Targeted 4-1BB Activation: Enhancing Immunotherapy for B Cell Malignancies with CD19-4-1BBL and CD20 Antibodies

The 4-1BB co-stimulatory pathway has demonstrated potential in anti-tumor activity, but the development of related antibodies has been hindered by liver toxicity caused by FcγR-mediated crosslinking. A new approach involves CD19-4-1BBL, an antibody fusion protein that combines split trimeric 4-1BB ligands with a CD19 targeting moiety and a silent Fc part. This construct avoids Fc-mediated toxicity while enabling 4-1BB hyperclustering upon binding to CD19-expressing B cells. CD19-4-1BBL exhibits IgG-like pharmacokinetics in mice and cynomolgus monkeys and is biologically active in co-stimulating T cells when cross-linked via CD19.

To enhance T cell activation, CD19-4-1BBL is combined with a CD20 T cell bispecific antibody (CD20-TCB), which mediates the clustering of CD19-4-1BBL at the T cell-tumor cell interaction synapse. This combination results in prolonged T cell-tumor contact and efficient tumor cell killing. In human stem cell engrafted NSG mice bearing WSU-DLCL2 tumors, treatment with CD20-TCB upregulates 4-1BB on activated T cells, leading to tumor growth inhibition. The combined use of CD19-4-1BBL and CD20-TCB at suboptimal doses completely eradicates tumors and induces strong T cell infiltration into the tumor, increasing the CD8/Treg ratio.

Additionally, the combination of CD19-4-1BBL with the Type II CD20 antibody obinutuzumab, which enhances antibody-dependent cellular cytotoxicity (ADCC), leads to complete tumor remissions in the same mouse model. This suggests that CD19-4-1BBL can effectively co-stimulate both pre-activated T cells by a TCB and pre-activated NK cells by an ADCC mediating antibody.

In summary, CD19-4-1BBL represents a novel strategy for targeted 4-1BB co-stimulation, providing a safe and potent method to enhance T cell and NK cell activity against B cell malignancies. This approach holds promise for "chemo-free" treatments and warrants further clinical investigation.