PRMT5 regulates T cell interferon response and is a target for acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a T cell-mediated immunological disorder and the leading cause of nonrelapse mortality in patients who receive allogeneic hematopoietic cell transplants. Based on recent observations that protein arginine methyltransferase 5 (PRMT5) and arginine methylation are upregulated in activated memory T cells, we hypothesized that PRMT5 is involved in the pathogenesis of aGVHD. Here, we show that PRMT5 expression and enzymatic activity were upregulated in activated T cells in vitro and in T cells from mice developing aGVHD after allogeneic transplant. PRMT5 expression was also upregulated in T cells of patients who developed aGVHD after allogeneic hematopoietic cell transplant compared with those who did not develop aGVHD. PRMT5 inhibition using a selective small-molecule inhibitor (C220) substantially reduced mouse and human allogeneic T cell proliferation and inflammatory IFN-γ and IL-17 cytokine production. Administration of PRMT5 small-molecule inhibitors substantially improves survival, reducing disease incidence and clinical severity in mouse models of aGVHD without adversely affecting engraftment. Importantly, we show that PRMT5 inhibition retained the beneficial graft-versus-leukemia effect by maintaining cytotoxic CD8+ T cell responses. Mechanistically, we show that PRMT5 inhibition potently reduced STAT1 phosphorylation as well as transcription of proinflammatory genes, including interferon-stimulated genes and IL-17. Additionally, PRMT5 inhibition deregulates the cell cycle in activated T cells and disrupts signaling by affecting ERK1/2 phosphorylation. Thus, we have identified PRMT5 as a regulator of T cell responses and as a therapeutic target in aGVHD.

Multifaceted Role of BTLA in the Control of CD8+ T-cell Fate after Antigen Encounter

Purpose: Adoptive T-cell therapy using autologous tumor-infiltrating lymphocytes (TIL) has shown an overall clinical response rate 40%-50% in metastatic melanoma patients. BTLA (B-and-T lymphocyte associated) expression on transferred CD8⁺ TILs was associated with better clinical outcome. The suppressive function of the ITIM and ITSM motifs of BTLA is well described. Here, we sought to determine the functional characteristics of the CD8⁺BTLA⁺TIL subset and define the contribution of the Grb2 motif of BTLA in T-cell costimulation.Experimental Design: We determined the functional role and downstream signal of BTLA in both human CD8⁺ TILs and mouse CD8⁺ T cells. Functional assays were used including single-cell analysis, reverse-phase protein array (RPPA), antigen-specific vaccination models with adoptively transferred TCR-transgenic T cells as well as patient-derived xenograft (PDX) model using immunodeficient NOD-scid IL2Rgammanull (NSG) tumor-bearing mice treated with autologous TILs.Results: CD8⁺BTLA^- TILs could not control tumor growth in vivo as well as their BTLA⁺ counterpart and antigen-specific CD8⁺BTLA^- T cells had impaired recall response to a vaccine. However, CD8⁺BTLA⁺ TILs displayed improved survival following the killing of a tumor target and heightened "serial killing" capacity. Using mutants of BTLA signaling motifs, we uncovered a costimulatory function mediated by Grb2 through enhancing the secretion of IL-2 and the activation of Src after TCR stimulation.Conclusions: Our data portrays BTLA as a molecule with the singular ability to provide both costimulatory and coinhibitory signals to activated CD8⁺ T cells, resulting in extended survival, improved tumor control, and the development of a functional recall response. Clin Cancer Res; 23(20); 6151-64. ©2017 AACR.

Manipulating the tumor microenvironment ex vivo for enhanced expansion of tumor-infiltrating lymphocytes for adoptive cell therapy

PURPOSE

Cultured tumor fragments from melanoma metastases have been used for years as a source of tumor-infiltrating lymphocytes (TIL) for adoptive cell therapy (ACT). The expansion of tumor-reactive CD8(+) T cells with interleukin-2 (IL2) in these early cultures is critical in generating clinically active TIL infusion products, with a population of activated 4-1BB CD8(+) T cells recently found to constitute the majority of tumor-specific T cells.

EXPERIMENTAL DESIGN

We used an agonistic anti-4-1BB antibody added during the initial tumor fragment cultures to provide in situ 4-1BB costimulation.

RESULTS

We found that addition of an agonistic anti-4-1BB antibody could activate 4-1BB signaling within early cultured tumor fragments and accelerated the rate of memory CD8(+) TIL outgrowth that were highly enriched for melanoma antigen specificity. This was associated with NFκB activation and the induction of T-cell survival and memory genes, as well as enhanced IL2 responsiveness, in the CD8(+) T cells in the fragments and emerging from the fragments. Early provision of 4-1BB costimulation also affected the dendritic cells (DC) by activating NFκB in DC and promoting their maturation inside the tumor fragments. Blocking HLA class I prevented the enhanced outgrowth of CD8(+) T cells with anti-4-1BB, suggesting that an ongoing HLA class I-mediated antigen presentation in early tumor fragment cultures plays a role in mediating tumor-specific CD8(+) TIL outgrowth.

CONCLUSIONS

Our results highlight a previously unrecognized concept in TIL ACT that the tumor microenvironment can be dynamically regulated in the initial tumor fragment cultures to regulate the types of T cells expanded and their functional characteristics.

Activating the TNFR super family member 4-1BB pathway for the expansion of tumor infiltrating lymphocytes for adoptive T cell therapy for metastatic melanoma patients. (P2119)

Adoptive T cell therapy using tumor infiltrating lymphocytes ‘TIL’ is the most effective therapy for metastatic melanoma patients that have failed first and second line therapies. The expansion of TIL from melanoma tumors occurs in two phases. The first phase expands the TIL from the excised melanoma tumor fragments using IL-2. The second phase is the Rapid Expansion Protocol, in which the TIL are activated with anti-CD3 antibody, IL-2 and feeder cells and expanded for 2 weeks. We believe there are shortcomings of Adoptive T cell therapy, such as the inability to grow TIL from all melanoma patients, the amount of time it takes to grow out the TIL and the lack of adequate co-stimulation for the TIL during expansion. 4-1BB is a co-stimulatory molecule expressed on CD8+ T cells after TCR stimulation. We found that 4-1BB is expressed on freshly isolated melanoma CD8+ TIL, suggesting recent tumor antigen exposure. Our hypothesis is that providing co-stimulation through the 4-1BB signaling pathway during the initial TIL outgrowth from tumor fragments accelerates TIL expansion, improves the output of CD8+ T cells, their effector-memory phenotype and anti-tumor specificity. We found that 4-1BB co-stimulation increased CD8+ TIL expansion, maintained CD28 expression and increased Granzyme B expression. Our findings suggest that augmenting the TNFR pathway through 4-1BB co-stimulation during initial melanoma TIL expansion improves proliferation and effector phenotype of the TIL.

Usurpation of a lymphocyte costimulatory molecule as a novel melanoma cell survival pathway (P2187)

BTLA (B- and T- lymphocyte attenuator), binds to the TNF-R family member HVEM (herpes virus entry mediator). HVEM through its interaction with BTLA in trans or in cis has been shown to act as a pro-survival signal through activation of NF-κB. In contrast, signaling through BTLA following HVEM engagement has been found to induce a negative signaling pathway by activating SHP1/2 phosphatases. During an initial immunohistochemistry screen for the expression of BTLA in melanoma tumor sections, we unexpectedly found that a many tumor cells also exhibited a uniform and strong positive intracellular expression of BTLA. BTLA was expressed in both primary and metastatic melanoma cells with low to negative expression in benign nevi. PCR analysis also revealed that although most tumor lines expressed isoform 1 of BTLA, some lines expressed both isoform 1 and 2 suggesting BTLA by be secreted. Moreover, we also found that melanoma cells express both surface and intracellular HVEM. Intriguingly, significant pools of BTLA were found to be co-localized with intracellular HVEM in the melanoma cells. This co-localization suggests that tumor cells may use HVEM activation as a mechanism of cell survival. Blockade of BTLA or inhibition of BTLA or HVEM expression on melanoma cells may therefore be a novel approach to inhibit tumor cell survival as well as prevent negative signaling through BTLA in immune cells.