Nonclinical Investigation of Cytokine Mitigation Strategies for T-cell-Engaging Bispecifics in the Cynomolgus Macaque

SUMMARY

T-cell-directed cancer therapies such as T-cell-engaging bispecifics (TCBs) are commonly associated with cytokine release syndrome and associated clinical signs that can limit their tolerability and therapeutic benefit. Strategies for reducing cytokine release are therefore needed. Here, we report on studies performed in cynomolgus monkeys to test different approaches for mitigating cytokine release with TCBs. A "priming dose" as well as subcutaneous dosing reduced cytokine release compared with intravenous dosing but did not affect the intended T-cell response to the bispecific. As another strategy, cytokines or cytokine responses were blocked with an anti-IL-6 antibody, dexamethasone, or a JAK1/TYK2-selective inhibitor, and the effects on toxicity as well as T-cell responses to a TCB were evaluated. The JAK1/TYK2 inhibitor and dexamethasone prevented CRS-associated clinical signs on the day of TCB administration, but the anti-IL-6 had little effect. All interventions allowed for functional T-cell responses and expected damage to target-bearing tissues, but the JAK1/TYK2 inhibitor prevented the upregulation of activation markers on T cells, suggesting the potential for suppression of T-cell responses. Our results suggest that short-term prophylactic dexamethasone treatment may be an effective option for blocking cytokine responses without affecting desired T-cell responses to TCBs.

Current approaches to evaluate the function of cytotoxic T-cells in non-human primates

Cytotoxic T-lymphocytes (CTL) are a subset of T-cells that play a critical role in protecting against intracellular infections and cancer, and have the ability to identify and kill infected or transformed cells expressing non-self peptides associated with major histocompatibility (MHC) Class I molecules. Conversely, aberrant CTL activity can contribute to immune-related pathology under conditions of overwhelming infection or autoimmunity. Disease-modifying therapeutics can have unintended effects on CTL, and a growing number of therapeutics are intended to either suppress or enhance CTL or their functions. The susceptibility of CTL to unintended effects from common therapeutic modalities underscores the need for a better understanding of the impact that such therapies have on CTL function and the associated safety implications. While there are reliable ways of quantifying CTL, notably via flow cytometric analysis of specific CTL markers, it has been a greater challenge to implement fit-for-purpose methods measuring CTL function in the context of safety studies of therapeutics. This review focuses on methods for measuring CTL responses in the context of drug safety and pharmacology testing, with the goals of informing the reader about current approaches, evaluating their pros and cons, and providing perspectives on the utility of these approaches for safety evaluation.

Cold Agglutinin Disease in a Rhesus Macaque (Macaca mulatta)

Cold agglutinin disease (CAD) is a condition involving anemia and its related symptoms; it is caused by autoantibodies that bind and agglutinate red blood cells in areas susceptible to hypothermia, such as extremities exposed to cold temperatures. CAD is rare, with 5 to 20 human cases per million individuals. In this report, we describe a case of CAD in a previously healthy and experimentally naïve adult Indian rhesus macaque that was housed indoors and presented with blood in the urine. After our observations of hemoglobinuria and anemia led us to suspect CAD, we demonstrated that the macaque's blood agglutinated at reduced temperatures. We also noticed that the provision of cold foraging treats triggered episodes of hemoglobinuria. Further investigation revealed that serum from the macaque agglutinated RBCs in vitro with high thermal amplitude (at or below 30 °C) and had an antibody titer of 8 to 32. The serum contained autoantibodies of the immunoglobulin M (IgM) isotype; agglutinins of the IgG isotype were not detected. The cold-dependent IgM autoantibodies in the serum from the affected macaque reacted against a common RBC antigen because RBCs collected from other macaques were bound and agglutinated by the affected animal's IgM under cold conditions. This in vitro binding activity was reversible when the test temperature was returned to normal body temperature (37 °C). These findings demonstrated cold-dependent RBC-specific IgM agglutinins and led us to a diagnosis of CAD. This is the first documented case of spontaneous CAD in a rhesus macaque.

Cold Agglutinin Disease in a Rhesus Macaque (Macaca mulatta)

Cold agglutinin disease (CAD) is a condition involving anemia and its related symptoms; it is caused by autoantibodiesthat bind and agglutinate red blood cells in areas susceptible to hypothermia, such as extremities exposed to cold temperatures.CAD is rare, with 5 to 20 human cases per million individuals. In this report, we describe a case of CAD in a previouslyhealthy and experimentally naïve adult Indian rhesus macaque that was housed indoors and presented with blood in theurine. After our observations of hemoglobinuria and anemia led us to suspect CAD, we demonstrated that the macaque'sblood agglutinated at reduced temperatures. We also noticed that the provision of cold foraging treats triggered episodes ofhemoglobinuria. Further investigation revealed that serum from the macaque agglutinated RBCs in vitro with high thermalamplitude (at or below 30 °C) and had an antibody titer of 8 to 32. The serum contained autoantibodies of the immunoglobulinM (IgM) isotype; agglutinins of the IgG isotype were not detected. The cold-dependent IgM autoantibodies in the serum fromthe affected macaque reacted against a common RBC antigen because RBCs collected from other macaques were bound andagglutinated by the affected animal's IgM under cold conditions. This in vitro binding activity was reversible when the testtemperature was returned to normal body temperature (37 °C). These findings demonstrated cold-dependent RBC-specific IgMagglutinins and led us to a diagnosis of CAD. This is the first documented case of spontaneous CAD in a rhesus macaque.

A Phase 1 Dose-Escalation Study of PF-06671008, a Bispecific T-Cell-Engaging Therapy Targeting P-Cadherin in Patients With Advanced Solid Tumors

P-cadherin is a cell-cell adhesion molecule that is overexpressed in several solid tumors. PF-06671008 is a T-cell–redirecting bispecific antibody that engages both P-cadherin on tumors and CD3ϵ on T cells and induces antitumor activity in preclinical models. We conducted a phase 1, open-label, first-in-human, dose-escalation study to characterize the safety and tolerability of PF-06671008, towards determining the recommended phase 2 dose. Adult patients with treatment-refractory solid tumors received PF-06671008 (1.5–400 ng/kg) as a weekly intravenous (IV) infusion on a 21-day/3-week cycle. Parallel cohorts evaluated dosing via subcutaneous injection (SC) or an IV-prime dose. Of the 27 patients enrolled in the study, 24 received PF-06671008 IV in escalating doses, two received SC, and one IV-prime. A dose-limiting toxicity of cytokine release syndrome (CRS) occurred in the 400-ng/kg IV group, prompting evaluation of SC and IV-prime schedules. In all, 25/27 patients who received PF-06671008 reported at least one treatment-related adverse event (TRAE); the most common were CRS (21/27), decreased lymphocyte count (9/27), and hypophosphatemia (8/27). Seven patients permanently discontinued treatment due to adverse events and no treatment-related deaths occurred. Cytokine peak concentrations and CRS grade appeared to positively correlate with C_max. Although the study was terminated due to limited antitumor activity, it provides important insights into understanding and managing immune-related adverse events resulting from this class of molecules.

Industry experiences with immune-mediated findings in biotherapeutic nonclinical toxicology studies

With the growth of monoclonal antibodies and other proteins as major modalities in the pharmaceutical industry, there has been an increase in pharmacology and toxicity testing of biotherapeutics in animals. Animals frequently mount an immune response to human therapeutic proteins. This can result in asymptomatic anti-drug antibody formation, immune complexes that affect drug disposition and/or organ function such as kidney, cytokine release responses, fatal hypersensitivity, or a range of reactions in between. In addition, an increasing number of oncology therapeutics are being developed that enhance or directly stimulate immune responses by a variety of mechanisms, which could increase the risk of autoreactivity and an autoimmune-like syndrome in animals and humans. When evaluating the risk of biotherapeutics prior to entering the clinic, the nonclinical safety data may include any of these responses and it is critical to understand whether they represent a safety liability for humans. The DruSafe Leadership group of the IQ Consortium conducted a survey of industry to understand sponsors' experiences with these immune reactions in nonclinical studies related to both immunogenicity and pharmacologically-mediated immune perturbations. The survey covered what pathways were affected, how the immune responses were presented, how the company and health authorities interpreted the data and whether the immune responses were observed in the clinic. Additionally, the survey gathered information on association of these findings with anti-drug antibodies as well as sponsor's use of immunogenicity predictive tools. The data suggests that the ability of a biotherapeutic to activate the immune system, intended or not, plays a significant role on characteristics of the response and whether theys are translatable.

Pharmacologic Properties and Preclinical Activity of Sasanlimab, A High-affinity Engineered Anti-Human PD-1 Antibody

Development of antagonistic mAbs that specifically target the immune checkpoint receptor, programmed cell death protein-1 (PD-1), is of great interest for cancer immunotherapy. Here, we report the biophysical characteristics and nonclinical antagonistic activities of sasanlimab (PF-06801591), a humanized anti-PD-1 antibody of IgG4 isotype. We show that sasanlimab binds selectively and with similar high potency to human and cynomolgus monkey PD-1 receptor and blocks its interaction with PD-L1 and PD-L2, with no detectable Fc-dependent effector function. The binding of sasanlimab to human and cynomolgus PD-1 is associated with the formation of a stable complex, which is likely to be the main driver of this high-affinity interaction. In vitro, sasanlimab significantly augmented T-cell proliferation and cytokine production in mixed lymphocyte reaction and superantigen stimulation assays. In vivo, sasanlimab accelerated the incidence of GvHD by enhancing T-cell proliferation and cytokine secretion in a xenogeneic model of acute GvHD and halted the growth of MC-38 colon adenocarcinoma tumors in human PD-1 knock-in mice. Pharmacokinetic and toxicokinetic findings from cynomolgus monkey showed that sasanlimab was active and well-tolerated. Taken together, the data presented here support the clinical development of sasanlimab for the treatment of patients with advanced cancers as a single agent or in combination with other immunotherapies.

Abstract 2283: A novel GUCY2C - CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors

Gastrointestinal malignancies, including colorectal cancer (CRC) remain an area of high unmet need. Here we demonstrate tumor selective and potent in vitro and in vivo efficacy with PF-07062119, a novel T cell engaging CD3 bispecific against tumors expressing the Guanylyl Cyclase C (GUCY2C) receptor, a target expressed in more than 90% of CRC, and in other gastrointestinal cancers. Additionally, to address immune evasion mechanisms, combinations of the GUCY2C-CD3 bispecific are explored with immune checkpoint blockade therapy, as well as with chemotherapeutic and anti-angiogenic agents that could enhance immune infiltration into tumors. Our preclinical in vivo data demonstrate that GUCY2C-positive tumors can be targeted with an anti-GUCY2C/anti-CD3ϵ bispecific, with selective drug biodistribution to tumors. PF-07062119 showed potent T cell mediated anti-tumor activity in several human xenograft models of CRC, using adoptive transfer of human T cells, including those with KRAS and BRAF mutations, as well as in models with syngeneic tumors in immunocompetent human CD3 transgenic mice. PF-07062119 activity was further enhanced when combined with anti PD-1/PD-L1 treatment or in combination with chemotherapy or anti-angiogenic therapy. A combination of immunohistochemistry, flow cytometry and CyTOF analyses was used to demonstrate the mechanism of action of PF-07062119 in single agent and combination studies in vivo. Toxicity and pharmacokinetic studies were done in cynomolgus macaques and indicated a monitorable and manageable toxicity profile. These data highlight the potential for PF-07062119 to demonstrate efficacy and improve patient outcomes in CRC and other gastrointestinal malignancies. A clinical Phase I study has been initiated in patients with CRC, gastric and esophageal adenocarcinomas (NCT04171141).

Citation Format: Divya Mathur, Adam Root, Bozena Bugaj-Gaweda, Xingzhi Tan, Wei Fang, Stephanie Bisulco, Jonathan Golas, Diane Fernandez, Jessica Kearney, Eric Upeslacis, Johnny Yao, Edward Rosfjord, Chad Stevens, Keith Kobylarz, Lindsay King, Jatin Narula, Kerry Kelleher, David Schaer, Cris Kamperschroer, Bernard Buetow, Cynthia Rohde, Allison Moreau, Gilbert Wong, Puja Sapra. A novel GUCY2C - CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2283.

A Modeling Framework to Characterize Cytokine Release upon T-Cell-Engaging Bispecific Antibody Treatment: Methodology and Opportunities

T‐cell–engaging bispecific antibodies (T‐BsAbs) are an important class of antibody therapeutics in immuno‐oncology. T‐BsAbs simultaneously bind to CD3 on T cells and a tumor‐associated antigen on tumor cells, activate T cells, and redirect T cells’ cytotoxicity against tumor cells. Cytokine release syndrome (CRS), a common dose‐limiting adverse event for T‐BsAbs, is associated with T‐cell activation. A “priming” dose strategy (i.e., a lower initial dose followed by a higher maintenance dose) has been implemented in the clinic to mitigate CRS and to achieve efficacious doses with T‐BsAbs. So far, the selection of the optimal priming dosing regimen is largely empirical. A “fit‐for‐purpose” semimechanistic pharmacokinetic/pharmacodynamic model was developed to characterize the cytokine release profiles upon T‐BsAb treatment, including the priming effect observed with repeated dosing. This model can be utilized to simulate cytokine profiles following various dosing regimens and may assist the design of clinical dosing strategies for T‐BsAbs programs.

Correction to: A Translational Quantitative Systems Pharmacology Model for CD3 Bispecific Molecules: Application to Quantify T Cell-Mediated Tumor Cell Killing by P-Cadherin LP DART®

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A Translational Quantitative Systems Pharmacology Model for CD3 Bispecific Molecules: Application to Quantify T Cell-Mediated Tumor Cell Killing by P-Cadherin LP DART®

CD3 bispecific antibody constructs recruit cytolytic T cells to kill tumor cells, offering a potent approach to treat cancer. T cell activation is driven by the formation of a trimolecular complex (trimer) between drugs, T cells, and tumor cells, mimicking an immune synapse. A translational quantitative systems pharmacology (QSP) model is proposed for CD3 bispecific molecules capable of predicting trimer concentration and linking it to tumor cell killing. The model was used to quantify the pharmacokinetic (PK)/pharmacodynamic (PD) relationship of a CD3 bispecific targeting P-cadherin (PF-06671008). It describes the disposition of PF-06671008 in the central compartment and tumor in mouse xenograft models, including binding to target and T cells in the tumor to form the trimer. The model incorporates T cell distribution to the tumor, proliferation, and contraction. PK/PD parameters were estimated for PF-06671008 and a tumor stasis concentration (TSC) was calculated as an estimate of minimum efficacious trimer concentration. TSC values ranged from 0.0092 to 0.064 pM across mouse tumor models. The model was translated to the clinic and used to predict the disposition of PF-06671008 in patients, including the impact of binding to soluble P-cadherin. The predicted terminal half-life of PF-06671008 in the clinic was approximately 1 day, and P-cadherin expression and number of T cells in the tumor were shown to be sensitive parameters impacting clinical efficacy. A translational QSP model is presented for CD3 bispecific molecules, which integrates in silico, in vitro and in vivo data in a mechanistic framework, to quantify and predict efficacy across species.

Abstract 2667: In vitro properties and pre-clinical activity of PF-06801591, a high-affinity engineered anti-human PD-1

Monoclonal-antibody-based therapies targeting the immune checkpoint receptors have become the new standard of care in many cancers. Antibodies that specifically target programmed death receptor-1 (PD-1) or its cognate ligand, programmed death receptor ligand-1 (PD-L1), alone or in combination, have yielded clinical benefits and durable responses in patient subsets with various cancers (including metastatic melanoma, NSCLC, RCC, urothelial cancer, cHL and others). Here we report on the biophysical characteristics and non-clinical antagonistic activities of PF-06801591. PF-06801591 is a humanized anti-PD-1 antibody of human IgG4 isotype, that binds selectively and with similar potency to human and cynomolgus monkey PD-1 receptor (EC50 ~50 pM) and blocks its interaction with its cognate ligands PD-L1 and PD-L2 (IC50 < 1 nM) with no detectable Fc effector function. The interaction of PF-06801591 to PD-1 rescues T cell suppression and exhaustion that translates into NFAT activation, IL-2 and IFN-gamma secretion and T cell proliferation both in vitro cultures and in vivo using an acute xeno GvHD model with human PBMC transfer. Binding of PF-068001591 to human and cynomolgus PD-1 is characterized by the formation of a very stable complex (T1/2 = 2 h) as measured by SPR at 37 C, resulting in high affinity (KD ~20 pM) as measured in solution by KinExA at 23 C. In addition, we explored therapeutic potential of anti-PD-1 in combination with other immunotherapy agents using surrogate antibodies in non-clinical tumor models. The data presented here support future development of PF-06801591 as a single agent or in combination with other immunotherapies.

Citation Format: Sawsan Youssef, Yasmina Abdiche, HoangKim Nguyen, Joyce Chou, Sherman Michael Chin, Cris Kamperschroer, Patricia A. Schneider, Eugenia Kraynov, Heike I. Krupka, Arvind Rajpal, John Lin. In vitro properties and pre-clinical activity of PF-06801591, a high-affinity engineered anti-human PD-1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2667. doi:10.1158/1538-7445.AM2017-2667

HESI/FDA workshop on immunomodulators and cancer risk assessment: Building blocks for a weight-of-evidence approach

Profound immunosuppression (e.g., AIDS, transplant therapy) is epidemiologically associated with an increased cancer risk, and often with oncogenic viruses. It is currently unclear how broadly this association translates to therapeutics that modulate immunity. A workshop co-sponsored by the FDA and HESI examined how perturbing the immune system may contribute to carcinogenesis, and highlighted priorities for improving non-clinical risk assessment of targeted immunomodulatory therapies. Conclusions from the workshop were as follows. 1) While profound altered immunity can promote tumorigenesis, not all components of the immune system are equally important in defense against or promotion of cancer and a similar cancer risk for all immunomodulatory molecules should not be assumed. 2) Rodent carcinogenicity studies have limitations and are generally not reliable predictors of cancer risk associated with immunosuppression. 3) Cancer risk needs to be evaluated based on mechanism-based weight-of-evidence, including data from immune function tests most relevant to tumor immunosurveillance or promotion. 4) Information from nonclinical experiments, clinical epidemiology and immunomodulatory therapeutics show that immunosurveillance involves a complex network of cells and mediators. To support a weight-of-evidence approach, an increased focus on understanding the quantitative relationship between changes in relevant immune function tests and cancer risk is needed.

The genomic sequence of lymphocryptovirus from cynomolgus macaque

Lymphocryptoviruses such as Epstein-Barr virus (EBV) cause persistent infections in human and non-human primates, and suppression of the immune system can increase the risk of lymphocryptovirus (LCV)-associated tumor development in both human and non-human primates. To enable LCV infection as a non-clinical model to study effects of therapeutics on EBV immunity, we determined the genomic DNA sequence of the LCV from cynomolgus macaque, a species commonly used for non-clinical testing. Comparison to rhesus macaque LCV and human EBV sequences indicates that LCV from the cynomolgus macaque has the same genomic arrangement and a high degree of similarity in most genes, especially with rhesus macaque LCV. Genes showing lower similarity were those encoding proteins involved in latency and/or tumor promotion or immune evasion. The genomic sequence of LCV from cynomolgus macaque should aid the development of non-clinical tools for identifying therapeutics that impact LCV immunity and carry potential lymphoma risk.

Developmental toxicity assessment of tanezumab, an anti-nerve growth factor monoclonal antibody, in cynomolgus monkeys (Macaca fascicularis)

Two intravenous studies with tanezumab, an anti-nerve growth factor monoclonal antibody, were conducted in pregnant cynomolgus monkeys to assess potential effects on pregnancy and pre- and postnatal development. Study 1 evaluated infants up to 12 months of age following weekly maternal dosing (0, 0.5, 4 or 30 mg/kg; 18 per group) from gestation day (GD) 20 through parturition. Study 2 evaluated infants 2 months postnatally following weekly maternal dosing (0, 0.5 or 30 mg/kg; 20-21 per group) from GD 20 through 48. In the absence of maternal toxicity, tanezumab increased stillbirth and post-birth infant mortality/morbidity, decreased infant growth and resulted in microscopic changes in the peripheral sympathetic and sensory nervous system of the infants at all doses. Decreased primary antibody responses and increased incidences in skin changes in infants were also observed. The no-observed-adverse-effect-level for maternal toxicity was 30 mg/kg and <0.5 mg/kg for developmental toxicity.

Characterization of CMV- and LCV-specific T cell responses and their sensitivity to immunosuppression in cynomolgus macaques (P6367)

Herpesviruses such as cytomegalovirus (CMV) and Epstein Barr virus (EBV) often cause disease under conditions of immunosuppression, such as transplant or AIDS. Loss of control of herpesvirus infections occurs at least in part due to loss or dysfunction of virus-specific T cells. An increasing array of immunosuppressive therapeutics are being developed that target different subsets of T cells or their functions. To better understand effects of therapeutics on antiviral T cells, we have used ELISPOT and ICS to measure T cell responses against CMV and lymphcryptovirus (LCV; analogous to EBV) in cynomolgus macaques. Our work has shown that nearly all monkeys respond against both viruses, although the numbers of T cells specific for CMV are larger than those against LCV. We have also characterized the variability in the magnitude of the T responses to both viruses over time. In addition, we have examined the effects of immunosuppressive agents on the numbers and function of antiviral T cells. Our work reveals remarkable stability of herpesvirus-specific T cells, even under conditions where drugs abolish T cell stimulation for a period of several weeks.

Measuring T-cell responses against LCV and CMV in cynomolgus macaques using ELISPOT: potential application to non-clinical testing of immunomodulatory therapeutics

A number of immunomodulatory therapeutics increase the risk of disease associated with latent herpesviruses such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), a member of the lymphocryptovirus (LCV) family that infects humans. The diseases associated with loss of immunity to these viruses can have major impacts on patients as well as on the commercial viability of the immunomodulatory therapeutics. In an effort to develop non-clinical methods for measuring effects on anti-viral immunity, we have developed an interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISPOT) assay to quantify the number of CMV or LCV-reactive T-cells in peripheral blood of cynomolgus macaques. After optimization of various parameters, the IFN-γ ELISPOT assay was characterized for specificity, intra-assay, monkey-to-monkey, and longitudinal variability and sensitivity to immunosuppression. The results show that nearly all animals have detectable responses against both CMV and LCV and responses were derived from T-cells specific to the virus of interest. Analyses of variability show assay reproducibility (≤23% CV), and that variability over time in anti-viral responses in individual animals (larger for LCV than for CMV) was ∼2-fold in most animals over a 3-month time period, which is predicted to allow for detection of drug-induced changes when using group sizes typical of non-clinical studies. In addition, the IFN-γ ELISPOT assay was capable of detecting decreases in the numbers of CMV and LCV reactive T-cells induced by immunosuppressive drugs in vitro. This assay may allow for non-clinical assessment of the effects of immunomodulatory therapeutics on anti-viral T-cell immunity in monkeys, and may help determine if therapeutics increase the risk of reactivating latent viral infections.

Targeting of 4-1BB by monoclonal antibody PF-05082566 enhances T-cell function and promotes anti-tumor activity

4-1BB (CD137, TNFRSF9) is a costimulatory receptor expressed on several subsets of activated immune cells. Numerous studies of mouse and human T cells indicate that 4-1BB promotes cellular proliferation, survival, and cytokine production. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings in both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T-cell memory responses. PF-05082566 is a fully human IgG2 that binds to the extracellular domain of human 4-1BB with high affinity and specificity. In preclinical studies, this agonist antibody demonstrated its ability to activate NF-κB and induce downstream cytokine production, promote leukocyte proliferation, and inhibit tumor growth in a human PBMC xenograft tumor model. The mechanism of action and robust anti-tumor efficacy of PF-05082566 support its clinical development for the treatment of a broad spectrum of human malignancies.

Abstract 4384: Targeting of 4-1BB by monoclonal antibody, PF-05082566, enhances T cell function and promotes antitumor activity

4-1BB (CD137, TNFRSF9) is a costimulatory receptor expressed in an activation induced manner on several subsets of immune cells. Numerous studies of mouse and human T cells indicate that 4-1BB promotes enhanced cellular proliferation, survival, and cytokine production. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings in both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T cell memory responses. PF-05082566 is a fully human IgG2 which binds to the extracellular domain of human 4-1BB with high affinity and specificity. In preclinical studies this agonist antibody demonstrated its ability to activate NF-κB and induce downstream cytokine production, promote leukocyte proliferation, and inhibit tumor growth in a human PBMC xenograft tumor model. The mechanism of action and robust anti-tumor efficacy of PF-05082566 support its clinical development for the treatment of a broad spectrum of human malignancies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4384. doi:1538-7445.AM2012-4384

Summary of roundtable discussion meeting: non-human primates to assess risk for EBV-related lymphomas in humans

Epstein-Barr virus (EBV)-associated lymphomas are a known risk for immunosuppressed individuals. Non-clinical methods to determine the potential of new immunomodulatory compounds to produce EBV-associated lymphomas (hazard identification) have not been developed. Since lymphocryptovirus (LCV) in non-human primates (NHP) has similar characteristics to EBV in humans, a Roundtable meeting was held in October 2010 to explore how the potential for EBV-related lymphomas in humans can be assessed by using surrogate biomarkers for lymphoma risk in NHP toxicity studies. Stakeholders from regulatory agencies, academia, and industry came together to determine the research gaps and potential benefits and considerations of such an approach given the current state-of-the-science. Key conclusions from the discussion included considerations raised about the potential usefulness of LCV-related biomarkers from NHP studies since there is significant controversy over the reliability of using EBV viral load or EBV-specific T-lymphocytes to predict for lymphoproliferative disorders in transplant patients. In addition, there are technical challenges that need to be further addressed in order to develop methods to measure LCV viral load and LCV-specific T-lymphocytes from cynomolgus monkeys.

IL-2 and antigen dose differentially regulate perforin- and FasL-mediated cytolytic activity in antigen specific CD4+ T cells

CD4 T cell effectors can promote survival against lethal influenza virus via perforin mediated cytolytic mechanisms; however, our understanding of how naïve CD4 cells differentiate into class II restricted killers remains obscure. To address this, TCR Tg CD4 cells were activated in vitro and examined for their ability to lyse target cells. We found that cytokine polarized CD4 T cell effectors displayed cytolytic activity with the hierarchy Th0>Th1>Th2. Further, IL-4 inhibited the generation of cytotoxic CD4 cells. LPS stimulated B cells and bone marrow derived dendritic cells (BMDC) both induced potent cytolytic activity; however, IL-6, TGF-beta, IL-10, IL-12 or TNF-alpha were not required for inducing cytolytic activity in CD4 effectors. Antigen dose had a marked effect on cytotoxicity: low concentrations of peptide induced more potent cytolytic activity than relatively high concentrations. At low peptide concentration, exogenous IL-2 was necessary to drive granzyme B (GrB) expression and perforin mediated lysis. Thus, low antigen dose and early activation signals via IL-2 direct the CD4 T cell response toward effectors with perforin mediated cytolytic potential. These data have implications for the design of vaccines that may induce cytolytic CD4 cells in vivo and improve cell-mediated immunity to viral and bacterial infections.

SAP enables T cells to help B cells by a mechanism distinct from Th cell programming or CD40 ligand regulation

Genetic mutations disrupting the function of signaling lymphocytic activation molecule-associated protein (SAP) lead to T cell intrinsic defects in T cell-dependent Ab responses. To better understand how SAP enables Th cells to help B cells, we first assessed whether molecules important for B cell help are dysregulated in SAP-deficient (SAP knockout (KO)) mice. CD40 ligand (CD40L) expression was enhanced on unpolarized SAP KO T cells; however, Th2 polarization returned their CD40L expression to wild-type levels without rescuing their ability to help B cells. CD40L also localized normally to the site of contact between SAP KO T cells and Ag-bearing B cells. Finally, CD40L-deficient Th cells and SAP KO Th cells differed in their abilities to help B cells in vitro. These data argue that Ab defects caused by SAP deficiency do not result from a loss of CD40L regulation or CD40L function on CD4 T cells. SAP KO Th cells additionally displayed normal patterns of migration and expression of ICOS and CXCR5. Global gene expression was remarkably similar in activated SAP KO vs wild-type T cells, prompting us to investigate whether SAP is necessary for "programming" T cells to become B cell helpers. By restricting SAP expression during differentiation, we determined that SAP is not required during the first 5 days of T cell activation/differentiation to generate Th cells capable of helping B cells. Instead, SAP is necessary for very late stages of differentiation or, most likely, for allowing Th cells to communicate during cognate T:B interactions.

SAP is required for Th cell function and for immunity to influenza

Ab is a crucial component of protective immunity to infection, but Ab responses do not proceed normally when defects occur in a protein called signaling lymphocytic activation molecule-associated protein (SAP). To explain this Ab defect, we analyzed B cell and plasma cell responses under conditions of SAP deficiency. Our results demonstrate that SAP-deficient (SAP knockout (KO)) mice have a profound CD4 T cell-intrinsic defect in generating Ag-specific plasma cells following challenge with model Ags or influenza virus, resulting in low Ag-specific Ab titers. We also show that SAP is required in CD4 T cells for normal division and expansion of B cells. These B cell and plasma cell defects were observed during the expansion phase of the primary immune response, indicating early defects in Th cell activity. In fact, additional experiments revealed a nearly complete lack of T cell help for B cells in SAP KO mice. Our work suggests that the ability of SAP to promote T-dependent humoral immune responses is important for antiviral immunity because mice lacking SAP are unable to prevent high dose secondary influenza infection, and because passive transfer of IgG in immune serum from wild-type, but not SAP KO mice can protect mice from an otherwise lethal influenza infection. Overall, our results demonstrate that SAP is required in CD4 T cells for their ability to help B cell responses and promote influenza-specific immunity.

CD4+ T-cell memory: generation and multi-faceted roles for CD4+ T cells in protective immunity to influenza

We have outlined the carefully orchestrated process of CD4+ T-cell differentiation from naïve to effector and from effector to memory cells with a focus on how these processes can be studied in vivo in responses to pathogen infection. We emphasize that the regulatory factors that determine the quality and quantity of the effector and memory cells generated include (i) the antigen dose during the initial T-cell interaction with antigen-presenting cells; (ii) the dose and duration of repeated interactions; and (iii) the milieu of inflammatory and growth cytokines that responding CD4+ T cells encounter. We suggest that heterogeneity in these regulatory factors leads to the generation of a spectrum of effectors with different functional attributes. Furthermore, we suggest that it is the presence of effectors at different stages along a pathway of progressive linear differentiation that leads to a related spectrum of memory cells. Our studies particularly highlight the multifaceted roles of CD4+ effector and memory T cells in protective responses to influenza infection and support the concept that efficient priming of CD4+ T cells that react to shared influenza proteins could contribute greatly to vaccine strategies for influenza.

SAP Deficiency Results in a Striking Alteration of the Protein Profile in Activated CD4 T Cells

Deficiency in a protein called signaling lymphocytic activation molecule-associated protein (SAP) causes X-linked lymphoproliferative disease (XLP) and helper T cell-dependent antibody defects. To identify proteins regulated by SAP, we performed proteomic analyses of SAP deficient vs wild type T cells. Our results reveal protein species whose abundances are profoundly altered by SAP. Our work therefore identifies candidate cellular mediators of SAP-dependent T cell help.

The role of proinflammatory cytokines in wasting disease during lymphocytic choriomeningitis virus infection

Infection with pathogens often leads to loss of body weight, but the cause of weight loss during infection is poorly understood. We used the infection of mice with lymphocytic choriomeningitis virus (LCMV) as a model to study how pathogens induce weight loss. If LCMV is introduced into the CNS of CTL-deficient mice, the immune response against the virus leads to a severe weight loss called wasting disease. We planned to determine what components of this antiviral immune response mediate wasting disease. By adoptive transfer, we show that CD4 T cells activated by LCMV infection are sufficient to cause wasting disease. We examined the role of cytokines in LCMV-induced wasting disease using mice lacking specific cytokines or cytokine receptors. Results of adoptive transfer experiments suggest that TNF-alpha is not involved in LCMV-induced wasting disease and show that IFN-gamma contributes to the disease. Consistent with a role for IFN-gamma in wasting, we find that IFN-gamma is necessary for LCMV-specific CD4 T cell responses in the CNS, most likely because it is required to induce MHC class II expression. Our data also indicate that IL-1 is required for LCMV-induced wasting and that IL-6 contributes to the wasting disease. Additionally, our results identify alpha-melanocyte-stimulating hormone as a potential mediator of the disease. Overall, this work defines the critical role of virus-primed CD4 T cells and of proinflammatory cytokines in the pathogenesis of wasting disease induced by LCMV infection.

Quantification of epitope-specific MHC class-II-restricted T cells following lymphocytic choriomeningitis virus infection

CD4(+) T cells are critical for the control of many viruses; however, the numbers of virus-specific CD4(+) cells that are expanded following infection are unknown. We have addressed this issue by enumerating virus-specific, MHC class-II-restricted T cells following infection of mice with lymphocytic choriomeningitis virus (LCMV). We have found that the numbers of T cells that produce interferon-gamma in response to stimulation with three different class-II-restricted LCMV epitopes increase from undetectable numbers in noninfected animals to between 4 x 10(5) and 2 x 10(6) cells per spleen at the peak of the T cell response. This contrasts with the numbers of virus-specific class-I-restricted T cells which expand to 1 x 10(7) to 2 x 10(7) cells per spleen during the same time period. We could not reproducibly detect virus-specific class-I-restricted or class-II-restricted T cells that produced interleukin-4 at any time following LCMV infection, indicating that infection with this virus induces a predominantly type 1 cytokine response. In contrast to the rapid decrease in the numbers of class-I-restricted T cells, the numbers of LCMV-specific class-II-restricted T cells declined gradually following the peak of the T cell response. We demonstrate, therefore, that following infection with LCMV there is expansion of both class-I-restricted and class-II-restricted virus-specific T cells; however, the degree of expansion of class-II-restricted T cells is substantially less than that observed for class-I-restricted cells. Furthermore, the downregulation phase of the class-II-restricted response is protracted compared with the precipitous contraction of the antiviral CD8(+) T cell response.