CTLA4 and Merkel cell skin cancer: Further clinical grade mono-scFv-substituted constructs are being based on Xencor’s and Amgen’s heterodimeric platform XmAb, which utilizes engineered Fc isoelectric point differences and amino acid substitutions to achieve heterodimer yields over 95% [109]: the anti-PD-1/CTLA-4 XmAb717 (NCT03517488) and anti-CTLA4/LAG-3 XmAb841 (NCT03849469) for advanced solid tumors, the anti-SSTR2/CD3 XmAb18087 (aka Tidutamab, NCT04590781) for advanced small-cell lung cancer (SCLC) and Merkel cell carcinoma, and the anti-CD20/CD3 XmAb13676 (aka Plamotamab, NCT02924402) for r/r B-NHL.