Induction and increase of HLA-DR antigen expression by immune interferon on ML-3 cell line enhances the anti-HLA-DR immunotoxin activity.
In order to evaluate the impact of induction and increase target antigen expression on immunotoxin potency, we measured the potentiating effect of recombinant immune interferon-gamma (rIFN-gamma) on the cytotoxicity of an anti HLA-DR ricin A-chain immunotoxin (2G5 RTA-IT) on the myeloid cell line ML-3. After 48 h of incubation with rIFN-gamma (500 U/ml) the percentage of 2G5-positive cells increased from 40% to 79%, and the 2G5 mean density was enhanced by 10-fold (11,000 versus 110,000 molecules/cell). Concurrently, rIFN-gamma pretreatment induced a dramatic improvement of 2G5 RTA-IT dose-effect cytotoxicity, as well as immunotoxin cytotoxicity kinetics. When 2G5 RTA-IT was used at the optimal dose of 10(-8)M (the maximum dose which avoided non-specific ricin A-chain cytotoxicity), the immunotoxin-induced cell kill increased with the percentage of DR-positive ML-3 cells according to a similar linear-logarithmic function of rIFN-gamma concentration. Moreover, in the same range of rIFN-gamma concentrations, the killing values and the percentage of DR-positive ML-3 cells were similar if not identical. These findings imply that the enhancement of 2G5 RTA-IT cytotoxicity by rIFN-gamma is mainly related to the rIFN-gamma 2G5 antigen induction on HLA-DR negative cells when immunotoxin was used at 10(-8) M. Furthermore, 2G5 RTA-IT dose-effect cytotoxicity on DR-expressing ML-3 cells, when used at lower concentrations, was also increased by rIFN-gamma in a dose-dependent manner. This result suggests that for immunotoxin concentrations close to the limiting membrane saturation dose (10(-10)M), rIFN-gamma may not solely act by inducing HLA-DR expression on DR-negative ML-3 subpopulation but also by increasing individual cellular DR density on DR expressing ML-3 cells. Finally, our study showed that immunotoxin potency on malignant cell populations which display an heterogeneous antigen expression, could be greatly improved by the use of rIFN-gamma.
Chiron
M
M
Laboratory of Pharmacology and Toxicology, CNRS, Toulouse, France.
Jaffrezou
J P
JP
Carayon
P
P
Bordier
C
C
Roubinet
F
F
Xavier
C
C
Brandely
M
M
Laurent
G
G
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006684:HLA-DR Antigens / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D007371:Interferon-gamma / Q000008:administration & dosage / Q000494:pharmacology*; D007951:Leukemia, Myeloid / Q000276:immunology / Q000473:pathology; D011994:Recombinant Proteins; D012276:Ricin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000276:immunology / Q000473:pathology
D000911:Antibodies, Monoclonal; D006684:HLA-DR Antigens; D000922:Immunotoxins; D011994:Recombinant Proteins; D007371:Interferon-gamma; D012276:Ricin