CD8+ T-cell functions are critical for preventing chronic viral infections by eliminating infected cells. For healthy immune responses, beneficial destruction of infected cells must be balanced against immunopathology resulting from collateral damage to tissues. These processes are regulated by factors controlling CD8+ T-cell function, which are still incompletely understood. Here, we show that the interferon regulatory factor 4 (IRF4) and its cooperating binding partner B-cell-activating transcription factor (BATF) are necessary for sustained CD8+ T-cell effector function. Although Irf4–/– CD8+ T cells were initially capable of proliferation, IRF4 deficiency resulted in limited CD8+ T-cell responses after infection with the lymphocytic choriomeningitis virus. Consequently, Irf4–/– mice established chronic infections, but were protected from fatal immunopathology. Absence of BATF also resulted in reduced CD8+ T-cell function, limited immunopathology, and promotion of viral persistence. These data identify the transcription factors IRF4 and BATF as major regulators of antiviral cytotoxic T-cell immunity.

2523 Background: T-cell targeting of mutation-derived epitopes (neoantigens) has been demonstrated to drive anti-tumor responses. Immunizing patients against such neoantigens in combination with a checkpoint inhibitor (CPI) may elicit greater anti-tumor responses than CPI alone. Mutations are rarely shared between patients, thus requiring a personalized approach to vaccine design. Methods: A phase I dose escalation study of mRNA-4157 as adjuvant monotherapy in patients with resected solid tumors (melanoma, bladder carcinoma, HPV negative HNSCC, NSCLC, SCLC, MSI-High, or TMB High cancers) and in combination with pembrolizumab in patients with advanced or metastatic cancer is being conducted to evaluate safety. mRNA-4157 is a lipid encapsulated personalized vaccine encoding multiple neoantigens selected using a proprietary algorithm designed to induce neoantigen specific T cells and associated anti-tumor responses. Patients may receive up to 9 cycles (Q3W) of mRNA-4157 by intramuscular injection (0.04 – 1 mg). In the combination arm, pembrolizumab (200 mg) is administered for two cycles prior to combination with mRNA-4157; patients may continue pembrolizumab after completion of 9 cycles of combination therapy. Primary end points include safety, tolerability, and recommended phase 2 dose. Results: 33 patients received mRNA-4157; 13 as monotherapy and 20 in combination with pembrolizumab. No DLTs were reported, and treatment related AEs have generally been of low grade and reversible, and no drug related SAEs or AEs ≥ grade 3 have been observed. Of the 13 patients on adjuvant monotherapy (3 melanoma, 8 NSCLC, 2 MSI-High), 12 patients remain disease free on study, median follow-up of 8 months. 20 patients have been treated in combination (1 TMB-high, 4 bladder, 2 HNSCC, 1 melanoma, 7 NSCLC, 2 SCLC, 3 MSI-high), 12 had progressed on prior CPI, 16 have been restaged and there are 1 CR (on pembrolizumab prior to vaccination), 2 PR, 5 SD for at least 5 combination cycles, 5 PD, 2 iuPD, and 1 patient is non-evaluable for response but remains on study. Neoantigen specific T cell responses have been detected by IFN-γ ELISpot from PBMCs. Conclusions: mRNA-4157 is safe and well tolerated at all dose levels tested. Clinical responses have been observed in combination with pembrolizumab and neoantigen-specific T cells have been induced, supporting the advancement of mRNA-4157 to phase 2. Clinical trial information: NCT03313778.

BackgroundB7-H3 and B7-H4 are highly expressed by many human malignancies making them attractive immunotherapeutic targets. However, their expression patterns and immune contexts in epithelial ovarian cancer have not been well characterized.MethodsWe used flow cytometry, immunohistochemistry, and genomic analyses to determine the patterns of B7-H3, B7-H4, and PD-L1 expression by tumor, stromal, and immune cells in the ovarian tumor microenvironment (TME). We analyzed immune cell frequency and expression of PD-1, TIM3, LAG3, ICOS, TIA-1, granzyme B, 2B4, CD107a, and GITR on T cells; CD20, CD22, IgD, BTLA, and CD27 on B cells; CD16 on monocytes; and B7-H3, B7-H4, PD-L1, PD-L2, ICOSL, CD40, CD86, and CLEC9a on antigen-presenting cells by flow cytometry. We determined intratumoral cellular location of immune cells using immunohistochemistry. We compared differences in immune infiltration in tumors with low or high tumor-to-stroma ratio and in tumors from the same or unrelated patients.ResultsOn non-immune cells, B7-H4 expression was restricted to tumor cells whereas B7-H3 was expressed by both tumor and stromal cells. Stromal cells of the ovarian TME expressed high levels of B7-H3 compared to tumor cells. We used this differential expression to assess the tumor-to-stroma ratio of ovarian tumors and found that high tumor-to-stroma ratio was associated with increased expression of CD16 by monocytes, increased frequencies of PD-1high CD8+ T cells, increased PD-L1 expression by APCs, and decreased CLEC9a expression by APCs. We found that expression of PD-L1 or CD86 on APCs and the proportion of PD-1high CD4+ T cells were strongly correlated on immune cells from tumors within the same patient, whereas expression of CD40 and ICOSL on APCs and the proportion of PD-1high CD8+ T cells were not.ConclusionsThis study provides insight into the expression patterns of B7-H3 and B7-H4 in the ovarian TME. Further, we demonstrate an association between the tumor-to-stroma ratio and the phenotype of tumor-infiltrating immune cells. We also find that some but not all immune parameters show consistency between peritoneal metastatic sites. These data have implications for the design of immunotherapies targeting these B7 molecules in epithelial ovarian cancer.