Background CD8⁺ T cell fate decision refers to the differentiation of a naïve T cell into effector, memory, exhausted, or other fates. Evidence from chronic infection and cancer models suggest that signals during T cell priming are especially important in determining T cell fate and thus the functional quality of the T cell response.^1–4 Priming interactions are highly complex, requiring integration of multiple signals, each of which varies in strength and duration. Thus, we currently do not comprehend the combinatorial specificities and molecular underpinnings that determine T cell fate during priming. Understanding the factors that drive different T cell fates could be therapeutically harnessed to reduce exhaustion phenotypes and increase effector functions and memory potential of CD8⁺ T cells in cancer.

Methods We used therapeutic interventions as a tool to alter signals received by a T cell during priming and characterized their impact on T cell fate. Using a BRAF^V600EPTEN^-/- melanoma cell line that expresses the model antigen SIYRYYGL (SIY), we implanted subcutaneous tumors into mice and provided therapy during priming. We surveyed the effects of checkpoint blockade therapy (anti-PD1), costimulatory agonists (anti-CD40), and type-I Interferon (IFNb) on tumor-reactive CD8⁺ T cells during priming via flow cytometry and single-cell RNA sequencing.

Results All treatments resulted in an increase of effector-like (TCF1^-TIM3⁺) tumor-reactive T cells. However, each intervention induced differential expression of fate-driving transcription factors. IFNb-treated T cells had high expression of genes associated with cytotoxic capacity, consistent with the activation of an effector-fate program, while aPD1-treated T cells were transcriptionally similar to untreated controls. Using adoptive T cell transfers, we showed that anti-PD1 or IFNb treatment during priming resulted in increased memory potential and ability to control a secondary tumor. Surprisingly, although augmenting CD40 signaling during priming made T cells appear more memory-like, no functional improvements in memory potential were observed. To mimic neoadjuvant treatment, mice were treated with therapy during priming against subcutaneous tumors, which were subsequently surgically resected. Immunological memory was allowed to form, and mice were challenged with lung tumors, a relevant tissue for melanoma metastasis. Overall survival is being evaluated to assess the therapeutic potential for each neoadjuvant treatment.

Conclusions Changing the signals received by a CD8⁺ T cell during priming alters the phenotypic and transcriptional profile of these cells. These early transcriptional changes appear to generate different CD8⁺ T cell fates, providing an opportunity to rationally improve anti-tumor immunity, particularly in a neoadjuvant setting.

References

1. Prokhnevska N, Cardenas MA, Valanparambil RM, Sobierajska E, Barwick BG, Jansen C, et al. CD8(+) T cell activation in cancer comprises an initial activation phase in lymph nodes followed by effector differentiation within the tumor. Immunity 2023;56(1):107–24 e5.

2. Quezada LK, Jin W, Liu YC, Kim ES, He Z, Indralingam CS, et al. Early transcriptional and epigenetic divergence of CD8+ T cells responding to acute versus chronic infection. PLoS Biol 2023;21(1):e3001983.

3. Horton BL, Morgan DM, Momin N, Zagorulya M, Torres-Mejia E, Bhandarkar V, et al. Lack of CD8(+) T cell effector differentiation during priming mediates checkpoint blockade resistance in non-small cell lung cancer. Sci Immunol 2021;6(64):eabi8800.

4. Zagorulya M, Yim L, Morgan DM, Edwards A, Torres-Mejia E, Momin N, et al. Tissue-specific abundance of interferon-gamma drives regulatory T cells to restrain DC1-mediated priming of cytotoxic T cells against lung cancer. Immunity 2023.

Ethics Approval All mouse experiments in this study were approved by MIT’s Committee on Animal Care (CAC) - DHHS Animal Welfare Assurance # D16-00078.