CTLA-4 antibody discovery for next-generation immunotherapies

In 2026, how can we design anti-CTLA-4 antibodies that stand out for their efficacy, safety, and intellectual property profiles? Monoclonal, bispecific, or novel antibodies, which format should we choose to compete with first-generation products and next-generation molecules?

In this article, we will discuss the role of CTLA-4, the antibodies already developed against this target and recent approaches to designing high-performing candidates. We will also emphasize the differentiation criteria useful for R&D, licensing and competitive positioning.

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What is CTLA-4 and what is its role in the immune response?

CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) is an inhibitory receptor expressed on the surface of activated T lymphocytes. It is also constitutively present on regulatory T cells (Tregs). It competes with CD28 for binding to the co-receptors CD80 and CD86 (also known as B7-1 and B7-2). CTLA-4 negatively modulates signaling, as its affinity and avidity are higher than those of CD28.

CTLA-4 exerts a dual inhibition:

• intrinsic, through the recruitment of phosphatases which limit TCR/PI3K signaling in the T lymphocyte and inhibit its activation;
• extrinsically, through a trans-endocytosis mechanism, where CTLA-4 captures CD80/CD86 from the surface of antigen-presenting cells, reducing the co-stimulation available to all surrounding T cells.

Structurally, CTLA-4 is a type I transmembrane glycoprotein that forms a 41–43 kDa homodimer with an extracellular IgV domain involved in CD80 and CD86 recognition. Its C-terminal domain recruits phosphatases and adaptors that decrease downstream TCR signaling and reduce IL-2 production and T cell proliferation.

In Tregs, high CTLA-4 expression maintains peripheral tolerance. Murine models with specific CTLA-4 deletion in Tregs have demonstrated the development of severe systemic autoimmunity.

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Why target CTLA-4 in therapy?

In many solid tumors, the CTLA-4/CD28 axis plays a role in immune evasion by limiting T lymphocyte priming and enhancing the suppressive effect of Tregs. CTLA-4 is exploited to escape immune surveillance by inhibiting the T cell response from the earliest stages of activation.

Anti-CTLA-4 antibodies thus have two main objectives:

• restoration of T cell activation in lymph nodes;
• potential reduction in the number or function of Tregs in the tumor microenvironment.

Approved indications and combinations CTLA-4

The first clinical successes were demonstrated in metastatic melanoma. Ipilimumab showed a significant improvement in overall survival. This antibody thus introduced the concept of durable responses in a subgroup of patients. It received FDA approval in 2011.

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Since then, the combination of ipilimumab with an anti-PD-1 agent (Nivolumab) has become a standard of care in advanced melanoma, intermediate- to low-risk renal cell carcinoma, and certain subtypes of non-small cell lung cancer (NSCLC). Additional survival gains have been achieved, but at the cost of increased toxicity.

Conversely, negative trials in less immunogenic contexts (mesothelioma, certain prostate or lung cancers as monotherapy) show that CTLA-4 blockade alone is insufficient in so-called "cold" or highly immunosuppressive tumors.

In these indications, targeting CTLA-4 is more advantageous in a combination strategy, for example, as a dual checkpoint inhibitor, in combination with radiotherapy, immunogenic chemotherapy, or targeted therapies.

The challenges of projects involving anti-CTLA-4 antibodies

Today, projects using anti-CTLA-4 solutions face several constraints:

• immune toxicity, with adverse events related to diffuse immune system activation being more frequent and more severe than with anti-PD-1 agents, particularly in combination;
• product differentiation, with Ipilimumab and Tremelimumab already well established. Several next-generation candidates are also seeking to position themselves with a better efficacy/safety compromise or with innovative architectures (bispecific, probodies, ADCs).

The challenge is therefore to design a differentiated and differentiating antibody, with better control of Tregs, reduced toxicity, a pH-sensitive or masked design, or even a bispecific format.

👉 Explore our pipeline to identify untapped opportunities and competitive positioning.

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Overview of anti-CTLA-4 antibodies, from the first to the second generation

First-generation anti-CTLA-4 antibodies

Two molecules have historically dominated the class of first-generation anti-CTLA-4 antibodies.
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Ipilimumab, a fully human IgG1 antibody, is the market leader when used in combination with anti-PD-1 agents. Its mechanisms of action are:

• blockade of the CTLA-4/B7 (CTLA-4/CD28) axis;
• amplification of T lymphocyte priming;
• possible depletion of intratumoral Tregs with FcγR engagement;
• induction of ADCC/ADCP in murine models.

Tremelimumab, on the other hand, is a fully human IgG2 antibody with a lower capacity to recruit effector Fc cells. After failures as monotherapy, it has been successfully repositioned in the STRIDE regimen (a single dose of Tremelimumab and Durvalumab as maintenance therapy) for unresectable hepatocellular carcinoma.

These experiences have fueled a debate on anti-tumor efficacy. Does it depend primarily on checkpoint blockade of effector T cells, or on the depletion of Tregs highly expressing CTLA-4 in the tumor? Preclinical results strongly support the importance of Treg depletion, while human data are more nuanced.

Next-generation anti-CTLA-4 antibodies

The second wave of antibodies broadens the therapeutic index with similar or better efficacy, but less toxicity.

Examples include:

• pH-sensitive antibodies designed to detach from CTLA-4 in the acidic endosome, allowing the receptor to be recycled rather than degraded, thus reducing CTLA-4 loss and potentially limiting toxicities;
• anti-CTLA-4 probodies, antibodies masked by a peptide cleaved by tumor proteases, inactive in circulation and activated locally in the tumor microenvironment, with reduced toxicities in murine models;
• bispecific antibodies, antibodies simultaneously targeting CTLA-4 and a second target (PD-1, OX40, etc.), with Fc designs modulated depending on whether or not cytotoxicity is desired;
• Anti-CTLA-4 ADCs that use an anti-CTLA-4 antibody as a vector to deliver a cytotoxic agent to CTLA-4-expressing Treg cells in the tumor, allowing their elimination.

Several questions arise from these trends. Which isotype? Which Fc capacities? Should we opt for a pH-sensitive, masked, or bispecific format? Which CTLA-4 regions should we target to optimize these properties?

👉 With the progressive expiration of Ipilimumab patents and Tremelimumab, the market opens to biosimilars. While this threatens originators' revenues, it creates opportunities for differentiated next-gen candidates: better efficacy/safety ratio, innovative formats, and strong IP. The key is to position ahead of the generic wave.

Why choose MAbSilico to design anti-CTLA-4 antibodies?

The available data allow us to understand the biology and clinical aspects of the CTLA-4 protein. In contrast, the design of a competitive anti-CTLA-4 antibody requires a comprehensive range of structures, experimental data, and the intellectual property landscape.