Unprimed CD4+ and CD8+ T cells can be rapidly activated by a CD3 x CD19 bispecific antibody to proliferate and become cytotoxic.

We previously reported that a CD3 x CD19 bispecific antibody (bsAb) can induce efficient killing of tumour cells by preactivated T cells isolated from patients with B cell malignancy. For future intravenous application we investigated whether resting T cells from peripheral blood can be stimulated to proliferate and become cytotoxic with the CD3 x CD19 bsAb alone. Indeed peripheral blood mononuclear cells, isolated from healthy donors or patients with B cell malignancy, started to proliferate within 1 day in response to CD3 x CD19 bsAb. Within the same time span cytotoxic activity against CD19-positive tumour cells was already detectable. Maintenance of cytotoxic activity was seen during 3 days of culture but optimal lysis of the target cells then required fresh CD3 x CD19 bsAb in the cytotoxicity assay. Essentially the same results for proliferation and cytotoxicity were found when separated CD4-positive and CD8-positive T cells were activated by the bsAb in the presence of autologous monocytes. These results may be relevant for the in vivo application of the bsAb when used as immunotherapy in patients with B cell malignancy.