Targeting PARP11 to avert immunosuppression and improve CAR T therapy in solid tumors.

Evasion of antitumor immunity and resistance to therapies in solid tumors are aided by an immunosuppressive tumor microenvironment (TME). We found that TME factors, such as regulatory T cells and adenosine, downregulated type I interferon receptor IFNAR1 on CD8+ cytotoxic T lymphocytes (CTLs). These events relied upon poly-ADP ribose polymerase-11 (PARP11), which was induced in intratumoral CTLs and acted as a key regulator of the immunosuppressive TME. Ablation of PARP11 prevented loss of IFNAR1, increased CTL tumoricidal activity and inhibited tumor growth in an IFNAR1-dependent manner. Accordingly, genetic or pharmacologic inactivation of PARP11 augmented the therapeutic benefits of chimeric antigen receptor T cells. Chimeric antigen receptor CTLs engineered to inactivate PARP11 demonstrated a superior efficacy against solid tumors. These findings highlight the role of PARP11 in the immunosuppressive TME and provide a proof of principle for targeting this pathway to optimize immune therapies.

The immunostimulatory RNA RN7SL1 enables CAR-T cells to enhance autonomous and endogenous immune function.

Poor tumor infiltration, development of exhaustion, and antigen insufficiency are common mechanisms that limit chimeric antigen receptor (CAR)-T cell efficacy. Delivery of pattern recognition receptor agonists is one strategy to improve immune function; however, targeting these agonists to immune cells is challenging, and off-target signaling in cancer cells can be detrimental. Here, we engineer CAR-T cells to deliver RN7SL1, an endogenous RNA that activates RIG-I/MDA5 signaling. RN7SL1 promotes expansion and effector-memory differentiation of CAR-T cells. Moreover, RN7SL1 is deployed in extracellular vesicles and selectively transferred to immune cells. Unlike other RNA agonists, transferred RN7SL1 restricts myeloid-derived suppressor cell (MDSC) development, decreases TGFB in myeloid cells, and fosters dendritic cell (DC) subsets with costimulatory features. Consequently, endogenous effector-memory and tumor-specific T cells also expand, allowing rejection of solid tumors with CAR antigen loss. Supported by improved endogenous immunity, CAR-T cells can now co-deploy peptide antigens with RN7SL1 to enhance efficacy, even when heterogenous CAR antigen tumors lack adequate neoantigens.

Opposing Functions of Interferon Coordinate Adaptive and Innate Immune Responses to Cancer Immune Checkpoint Blockade.

Interferon-gamma (IFNG) augments immune function yet promotes T cell exhaustion through PDL1. How these opposing effects are integrated to impact immune checkpoint blockade (ICB) is unclear. We show that while inhibiting tumor IFNG signaling decreases interferon-stimulated genes (ISGs) in cancer cells, it increases ISGs in immune cells by enhancing IFNG produced by exhausted T cells (TEX). In tumors with favorable antigenicity, these TEX mediate rejection. In tumors with neoantigen or MHC-I loss, TEX instead utilize IFNG to drive maturation of innate immune cells, including a PD1+TRAIL+ ILC1 population. By disabling an inhibitory circuit impacting PD1 and TRAIL, blocking tumor IFNG signaling promotes innate immune killing. Thus, interferon signaling in cancer cells and immune cells oppose each other to establish a regulatory relationship that limits both adaptive and innate immune killing. In melanoma and lung cancer patients, perturbation of this relationship is associated with ICB response independent of tumor mutational burden.

Epitope-Specific Vaccination Limits Clonal Expansion of Heterologous Naive T Cells during Viral Challenge.

Despite robust secondary T cell expansion primed by vaccination, the impact on primary immune responses to heterotypic antigens remains undefined. Here we show that secondary expansion of epitope-specific memory CD8+ T cells primed by prior infection with recombinant pathogens limits the primary expansion of naive CD8+ T cells with specificity to new heterologous antigens, dampening protective immunity against subsequent pathogen challenge. The degree of naive T cell repression directly paralleled the magnitude of the recall response. Suppressed primary T cell priming reflects competition for antigen accessibility, since clonal expansion was not inhibited if the primary and secondary epitopes were expressed on different dendritic cells. Interestingly, robust recall responses did not impact antigen-specific NK cells, suggesting that adaptive and innate lymphocyte responses possess different activation requirements or occur in distinct anatomical locations. These findings have important implications in pathogen vaccination strategies that depend on the targeting of multiple T cell epitopes.

BNIP3- and BNIP3L-Mediated Mitophagy Promotes the Generation of Natural Killer Cell Memory.

Natural killer (NK) cells are innate lymphocytes that possess traits of adaptive immunity, such as clonal expansion, contraction, and generation of long-lived "memory" cells, processes poorly understood at the molecular level. Here, we found that as proliferating NK cells accumulated dysfunctional mitochondria during viral infection, a protective mitophagy pathway was induced during the contraction phase to promote their survival in a reactive oxygen species (ROS)-dependent manner. Inhibition of mechanistic target of rapamycin (mTOR) or activation of AMP-activated protein kinase (AMPK) during the contraction-to-memory phase transition of the antiviral response increased autophagic activity and enhanced memory NK cell numbers through an Atg3-dependent mechanism. Furthermore, we demonstrated a temporally regulated role for mitophagy-inducing proteins BCL2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3) and BNIP3-like (BNIP3L) in the generation of robust NK cell memory. Thus, our study reveals the functional importance of mitophagy during the dynamic response of these cytolytic innate lymphocytes.