Granzyme F: Exhaustion Marker and Modulator of Chimeric Antigen Receptor T Cell-Mediated Cytotoxicity.

Granzymes are a family of proteases used by CD8 T cells to mediate cytotoxicity and other less-defined activities. The substrate and mechanism of action of many granzymes are unknown, although they diverge among the family members. In this study, we show that mouse CD8+ tumor-infiltrating lymphocytes (TILs) express a unique array of granzymes relative to CD8 T cells outside the tumor microenvironment in multiple tumor models. Granzyme F was one of the most highly upregulated genes in TILs and was exclusively detected in PD1/TIM3 double-positive CD8 TILs. To determine the function of granzyme F and to improve the cytotoxic response to leukemia, we constructed chimeric Ag receptor T cells to overexpress a single granzyme, granzyme F or the better-characterized granzyme A or B. Using these doubly recombinant T cells, we demonstrated that granzyme F expression improved T cell-mediated cytotoxicity against target leukemia cells and induced a form of cell death other than chimeric Ag receptor T cells expressing only endogenous granzymes or exogenous granzyme A or B. However, increasing expression of granzyme F also had a detrimental impact on the viability of the host T cells, decreasing their persistence in circulation in vivo. These results suggest a unique role for granzyme F as a marker of terminally differentiated CD8 T cells with increased cytotoxicity, but also increased self-directed cytotoxicity, suggesting a potential mechanism for the end of the terminal exhaustion pathway.

Outcomes of Critically Ill Children With Acute Lymphoblastic Leukemia and Cytokine Release Syndrome Due to Chimeric Antigen Receptor T Cell Therapy: US, Multicenter PICU, Cohort Database Study.

OBJECTIVES: Cytokine release syndrome (CRS) is a potentially lethal toxicity associated with chimeric antigen receptor T cell therapy for pediatric acute lymphoblastic leukemia (ALL). Outcomes after critical illness due to severe CRS are poorly described. Our aim was to characterize critical illness outcomes across a multicenter cohort of PICU patients with ALL and CRS. DESIGN: Multicenter retrospective cohort study. SETTING: Twenty-one PICUs contributing data to Virtual Pediatric Systems, LLC (January 2020-December 2021). PATIENTS: PICU patients with ALL or unclassified leukemia and CRS. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We identified 55 patients; 34 (62%) were 12 years or older, 48 (87%) were admitted from a hospital inpatient ward, and 23 (42%) received advanced organ failure support or monitoring. Fifty-one survived to PICU discharge (93%) including 19 of 23 (83%) who received advanced organ failure support or monitoring defined as receipt of noninvasive or invasive ventilation, cardiopulmonary resuscitation, extracorporeal membrane oxygenation, continuous renal replacement therapy, or placement of a tracheostomy, arterial catheter, hemodialysis catheter, or intracranial catheter. Twelve patients (22%) received invasive ventilation, nine of whom survived to PICU discharge. Two of four patients who received continuous renal replacement therapy and one of three patients who required cardiopulmonary resuscitation survived to PICU discharge. Lengths of PICU stay were median 3.0 days (interquartile range, 1.4-7.8 d) among PICU survivors, 7.8 (5.4-11.1) among those receiving advanced organ failure support or monitoring, and 7.2 days (interquartile range, 2.9-14.7 d) among nonsurvivors. Of the 51 patients who survived to PICU discharge, 48 (94%) survived the hospitalization. CONCLUSIONS: PICU patients with CRS frequently received a high level of support, and the majority survived their PICU stay and hospitalization. Additional multicenter investigations of severe CRS are necessary to inform evidence-based practice.

Does lineage plasticity enable escape from CAR-T cell therapy? Lessons from MLL-r leukemia.

The clinical success of engineered, CD19-directed chimeric antigen receptor (CAR) T cells in relapsed, refractory B-cell acute lymphoblastic leukemia (B-ALL) has generated great enthusiasm for the use of CAR T cells in patients with cytogenetics that portend a poor prognosis with conventional cytotoxic therapies. One such group includes infants and children with mixed lineage leukemia (MLL1, KMT2A) rearrangements (MLL-r), who fare much worse than patients with low- or standard-risk B-ALL. Although early clinical trials using CD19 CAR T cells for MLL-r B-ALL produced complete remission in most patients, relapse with CD19-negative disease was a common mechanism of treatment failure. Whereas CD19neg relapse has been observed across a broad spectrum of B-ALL patients treated with CD19-directed therapy, patients with MLL-r have manifested the emergence of AML, often clonally related to the B-ALL, suggesting that the inherent heterogeneity or lineage plasticity of MLL-r B-ALL may predispose patients to a myeloid relapse. Understanding the factors that enable and drive myeloid relapse may be important to devise strategies to improve durability of remissions. In this review, we summarize clinical observations to date with MLL-r B-ALL and generally discuss lineage plasticity as a mechanism of escape from immunotherapy.