy, underscoring the need for better therapies. Adoptive immunotherapy using genetically targeted T cells represents a promising new treatment for hematologic malignancies. However, solid tumors impose additional obstacles, including the lack of suitable targets for safe systemic therapy and the need to achieve effective T cell homing to sites of disease. Because EOC undergoes transcœlomic metastasis, both of these challenges may be circumvented by T cell administration to the peritoneal cavity. In this study, we describe such an immunotherapeutic approach for EOC, in which human T cells were targeted against the extended ErbB family, using a chimeric Ag receptor named T1E28z. T1E28z was coexpressed with a chimeric cytokine receptor named 4αß (combination termed T4), enabling the selective ex vivo expansion of engineered T cells using IL-4. Unlike control T cells, T4(+) T cells from healthy donors and patients with EOC were activated by and destroyed ErbB(+) EOC tumor cell lines and autologous tumor cultures. In vivo antitumor activity was demonstrated in mice bearing established luciferase-expressing SKOV-3 EOC xenografts. Tumor regression was accompanied by mild toxicity, manifested by weight loss. Although efficacy was transient, therapeutic response could be prolonged by repeated T cell administration. Furthermore, prior treatment with noncytotoxic doses of carboplatin sensitized SKOV-3 tumors to T4 immunotherapy, promoting enhanced disease regression using lower doses of T4(+) T cells. By combining these approaches, we demonstrate that repeated administration of carboplatin followed by T4(+) T cells achieved optimum therapeutic benefit in the absence of significant toxicity, even in mice with advanced tumor burdens.

Flexible targeting of ErbB dimers that drive tumorigenesis by using genetically engineered T cells.

Pharmacological targeting of individual ErbB receptors elicits antitumor activity, but is frequently compromised by resistance leading to therapeutic failure. Here, we describe an immunotherapeutic approach that exploits prevalent and fundamental mechanisms by which aberrant upregulation of the ErbB network drives tumorigenesis. A chimeric antigen receptor named T1E28z was engineered, in which the promiscuous ErbB ligand, T1E, is fused to a CD28 + CD3ζ endodomain. Using a panel of ErbB-engineered 32D hematopoietic cells, we found that human T1E28z⁺ T cells are selectively activated by all ErbB1-based homodimers and heterodimers and by the potently mitogenic ErbB2/3 heterodimer. Owing to this flexible targeting capability, recognition and destruction of several tumor cell lines was achieved by T1E28⁺ T cells in vitro, comprising a wide diversity of ErbB receptor profiles and tumor origins. Furthermore, compelling antitumor activity was observed in mice bearing established xenografts, characterized either by ErbB1/2 or ErbB2/3 overexpression and representative of insidious or rapidly progressive tumor types. Together, these findings support the clinical development of a broadly applicable immunotherapeutic approach in which the propensity of solid tumors to dysregulate the extended ErbB network is targeted for therapeutic gain.

Dual targeting of ErbB2 and MUC1 in breast cancer using chimeric antigen receptors engineered to provide complementary signaling.

PURPOSE: Chimeric antigen receptor (CAR) engineered T-cells occupy an increasing niche in cancer immunotherapy. In this context, CAR-mediated CD3ζ signaling is sufficient to elicit cytotoxicity and interferon-γ production while the additional provision of CD28-mediated signal 2 promotes T-cell proliferation and interleukin (IL)-2 production. This compartmentalisation of signaling opens the possibility that complementary CARs could be used to focus T-cell activation within the tumor microenvironment. METHODS: Here, we have tested this principle by co-expressing an ErbB2- and MUC1-specific CAR that signal using CD3ζ and CD28 respectively. Stoichiometric co-expression of transgenes was achieved using the SFG retroviral vector containing an intervening Thosea asigna peptide. RESULTS: We found that "dual-targeted" T-cells kill ErbB2(+) tumor cells efficiently and proliferate in a manner that requires co-expression of MUC1 and ErbB2 by target cells. Notably, however, IL-2 production was modest when compared to control CAR-engineered T-cells in which signaling is delivered by a fused CD28 + CD3ζ endodomain. CONCLUSIONS: These findings demonstrate the principle that dual targeting may be achieved using genetically targeted T-cells and pave the way for testing of this strategy in vivo.

Selective expansion of chimeric antigen receptor-targeted T-cells with potent effector function using interleukin-4.

Polyclonal T-cells can be directed against cancer using transmembrane fusion molecules known as chimeric antigen receptors (CARs). Although preclinical studies have provided encouragement, pioneering clinical trials using CAR-based immunotherapy have been disappointing. Key obstacles are the need for robust expansion ex vivo followed by sustained survival of infused T-cells in patients. To address this, we have developed a system to achieve selective proliferation of CAR(+) T-cells using IL-4, a cytokine with several pathophysiologic and therapeutic links to cancer. A chimeric cytokine receptor (4alphabeta) was engineered by fusion of the IL-4 receptor alpha (IL-4Ralpha) ectodomain to the beta(c) subunit, used by IL-2 and IL-15. Addition of IL-4 to T-cells that express 4alphabeta resulted in STAT3/STAT5/ERK phosphorylation and exponential proliferation, mimicking the actions of IL-2. Using receptor-selective IL-4 muteins, partnering of 4alphabeta with gamma(c) was implicated in signal delivery. Next, human T-cells were engineered to co-express 4alphabeta with a CAR specific for tumor-associated MUC1. These T-cells exhibited an unprecedented capacity to elicit repeated destruction of MUC1-expressing tumor cultures and expanded through several logs in vitro. Despite prolonged culture in IL-4, T-cells retained specificity for target antigen, type 1 polarity, and cytokine dependence. Similar findings were observed using CARs directed against two additional tumor-associated targets, demonstrating generality of application. Furthermore, this system allows rapid ex vivo expansion and enrichment of engineered T-cells from small blood volumes, under GMP-compliant conditions. Together, these findings provide proof of principle for the development of IL-4-enhanced T-cell immunotherapy of cancer.

Trafficking of CAR-engineered human T cells following regional or systemic adoptive transfer in SCID beige mice.

Adoptive immunotherapy using chimeric antigen receptor-engrafted T cells is a promising emerging therapy for cancer. Prior to clinical testing, it is mandatory to evaluate human therapeutic cell products in meaningful in vivo pre-clinical models. Here, we describe the use of fused single-photon emission CT-CT imaging to monitor real-time migration of chimeric antigen receptor-engineered T cells in immune compromised (SCID Beige) mice. Following intravenous administration, human T cells migrate in a highly similar manner to that reported in man, but penetrate poorly into established tumors. By contrast, when delivered via intraperitoneal or subcutaneous routes, T cells remain at the site of inoculation with minimal systemic absorption-irrespective of the presence or absence of tumor. Together, these data support the validity of pre-clinical testing of human T-cell immunotherapy in SCID Beige mice. In light of their established efficacy, regional administration of engineered human T cells represents an attractive therapeutic option to minimize toxicity in the treatment of selected malignancies.

Transforming growth factor-ß1 is constitutively secreted by Chinese hamster ovary cells and is functional in human cells.

Chinese hamster ovary (CHO) cells are widely used for the production of recombinant proteins for clinical use as well as academic research. They are particularly important for the production of glycoproteins where bacteria cannot be used. TGFß1 is a potent cytokine highly conserved across species with multiple immunological and non-immunological effects. We have discovered that CHOK1, the CHO clone most commonly used by the pharmaceutical industry, constitutively secretes latent TGFß1 and that this hamster TGFß1 is active on human cells inducing profound immunological effects. As far as we are aware, the production of TGFß1 by CHOK1 cells has not been reported before in the literature. As TGFß1 exerts powerful and pleiotropic effects on diverse cell types, and as CHO cells are used to produce a large number of clinical and non-clinical products, our findings are highly relevant to studies that rely on recombinant proteins.

Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin in dogs following single oral administration of enrofloxacin at 7.5, 10, or 20 mg/kg.

Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin were monitored following oral administration of enrofloxacin at 7.5, 10, and 20 mg/kg to six healthy female bloodhounds using a randomized crossover design. Plasma samples were collected at various times over 24 hours following drug administration. Both the parent drug and its metabolite were detected by high-performance liquid chromatography, and plasma drug concentration-versus-time curves were subjected to noncompartmental pharmacokinetic analysis. Descriptive statistics were determined for each dosage, and comparisons were made among dosage groups for selected pharmacokinetic parameters. Increasing dosages of enrofloxacin resulted in increased plasma concentrations of both enrofloxacin and ciprofloxacin. Maximum concentration (Cmax) was 2.12 +/- 0.59, 2.1 +/- 0.34, and 4.74 +/- 1.05 mcg/ml for enrofloxacin and 1.30 +/- 0.31, 1.30 +/- 0.32, and 1.86 +/- 0.35 mcg/ml for ciprofloxacin when enrofloxacin was given at dosages of 7.5, 10, and 20 mg/kg, respectively. Cmax and area under the curve (AUC) for both enrofloxacin and ciprofloxacin were significantly greater at 20 mg/kg than at 7.5 and 10 mg/kg. Disappearance half-life was similar for all dosages, ranging from 4.6 to 5.2 hours for enrofloxacin and 8.8 to 10.7 hours for ciprofloxacin. Ciprofloxacin contributed up to 42% of the Cmax and up to 55% of the AUC of the total (enrofloxacin plus ciprofloxacin). For organisms with a minimum inhibitory concentration (MIC) of 0.5 mcg enrofloxacin/ml, an inhibitory quotient (IQ; Cmax:MIC) of 8 or more was achieved in plasma only at 20 mg/kg.

Dosing regimen and hematologic effects of pentoxifylline and its active metabolites in normal dogs.

The disposition of pentoxifylline and two of its active metabolites (metabolite 1 [M1] and metabolite 5 [M5]) were studied following i.v. (8 mg/kg) and p.o. (30 mg/kg) administration to eight normal dogs using a randomized crossover design. Blood samples were collected at fixed time intervals after drug administration for determination of drug concentrations, platelet aggregation, and plasma fibrinogen. Complete blood counts, serum chemistry profiles, fibrinogen, and urinalysis were monitored at the beginning and end of each phase of the study (p.o. versus i.v. administration). Pentoxifylline was readily metabolized and bioavailable (50% +/- 26%). Both M1 and M5 were present throughout the study, with M5 predominating. Human drug therapeutic concentrations (1,000 ng/ml) were present for 170 +/- 24 minutes following i.v. administration and 510 +/- 85 minutes after p.o. dosing. These findings suggest that a 12-hour dosing regimen is appropriate. None of the dogs experienced any adverse effects after pentoxifylline administration. The lack of hematologic effects suggests that the immunologic effects of pentoxifylline may be of more importance in dogs.

CAR mechanics: driving T cells into the MUC of cancer.

Several monoclonal antibodies bind in a highly selective manner to tumor-associated glycoforms of MUC1. We set out to exploit this by developing a MUC1-specific chimeric antigen receptor. Difficulties were encountered in this endeavor, owing to MUC1-imposed steric hindrance and antigenic heterogeneity. These issues were addressed by the iterative engineering of all components of the fusion receptor. Our experience underlines the need for careful individual optimization of immunotherapeutic reagents as dictated by the molecular vagaries of the target under study.

Retargeting of human T cells to tumor-associated MUC1: the evolution of a chimeric antigen receptor.

MUC1 is a highly attractive immunotherapeutic target owing to increased expression, altered glycosylation, and loss of polarity in >80% of human cancers. To exploit this, we have constructed a panel of chimeric Ag receptors (CAR) that bind selectively to tumor-associated MUC1. Two parameters proved crucial in optimizing the CAR ectodomain. First, we observed that the binding of CAR-grafted T cells to anchored MUC1 is subject to steric hindrance, independent of glycosylation status. This was overcome by insertion of the flexible and elongated hinge found in immunoglobulins of the IgD isotype. Second, CAR function was highly dependent upon strong binding capacity across a broad range of tumor-associated MUC1 glycoforms. This was realized by using an Ab-derived single-chain variable fragment (scFv) cloned from the HMFG2 hybridoma. To optimize CAR signaling, tripartite endodomains were constructed. Ultimately, this iterative design process yielded a potent receptor termed HOX that contains a fused CD28/OX40/CD3zeta endodomain. HOX-expressing T cells proliferate vigorously upon repeated encounter with soluble or membrane-associated MUC1, mediate production of proinflammatory cytokines (IFN-gamma and IL-17), and elicit brisk killing of MUC1(+) tumor cells. To test function in vivo, a tumor xenograft model was derived using MDA-MB-435 cells engineered to coexpress MUC1 and luciferase. Mice bearing an established tumor were treated i.p. with a single dose of engineered T cells. Compared with control mice, this treatment resulted in a significant delay in tumor growth as measured by serial bioluminescence imaging. Together, these data demonstrate for the first time that the near-ubiquitous MUC1 tumor Ag can be targeted using CAR-grafted T cells.

RB activation defect in tumor cell lines.

Activation of the retinoblastoma (RB) protein through dephosphorylation arises in cells upon exit from M phase and in response to environmental stresses, including DNA damage. We provide here for the first time evidence that these responses are co-ordinately affected in a subset of tumor derived cell lines. We find that RB dephosphorylation is not apparent in these cells during progression into G(1). Importantly these cells also do not respond with RB activation after DNA damage during S phase. Moreover and as a consequence they display phenotypes classically associated with RB(-) cells, showing accelerated apoptosis after DNA damage and DNA re-replication after spindle-checkpoint activation. A large body of literature provides evidence that controls governing inactivation of RB are lost in tumors. The results presented here indicate that the reverse reaction, namely the activation of RB from an inactive precursor, may also be compromised. Our findings indicate that this type of defect may be coupled with hypersensitivity to DNA damage and an increase in genomic instability in response to spindle-checkpoint activation thus bearing potentially important medical implications.