Influence of ATLG serum levels on CD3/CD19-depleted hematopoietic grafts and on immune recovery in pediatric haplo-HSCT

ABSTRACT

Anti-T lymphocyte globulin (ATLG) significantly reduces the risk of engraftment failure in allogeneic hematopoietic stem cell transplant (HSCT) but hampers posttransplant immune reconstitution. We hypothesized that in patients receiving haploidentical CD3/CD19-depleted grafts, these double-edged effects could be better balanced by attaining high ATLG serum concentrations before transplant but as low as possible on the day of transplant. Therefore, we moved the start of ATLG application to day -12 and determined serum concentrations of T-cell-specific ATLG in pediatric patients treated with 3 established dosing regimens (15, 30, or 60 mg/kg). Corresponding mean T-cell-specific ATLG serum concentrations at day 0 were 1.14, 2.99, or 12.10 μg/mL, respectively. Higher ATLG doses correlated with higher peak levels at days -8 and -7 and reduced graft rejection, whereas lower ATLG doses correlated with significantly faster posttransplant recovery of T and natural killer cells. The rate of graft-versus-host disease remained low, independent of ATLG doses. Moreover, in vitro assays showed that ATLG concentrations of 2.0 μg/mL and lower only slightly reduced the activity of natural killer cells, and therefore, the function of such effector cells might be preserved in the grafts. Pharmacokinetic analysis, compatible with linear first-order kinetics, revealed similar half-life values, independent of ATLG doses. Hence, the day on which a desired ATLG serum level is reached can be calculated before HSCT. Our retrospective study demonstrates the relevance of dosing and time of administration of ATLG on engraftment and immune recovery in ex vivo CD3/CD19-depleted haploidentical HSCT.

Catumaxomab: Pharmacodynamic and pharmacokinetic data from phase IIIb CASIMAS study in patients with malignant ascites

e13108^

Background: Catumaxomab (anti-EpCAM x anti-CD3) is approved in the EU for the i.p. locoregional treatment of malignant ascites (MA). The peritoneal cavity invaded by epithelial tumor cells provides an environment for tumor-specific, EpCAM-targeted catumaxomab immunotherapy. In order to monitor the local and systemic pharmacodynamic/ pharmacokinetic (PD/PK) profile of catumaxomab, plasma and ascites samples from patients in the CASIMAS study were investigated. Methods: Plasma and ascites samples were collected in patients prior, during and after catumaxomab i.p. infusions. Samples were analysed for a) Selected cytokines (IL-2, -4, -6, -8, -10, and -12, IFN-gamma, TNF-alpha, and GM-CSF) in 20 patients, b) catumaxomab drug levels in 31 patients (14 patients with MA who received all 4 infusions of 10, 20, 50, and 150 µg were evaluable for systemic PK analysis), c) number of EpCAM+ tumor cells in ascites in 11 patients. Results: Drug levels were highest in ascites fluid ranging from 0 to 219.4 ng/mL at day 10 (n=31/31 patients). Low systemic plasma levels were detected in 7/14 patients (median cmax: 623 pg/mL). In 7/14 subjects no catumaxomab was detected systemically. Furthermore, cytokine concentrations in ascites were higher compared to plasma. Mainly IL-6, -8 & -10 and IFN-gamma were detected; in few cases TNF-alpha and IL-2. Whereas IL-4, -12, and GM-CSF were not detected at all. Anti-tumor activity was proven by i.p. tumor cell elimination. Tumor cell count in ascites dropped markedly below baseline. In the majority (7/11) of patients no EpCAM+ tumor cells were detectable after therapy. Before therapy, in 165/166 evaluable patient samples EpCAM+ tumor cells were detected in the ascites fluid. Conclusions: Catumaxomab represents a locoregional immunological i.p. treatment eliminating tumor cells in the peritoneal cavity and thereby effectively controlling MA. Catumaxomab primarily remains in the peritoneal cavity with low systemic exposure. In line with this, cytokines are mainly released locally, at the site of action. These PD/PK results confirm the results obtained in the pivotal phase II/III study.

Protein scaffold and expression level determine antiviral activity of membrane-anchored antiviral peptides

Cell membrane-anchored (ma) antiviral peptides derived from the C-terminal heptad repeat of the HIV-1 transmembrane glycoprotein gp41 (C-peptides) and expressed from retroviral vectors were shown to efficiently inhibit HIV-1 entry into target cells. Here, we analyzed the influence of the vector backbone, the scaffold modules that anchor the peptide to the membrane and the length of the C-peptide on expression level and antiviral activity. In general, antiviral activity was determined primarily by the density of the C-peptide on the cell surface. By influencing expression levels, the scaffold elements indirectly also determined antiviral activity. Additional direct effects of the scaffold on antiviral activity were minor. At comparable expression levels, the elongated C-peptide (maC46) was found to be more potent than the shorter maC36. On the basis of these findings, a dose-response assay was established that quantifies antiviral activity relative to the expression level of the antiviral gene product. Taken together, these data demonstrate the importance of analyzing the efficacy of therapeutic genes relative to the dose of the gene product.

Transfer of Autologous Gene-modified T Cells in HIV-infected Patients with Advanced Immunodeficiency and Drug-resistant Virus

Drug toxicity and viral resistance limit the long-term efficacy of antiviral drug treatment for human immunodeficiency virus (HIV) infection. Thus, alternative therapies need to be explored. We tested the infusion of T lymphocytes transduced with a retroviral vector (M87o) that expresses an HIV entry-inhibitory peptide (maC46). Gene-modified autologous T cells were infused into ten HIV-infected patients with advanced disease and multidrug-resistant virus during anti-retroviral combination therapy. T-cell infusions were tolerated well, with no severe side effects. A significant increase of CD4 counts was observed after infusion. At the end of the 1-year follow-up, the CD4 counts of all patients were still around or above baseline. Gene-modified cells could be detected in peripheral blood, lymph nodes, and bone marrow throughout the 1-year follow-up, and marking levels correlated with the cell dose. No significant changes of viral load were observed during the first 4 months. Four of the seven patients who changed their antiviral drug regimen thereafter responded with a significant decline in plasma viral load. In conclusion, the transfer of gene-modified cells was safe, led to sustained levels of gene marking, and may improve immune competence in HIV-infected patients with advanced disease and multidrug-resistant virus.

Inhibition of human immunodeficiency virus type 1 entry in cells expressing gp41-derived peptides

As the limitations of antiretroviral drug therapy, such as toxicity and resistance, become evident, interest in alternative therapeutic approaches for human immunodeficiency virus (HIV) infection is growing. We developed the first gene therapeutic strategy targeting entry of a broad range of HIV type 1 (HIV-1) variants. Infection was inhibited at the level of membrane fusion by retroviral expression of a membrane-anchored peptide derived from the second heptad repeat of the HIV-1 gp41 transmembrane glycoprotein. To achieve maximal expression and antiviral activity, the peptide itself, the scaffold for presentation of the peptide on the cell surface, and the retroviral vector backbone were optimized. This optimized construct effectively inhibited virus replication in cell lines and primary blood lymphocytes. The membrane-anchored C-peptide was also shown to bind to free gp41 N peptides, suggesting that membrane-anchored antiviral C peptides have a mode of action similar to that of free gp41 C peptides. Preclinical toxicity and efficacy studies of this antiviral vector have been completed, and clinical trials are in preparation.