Mixed Lymphocyte Reaction Assay Research Articles

Stealth transgenes enable CAR-T cells to evade host immune responses

BackgroundAdoptive cell therapy, such as chimeric antigen receptor (CAR)-T cell therapy, has improved patient outcomes for hematological malignancies. Currently, four of the six FDA-approved CAR-T cell products use the FMC63-based...

Abstract LB074: Preclinical development of API-192: An engineered CAR-NKT allogeneic cell therapy targeting CD19 and CD20 for the treatment of B-cell malignancies

Abstract Autologous chimeric antigen receptor (CAR)-T therapies have elicited high rates of durable complete responses in B cell lymphomas. Unfortunately, disease progression, manufacturing failures, and prohibitive costs highlight the need for an alternative source of cells that would provide a consistent and readily available therapy for patients. The “Appia Cells Utilized for Allogeneic” (ACUA) platform is an innovative process that differentiates cord blood-derived CD34+ hematopoietic stem and progenitor cells into large numbers of natural killer T (NKT) cells to support off-the-shelf treatment. NKT cells express an invariant T cell receptor (iTCR) and are naturally non-alloreactive, making them an ideal cell type for an allogeneic product. The ACUA platform circumvents the challenge of expanding NKT cells from the periphery where the cells comprise less than 1% of T cells. API-192 is an ACUA-derived, NKT cell product engineered to express dual CARs targeting CD19 and CD20 to prevent tumor antigen escape. At research scale, API-192 is a highly pure product (>90% iTCR+ 19CAR+ 20CAR+) that secretes soluble interleukin-15 for improved expansion and persistence. The transgenic iTCR is not expressed above physiologic levels and upon engagement, API-192 proliferates in response to and is cytotoxic against CD1d+ tumor cells in a ligand-dependent manner. In response to Raji and Nalm6 tumor cells, API-192 secretes pro-inflammatory cytokines, proliferates, and is cytotoxic in a dose- and CAR-dependent manner. API-192 can also control multiple rounds of tumor cell rechallenge in vitro. Using human tumor xenograft mouse models, we show that API-192 expands, controls tumor growth, and prolongs survival. Furthermore, API-192 persists in the periphery, enabling control of a tumor rechallenge at 70 days after initial dosing of effector cells. Indicative of a favorable immunogenic profile, API-192 expresses lower levels of MHC I and MHC II molecules relative to conventional CAR-T cells and elicits less interferon (IFN)-γ release by NK and T cells in a mixed lymphocyte reaction (MLR) assay. To address a theoretical concern that endogenous TCRαβ rearrangement could occur during the ACUA process, we performed genomic DNA based TCR sequencing to quantify the level of TCRα or TCRβ rearrangement and preliminary data suggested negligible levels (<0.2%). Using a MLR assay, we demonstrate that compared to conventional CAR-T cells, API-192 secretes minimal levels of IFN-γ in response to co-culture with healthy donor peripheral blood mononuclear cells, consistent with a low graft vs host risk. In an autonomous growth assay, API-192 expands at a low level and subsequently contracts, suggesting a lack of dysregulated growth. Collectively, these results demonstrate the favorable manufacturability, potency, and safety of API-192 and its potential as a novel allogeneic therapy. Citation Format: Lanny Gov, Jiaji Yu, Maha Qubain, Saige L. Pompura, Sean D. Allen, Michael A. Christopher, Jeff Wiezorek. Preclinical development of API-192: An engineered CAR-NKT allogeneic cell therapy targeting CD19 and CD20 for the treatment of B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB074.

Calcium chloride declotted human platelet lysate promotes the expansion of mesenchymal stromal cells and allows manufacturing of immunomodulatory active extracellular vesicle products

BackgroundMesenchymal stromal cells (MSCs) exert immunomodulatory effects, primarily through released extracellular vesicles (EVs). For the clinical-grade manufacturing of MSC-EV products culture conditions need to support MSC expansion and allow the manufacturing of potent MSC-EV products. Traditionally, MSCs are expanded in fetal bovine serum-supplemented media. However, according to good manufacturing practice (GMP) guidelines the use of animal sera should be avoided. To this end, human platelet lysate (hPL) has been qualified as an animal serum replacement. Although hPL outcompetes animal sera in promoting MSC expansion, hPL typically contains components of the coagulation system that need to be inhibited or removed to avoid coagulation reactions in the cell culture. Commonly, heparin is utilized as an anticoagulant; however, higher concentrations of heparin can negatively impact MSC viability, and conventional concentrations alone do not sufficiently prevent clot formation in prepared media. MethodsTo circumvent unwanted coagulation processes, this study compared various clotting prevention strategies, including different anticoagulants and calcium chloride (CaCl2)-mediated declotting methods, which in combination with heparin addition was found effective. We evaluated the influence of the differently treated hPLs on the proliferation and phenotype of primary bone marrow-derived MSCs and identified the CaCl2-mediated declotting method as the most effective option. To determine whether CaCl2 declotted hPL allows the manufacturing of immunomodulatory MSC-EV products, EVs were prepared from conditioned media of MSCs expanded with either conventional or CaCl2 declotted hPL. In addition to metric analyses, the immunomodulatory potential of resulting MSC-EV products was assessed in a recently established multi-donor mixed lymphocyte reaction assay. Results and ConclusionsOur findings conclusively show that CaCl2-declotted hPLs support the production of immunomodulatory-active MSC-EV products.

Abstract 1363: Blocking inhibitory receptor ILT3 by an antibody with enhanced Fc function promoted adaptive immunity against hematopoietic malignancy independent of ADCC

Abstract Immunoglobulin-like transcript 3 (ILT3) is an inhibitory receptor that is expressed by mature monocytes, dendritic cells (DC), plasma blasts, and the malignant cells arising thereof including acute myeloid leukemia (AML), B cell lymphoma and multiple myeloma (MM). We developed an anti-ILT3 blocking monoclonal antibody (mAb) 17G8 to test the hypothesis that blockade of ILT3 on hematopoietic malignant cells might drive anti-cancer responses through several mechanisms such as cell migration, ADCC, and T cell driven immune responses. Blockade of ILT3 using 17G8 without Fc effector function impaired AML cell line THP1 dissemination into distant sites in vivo and using 17G8 with enhanced Fc function through afucosylation further reduced the tumor burden. This effect of afucosylated 17G8 appears to be mediated by a mechanism other than ADCC, since afucosylated 17G8 showed modest tumor inhibition in ICR mice carrying ILT3 positive AML and MM xenografts. In immune competent mice carrying murine syngeneic AML cell C1498 expressing human ILT3, 17G8 also showed modest anti-tumor effects as a single agent, however, when combined with anti-PD1, afucosylated 17G8 increased CD8+ effector memory T cells, reduced proportion of cells with an exhausted phenotype and significantly improved survival when compared to different controls. Since T cells don’t express ILT3, the effects of 17G8 on T cells are hypothesized to be mediated by blocking ILT3 expressed on myeloid cells. The expression of ILT3 on immature human monocyte-derived DC (moDC) is higher than on mature moDC. Blocking ILT3 with afucosylated 17G8 on immature moDC potentiated maturation of moDC when compared to the controls in vitro. Surprisingly, afucosylated 17G8 stimulated IFNγ production from moDC during maturation. The enhanced DC function induced by afucosylated 17G8 was subsequently found to be translated into enhanced T cell function in an allogeneic mixed lymphocyte reaction (allo-MLR) assay, in which afucosylated 17G8 significantly increased IFNγ production when combined with anti-PD1. The activation of effector T cells was also monitored through a cytotoxicity assay by mixing THP-1 cells with human PBMC in culture. Afucosylated 17G8 induced strong cytotoxicity on THP-1 cells with minimal effects on normal ILT3 positive cells such as monocytes or moDC, suggesting that blockade of ILT3 with afucosylated 17G8 induced more potent T cell mediated allogeneic cytotoxicity than innate cell mediated ADCC killing. In summary, ILT3 is a highly selective M4/M5 AML target. Developing a blocking antibody with enhanced Fc function could add an additional therapeutic strategy of inducing host anti-tumor immunity to current AML treatments which induce direct tumor killing, such as chemotherapy, targeted therapy, and antibody drug conjugate. Citation Format: Shiming Ye, Dong Zhang, Min-Zu Wu, Harini Raghu, Diane Cohen, Mally Romero, Siu-Sze Tan, Donghee Choi, Jonathan Hickson, John Engelhardt, Alex Shoemaker. Blocking inhibitory receptor ILT3 by an antibody with enhanced Fc function promoted adaptive immunity against hematopoietic malignancy independent of ADCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1363.

Abstract 90: In vitro functional evaluation of immuno-oncology drug candidates in customized bioassays

Abstract Increased understanding of the complex tumor microenvironment and its interactors has boosted therapeutic interest and highlighted the importance of the development of innovative in vitro bioassays to represent all the players of the cancer immune response and thereby potentially provide pivotal information on the functional dynamics of candidate therapeutics. Regulatory T cells play an important role by downregulating the anti-tumor response. Their regulation mechanisms constitute an important target for new therapeutics. To study these mechanisms in a human model, suppressive Treg bioassays, mimicking the suppressive action of these cells, were developed and optimized. We further highlight the study of neutrophil function in vitro using flow-cytometry or the Incucyte® live imaging system to monitor neutrophil functions such as antibody-dependent cell-mediated cytotoxicity (ADCC), Neutrophil Extracellular Traps (NETs) formation and the release of Reactive Oxygen Species (ROS). Additionally, multiplex cytokine and peroxidase enzyme analysis after activation and stimulation of neutrophils can be evaluated using ELISA or Luminex technology. Moreover, to refine/reduce non-human primate (NHP) usage, we aimed to develop cost-effective NHP in vitro assays with predictive value for in vivo studies. We isolated Cynomolgus Macaque monocytes and successfully differentiated/polarized them into M0- and M2-like macrophages with a cell surface phenotype comparable to that of their human counterparts. We further developed a Cynomolgus Macaque PBMC x human dendritic cell (DC) mixed lymphocyte reaction (MLR) assay for functional evaluation of test compounds, effectively generated Cynomolgus Macaque immature DCs and implemented Cynomolgus Macaque cytokine release assays.Using high quality primary human immune cells from our own biobank, in vitro bioassays have been developed with superior robustness and reproducibility to screen candidate Immuno-Oncology therapeutics. Citation Format: Martijn Vlaming, Emmanuelle Sidot, Jezabel Lefèvre, Ellen Boelen, Sofie Pattyn. In vitro functional evaluation of immuno-oncology drug candidates in customized bioassays [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 90.

Abstract 2719: Papiliximab, a bispecific nanobody targeting CD47 and PDL1 retards tumor growth without hemolysis

Abstract Cancer cells are known to express immune checkpoint proteins, enabling them to evade immune surveillance. In response, anti-cancer therapies targeting these proteins have been developed. While immune checkpoint inhibitors targeting PD-L1 have been clinically approved, their effectiveness as standalone therapies is limited, with only a 20% response rate. To improve responsiveness, bispecific monoclonal antibodies (MoAbs) targeting both CD47 and PD-L1 have been developed. These bispecific antibodies activate both the innate (by blocking CD47) and adaptive (by blocking PD-L1) immune systems simultaneously. However, conventional antibodies targeting CD47 have been dropped during development due to the risk of hemolysis. In this study, we developed a bispecific single-domain antibody (nanobody, Nb) that targets both CD47 and PD-L1 with a minimal hemagglutination risk. Using phage display libraries from alpacas immunized with recombinant antigens, we screened for an anti-CD47 Nb and an anti-PD-L1 Nb. The affinities (Kd) of these Nbs for their antigens were 7.0 × 10−9 and 9.7 × 10−9, respectively. To maximize affinity for both antigens, a bispecific antibody (Papiliximab) was designed to tandemly array anti-CD47 and PD-L1 Nbs with the Fc region of IgG4. Papiliximab has a lower affinity for RBC (up to 3 μM) than conventional anti-CD47 MoAbs reported earlier. Papiliximab successfully inhibited interactions between CD47/SIRP-α and PD-L1/PD-1, with IC50 values of 7.09 nM and 2.67 nM, respectively. Papiliximab induced the expression of IFN-γ by inhibiting the PD-L1/PD-1 interaction in the PBMC-based MLR (Mixed Lymphocyte reaction) assay. In addition, Papiliximab demonstrated the induction of a phagocytosis effect through CD47 blocking and its IgG4 Fc domain. Therefore, Papiliximab is a multifunctional hybrid bispecific antibody that modulates both innate and acquired immunity. Papiliximab exhibited no cross-reactivity with mouse antigens, but did with cynomolgus antigens. We tested its efficacy on the growth of human B cell lymphoma (Raji cells) and human breast cancer (MDA-MB-231 cells) in humanized NSG mice. Papiliximab was more effective in inhibiting tumor growth than mono-specific Abs and Nbs for PD-L1 or CD47, and their combination. These observations suggest that Papiliximab might be able to improve clinical remission more effectively than the combination of monotherapies without the risk of anemia associated with anti-CD47 MoAbs. We are now working to elucidate the mechanisms behind Papiliximab's superior efficacy and safety compared to the combination of monotherapies. Citation Format: Bum Seo Baek, Min Geun Kim, Jong Hyun Kim, In Young Jang, Sung Min Kim, Jeong Hwan Kim, Sang Beum Lee, Hyoung Tae Kim, Seung-Yong Seong. Papiliximab, a bispecific nanobody targeting CD47 and PDL1 retards tumor growth without hemolysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2719.

Abstract 2729: Discovery and characterization of LILRB2XPD-L1 bispecific antibody SPX-303

Abstract The advent of immunotherapy has led to deep and sometimes durable remissions in certain cancers. However, the variable response rates and development of resistance mechanisms pose significant challenges to the current therapies. The immunosuppressive nature in the tumor microenvironment (TME) can drive many of these observations. Reversing this immunosuppression is a promising avenue for enhancing and broadening the applicability of IO therapies. Macrophages are critically modulated by LILRB2, a pivotal receptor in their maturation and polarization to the M2 immunosupressive phenotype. We report the discovery and development of a novel anti-LILRB2/PD-L1 bispecific antibody, SPX-303, designed using an anti-LILRB2 IgG4 derived from a mouse hybridoma screen and linked with an anti-PD-L1 epitope. SPX-303 demonstrates sub-nanomolar binding affinity to both LILRB2 and PD-L1 targets, effectively blocking the interaction between LILRB2 and its ligand, as well as inhibiting PD-1 binding to PD-L1. In in vitro functional assays, SPX-303 exhibits effects comparable to the parental monomeric anti-LILRB2 (SPX-104) in redirecting macrophage polarization from M2 to M1 stage, as observed in both cultured PBMC and human monocyte-derived macrophage (HMDM) models. Furthermore, SPX-303 demonstrates a synergistic effect in inducing T cell activation in the autologous mixed lymphocyte reaction assay (auto-MLR), surpassing the effects of the anti-LILRB2 epitope (SPX-104) and the anti-PDL1 fragment (single-domain anti-PDL1) alone or in combination. In vivo experiments reveal that SPX-303 significantly inhibits tumor growth. Collectively, these results support SPX-303 as a novel therapeutic antibody that effectively enhances anti-cancer immunity in the treatment of advanced solid tumors. The pre-clinical data as well as the clinical plan of SPX-303 will be presented. Citation Format: Anthony Haight, Qian Chen, Brandon William, Dinh-Duc Nguyen, Robert Cai, Jichun Ma, Michael White, Jindong Jin, Jadon Shen, Martin Siekierzycki, Victoria Hall, Hua Jin, Roland Meier, Justin Moser. Discovery and characterization of LILRB2XPD-L1 bispecific antibody SPX-303 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2729.

Extracorporeal photopheresis as a promising strategy for the treatment of graft-versus-host disease after CAR T-cell therapy

AbstractGraft-versus-host disease (GVHD) occurs in about 10% to 33% of patients receiving “allogeneic” or “autologous” chimeric antigen receptor T (CAR-T) cells after preceding allogeneic hematopoietic stem cell transplantation (allo-HSCT) due to the substantial presence of alloreactive T cells. Extracorporeal photopheresis (ECP) shows promising clinical outcomes in the treatment of GVHD after allo-HSCT without hampering antitumor and antiviral effects. This raises an interesting question: whether ECP might constitute a new way to treat patients with GVHD after CAR T-cell therapy without compromising CAR-T cells significantly. Third-generation CD19-specific CAR-T cells were generated and an in vitro ECP protocol was established. The impact of ECP on CAR-T cells was comprehensively investigated in 2 models: the nondilution model reflects days after CAR T-cell infusion and the dilution model weeks after infusion. The therapeutic effect of ECP on GVHD was examined in an in vitro mixed lymphocyte reaction (MLR) assay. We found, ECP-treated CAR-T cells demonstrated reduced potency in inducing alloreaction compared with that of the group without ECP treatment in MLR assay. ECP could selectively induce apoptosis, thereby enriching the naive and central memory CAR-T cells with a reduced alloreactivity. The cytokine milieu of CAR-T cells could be switched from immune stimulation to immune tolerance in both models. Moreover, ECP could modulate the proliferative capacity of CAR-T cells without hampering their long-term functionality in the dilution model. In conclusion, ECP constitutes a promising treatment strategy for GVHD after allo-HSCT and CAR T-cell transfusion, as ECP reduces the alloreactivity without hampering CAR T-cell functionality.

Characterization of CD4+ and CD8+ T cells responses in the mixed lymphocyte reaction by flow cytometry and single cell RNA sequencing.

The Mixed Lymphocyte Reaction (MLR) consists in the allogeneic co-culture of monocytes derived dendritic cells (MoDCs) with T cells from another donor. This in vitro assay is largely used for the assessment of immunotherapy compounds. Nevertheless, the phenotypic changes associated with lymphocyte responsiveness under MLR have never been thoroughly evaluated. Here, we used multiplex cytokine and chemokine assays, multiparametric flow cytometry and single cell RNA sequencing to deeply characterize T cells activation and function in the context of CD4+- and CD8+-specific MLR kinetics. We showed that CD4+ and CD8+ T cells in MLR share common classical markers of response such as polyfunctionality, increased proliferation and CD25 expression but differ in their kinetics and amplitude of activation as well as their patterns of cytokines secretion and immune checkpoints expression. The analysis of immunoreactive Ki-67+CD25+ T cells identified PBK, LRR1 and MYO1G as new potential markers of MLR response. Using cell-cell communication network inference and pathway analysis on single cell RNA sequencing data, we also highlighted key components of the immunological synapse occurring between T cells and the stimulatory MoDCs together with downstream signaling pathways involved in CD4+ and CD8+ T cells activation. These results provide a deep understanding of the kinetics of the MLR assay for CD4+ or CD8+ T cells and may allow to better characterize compounds impacting MLR and eventually identify new strategies for immunotherapy in cancer.

Soluble CD83 modulates human-monocyte-derived macrophages toward alternative phenotype, function, and metabolism.

Alterations in macrophage (Mφ) polarization, function, and metabolic signature can foster development of chronic diseases, such as autoimmunity or fibrotic tissue remodeling. Thus, identification of novel therapeutic agents that modulate human Mφ biology is crucial for treatment of such conditions. Herein, we demonstrate that the soluble CD83 (sCD83) protein induces pro-resolving features in human monocyte-derived Mφ biology. We show that sCD83 strikingly increases the expression of inhibitory molecules including ILT-2 (immunoglobulin-like transcript 2), ILT-4, ILT-5, and CD163, whereas activation markers, such as MHC-II and MSR-1, were significantly downregulated. This goes along with a decreased capacity to stimulate alloreactive T cells in mixed lymphocyte reaction (MLR) assays. Bulk RNA sequencing and pathway analyses revealed that sCD83 downregulates pathways associated with pro-inflammatory, classically activated Mφ (CAM) differentiation including HIF-1A, IL-6, and cytokine storm, whereas pathways related to alternative Mφ activation and liver X receptor were significantly induced. By using the LXR pathway antagonist GSK2033, we show that transcription of specific genes (e.g., PPARG, ABCA1, ABCG1, CD36) induced by sCD83 is dependent on LXR activation. In summary, we herein reveal for the first time mechanistic insights into the modulation of human Mφ biology by sCD83, which is a further crucial preclinical study for the establishment of sCD83 as a new therapeutical agent to treat inflammatory conditions.

Abstract A114: Naturally occurring LAG3-blocking recombinant antibodies as a novel class of checkpoint inhibitors

Abstract LAG3 is a promising cancer immunotherapeutic target due to its negative regulatory role on T cells, NK cells, and B cells. Using our proprietary technology [US patent US9810694; 2017], we have isolated, sequenced, and pre-examined the potential immunological capability of fully human, naturally occurring anti-LAG3 antibodies. The best candidate, monoclonal antibody IG2 with molecular weight of 150 kDa and affinity of 4.4 nM, a complete recombinant reproduction of the antibody isolated from the human donor, was selected from 6 candidates for future research. In vitro allogeneic mixed lymphocyte reaction (MLR) assays using human T cells were performed to evaluate lymphocyte responses to stimulation with IG2 (5 μg/ml) or regular RPMI media alone. LAG3 blockade systematically resulted in an enhancement of CD3+ T cell proliferation by 45%. The main impact was on proliferation of CD4+ T cells with 50% increase. The count of CD8+ T cells also increased by 36%. Another assay evaluated IFNγ expression in NK92 cells treated with anti-LAG3 antibody. NK92 cells were starved without IL-2 for 24 hours in complete NK cell media and then cultivated with IG2 (5 μg/ml and 10 μg/ml) or media for 24 hours. Even short-term cultivation led to an increase in IFNg expression by 50%. Increasing the dose of the antibody did not affect the level of IFNγ expression. We did not observe any antibody dependent cellular cytotoxicity (ADCC) in co-cultures of NK92 cells with 786-O (renal), H358 (lung) or Hct116 (colon) cancer cell lines. Several studies demonstrate that NK cells can stimulate the expression of pro-imflammatory/pro-tumorigenic cytokines, IL-6 and IL-8, by tumor cells. Therefore, we evaluated the effects of IG2 on those genes’ expression induced by NK cells. Clear cell RCC cells (786-O) and NSCLC (H358) cell lines were co-cultured with NK92 cells for 2 hours and overnight with IG2 (1 mcg/ml) or media only. Co-cultivation of NK cells, cancer cells, and IG2 did not result in robust up-regulation of IL-6 and IL-8 by tumor cells. In order to evaluate the direct impact of the IG2 antibody on tumor cells, we incubated 786-O renal carcinoma cells with escalating concentrations of anti-LAG3 antibodies for 72 hours followed by Cell Titer Blue analysis when compared to un-treated cells (0 ug/ml). As expected, there was no direct cytotoxic effect of the antibody on tumor cells. Finally, assuming that novel naturally occurring antibodies may lead to fewer adverse events, we evaluated the preliminary toxicity in vivo. Eighteen mice were randomized in a 1:1 ratio to IG2 antibody group (1 mg/kg, intravenously, twice a week, 6 weeks) or to the untreated control group. The use of the antibody at this dose did not lead to the development of toxicity and a change in the weight of the animals compared to the control group. The results of the first studies demonstrate the potential activity and safety of a recombinant anti-LAG3 antibody reproduced from a human donor. Citation Format: Ilya Tsimafeyeu, Petr Makhov, Gennady Bratslavsky. Naturally occurring LAG3-blocking recombinant antibodies as a novel class of checkpoint inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A114.

Abstract A077: A novel, tumor-targeted immunocytokine comprising an anti-PD-L1 Affimer® fused to IL-15 exhibits potent anti-tumor activity

Abstract Affimer® biotherapeutics are novel 15kDa scaffold proteins based on the human protease inhibitor Stefin A. Affimer® proteins lack disulfide bonds and post translational modifications including glycosylation. Large, diverse phage display libraries have been created which incorporate peptide loops into the scaffold backbone. We have previously identified high-affinity competitive binders to human programmed death-ligand 1 (PD-L1) using phage display which block interaction with programmed death 1 (PD-1). Lead anti-PD-L1 Affimer® proteins were formatted by fusing to human Fc or as in-line-fusions to a serum albumin binding Affimer® to extend pharmacokinetic half-life. Here we describe novel immunocytokines that consist of half-life extended Affimer® antagonist to PD-L1 fused to human Interleukin 15 (IL-15) receptor alpha sushi domain and human IL-15 (PDL1-IL15 Affimer® fusion proteins). PD-L1 is upregulated on tumor cells, macrophages, and dendritic cells in the tumor microenvironment. PD-L1 engagement with PD-1 on T cells inhibits T cell proliferation, transcriptional activation, and cytokine release, resulting in suppressed anti-tumor response. IL-15 signals through the IL-2 receptor beta chain and the common gamma chain (IL-2Rβ/γ) and induces differentiation and proliferation of CD8+ T cells and Natural Killer (NK) cells; it does not stimulate regulatory T cells (Tregs). Immunostimulatory cytokines have therapeutic potential but are often associated with toxicity when administered systemically. PDL1-IL15 Affimer® fusion proteins have the potential to bring the immunomodulatory cytokine directly to the tumor and reverse the immunosuppressive tumor microenvironment by enhancing T cell activation, while also introducing a checkpoint inhibitor to augment the anti-tumor immune response. We characterized binding and activity of PDL1-IL15 Affimer® fusion proteins in in vitro assays. PDL1-IL15 Affimer® fusion proteins bind both PD-L1 and IL-2Rβ/γ and exhibit PD-1:PD-L1 blocking activity and IL-2Rβ/γ activation. PDL1-IL15 Affimer® fusion proteins reversed T cell exhaustion in a human mixed lymphocyte reaction assay: PDL1-IL15 Affimer® fusion proteins showed greater activity than either the PD-L1 or the IL-15 component alone. Furthermore, PDL1-IL15 Affimer® fusion proteins enhanced immune cell killing of tumor cells in co-culture assays of human peripheral blood mononuclear cells and tumor cells. In summary, data suggests that PDL1-IL15 Affimer® fusion proteins can reverse T cell exhaustion and induce immune cell activation to elicit an anti-tumor effect. Ongoing in vivo work aims to investigate the efficacy and tolerability profile of PDL1-IL15 Affimer® fusion proteins to direct future development of this therapeutic. In addition, the data will support wider utility of the Affimer® platform to develop new ways of targeting the tumor while reducing systemic toxicity. Citation Format: Victoria Juskaite, Deepa Avisetti, David H Jones, Ahmad Sobri, Gregory Billenness, Hanna Buist, Tik Nga Tong, Norhakim Yahya, Fiona McLaughlin. A novel, tumor-targeted immunocytokine comprising an anti-PD-L1 Affimer® fused to IL-15 exhibits potent anti-tumor activity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A077.

Durable Multiplex Epigenetic Editing for Generation of Allogeneic CAR T without Chromosomal Rearrangements

CAR T therapies have provided significant breakthroughs for patients with CD19+ malignancies and multiple myeloma, but a major limitation is the need for individualized manufacturing of autologous T cells, increasing the cost and reducing the availability of these life-saving drugs. An allogeneic CAR T product, available off-the-shelf, could greatly reduce manufacturing burden and improve access to therapy. To date, allogeneic CAR T clinical trials have shown limited durable responses and have reduced only TCR expression to avoid a graft versus host response. Further editing to reduce MHC class I and II expression may produce a cell resistant to allogeneic CD4+ and CD8+ T cell rejection to potentially improve allogeneic CAR T persistence. Conventional genome editing technologies that rely on double or single stranded DNA breaks have the potential to introduce genomic changes including translocations, especially when multiple edits are introduced. Epigenetic editing, in contrast, enables durable modulation of gene expression without cutting or nicking the DNA sequence and is extremely well-suited for simultaneous targeting of multiple genes to enable generation of persistent allogeneic CAR T cells. In this study, we evaluated the use of a dCas9-based epigenetic editor to silence TCR and MHC class I and II expression in primary T cells to produce allogeneic CAR T transduced for expression of CAR and HLA-E. Epigenetic editor mRNA and sgRNAs targeting the genes of interest were delivered via nucleofection to activated T cells. Edited T cells were then maintained in proliferative culture, with CD3/CD28 or PMA/ionomycin restimulation, and expression of the target genes was assessed by flow cytometry. Expression of TCR and MHC class I and II was durably suppressed in both single and multiple gene target silencing, demonstrating the robustness of epigenetic editing for ex vivo cell therapies. In addition, genomic integrity assessments demonstrated that epigenetic editing did not induce genomic changes as detected by either a quantitative sequencing-based assay or a fluorescence-based technique with single-cell resolution. In primary T cells, multiplex silencing did not cause genomic rearrangements, including translocations and truncations, above the level observed in controls, whereas Cas9 multiplex editing did. Mixed lymphocyte reaction (MLR), specific killing, and degranulation assays were used to demonstrate allogeneic function of silencing edits and the overexpression of an NK shield in vitro. In these assays, epigenetically-edited cells performed similarly to control gene edited cells in which the same gene targets were knocked out. TCR-silenced T cells did not proliferate or produce IFN-γ in response to allogeneic PBMCs in an MLR assay, and MHC class I- and II-silenced T cells did not evoke a proliferative response or IFN-γ production from allogeneic CD4+ or CD8+ T cells. Furthermore, overexpression of the HLA-E NK shield protected HLA-E expressing cells relative to B2M KO cells in a specific killing assay and reduced the degranulation response of NKG2A+ NK cells without a corresponding increase in NKG2C+ NK cell degranulation observed with other single chain HLA-E constructs tested. Finally, multiplex epigenetically-edited allogeneic CAR T were produced by transduction for expression of an anti-BCMA CAR, followed by simultaneous editing to silence target genes. These cells displayed potent anti-tumor activity against the BCMA+ MM.1S cell line, comparable to activity of unedited CAR T cells. These data support multiplex epigenetic editing to produce functional allogeneic CAR T cells that (1) do not exhibit a GVHD response; (2) resist CD8+ and CD4+ T cell alloresponses; and (3) resist the NK missing-self response normally consequent of reduced MHC class I expression without introduction of genotoxic events.

API-192, an Allogeneic CD19/20 CAR-NKT Cell Product Derived from Cord Blood CD34+ HSPCs for the Treatment of B-Cell Malignancies

Autologous chimeric antigen receptor (CAR)-T cell therapies induce durable remissions and improve survival in patients with advanced B cell malignancies. However, challenges such as manufacturing variability, cost, and time to treatment highlight the need for an allogeneic, off-the-shelf approach that preserves the efficacy of autologous CAR-T. Additionally, antigen escape is one of the established mechanisms of resistance to current CAR-T therapies which target a single antigen. Classical natural killer T (NKT) cells express an invariant T cell receptor (iTCR) that is restricted to the conserved CD1d protein, making it a promising cell type for allogeneic therapies as they do not require TCR gene editing to avoid graft-vs-host (GvH) disease. Furthermore, NKT cells mediate dendritic cell cross-priming, target immunosuppressive myeloid cells/macrophages in the tumor microenvironment, and directly kill CD1d + tumor cells through the iTCR. Endogenous NKT cells are an extremely rare population in the blood (<1% of lymphocytes), posing manufacturing challenges. API-192 is a human cord blood CD34 + hematopoietic stem and progenitor cell-derived NKT cell product engineered to express dual CARs targeting CD19 and CD20 and armored with soluble IL-15 for improved expansion and persistence. The Appia Cells Utilized for Allogeneic (ACUA) platform enables the production of large numbers of product NKT cells co-expressing multiple transgenes at high purity (>90% iTCR + 19CAR + 20CAR +) with no purification step or gene editing. Phenotypically, API-192 cells are predominantly CD4 -CD8 - or CD4 -CD8 +, express major activating NK receptors, and harbor intracellular stores of cytotoxic molecules, resembling endogenous NKT cells. API-192 kills Raji and Nalm6 tumor cells in a CAR-specific and dose-dependent manner and can control multiple rounds of tumor challenge in vitro. API-192 secretes pro-inflammatory cytokines and proliferates in response to tumor antigen . In human tumor xenograft models in immunocompromised mice, API-192 robustly expands, suppresses tumor growth, and exhibits prolonged persistence, enabling control of a tumor rechallenge 70 days after initial dosing. API-192 expresses lower levels of MHC I and MHC II molecules relative to conventional CAR-T cells and elicits less IFN-γ release by NK and T cells in mixed lymphocyte reaction (MLR) assays, indicative of a more favorable immunogenic profile. Compared to conventional CAR-T cells, API-192 also secretes minimal levels of IFN-γ in response to co-culture with healthy donor peripheral blood mononuclear cells, consistent with the expression of a non-HLA restricted TCR and low GvH risk. These results demonstrate the feasibility, potency, and potential safety of API-192, warranting further development as a novel allogeneic therapy.

Cellular Mechanisms Affecting Allogeneic CAR T Cell Expansion and Rejection in Large B-Cell Lymphoma

Allogeneic chimeric antigen receptor (CAR) T cell therapies hold promise to improve CAR T access. However, limited expansion and persistence due to rejection in some recipients may impact efficacy. Elucidation of cellular mechanisms governing allogeneic CAR T expansion and persistence may inform patient management and technology development. We hypothesized that cell-extrinsic and intrinsic mechanisms differentially regulate rejection and expansion of allogeneic CAR T cells in patients with large B-cell lymphoma. We identified 11 patients with relapsed/refractory large B-cell lymphoma treated on the ALPHA-2 phase 1 trial (NCT04416984) with ALLO-501A, a healthy donor-derived CD19 CAR T with T cell receptor (TCR) knockout. ALLO-501A uses Cellectis technologies. Despite treatment with a single ALLO-501A lot, we observed heterogeneity in CAR T expansion and clinical outcomes. Six patients had robust expansion (expanders), and five patients had relatively poor expansion (non-expanders) [median maximum CAR vector copy number 21,571 (range 10,296-104,784) versus 141 (range 55-502) copies/µg DNA, p < 0.01]. As with autologous therapies, expanders exhibited longer CAR T persistence and a higher frequency of clinical responses than non-expanders. To elucidate cell-extrinsic mechanisms involved in allogeneic CAR T rejection, we hypothesized that recipient-derived alloreactive T cells limit expansion in non-expanders. We adapted a mixed lymphocyte reaction assay to identify alloreactive CD4 + and CD8 + T cell clones from pre-lymphodepletion PBMC samples. Briefly, labeled recipient PBMCs were incubated with irradiated ALLO-501A cells from the treatment lot. Proliferating recipient CD4 + and CD8 + T cells were isolated and underwent TCR sequencing. Alloreactive clones were defined as those enriched in this sample compared to an unstimulated sample from the same patient (p < 0.05 by Fisher's test) and were tracked post-treatment. Two expanders and two non-expanders were selected for analysis. Non-expanders exhibited more robust in vitro T cell proliferation in response to ALLO-501A than expanders (85 vs. 40% proliferating; p = 0.03). Thus, more alloreactive clones were identified in non-expanders (median 762 CD4 + clones, 314 CD8 + clones) than expanders (median 313 CD4 + clones, 90 CD8 + clones). Non-expanders also had higher median alloreactive CD8 + T cell frequencies than expanders at days 7 and 14 following allogeneic CAR T infusion ( Figure A). A similar pattern was not observed for alloreactive CD4 + clones or non-alloreactive T cell clones, highlighting the potential role of recipient alloreactive CD8 + T cells in the rejection process and the need to control this process for the success of allogeneic CAR T. Next, to define the role of cell-intrinsic mechanisms in allogeneic CAR T expansion, we tracked clonal evolution of the CAR T repertoire through TCR sequencing of the infusion product (IP) and post-treatment PBMC samples in all patients. At day 14 (peak allogeneic CAR T expansion), all expanders had numerous IP-derived clones and substantial clonotype overlap with each other. In contrast, no clonotype overlap was observed among non-expanders ( Figure B). Furthermore, we identified the same high-frequency IP-derived clones in multiple expanders and their relative abundance reflected the original clonal hierarchy of the IP. This pattern differs from autologous therapies, where clonal hierarchy is not maintained after infusion (Sheih, et al. Nat. Comm. 2020), and suggests that cell-intrinsic mechanisms may influence allogeneic CAR T expansion potential. Single-cell RNA and proteomic studies to characterize these expanding clones are ongoing. In conclusion, we compared expansion kinetics across 11 allogeneic CAR T recipients to elucidate the cellular mechanisms governing allogeneic CAR T expansion and rejection. We revealed the impact of recipient alloreactive CD8 + T cells in allogeneic CAR T rejection and identified expansion of identical allogeneic CAR T clonotypes with retained clonal hierarchy in multiple patients. While patient factors such as tumor burden and target antigen expression likely play a role as well, our results suggest that strategies to eliminate alloreactive recipient cells and enhance allogeneic CAR T fitness through improved product design, manufacturing and lymphodepletion could improve allogeneic CAR T expansion, persistence and efficacy.

The Effects of IL-23/IL-18-Polarized Neutrophils on Renal Ischemia-Reperfusion Injury and Allogeneic-Skin-Graft Rejection in Mice.

Neutrophils display heterogeneity and plasticity with different subgroups and immune-regulatory functions under various surrounding conditions. Neutrophils induced by IL-23/IL-18 (referred to N(IL-23+IL-18) neutrophils) have a unique gene-expression profile, with highly expressing IL-17, MHC-II, and costimulatory molecules. The adoptive transfer of N(IL-23+IL-18) neutrophils significantly increased the pathogenesis in a renal ischemia-reperfusion injury mouse model. N(IL-23+IL-18) neutrophils directly and efficiently induced allogeneic T cell proliferation in vitro. N(IL-23+IL-18) neutrophils enhanced the syngeneic T cell response to allogeneic antigens in mixed-lymphocyte reaction assays. The adoptive transfer of the donor or host N(IL-23+IL-18) neutrophils significantly enhanced the antidonor antibody production in an allogeneic-skin-transplanted mouse model, accompanied by increased Tfh cells in the spleens. Therefore, the neutrophil subset induced by IL-23/IL-18 promotes tissue injury and antidonor humoral response in the allogeneic transplantation mouse model.

The Potential Use of THP-1, a Monocytic Leukemia Cell Line, to Predict Immune-Suppressive Potency of Human Bone-Marrow Stromal Cells (BMSCs) In Vitro: A Pilot Study.

Adoptive transfer of cultured BMSCs was shown to be immune-suppressive in various inflammatory settings. Many factors play a role in the process, but no master regulator of BMSC-driven immunomodulation was identified. Consequently, an assay that might predict BMSC product efficacy is still unavailable. Below, we show that BMSC donor variability can be monitored by IL-10 production of monocytes/macrophages using THP-1 cells (immortalized monocytic leukemia cells) co-cultured with BMSCs. Using a mixed lymphocyte reaction (MLR) assay, we also compared the ability of the different donor BMSCs to suppress T-cell proliferation, another measure of their immune-suppressive ability. We found that the BMSCs from a donor that induced the most IL-10 production were also the most efficient in suppressing T-cell proliferation. Transcriptome studies showed that the most potent BMSC batch also had higher expression of several known key immunomodulatory molecules such as hepatocyte growth factor (HGF), PDL1, and numerous members of the PGE2 pathway, including PTGS1 and TLR4. Multiplex ELISA experiments revealed higher expression of HGF and IL6 by the most potent BMSC donor. Based on these findings, we propose that THP-1 cells may be used to assess BMSC immunosuppressive activity as a product characterization assay.

Novel Human Umbilical Di-Chimeric (HUDC) cell therapy for transplantation without life-long immunosuppression.

Cell-based therapies are promising for tolerance induction in bone marrow (BM), solid organs, and vascularized composite allotransplantation (VCA). The toxicity of bone marrow transplantation (BMT) protocols precludes this approach from routine clinical applications. To address this problem, we developed a new therapy of Human Umbilical Di-Chimeric (HUDC) cells for tolerance induction in transplantation. This study established in vitro characterization of the created HUDC cells. We performed sixteen ex vivo polyethylene glycol (PEG)-mediated fusions of human umbilical cord blood (UCB) cells from two unrelated donors. Fusion feasibility was confirmed in vitro by flow cytometry (FC) and confocal microscopy (CM). The HUDC cells' genotype was assessed by lymphocytotoxicity test and short tandem repeat-polymerase chain reaction (STR-PCR) analysis, phenotype by FC, viability by LIVE/DEAD® assay, and apoptosis level by Annexin V staining. We used COMET assay to assess HUDC cells' genotoxicity after the fusion procedure. Clonogenic properties of HUDC cells were evaluated by colony forming unit (CFU) assay. Mixed lymphocyte reaction (MLR) assay assessed immunogenic and tolerogenic properties of HUDC cells. We confirmed the creation of HUDC cells from two unrelated human donors of UCB cells by FC and CM. Human leukocyte antigen (HLA) class I and II typing, and STR-PCR analysis of HUDC cells confirmed the presence of alleles and loci from both unrelated UCB donors (donor chimerism: 49%±8.3%, n=4). FC confirmed the hematopoietic phenotype of HUDC cells. We confirmed high HUDC cells' viability (0.47% of dead cells) and a low apoptosis level of fused HUDC cells (15.9%) compared to positive control of PKH-stained UCB cells (20.4%) before fusion. COMET assay of HUDC cells revealed a lack of DNA damage. CFU assay confirmed clonogenic properties of HUDC cells, and MLR assay revealed a low immunogenicity of HUDC cells. This study confirmed creation of a novel HUDC cell line by ex vivo PEG-mediated fusion of UCB cells from two unrelated donors. The unique concept of creating a HUDC cell line, representing the genotype and phenotype of both, transplant donor and the recipient, introduces a promising approach for tolerance induction in BM, solid organs, and VCA transplantation.

CDX-585, a Bispecific Antibody with Dual Targeting of ILT4 and PD-1 Checkpoint Pathways

Immunoglobulin-like transcript 4 (ILT4) is an immunosuppressive molecule predominantly expressed on myeloid cells. Recent studies combining ILT4 suppression with programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) blockade have shown promising signs of activity in immune checkpoint inhibitor refractory patients. We theorized that coupling ILT4 and PD-1/PD-L1 blockade in a bispecific antibody (bsAb) may provide greater immune activating properties than combining the individual mAbs due to enhanced bridging of APCs to T cells. To test this approach, we developed CDX-585, a tetravalent ILT4xPD-1 IgG1-scFv bsAb from novel PD-1 and ILT-4 mAbs. CDX-585 is a potent antagonist of both PD-1 and ILT4. CDX-585 promotes M1 macrophage polarization and enhances pro-inflammatory cytokine secretion in response to lipopolysaccharide or CD40 agonist mAb treatment. In mixed lymphocyte reaction (MLR) assays, CDX-585 is more potent than the combination of parental antibodies. In a humanized NCG mouse SK-MEL-5 tumor model, CDX-585 exhibits greater antitumor activity than the combination of parental mAbs. A pilot study of CDX-585 in cynomolgus macaques confirmed a mAb-like pharmacokinetic profile without noted toxicities. These studies demonstrate that CDX-585 effectively combines ILT4 and the PD-1 blockade into one molecule that is more potent than the combination of the parental antibodies, providing the rationale to advance this bsAb into clinical studies.

Minocycline induces tolerance to dendritic cell production probably by targeting the SOCS1/ TLR4/NF-κB signaling pathway

ObjectiveDendritic cells (DCs) are professional antigen-presenting cells that play a key role in maintaining peripheral immune tolerance. The use of tolerogenic DCs (tolDCs), i.e., semi-mature DCs that express co-stimulatory molecules but not pro-inflammatory cytokines, has been proposed. However, the mechanism of tolDCs induced by minocycline is still unclear. Our previous bioinformatics analyses based on multiple databases suggested that the suppressor of cytokine signaling 1/Toll-like receptor 4/NF-κB (SOCS1/TLR4/NF-κB) signal pathway was associated with DCs maturation. Thus, we studied whether minocycline could induce DC tolerance through this pathway. MethodsA search for potential targets was carried out through public databases, and pathway analysis was performed on these potential targets to obtain pathways relevant to the experiment. Flow cytometry was used to detect the expression of DC surface markers CD11c, CD86, and CD80, and major histocompatibility complex II. The secretion of interleukin (IL)-12p70, tumor necrosis factor alpha (TNF- α), and IL-10 in the DC supernatant was detected by enzyme-linked immunoassay. The ability of three groups (Ctrl-DCs, Mino-DCs, and LPS-DCs) of DCs to stimulate allogeneic CD4+ T cells was analyzed using a mixed lymphocyte reaction assay. Western blotting was used to detect the expression of TLR4, NF-κB-p65, NF-κB-p-p65, IκB-α, and SOCS1 proteins. ResultsThe hub gene plays a vital role in biological processes; in related pathways, the regulation of other genes is often affected by it. The SOCS1/TLR4/NF-κB signaling pathway was further validated by searching for potential targets through public databases to obtain relevant pathways. The minocycline-induced tolDCs showed characteristics of semi-mature DCs. Moreover, the IL-12p70 and TNF-α levels in the minocycline-stimulated DC group (Mino-DC group) were lower than those in the lipopolysaccharide (LPS)-DC group, and the IL-10 levels were higher in the Mino-DC group than in the LPS-DC and control DC groups. In addition, the Mino-DC group had decreased protein expression levels of TLR4 and NF-κB-p65 and upregulated protein levels of NF-κB-p-p65, IκB-α, and SOCS1 compared with the other groups. ConclusionThe results of this study indicate that minocycline could improve the tolerance of DCs probably by blocking the SOCS1/TLR4/NF-κB signaling pathway.