V(L)IgMM transgene expression in DC via a GPI-anchor using a novel retroviral vector induces an in vitro autologous T-cell proliferation restricted to MHC class I molecules.

INTRODUCTION: In order to improve the treatment and cure rate of multiple myeloma (MM), immunotherapy is a novel therapeutic approach. Since neoplastic plasma cells do not undergo further hypermutation, the variable region of the immunoglobulin light chain obtained from MM patients (V(L)IgMM) could serve as a tumor-specific antigen. In addition, dendritic cells (DC) have been identified as potent stimulators of an antigen-specific immune response. Here, we analyze in vitro autologous T-cell proliferation against the V(L)IgMM on presentation by retrovirally transduced dendritic cells. MATERIALS AND METHODS: Expression of the tumor antigen in DC has been achieved using a novel retroviral vector containing NH(2)(34a.a)DAF-FLAG-V(L)IgMM-DAF(37a.a)COOH transgene. After cleavage of the amino- and carboxy-terminal hydrophobic domains of DAF, the FLAG-V(L)IgMM fusion gene is attached to the membrane via a GPI-anchor molecule. Thus, transduced cells can be detected using monoclonal anti-FLAG antibodies. RESULTS: PI-PLC releases cell surface FLAG-antigen from transduced CD34(+) cells indicating that the vector directs the fusion protein to the cell surface via GPI-anchor. V(L)IgMM transgene expression in DC using our retroviral vector elicited an autologous T-cell proliferation restricted to MHC class I molecules. The proliferative response is more prominent in PMA-derived DC compared to cytokine-derived DC indicating that PMA-derived DC are more potent in activating autologous T-cell proliferation. CONCLUSION: V(L)IgMM is an immunogenic peptide, which under certain conditions could provide a basis for a V(L)Ig-based immunotherapy in MM.

Idiotype vaccination in multiple myeloma induced a reduction of circulating clonal tumor B cells.

Myeloma cells express the idiotype (Id)-specific antigen that may be targeted by Id vaccination. Six patients with stage I IgG myeloma were immunized with the autologous purified M component together with the adjuvant cytokines interleukin 12 (IL-12) alone or in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF). The effect of Id vaccination on circulating clonal tumor B cells was monitored by a real-time allele-specific oligonucleotide polymerase chain reaction method. No other treatment was given. Reduction of blood tumor mass was observed in 4 of 6 patients, with one patient achieving a complete molecular remission in blood. In 3 of these 4 patients an Id-specific T-cell response was induced. In the remaining 2 patients with an unchanged level of blood tumor cells, one patient mounted a T-cell response, whereas the other did not. No significant change in the serum M protein level was noted. Id vaccination may target clonal B cells, suggesting that this strategy might be conducive to achieving tumor control. The clinical significance of these findings remains to be established.

Transfer of idiotypic protein primed allogeneic marrow grafts elicits potent graft-versus-myeloma effects in mice.

The active immunization of bone marrow (BM) donors with myeloma immunoglobulin (Ig) results in an idiotypic T cell response that can be transferred to the recipient. Using a murine model we evaluated the effectiveness, side-effects and underlying mechanisms of this approach. Balb/c (H-2d) mice were given a dose of HOPC-1F myeloma cells secreting the monoclonal IgG2a followed by lethal total body irradiation (7.5 Gy) 2 days later and a subsequent transplantation of 2 x 10(7) allogeneic MHC-matched DBA/2-derived marrow cells. Donors were pre-immunized with three i.p. injections of HOPC(IgG2a) or control Ig given with incomplete Freund's adjuvants (IFA) spaced 1 week apart. In some experiments, donor-spleen cells were additionally transferred 2 h post transplant. Injection of HOPC-myeloma led to death of all animals after a median survival time (MST) of 42 days. A lethal dose of TBI followed by transfer of unmanipulated marrow grafts plus splenocytes resulted in moderate antimyeloma effects with 8% of mice achieving long-term survival. Nearly the same results were obtained after transplantation of BM immunized with the control Ig. In contrast, transplantation of marrow grafts from HOPC(IgG2a) immunized donors exerted a significant GVM effect with 63% long-term survival for more than 180 days. The additional transfer of 2 x 10(7) immune splenocytes derived from the same donor resulted in even stronger anti-myeloma effects (FFR 87%). No increase in the incidence of severe acute GVHD was observed. In vitro data suggest that allogeneic CD8+ idiotype-specific T cells may be the major effector cells. Our results demonstrate that active immunization of the donor with the myeloma-specific Ig can induce powerful graft-versus-myeloma effects after allogeneic BMT.