Anti-CD19 and anti-CD22 monoclonal antibodies increase the effectiveness of chemotherapy in Pre-B acute lymphoblastic leukemia cell lines

Abstract

The monoclonal antibodies (MAbs) HD37 and RFB4 bind to receptors on precursor B acute lymphoblastic leukemia (ALL) cells. These MAbs were tested alone and in combination with chemotherapy for their anti-leukemic activity. HD37 and not RFB4 increased the in vitro cytotoxicity of daunorubicin (DNR) and vincristine (VCR) in three Pre-B ALL cell lines. HD37 alone induced apoptosis in 30% of the cells versus 2% for RFB4. The treatment of SCID/ALL mice with either chemotherapy agent minimally prolonged their mean survival time (MST) versus controls but HD37 or RFB4 plus VCR significantly extended the MST. Forty percent of the mice treated with HD37 plus VCR survived. In conclusion, chemotherapy was made more effective when combined with HD37, and less so with RFB4.

Figures

Figure 1. Decrease in [3H]-thymidine incorporation using a combination of HD37 or RFB4 with VCR or DNR in three Pre-B ALL cell lines

Cells (105) were incubated for 48 hr at 37°C with three different concentrations (IC10, IC50, and IC90) of either VCR (left column of figures) or DNR (right column of figures) alone (open fig.) or combined with a fixed concentration (IC50) of HD37 (closed fig.). The cells were washed, and then pulsed for 4 hr at 37°C in 5% CO2 with 1 μCi [3H]-thymidine. The graphs represent the Nalm-6-UM1 (A and B); REH (C and D); and JM-1 (E and F) cell lines. The values are of three separate experiments represented as percentage of control ± standard error of the mean. Significant differences between mean results with and without HD37 are indicated: *, P<.1; **, P<.05; ***, P<.01.

Figure 2. Apoptosis due to Combination of HD37 with VCR or DNR in three Pre-B ALL cell lines

Cells (105) were incubated for 24 and 48 hr with three different concentrations (IC10,-black bar; IC50,-gray bar; and IC90 -white bar) of either VCR (Fig A, C, and E) or DNR (Fig B, D, and F) alone or in combination with a fixed concentration of HD37 (IC50). The percentage of cells that were Annexin V+, PI− (apoptotic) were determined for each treatment using flow cytometry. The results are cumulative data of three separate experiments with results represented as % apoptosis over time ± SEM.

Figure 3. Survival of SCID/human ALL mice treated with HD37 or RFB4 in combination with DNR or VCR

Pre-irradiated SCID mice were injected in the tail vein with 5×106 Nalm-6-UM1 cells 24 hr prior to treatment. Mice received 4 daily i.p. injections of HD37 (3A) or RFB4 (3B) alone or in combination with VCR or DNR. In four separate experiments, mice received either saline (•) (n=15), RFT5 (○) (n=20), HD37 (■) (n=10), HD37+ DNR (□) (n=10), HD37 + VCR (◆) (n=10), VCR (Δ) (n=20), DNR (▼)(n=20), RFB4 (■) (n=10), RFB4 + DNR (□), (n=10), and RFB4 + VCR (◆) (n=10).

Figure 3. Survival of SCID/human ALL mice treated with HD37 or RFB4 in combination with DNR or VCR

Pre-irradiated SCID mice were injected in the tail vein with 5×106 Nalm-6-UM1 cells 24 hr prior to treatment. Mice received 4 daily i.p. injections of HD37 (3A) or RFB4 (3B) alone or in combination with VCR or DNR. In four separate experiments, mice received either saline (•) (n=15), RFT5 (○) (n=20), HD37 (■) (n=10), HD37+ DNR (□) (n=10), HD37 + VCR (◆) (n=10), VCR (Δ) (n=20), DNR (▼)(n=20), RFB4 (■) (n=10), RFB4 + DNR (□), (n=10), and RFB4 + VCR (◆) (n=10).