The use of hybrid hybridomas to target human cytotoxic T lymphocytes

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Abstract
This study describes a general strategy to produce hybrid monoclonal antibodies that are capable of targeting human cytotoxic T lymphocytes (CTL) against any cell carrying the appropriate target antigen. This is done by fusing a HAT-sensitive, G418-resistant anti-T3 hybridoma with immune spleen cells (or with other hybridomas) that produce antibodies against the desired target antigen. In the hybrid hybridomas the reassortment of Ig heavy and light chains results in the production of bifunctional antibody molecules. Because of their double specificity, these antibodies are able to bridge human CTL to target cells and trigger cytotoxic function. We have isolated several stable hybrid hybridomas in which one specificity is against T3 and one either against HLA antigens (class II, DC-1, A3), human Ig (IgM, IgE, x), Toxoplasma gondii or an ovary carcinoma-associated antigen. In all of these cases we show that culture supernatants can efficiently and specifically target any CTL clone against any target cell that possesses the relevant surface antigen recognized by the antibody. Furthermore, the killing requires as little as 0.1 ng/ml of antibody, occurs at effector to target ratios comparable to those used in conventional cytotoxic assays and does not affect bystander cells. Nonspecific killing of Fc receptor-positive cells can be avoided using F(ab′)2 fragments. As an example, we show that it is possible to (a) change the major histocompatibility complex class and allospecificity of a CTL clone and (b) target CTL against non-major histocompatibility complex antigens such as Ig, parasites and tumor-associated antigens.