Preclinical evaluation of anti-ROR1 CAR T cells employing a ROR1 binding SCFV derived from the clinical stage mab cirmtuzumab

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Background: Chimeric antigen receptor (CAR)-modified T cells (CAR-T) were generated targeting cells expressing ROR1, which is present on many malignant cancers and has been associated with cancer stemness and chemo-resistance. The ROR1 CAR utilizes the humanized single-chain fragment variable (scFv) binding domain of UC-961 (cirmtuzumab), which exhibits high affinity and specificity for human ROR1 and has demonstrated an excellent safety profile in Phase 1 studies. Methods: CAR constructs with varying spacer regions and intracellular co-stimulatory domains, using the scFV of cirmtuzumab, were constructed and used to generate CAR-T cells from healthy donors. These ROR1 CAR-T cells were tested for cytotoxicity against lymphoid cancer cells in vitro and in vivo studies that employed immune-deficient mice engrafted with labeled human leukemia cells MEC1 or MEC1-ROR1, which had been transfected to stably express ROR1. Results: The 2nd generation and 3rd generation CAR-T-cells with analogous spacer regions were comparably potent and selectively cytotoxic for cells bearing the ROR1 target antigen. But the 2nd generation CARs demonstrated greater potency in vitro even at low effector to target ratios. For the in vivo studies, mice received a single injection of ROR1 CAR-T cells or activated T cells from the same donor as a control. The ROR1 CAR-T cells rapidly cleared the leukemic cells from the animals, whereas animals receiving control T cells or no therapy quickly succumbed to progressive disease within 3 weeks. The administered CAR-T products remained highly active following administration and could be detected for ≥ 3 months without evidence for T cell exhaustion. Conclusions: The generated CAR-T cells utilizing constructs with the Fv of cirmtuzumab, a humanized mAb highly specific for ROR1, onco-embryonic surface antigen, effectively and selectively killed neoplastic cells bearing ROR1 both in vitro and in vivo. As ROR1 expression and signaling has been associated with cancer stemness and chemo-resistance utilizing ROR1 CAR-T therapy to target cancer cells might mitigate tumor escape. These data strongly support the rationale for continued development of our ROR1 CAR-T.

Phase I Trial: Cirmtuzumab Inhibits ROR1 Signaling and Stemness Signatures in Patients with Chronic Lymphocytic Leukemia

Cirmtuzumab is a humanized monoclonal antibody (mAb) that targets ROR1, an oncoembryonic orphan receptor for Wnt5a found on cancer stem cells (CSCs). Aberrant expression of ROR1 is seen in many malignancies and has been linked to Rho-GTPase activation and cancer stem cell self-renewal. For patients with chronic lymphocytic leukemia (CLL), self-renewing, neoplastic B cells express ROR1 in 95% of cases. High-level leukemia cell expression of ROR1 is associated with an unfavorable prognosis. We conducted a phase 1 study involving 26 patients with progressive, relapsed, or refractory CLL. Patients received four biweekly infusions, with doses ranging from 0.015 to 20 mg/kg. Cirmtuzumab had a long plasma half-life and did not have dose-limiting toxicity. Inhibition of ROR1 signaling was observed, including decreased activation of RhoA and HS1. Transcriptome analyses showed that therapy inhibited CLL stemness gene expression signatures in vivo. Cirmtuzumab is safe and effective at inhibiting tumor cell ROR1 signaling in patients with CLL.

CD40-ligand (CD154) gene therapy for chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) cells can be made to express recombinant CD40-ligand (CD154) by transduction with a replication-defective adenovirus vector (Ad-CD154). Ad-CD154-transduced and bystander leukemia cells become highly effective antigen-presenting cells that can induce CLL-specific autologous cytotoxic T lymphocytes in vitro. This study investigated the immunologic and clinical responses to infusion of autologous Ad-CD154-CLL cells in patients with CLL. After a one-time bolus infusion of autologous Ad-CD154-transduced leukemia cells, there was increased or de novo expression of immune accessory molecules on bystander, noninfected CLL cells in vivo. Treated patients also developed high plasma levels of interleukin-12 and interferon-gamma, the magnitudes of which corresponded to absolute blood CD4(+) T-cell counts before therapy. On average, patients experienced a greater than 240% increase in absolute blood T-cell counts within 1 to 4 weeks of treatment. Moreover, treatment increased the numbers of leukemia-specific T cells, demonstrated by autologous ELISPOT assay and mixed lymphocyte reactions. These biologic effects were associated with reductions in leukemia cell counts and lymph node size. Treatment did not induce autoimmune thrombocytopenia or hemolytic anemia and no dose-limiting toxicity was observed. This approach may provide a novel and effective form of gene therapy for patients with this disease.

Cytotoxic T-lymphocyte induction in asymptomatic HIV-1-infected patients immunized with Retrovector-transduced autologous fibroblasts expressing HIV-1IIIB Env/Rev proteins

OBJECTIVE

To demonstrate the safety and enhancement of HIV-1-specific immune responses in HIV-infected asymptomatic patients following treatment with retroviral vector (Retrovector)-transduced autologous fibroblasts (VTAF) expressing HIV-1IIIB Env/Rev proteins.

DESIGN

A non-placebo-controlled, single arm Phase I study.

PARTICIPANTS

Four HIV-1-seropositive asymptomatic volunteers were selected based on age (18-50 years), CD4/CD3 lymphocyte counts (> 600 x 10(6)/l or > 40%), and positive delayed-type hypersensitivity test to at least one recall antigen.

INTERVENTIONS

Patients were treated at 2-week intervals with a total of three intramuscular injections of irradiated autologous fibroblasts transduced with a molecularly engineered, non-replicating amphotropic murine retrovector encoding the HIV-1IIIB Env/Rev proteins.

MAIN OUTCOME MEASURES

The clinical status of patients was assessed by history, physical examination, serum chemistry and hematology, CD4/CD3 lymphocyte counts, HIV viral burden, and monitored throughout the study to detect potentially treatment-induced toxic or unwanted side-effects. In addition, HIV-1-specific cytotoxic T-lymphocyte (CTL) activity was measured to determine the biological activity of VTAF.

RESULTS

No acute local or systemic adverse events occurred following three injections with VTAF. Furthermore, a statistically significant increase of CD8+ CTL activity against HIV-1IIIB Env/Rev-expressing targets was observed in peripheral blood mononuclear cells from two out of four patients.

CONCLUSIONS

This is the first report of the administration of a gene transfer treatment to HIV-1-infected patients and provides initial support for the safety and activity of retrovector-transduced fibroblasts administered to asymptomatic patients. This treatment resulted in the detection of increased HIV-1IIIB Env/Rev-specific CTL activity in two HIV-seropositive patients and could provide a better understanding of the role of CTL activity in HIV disease progression.

Primase p49 mRNA expression is serum stimulated but does not vary with the cell cycle

Expression of the small-subunit p49 mRNA of primase, the enzyme that synthesizes oligoribonucleotides for initiation of DNA replication, was examined in mouse cells stimulated to proliferate by serum and in growing cells. The level of p49 mRNA increased approximately 10-fold after serum stimulation and preceded synthesis of DNA and histone H3 mRNA by several hours. Expression of p49 mRNA was not sensitive to inhibition by low concentrations of cycloheximide, which suggested that the increase in mRNA occurred before the restriction point control for cell cycle progression described for mammalian cells and was not under its control. p49 mRNA levels were not coupled to DNA synthesis, as observed for the replication-dependent histone genes, since hydroxyurea or aphidicolin had no effect on p49 mRNA levels when added before or during S phase. These inhibitors did have an effect, however, on the stability of p49 mRNA and increased the half-life from 3.5 h to about 20 h, which suggested an interdependence of p49 mRNA degradation and DNA synthesis. When growing cells were examined after separation by centrifugal elutriation, little difference was detected for p49 mRNA levels in different phases of the cell cycle. This was also observed when elutriated G1 cells were allowed to continue growth and then were blocked in M phase with colcemid. Only a small decrease in p49 mRNA occurred, whereas H3 mRNA rapidly decreased, when cells entered G2/M. These results indicate that the level of primase p49 mRNA is not cell cycle regulated but is present constitutively in proliferating cells.

Peptide production from proteins separated by sodium dodecyl-sulfate polyacrylamide gel electrophoresis

The development of amino acid sequencers with subnanomolar sensitivities has increased the need for both selective and highly efficient methods for both protein and peptide isolation. In this paper, we describe a simple procedure that utilizes the high resolving capacity of polyacrylamide gel electrophoresis to isolate a single target polypeptide, which can subsequently be subjected to proteolytic digestion and sequencing. Polypeptides are visualized in polyacrylamide gels as dodecyl sulfate/protein complexes, which are passively diffused from gel slices. Free dodecyl sulfate eluted with the protein solution is removed by KCl precipitation, allowing protein digestion with small amounts of trypsin or other proteolytic enzymes. Following enzymatic digestion, the peptide solution is made 6 M guanidine-HCl to remove interfering contaminants and thereby improve resolution of the digest by reverse-phase high-performance liquid chromatography. The peptides generated by this method are suitable for amino acid sequencing with good overall yields, averaging 15-30% on a gas-phase sequenator. The method described is useful for obtaining multiple peptide sequences from a single polypeptide isolated from a complex protein mixture.

DNA polymerase alpha activity is not affected by protein kinases or alkaline phosphatase

Recent studies with crude or partially purified cell extracts have suggested that DNA polymerase alpha activity may be regulated by enzymatic phosphorylation. To further investigate these findings, we have examined the effects of protein kinases and phosphatases on highly purified DNA polymerase alpha from mouse cells. Incubation of DNA polymerase alpha with a variety of protein kinases, including protein kinase C, had no effect on polymerase activity. In addition, treatment of the polymerase with soluble calf intestinal alkaline phosphatase had no effect on DNA polymerase alpha activity, further indicating that phosphorylation does not have a direct role in modulating polymerase activity. In contrast, incubation of DNA polymerase alpha with calf intestinal alkaline phosphatase crosslinked to agarose beads resulted in a time dependent disappearance of polymerase activity. This loss of DNA polymerase activity was dependent on phosphatase activity, as the alkaline phosphatase inhibitors, potassium phosphate or levamisole, prevented the loss of polymerase activity in the presence of the beaded phosphatase. The loss of DNA polymerase alpha activity following beaded phosphatase treatment was not a general phenomena as the large fragment of Escherichia coli DNA polymerase I, T4 DNA polymerase or mouse primase were not affected by similar treatment. The decreased DNA polymerase activity following incubation with phosphatase beads correlated with the binding of the DNA polymerase polypeptides, p185 and p68, to the agarose beads and this binding could not be reversed by either 150 mM potassium chloride or sodium sulfate. The binding of the polymerase to the agarose beads was dependent on the phosphatase activity, as the polymerase could be first treated with soluble calf intestinal phosphatase and subsequently bound to added Sepharose 4B beads. Surprisingly, Sepharose CL4B, a highly desulfated agarose preparation, did not bind the phosphatase-treated polymerase suggesting that sulfated polysaccharides are required for polymerase binding. The physiological correlate of this binding is unknown, but it has been reported that sulfated polysaccharides exist in a variety of intracellular compartments. It would be interesting to speculate that phosphorylation controls the intracellular compartmentalization of DNA polymerase alpha.

Mouse primase p49 subunit molecular cloning indicates conserved and divergent regions

Primase is a specialized RNA polymerase that synthesizes RNA primers for initiation of DNA synthesis. A full cDNA clone of the p49 subunit of mouse primase, a heterodimeric enzyme, has been isolated using a primase p49-specific polyclonal antibody to screen a lambda gt11 mouse cDNA expression library. The cDNA indicated the subunit is a 417-amino acid polypeptide with a calculated molecular mass of 49,295 daltons. The p49 mRNA is approximately 1500 nucleotides long with a 5'-untranslated region of 74 nucleotides and a 3'-untranslated region of 200 nucleotides. Comparison with a similar sized primase subunit from yeast showed highly conserved amino acid sequences in the N-terminal halves of the polypeptides and included a potential metal-binding domain suggesting the functional importance of this region for DNA binding. In contrast, the 3' portion of the cDNA has rapidly diverged in nucleotide sequence, as primase mRNA can be detected in mouse and rat cells with a 3' probe (including coding and noncoding) but not in RNA from hamster or human cells. A full-length cDNA probe detected mRNA from hamster and human cell lines, indicating a conserved 5' portion and divergent 3' region of the expressed gene. The rapid divergence may be related to the species-specific protein interactions found for the DNA polymerase alpha-primase complex. The mRNA is detected in proliferating but not in quiescent cells consistent with its function in DNA replication.

Sequence and structural requirements for primase initiation in the SV40 origin of replication

Primase synthesizes decaribonucleotides for priming of lagging and possibly leading strand synthesis at a replication fork. The sites of initiation by purified mouse primase were shown to be highly specific within the SV40 origin of replication. This study further examines the role of the 27-bp inverted repeat in the origin for initiation. A site is observed on the L-strand template at nucleotide position (np) 22 positioned a similar distance from the 27-bp inverted repeat as sites previously reported on the E-strand. The initiations adjacent to the 27-bp repeat have a higher Km for rATP than other sites. A deletion within the inverted repeat eliminated initiation at sites proximal to the hairpin on both E and L strands but had no effect at more distant sites. A deletion mutant which left the inverted repeat intact but deleted the initiation sites at np 5210-5220 on the E-strand was not active as a template for proximal sites. These results indicate that primase has two modes of recognition, one that requires the SV40 inverted repeat structure and a specific sequence and another that requires sequence alone. Additional regions of the SV40 genome have also been examined and of approximately 2000 nucleotides of single stranded template examined, only one additional site was observed at np 2412 on the E-strand. This indicates that primase initiations are highly specific for the SV40 origin and their potential functional role is discussed.

Isolation of the DNA polymerase alpha core enzyme from mouse cells

DNA polymerase alpha has been purified from mouse hybridoma cells approximately 30,000-fold using a combination of conventional and high performance liquid chromatography. In contrast to previous characterizations of mammalian DNA polymerase alpha, this enzyme has a single high molecular mass polypeptide (185 kDa) in tight association with a 68-kDa polypeptide and this structure appears to be the core DNA polymerase of the mouse cells. The biochemically purified enzyme, with a specific activity of approximately 200,000 units/mg protein, has an estimated molecular mass by gel filtration chromatography of 240 kDa and sedimentation value of 9 S, consistent with the enzyme being a heterodimer of 185 and 68 kDa. The enzyme is sensitive to both N-ethylmaleimide and aphidicolin and insensitive to ddTTP. Using an activated DNA template, the apparent Km values for the deoxynucleotide triphosphates are approximately 0.5-1 microM. The purified DNA polymerase has neither exonuclease nor primase activities and is the predominant DNA polymerase alpha activity in the mouse cells.

The formation of radiolabeled N1- and N8-acetylspermidine in various rat organs following [14C]spermidine administration

To detect the in vivo formation of acetylspermidine, three female Sprague-Dawley rats were injected intravenously with 20 muCi of [14C]spermidine. Twenty-four hours after the injection of the radiolabel, the kidneys, liver, lungs, pancreas, small intestine, spleen, stomach and thymus were removed under Halothane anesthesia. High performance liquid chromatography (HPLC) of the pooled radiolabeled extracts from each tissue demonstrated the presence of a 14C-labeled material which co-chromatographed with an acetylspermidine standard. Thin layer chromatography (TLC) of the HPLC eluent demonstrated the presence of both radiolabeled N1- and N8-acetylspermidine in the tissues. Concentrations of labeled acetylspermidine ranged from 0.27 to 1.9% of the total tissue radiolabel. The N1-to N8-acetylspermidine ratio in tissues ranged from approx. 5 to 1 in the thymus to 1.5 to 1 in the liver.

Single-step high-performance liquid chromatographic method for the analysis of acetylated polyamines

A high-performance liquid chromatography method for the determination of urinary acetyl derivatives of the polyamines putrescine, cadaverine and spermidine is described. This procedure utilizes an ion-exchange column for the separation of acetyl derivatives and the compounds are quantitated by fluorescence after reaction with o-phthalaldehyde. The steps necessary for sample preparation are minimized, and the assay is both sensitive and reproducible. This chromatographic procedure was used for the determination of the urinary acetylated polyamines of seven normal volunteers and three cancer patients.