PTHLH and neoplasm: To investigate the specific effects of PTHrP and to rule out many other tumor-derived factors that potentially affect MDSCs, we first infused recombinant PTHrP (amino acids 1-34, a PTH1R receptor-binding fragment) or control PBS diluent continuously for three weeks using in vivo subcutaneous implantable pumps in tumor-naïve mice (Fig. 1a).