Treatment with si[IGLC_CR] in patient cells reduces IgL. (A) A flow cytometry plot of CD138⁺ marrow plasma cells from a patient with a λ-light-chain monoclonal gammopathy causing systemic AL shows the results of treatment with si[IGL_CR] or si[-]. The upper panel shows the marked reduction in IgL at 20 hours, and the lower panel shows histograms indicating a reduction of MFI in si[IGLC_CR]-treated cells of 85%. (B) Real-time PCR (qPCR) was performed on CD138⁺ plasma cells (from patients with AL) treated with si[IGLC_CR] or si[-] control. Overall the average residual λ-light-chain message by qPCR was 0.28 ± 0.2 of control (mean ± SD; mean is shown in figure, n = 16). (C) Flow cytometry for intracellular IgL was performed on CD138⁺ plasma cells (from patients with AL) treated with si[IGLC_CR] or si[-] control, showing that the average residual MFI was 49% (n = 13). (D) In 10 cases, we had sufficient CD138⁺ plasma cells to perform both qPCR (>4 × 10⁵) and flow cytometry (>10⁶) after treatment with si[IGLC_CR] or si[-] control. The correlation is shown between residual MFI and residual message by linear regression (line of best fit) with 95% confidence intervals (r² = 0.56, P < .01). (E) In 5 specimens, both the intracellular IgL and IgH in CD138⁺ cells were evaluated simultaneously by flow cytometry after si[IGLC_CR] treatment. This figure suggests that the lower the IgL MFI became with si[IGLC_CR] treatment, the higher the residual intracellular IgH MFI became (P > .05). (F) Five specimens of CD138⁺ plasma cells from patients with AL and abnormal λ-light-chain levels but with immunoglobulin heavy chains (IgGλ = 4, IgAλ = 1; open circles are 2 specimens from the same patient 3 months apart) were treated with si[IGLC_CR] or si[-]. Caspase 3/7 activity was evaluated by bioluminescence 20 hours later, and significantly higher levels of caspase 3/7 activity were seen with si[IGLC_CR] treatment. (P = .04 with 2-tailed paired Student t test).