A novel xenograft mouse model for testing approaches targeting human kappa light-chain diseases.

Patients with immunoglobulin (Ig) light-chain (LC) diseases such as LC light-chain amyloidosis die with organ failure and need new therapies. We sought a model to test anti-LC siRNA delivery to human plasma cells, requiring circulating LC, in vivo indicators of tumor presence, and capacity for multiple injections of delivery vehicle. The JJN-3 human myeloma reporter cell line expressing firefly luciferase (FFL) implanted intraperitoneally (IP) in the NOD scid γ (NSG) mouse has a 90% prompt tumor-take, rapid LC production, and in vivo indicators of tumor measurable on day 5 post-implant (κ LC, bioluminescent signal, and soluble B-cell maturation antigen [sBCMA]) with median day 5 serum levels of κ LC of 1482 ng/mL (range, 255-4831) and robust correlations with all in vivo indicators. In preliminary attempts to deliver siRNA against κ LC constant region mRNA, we identified the 306-O18B3 lipidoid nanoparticle (LNP) as promising, safe and efficient in vitro. In vivo in the JJN-3 NSG IP model, after daily IP 306-O18B3:siRNA injections on days 5-10, a reduction in κ LC was observed on day 8 between control and test groups that continued through day 12 at sacrifice. This model is potentially useful as a platform for refining anti-LC therapies.

Daratumumab binds to mobilized CD34+ cells of myeloma patients in vitro without cytotoxicity or impaired progenitor cell growth.

BACKGROUND: The monoclonal antibody daratumumab, approved for treating myeloma, targets CD38, a protein on myeloma and also on CD34+ hematopoietic progenitor cells. Because mobilized CD34+ cells are critical for stem cell transplant, we investigated the in vitro activity of daratumumab on mobilized CD34+ cells from myeloma patients with no prior exposure to daratumumab. METHODS: We determined the number of CD38 molecules per CD34+ cell, and whether daratumumab bound to CD34+ cells, whether C1q bound to daratumumab-coated CD34+ cells and whether daratumumab-related complement-dependent cytotoxicity (CDC) occurred. We also examined CD34+ cell progenitor cell colony capacity in assays with pre-plating incubation of CD34+ cells with daratumumab alone or with daratumumab and the CD59 inhibitory antibody BRIC229, and also assessed CD34+ cell responses to increasing doses of daratumumab in caspase 3/7 activity assays. RESULTS: Although 75% of mobilized CD34+ cells co-express CD38, CD38 was minimally present on CD34+ cells compared to Daudi and KG-1 controls, C1q did not bind to daratumumab-coated CD34+ cells, and CDC did not occur. CD34+ cells incubated in complement-rich human serum with daratumumab alone or with daratumumab and BRIC229, and then plated in progenitor cell assays, produced similar numbers of colonies as controls. In progenitor cell assays with cryopreserved or fresh unselected or CD34-selected cells, daratumumab did not affect progenitor cell capacity, and in caspase 3/7 activity assays CD34+ cells were not affected by increasing doses of daratumumab. CONCLUSION: In vitro, daratumumab is not toxic to mobilized CD34+ progenitor cells from myeloma patients.