Immunotherapeutic strategies in neuroblastoma: antitumoral activity of deglycosylated Ricin A conjugated anti-GD2 antibodies and anti-CD3xanti-GD2 bispecific antibodies.

The antigen GD2 is selectively expressed on the surface of neuroblastoma cells, and is detected by the monoclonal antibody BW704. In this study, we describe the antitumoral capacity of the immunotoxin BW704dgA (BW704 conjugated to deglycosylated ricin A), and of anti-CD3xanti-GD2 bispecific antibodies that are capable of redirecting cytotoxic T cells towards neuroblastoma cells. We further investigate the in vivo activity of BW704dgA immunotoxins in a human neuroblastoma model in SCID mice. BW704dgA immunotoxins were injected i.p. as a single close (48 microg/mouse) on day 4 or divided into three doses on day 4, 5, and 6 after i.v. inoculation of the human neuroblastoma cell line IMR5-75. The mean survival time (MST) of BW704dgA treated animals was significantly increased (MST 49 days) compared to the control animals treated with irrelevant immunotoxin, unconjugated BW704, or control buffer (MST 33 to 39 days, P < 0.0001), without differences in the application schedules. Anti-CD3xanti-NP antibodies and NP-conjugated GD2-antibodies (BW704-NP) were used in a cytotoxicity assay with cytotoxic T-cells as effectors, and tracer labeled neuroblastoma cell line IMR5 as target cells. Anti-CD3xanti-NP antibodies, together with BW704-NP, showed increased cytotoxic activity compared to the incubation with CD3xanti-NP antibodies alone or with unconjugated anti-GD2. Additionally, a dose-dependent effect of NP-conjugated anti-GD2-antibodies upon the lysis of the target cells could be demonstrated. In this report, we describe two immunotherapeutic approaches using GD2 binding BW704 antibodies, modified as immunotoxin and a bispecific antibody, for the targeting and elimination of neuroblastoma cells. We envisage a combined immunotherapeutic regimen consisting of BW704dgA mediated stem cell purging, followed by a systemic treatment with anti-CD3xanti-GD2 bispecific antibodies in neuroblastoma.