Artificial Anti-Tumor Opsonizing Proteins with Fibronectin Scaffolds Engineered for Specificity to Each of the Murine FcγR Types

We have engineered a panel of novel Fn3 scaffold-based proteins that bind with high specificity and affinity to each of the individual mouse Fcγ receptors (mFcγR). These binders were expressed as fusions to anti-tumor antigen single-chain antibodies and mouse serum albumin, creating opsonizing agents that invoke only a single mFcγR response rather than the broader activity of natural Fc isotypes, as well as all previously reported Fc mutants. This panel isolated the capability of each of the four mFcγRs to contribute to macrophage phagocytosis of opsonized tumor cells and in vivo tumor growth control with these monospecific opsonizing fusion proteins. All activating receptors (mFcγRI, mFcγRIII, and mFcγRIV) were capable of driving specific tumor cell phagocytosis to an equivalent extent, while mFcγRII, the inhibitory receptor, did not drive phagocytosis. Monospecific opsonizing fusion proteins that bound mFcγRI alone controlled tumor growth to an extent similar to the most active IgG2a murine isotype. As expected, binding to the inhibitory mFcγRII did not delay tumor growth, but unexpectedly, mFcγRIII also failed to control tumor growth. mFcγRIV exhibited detectable but lesser tumor-growth control leading to less overall survival compared to mFcγRI. Interestingly, in vivo macrophage depletion demonstrates their importance in tumor control with mFcγRIV engagement, but not with mFcγRI. This panel of monospecific mFcγR-binding proteins provides a toolkit for isolating the functional effects of each mFcγR in the context of an intact immune system.

Temporally Programmed CD8α+ DC Activation Enhances Combination Cancer Immunotherapy

Numerous synergistic cancer immunotherapy combinations have been identified, but the effects of relative dose timing are rarely considered. In established syngeneic mouse tumor models, we found that staggering interferon-α (IFNα) administration after, rather than before or simultaneously with, serum-persistent interleukin-2 (IL-2) and tumor-specific antibody significantly increased long-term survival. Successful combination therapy required IFNα-induced activation of cross-presenting CD8α⁺ dendritic cells (DCs) following the release of antigenic tumor debris by the IL-2- and antibody-mediated immune response. Due to decreased phagocytic ability post-maturation, DCs activated too early captured less antigen and could not effectively prime CD8⁺ T cells. Temporally programming DC activation to occur after tumoricidal activity enhanced tumor control by multiple distinct combination immunotherapies, highlighting dose schedule as an underappreciated factor that can profoundly affect the success of multi-component immunotherapies.

Biopolymers codelivering engineered T cells and STING agonists can eliminate heterogeneous tumors

Therapies using T cells that are programmed to express chimeric antigen receptors (CAR T cells) consistently produce positive results in patients with hematologic malignancies. However, CAR T cell treatments are less effective in solid tumors for several reasons. First, lymphocytes do not efficiently target CAR T cells; second, solid tumors create an immunosuppressive microenvironment that inactivates T cell responses; and third, solid cancers are typified by phenotypic diversity and thus include cells that do not express proteins targeted by the engineered receptors, enabling the formation of escape variants that elude CAR T cell targeting. Here, we have tested implantable biopolymer devices that deliver CAR T cells directly to the surfaces of solid tumors, thereby exposing them to high concentrations of immune cells for a substantial time period. In immunocompetent orthotopic mouse models of pancreatic cancer and melanoma, we found that CAR T cells can migrate from biopolymer scaffolds and eradicate tumors more effectively than does systemic delivery of the same cells. We have also demonstrated that codelivery of stimulator of IFN genes (STING) agonists stimulates immune responses to eliminate tumor cells that are not recognized by the adoptively transferred lymphocytes. Thus, these devices may improve the effectiveness of CAR T cell therapy in solid tumors and help protect against the emergence of escape variants.

Abstract B120: Characterization and combination immunotherapy treatment of an inducible autochthonous murine lung cancer model expressing human carcinoembryonic antigen (CEA) as a tumor-associated self-antigen

Previous work from our lab has demonstrated that a combination of anti-tumor antibody and an IL-2 fusion protein that exhibits extended serum half-life elicits an immune response that can effectively control a wide variety of tumor models. We have since then combined this therapeutic regimen with a vaccine exhibiting efficient lymph node trafficking that can generate an impressive population of tumor-antigen specific CD8+ T-cells but by itself does not provide good anti-tumor efficacy. The efficacy of this combination immunotherapy is further boosted by immune checkpoint blockade, leading to a robust four-component therapy: 1) anti-tumor antigen antibody; 2) IL-2 fusion protein; 3) anti-tumor antigen vaccine; 4) anti-PD-1 antibody.

Although this four-pronged approach is demonstrably effective in the syngeneic subcutaneous melanoma model B16F10, we wish to test its efficacy in a more physiological model. To this end, we have turned to a model developed by the Jacks Lab, known as the KP model: an inducible lung tumor model where lentivirus-driven integration and expression of Cre is able to activate oncogenic Kras and completely remove p53 function. Because our therapeutic regimen requires a targetable tumor-associated antigen with respect to both the antibody and vaccine, we chose to induce expression of human carcinoembryonic antigen (CEA) in these tumors, as CEA has a well-studied structure and biology, and frequently expresses aberrantly in many forms of human adenocarcinomas. Additionally, our lab has previously engineered an antibody targeting CEA possessing picomolar affinity. Finally, to remove any endogenous immunological response against human CEA as a foreign antigen in our mouse system, we have crossed the KP model with a mouse model transgenic for human CEA, which in the literature has been described to have identical spatiotemporal expression of CEA as found in humans and should allow for central tolerance of this antigen.

In the course of this work, we have successfully introduced human CEA into our lentivirus constructs and shown tumorigenesis by these constructs in the KP model coincides with expression of tumor-associated CEA, as detected by qPCR. On the therapeutic side, we have tailored the vaccine to successfully drive an anti-CEA CD8+ T-cell response. Performing preliminary therapeutic experiments in a transplant model of the KP tumor with our four-component therapy, we saw tumor control compared to untreated tumors. Upon interrogating the CD8+ T-cell response against CEA, we found 1-15% of CD8+ T-cells in the blood respond to CEA stimulation by intracellular cytokine staining. With regards to the lung tumor model, in the course of establishing the system we have also observed that the growth kinetics of tumors expressing CEA lags behind those tumors without CEA, even in the transgenic background. Preliminary immunophenotyping work by flow cytometry suggests that tumors with CEA seem to have a reduced myeloid-derived suppressor cell (MDSC) population and a higher CD8a+ dendritic cell (DC) population compared to tumors without CEA, suggesting that the former may have a less immunosuppressive tumor microenvironment that is better able to prime an anti-tumor CD8+ T-cell response. We will be planning to conduct therapeutic trials in the more physiological lung tumor KP model in the near future, as well as investigate the differences in the immune response with tumors expressing or lacking CEA.

Citation Format: Eric F. Zhu, Kavya Rakhra, Naveen Mehta, Kelly D. Moynihan, Cary F. Opel, Darrell J. Irvine, K. Dane Wittrup. Characterization and combination immunotherapy treatment of an inducible autochthonous murine lung cancer model expressing human carcinoembryonic antigen (CEA) as a tumor-associated self-antigen. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B120.

Synergistic innate and adaptive immune response to combination immunotherapy with anti-tumor antigen antibodies and extended serum half-life IL-2

Cancer immunotherapies under development have generally focused on either stimulating T cell immunity or driving antibody-directed effector functions of the innate immune system such as antibody-dependent cell-mediated cytotoxicity (ADCC). We find that a combination of an anti-tumor antigen antibody and an untargeted IL-2 fusion protein with delayed systemic clearance induces significant tumor control in aggressive isogenic tumor models via a concerted innate and adaptive response involving neutrophils, NK cells, macrophages, and CD8(+) T cells. This combination therapy induces an intratumoral "cytokine storm" and extensive lymphocyte infiltration. Adoptive transfer of anti-tumor T cells together with this combination therapy leads to robust cures of established tumors and development of immunological memory.

A graphene-based physiometer array for the analysis of single biological cells

A significant advantage of a graphene biosensor is that it inherently represents a continuum of independent and aligned sensor-units. We demonstrate a nanoscale version of a micro-physiometer – a device that measures cellular metabolic activity from the local acidification rate. Graphene functions as a matrix of independent pH sensors enabling subcellular detection of proton excretion. Raman spectroscopy shows that aqueous protons p-dope graphene – in agreement with established doping trajectories, and that graphene displays two distinct pKa values (2.9 and 14.2), corresponding to dopants physi- and chemisorbing to graphene respectively. The graphene physiometer allows micron spatial resolution and can differentiate immunoglobulin (IgG)-producing human embryonic kidney (HEK) cells from non-IgG-producing control cells. Population-based analyses allow mapping of phenotypic diversity, variances in metabolic activity, and cellular adhesion. Finally we show this platform can be extended to the detection of other analytes, e.g. dopamine. This work motivates the application of graphene as a unique biosensor for (sub)cellular interrogation.

Quantitative modeling of viable cell density, cell size, intracellular conductivity, and membrane capacitance in batch and fed-batch CHO processes using dielectric spectroscopy

Dielectric spectroscopy was used to analyze typical batch and fed-batch CHO cell culture processes. Three methods of analysis (linear modeling, Cole-Cole modeling, and partial least squares regression), were used to correlate the spectroscopic data with routine biomass measurements [viable packed cell volume, viable cell concentration (VCC), cell size, and oxygen uptake rate (OUR)]. All three models predicted offline biomass measurements accurately during the growth phase of the cultures. However, during the stationary and decline phases of the cultures, the models decreased in accuracy to varying degrees. Offline cell radius measurements were unsuccessfully used to correct for the deviations from the linear model, indicating that physiological changes affecting permittivity were occurring. The beta-dispersion was analyzed using the Cole-Cole distribution parameters Deltaepsilon (magnitude of the permittivity drop), f(c) (critical frequency), and alpha (Cole-Cole parameter). Furthermore, the dielectric parameters static internal conductivity (sigma(i)) and membrane capacitance per area (C(m)) were calculated for the cultures. Finally, the relationship between permittivity, OUR, and VCC was examined, demonstrating how the definition of viability is critical when analyzing biomass online. The results indicate that the common assumptions of constant size and dielectric properties used in dielectric analysis are not always valid during later phases of cell culture processes. The findings also demonstrate that dielectric spectroscopy, while not a substitute for VCC, is a complementary measurement of viable biomass, providing useful auxiliary information about the physiological state of a culture.

Cyclical articular joint loading leads to cartilage thinning and osteopontin production in a novel in vivo rabbit model of repetitive finger flexion

OBJECTIVE

An in vivo rabbit model of repetitive joint flexion and loading was used to characterize the morphological effects of cyclical loading on articular cartilage.

DESIGN

The forepaw digits of eight anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with a mean peak digit load of 0.42 N for 2 h per day for 60 cumulative hours. Metacarpophalangeal joints were collected from loaded and contra-lateral control limbs, fixed, decalcified, embedded, and thin-sectioned. Serial sections were stained for histology or for immunohistochemistry. Morphometric data including the mean thicknesses of the uncalcified cartilage and of the calcified cartilage were collected from digital photomicrographs of safranin O-stained sections. The number of cells stained with anti-osteopontin antibody was counted.

RESULTS

We observed a decrease in uncalcified cartilage mean thickness with no significant change in calcified cartilage thickness. We also observed a significant increase in the number of cells positive for osteopontin (OPN) in the uncalcified cartilage. These changes occurred without overt cartilage surface degeneration.

CONCLUSIONS

Cyclical loading leads to changes at the tissue and cellular levels in articular cartilage. These changes are suggestive of tidemark advancement and may indicate a reactivation of cartilage mineralization steps analogous to endochondral ossification. This novel in vivo rabbit model of repetitive flexion and loading can be used to investigate the effects of cyclical loading on articular joints.