Specific epitope‐induced conversion of CD8⁺ memory cells into effector cytotoxic T lymphocytes in vitro: presentation of peptide antigen by CD8⁺ T cells

The requirements for the conversion of CD8⁺ memory T cells into effector class I major histocompatibility complex (MHC) K^d−restricted cytotoxic T (T_c) cells in vitro have been studied. Purified CD8⁺splenocytes from influenza A/WSN‐primed BALB/c (H‐2^d) mice stimulated with a synthetic nucleoprotein peptide 147–158 R156⁻ (NPP) alone generated T_c cells specific for influenza virus‐infected target cells. No additional requirements for accessory cells or their lymphokine products were necessary indicating that peptide antigen (Ag) in association with K^d was presented on CD8⁺ T cells. The evidence for presentation of NPP by CD8⁺ T cells was supported by the use of CD8⁺ memory T cells from semiallogeneic bone marrow radiation chimeras of P₁ → F₁ type (H2b→ [H‐2^d x H‐2^b]F₁). Memory CD8⁺ splenocytes from A/WSN‐immune chimeras did not develop into secondary effector T_c cells as a result of a 4‐day culture with NPP alone, however, were able to do so if NPP was presented by K^d−bearing Ag‐presenting cells. In addition, these results exclude the possibility of direct recognition of free NPP molecules by the specificT cell receptor of CD8⁺ memory T cells. CD8⁺ memory splenocytes (H‐2^b) from chimeras were also able to develop into functionally active T_c cells as a result of presentation of D^b−restricted synthetic peptide (NP 366–374) with a sequence derived from influenza virus nucleoprotein with high affinity for D^b MHC class I molecules. Blockade of endogenously produced interleukin 2 (IL‐2) activity by anti‐IL‐2 or anti‐IL‐2 receptor monoclonal antibody in the culture of CD8⁺ memory T cells during a 4‐day NPP stimulation completely abolished T_c cell generation, indicating that the utilization of this lymphokine is absolutely required for the secondary T_c cell development. These findings demonstrate that CD8⁺ memory T cells per se are able to recognize the restimulating epitope as a result of its presentation by CD8⁺ T cells and develop into cytolytically active and highly specific T_c cells with no requirements for other cellular helper components or their lymphokine products.