Precision modeling of tumor antigen-specific T-cell responses in humanized mice for preclinical assessment of cancer immunotherapies.

[BACKGROUND] Humanized mice are highly valuable models for the preclinical development of cancer immunotherapies. However, conventional models often fail to mount robust and trackable tumor antigen-specific (TA-specific) T-cell responses, which hinders the comprehensive evaluation of therapies that depend on this endogenous antitumor immunity.

[METHODS] To address this limitation, we generated a humanized mouse model by engrafting immunodeficient mice with human hematopoietic stem cells that were transduced with predefined T-cell receptor (TCR) specificities. This approach enables the de novo generation of naïve, functional TA-specific T cells at adjustable frequencies.

[RESULTS] We found that transgene-bearing human thymocytes have a developmental advantage in the murine thymus, likely due to the early formation of the transgenic TCR and associated autonomous signaling. In tumor studies, the presence of these TA-specific T cells delayed tumor growth and promoted increased phenotypic diversity of intratumoral T cells, including the formation of PD-1/TCF1 precursor exhausted T cells, which were absent in control mice. We demonstrate the utility of this model in two distinct therapeutic contexts. First, we found that high baseline frequencies of TA-specific T cells blunted the efficacy of a T-cell bispecific antibody (TCB), suggesting that pre-existing exhaustion limits TCB activity. Furthermore, the model enabled the evaluation of costimulatory agonists (FAP-CD40 and FAP-4-1BBL), and demonstrated their dependence on this T-cell compartment for antitumor efficacy.

[CONCLUSIONS] This adaptable and physiologically relevant model provides a platform to dissect the complex interplay between human tumors, immune cells, and immunotherapies and has the potential to significantly improve the translation of preclinical findings to the clinic.