T Cell Mediated Conversion of a Non-Anti-La Reactive B Cell to an Autoreactive Anti-La B Cell by Somatic Hypermutation

RevCAR-expressing immune effector cells for targeting of Fn14-positive glioblastoma

In recent studies, we have established the unique adapter chimeric antigen receptor (CAR) platform RevCAR which uses, as an extracellular CAR domain, a peptide epitope instead of an antibody domain. RevCAR adapters (termed RevCAR target modules, RevTMs) are bispecific antibodies that enable the reversible ON/OFF switch of the RevCAR system, improving the safety compared to conventional CARs. Here, we describe for the first time its use for retargeting of both T and NK-92 cells. In addition, we describe the development and preclinical validation of a novel RevTM for targeting of the fibroblast growth factor-inducible 14 (Fn14) surface receptor which is overexpressed on Glioblastoma (GBM) cells, and therefore serves as a promising target for the treatment of GBM. The novel RevTM efficiently redirects RevCAR modified T and NK-92 cells and leads to the killing of GBM cells both in vitro and in vivo. Tumor cell killing is associated with increased IL-2, TNF-α and/or IFN-γ secretion. Hence, these findings give an insight into the complementary potential of both RevCAR T and NK-92 systems as a safe and specific immunotherapeutic approach against GBM.

Immunotheranostic target modules for imaging and navigation of UniCAR T-cells to strike FAP-expressing cells and the tumor microenvironment

BACKGROUND

Chimeric antigen receptor (CAR) T-cells are a promising approach in cancer immunotherapy, particularly for treating hematologic malignancies. Yet, their effectiveness is limited when tackling solid tumors, where immune cell infiltration and immunosuppressive tumor microenvironments (TME) are major hurdles. Fibroblast activation protein (FAP) is highly expressed on cancer-associated fibroblasts (CAFs) and various tumor cells, playing an important role in tumor growth and immunosuppression. Aiming to modulate the TME with increased clinical safety and effectiveness, we developed novel small and size-extended immunotheranostic UniCAR target modules (TMs) targeting FAP.

METHODS

The specific binding and functionality of the αFAP-scFv TM and the size-extended αFAP-IgG4 TM were assessed using 2D and 3D in vitro models as well as in vivo. Their specific tumor accumulation and diagnostic potential were evaluated using PET studies after functionalization with a chelator and suitable radionuclide.

RESULTS

The αFAP-scFv and -IgG4 TMs effectively and specifically redirected UniCAR T-cells using 2D, 3D, and in vivo models. Moreover, a remarkably high and specific accumulation of radiolabeled FAP-targeting TMs at the tumor site of xenograft mouse models was observed.

CONCLUSIONS

These findings demonstrate that the novel αFAP TMs are promising immunotheranostic tools to foster cancer imaging and treatment, paving the way for a more convenient, individualized, and safer treatment of cancer patients.

FLT3-directed UniCAR T-cell therapy of acute myeloid leukaemia

Adaptor chimeric antigen receptor (CAR) T-cell therapy offers solutions for improved safety and antigen escape, which represent main obstacles for the clinical translation of CAR T-cell therapy in myeloid malignancies. The adaptor CAR T-cell platform 'UniCAR' is currently under early clinical investigation. Recently, the first proof of concept of a well-tolerated, rapidly switchable, CD123-directed UniCAR T-cell product treating patients with acute myeloid leukaemia (AML) was reported. Relapsed and refractory AML is prone to high plasticity under therapy pressure targeting one single tumour antigen. Thus, targeting of multiple tumour antigens seems to be required to achieve durable anti-tumour responses, underlining the need to further design alternative AML-specific target modules (TM) for the UniCAR platform. We here present the preclinical development of a novel FMS-like tyrosine kinase 3 (FLT3)-directed UniCAR T-cell therapy, which is highly effective for in vitro killing of both AML cell lines and primary AML samples. Furthermore, we show in vivo functionality in a murine xenograft model. PET analyses further demonstrate a short serum half-life of FLT3 TMs, which will enable a rapid on/off switch of UniCAR T cells. Overall, the presented preclinical data encourage the further development and clinical translation of FLT3-specific UniCAR T cells for the therapy of AML.

A novel ACE2 decoy for both neutralization of SARS-CoV-2 variants and killing of infected cells

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to millions of infections and deaths worldwide. As this virus evolves rapidly, there is a high need for treatment options that can win the race against new emerging variants of concern. Here, we describe a novel immunotherapeutic drug based on the SARS-CoV-2 entry receptor ACE2 and provide experimental evidence that it cannot only be used for (i) neutralization of SARS-CoV-2 in vitro and in SARS-CoV-2-infected animal models but also for (ii) clearance of virus-infected cells. For the latter purpose, we equipped the ACE2 decoy with an epitope tag. Thereby, we converted it to an adapter molecule, which we successfully applied in the modular platforms UniMAB and UniCAR for retargeting of either unmodified or universal chimeric antigen receptor-modified immune effector cells. Our results pave the way for a clinical application of this novel ACE2 decoy, which will clearly improve COVID-19 treatment.

Immunotargeting of Cancer Stem Cells

The generally accepted view is that CSCs hijack the signaling pathways attributed to normal stem cells that regulate the self-renewal and differentiation processes. Therefore, the development of selective targeting strategies for CSC, although clinically meaningful, is associated with significant challenges because CSC and normal stem cells share many important signaling mechanisms for their maintenance and survival. Furthermore, the efficacy of this therapy is opposed by tumor heterogeneity and CSC plasticity. While there have been considerable efforts to target CSC populations by the chemical inhibition of the developmental pathways such as Notch, Hedgehog (Hh), and Wnt/β-catenin, noticeably fewer attempts were focused on the stimulation of the immune response by CSC-specific antigens, including cell-surface targets. Cancer immunotherapies are based on triggering the anti-tumor immune response by specific activation and targeted redirecting of immune cells toward tumor cells. This review is focused on CSC-directed immunotherapeutic approaches such as bispecific antibodies and antibody-drug candidates, CSC-targeted cellular immunotherapies, and immune-based vaccines. We discuss the strategies to improve the safety and efficacy of the different immunotherapeutic approaches and describe the current state of their clinical development.

Development and Functional Characterization of a Versatile Radio-/Immunotheranostic Tool for Prostate Cancer Management

Simple Summary

In previous studies, we described a modular Chimeric Antigen Receptor (CAR) T cell platform which we termed UniCAR. In contrast to conventional CARs, the interaction of UniCAR T cells does not occur directly between the CAR T cell and the tumor cell but is mediated via bispecific adaptor molecules so-called target modules (TMs). Here we present the development and functional characterization of a novel IgG4-based TM, directed to the tumor-associated antigen (TAA) prostate stem cell antigen (PSCA), which is overexpressed in prostate cancer (PCa). We show that this anti-PSCA IgG4-TM cannot only be used for (i) redirection of UniCAR T cells to PCa cells but also for (ii) positron emission tomography (PET) imaging, and (iii) alpha particle-based endoradiotherapy. For radiolabeling, the anti-PSCA IgG4-TM was conjugated with the chelator DOTAGA. PET imaging was performed using the ⁶⁴Cu-labeled anti-PSCA IgG4-TM. According to PET imaging, the anti-PSCA IgG4-TM accumulates with high contrast in the PSCA-positive tumors of experimental mice without visible uptake in other organs. For endoradiotherapy the anti-PSCA IgG4-TM-DOTAGA conjugate was labeled with ²²⁵Ac³⁺. Targeted alpha therapy resulted in tumor control over 60 days after a single injection of the ²²⁵Ac-labeled TM. The favorable pharmacological profile of the anti-PSCA IgG4-TM, and its usage for (i) imaging, (ii) targeted alpha therapy, and (iii) UniCAR T cell immunotherapy underlines the promising radio-/immunotheranostic capabilities for the diagnostic imaging and treatment of PCa.

Abstract

Due to its overexpression on the surface of prostate cancer (PCa) cells, the prostate stem cell antigen (PSCA) is a potential target for PCa diagnosis and therapy. Here we describe the development and functional characterization of a novel IgG4-based anti-PSCA antibody (Ab) derivative (anti-PSCA IgG4-TM) that is conjugated with the chelator DOTAGA. The anti-PSCA IgG4-TM represents a multimodal immunotheranostic compound that can be used (i) as a target module (TM) for UniCAR T cell-based immunotherapy, (ii) for diagnostic positron emission tomography (PET) imaging, and (iii) targeted alpha therapy. Cross-linkage of UniCAR T cells and PSCA-positive tumor cells via the anti-PSCA IgG4-TM results in efficient tumor cell lysis both in vitro and in vivo. After radiolabeling with ⁶⁴Cu²⁺, the anti-PSCA IgG4-TM was successfully applied for high contrast PET imaging. In a PCa mouse model, it showed specific accumulation in PSCA-expressing tumors, while no uptake in other organs was observed. Additionally, the DOTAGA-conjugated anti-PSCA IgG4-TM was radiolabeled with ²²⁵Ac³⁺ and applied for targeted alpha therapy. A single injection of the ²²⁵Ac-labeled anti-PSCA IgG4-TM was able to significantly control tumor growth in experimental mice. Overall, the novel anti-PSCA IgG4-TM represents an attractive first member of a novel group of radio-/immunotheranostics that allows diagnostic imaging, endoradiotherapy, and CAR T cell immunotherapy.

A Small Step, a Giant Leap: Somatic Hypermutation of a Single Amino Acid Leads to Anti-La Autoreactivity

The anti-La mab 312B, which was established by hybridoma technology from human-La transgenic mice after adoptive transfer of anti-human La T cells, immunoprecipitates both native eukaryotic human and murine La protein. Therefore, it represents a true anti-La autoantibody. During maturation, the anti-La mab 312B acquired somatic hypermutations (SHMs) which resulted in the replacement of four aa in the complementarity determining regions (CDR) and seven aa in the framework regions. The recombinant derivative of the anti-La mab 312B in which all the SHMs were corrected to the germline sequence failed to recognize the La antigen. We therefore wanted to learn which SHM(s) is (are) responsible for anti-La autoreactivity. Humanization of the 312B ab by grafting its CDR regions to a human Ig backbone confirms that the CDR sequences are mainly responsible for anti-La autoreactivity. Finally, we identified that a single amino acid replacement (D > Y) in the germline sequence of the CDR3 region of the heavy chain of the anti-La mab 312B is sufficient for anti-La autoreactivity.

And Yet It Moves: Oxidation of the Nuclear Autoantigen La/SS-B Is the Driving Force for Nucleo-Cytoplasmic Shuttling

Decades ago, we and many other groups showed a nucleo-cytoplasmic translocation of La protein in cultured cells. This shuttling of La protein was seen after UV irradiation, virus infections, hydrogen peroxide exposure and the Fenton reaction based on iron or copper ions. All of these conditions are somehow related to oxidative stress. Unfortunately, these harsh conditions could also cause an artificial release of La protein. Even until today, the shuttling and the cytoplasmic function of La/SS-B is controversially discussed. Moreover, the driving mechanism for the shuttling of La protein remains unclear. Recently, we showed that La protein undergoes redox-dependent conformational changes. Moreover, we developed anti-La monoclonal antibodies (anti-La mAbs), which are specific for either the reduced form of La protein or the oxidized form. Using these tools, here we show that redox-dependent conformational changes are the driving force for the shuttling of La protein. Moreover, we show that translocation of La protein to the cytoplasm can be triggered in a ligand/receptor-dependent manner under physiological conditions. We show that ligands of toll-like receptors lead to a redox-dependent shuttling of La protein. The shuttling of La protein depends on the redox status of the respective cell type. Endothelial cells are usually resistant to the shuttling of La protein, while dendritic cells are highly sensitive. However, the deprivation of intracellular reducing agents in endothelial cells makes endothelial cells sensitive to a redox-dependent shuttling of La protein.

Two Be or Not Two Be: The Nuclear Autoantigen La/SS-B Is Able to Form Dimers and Oligomers in a Redox Dependent Manner

According to the literature, the autoantigen La is involved in Cap-independent translation. It was proposed that one prerequisite for this function is the formation of a protein dimer. However, structural analyses argue against La protein dimers. Noteworthy to mention, these structural analyses were performed under reducing conditions. Here we describe that La protein can undergo redox-dependent structural changes. The oxidized form of La protein can form dimers, oligomers and even polymers stabilized by disulfide bridges. The primary sequence of La protein contains three cysteine residues. Only after mutation of all three cysteine residues to alanine La protein becomes insensitive to oxidation, indicating that all three cysteines are involved in redox-dependent structural changes. Biophysical analyses of the secondary structure of La protein support the redox-dependent conformational changes. Moreover, we identified monoclonal anti-La antibodies (anti-La mAbs) that react with either the reduced or oxidized form of La protein. Differential reactivities to the reduced and oxidized form of La protein were also found in anti-La sera of autoimmune patients.