Local Radiation Enhances Systemic CAR T Cell Efficacy by Augmenting Antigen Cross-Presentation and T-cell Infiltration.

Chimeric antigen receptor (CAR) T cell therapy targeting CD19 (CART-19) represents a significant advance in the treatment of patients with relapsed or refractory CD19-positive B-cell lymphomas. However, a significant portion of patients either relapse or fail to respond. Moreover, many patients have symptomatic disease, requiring bridging radiation therapy (RT) during the period of CAR-T cells manufacturing. To investigate the impact of 1-2 fractions of low-dose RT on CART-19 treatment response, we developed a mouse model using A20 lymphoma cells for CART-19 therapy. We found that low dose fractionated RT had a positive effect on generating abscopal systemic antitumor responses beyond the irradiated site. The combination of RT with CART-19 therapy resulted in additive effects on tumor growth in irradiated masses. Notably, a significant additional increase in antitumor effect was observed in non-irradiated tumors. Mechanistically, our results validate activation of the cGAS/STING pathway, tumor-associated antigen (TAA) cross-priming, and elicitation of epitope spreading. Collectively, our findings suggest that RT may serve as an optimal priming and bridging modality for CAR-T cell therapy overcoming treatment resistance and improving clinical outcomes in patients with CD19-positive hematologic malignancies.

Parkin Deficiency Suppresses Antigen Presentation to Promote Tumor Immune Evasion and Immunotherapy Resistance.

Parkin is an E3 ubiquitin ligase, which plays a key role in the development of Parkinson disease. Parkin defects also occur in numerous cancers, and a growing body of evidence indicates that Parkin functions as a tumor suppressor that impedes a number of cellular processes involved in tumorigenesis. Here, we generated murine and human models that closely mimic the advanced-stage tumors where Parkin deficiencies are found to provide deeper insights into the tumor suppressive functions of Parkin. Loss of Parkin expression led to aggressive tumor growth, which was associated with poor tumor antigen presentation and limited antitumor CD8+ T-cell infiltration and activation. The effect of Parkin deficiency on tumor growth was lost following depletion of CD8+ T cells. In line with previous findings, Parkin deficiency was linked with mitochondria-associated metabolic stress, PTEN degradation, and enhanced Akt activation. Increased Akt signaling led to dysregulation of antigen presentation, and treatment with the Akt inhibitor MK2206-2HCl restored antigen presentation in Parkin-deficient tumors. Analysis of data from patients with clear cell renal cell carcinoma indicated that Parkin expression was downregulated in tumors and that low expression correlated with reduced overall survival. Furthermore, low Parkin expression correlated with reduced patient response to immunotherapy. Overall, these results identify a role for Parkin deficiency in promoting tumor immune evasion that may explain the poor prognosis associated with loss of Parkin across multiple types of cancer. SIGNIFICANCE: Parkin prevents immune evasion by regulating tumor antigen processing and presentation through the PTEN/Akt network, which has important implications for immunotherapy treatments in patients with Parkin-deficient tumors.

Modulation of the gut microbiota engages antigen cross-presentation to enhance antitumor effects of CAR T cell immunotherapy.

Several studies have shown the influence of commensal microbes on T cell function, specifically in the setting of checkpoint immunotherapy for cancer. In this study, we investigated how vancomycin-induced gut microbiota dysbiosis affects chimeric antigen receptor (CAR) T immunotherapy using multiple preclinical models as well as clinical correlates. In two murine tumor models, hematopoietic CD19+-A20 lymphoma and CD19+-B16 melanoma, mice receiving vancomycin in combination with CD19-directed CAR T cell (CART-19) therapy displayed increased tumor control and tumor-associated antigens (TAAs) cross-presentation compared with CART-19 alone. Fecal microbiota transplant from human healthy donors to pre-conditioned mice recapitulated the results obtained in naive gut microbiota mice. Last, B cell acute lymphoblastic leukemia patients treated with CART-19 and exposed to oral vancomycin showed higher CART-19 peak expansion compared with unexposed patients. These results substantiate the role of the gut microbiota on CAR T cell therapy and suggest that modulation of the gut microbiota using vancomycin may improve outcomes after CAR T cell therapy across tumor types.