Targeting the High Affinity Receptor, FcγRI, in Autoimmune Disease, Neuropathy, and Cancer

Engineering immune-evasive allogeneic cellular immunotherapies

Allogeneic cellular immunotherapies hold a great promise for cancer treatment owing to their potential cost-effectiveness, scalability and on-demand availability. However, immune rejection of adoptively transferred allogeneic T and natural killer (NK) cells is a substantial obstacle to achieving clinical responses that are comparable to responses obtained with current autologous chimeric antigen receptor T cell therapies. In this Perspective, we discuss strategies to confer cell-intrinsic, immune-evasive properties to allogeneic T cells and NK cells in order to prevent or delay their immune rejection, thereby widening the therapeutic window. We discuss how common viral and cancer immune escape mechanisms can serve as a blueprint for improving the persistence of off-the-shelf allogeneic cell therapies. The prospects of harnessing genome editing and synthetic biology to design cell-based precision immunotherapies extend beyond programming target specificities and require careful consideration of innate and adaptive responses in the recipient that may curtail the biodistribution, in vivo expansion and persistence of cellular therapeutics.

Combining Cellular Immunization and Phage Display Screening Results in Novel, FcγRI-Specific Antibodies

Antibodies that specifically bind to individual human fragment crystallizable γ receptors (FcγRs) are of interest as research tools in studying immune cell functions, as well as components in bispecific antibodies for immune cell engagement in cancer therapy. Monoclonal antibodies for human low-affinity FcγRs have been successfully generated by hybridoma technology and are widely used in pre-clinical research. However, the generation of monoclonal antibodies by hybridoma technology that specifically bind to the high-affinity receptor FcγRI is challenging. Monomeric mouse IgG2a, IgG2b, and IgG3 bind human FcγRI with high affinity via the Fc part, leading to an Fc-mediated rather than a fragment for antigen binding (Fab)-mediated selection of monoclonal antibodies. Blocking the Fc-binding site of FcγRI with an excess of human IgG or Fc during screening decreases the risk of Fc-mediated interactions but can also block the potential epitopes of new antibody candidates. Therefore, we replaced hybridoma technology with phage display of a single-chain fragment variable (scFv) antibody library that was generated from mice immunized with FcγRI-positive cells and screened it with a cellular panning approach assisted by next-generation sequencing (NGS). Seven new FcγRI-specific antibody sequences were selected with this methodology, which were produced as Fc-silent antibodies showing FcγRI-restricted specificity.

Identification of the Linear Fc-Binding Site on the Bovine IgG1 Fc Receptor (boFcγRIII) Using Synthetic Peptides

The bovine IgG1 Fc receptor (boFcγRIII) is a homologue to human FcγRIII (CD16) that binds bovine IgGI with medium-low affinity. In order to identify the Fc-binding site on the bovine IgG1 Fc receptor (boFcγRIII), peptides derived from the second extracellular domain (EC2) of boFcγRIII were synthesized and conjugated with the carrier protein. With a Dot-blot assay, the ability of the peptides to bind bovine IgG1 was determined, and the IgG1-binding peptide was also identified via truncation and mutation. The minimal peptide AQRVVN corresponding to the sequence 98-103 of boFcγRIII bound bovine IgG1 in Dot-blot, suggesting that it represents a linear ligand-binding site located in the putative A-B loop of the boFcγRIII EC2 domain. Mutation analysis of the peptide showed that the residues of Ala98, Gln99, Val101, Val102 and Asn103 within the Fc-binding site are critical for IgG1 binding on boFcγRIII. The functional peptide identified in this paper is of great value to the IgG-Fc interaction study and FcR-targeting drug development.

Interactions of the anti-FcRn monoclonal antibody, rozanolixizumab, with Fcγ receptors and functional impact on immune cells in vitro

Rozanolixizumab is a humanized anti-neonatal Fc receptor (FcRn) monoclonal antibody (mAb) of the immunoglobulin G4 (IgG4) sub-class, currently in clinical development for the treatment of IgG autoantibody-driven diseases. This format is frequently used for therapeutic mAbs due to its intrinsic lower affinity for Fc gamma receptors (FcγR) and lack of C1q engagement. However, with growing evidence suggesting that no Fc-containing agent is truly "silent" in this respect, we explored the engagement of FcγRs and potential functional consequences with rozanolixizumab. In the study presented here, rozanolixizumab was shown to bind to FcγRs in both protein-protein and cell-based assays, and the kinetic data were broadly as expected based on published data for an IgG4 mAb. Rozanolixizumab was also able to mediate antibody bipolar bridging (ABB), a phenomenon that led to a reduction of labeled FcγRI from the surface of human macrophages in an FcRn-dependent manner. However, the presence of exogenous human IgG, even at low concentrations, was able to prevent both binding and ABB events. Furthermore, data from in vitro experiments using relevant human cell types that express both FcRn and FcγRI indicated no evidence for functional sequelae in relation to cellular activation events (e.g., intracellular signaling, cytokine production) upon either FcRn or FcγR binding of rozanolixizumab. These data raise important questions about whether therapeutic antagonistic mAbs like rozanolixizumab would necessarily engage FcγRs at doses typically administered to patients in the clinic, and hence challenge the relevance and interpretation of in vitro assays performed in the absence of competing IgG.

iPSC-derived natural killer cells expressing the FcγR fusion CD64/16A can be armed with antibodies for multitumor antigen targeting

BACKGROUND

Antibody therapies can direct natural killer (NK) cells to tumor cells, tumor-associated cells, and suppressive immune cells to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). This antigen-specific effector function of human NK cells is mediated by the IgG Fc receptor CD16A (FcγRIIIA). Preclinical and clinical studies indicate that increasing the binding affinity and avidity of CD16A for antibodies improves the therapeutic potential of ADCC. CD64 (FcγRI), expressed by myeloid cells but not NK cells, is the only high affinity IgG Fc receptor and is uniquely capable of stably binding to free monomeric IgG as a physiological function. We have reported on the generation of the FcγR fusion CD64/16A, consisting of the extracellular region of CD64 and the transmembrane and cytoplasmic regions from CD16A, retaining its signaling and cellular activity. Here, we generated induced pluripotent stem cell (iPSC)-derived NK (iNK) cells expressing CD64/16A as a potential adoptive NK cell therapy for increased ADCC potency.

METHODS

iPSCs were engineered to express CD64/16A as well as an interleukin (IL)-15/IL-15Rα fusion (IL-15RF) protein and differentiated into iNK cells. iNK cells and peripheral blood NK cells were expanded using irradiated K562-mbIL21-41BBL feeder cells and examined. NK cells, ovarian tumor cell lines, and therapeutic monoclonal antibodies were used to assess ADCC in vitro, performed by a DELFIA EuTDA assay or in real-time by IncuCyte assays, and in vivo. For the latter, we developed a xenograft mouse model with high circulating levels of human IgG for more physiological relevance.

RESULTS

We demonstrate that (1) iNK-CD64/16A cells after expansion or thaw from cryopreservation can be coupled to therapeutic antibodies, creating armed iNK cells; (2) antibody-armed iNK-CD64/16A cells can be redirected by added antibodies to target new tumor antigens, highlighting additional potential of these cells; (3) cytokine-autonomous activity by iNK-CD64/16A cells engineered to express IL-15RF; and that (4) antibody-armed iNK-CD64/16A cells thawed from cryopreservation are capable of sustained and robust ADCC in vitro and in vivo, as determined by using a modified tumor xenograft model with high levels of competing human IgG.

CONCLUSIONS

iNK cells expressing CD64/16A provide an off-the-shelf multiantigen targeting platform to address tumor heterogeneity and mitigate antigen escape.

Blockade of innate inflammatory cytokines TNF, IL-1, or IL-6 overcomes virotherapy-induced cancer equilibrium to promote tumor regression

Cancer therapeutics can lead to immune equilibrium in which the immune response controls tumor cell expansion without fully eliminating the cancer. The factors involved in this equilibrium remain incompletely understood, especially those that would antagonize the anti-tumor immune response and lead to tumor outgrowth. We previously demonstrated that continuous treatment with a non-replicating herpes simplex virus 1 expressing interleukin (IL)-12 induces a state of cancer immune equilibrium highly dependent on interferon-γ. We profiled the IL-12 virotherapy-induced immune equilibrium in murine melanoma, identifying blockade of innate inflammatory cytokines, tumor necrosis factor alpha (TNFα), IL-1β, or IL-6 as possible synergistic interventions. Antibody depletions of each of these cytokines enhanced survival in mice treated with IL-12 virotherapy and helped to overcome equilibrium in some tumors. Single-cell RNA-sequencing demonstrated that blockade of inflammatory cytokines resulted in downregulation of overlapping inflammatory pathways in macrophages, shifting immune equilibrium towards tumor clearance, and raising the possibility that TNFα blockade could synergize with existing cancer immunotherapies.

Co-transient expression of PSA-Fc and PAP-Fc fusion protein in plant as prostate cancer vaccine candidates and immune responses in mice

KEY MESSAGE

PAP-FcK and PSA-FcK prostate cancer antigenic proteins transiently co-expressed in plant induce their specific humoral immune responses in mice. Prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP) have been considered as immunotherapeutic antigens for prostate cancer. The use of a single antigenic agent is unlikely to be effective in eliciting immunotherapeutic responses due to the heterogeneous and multifocal nature of prostate cancer. Thus, multiple antigens have been combined to enhance their anti-cancer effects. In the current study, PSA and PAP were fused to the crystallizable region (Fc region) of immunoglobulin G1 and tagged with KDEL, the endoplasmic reticulum (ER) retention signal motif, to generate PSA-FcK and PAP-FcK, respectively, and were transiently co-expressed in Nicotiana benthamiana. Western blot analysis confirmed the co-expression of PSA-FcK and PAP-FcK (PSA-FcK + PAP-FcK) with a 1:3 ratios in the co-infiltrated plants. PSA-FcK, PAP-FcK, and PSA-FcK + PAP-FcK proteins were successfully purified from N. benthamiana by protein A affinity chromatography. ELISA showed that anti-PAP and anti-PSA antibodies successfully detected PAP-FcK and PSA-FcK, respectively, and both detected PSA-FcK + PAP-FcK. Surface plasmon resonance (SPR) analysis confirmed the binding affinity of the plant-derived Fc fusion proteins to FcγRI/CD64. Furthermore, we also confirmed that mice injected with PSA-FcK + PAP-FcK produced both PSA- and PAP-specific IgGs, demonstrating their immunogenicity. This study suggested that the transient plant expression system can be applied to produce the dual-antigen Fc fusion protein (PSA-FcK + PAP-FcK) for prostate cancer immunotherapy.

In vitro flow cytometry assay to assess primary human and mouse macrophage phagocytosis of live cells

Although tumor-associated macrophages are generally immunosuppressive, macrophages may also promote tumor clearance via phagocytosis of live tumor cells. Here, we present a protocol for assessing macrophage engulfment of tumor cells in vitro using flow cytometry. We describe steps for cell preparation, reseeding macrophages, and setting up phagocytosis. We then detail procedures for collecting samples, staining macrophages, and flow cytometry. The protocol is applicable to both mouse bone-marrow-derived macrophages and human monocyte-derived macrophages. For complete details on the use and execution of this protocol, please refer to Roehle et al. (2021).1.