A high medical need remains for the refractory disease setting, often characterized by suboptimal target levels . We have developed a 65-kDa multispecific antibody construct, CLN-978, with affinities tuned to optimize killing of low-CD19 expressing tumor cells . In primates, we observed a long serum half-life, deep and sustained depletion of normal B cells, and remarkable tolerability . An ongoing clinical phase 1 trial is investigating safety, pharmacokinetics and pharmacodynamics in patients with non-Hodgkin’s lymphoma .