Late-onset inflammatory toxicities resembling hemophagocytic lymphohistiocytosis (HLH) or macrophage activation syndrome (MAS) occur after chimeric antigen receptor T cell (CAR T cell) infusion and represent a therapeutic challenge. Given the established link between perforin deficiency and primary HLH, we investigated the role of perforin in anti-CD19 CAR T cell efficacy and HLH-like toxicities in a syngeneic murine model. Perforin contributed to both CD8⁺ and CD4⁺ CAR T cell cytotoxicity but was not required for in vitro or in vivo leukemia clearance. Upon CAR-mediated in vitro activation, perforin-deficient CAR T cells produced higher amounts of proinflammatory cytokines compared with WT CAR T cells. Following in vivo clearance of leukemia, perforin-deficient CAR T cells reexpanded, resulting in splenomegaly with disruption of normal splenic architecture and the presence of hemophagocytes, which are findings reminiscent of HLH. Notably, a substantial fraction of patients who received anti-CD22 CAR T cells also experienced biphasic inflammation, with the second phase occurring after the resolution of cytokine release syndrome, resembling clinical manifestations of HLH. Elevated inflammatory cytokines such as IL-1β and IL-18 and concurrent late CAR T cell expansion characterized the HLH-like syndromes occurring in the murine model and in humans. Thus, a murine model of perforin-deficient CAR T cells recapitulated late-onset inflammatory toxicities occurring in human CAR T cell recipients, providing therapeutically relevant mechanistic insights.

The relationship between cancer and autoimmunity is complex. However, the incidence of solid tumors such as melanoma has increased significantly among patients with previous or newly diagnosed systemic autoimmune disease (AID). At the same time, immune checkpoint blockade (ICB) therapy of cancer induces de novo autoinflammation and exacerbates underlying AID, even without evident antitumor responses. Recently, systemic lupus erythematosus (SLE) activity was found to drive myeloid-derived suppressor cell (MDSC) formation in patients, a known barrier to healthy immune surveillance and successful cancer immunotherapy. Cross-talk between MDSCs and macrophages generally drives immune suppressive activity in the tumor microenvironment. However, it remains unclear how peripheral pregenerated MDSC under chronic inflammatory conditions modulates global macrophage immune functions and the impact it could have on existing tumors and underlying lupus nephritis. Here we show that pathogenic expansion of SLE-generated MDSCs by melanoma drives global macrophage polarization and simultaneously impacts the severity of lupus nephritis and tumor progression in SLE-prone mice. Molecular and functional data showed that MDSCs interact with autoimmune macrophages and inhibit cell surface expression of CD40 and the production of IL27. Moreover, low CD40/IL27 signaling in tumors correlated with high tumor-associated macrophage infiltration and ICB therapy resistance both in murine and human melanoma exhibiting active IFNγ signatures. These results suggest that preventing global macrophage reprogramming induced by MDSC-mediated inhibition of CD40/IL27 signaling provides a precision melanoma immunotherapy strategy, supporting an original and advantageous approach to treat solid tumors within established autoimmune landscapes.Significance: Myeloid-derived suppressor cells induce macrophage reprogramming by suppressing CD40/IL27 signaling to drive melanoma progression, simultaneously affecting underlying autoimmune disease and facilitating resistance to immunotherapy within preexisting autoimmune landscapes.

The purpose of this study was to evaluate the effects of the route of administration on the immunogenicity and efficacy of a combined western, eastern, and Venezuelan equine encephalitis (WEVEE) virus-like replicon particle (VRP) vaccine in cynomolgus macaques. The vaccine consisted of equal amounts of WEEV, EEEV, and VEEV VRPs. Thirty-three animals were randomly assigned to five treatment or control groups. Animals were vaccinated with two doses of WEVEE VRPs or the control 28 days apart. Blood was collected 28 days following primary vaccination and 21 days following boost vaccination for analysis of the immune response to the WEVEE VRP vaccine. NHPs were challenged by aerosol 28 or 29 days following second vaccination with WEEV CBA87. Vaccination with two doses of WEVEE VRP was immunogenic and resulted in neutralizing antibody responses specific for VEEV, EEEV and WEEV. None of the vaccinated animals met euthanasia criteria following aerosol exposure to WEEV CBA87. However, one NHP control (total of 11 controls) met euthanasia criteria after infection with WEEV CBA87. Statistically significant differences in median fever hours were noted in control NHPs compared to vaccinated NHPs, providing a quantitative measure of infection and efficacy of the vaccine against a WEEV challenge. Alterations in lymphocytes, monocytes, and neutrophils were observed. Lymphopenia was observed in control NHPs.

Licensed antiviral therapeutics and vaccines to protect against eastern equine encephalitis virus (EEEV) in humans currently do not exist. Animal models that faithfully recapitulate the clinical characteristics of human EEEV encephalitic disease, including fever, drowsiness, anorexia, and neurological signs such as seizures, are needed to satisfy requirements of the Food and Drug Administration (FDA) for clinical product licensing under the Animal Rule. In an effort to meet this requirement, we estimated the median lethal dose and described the pathogenesis of aerosolized EEEV in the common marmoset (Callithrix jacchus). Five marmosets were exposed to aerosolized EEEV FL93-939 in doses ranging from 2.4 × 101 PFU to 7.95 × 105 PFU. The median lethal dose was estimated to be 2.05 × 102 PFU. Lethality was observed as early as day 4 post-exposure in the highest-dosed marmoset but animals at lower inhaled doses had a protracted disease course where humane study endpoint was not met until as late as day 19 post-exposure. Clinical signs were observed as early as 3 to 4 days post-exposure, including fever, ruffled fur, decreased grooming, and leukocytosis. Clinical signs increased in severity as disease progressed to include decreased body weight, subdued behavior, tremors, and lack of balance. Fever was observed as early as day 2–3 post-exposure in the highest dose groups and hypothermia was observed in several cases as animals became moribund. Infectious virus was found in several key tissues, including brain, liver, kidney, and several lymph nodes. Clinical hematology results included early neutrophilia, lymphopenia, and thrombocytopenia. Key pathological changes included meningoencephalitis and retinitis. Immunohistochemical staining for viral antigen was positive in the brain, retina, and lymph nodes. More intense and widespread IHC labeling occurred with increased aerosol dose. We have estimated the medial lethal dose of aerosolized EEEV and described the pathology of clinical disease in the marmoset model. The results demonstrate that the marmoset is an animal model suitable for emulation of human EEEV disease in the development of medical countermeasures.

Venezuelan equine encephalitis virus (VEEV) outbreaks occur sporadically. Additionally, VEEV has a history of development as a biothreat agent. Yet, no FDA-approved vaccine or therapeutic exists for VEEV disease. The sporadic outbreaks present a challenge for testing medical countermeasures (MCMs) in humans; therefore, well-defined animal models are needed for FDA Animal Rule licensure. The cynomolgus macaque (CM) model has been studied extensively at high challenge doses of the VEEV Trinidad donkey strain (>1.0 × 10⁸ plaque-forming units [PFU]), doses that are too high to be a representative human dose. Based on viremia of two subtypes of VEEV, IC, and IAB, we found the CM infectious dose fifty (ID₅₀) to be low, 12 PFU, and 6.7 PFU, respectively. Additionally, we characterized the pattern of three clinical parameters (viremia, temperature, and lymphopenia) across a range of doses to identify a challenge dose producing consistent signs of infection. Based on these studies, we propose a shift to using a lower challenge dose of 1.0 × 10³ PFU in the aerosol CM model of VEEV disease. At this dose, NHPs had the highest viremia, demonstrated a fever response, and had a measurable reduction in complete lymphocyte counts—biomarkers that can demonstrate MCM efficacy.

Venezuelan (VEE), eastern (EEE), and western (WEE) equine encephalitis viruses are encephalitic New World alphaviruses that cause periodic epizootic and epidemic outbreaks in horses and humans that may cause severe morbidity and mortality. Currently there are no FDA-licensed vaccines or effective antiviral therapies. Each year, there are a limited number of human cases of encephalitic alphaviruses; thus, licensure of a vaccine or therapeutic would require approval under the FDA animal rule. Approval under the FDA animal rule requires the disease observed in the animal model to recapitulate what is observed in humans. Currently, initial testing of vaccines and therapeutics is performed in the mouse model. Unfortunately, alphavirus disease manifestations in a mouse do not faithfully recapitulate human disease; the VEEV mouse model is lethal whereas in humans VEEV is rarely lethal. In an effort to identify a more appropriate small animal model, we evaluated hamsters in an aerosol exposure model of encephalitic alphavirus infection. The pathology, lethality, and viremia observed in the infected hamsters was inconsistent with what is observed in NHP models and humans. These data suggest that hamsters are not an appropriate model for encephalitic alphaviruses to test vaccines or potential antiviral therapies.