Faculty Bibliography

T cells in multiple myeloma (MM) patients are highly susceptible to activation with the anti-CD3 monoclonal antibody (mAb) OKT3. When short-term OKT3 stimulation is carried out on bone marrow mononuclear cells (BMMC), large numbers of CD3+ CD25+ HLA-DR+ cells are rapidly generated and autologous malignant plasma cells are killed. OKT3 may thus be exploited in autologous bone marrow transplantation (ABMT) to purge residual plasma cells and simultaneously activate T cells to induce graft-versus-leukemia-like (GVL-like) activity upon reinfusion. However, the possible impact of ex-vivo short-term OKT3 stimulation on haematological recovery is unknown. The aim of this work was to investigate the effect of OKT3 stimulation in vitro on autologous haemopoietic progenitor cells (HPC) of MM patients. Colony formation by granulocyte-macrophage progenitor cells (granulocyte-macrophage colony-forming units, CFU-GM) was highly suppressed, although supernatants of OKT3-activated T cells contained up to 2,500 pg/ml of granulocyte-macrophage colony-stimulating factor (GM-CSF). T cell depletion completely prevented this suppression. Neutralizing antibodies against TNF-alpha, TNF-beta and IFN-gamma (which are also produced by OKT3-activated MM T cells) did not prevent it, and Transwell cultures showed that cell-to-cell contact was the main mechanism involved. OKT3-activated T cells also suppressed erythroid burst-forming units (BFU-E) and CFU-GM generation from HPC responsible for long-term maintenance of in vitro myelopoiesis. When tested on normal allogeneic BM, MM supernatants of OKT3-stimulated BMMC partially suppressed the generation of day 7 CFU-GM, but had no effect on day 14 CFU-GM. These data indicate that short-term stimulation of BMMC with OKT3 can be used to generate anti-tumour effector T cells for autologous adoptive immunotherapy. It is not a feasable approach for ex-vivo purging and activation procedures in ABMT because of its potent inhibition of autologous haemopoiesis.

Interferon-alpha (IFN-alpha), interferon-gamma (IFN-gamma) and dexamethasone (DEX) have shown anti-tumour effects in multiple myeloma (MM) cells. Bone marrow plasma cells from 39 MM patients were cultured to clarify the intensity and specific activity of each compound on bromo-deoxyuridine (BrdUrd) uptake and immunoglobulin (Ig) secretion. BrdUrd uptake was inhibited by recombinant human IFN-gamma (100 U/ml) and by DEX (10(-6) M). The stimulation index (StI), i.e. labelling index (LI) of treated samples/controls, was 0.49 +/- 0.09 (mean +/- standard error of the mean, M +/- SEM), P = 0.0003, and 0.52 +/- 0.07 (M +/- SEM), P < 0.0001, respectively. Ig secretion was reduced by IFN-alpha (100 U/ml) and DEX. The secretion index (SI), i.e. Ig quantitation of treated samples/controls, was 0.04 (M +/- SEM), P < 0.0001, and 0.52 +/- 0.04 (M +/- SEM), P < 0.0001, respectively. Finally, IFN-gamma inhibits BrdUrd uptake only and IFN-alpha secretion only. In 18 patients the simultaneous addition of IFN-alpha plus IFN-gamma mainly parallel the effect of IFN-gamma on BrdUrd uptake and IFN-alpha on secretion, but not result in any additive or synergistic effect, though both BrdUrd uptake and Ig secretion were decreased to about the same extent as with DEX. These data indicate that the combination of IFN-alpha plus IFN-gamma and DEX are the strongest inhibitors of both BrdUrd uptake and secretion. Since IFN-alpha and IFN-gamma appear to have a different mechanism of action, their combined use could be considered as a possible new treatment strategy.