Acquisition of specific cytotoxic activity by human T4⁺ T lymphocytes in culture

Abstract

Mature human T lymphocytes can be separated by monoclonal antibodies OKT4 and OKT8 according to their surface phenotypes into T4⁺T8⁻ and T4⁻T8⁺ subsets^1,2. From shortterm experiments using bulk cultures, the helper/inducer function has been assigned to the T4⁺T8⁻ subset and the cytotoxic/suppressor function to the T4⁻T8⁺ subset^1,2. Thus if T lymphocytes are separated after stimulation in a mixed lymphocyte reaction (MLR), the entire cytotoxic activity is found hi the T4⁻T8⁺ fraction whereas the T4⁺T8⁻ fraction shows no detectable cytotoxicity¹. If, however, T lymphocytes are cloned after MLR and grown in long-term culture, a surprisingly large fraction of T4⁺ T lymphocyte clones (TLC) shows cytotoxic activity^3,4. Here we report that T4⁺ TLC can acquire specific cytotoxicity during in vitro cultivation.