Fc-optimized GITR antibody enhances a CD4 T cell–dendritic cell crosstalk to promote antitumor immunity
The Fc Review:
When you engineer the Fc to enhance one mechanism, what else changes?
A recent
Nature Cancer study takes a closer look at that question using an agonistic anti-GITR antibody, showing how Fc optimization can influence not only FcγR engagement and Treg depletion, but other immune pathways contributing to antitumor activity.
Background:
GITR is a stimulatory immune checkpoint receptor being explored as a target for cancer immunotherapy. While agonistic anti-GITR antibodies have shown promise preclinically, clinical efficacy has been limited.
Because FcγR engagement can contribute to the activity of these antibodies, the authors used Fc protein engineering and glycoengineering to alter interactions with different human FcγRs and examine how those changes affected antitumor activity.
The study highlights:
- Fc variants with enhanced engagement of activating FcγRIIa or FcγRIIIa increased antitumor activity, while preferentially enhancing engagement of inhibitory FcγRIIb did not improve tumor control.
- Combining G236A with reduced fucosylation enhanced engagement of both activating FcγRIIa and FcγRIIIa, without enhanced binding to FcγRIIb. This combined variant showed greater antitumor activity than variants enhancing either activating receptor individually in the tested model.
- Fc-active variants depleted Tregs within the tumor. However, the optimized variant and IgG1 produced similar Treg depletion despite differences in therapeutic activity, pointing to an additional FcγR-mediated mechanism.
- The Fc-optimized antibody also increased dendritic cell activation, and the authors found that conventional DCs, particularly cDC1s, were required for the Fc-mediated antitumor effect in their models.
- Further experiments connected this activity to CD4 T cell–DC engagement, with downstream CD4 T cell cytotoxicity and enhanced CD8 T cell activity
Figure 3. (a) Frequency of intratumoral Tregs 4 days post-treatment onset with the indicated anti-GITR Fc variant in MC38-bearing C57BL/6 mice. n = 6 mice per group. One representative experiment of two independent repeats is shown. (b-c) Frequency of DCs and their CD80 and CD86 expression levels in tumor (b) and dLN (c) 4 days post-treatment onset with the indicated anti-GITR Fc variant in MC38 tumor-bearing C57BL/6 mice. b: n = 6 mice per group; c: n = 5 mice per group (Untreated, mIgG2a) n= 6 mice (mIgG2a N297A). (d) MC38 tumor growth in ZBTB46-DTR mice following treatment with the indicated anti-GITR Fc variant, with or without diphtheria toxin administration. n = 10 mice per group. One representative experiment of two independent repeats is shown. (e) Gene-gene comparison of GA-aFuc versus N297A in dendritic cell subsets. Average log2 normalized gene expression of the indicated dendritic cell subsets comparing N297A (y-axis) and GA-aFuc (x-axis). Leading differentially expressed genes (DEGs) (p < 0.05 and |log2FC| ≥ 0.5) are annotated. Unless otherwise stated or in case of n < 3, results are presented as means ± SEM. P values are displayed on the graphs and in Supplementary Table 2. Data were analyzed by Ordinary one-way ANOVA with Tukey’s multiple comparisons test (a, b and c).
Implications:
This study shows how an Fc engineering strategy can affect more than the mechanism it was initially designed to enhance. Here, stronger engagement of activating FcγRs improved antitumor activity, but the resulting biology extended beyond Treg depletion to include dendritic cell activation and T cell responses.
For antibody developers, it is a useful example of why the effects of Fc engineering may need to be considered across multiple receptors, cell types, and mechanisms rather than through a single endpoint.
Our perspective:
Fc engineering often starts with a specific goal, whether that is enhancing engagement with a particular FcγR, increasing a desired effector mechanism, or reducing one.
But the resulting biology may extend beyond that goal.
This study is a great example. Treg depletion was part of the story, but it did not fully explain the improved antitumor activity of the Fc-optimized antibody. Looking more broadly revealed additional effects involving dendritic cells and T cell responses.
For us, this reinforces the value of looking across FcγR engagement and multiple immune functions when characterizing an engineered antibody. It can help show whether the Fc is doing what it was designed to do, while also uncovering functional changes that may not have been obvious from the original engineering strategy.
References:
Avraham, Y., Barth, N., Yair Bar-On, T. et al. Fc-optimized GITR antibody enhances a CD4 T cell–dendritic cell crosstalk to promote antitumor immunity. Nat Cancer (2026). https://doi.org/10.1038/s43018-026-01207-1
