Immuno-PET monitoring of lymphocytes using the CD8-specific antibody REGN5054

Assessment of immune-cell subsets within the tumor immune microenvironment is a powerful approach to better understand cancer immunotherapy responses. However, the use of biopsies to assess the tumor immune microenvironment poses challenges, including the potential for sampling error, restricted sampling over time and inaccessibility of some tissues/organs, as well as the fact that single biopsy analyses do not reflect discordance across multiple intrapatient tumor lesions. Immuno-PET presents a promising translational imaging approach to address the limitations and assess changes in the tumor microenvironment. We have developed 89Zr-DFO-REGN5054, a fully human CD8A-specific antibody conjugate, to assess CD8+ tumor-infiltrating lymphocytes (TILs) pre- and post-therapy. We used multiple assays, including in vitro T-cell activation, proliferation, and cytokine production, and in vivo viral clearance and CD8 receptor occupancy, to demonstrate that REGN5054 has minimal impact on T-cell activity. Preclinical immuno-PET studies demonstrated that 89Zr-DFO-REGN5054 specifically detected CD8+ T cells in lymphoid tissues of CD8-genetically humanized immunocompetent mice (VelociT mice) and discerned therapy-induced changes in CD8+ TILs in two models of response to a CD20xCD3 T-cell activating bispecific antibody (REGN1979, odronextamab). Toxicology studies in cynomolgus monkeys showed no overt toxicity, and immuno-PET imaging in cynomolgus monkeys demonstrated dose-dependent clearance and specific targeting to lymphoid tissues. This work supports the clinical investigation of 89Zr-DFO-REGN5054 to monitor T-cell responses in patients undergoing cancer immunotherapy.

Abstract 3432: A novel anti-CLDN6-CD137 bispecific antibody (NBL-028) for treating Claudin 6 positive solid tumors

Claudin-6 is a tetraspan membrane protein associated with tight junction formation. Its expression in normal tissues is restricted to the fetal organs but is not detected in the adult tissues. Increased expression of CLDN6 has been shown in several human malignancies such as testicular, ovarian, uterine, liver and lung adenocarcinoma, and is associated with poor prognosis in these cancer patients. Therefore, CLDN6 is a promising tumor-associated antigen (TAA) for tumor-targeting therapeutics such as CART and T cell engaging bispecific antibodies. CD137 co-stimulation has been reported to lead to extended T-cell proliferation, reactivating anergic T cells, promoting memory T cell formation and maintenance. Activating CD137 with agonistic antibodies presents a great opportunity to improve the therapeutic efficacy of immune checkpoint inhibitors (ICIs) or overcome resistance to ICIs. Additionally, a bispecific antibody that activates CD137 signaling only in the presence of TAA would help reduce the dose-dependent hepatotoxicity that was observed in clinical trials with monoclonal anti-CD137 agonistic antibody due to the activation of CD137 signaling in liver resident Kupffer cells. NBL-028 is a novel tetravalent bispecific antibody uniquely designed to activate the CD137 co-stimulatory pathway in the tumor microenvironment through the CLDN6-mediated clustering of CD137. NBL-028 binds to Claudin 6 with high affinity and specificity, activates CD137 in a CLDN6-dependent manner with fast-on and fast-off CD137 binding properties. NBL-028 demonstrated strong CLDN6-dependent T-cell activation and T-cell mediated cytotoxicity in vitro. NBL-028 elicits potent anti-tumor effects and immunological memory in mouse models without detectable liver damages or systemic toxicity. The tumor infiltrated Lymphocyte (TIL) analysis also demonstrated that NBL-028 treatment induced CD45+ immune cells infiltration, decreased Treg/CD8 ratio and increased M1/M2 like macrophage ratio. Furthermore, NBL-028 is designed upon a proprietary molecular scaffold with superior developability features, demonstrated by stability, yield and ease to purify. NBL-028 is currently at the stage of IND-enabling activities with the aim to enter clinical studies for treating Claudin 6 positive solid tumors in 1Q 2023.

Citation Format: Raymond Yu, Yong Tong, Huarui Lu, Makenzie Danton, Samantha Dillman, Joshua Dewe, Joshua Karchin, Samruddhi Patil, Danielle Lavery, Haichun Huang, James Pei, Zhong Liu, Han Li, Ming Lei. A novel anti-CLDN6-CD137 bispecific antibody (NBL-028) for treating Claudin 6 positive solid tumors [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 3432.

Abstract 1869: Novel TNFR2 antibodies to overcome T cell exhaustion and suppressive tumor microenvironment

TNFR2 is highly expressed on the surface of activated T effector cells, T regulatory cells and myeloid cells, and it plays essential roles in modulating the tumor microenvironment. In most cancer types, higher TNFR2 expression correlates with increased immune cell infiltration. Furthermore, the TNFR2 gene is differentially expressed in various cancer types, including breast, lung, renal, liver and skin cancers. In cancers such as head and neck cancer and cutaneous melanoma, high TNFR2 expression correlates with better overall survival. The therapeutic potential of antibodies targeting TNFR2 has been demonstrated by agonist antibodies for the T effector cells, and antibodies that antagonize or deplete the T regulatory cells and suppressive myeloid cells. We discovered novel TNFR2 antibodies that demonstrate unique mechanisms to overcome T cell exhaustion and the suppressive tumor microenvironment for more effective immunotherapy. In vitro studies have shown that our antibodies block TNFα ligand binding and potently inhibit TNFR2 signaling in the monocytic cells. Moreover, these antibodies enhance CD8 T cell function to overcome the suppressive effect from the T regulatory cells and can invigorate exhausted CD8 T cells in an FcγR-dependent manner. In a humanized mouse model, our antibodies demonstrate strong anti-tumor efficacy as single agents or in combination with a PD-L1 inhibitor. Therefore, these antibodies offer potential advantages when the tumor microenvironment is enriched in the exhausted T cells, the suppressive myeloid cells, or the regulatory T cells, as found in anti-PD-1/PD-L1 resistant and PD-1 refractory patients. In conclusion, the data obtained indicate that our TNFR2 antibodies are a novel and promising class of drug candidates for cancer immunotherapeutics. Our lead antibody is currently at the IND-enabling stage with the target of entering clinical studies in early 2022.

Citation Format: Chi Shing Sum, Makenzie Danton, Qii hu, Alla Pritsker, Ray Lin, Raymond Yu, Kevin Chen, Fangqiang Tang, Thomas Pohl, Samantha Wallner, Ahmed Hassan, Huarui Lu, Haichun Huang, James Pei, Zhong Liu, Han Li, Ming Lei. Novel TNFR2 antibodies to overcome T cell exhaustion and suppressive tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1869.

Preclinical PET imaging with the novel human antibody 89Zr-DFO-REGN3504 sensitively detects PD-L1 expression in tumors and normal tissues

Background

Programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) blocking antibodies including cemiplimab have generated profound clinical activity across diverse cancer types. Tumorous PD-L1 expression, as assessed by immunohistochemistry (IHC), is an accepted predictive marker of response to therapy in some cancers. However, expression is often dynamic and heterogeneous, and therefore not reliably captured by IHC from tumor biopsies or archival samples. Thus, there is significant need for accurate whole-body quantification of PD-L1 levels.

Methods

We radiolabeled the novel human anti-PD-L1 antibody REGN3504 with zirconium-89 (⁸⁹Zr) using the chelator p-SCN-Bn-Deferoxamine to enable non-invasive immuno-positron emission tomography (immuno-PET) of PD-L1 expression. PET imaging assessed the localization of ⁸⁹Zr-REGN3504 to multiple human tumor xenografts. Mice genetically humanized for PD-1 and PD-L1 were used to assess the biodistribution of ⁸⁹Zr-REGN3504 to normal tissues and the estimated human radiation dosimetry of ⁸⁹Zr-REGN3504 was also determined. Pharmacokinetics of REGN3504 was assessed in monkeys.

Results

Clear localization of ⁸⁹Zr-REGN3504 to human tumor xenografts was observed via PET imaging and ex vivo biodistribution studies demonstrated high (fourfold to sixfold) tumor:blood ratios. ⁸⁹Zr-REGN3504 specifically localized to spleen and lymph nodes in the PD-1/PD-L1 humanized mice. ⁸⁹Zr-REGN3504 immuno-PET accurately detected a significant reduction in splenic PD-L1 positive cells following systemic treatment with clodronate liposomes. Radiation dosimetry suggested absorbed doses would be within guidelines for other ⁸⁹Zr radiolabeled, clinically used antibodies. Pharmacokinetics of REGN3504 was linear.

Conclusion

This work supports the clinical translation of ⁸⁹Zr-REGN3504 immuno-PET for the assessment of PD-L1 expression. Future clinical studies will aim to investigate the utility of ⁸⁹Zr-REGN3504 immuno-PET for predicting and monitoring response to anti-PD-1 therapy.

A PSMA-Targeting CD3 Bispecific Antibody Induces Antitumor Responses that Are Enhanced by 4-1BB Costimulation

Patients with hematologic cancers have improved outcomes after treatment with bispecific antibodies that bind to CD3 on T cells and that redirect T cells toward cancer cells. However, clinical benefit against solid tumors remains to be shown. We made a bispecific antibody that targets both the common prostate tumor-specific antigen PSMA and CD3 (PMSAxCD3) and provide evidence for tumor inhibition in several preclinical solid tumor models. Mice expressing the human extracellular regions of CD3 and PSMA were generated to examine antitumor efficacy in the presence of an intact immune system and PSMA expression in normal tissues. PSMAxCD3 accumulated in PSMA-expressing tissues and tumors as detected by immuno-PET imaging. Although PSMAxCD3 induced T-cell activation and showed antitumor efficacy in mice with low tumor burden, PSMAxCD3 lost efficacy against larger solid tumors, mirroring the difficulty of treating solid tumors in the clinic. Costimulatory receptors can enhance T-cell responses. We show here that costimulation can enhance the antitumor efficacy of PSMAxCD3. In particular, 4-1BB stimulation in combination with PSMAxCD3 enhanced T-cell activation and proliferation, boosted efficacy against larger tumors, and induced T-cell memory, leading to durable antitumor responses. The combination of CD3 bispecific antibodies and anti-4-1BB costimulation represents a therapeutic approach for the treatment of solid tumors.

Safety and pharmacodynamics of anti-CD2 monoclonal antibody treatment in cynomolgus macaques - an experimental study

Anti-CD2 treatment provides targeted immunomodulatory properties that have demonstrated clinical usefulness to condition the immune system and to treat transplant rejection. The treatment is species-specific due to structural CD2 antigen differences between nonhuman primates and humans. Herein, we report the safety profile and efficacy of two modifications of the same anti-CD2 monoclonal antibody in cynomolgus macaques. Twelve subjects received one i.v. anti-CD2 (of rat or rhesus type) dose each, range 1-4 mg/kg, and were followed for 1-7 days. Treatment effects were evaluated with flow cytometry on peripheral blood and histopathological evaluation of secondary lymphoid organs. In vitro inhibitory activity on primary MHC disparate mixed lymphocyte reactions (MLRs) was determined. Upon anti-CD2 treatment, CD4⁺ , CD8⁺ memory subsets were substantially depleted. Naïve T cells and Tregs were relatively spared and exhibited lower CD2 expression than memory T cells. Early immune reconstitution was noted for naïve cells, while memory counts had not recovered after one week. Both antibodies displayed a concentration-dependent MLR inhibition. Lymph node examination revealed no significant lymphocyte depletion. None of the animals experienced any significant study drug-related adverse events. This study outlines the safety and pharmacodynamic profile of primate-specific anti-CD2 treatment, relevant for translation of anti-CD2-based animal models into clinical trials.

Abstract 1131: CD8 immuno-PET using a fully human mAb can detect increases in tumor-infiltrating T cells by a T cell activating immunotherapy

Detection and quantification of immune cell subsets and changes in the tumor immune microenvironment would be a powerful tool to correlated to response in cancer immunotherapy. Currently, biopsies used to monitor the tumor microenvironment suffer from sampling error, restricted sampling over time and to inaccessible tissues/organs, and do not reflect discordance across tumor lesions of the same patient. Immuno-PET detection of CD8-expressing T cells is a promising translational imaging approach to assess CD8+ tumor-infiltrating lymphocytes (TILs) pre- and post-therapy. We have developed a fully human anti-CD8 antibody that was radiolabeled with the positron emitting radionuclide Zirconium-89 (89Zr) using the bifunctional chelator p-SCN-Bn-Desferoxamine (DFO). CD8-genetically humanized immunocompetent mice were used to validate dose dependent targeting of 89Zr-CD8 to lymphoid tissues. Next, two models were developed to monitor the response of the T cell activating bispecific antibody REGN1979 (CD3xCD20). In the first model designed to lack a CD8 antigen sink, Raji lymphoma cells were co-implanted with human peripheral blood mononuclear cells (hPBMCs) in immune deficient NSG mice and treated with REGN1979. Here, 89Zr-CD8 detected a two-fold increase in CD8+ TILs as quantified by flow cytometry compared to control antibody treated mice. To determine if 89Zr-CD8 could detect changes in CD8+ TILs in the presence of increased circulating and splenic T cells, a different model was developed. Raji lymphoma cells were implanted subcutaneously and hPBMCs were implanted intraperitoneally in immune deficient SRG-15 mice (hSIRP KI, Rag2 KO, IL2Rg KO, hIL-15 KI). Due to the humanization of IL-15, T cells from the implanted hPBMCs rapidly expanded and produced a CD8 antigen sink. In the SRG-15 model, total tumor uptake of 89Zr-CD8 was lower and spleen uptake higher than in the NSG model due to the presence of the antigen sink. These SGR-15 mice treated with REGN1979 also demonstrated an increase in CD8+ TILs by flow cytometry that was specifically detected with 89Zr-CD8. This work demonstrates that 89Zr-CD8 can specifically detect CD8+ T cells in lymphoid tissues of CD8 humanized mice and therapy-induced alterations of CD8+ TILs. Importantly, the detection of CD8+ TILs occurs in both the presence and absence of an antigen sink. This work supports the clinical translation of 89Zr-CD8 immuno-PET to investigate its utility for predicting and monitoring response in patients undergoing immunotherapy.

Citation Format: Richard Tavare, Makenzie Danton, Jason T. Giurleo, Marcus P. Kelly, Sosina Makonnen, Carlos Hickey, Tomas C. Arnold, Dangshe Ma, William C. Olson, Gavin Thurston, Jessica R. Kirshner. CD8 immuno-PET using a fully human mAb can detect increases in tumor-infiltrating T cells by a T cell activating immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1131.

Role of Intrinsic (Graft) Versus Extrinsic (Host) Factors in the Growth of Transplanted Organs Following Allogeneic and Xenogeneic Transplantation

In our studies of life-supporting α-1,3-galactocyltransferase knockout (GalT-KO) pig-to-baboon kidneys, we found that some recipients developed increased serum creatinine with growth of the grafts, without histological or immunological evidence of rejection. We hypothesized that the rapid growth of orthotopic pig grafts in smaller baboon recipients may have led to deterioration of organ function. To test this hypothesis for both kidneys and lungs, we assessed whether the growth of outbred (Yorkshire) organ transplants in miniature swine was regulated by intrinsic (graft) or extrinsic (host environment) factors. Yorkshire kidneys exhibited persistent growth in miniature swine, reaching 3.7 times their initial volume over 3 mo versus 1.2 times for miniature swine kidneys over the same time period. Similar rapid early growth of lung allografts was observed and, in this case, led to organ dysfunction. For xenograft kidneys, a review of our results suggests that there is a threshold for kidney graft volume of 25 cm³ /kg of recipient body weight at which cortical ischemia is induced in transplanted GalT-KO kidneys in baboons. These results suggest that intrinsic factors are responsible, at least in part, for growth of donor organs and that this property should be taken into consideration for growth-curve-mismatched transplants, especially for life-supporting organs transplanted into a limited recipient space.

Harderoporphyrin: a misnomer

More than 30 years ago it was reported that rodent Harderian glands contained a tricarboxylic acid porphyrin, which the authors named Harderoporphyrin. The recent finding in rat Harderian glands of the porphyrin glycoconjugate, protoporphyrin-1-O-acyl-beta-xyloside as a major component led to scrutiny of earlier publications. It became apparent that the results were flawed and that the conclusions were unsustainable. The procedural artefacts which led to the errors are discussed and their bases are demonstrated experimentally. Harderoporphyrin as originally defined never existed.

Is the secretion of atrial natriuretic peptide in man under neural control?

AIMS

Previous work has described short-term variation in the circulating plasma level of atrial natriuretic peptide (ANP), but the mechanism remains unknown. Our aim was to investigate the role of cardiac innervation in this variability.

METHODS AND RESULTS

Blood samples were obtained from the right atrium via a pulmonary artery flotation catheter every 2 min over a 90 min period. Seven patients who underwent cardiac transplantation by the standard biatrial technique (partial innervation) and ten patients who underwent transplantation by the bicaval technique (total denervation) were studied. ANP levels were measured by radioimmunoassay. The median ANP levels were somewhat higher in the biatrial group compared to the bicaval group [470 (150-1095) vs. 216 (100-605) pg. ml(-1); median (range); P = ns], and both were much higher than normal levels in the pulmonary artery (40 (24, 56) pg ml(-1); median and interquartile range). In both transplant groups circulating plasma ANP levels showed considerable variability. The median number of 'peaks' and 'troughs', as counted by visual inspection, were not significantly different between the two groups. Computer analysis identified 12-16 and 6-15 'pulses' in the biatrial and bicaval group, respectively. Further analysis revealed that pulse amplitude, height and area were significantly higher in the biatrial compared to the bicaval group.

CONCLUSION

It would appear that variability of circulating plasma levels of ANP is preserved despite complete or partial cardiac denervation, and so a neural mechanism does not appear to account for such variation.

Narrowing of the region of allelic loss in 21q11-21 in squamous non-small cell lung carcinoma and cloning of a novel ubiquitin-specific protease gene from the deleted segment

We examined 42 fresh non-small cell lung carcinomas for allelic loss using 4 microsatellite markers located in a 4.5 Mb region in 21q11-21, a gene-poor interval recently found by others to be homozygously deleted and exhibiting frequent allelic loss in lung cancer. We found allelic loss across the entire segment in 13/34 informative squamous carcinomas, with 2 cases showing loss in only part of the region. Analysis by fluorescence in situ hybridization of P1-derived artificial chromosomes from the region directly on paraffin sections of the tumor is in concordance with the loss of heterozygosity (LOH) results, and tentatively excludes a 2 Mb segment bearing 2 of the only 3 known genes in the area. Exon trapping in the remaining segment of loss led to identification and cloning of a novel gene spanning 150 kb within the deletion. The full-length gene encodes a protein of 1,055 amino acids with homology to ubiquitin-specific proteases across the eukaryotic evolutionary spectrum. The expressed protein acts as a de-ubiquitinating enzyme as proved by the ability to cleave ubiquitin from a model fusion protein. We found no mutations in the sequence of the functional domains of this gene in any of the LOH-exhibiting tumor DNA samples. It is, however, interesting that genes of the same superfamily have been reported on 3p21, a locus showing the most frequent allelic instability and deletions in lung cancer. Genes Chromosomes Cancer 27:153-161, 2000.

Conformational studies of the beta-subunit of the high affinity IgE receptor: circular dichroism and molecular modelling

The receptor with high affinity for immunoglobulin E (Fc epsilon RI) on mast cells and basophils plays an important role in mediating many of the pathophysiological phenomena associated with allergy. Fc epsilon RI is a tetrameric complex, alpha beta gamma2, of non-covalently attached subunits: one IgE-binding alpha-subunit with the binding site in the extracellular part of the chain, one beta-subunit and a dimer of disulphide linked gamma-subunits. In the present work, prediction of the three-dimensional structure of the four membrane-spanning segments of the beta-subunit has been achieved using rules of helix-helix packing arrangements and molecular dynamics calculations. It yielded a four-helix bundle with specific Van der Waals interactions between the helices. This four-helix bundle was used as a framework upon which to calculate the conformation of the beta-subunit excluding the C and N terminal cytoplasmic tails, but including the three chains that connect the four helices in the bundle. Separately, these synthetic 11, 17 and 29 residue bridge peptides were examined by circular dichroism (CD) spectroscopy and a degree of alpha-helical content in these bridge peptides was found. Additional molecular modelling of the bridge peptides indicate the central residues of these as the location of the helical moieties. Finally, in the model proposed for the beta-subunit, for each pair of consecutive transmembrane (TM) helices and its bridge peptide, a helix-loop-helix-loop-helix motif was found.

Prophylactic digitalisation in pulmonary surgery

BACKGROUND

Prophylactic digoxin is widely used in patients undergoing pulmonary surgery to prevent or control cardiac arrhythmias, but whether it is helpful or not is uncertain.

METHODS

An open, controlled randomised prospective clinical study of 111 patients was undertaken to compare the incidence of cardiac arrhythmias in the 58 patients who received preoperative digoxin and the 53 who did not.

RESULTS

Cardiac arrhythmia occurred in half (29/58) of those given prophylactic digoxin and in 36% (19/53) of those who were not. The overall incidence of arrhythmia was 43%, with no statistically significant difference between the groups.

CONCLUSION

Cardiac arrhythmias remain an important complication of pulmonary surgery and the incidence is not reduced by prophylactic digoxin.