Sperm protein 17 (Sp17) in multiple myeloma: opportunity for myeloma-specific donor T cell infusion to enhance graft-versus-myeloma effect without increasing graft-versus-host disease risk

We recently found that sperm protein 17 (Sp17), a spermatozoa-restricted protein, is aberrantly expressed on the tumor cells in patients with multiple myeloma (MM). It may therefore be possible to generate donor-derived Sp17-specific CTL for administration following allogeneic stem cell transplant to augment graft-versus-myeloma (GVM) effect without inducing a global GVHD. To assess this approach, we have produced recombinant Sp17 protein and used Sp17 protein-pulsed dendritic cells to generate HLA class I-restricted Sp17-specific CTL from a previously unimmunized healthy donor. These CTL were able to lyse autologous Epstein-Barr virus-transformed lymphoblastoid cells in a Sp17-dependent manner. Target lysis was HLA-A1 and HLA-B27 restricted. Cytotoxicity could be blocked by antibodies against monomorphic HLA class I, HLA-A1 and HLA-B27 molecules but not HLA class II molecules. Most importantly, the CTL lysed HLA class I-matched Sp17-positive tumor cells, suggesting that Sp17 is processed and presented in association with the HLA class I molecules in Sp17-positive tumor cells in a concentration and configuration that could be recognized by recombinant protein-primed CTL. Analysis by flow cytometry of the CTL indicated that they were predominantly CD8 in phenotype and they produced IFN-gamma and very little IL-4. Our results suggest the potential for the generation and administration of donor-derived Sp17-specific CTL to augment GVM without inducing GVHD following allogeneic stem cell transplant for MM.