A Phase 1, Multiple-Dose Study to Evaluate the Safety and Tolerability of XmAb®819 in Subjects with Relapsed or Refractory Clear Cell Renal Cell Carcinoma.

Inclusion Criteria: - Subjects must have measurable disease by Response Evaluation Criteria in Solid Tumors (RECIST 1.1) as assessed by the local site investigator. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. - Subjects who have relapsed and refractory ccRCC with evidence of disease progression on standard-of-care therapies - ECOG performance status of 0 or 1. - All subjects must have adequate tumor sample available (slides or archival FFPE blocks) Exclusion Criteria: - Prior treatment with an investigational anti-ENPP3/CD203c therapy - History of serious allergic or anaphylactic/hypersensitivity reaction to monoclonal antibody therapy - Systemic antineoplastic therapy within 5 half-lives on the first dose of study treatment. - Failure to recover from any clinically significant toxicity related to previous anticancer treatment - Have known active central nervous system metastases and/or carcinomatous meningitis. Subjects with previously treated brain metastases may participate provided they are radiologically stable, - Active known autoimmune disease (except that subjects are permitted to enroll if they have vitiligo; type 1 diabetes mellitus; residual hypothyroidism due to an autoimmune condition that is treatable with hormone replacement therapy only; psoriasis, atopic dermatitis, or another autoimmune skin condition that is managed without systemic therapy; or arthritis that is managed without systemic therapy beyond oral acetaminophen and nonsteroidal anti-inflammatory drugs) - Evidence of any serious infection requiring IV anti-infective treatment within 14 days prior to the first dose of study drug - Have a known additional malignancy that is progressing or has required active treatment within the past 2 years