Identification of unique molecular heterogeneity of human CD79, the signaling component of the human B cell antigen receptor (BCR), and synergistic potentiation of the CD79-targeted therapy of B cell tumors by co-targeting of CD79a and CD79b.

We identified unique molecular heterogeneity of CD79 of human B cell antigen receptor (BCR) that may open a new approach to the ongoing CD79b-targeted therapy of B cell tumors. The primary purpose of the present study is to gain new information valuable for the enhanced CD79-targeted therapy. The molecular heterogeneity of CD79 was identified by sequential immunoprecipitation of BCR by use of anti-CD79b monoclonal antibody (mAb) SN8 and anti-CD79a mAb SN8b. SN8 is the antibody component of polatuzumab vedotin, an anti-CD79b antibody drug conjugate, that has been widely used for therapy of diffuse large B-cell lymphoma (DLBCL). The sequential immunoprecipitation shows that anti-CD79b mAb will be able to react only with a subgroup of CD79 molecules while anti-CD79a mAb will react with another subgroup of CD79 molecules; CD79 is a disulfide-linked heterodimer of CD79a and CD79b. Therapeutic study of SCID mice bearing human B-cell tumor shows synergistic potentiation by co-targeting CD79b and CD79a. Furthermore, simultaneous targeting of PD-1 strongly potentiates CD79a/CD79b-targeted therapy of B cell tumors. Flow cytometry analyses of CD79a/CD79b on malignant B cells of patients may provide a method for selection of the candidate patients for the CD79a/CD79b dual targeting therapy.

Facilitation of endoglin-targeting cancer therapy by development/utilization of a novel genetically engineered mouse model expressing humanized endoglin (CD105).

Endoglin (ENG) is a TGF-ß coreceptor and essential for vascular development and angiogenesis. A chimeric antihuman ENG (hENG) monoclonal antibody (mAb) c-SN6j (also known as TRC105) shows promising safety and clinical efficacy features in multiple clinical trials of patients with various advanced solid tumors. Here we developed a novel genetically engineered mouse model to optimize the ENG-targeting clinical trials. We designed a new targeting vector that contains exons 4-8 of hENG gene to generate novel genetically engineered mice (GEMs) expressing functional human/mouse chimeric (humanized) ENG with desired epitopes. Genotyping of the generated mice confirmed that we generated the desired GEMs. Immunohistochemical analysis demonstrated that humanized ENG protein of the GEMs expresses epitopes defined by 7 of our 8 anti-hENG mAbs tested. Surprisingly the homozygous GEMs develop normally and are healthy. Established breast and colon tumors as well as metastasis and tumor microvessels in the GEMs were effectively suppressed by systemic administration of anti-hENG mAbs. Additionally, test result indicates that synergistic potentiation of antitumor efficacy can be induced by simultaneous targeting of two distinct epitopes by anti-hENG mAbs. Sorafenib and capecitabine also showed antitumor efficacy in the GEMs. The presented novel GEMs are the first GEMs that express the targetable humanized ENG. Test results indicate utility of the GEMs for the clinically relevant studies. Additionally, we generated GEMs expressing a different humanized ENG containing exons 5-6 of hENG gene, and the homozygous GEMs develop normally and are healthy.