Perforin-deficient CAR T cells recapitulate late-onset inflammatory toxicities observed in patients

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.

JAK/STAT pathway inhibition sensitizes CD8 T cells to dexamethasone-induced apoptosis in hyperinflammation

Cytokine storm syndromes (CSS) are severe hyperinflammatory conditions characterized by excessive immune system activation leading to organ damage and death. Hemophagocytic lymphohistiocytosis (HLH), a disease often associated with inherited defects in cell-mediated cytotoxicity, serves as a prototypical CSS for which the 5-year survival is only 60%. Frontline therapy for HLH consists of the glucocorticoid dexamethasone (DEX) and the chemotherapeutic agent etoposide. Many patients, however, are refractory to this treatment or relapse after an initial response. Notably, many cytokines that are elevated in HLH activate the JAK/STAT pathway, and the JAK1/2 inhibitor ruxolitinib (RUX) has shown efficacy in murine HLH models and humans with refractory disease. We recently reported that cytokine-induced JAK/STAT signaling mediates DEX resistance in T cell acute lymphoblastic leukemia (T-ALL) cells, and that this could be effectively reversed by RUX. On the basis of these findings, we hypothesized that cytokine-mediated JAK/STAT signaling might similarly contribute to DEX resistance in HLH, and that RUX treatment would overcome this phenomenon. Using ex vivo assays, a murine model of HLH, and primary patient samples, we demonstrate that the hypercytokinemia of HLH reduces the apoptotic potential of CD8 T cells leading to relative DEX resistance. Upon exposure to RUX, this apoptotic potential is restored, thereby sensitizing CD8 T cells to DEX-induced apoptosis in vitro and significantly reducing tissue immunopathology and HLH disease manifestations in vivo. Our findings provide rationale for combining DEX and RUX to enhance the lymphotoxic effects of DEX and thus improve the outcomes for patients with HLH and related CSS.

CD8 T cell-derived perforin aggravates secondary spinal cord injury through destroying the blood-spinal cord barrier

Perforin plays an important role in autoimmune and infectious diseases, but its function in immune inflammatory responses after spinal cord injury (SCI) has received insufficient attention. The goal of this study is to determine the influence of perforin after spinal cord injury (SCI) on secondary inflammation. Compared recovery from SCI in perforin knockout (Prf1^-/-) and wild-type(WT)mice, WT mice had significantly lower the Basso mouse score (BMS), CatWalk XT, and motor-evoked potentials (MEPs) than Prf1^-/- mice. Spinal cord lesions were also more obvious through glial fibrillary acidic protein (GFAP), Nissl, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. Furthermore, the blood-spinal cord barrier (BSCB) disruption was more severe and inflammatory cytokine levels were higher. Flow cytometry indicated that perforin mainly originated from CD8 T cells. With flow cytometry and enzyme-linked immunosorbent assay (ELISA), human cerebrospinal fluid (CSF) yielded similar results. Together, this study firstly demonstrated that CD8 T cell-derived perforin is detrimental to SCI recovery in the mouse model. Mechanistically, this effect occurs because perforin increases BSCB permeability, causing inflammatory cells and related cytokines to infiltrate and disrupt the nervous system.

The specific NK cell response in concert with perforin prevents CD8(+) T cell-mediated immunopathology after mouse cytomegalovirus infection

Natural killer (NK) and CD8(+) T cells play a crucial role in the control of mouse cytomegalovirus (MCMV) infection. These effector cells exert their functions by releasing antiviral cytokines and by cytolytic mechanisms including perforin activation. In addition to their role in virus control, NK cells play an immunoregulatory role since they shape the CD8(+) T cell response to MCMV. To investigate the role of perforin-dependent cytolytic mechanism in NK cell modulation of CD8(+) T cell response during acute MCMV infection, we have used perforin-deficient C57BL/6 mice (Prf1(-/-)) and have shown that virus control by CD8(+) T cells in Prf1(-/-) mice is more efficient if NK cells are activated by the engagement of the Ly49H receptor with the m157 MCMV protein. A lack of perforin results in severe liver inflammation after MCMV infection, which is characterized by immunopathological lesions that are more pronounced in Prf1(-/-) mice infected with virus unable to activate NK cells. This immunopathology is caused by an abundant infiltration of activated CD8(+) T cells. The depletion of CD8(+) T cells has markedly reduced pathohistological lesions in the liver and improved the survival of Prf1(-/-) mice in spite of an increased viral load. Altogether, the results of our study suggest that a lack of perforin and absence of the specific activation of NK cells during acute MCMV infection lead to an unleashed CD8(+) T cell response that is detrimental for the host.

Destruction of lymphoid organ architecture and hepatitis caused by CD4+ T cells

Immune responses have the important function of host defense and protection against pathogens. However, the immune response also causes inflammation and host tissue injury, termed immunopathology. For example, hepatitis B and C virus infection in humans cause immunopathological sequel with destruction of liver cells by the host's own immune response. Similarly, after infection with lymphocytic choriomeningitis virus (LCMV) in mice, the adaptive immune response causes liver cell damage, choriomeningitis and destruction of lymphoid organ architecture. The immunopathological sequel during LCMV infection has been attributed to cytotoxic CD8(+) T cells. However, we now show that during LCMV infection CD4(+) T cells selectively induced the destruction of splenic marginal zone and caused liver cell damage with elevated serum alanin-transferase (ALT) levels. The destruction of the splenic marginal zone by CD4(+) T cells included the reduction of marginal zone B cells, marginal zone macrophages and marginal zone metallophilic macrophages. Functionally, this resulted in an impaired production of neutralizing antibodies against LCMV. Furthermore, CD4(+) T cells reduced B cells with an IgM(high)IgD(low) phenotype (transitional stage 1 and 2, marginal zone B cells), whereas other B cell subtypes such as follicular type 1 and 2 and germinal center/memory B cells were not affected. Adoptive transfer of CD4(+) T cells lacking different important effector cytokines and cytolytic pathways such as IFNγ, TNFα, perforin and Fas-FasL interaction did reveal that these cytolytic pathways are redundant in the induction of immunopathological sequel in spleen. In conclusion, our results define an important role of CD4(+) T cells in the induction of immunopathology in liver and spleen. This includes the CD4(+) T cell mediated destruction of the splenic marginal zone with consecutively impaired protective neutralizing antibody responses.

Modulation of peripheral cytotoxic cells and ictogenesis in a model of seizures

PURPOSE

A link between seizure susceptibility, blood-brain barrier (BBB) failure, and the activation of peripheral white blood cells has been recently proposed. However, the molecular players involved in this cascade of events are unknown. We tested the hypothesis that immunosupression by splenectomy or lack of perforin, a downstream factor of natural killer (NK) and cytotoxic T cells, could reduce seizure onset.

METHODS

Pilocarpine was used to induce seizures in adult rats wild-type and perforin-deficient mice. Splenectomy was performed prior to pilocarpine injection. Seizure onset was evaluated by electroencephalography (EEG) and joint time-frequency analysis. Spleens from control and pilocarpine-treated groups were analyzed for anatomical changes and CD3+ cell content. BBB damage was assessed by measuring albumin parenchymal extravasation. Fluorescence-activated cell sorting (FACS) analysis was performed on spleen and brain tissue of wild-type and perforin-deficient mice treated, or not, with pilocarpine.

KEY FINDINGS

Splenectomy significantly reduced seizure-associated mortality. Histologic analysis of the spleens exposed to pilocarpine revealed altered white and red pulp anatomy and an increase in CD3+ T cells. Onset of status epilepticus (SE) and mortality were significantly decreased in perforin-deficient mice. Pilocarpine significantly increased spleen NK 1.1 and CD8+ cell percentage; in contrast, the brain inflammatory cell profile remained unchanged at the time of pilocarpine SE. BBB damage was reduced in the perforin-deficient pilocarpine-treated mice.

SIGNIFICANCE

Immunosuppressant maneuvers such as splenectomy or lack of perforin decrease the onset or the severity of pilocarpine SE. Our results suggest that cytotoxic lymphocytes, and specifically the cytolytic factor perforin, may be key molecular players involved in the axis between peripheral intravascular inflammation and seizures.

CD8+ T cells cause disability and axon loss in a mouse model of multiple sclerosis

Background

The objective of this study was to test the hypothesis that CD8⁺ T cells directly mediate motor disability and axon injury in the demyelinated central nervous system. We have previously observed that genetic deletion of the CD8⁺ T cell effector molecule perforin leads to preservation of motor function and preservation of spinal axons in chronically demyelinated mice.

Methodology/Principal Findings

To determine if CD8⁺ T cells are necessary and sufficient to directly injure demyelinated axons, we adoptively transferred purified perforin-competent CD8⁺ spinal cord-infiltrating T cells into profoundly demyelinated but functionally preserved perforin-deficient host mice. Transfer of CD8⁺ spinal cord-infiltrating T cells rapidly and irreversibly impaired motor function, disrupted spinal cord motor conduction, and reduced the number of medium- and large-caliber spinal axons. Likewise, immunodepletion of CD8⁺ T cells from chronically demyelinated wildtype mice preserved motor function and limited axon loss without altering other disease parameters.

Conclusions/Significance

In multiple sclerosis patients, CD8⁺ T cells outnumber CD4⁺ T cells in active lesions and the number of CD8⁺ T cells correlates with the extent of ongoing axon injury and functional disability. Our findings suggest that CD8⁺ T cells may directly injure demyelinated axons and are therefore a viable therapeutic target to protect axons and motor function in patients with multiple sclerosis.

Mycobacterium tuberculosis-specific CD8+ T cells require perforin to kill target cells and provide protection in vivo

Optimal immunity to Mycobacterium tuberculosis (Mtb) infection requires CD8(+) T cells, and several current Mtb vaccine candidates are being engineered to elicit enhanced CD8(+) T cell responses. However, the function of these T cells and the mechanism by which they provide protection is still unknown. We have previously shown that CD8(+) T cells specific for the mycobacterial Ags CFP10 and TB10.4 accumulate in the lungs of mice following Mtb infection and have cytolytic activity in vivo. In this study, we determine which cytolytic pathways are used by these CD8(+) T cells during Mtb infection. We find that Mtb-specific CD8(+) T cells lacking perforin have reduced cytolytic capacity in vivo. In the absence of perforin, the residual cytolytic activity is CD95 and TNFR dependent. This is particularly true in Mtb-infected lung tissue where disruption of both perforin and CD95 eliminates target cell lysis. Moreover, adoptive transfer of immune CD8(+) T cells isolated from wild-type, but not perforin-deficient mice, protect recipient mice from Mtb infection. We conclude that CD8(+) T cells elicited following Mtb infection use several cytolytic pathways in a hierarchical and compensatory manner dominated by perforin-mediated cytolysis. Finally, although several cytolytic pathways are available, adoptively transferred Mtb-specific CD8(+) T cells require perforin-mediated cytolysis to protect animals from infection. These data show that CD8(+) T cell-mediated protection during Mtb infection requires more than the secretion of IFN-gamma and specifically defines the CD8(+) cytolytic mechanisms utilized and required in vivo.