Figure 2

Efficient T-cell mediated killing of target cell lines with varying CD33 expression levels is induced in the presence of bsAb-releasing hMSCs. (a) HEK293T, OCI-AML3, U937 and MOLM-13 were analyzed for CD33 surface expression levels by staining with anti-CD33/PE mAb (in black) or matched isotype control Ab (in gray), respectively. Numbers represent mean fluorescence intensity (MFI) of total cells. (b) In a standard chromium release assay ⁵¹Cr labeled CD33⁺ MOLM-13 cells and CD33^- HEK293T cells were incubated with freshly isolated T cells at effector-to-target (e:t) cell ratio of 5:1 for 20 h with decreasing concentrations of the purified bsAb CD33–CD3. Mean±s.d. of two independent donors is shown. (c) Specific cell lysis of AML cell lines U937 (upper) and MOLM-13 (lower) measured with standard chromium release assay. Freshly isolated CD3⁺ T cells were co-cultured for 10 and 20 h with ⁵¹Cr labeled CD33⁺ target cells at an e:t cell ratio of 5:1 in the presence of hMSC lines seeded at different concentrations 48 h before adding effector T cells and target cells. Data are presented as means±s.d. from two or three different donors, respectively. (d) Decreasing densities of ⁵¹Cr labeled gene-modified hMSCs were co-cultured with PBMCs in the presence or absence of CD33⁺ MOLM-13 cells at an e:t ratio of 5:1. After 20 h of co-incubation the specific hMSCs lysis was examined via chromium release assay. Data shown as mean±s.d. from two independent donors.