The clinical success of chimeric antigen receptor (CAR) T cell therapy for CD19 B cell malignancies can be limited by acute toxicities and immunoglobulin replacement needs due to B cell aplasia from persistent CAR T cells. Life-threatening complications include cytokine release syndrome and neurologic adverse events, the exact etiologies of which are unclear. To elucidate the underlying toxicity mechanisms and test potentially safer CAR T cells, we developed a mouse model in which human CD19 (hCD19)-specific mouse CAR T cells were adoptively transferred into mice whose normal B cells express a hCD19 transgene at hemizygous levels. Compared to homozygous hCD19 transgenic mice that have ∼75% fewer circulating B cells, hemizygous mice had hCD19 frequencies and antigen density more closely simulating human B cells. Hemizygous mice given a lethal dose of hCD19 transgene-expressing lymphoma cells and treated with CAR T cells had undetectable tumor levels. Recipients experienced B cell aplasia and antigen- and dose-dependent acute toxicities mirroring patient complications. Interleukin-6 (IL-6), interferon γ (IFN-γ), and inflammatory pathway transcripts were enriched in affected tissues. As in patients, antibody-mediated neutralization of IL-6 (and IFN-γ) blunted toxicity. Apparent behavioral abnormalities associated with decreased microglial cells point to CAR-T-cell-induced neurotoxicity. This model will prove useful in testing strategies designed to improve hCD19-specific CAR T cell safety.

A series of zerovalent group VI metal complexes of tris(diisopropylphosphinomethyl)phenylborate ([PhB(CH2PiPr2)3]-, PhBPiPr3), including [PPN][M(CO)3(PhBPiPr3)] (M = Cr, Mo, W) and the first bimetallics in which PhBPiPr3 serves as a bridging ligand via binding M(CO)3 units at the three phosphorus atoms and the borate phenyl substituent, have been synthesized and fully characterized. Two new tris(phosphinomethyl)borates featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents were prepared as crystallographically characterized thallium salts, and metallated giving their inaugural transition metal complexes [PPN][M(CO)3(((3,5-Me)C6H3)BPPh3)] and [PPN][M(CO)3(((3,5-CF3)C6H3)BPPh3)]. A comparative ν(CO) infrared spectroscopic analysis and examination of half wave potentials assessed by cyclic voltammetry supports a ligand donor ranking of Tp > PhBPiPr3 ≥ Cp > PhBPPh3 > triphos. For these anionic complexes, in which a lower electrostatic contribution to zerovalent metal-PhBPR3 binding is likely operative relative to that present in the zwitterionic complexes most commonly prepared with tris(phosphinomethyl)borates, PhBPR3 ligands do not function as strongly donating scorpionates. Nevertheless, PhBPPh3 is a substantially stronger donor than triphos towards zerovalent M(CO)3; the half wave potentials of [Et4N][M(CO)3(PhBPPh3)] are ∼340 mV lower than those of M(CO)3(triphos). The potentials of the ((3,5-Me)C6H3)BPPh3 group VI metal tricarbonyl anions are more negative than those of the corresponding ((3,5-CF3)C6H3)BPPh3 group VI metal tricarbonyl anions by ∼50 mV, suggesting a modest, yet rational, tuning of PhBPPh3 donation via inductive modulation of the borate anion charge.

No abstract

Current Food and Drug Administration (FDA)-approved CD19-specific chimeric antigen receptor (CAR) T-cell therapies for B-cell malignancies are constitutively active and while efficacious, can cause morbidity and mortality. Their toxicities might be reduced if CAR T-cell activity was regulatable rather than constitutive. To test this, we compared the efficacies and morbidities of constitutively active (conventional) and regulatable (switchable) CAR (sCAR) T-cells specific for human CD19 (huCD19) in an immune-competent huCD19+transgenic mouse model.Conventional CAR (CAR19) and sCAR T-cells were generated by retrovirally transducing C57BL/6 (B6) congenic T-cells with constructs encoding antibody-derived single chain Fv (sFv) fragments specific for huCD19 or a peptide neoepitope (PNE), respectively. Transduced T-cells were adoptively transferred into huCD19 transgenic hemizygous (huCD19Tg/0) B6 mice; healthy B-cells in these mice expressedhuCD19Tg. Prior to transfer, recipients were treated with a lymphodepleting dose of cyclophosphamide to enhance T-cell engraftment. In tumor therapy experiments, CAR19 or sCAR T-cells were adoptively transferred intohuCD19Tg/0mice bearing a syngeneic B-cell lymphoma engineered to express huCD19. To regulate sCAR T cell function, a switch protein was generated that contained the sCAR-specific PNE genetically fused to an anti-huCD19 Fab fragment. Recipients of sCAR T-cells were injected with the switch to link sCAR effector with huCD19+target cells. Mice were monitored for survival, tumor burden (where appropriate), morbidity (as measured by weight loss and clinical scores), and peripheral blood lymphocyte frequency.CAR19 and sCAR T-cells functioned comparably regarding in vivo expansion and B-cell depletion. However, sCAR T-cells were better tolerated as evidenced by the recipients’ enhanced survival, reduced weight loss, and improved clinical scores. Discontinuing switch administration allowed healthy B-cell frequencies to return to pretreatment levels.In our mouse model, sCAR T-cells killed huCD19+healthy and malignant B-cells and were better tolerated than CAR19 cells. Our data suggest sCAR might be clinically superior to the current FDA-approved therapies for B-cell lymphomas due to the reduced acute and chronic morbidities and mortality, lower incidence and severity of side effects, and B-cell reconstitution on cessation of switch administration.