Enabling the development of next-generation PD-1/PD-L1 combination immunotherapies with advanced humanized models

PD-1 signaling: a central regulator of immune responses

The PD-1/PD-L1 axis has become one of the most influential therapeutic targets in modern immuno-oncology. Since the clinical success of immune checkpoint inhibitors (ICIs), blockade of PD-1 signaling has transformed the treatment landscape across multiple malignancies, including melanoma, non-small cell lung cancer, renal cell carcinoma, and several hematological cancers. Nevertheless, despite unprecedented clinical benefits in some patients, a substantial proportion fail to respond or eventually develop resistance, emphasizing the urgent need for novel combination strategies and predictive preclinical models to test them.

Programmed death-1 (PD-1, CD279) is an inhibitory receptor expressed primarily on activated T cells, but also on B cells, NK cells, and other immune populations. Engagement of PD-1 by its ligands PD-L1 or PD-L2 attenuates T-cell receptor signaling, limits cytokine production, reduces cytotoxic activity, and promotes immune tolerance (Chen et al., 2023; Lin et al., 2024). While this pathway is essential for preventing excessive immune activation and maintaining peripheral tolerance, tumors frequently exploit PD-1 signaling to evade immune surveillance by upregulating PD-L1 within the tumor microenvironment (Han et al., 2020; Lin et al., 2024). As a result, blockade of PD-1 or PD-L1 can restore antitumor immunity and generate durable responses in a subset of patients.

Overcoming the limitations of PD-1 monotherapy

Despite the remarkable clinical impact of PD-1 blockade, monotherapies frequently encounter important limitations. Primary resistance affects many tumor types, while acquired resistance develops in a significant fraction of initial responders. Mechanisms include impaired antigen presentation, exclusion of effector lymphocytes, immunosuppressive myeloid populations, regulatory T-cell expansion, and activation of alternative inhibitory pathways such as CTLA-4, LAG-3, TIM-3 and TIGIT (Bernardo et al., 2021; Shi et al., 2022). Furthermore, immune-related adverse events can limit treatment intensity and patient eligibility (Chen et al., 2023). These challenges have fueled the rapid development of combination approaches designed to overcome resistance and broaden clinical benefit.

Current combination strategies extend far beyond traditional checkpoint blockade. A major strategy involves combining PD-1 inhibitors with other immune checkpoint modulators, such as CTLA-4, LAG-3, TIM-3, TIGIT, and VISTA antagonists, to counteract compensatory inhibitory pathways that emerge during treatment and contribute to T-cell dysfunction and therapeutic resistance (Tawbi et al., 2022; Andrews et al., 2019). Co-stimulatory agonists targeting receptors including ICOS, OX40, CD137 (4-1BB), and GITR have been explored to enhance T-cell expansion, survival, and effector function within the tumor microenvironment (Burgueno-Bucio et al., 2021). Beyond checkpoint modulation, cytokine-based therapies seek to reshape antitumor immunity by promoting the activation and persistence of effector lymphocytes (Chen and Mellman, 2017; Waldmann, 2018; Murer et al., 2025; Cohen et al., SITC 2024). Similarly, myeloid-targeting approaches directed against suppressive macrophages and myeloid-derived suppressor cells aim to reverse immune exclusion and improve responsiveness to checkpoint inhibitors (Mantovani et al., 2017).

T-cell engagers (TCEs) have emerged as another particularly promising class of combination partners. Combining TCEs with PD-1 blockade has the potential to increase tumor-specific T-cell activity while preventing the exhaustion that commonly develops following sustained T-cell activation (Upadhyay et al., 2021). Collectively, these approaches are designed to address the multifactorial mechanisms of resistance that limit the efficacy of PD-1 monotherapy. However, evaluation of these increasingly sophisticated and often human-specific therapeutics requires translationally relevant in vivo systems capable of reproducing human target engagement while maintaining intact immune responses.

A portfolio of humanized PD-1 models for combination immunotherapy

Traditional murine models often fail to address this challenge because many therapeutic antibodies do not cross-react with murine proteins. Consequently, humanized mouse models have become indispensable tools for immunotherapy development. By replacing murine targets with their human counterparts, these models enable pharmacological assessment of clinically relevant antibodies in immunocompetent animals while preserving the complexity of tumor-immune interactions (Barham et al., 2023; De La Rochere et al., 2026). Such models provide critical insights into efficacy, mechanism of action, biomarker identification, and safety before clinical translation.

Consequently, PD-1 humanized models have become attractive tools. In response to this, genOway has developed a comprehensive portfolio of humanized PD-1 models specifically designed to support the development of next-generation immunotherapies and combination strategies while providing robust data generated by leading biopharma companies. The foundational genO-hPD-1 mouse model enables direct evaluation of human PD-1-targeting therapeutics, including clinically validated antibodies, such as pembrolizumab and nivolumab (Avrustkaya et al., AACR 2029; Metzger et al., AACR 2023), as well as innovative therapeutic modalities (Murer et al., 2025). This model has demonstrated significant utility in syngeneic tumor studies and in evaluating combination therapies. For dual checkpoint blockade, models such as genO-hPD-1/hCTLA-4 have been exploited by AstraZeneca, who demonstrated that MEDI5752, a monovalent bispecific antibody targeting PD-1 and CTLA-4, preferentially targets PD-1⁺ T cells and enhances CTLA-4 blockade, leading to superior antitumor efficacy with potentially reduced toxicity compared to combination therapy (Dovedi et al., 2021). Additionally, models such as genO-hPD-1/hLAG-3 (Weber et al., 2026), genO-hPD-1/hTIM-3 (Rohrberg et al., 2026), genO-hPD-1/hPD-L1, and genO-hPD-1/hVISTA also enable the evaluation of therapies targeting complementary inhibitory pathways involved in T-cell exhaustion and resistance to PD-1 blockade. For immune activation approaches, the genO-hPD-1/hICOS and genO-hPD-1/hGITR/hGITRL models support the assessment of agonistic therapies designed to enhance effector T-cell responses and modulate regulatory T-cell activity. AbbVie has demonstrated the usefulness of this approach, by showing that an anti-PD-1–GITR-L bispecific agonist effectively induces T cell activation and tumor growth inhibition through optimized GITR clustering, offering a promising strategy for cancer immunotherapy (Chan et al., 2022). Finally, the genO-panhCD3/hPD-1 model enables the evaluation of T-cell engagers (TCEs) and other CD3-based immune-cell-redirecting therapies used in combination with PD-1 blockade. Additionally, the genO-BRGSF-HIS, a mouse model with a functional human myeloid and lymphoid cell compartment, also enables the testing of new PD-1-based therapies. This was recently demonstrated by Teva Pharmaceuticals, who employed this model to demonstrate the capability of a new PD-1/IL-2 fusion protein to reprogram the tumor microenvironment by increasing T cell proliferation and infiltration and reducing T cell exhaustion (Cohen et al., SITC 2024).

As the immuno-oncology field continues to evolve, successful preclinical development requires more than demonstrating antitumor efficacy. Increasing attention is being given to factors such as Fc-mediated effector functions, target engagement, pharmacokinetics, and treatment durability, all of which can significantly influence clinical outcomes. Since the Fc region of PD-1-targeting antibodies used in immunotherapy (IO) is often silenced or engineered to have low affinity for FcγR to avoid depleting target cells, a mouse model that allows assessment of both regions of the antibody would be valuable. To enable this, the genO-hPD-1/hFcγR was generated by combining two extensively validated models, genO-hPD-1 and genO-hFcγR (Van Damme et al., 2026).

PD-1 therapies beyond cancer

The success of PD-1 therapies in immuno-oncology has paved the way for their application in the treatment of autoimmune diseases, since PD-1 signaling also plays a central role in regulating inflammation and autoimmunity. The pathway contributes to immune homeostasis by suppressing autoreactive T-cell responses and promoting regulatory T-cell function (Francisco et al., 2010; Chen et al., 2023). Dysregulation of PD-1 signaling has been implicated in disorders such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes, and inflammatory bowel disease (Dai et al., 2014; Liu et al., 2026). PD-1 agonists are emerging as promising treatments for autoimmune diseases, illustrating the broad therapeutic potential of this pathway across multiple immune-mediated conditions (Helou et al., 2023; Zhong et al., 2026).

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参考文献

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