RECOMBINANT IMMUNOCYTOKINES TARGETING THE MOUSE TRANSFERRIN RECEPTOR - CONSTRUCTION AND BIOLOGICAL-ACTIVITIES

Localized cytokine therapies with recombinant monoclonal antibody-cyto kine fusion proteins, designated immunocytokines, have become of incre asing interest for tumor immunotherapy, since they direct immunomodula tory cytokines into the tumor microenvironment. To investigate their m echanisms of action in a variety of syngeneic tumor models, recombinan t mouse cytokines IL2 and GM-CSF were engineered as fusion proteins to the carboxyl terminus of a chimeric rat/mouse antitransferrin recepto r antibody, ch17217 and expressed in stable-transfected Chinese hamste r ovary cells. The recombinant immunocytokines were readily purified b y affinity chromatography and their binding characteristics were ident ical to those shown for the ch17217 antibody. The IL2 immunocytokine h ad an activity similar to recombinant mouse IL2, whereas the GM-CSF im munocytokine had enhanced cytokine activity relative to recombinant mo use GM-CSF. The clearance rates of ch17217 and the GM-CSF and IL2 immu nocytokines were relatively similar with elimination phases (t(1/2 alp ha)) of 1.8 h and distribution phases (t(1/2 beta)) of 83, 88, and 91 h, respectively. Both immunocytokines demonstrated effective antitumor activity by suppressing the growth of hepatic metastases of mouse neu roblastoma and pulmonary metastases of mouse colon carcinoma in syngen eic A/J and BALB/c mice, respectively. These results indicate that bio logically effective IL2 and GM-CSF immunocytokines combine the targeti ng ability of an antitransferrin receptor monoclonal antibody with the immunomodulatory functions of each cytokine. Because of the universal expression of the transferrin receptor on mouse tumor cell lines, the se constructs should prove useful to determine their efficacy in a wid e variety of syngeneic mouse tumor models and to perform detailed stud ies of their modes of action.