The chronic lymphocytic leukemia antigen (cCLLa) as immunotherapy target: pharmacokinetics and biodistribution of two divalent, ricin-based immunotoxins in xenografted athymic mice

Surface immunoglobulin on B lymphocytes as a potential target for specific peptide ligands in chronic lymphocytic leukaemia

With the aim of producing unique targets for malignant cells we have identified peptide ligands for the clonal surface immunoglobulin isolated from the B cells of a chronic lymphocytic leukaemia (CLL) patient. The peptides were identified from random-peptide phage-display libraries. The obtained ligands bound specifically to the surface of the target lymphocytes as well as to clonal immunoglobulin in lysate from the same cells. Peptide-based antigen mimotopes may have a future use in targeted therapy of CLL and other B-cell-derived malignancies displaying surface immunoglobulin.

The chronic lymphocytic leukemia antigen (cCLLa) as immunotherapy target: assessment of LD50 and MTD of four ricin-based anti-cCLLa immunotoxins (ITs) in Balb/c mice

The chronic lymphocytic leukemia (CLL) antigen (cCLLa) is a promising immunotherapy target given its disease-restricted expression, its highest prevalence among CLL surface antigens, and its lack of expression by normal T- and B-lymphocytes. The objectives of this study were to assess the 50% lethal dose (LD50) and the maximum tolerated dose (MTD) in Balb/c mice of four anti-cCLLa immunotoxins (ITs) derived from the intact monoclonal antibody (MoAb) or its Fab fraction, each conjugated to either ricin chain-A (RTA) or its deglycosylated derivative (dgA). The IgG fraction of anti-cCLLa monoclonal antibody CLL2m and its Fab fraction were conjugated to RTA or dgA to generate four ITs: IgG/RTA, IgG/dgA, Fab/RTA and Fab/dgA. Progressive concentrations of each IT (ranging between 2.60 mg/kg and 100.00 mg/kg) were injected intravenously into groups of 5 mice each. After injection, mice were monitored daily for 10 days for survival. Observed mortality data in each group were matched to those in Weil's tables for estimating LD50 (mg/kg) from the moving average interpolation method. Estimated LD50 (in mg/kg) were: IgG/RTA, 13.33; Fab/RTA, 25.53; IgG/dgA, 55.33; Fab/dgA, 55.33. Their respective MTD (mg/kg), defined as the highest dose level survived by all mice, were 8.78, 13.17, 29.63 and 29.63. Depending on the animal-to-human extrapolation method used, the calculated LD50 and MTD in humans ranged from 1.2 mg/kg and 0.8 mg/kg (IgG/RTA), to 55.6 mg/kg and 36.9 mg/kg (IgG/dgA and Fab/dgA), respectively. The following conclusions are drawn. 1. Antibody valence exerted little influence on either the LD50 or the MTD; 2. The LD50 to MTD ratios were approximately 2:1; 3. dgA-derived ITs were approximately one half as toxic as their RTA-derived counterparts; and 4. Extrapolation of LD50 and MTD mouse data to humans resulted in dose levels comparable to or exceeding those reported in most IT human trials. These data suggest the suitability of anti-cCLLa ITs for clinical immunotherapy trials.