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) Kd-restricted cytotoxic T (Tc) cells in vitro have been studied. Purified CD8+ splenocytes from influenza A/WSN-primed BALB/c (H-2d) mice stimulated with a synthetic nucleoprotein peptide 147-158 R156- (NPP) alone generated Tc 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 Kd 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-2d x H-2b]F1). Memory CD8+ splenocytes from A/WSN-immune chimeras did not develop into secondary effector Tc cells as a result of a 4-day culture with NPP alone, however, were able to do so if NPP was presented by Kd-bearing Ag-presenting cells. In addition, these results exclude the possibility of direct recognition of free NPP molecules by the specific T cell receptor of CD8+ memory T cells. CD8+ memory splenocytes (H-2b) from chimeras were also able to develop into functionally active Tc cells as a result of presentation of Db-restricted synthetic peptide (NP 366-374) with a sequence derived from influenza virus nucleoprotein with high affinity for Db 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 Tc cell generation, indicating that the utilization of this lymphokine is absolutely required for the secondary Tc 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 Tc cells with no requirements for other cellular helper components or their lymphokine products.