Immunocytokines with target cell-restricted IL-15 activity for treatment of B cell malignancies

Despite the advances in cancer treatment achieved, for example, by the CD20 antibody rituximab, an urgent medical need remains to optimize the capacity of such antibodies to induce antibody-dependent cellular cytotoxicity (ADCC) that determines therapeutic efficacy. The cytokine IL-15 stimulates proliferation, activation, and cytolytic capacity of NK cells, but broad clinical use is prevented by short half-life, poor accumulation at the tumor site, and severe toxicity due to unspecific immune activation. We here report modified immunocytokines consisting of Fc-optimized CD19 and CD20 antibodies fused to an IL-15 moiety comprising an L45E-E46K double mutation (MIC+ format). The E46K mutation abrogated binding to IL-15Rα, thereby enabling substitution of physiological trans-presentation by target binding and thus conditional IL-15Rβγ stimulation, whereas the L45E mutation optimized IL-15Rβγ agonism and producibility. In vitro analysis of NK activation, anti-leukemia reactivity, and toxicity using autologous and allogeneic B cells confirmed target-dependent function of MIC+ constructs. Compared with Fc-optimized CD19 and CD20 antibodies, MIC+ constructs mediated superior target cell killing and NK cell proliferation. Mouse models using luciferase-expressing human NALM-6 lymphoma cells, patient acute lymphoblastic leukemia (ALL) cells, and murine EL-4 lymphoma cells transduced with human CD19/CD20 as targets and human and murine NK cells as effectors, respectively, confirmed superior and target-dependent anti-leukemic activity. In summary, MIC+ constructs combine the benefits of Fc-optimized antibodies and IL-15 cytokine activity and mediate superior NK cell immunity with potentially reduced side effects. They thus constitute a promising new immunotherapeutic approach shown here for B cell malignancies.

PD-1 checkpoint inhibition enhances the antilymphoma activity of CD19-CAR-iNKT cells that retain their ability to prevent alloreactivity

BACKGROUND

Relapse and graft-versus-host disease (GVHD) are the main causes of death after allogeneic hematopoietic cell transplantation (HCT). Preclinical murine models and clinical data suggest that invariant natural killer T (iNKT) cells prevent acute and chronic GVHD. In addition, iNKT cells are crucial for efficient immune responses against malignancies and contribute to reduced relapse rates after transplantation. Chimeric antigen receptors (CAR) redirect effector cells to cell surface antigens and enhance killing of target cells. With this study, we aimed to combine enhanced cytotoxicity of CD19-CAR-iNKT cells against lymphoma cells with their tolerogenic properties.

METHODS

iNKT cells were isolated from peripheral blood mononuclear cells and transduced with an anti-CD19-CAR retrovirus. After in vitro expansion, the functionality of CD19-CAR-iNKT cells was assessed by flow cytometry, image stream analysis and multiplex analysis in single-stimulation or repeated-stimulation assays. Moreover, the immunoregulatory properties of CD19-CAR-iNKT cells were analyzed in apoptosis assays and in mixed lymphocyte reactions. The effect of checkpoint inhibition through nivolumab was analyzed in these settings.

RESULTS

In this study, we could show that the cytotoxicity of CD19-CAR-iNKT cells was mediated either through engagement of their CAR or their invariant T-cell receptor, which may circumvent loss of response through antigen escape. However, encounter of CD19-CAR-iNKT cells with their target induced a phenotype of exhaustion. Consequently, checkpoint inhibition increased cytokine release, cytotoxicity and survival of CD19-CAR-iNKT cells. Additionally, they showed robust suppression of alloreactive immune responses.

CONCLUSION

In this work, we demonstrate that CAR-iNKT cells are a powerful cytotherapeutic option to prevent or treat relapse while potentially reducing the risk of GVHD after allogeneic HCT.

DNMT and HDAC inhibition induces immunogenic neoantigens from human endogenous retroviral element-derived transcripts

Immunotherapies targeting cancer-specific neoantigens have revolutionized the treatment of cancer patients. Recent evidence suggests that epigenetic therapies synergize with immunotherapies, mediated by the de-repression of endogenous retroviral element (ERV)-encoded promoters, and the initiation of transcription. Here, we use deep RNA sequencing from cancer cell lines treated with DNA methyltransferase inhibitor (DNMTi) and/or Histone deacetylase inhibitor (HDACi), to assemble a de novo transcriptome and identify several thousand ERV-derived, treatment-induced novel polyadenylated transcripts (TINPATs). Using immunopeptidomics, we demonstrate the human leukocyte antigen (HLA) presentation of 45 spectra-validated treatment-induced neopeptides (t-neopeptides) arising from TINPATs. We illustrate the potential of the identified t-neopeptides to elicit a T-cell response to effectively target cancer cells. We further verify the presence of t-neopeptides in AML patient samples after in vivo treatment with the DNMT inhibitor Decitabine. Our findings highlight the potential of ERV-derived neoantigens in epigenetic and immune therapies.

Phase I/II trial of a peptide-based COVID-19 T-cell activator in patients with B-cell deficiency

T-cell immunity is central for control of COVID-19, particularly in patients incapable of mounting antibody responses. CoVac-1 is a peptide-based T-cell activator composed of SARS-CoV-2 epitopes with documented favorable safety profile and efficacy in terms of SARS-CoV-2-specific T-cell response. We here report a Phase I/II open-label trial (NCT04954469) in 54 patients with congenital or acquired B-cell deficiency receiving one subcutaneous CoVac-1 dose. Immunogenicity in terms of CoVac-1-induced T-cell responses and safety are the primary and secondary endpoints, respectively. No serious or grade 4 CoVac-1-related adverse events have been observed. Expected local granuloma formation has been observed in 94% of study subjects, whereas systemic reactogenicity has been mild or absent. SARS-CoV-2-specific T-cell responses have been induced in 86% of patients and are directed to multiple CoVac-1 peptides, not affected by any current Omicron variants and mediated by multifunctional T-helper 1 CD4+ T cells. CoVac-1-induced T-cell responses have exceeded those directed to the spike protein after mRNA-based vaccination of B-cell deficient patients and immunocompetent COVID-19 convalescents with and without seroconversion. Overall, our data show that CoVac-1 induces broad and potent T-cell responses in patients with B-cell/antibody deficiency with a favorable safety profile, which warrants advancement to pivotal Phase III safety and efficacy evaluation. ClinicalTrials.gov identifier NCT04954469.

An optimized IgG-based B7-H3xCD3 bispecific antibody for treatment of gastrointestinal cancers

T cell-based immunotherapy has revolutionized oncological treatment. However, many patients do not respond to treatment, and long-term remissions remain rare, particularly in gastrointestinal cancers like colorectal cancer (CRC). B7-H3 is overexpressed in multiple cancer entities including CRC on both tumor cells and tumor vasculature, the latter facilitating influx of effector cells into the tumor site upon therapeutic targeting. We generated a panel of T cell-recruiting B7-H3xCD3 bispecific antibodies (bsAbs) and show that targeting a membrane-proximal B7-H3 epitope allows for a 100-fold reduction of CD3 affinity. In vitro, our lead compound CC-3 showed superior tumor cell killing, T cell activation, proliferation, and memory formation, whereas undesired cytokine release was reduced. In vivo, CC-3 mediated potent antitumor activity in three independent models using immunocompromised mice adoptively transferred with human effector cells with regard to prevention of lung metastasis and flank tumor growth as well as elimination of large established tumors. Thus, fine-tuning of both target and CD3 affinities as well as binding epitopes allowed for the generation of a B7-H3xCD3 bsAbs with promising therapeutic activity. CC-3 is presently undergoing good manufacturing practice (GMP) production to enable evaluation in a clinical "first-in-human" study in CRC.

Abstract 2865: CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers

Despite substantial improvements over the last decades, survival rates in metastatic gastrointestinal cancer are still far from satisfactory, with an accordingly high medical need for new treatment strategies. B7-H3 (CD276) is a member of the B7 immune checkpoint family. Initially thought to act as co-stimulator, recent studies revealed that B7-H3 rather has an inhibitory role for T cells and contributes to tumor immune evasion. Clinically, its overexpression has been linked to invasive and metastatic potential as well as poor prognosis. Due to its expression on both, tumor cells and tumor vasculature, in a variety of cancer entities including colorectal cancer, B7-H3 attracted our interest as therapeutic target for T cell-recruiting bispecific antibodies (bsAbs). We postulate that “dual targeting” of both, the cancer cells and the tumor vasculature may support the influx of T cells into the tumor site, a critical prerequisite for successful immunotherapy of solid tumors allowing for subsequent destruction of antigen-positive malignant cells. We generated a panel of monoclonal antibodies directed to different epitopes of the B7-H3 molecule. After biochemical characterization, we selected two antibodies with distinct binding proprieties and subsequently used them for the construction of Tcell-recruiting B7-H3xCD3 bsAbs in an IgG-based (IgGsc) format. To reduce side effects, constructs were cloned using a UCHT-1 derived low affinity anti-CD3 sequence. In vitro characterization using colorectal and other carcinoma cells allowed for selection of a construct with optimal functional properties (thereafter termed CC-3) as revealed by target cell-restricted induction of T cell activation, proliferation and tumor cell killing. In vivo, potent efficacy of CC-3 was documented in a lung metastasis model and by its ability to eliminate large established flank tumors using immunocompromised NSG mice adoptively transferred with human effector cells. Despite the high therapeutic efficacy of CC-3, no toxicity was observed in the absence of target cells. In summary, CC-3 is a bsAb with promising therapeutic activity against B7-H3 positive tumors. GMP compliant production of CC-3 is presently ongoing to enable evaluation in a clinical “first in human” study in patients with colorectal cancer.

Citation Format: Latifa Zekri, Martina S. Lutz, Ilona Hagelstein, Timo Manz, Monika Engel, Boris Klimovich, Nisha Prakash, Anna Chashchina, Sebastian Hörner, Stefanie Müller, Melanie Märklin, Martin Pflügler, Gundram Jung, Helmut R. Salih. CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2865.

Abstract 2864: A CLEC12A immunocytokine with target cell-restricted IL-15 activity shows a favorable toxicity profile and high potency in AML

IL-15, often referred to as the “anti-cancer cytokine”, potently stimulates proliferation and activation of NK and T cells, but unlike its close relative IL-2, does neither promote activation-induced death of lymphocytes nor activity of immunoinhibitory Tregs. So far, short half-life, poor accumulation at the tumor site and severe toxicity upon systemic application limit IL-15 efficacy in patients. Fusion of IL-15 to antibodies directed to tumor antigens (classical immunocytokines, ICs) improves on accumulation at the tumor site and pharmacokinetics. However, since the activity of the cytokine moiety within classical ICs does not depend on antigen binding, the application of clinically effective doses is still prevented by toxicity due to unspecific immune activation. To overcome this problem, we took advantage of the unique mechanism of action of IL-15 which stimulates IL-15Rβ/γ on NK and T cells as a membrane-bound complex with IL-15Rα on monocytes and DCs (trans-presentation). We used an Fc-optimized antibody directed to CLEC12A, a surface antigen abundantly expressed on AML cells and leukemic stem cells but not on healthy stem cells. This antibody termed 33C2-SDIE was fused to an IL-15E46K mutant with abolished binding to IL-15Rα, allowing to substitute physiological trans-presentation of IL-15 by binding of the construct to its tumor-expressed target. Antigen-specific binding of the resulting modified immunocytokine (MIC12) was confirmed using multiple CLEC12A-expressing cell lines and primary AML samples from patients. Functional analysis of activation, cytokine release, and target cell lysis demonstrated that MIC proteins, in contrast to classical IC, stimulate cytotoxic lymphocytes in a highly target cell-restricted manner, allowing for the desired reduction of unspecific immune activation. At the same time, significantly superior NK cell reactivity against AML cells as compared to even the Fc-optimized antibody was observed. Both, IL-15 signaling and engagement of Fc-receptors by the optimized Fc-domain were found to be essential for optimal activity of our MIC constructs. Importantly, only treatment with MIC12 was capable to induce NK cell proliferation, which is required to overcome unfavorable target to effector ratios that prevail in overt cancer disease. In summary, our novel CLEC12A-targeting immunocytokine allows for tumor-restricted stimulation of cytotoxic lymphocytes and reduced toxicity while displaying superior anti-leukemic activity and constitutes a promising compound for the treatment of AML.

Citation Format: Boris Klimovich, Leonard Anton, Yangmi Lim, Jonghwa Won, Anna Chashchina, Martin Pflügler, Latifa Zekri, Gundram Jung, Helmut R. Salih. A CLEC12A immunocytokine with target cell-restricted IL-15 activity shows a favorable toxicity profile and high potency in AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2864.

Abstract 2859: Platelet-derived TGFβ undermines treatment efficacy of t cell recruiting bispecific antibodies

Immunotherapeutic strategies such as T cell-recruiting bispecific antibodies (bsAb), chimeric antigen receptor (CAR) T cells, and immune checkpoint inhibition have revolutionized oncological treatment. However, many patients do not respond to treatment with the so far available therapeutics, others for limited time only. Various tumor immune evasion mechanisms have been reported to counteract efficiency of T cell engaging therapeutics. Thrombocytes have recently been described to affect cancer biology by mediating epithelial-mesenchymal transition, tumor invasion, metastasis and notably also immune evasion. Here we report that, upon treatment of prostate cancer patients within a clinical trial evaluating a novel PSMAxCD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. Upon modelling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4+ and CD8+ T cell reactivity as revealed by impaired T cell activation, reduced secretion of perforin and ultimately inhibition of target cell lysis. The immunosuppressive effect mediated by platelets occurred in a TGFβ-dependent manner and was not restricted to the PSMAxCD3 bsAb, but was also observed with various other CD3-directed bispecific constructs including the clinically approved CD19xCD13 bsAb Blinatumomab. BsAb-mediated T cell reactivity could generally be restored by inhibiting platelets using dabigatran, but also specifically by blocking the TGFβ axis. Together, our findings unravel that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function and TGFβ as means to reinforce the effectiveness of bsAb treatment.

Citation Format: Martina S. Lutz, Boris Klimovich, Stefanie Maurer, Jonas S. Heitmann, Melanie Maerklin, Latifa Zekri, Gundram Jung, Helmut R. Salih, Clemens Hinterleitner. Platelet-derived TGFβ undermines treatment efficacy of t cell recruiting bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2859.

Partial p53 reactivation is sufficient to induce cancer regression

Background

Impaired p53 function is one of the central molecular features of a tumor cell and even a partial reduction in p53 activity can increase the cancer risk in mice and men. From a therapeutic perspective it is noteworthy that tumor cells often become addicted to the absence of p53 providing a rationale for developing p53 reactivating compounds to treat cancer patients. Unfortunately, many of the compounds that are currently undergoing preclinical and clinical testing fail to fully reactivate mutant p53 proteins, raising the crucial question: how much p53 activity is needed to elicit a therapeutic effect?

Methods

We have genetically modelled partial p53 reactivation using knock-in mice with inducible expression of the p53 variant E177R. This variant has a reduced ability to bind and transactivate target genes and consequently causes moderate cancer susceptibility. We have generated different syngeneically transplanted and autochthonous mouse models of p53-deficient acute myeloid leukemia and B or T cell lymphoma. After cancer manifestation we have activated E177R expression and analyzed the in vivo therapy response by bioluminescence or magnetic resonance imaging. The molecular response was further characterized in vitro by assays for gene expression, proliferation, senescence, differentiation, apoptosis and clonogenic growth.

Results

We report the conceptually intriguing observation that the p53 variant E177R, which promotes de novo leukemia and lymphoma formation, inhibits proliferation and viability, induces immune cell infiltration and triggers cancer regression in vivo when introduced into p53-deficient leukemia and lymphomas. p53-deficient cancer cells proved to be so addicted to the absence of p53 that even the low-level activity of E177R is detrimental to cancer growth.

Conclusions

The observation that a partial loss-of-function p53 variant promotes tumorigenesis in one setting and induces regression in another, underlines the highly context-specific effects of individual p53 mutants. It further highlights the exquisite sensitivity of cancer cells to even small changes in p53 activity and reveals that changes in activity level are more important than the absolute level. As such, the study encourages ongoing research efforts into mutant p53 reactivating drugs by providing genetic proof-of-principle evidence that incomplete p53 reactivation may suffice to elicit a therapeutic response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02269-6.

Platelets subvert antitumor efficacy of T cell-recruiting bispecific antibodies

T cell-based immunotherapy, for example, with T cell-recruiting bispecific antibody (bsAb), has revolutionized oncological treatment. However, many patients do not respond to treatment, and long-term remissions are still rare. Several tumor immune evasion mechanisms have been reported to counteract efficiency of T cell-engaging therapeutics. Platelets largely affect cancer pathophysiology by mediating tumor invasion, metastasis, and immune evasion. On treatment of patients in a clinical trial with a PSMA×CD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. On modeling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4⁺ and CD8⁺ T-cell reactivity as revealed by impaired T-cell degranulation, secretion of perforin, and ultimately, inhibition of target cell lysis. This effect occurred in a transforming growth factor beta (TGF-β)-dependent manner and was not restricted to PSMA×CD3 bsAb, but rather observed with various CD3-directed bispecific constructs, including the approved CD19×CD3 bsAb blinatumomab. BsAb-mediated T-cell reactivity could be restored by platelet inhibition and specifically by blocking the TGF-β axis. Together, our findings demonstrate that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function as a means to reinforce the effectiveness of bsAb treatment.

DNAM-1/CD226 is functionally expressed on acute myeloid leukemia (AML) cells and is associated with favorable prognosis

DNAM-1 is reportedly expressed on cytotoxic T and NK cells and, upon interaction with its ligands CD112 and CD155, plays an important role in tumor immunosurveillance. It has also been reported to be functionally expressed by myeloid cells, but expression and function on malignant cells of the myeloid lineage have not been studied so far. Here we analyzed expression of DNAM-1 in leukemic cells of acute myeloid leukemia (AML) patients. We found substantial levels of DNAM-1 to be expressed on leukemic blasts in 48 of 62 (> 75%) patients. Interaction of DNAM-1 with its ligands CD112 and CD155 induced release of the immunomodulatory cytokines IL-6, IL-8 IL-10 and TNF-α by AML cells and DNAM-1 expression correlated with a more differentiated phenotype. Multivariate analysis did not show any association of DNAM-1 positivity with established risk factors, but expression was significantly associated with clinical disease course: patients with high DNAM-1 surface levels had significantly longer progression-free and overall survival compared to DNAM-1^low patients, independently whether patients had undergone allogenic stem cell transplantation or not. Together, our findings unravel a functional role of DNAM-1 in AML pathophysiology and identify DNAM-1 as a potential novel prognostic maker in AML.

Inactivation of Mdm2 restores apoptosis proficiency of cooperativity mutant p53 in vivo

TP53 mutations are found in 50% of all cancers and mutated TP53 status is considered poor for treatment. However, some TP53 mutations exhibit only partial loss-of-function (LOF), meaning they retain residual transcriptional and non-transcriptional activities that are potentially beneficial for therapy. Earlier we have characterized a knock-in mouse model for the partial LOF mutant Trp53^E177R (p53RR). Reduced DNA binding cooperativity of this mutant led to the loss of p53-dependent apoptosis, while p53 functions in cell cycle control, senescence, metabolism, and antioxidant defense remained intact. Concomitantly, tumor suppression was evident but strongly compromised compared to wild-type mice. Here we used the Trp53^E177R mouse as a model to investigate whether residual functions of mutant p53 can be engaged to induce cell death, which is considered the most desirable outcome of tumor therapy. We made use of Mdm2 knock-out in developing embryos as a sensitive tool for detecting remaining p53 activities. Genetic ablation of Mdm2 led to embryonic lethality in Trp53^E177R/E177R homozygotes at days 9.5-11.5. This effect was not rescued by concomitant p21-knockout, indicating its independence of p21-mediated cell cycle arrest. Instead, immunohistochemical analysis showed widespread apoptosis in tissues of defective embryos accompanied by persistent accumulation of p53RR protein. This led to partial restoration of the mutant's proficiency in transcriptional induction of the pro-apoptotic genes Bbc3 (Puma) and Bax. These data indicate that increased quantity can compensate for qualitative defects of p53 mutants and suggest that Mdm2-targeting (potentially in combination with other drugs) might be effective against cells bearing p53 partial LOF mutants.

Residual apoptotic activity of a tumorigenic p53 mutant improves cancer therapy responses

Engineered p53 mutant mice are valuable tools for delineating p53 functions in tumor suppression and cancer therapy. Here, we have introduced the R178E mutation into the Trp53 gene of mice to specifically ablate the cooperative nature of p53 DNA binding. Trp53^R178E mice show no detectable target gene regulation and, at first sight, are largely indistinguishable from Trp53^−/− mice. Surprisingly, stabilization of p53^R178E in Mdm2^−/− mice nevertheless triggers extensive apoptosis, indicative of residual wild‐type activities. Although this apoptotic activity suffices to trigger lethality of Trp53^R178E;Mdm2^−/− embryos, it proves insufficient for suppression of spontaneous and oncogene‐driven tumorigenesis. Trp53^R178E mice develop tumors indistinguishably from Trp53^−/− mice and tumors retain and even stabilize the p53^R178E protein, further attesting to the lack of significant tumor suppressor activity. However, Trp53^R178E tumors exhibit remarkably better chemotherapy responses than Trp53^−/− ones, resulting in enhanced eradication of p53‐mutated tumor cells. Together, this provides genetic proof‐of‐principle evidence that a p53 mutant can be highly tumorigenic and yet retain apoptotic activity which provides a survival benefit in the context of cancer therapy.

Development and characterization of three novel monoclonal antibodies against CA-125

Cancer antigen 125 (CA-125) is the most widely used tumor marker for ovarian cancer. Thus, monoclonal antibodies (MAbs) against CA-125 are valuable reagents for the development of diagnostic tests and immunotherapy. We describe here the generation and characterization of three novel hybridoma cell lines producing MAbs against CA-125. CA-125 purified from culture supernatant of ovarian carcinoma cell line OVCAR-3 by affinity chromatography, was used for immunization of BALB/c mice. Three stable cell lines (3C8, 2B6, and 5A12) were selected for production of antibodies against CA-125 and were expanded in mass culture. All three antibodies were shown to recognize linear epitopes. Antibodies 2B6 and 5A12 were determined to recognize epitope cluster B (M 11-like); MAb 3C8 was classified as group A-epitope binders (OC 125-like). The antibodies produced may be used for the development and improvement of CA-125 immunoassays.