Effect of IL7 on ImmTAC-mediated killing by T cells in vitro and T-cell fitness in patients.

2662 Background: A blood T cell fitness (TCF) signature, reflecting properties of naïve and stem cell memory T cells, was strongly associated with clinical benefit from tebentafusp (gp100 × CD3) and brenetafusp (PRAME × CD3) ImmTAC bispecific therapies¹. Here, we assessed whether TCF could be enhanced by IL7, a cytokine that plays a key role in T cell homeostasis and promotes the proliferation and survival of naïve and stem cell memory T cells. Methods: T cell exhaustion was induced in vitro by four weekly ImmTAC stimulations against the Non-Small Cell Lung Cancer (NSCLC) cell line NCIH1755 with or without IL7. Tumor killing, T cell cytokine secretion, and T cell phenotype were assessed using standard methods. Data are given as mean ± SEM; groups were compared using paired t test. IL7R gene expression and TCF (mean expression of TESPA1 , CD28 and GPR183 ) were measured in baseline whole blood from patients with unresectable or metastatic uveal melanoma (mUM) treated with tebentafusp (n=132 NCT02570308) or brenetafusp (N=37 NCT04262466) as previously described 1 . TCF high/low threshold was cut at the median. TCF was also assessed in baseline and on-treatment PBMC from patients with NSCLC and Triple-Negative Breast Cancer (TNBC) (n=15) receiving NTI7, a long acting recombinant human IL7 (rhIL7, NCT03752723, NCT04984811). Results: In vitro, repeated re-direction of T cells by ImmTAC resulted in reduced tumor cell lysis from 46±9% after a single stimulation to 3±1% after 4 weekly stimulations. In contrast, T cells cultured with IL7 retained tumor cell lysis after 4 stimulations (58±2% ImmTAC-redirected cytolysis compared with 3±1% in IL7-untreated T cells, p = 0.02), accompanied by a 14.3-fold increase in IFNγ secretion (p = 0.04). The proportion of naïve/stem cell memory T cells increased in response to IL7 treatment from 37±5% to 57±8% (p=0.009). In mUM patients, gene expression of IL7R strongly correlated with TCF signature in peripheral blood (R = 0.91, p < 0.001). As early as 3 weeks following a single dose of NTI7, TCF increased by ~3-fold in PBMC from NSCLC and TNBC patients. The proportion of TCF high patients increased from 36% at baseline to 93% post NTI7 monotherapy. This increase in TCF signature was sustained for at least 12 weeks. Conclusions: Despite repeated antigen stimulation in vitro, IL7 sustained naïve/memory T cells, enhanced ImmTAC-redirected T cell cytotoxicity and IFNγ production, and reduced T cell exhaustion. A single dose of rhIL7 resulted in a sustained increase in TCF signature and converted patients with low TCF signature into high TCF. These findings support combination with IL7 as a rational strategy to augment T cell fitness and potentially improve efficacy of ImmTAC bispecific T cell therapies. 1) Sacco et al ESMO 2024.