Bispecific antibody-activated T cells enhance NK cell-mediated antibody-dependent cellular cytotoxicity.

Resistance to anti-cancer monoclonal antibody (mAb) therapy remains a clinical challenge. Previous work in our laboratory has shown that T cell help in the form of interleukin-2 maintains long-term NK cell viability and NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC). Lack of such T cell help may be a potential mechanism for resistance to mAb therapy. Here, we evaluate whether concomitant treatment with anti-CD3 × anti-cancer bispecific antibodies (bsAbs) can overcome this resistance by enhancing T cell help, and thereby maintaining long-term NK cell-mediated ADCC. Normal donor peripheral blood mononuclear cells were depleted of T cells, replenished with defined numbers of autologous T cells (from 0.75 to 50%) and co-cultured with mono-/bispecific antibody-treated target tumor cells for up to 7 days. At low T cell concentrations, bsAb-activated T cells (mainly CD4+ T cells) were more effective than resting T cells at maintaining NK cell viability and ADCC. Brief (4 h to 2 day) bsAb exposure was sufficient to enhance long-term ADCC by NK cells. These findings raise the hypothesis that local T cell activation mediated by systemic treatment with anti-CD3 X anti-cancer bsAb may enhance the anti-tumor efficacy of monospecific mAbs that mediate their primary therapeutic effect via NK-mediated ADCC.