Bypassing immunization: Optimized design of "designer T cells" against carcinoembryonic antigen (CEA)-expressing tumors, and lack of suppression by soluble CEA

Tumor-associated antigens are typically nonimmunogenic in cancer patients, "immune surveillance" having manifestly failed. The fact that most tumor an tigens are normal human proteins presents significant obstacles to current cancer immunization approaches that researchers are presently striving to o vercome. An alternative strategy bypasses immunization altogether by direct genetic alteration of autologous patient T cells, to create "designer T ce lls" specific to a particular antigen. Chimeric immunoglobulin-T cell, rece ptors (IgTCR) with a specificity for carcinoembryonic antigen (CEA) were cr eated to evaluate the optimal IgTCR structure for cancer therapy. Antigen-b inding domains of a humanized antibody were combined with TCR signaling cha ins to yield four different chimeric IgTCR: single chain Fv fragment (sFv)- zeta, fragment antigen-binding (Fab)-zeta, sFV-epsilon, and Fab-epsilon. Al l of the IgTCR were well expressed on T cells, and all showed specific bind ing and activation, as demonstrated by IL-2 production on contact with immo bilized or cellular CEA, excepting sFv-epsilon alone which was inert solely against cellular targets for steric reasons unique to this construct. In c ontrast to prior studies of isolated TCR chains that related increased tyro sine-based activation moths in zeta as a reason for superior signaling pote ncy, these tests are the first to show that epsilon and zeta are indistingu ishable for T cell signaling when assayed in the context of the intact TCR complex. Further, Fab was equivalent to sFv as an IgTCR component for expre ssion and antigen binding, establishing an important alternative for IgTCR antigen recognition because sFvs may often lose antigen affinity. When IgTC R was expressed on normal human T cells, cytotoxic potency was demonstrated at low E:T ratios, with T cell recycling and progressive tumor cell destru ction. Contrary to recent speculations, these observations prove that high affinity TCR interactions are not an impediment to serial target engagement and disengagement by cytotoxic T cells, The multivalent intercellular inte ractions of target cell binding, activation, and cytotoxicity were resistan t to inhibition by soluble CEA. These studies establish a potentially impor tant new immunotherapeutic modality for the treatment of CEA-expressing tum ors.