Preprint Club
A cross-institutional Journal Club Initiative

Keywords

● Neoantigen-reactive T cells

● Adoptive T cell transfer (ACT)

● Tumor infiltrating lymphocyte (TIL) therapy

● B16F10 melanoma tumor models

● Tumor draining lymph node (TDLN) T cell trafficking

Main Findings

The mechanistic details pertaining to the response of adoptively transferred neoantigen-reactive T cells against patients with solid tumors remains largely unknown. Besides a patient’s response to treatment, the mechanisms involving transferred T cell trafficking, activation, and antitumor function are continually being investigated. In this preprint, the authors use two melanoma murine tumor models engineered to express either the WT or neoantigen forms of gp100. Using naïve pmel-1 T cell therapy, this model allowed them to compare gp100 neoantigen specific (melanoma T cell specific) T cell reactivity in a controlled setting. The authors propose a novel 3-step model of T cell activation in adoptive cell therapy: initial lymphoid homing, antigen-independent migration to secondary lymphoid organs, and sustained response.

Naïve pmel-1 T cells failed to control B16F10 tumors but mounted a robust response against B16KVP. 

Initially, the authors utilized both naïve and IL-2 expanded pmel-1 specific T cells. In a clinical setting, only antigen specific T cells are reinfused into the patient after IL-2 expansion. This proved to be ineffective in their murine models and the naïve pmel-1 T cell therapy performed better at controlling neoantigen tumor (B16KVP) growth. This data further supported their hypothesis that naïve CD8 T cells are necessary for a robust response. They showed that neoantigen tumor regression was 50% greater than the non-mutated B16F10 (WT) model, both receiving naïve pmel-1 T cell therapy. Lastly, transferred pmel-1 CD8 T cells engrafted at a significantly higher percentage in mice with neoantigen expressing tumors.

RNA transcriptional profiling of tumor tissues revealed differentially expressed genes associated with cytokine signaling and antigen presentation. 

Antigen presentation and cytokine signaling including Irf8, Cxcl9, and Cxcl10 were upregulated in B16KVP tumors compared to B16F10 WT tumors. Even at early time points, neoantigen expressing tumors encouraged a more immunogenic environment. Most importantly, pro inflammatory IFNy exhibited a 300-fold increase in B16KVP tumors compared to those of WT.

Adoptively transferred T cells rapidly traffic to the lymph node and preferentially expand in neoantigen-expressing tumors. 

Despite their naïve origin, pmel-1 cells in B16KVP tumor bearing mice acquired an effector phenotype. The authors showed this through increases in CD44 and CD62L expression in the TDLN of B16KVP mice compared to those of B16F10 WT. Pmel-1 cells expressed elevated PD-1 and CD69 levels across the lymph nodes, blood, tumor and spleen indicating persistent antigen engagement.

Lymph node egress is essential for the antitumor efficacy of transferred T cells.

Using the drug FTY720, the authors blocked lymphocyte egress from lymph node in their murine models. They showed that without lymphocyte egress from the lymph nodes, naïve pmel-1 T cell therapy was ineffective in controlling B16KVP tumors.

Limitations

- This study focused on only one cancer type with only one neoantigen-reactive T cell response. Neoantigen T cell targeting is proving to be an evolving contribution to improved patient response so neoantigen derived T cells of different origin will need to be investigated.

- Only the TDLNs were investigated and no other secondary lymph nodes, including the mesenteric lymph nodes.

Significance/Novelty

This study challenges the traditional paradigm of T cell activation in neoantigen adoptive transfer. In mice bearing neoantigen expressing tumors, naïve pmel-1 T cells underwent rapid CD44, CD62L, and TCF1 downregulation. These findings coincided with efficient and necessary lymph node homing and rapid T cell effector differentiation. A new paradigm is proposed;

1. Anti-independent migration to secondary lymphoid organs

2. Neoantigen-driven programing and effector T cell differentiation in the TDLNs

3. Sustained response and effector persistence across lymphoid tissues and tumors

Adoptive cell therapy is currently in the clinic and similar advancements need to be made directed towards understanding its mechanism and how to improve patient response. Neoantigen discovery platforms and technologies are pushing the field forward which makes these mechanistic discoveries even more vital.

Recommendations

In immune checkpoint blockade (ICB) therapy, neoantigen-specific T cells can be enriched. This supports adding ICT treated experimental arms to these studies. Pairing these mechanistic studies with additional cancer types and neoantigen discovery platforms would be a way to be clinically adaptable. Additionally, upon FYT270 treatment, the tumor infiltration phenotype needs to be investigated, not just tumor volume and overall survival.

Preprint rating

· Scientific quality: ***

· Novelty:*****

· Significance:*****

Credit

Reviewed by Samuel Andrewes as part of a cross-institutional journal club between the Icahn School of Medicine at Mount Sinai, the University of Oxford, the Karolinska Institute, the University of Toronto and MD Anderson Cancer Center. The author declares no conflict of interests in relation to their involvement in the review.