Biomedical subjects

J M Derocq

Publications and source records attributed to J M Derocq.

24 records · Page 2Linked to original sources

PubMed1989

Effects of an anti HLA-DR immunotoxin on leukaemia cells and hematopoietic progenitors.

An anti HLA-class II immunotoxin has been prepared by coupling to ricin A-chain (RTA) and anti-DR-DP monoclonal antibody (2G5-MoAb). Protein synthesis inhibition assays showed that 2G5-RTA immunotoxin is: highly cytotoxic to B-cell lymphoid neoplastic cells, and variable so to ALL cells, while AML cell lines display a generally poor susceptibility. Toxicity of 2G5-RTA on normal hematopoietic cells (HPC) was found to be dose-dependent, and to increase significantly with the addition of NH4Cl, used as an activating agent. After 4 h of incubation with 2G5-RTA (10(-8) M), without NH4Cl, percentages of CFU-GM and CFU-GEMM (colony forming units-granulo-monocytes and -multipotent, respectively) progenitor cell recovery were in the order of 50% and 30% respectively. In the same treatment conditions, 2G5-RTA induced a 6 log kill on RAJI cells--measured by clonogenic assay. Finally, this study shows that anti-DR immunotoxins may represent an original, efficient, and relatively safe approach for bone marrow purging of DR positive malignant B-cell populations; while their clinical potential pertaining to ALL and AML remains uncertain.

Animals↗

PubMed1989

Sensitivity of fresh leukemic cells to T101 ricin A-chain immunotoxin: a comparative study between Fab fragment and whole Ig conjugates.

We compared the cell killing potency of a whole Ig ricin A-chain immunotoxin (T101 IgG-RTA) against its Fab fragment counterpart (T101 Fab-RTA) on both CEM cells and fresh malignant lymphoid cells. A dye exclusion assay (DEA), was used to evaluate the kinetics of leukaemia cell viability mediated in vitro by each immunotoxin (IT). This study found that in the absence of ammonium chloride (NH4Cl), used as an enhancer agent, T101 Fab-RTA was significantly more toxic to both CEM and fresh leukaemia cells than T101 IgG-RTA. In the presence of NH4Cl (10(-2) M), while no differences could be found between the two IT on CEM cells, T101 Fab-RTA was clearly superior to T101 IgG-RTA on fresh leukaemia cells. These results suggest that T101 Fab-RTA may offer an excellent alternative to T101 IgG-RTA for IT treatment of CD5 positive leukaemia patients.

Ammonium Chloride↗

PubMed1989

Donor bone marrow treatment with T101 Fab fragment-ricin A-chain immunotoxin prevents graft-versus-host disease.

Thirty-eight patients with haematological malignancies were treated with bone marrow transplantation using histocompatible immunotoxin T cell-depleted marrow siblings. All patients received conventional postgraft immunosuppression (methotrexate and/or cyclosporin A). Donor bone marrow was treated ex vivo with T101 Fab fragment coupled to ricin A-chain (T101 Fab-RTA) at a concentration of 10(-8) M of A-chain in association with NH4Cl (2 x 10(-2) M) in pH adjusted (7.8) incubation medium. A median cytoreduction of 99.5% (91-99.5) was obtained. The median of follow-up was 300 days. Only three patients developed grade II acute graft-versus-host disease (GVHD) (actuarial rate of acute GVHD: 9.1%). No chronic GVHD occurred. All patients but one engrafted. Six out of the 37 patients developed a documented bone marrow rejection (actuarial rate of graft failure: 18%). Ten patients relapsed (actuarial rate of relapse: 36.9%). These findings demonstrate that treatment of donor marrow with T101 Fab-RTA in association with NH4Cl at critical pH value can achieve a high level of mature T cell depletion and greatly reduce the incidence of bone marrow rejection and relapse after T cell-depleted allogeneic bone marrow transplantation.

Adolescent↗

PubMed1988

Comparison of the cytotoxic potency of T101 Fab, F(ab')2 and whole IgG immunotoxins.

The in vitro killing of the human CEM cell line was studied by using ricin A-chain immunotoxins constructed with either the whole IgG or the Fab and F(ab')2 fragments of the same T101 (anti-CD5) antibody. In the presence of ammonium chloride as an activator, the "whole" immunotoxin as well as the "fragment" immunotoxins did not show any significant difference in the cell killing efficacy. In contrast, without the activator, the efficacy of the T101 immunotoxin was greatly improved when fragments were used. Indeed, at a saturating dose, a cytoreduction of three orders of magnitude was obtained with the fragment immunotoxins vs less than one order of magnitude for the whole immunotoxin, as assessed in a clonogenic assay. This enhancing effect was related to better cell killing kinetics, because with a similar amount of A-chain molecules bound per cell, T101 fragment immunotoxins achieved a twofold faster protein synthesis inactivation rate than the corresponding whole IgG immunotoxin. No significant difference in activity was shown between monovalent (Fab) and divalent (F(ab')2) forms of fragment immunotoxins. The observation that T101 fragment immunotoxins were more potent than intact immunotoxins was extended to another fragment immunotoxin constructed with an antibody (F111.98) directed against a different epitope of the CD5 Ag. In another model (anti-CD22 1G11 antibody on Raji cells), the fragment immunotoxin did not show any superiority over the IgG immunotoxin which was by itself very potent, strongly suggesting an Ag-dependent phenomenon.

Animals↗

PubMed1988

T-lymphocyte killing by T101-ricin A-chain immunotoxin: pH-dependent potentiation with lysosomotropic amines.

To maximize T-lymphocyte killing with anti-pan-T-lymphocyte immunotoxin (IT), prepared by linking ricin A-chain to monoclonal antibody (MoAb) T101 (T101-RTA IT), we have established the nature and the extent of parameters that influence the sensitivity of T lymphocytes to the IT. We showed that peripheral blood T lymphocytes, which are much less susceptible than malignant T cells to the T101-RTA IT, could become highly sensitive to the IT when used in conjunction with NH4Cl. However, enhancement of the IT by NH4Cl only occurred when the pH rose above neutrality. This pH-sensitive process of IT activation by NH4Cl, which led to an all-or-nothing effect within an extremely narrow pH window of 0.7 pH unit width, is due to the fact that NH3 is the effective enhancing component of NH4Cl. We also showed that F(ab')2 or Fab containing IT were much more effective than those produced using the whole IgG counterpart. From these data, we defined a procedure for an optimal and specific elimination of T lymphocytes in vitro by treating them with (Fab)T101-RTA at 10(-8) mol/L at pH 7.8 in the presence of NH4Cl for two hours. This peripheral blood cell processing elicited an abrogation of three logs of functional T-cell response. Under the same conditions, there was no reduction in the number of marrow hematopoietic precursor granulocyte-macrophage colony-forming units (CFU-GM).

Ammonium Chloride↗

PubMed1987

Rationale for the selection of ricin A-chain anti-T immunotoxins for mature T cell depletion.

A series of 25 different ricin A-chain immunotoxins (IT) were prepared with monoclonal antibodies reacting with several T cell antigens belonging to different clusters of differentiation (CD) to select the most appropriate immunotoxins (IT) for mature T cell depletion. Our screening procedure was performed in 2 steps. First, IT were evaluated using protein synthesis inhibition assay on clonogenic malignant cells in order to determine the most active IT for a given CD. Second, IT thus selected were evaluated for both mature T cell killing efficacy and tolerance on hematopoietic progenitor cells (HPC). This study showed that (1) different IT directed against the same CD antigen displayed a wide range of activity, suggesting the need for a large screening of IT to determine the most appropriate antibody for a given target antigen; (2) anti-CD3 and anti-CD5 ricin A-chain IT are the most active, displaying a cytoreduction of more than 2 logs on mature T cells; (3) the 3 different anti-CD2 ricin A-chain IT evaluated in this study induced poor mature T cell cytoreduction despite their relative efficacy on leukemic cells; (4) anti-CD8 ricin A-chain IT showed almost no efficacy on relevant target cells; (5) no toxicity on HPC was found for concentrations up to 10(-8) of A-chain whatever the IT used.

Antibodies, Monoclonal↗