GNTI-122: an autologous antigen-specific engineered Treg cell therapy for type 1 diabetes.

Tregs have the potential to establish long-term immune tolerance in patients recently diagnosed with type 1 diabetes (T1D) by preserving ß cell function. Adoptive transfer of autologous thymic Tregs, although safe, exhibited limited efficacy in previous T1D clinical trials, likely reflecting a lack of tissue specificity, limited IL-2 signaling support, and in vivo plasticity of Tregs. Here, we report a cell engineering strategy using bulk CD4+ T cells to generate a Treg cell therapy (GNTI-122) that stably expresses FOXP3, targets the pancreas and draining lymph nodes, and incorporates a chemically inducible signaling complex (CISC). GNTI-122 cells maintained an expression profile consistent with Treg phenotype and function. Activation of CISC using rapamycin mediated concentration-dependent STAT5 phosphorylation and, in concert with T cell receptor engagement, promoted cell proliferation. In response to the cognate antigen, GNTI-122 exhibited direct and bystander suppression of polyclonal, islet-specific effector T cells from patients with T1D. In an adoptive transfer mouse model of T1D, a mouse engineered-Treg analog of GNTI-122 trafficked to the pancreas, decreased the severity of insulitis, and prevented progression to diabetes. Taken together, these findings demonstrate in vitro and in vivo activity and support further development of GNTI-122 as a potential treatment for T1D.

Engineering new protein-protein interactions on the ß-propeller fold by yeast cell surface display.

REINVENTING THE WHEEL: The ß-propeller domain folds like a wheel to provide key protein-protein interactions in the cell. Here we used high-throughput yeast sorting to "invent" ß-propellers of new binding specificities with cellular targets.

Engineered red blood cells as an off-the-shelf allogeneic anti-tumor therapeutic.

Checkpoint inhibitors and T-cell therapies have highlighted the critical role of T cells in anti-cancer immunity. However, limitations associated with these treatments drive the need for alternative approaches. Here, we engineer red blood cells into artificial antigen-presenting cells (aAPCs) presenting a peptide bound to the major histocompatibility complex I, the costimulatory ligand 4-1BBL, and interleukin (IL)-12. This leads to robust, antigen-specific T-cell expansion, memory formation, additional immune activation, tumor control, and antigen spreading in tumor models in vivo. The presence of 4-1BBL and IL-12 induces minimal toxicities due to restriction to the vasculature and spleen. The allogeneic aAPC, RTX-321, comprised of human leukocyte antigen-A*02:01 presenting the human papilloma virus (HPV) peptide HPV16 E711-19, 4-1BBL, and IL-12 on the surface, activates HPV-specific T cells and promotes effector function in vitro. Thus, RTX-321 is a potential 'off-the-shelf' in vivo cellular immunotherapy for treating HPV + cancers, including cervical and head/neck cancers.

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.

Engineering Aglycosylated IgG Variants with Wild-Type or Improved Binding Affinity to Human Fc Gamma RIIA and Fc Gamma RIIIAs.

The binding of human IgG1 to human Fc gamma receptors (hFcγRs) is highly sensitive to the presence of a single N-linked glycosylation site at asparagine 297 of the Fc, with deglycosylation resulting in a complete loss of hFcγR binding. Previously, we demonstrated that aglycosylated human IgG1 Fc variants can engage the human FcγRII class of the low-affinity hFcγRs, demonstrating that N-linked glycosylation of the Fc is not a strict requirement for hFcγR engagement. In the present study, we demonstrate that aglycosylated IgG variants can be engineered to productively engage with FcγRIIIA, as well as the human Fc gamma RII subset. We also assess the biophysical properties and serum half-life of the aglycosylated IgG variants to measure stability. Aglycosylated constructs N297D/S298T (DTT)-K326I/A327Y/L328G (IYG) and N297D/S298A-IYG optimally drove tumor cell phagocytosis. A mathematical model of phagocytosis suggests that hFcγRI and hFcγRIIIA dimers were the main drivers of phagocytosis. In vivo tumor control of B16F10 lung metastases further confirmed the variant DTT-IYG to be the best at restoring wild-type-like properties in prevention of lung metastases. While deuterium incorporation was similar across most of the protein, several peptides within the CH2 domain of DTT-IYG showed differential deuterium uptake in the peptide region of the FG loop as compared to the aglycosylated N297Q. Thus, in this study, we have found an aglycosylated variant that may effectively substitute for wild-type Fc. These aglycosylated variants have the potential to allow therapeutic antibodies to be produced in virtually any expression system and still maintain effector function.

Protein Engineering and Selection Using Yeast Surface Display.

Yeast surface display is a powerful technology for engineering a broad range of protein scaffolds. This protocol describes the process for de novo isolation of protein binders from large combinatorial libraries displayed on yeast by using magnetic bead separation followed by flow cytometry-based selection. The biophysical properties of isolated single clones are subsequently characterized, and desired properties are further enhanced through successive rounds of mutagenesis and flow cytometry selections, resulting in protein binders with increased stability, affinity, and specificity for target proteins of interest.

Engineering fibronectin-based binding proteins by yeast surface display.

Yeast surface display (YSD) presents proteins on the surface of yeast through interaction of the agglutinin subunits Aga1p and Aga2p. The human 10th type III fibronectin (Fn3) is a small, 10-kDa protein domain that maintains its native fold without disulfide bonds. A YSD library of Fn3s has been engineered with a loop amino acid composition similar to that of human antibody complementarity-determining region heavy chain loop 3 (CDR-H3) and varying loop lengths, which has been shown to improve binding ability. There are many advantages of using these small, stable domains that maintain binding capabilities similar to that of antibodies. Here, we outline a YSD methodology to isolate Fn3 binders to a diverse set of target antigens.

Triepitopic antibody fusions inhibit cetuximab-resistant BRAF and KRAS mutant tumors via EGFR signal repression.

Dysregulation of epidermal growth factor receptor (EGFR) is a hallmark of many epithelial cancers, rendering this receptor an attractive target for cancer therapy. Much effort has been focused on the development of EGFR-directed antibody-based therapeutics, culminating in the clinical approval of the drugs cetuximab and panitumumab. Unfortunately, the clinical efficacy of these drugs has been disappointingly low, and a particular challenge to targeting EGFR with antibody therapeutics has been resistance, resulting from mutations in the downstream raf and ras effector proteins. Recent work demonstrating antibody cocktail-induced synergistic downregulation of EGFR motivated our design of cetuximab-based antibody-fibronectin domain fusion proteins that exploit downregulation-based EGFR inhibition by simultaneously targeting multiple receptor epitopes. We establish that, among our engineered multiepitopic formats, trans-triepitopic antibody fusions demonstrate optimal efficacy, inducing rapid EGFR clustering and internalization and consequently ablating downstream signaling. The combined effects of EGFR downregulation, ligand competition, and immune effector function conspire to inhibit tumor growth in xenograft models of cetuximab-resistant BRAF and KRAS mutant cancers. Our designed triepitopic constructs have the potential to enhance the efficacy and expand the scope of EGFR-directed therapies, and our multiepitopic may be readily applied to other receptor targets to formulate a new class of antibody-based therapeutics.

Role of dimerization in the catalytic properties of the Escherichia coli disulfide isomerase DsbC.

The bacterial protein-disulfide isomerase DsbC is a homodimeric V-shaped enzyme that consists of a dimerization domain, two alpha-helical linkers, and two opposing thioredoxin fold catalytic domains. The functional significance of the two catalytic domains of DsbC is not well understood yet. We have engineered heterodimer-like DsbC derivatives covalently linked via (Gly(3)-Ser) flexible linkers. We either inactivated one of the catalytic sites (CGYC), or entirely removed one of the catalytic domains while maintaining the putative binding area intact. Variants having a single active catalytic site display significant levels of isomerase activity. Furthermore, mDsbC[H45D]-dim[D53H], a DsbC variant lacking an entire catalytic domain but with an intact dimerization domain, also showed isomerase activity, albeit at lower levels. In addition, the absence of the catalytic domain allowed this protein to catalyze in vivo oxidation. Our results reveal that two catalytic domains in DsbC are not essential for disulfide bond isomerization and that a determining feature in isomerization is the availability of a substrate binding domain.