Current nonclinical approaches for immune assessments of immuno-oncology biotherapeutics

Harnessing the immune system to kill tumors has been revolutionary and, as a result, has had an enormous benefit for patients in extending life and resulting in effective cures in some. However, activation of the immune system can come at the cost of undesirable adverse events such as cytokine release syndrome, immune-related adverse events, on-target/off-tumor toxicity, neurotoxicity and tumor lysis syndrome, which are safety risks that can be challenging to assess non-clinically. This article provides a review of the biology and mechanisms that can result in immune-mediated adverse effects and describes industry approaches using in vitro and in vivo models to aid in the nonclinical safety risk assessments for immune-oncology modalities. Challenges and limitations of knowledge and models are also discussed.

Abstract LB097: A simian challenge model to evaluate the CD8-positive T cell response with cancer therapeutics

The demonstration that antibodies can be used to treat cancers has revolutionized the field of cancer immunotherapy and gave hope to many patients. Originally targeting tumor-specific antigen, new therapeutic antibodies target now immune checkpoint markers expressed on T cells. The advantage is to generate an active and long-lasting antitumor immunity with the achievement of a broad and polyclonal antitumor immunity, addressing better the heterogeneity of cancers and reducing the chances of immune escape. The development of such highly specific molecules is particularly challenging however when it comes to preclinical safety assessment and efficacy studies. An ideal animal model needs to possess the target so that the drug product is pharmacologically active. Moreover, such model should ideally provide further insight in determining the pharmacological action of the product and the determination of safety to maximize the usefulness in animal studies. Intriguingly, no equivalent of the traditional T-cell-dependent antibody response (TDAR) assay, which evaluates mainly the CD4+ T cells response, is currently available for the CD8+ T cell response. The goal of this study is to fill this gap with a Non-Human Primate (NHP) challenge model that will elicit a potent CD8+ T cell response. MHC I-genotyped Mauritian cynomolgus macaques (MCMs) were immunized with 3 replication incompetent recombinant adenovirus serotype 5 (Ad5) vectors encoding Gag, Nef or Pol SIV proteins. MCMs were distributed into 3 groups and received two intramuscular injections of adenoviruses 4 weeks apart. One group received the anti-PD-L1 Atezolizumab and a second received a molecule in early development targeting another immune checkpoint molecule. T cell activation was monitored with blood samples taken on a weekly basis for 8 weeks. Blood samples were used to characterize the T cell immunophenotypes and to correlate them with some functional assays. Vaccination was well tolerated and could be conducted on standard safety toxicology studies without compromising other endpoints. Adv5-SIVs modulated total T cells 2 weeks after a single vaccination, induced T-cell activation, T-cell proliferation and the expression of several checkpoint molecules. Moreover, functional assays confirmed that T-cell activation profile correlated with an antigen-specific CD8 T-cell response. Compounds administered differently enhanced the profile of T-cell activation, the upregulation of immune checkpoint molecules and antigen specific responses of their T cells. Moreover, both compounds extended the cytolytic activity of the antigen-specific CD8+ T cell up to 8 weeks. Taken together, the vaccination model we developed seems appropriate to study the pharmacology of new protein-based therapeutics targeting CD8+ T cells.

Citation Format: Richard Graveline, Morad Haida, Carolyne Dumont, Dominic Poulin, Florence Poitout-Belissent, Rana Samadfan, Sven Kronenberg, Franziska Regenass-Lechner, Rodney Prell, Marie-Soleil Piche. A simian challenge model to evaluate the CD8-positive T cell response with cancer therapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB097.

Toll-Like Receptor 7 Agonist RG7854 Mediates Therapeutic Efficacy and Seroconversion in Woodchucks With Chronic Hepatitis B

Conventional treatment of chronic hepatitis B (CHB) is rarely curative due to the immunotolerant status of patients. RG7854 is an oral double prodrug of a toll-like receptor 7 (TLR7) agonist that is developed for the treatment of CHB. The therapeutic efficacy, host immune response, and safety of RG7854 were evaluated in the woodchuck model of CHB. Monotreatment with the two highest RG7854 doses and combination treatment with the highest RG7854 dose and entecavir (ETV) suppressed viral replication, led to loss of viral antigens, and induced seroconversion in responder woodchucks. Since viral suppression and high-titer antibodies persisted after treatment ended, this suggested that a sustained antiviral response (SVR) was induced by RG7854 in a subset of animals. The SVR rate, however, was comparable between both treatment regimens, suggesting that the addition of ETV did not enhance the therapeutic efficacy of RG7854 although it augmented the proliferation of blood cells in response to viral antigens and magnitude of antibody titers. The induction of interferon-stimulated genes in blood by RG7854/ETV combination treatment demonstrated on-target activation of TLR7. Together with the virus-specific blood cell proliferation and the transient elevations in liver enzymes and inflammation, this suggested that cytokine-mediated non-cytolytic and T-cell mediated cytolytic mechanisms contributed to the SVR, in addition to the virus-neutralizing effects by antibody-producing plasma cells. Both RG7854 regimens were not associated with treatment-limiting adverse effects but accompanied by dose-dependent, transient neutropenia and thrombocytopenia. The study concluded that finite, oral RG7854 treatment can induce a SVR in woodchucks that is based on the retrieval of antiviral innate and adaptive immune responses. This supports future investigation of the TLR7 agonist as an immunotherapeutic approach for achieving functional cure in patients with CHB.

Development of a nonhuman primate challenge model to evaluate CD8+ T cell responses to an adenovirus-based vaccine expressing SIV proteins upon repeat-dose treatment with checkpoint inhibitors

Targeting immune checkpoint receptors expressed in the T cell synapse induces active and long-lasting antitumor immunity in preclinical tumor models and oncology patients. However, traditional nonhuman primate (NHP) studies in healthy animals have thus far demonstrated little to no pharmacological activity or toxicity for checkpoint inhibitors (CPIs), likely due to a quiescent immune system. We developed a NHP vaccine challenge model in Mauritius cynomolgus monkey (MCMs) that elicits a strong CD8⁺ T cell response to assess both pharmacology and safety within the same animal. MHC I-genotyped MCMs were immunized with three replication incompetent adenovirus serotype 5 (Adv5) encoding Gag, Nef and Pol simian immunodeficiency virus (SIV) proteins administered 4 weeks apart. Immunized animals received the anti-PD-L1 atezolizumab or an immune checkpoint-targeting bispecific antibody (mAbX) in early development. After a single immunization, Adv5-SIVs induced T-cell activation as assessed by the expression of several co-stimulatory and co-inhibitory molecules, proliferation, and antigen-specific T-cell response as measured by a Nef-dependent interferon-γ ELIspot and tetramer analysis. Administration of atezolizumab increased the number of Ki67⁺ CD8⁺ T cells, CD8⁺ T cells co-expressing TIM3 and LAG3 and the number of CD4⁺ T cells co-expressing 4–1BB, BTLA, and TIM3 two weeks after vaccination. Both atezolizumab and mAbX extended the cytolytic activity of the SIV antigen-specific CD8⁺ T cell up to 8 weeks. Taken together, this vaccine challenge model allowed the combined study of pharmacology and safety parameters for a new immunomodulatory protein-based therapeutic targeting CD8⁺ T cells in an NHP model.

Protein engineering of a stable and potent anti-inflammatory IL-37-Fc fusion with enhanced therapeutic potential

Harnessing the immunomodulatory activity of cytokines is a focus of therapies targeting inflammatory disease. The interleukin (IL)-1 superfamily contains pro-inflammatory and anti-inflammatory members that help orchestrate the immune response in adaptive and innate immunity. Of these molecules, IL-37 has robust anti-inflammatory activity across a range of disease models through inhibition of pro-inflammatory signaling cascades downstream of tumor necrosis factor, IL-1, and toll-like receptor pathways. We find that IL-37 is unstable with a poor pharmacokinetic and manufacturing profile. Here, we present the engineering of IL-37 from an unstable cytokine into an anti-inflammatory molecule with an excellent therapeutic likeness. We overcame these shortcomings through site-directed mutagenesis, the addition of a non-native disulfide bond, and the engineering of IL-37 as an Fc-fusion protein. Our results provide a platform for preclinical testing of IL-37 Fc-fusion proteins. The engineering approaches undertaken herein will apply to the conversion of similar potent yet short-acting cytokines into therapeutics.