Abstract 2956: TNRX-257, a novel multifunctional biologic effectively blocks LAG3 and conditionally delivers IL2Rg/b agonism to LAG3+ cells for robust anti-tumor immunity

While Interleukin-2 (IL-2) has produced remarkable clinical efficacy in a fraction of cancer patients, its clinical use is limited by its narrow therapeutic index due to systemic and pleotropic activation of both inflammatory and suppressive lymphocytes. Numerous approaches to improve the specificity and activity profile of IL-2 are being evaluated. Using Tentarix’s propriety Tentacles™ platform, which is based on fully human stabilized antibody VH domains, we generated TNRX-257, a novel multispecific biologic that effectively blocks LAG3 while simultaneously delivering IL2Rγ/β agonism to LAG3+ cells in a highly conditional manner. LAG3 expression is restricted to antigen-experienced and tumor-reactive immune cells with little expression on peripheral PBMC or immune cells in normal tissues. TNRX-257 was designed to combine LAG3 inhibition with an IL2R agonist moiety to activate and expand LAG3+ tumor-reactive T cells in tumor microenvironment while enhancing their effector function and anti-tumor immunity with minimal systemic toxicity. TNRX-257 blocks the interaction of LAG3 with MHC-II and enhances TCR signaling with similar potency as Relatlimab. TNRX-257 also selectively induces pSTAT5 on LAG3+ immune cells with little activity on LAG3- immune cells, including resting human PBMCs. Moreover, the lower level of pSTAT5 (Emax) induced by TNRX-257 than IL-2 indicates TNRX-257 mediates its activity as a partial agonist, a phenotype that preserves stemness. TNRX-257 induces higher and preferential activation of CD8+ T cells over CD4+ T cells due to higher expression of LAG3 on CD8+ T cells than CD4+ T cells, particularly within the tumor microenvironment. Unlike an undirected IL-15 agonist that induced total CD8+ T cell proliferation, TNRX-257 selectively induced proliferation of LAG3+ CD8+ T cells in a human melanoma TIL stimulation assay without expansion of Tregs. TNRX-257 treatment also preserved the stem-like CD8+ population compared to the undirected IL-15 agonist. TNRX-257 showed in vitro and in vivo molecular stability, as well as good pharmacokinetic (PK) and pharmacodynamic (PD) properties. TNRX-257 induced robust anti-tumor efficacy when tested in early and established tumor models using melanoma A375-CMV-pp65 or colorectal cancer HT-29 cells in humanized mice. In contrast, the corresponding untargeted IL2Rγ/β Tentacle had no efficacy. Together, these data show that TNRX-257 has drug-like properties and elicits strong anti-tumor efficacy, supporting its clinical development.

Citation Format: Rajesh K. Sharma, Jianying Dong, Natasha Del Cid, Yasamine Ghorbanian, Christina Carnevale, Christen Buetz, Matthew Lundberg, Glenn Capodagli, Jayd Hannah, Gavin Hong, Pricilla Walters, Arlene Sereno, Falene Chai, Abby Lin, James Furney, Wendy Zhang, Craig Pigott, Paul Kang, Michael Gallo, Margaret Karow, Stephen Demarest. TNRX-257, a novel multifunctional biologic effectively blocks LAG3 and conditionally delivers IL2Rg/b agonism to LAG3+ cells for robust anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2956.

Development of a potent high-affinity human therapeutic antibody via novel application of recombination signal sequence-based affinity maturation

Therapeutic antibody development requires discovery of an antibody molecule with desired specificities and drug-like properties. For toxicological studies, a therapeutic antibody must bind the ortholog antigen with a similar affinity to the human target to enable relevant dosing regimens, and antibodies falling short of this affinity design goal may not progress as therapeutic leads. Herein, we report the novel use of mammalian recombination signal sequence (RSS)–directed recombination for complementarity-determining region–targeted protein engineering combined with mammalian display to close the species affinity gap of human interleukin (IL)-13 antibody 731. This fully human antibody has not progressed as a therapeutic in part because of a 400-fold species affinity gap. Using this nonhypothesis-driven affinity maturation method, we generated multiple antibody variants with improved IL-13 affinity, including the highest affinity antibody reported to date (34 fM). Resolution of a cocrystal structure of the optimized antibody with the cynomolgus monkey (or nonhuman primate) IL-13 protein revealed that the RSS-derived mutations introduced multiple successive amino-acid substitutions resulting in a de novo formation of a π–π stacking–based protein–protein interaction between the affinity-matured antibody heavy chain and helix C on IL-13, as well as an introduction of an interface-distant residue, which enhanced the light chain–binding affinity to target. These mutations synergized binding of heavy and light chains to the target protein, resulting in a remarkably tight interaction, and providing a proof of concept for a new method of protein engineering, based on synergizing a mammalian display platform with novel RSS-mediated library generation.

Potent, Selective CARs as Potential T-Cell Therapeutics for HPV-positive Cancers

Next-generation T-cell therapies will likely continue to utilize T-cell receptors (TCRs) and chimeric antigen receptors (CARs) because each receptor type has advantages. TCRs often possess exceptional properties even when tested unmodified from patients' T cells. CARs are generally less sensitive, possibly because their ligand-binding domains are grafted from antibodies selected for binding affinity or avidity and not broadly optimized for a functional response. Because of the disconnect between binding and function among these receptor types, the ultimate potential of CARs optimized for sensitivity and selectivity is not clear. Here, we focus on a thoroughly studied immuno-oncology target, the HLA-A*02/HPV-E629-38 complex, and show that CARs can be optimized by a combination of high-throughput binding screens and low-throughput functional assays to have comparable activity to clinical TCRs in acute assays in vitro. These results provide a case study for the challenges and opportunities of optimizing high-performing CARs, especially in the context of targets utilized naturally by TCRs.

Comprehensive hereditary hemochromatosis genotyping

Hereditary hemochromatosis (HH) is an iron-overload disease common in populations of Northern European origin. Patients display increased iron absorption leading to excessive iron deposition and potential multiorgan failure. Using polymerase chain reaction sequence-specific primer (PCR-SSP) technology, we have developed an HH diagnosis assay capable of detecting 19 non-synonymous HFE mutations (including a previously unreported mutation, V295A) and several TFR2, SLC11A3 and H ferritin alleles implicated in HH. As part of the validation process, 159 UK renal donors were genotyped to determine HH allele frequencies in the UK population. The alleles nominally identified as HFE*01 (C282Y), HFE*02 (H63D) and HFE*03 (S65C) were found at frequencies of 0.085, 0.173 and 0.009, respectively. All other potential HH-associated alleles were absent, confirming their low prevalence in this population. This assay enables comprehensive routine HH genotyping, producing rapid, accurate and reproducible results at low cost.

Hybrids of pluripotent and nullipotent human embryonal carcinoma cells: partial retention of a pluripotent phenotype

To investigate whether the failure of human EC cells that do not differentiate is due to the loss of key differentiation-permissive functions or the acquisition of specific inhibitory functions, we tested the ability to differentiate of 2 hybrids produced between a relatively nullipotent human EC cell line, 2102Ep, and a pluripotent human EC cell line NTERA2. Both hybrids, which exhibited an EC phenotype, were able to differentiate readily in response to retinoic acid. Furthermore, 1 hybrid produced a well-differentiated xenograft tumor, which contained, like the NTERA2 tumors, glandular structures, loose mesenchymal tissues and nodules of cartilage, after injection into a SCID mouse. Thus, the failure of 2102Ep EC cells to differentiate is recessive and due to the loss of a key gene function or functions. Nevertheless, the hybrids differed from the pluripotent NTERA2 line by failing to differentiate in neurons, indicating that 2102Ep cells also had acquired a specific, dominantly-acting, inhibitory mutation specific to the neural lineage. Furthermore, the expression of collagen II by one hybrid before and after induction with retinoic suggested a propensity for spontaneous differentiation not evident in the parental NTERA2 cells. Thus, the mechanisms that restrict the differentiation capacity of the nullipotent 2102Ep line are complex and include both recessive and dominant acting factors.

The human embryonal carcinoma marker antigen TRA-1-60 is a sialylated keratan sulfate proteoglycan

Human embryonal carcinoma (EC) cells are the stem cells of teratocarcinomas, and they are key components of germ cell tumors (GCTs). They express several high molecular weight glycoprotein antigens that are down-regulated upon differentiation. One of these antigens, defined by monoclonal antibody TRA-1-60, can be detected in the serum of GCT patients and provides a useful complement to the established serum markers human chorionic gonadotropin and alpha-fetoprotein, especially in those patients without elevated serum human chorionic gonadotropin or alpha-fetoprotein. To examine the relationship of the TRA-1-60-defined antigen to similar antigens defined by other monoclonal antibodies, we have carried out comparative Western blot and immunoprecipitation analyses of human GCT-derived cell lines with monoclonal antibodies TRA-1-60, TRA-1-81, GCTM2, and K21. The TRA-1-60 antigen was detected by Western blot analysis in extracts of all human EC cell lines and in clinical specimens of GCT tested as a diffuse band with a molecular weight of >200,000. A similar but noticeably fainter band was detected in GCT composed of seminoma only. The antigen was not expressed by GCT-derived lines without an EC phenotype. Affinity bead-purified TRA-1-60, TRA-1-81, GCTM2 and K21 antigens reacted in Western blot analysis with each of the other antibodies tested, indicating that the epitopes recognized by each antibody are carried by the same molecular species. This molecule could be metabolically labeled with inorganic [35S]sulfate and was degraded by keratanase. Glycopeptides produced from affinity-purified TRA-1-60 antigen by extensive digestion with Pronase exhibited a molecular weight in excess of 10,000 and were degraded by keratanase. The TRA-1-60 epitope was destroyed by digestion with neuraminidase, but the epitopes defined by TRA-1-81, GCTM2, and K21 were not. Our results indicate that human EC cells generally express a cell surface sialylated keratan sulfate proteoglycan that is subject to modification to yield a variety of epitopes, one of which is recognized by the monoclonal antibody TRA-1-60. Sensitivity to milk alkaline digestion suggests that the oligosaccharides of this proteoglycan are O-linked to a core polypeptide.

The expression and function of cadherin-mediated cell-to-cell adhesion in human embryonal carcinoma cells

Human embryonal carcinoma (EC) cells typically require high cell densities to maintain their characteristic phenotype; they are generally subject to differentiation when cultured at low cell densities, marked by changes in morphology and expression of the surface antigen, SSEA-1. To test whether cadherin mediated cell-to-cell adhesion may be responsible for maintaining an EC phenotype we ascertained that human EC cells generally express E- and P-cadherins, and are subject to cadherin mediated, Ca2+ dependent aggregation. However, in the NTERA2 human EC cell line, inhibition of cadherin mediated adhesion by culture in low levels of Ca2+ did not result in the changes typically seen under low cell density conditions. Low Ca2+ levels also did not affect the pattern of differentiation in these cells following induction with retinoic acid. Therefore, cadherin-mediated cell adhesion does not appear to play a role in maintaining an EC phenotype. On the other hand, culture at both low cell density and in the absence of Ca2+ did result in changes in the patterns of cadherin expression suggesting a feedback regulatory effect of cell-to-cell adhesion. Further, lithium which inhibits the cytoplasmic kinase GSK3beta and hence influences beta-catenin levels did cause differentiation of NTERA2 cells. However, consideration of the phenotype of the resultant cells suggested that this effect may be because of lithium mimicking activation of a Wnt signalling pathway, rather than an effect on signalling consequent upon cadherin mediated cell to cell adhesion.