Introduction: TPM502 is a mixture of three distinct nanoparticles, each coupled with one celiac disease (CeD)-relevant gluten peptide, representing immunodominant and deamidated CD4⁺ T cell epitopes. TPM502 targets liver sinusoidal endothelial cells, which are unconventional antigen-presenting cells capable of inducing antigen-specific tolerance.

Aims & Methods: TCeD21 (NCT00565136) was a phase 2a double-blind, randomized, placebo-controlled study in HLA-DQ2.5-positive adults with confirmed CeD on a gluten-free diet. Patients achieving a predefined IL-2 response to a single dose (6 g) gluten challenge (GC1) were randomized into four cohorts to receive two intravenous infusions with escalating doses of TPM502 or placebo on day (D) 1 and D15. The GC was repeated 7 days after the second TPM502 dose (GC2). Peripheral blood mononuclear cells collected from each patient at predefined timepoints were analyzed by high-dimensional (30-color) flow cytometry, before and after HLA-DQ2.5-gliadin-specific tetramer (tet) enrichment, using surface staining for various phenotypic markers. The study aimed to characterize the phenotypes of gluten-specific T cells in CeD patients before and after TPM502 treatment to assess its immunomodulatory effects.

Results: Samples from 36 patients completing the study (12 placebo, 24 TPM502) were analyzed across five timepoints. In the placebo group, tet⁺ CD45RA^–CD62L^–CD4⁺ T (Ttet) cells increased after both GCs. By contrast, the TPM502 cohorts exhibited elevated Ttet cell numbers before GC2 (D22) but showed limited expansion afterward (D29), suggesting that TPM502 treatment may prevent further activation-induced expansion. Moreover, the frequency of activated Ttet cells—indicated by activation markers CD38, ICOS, and OX40—significantly decreased across all TPM502 dose levels after GC2 compared to the placebo group (fold change D22 vs D29, all p < 0.0001 by Kruskal-Wallis test). Notably, the diminished gluten response of Ttet cells post-treatment was accompanied by enhanced expression of co-inhibitory receptors TIGIT and PD-1 (D-21 vs D29, p < 0.0001), along with reduced CD127 expression (p < 0.01), indicative of decreased cell survival. These phenotypic changes, consistent with T cell exhaustion or anergy, persisted until study end and were visibly distinct from those in the placebo group, as illustrated by the heatmap of delta log-transformed flow cytometry data of Ttet cells across timepoints, clustered hierarchically. Gliadin-specific CD4⁺ regulatory T cells (CD25⁺CD127^– Ttet) and CD39⁺ Ttet cells increased post-treatment at the highest TPM502 dose, suggesting the induction of regulatory states in these T cells. Moreover, pre-enriched samples showed reduced activation of αEβ7⁺ γδ⁺ and CD8⁺ T cells after GC2 at the highest TPM502 dose, suggesting potential bystander effects.

Conclusion: Data from the first longitudinal tetramer-based flow cytometry analysis in CeD patients provide evidence that TPM502 induces antigen-specific tolerance through T-cell immunomodulation. These results corroborate other pharmacodynamic outcomes generated in this study, including a significant and dose-dependent reduction in ex vivo IL-2 and IFN-γ secretion by gluten-specific T cells after treatment. In addition to a good safety and tolerability profile of TPM502, this nanoparticle-mediated induction of antigen-specific tolerance may provide a novel therapeutic avenue to treat celiac disease.