The purpose of this study is to assess the safety and tolerability of XmAb®819 administered intravenous (IV) or subcutaneous (SC) in subjects with relapsed or refractory clear cell renal cell carcinoma and to identify the minimum safe and biologically active dose and the recommended dose (RD).

This is a Phase 1, multicenter, open-label, multiple-dose study designed in 2 parts: dose escalation, and dose expansion. The study is designed to establish the dosing schedule of XmAb819 administered IV and the dosing schedule of XmAb819 administered SC. The study is designed to evaluate safety and tolerability; to assess PK/PD and immunogenicity; and to preliminarily assess antitumor activity of XmAb819 in subjects with ccRCC and other solid tumors. All eligible subjects will have relapsed or refractory disease after standard therapy.

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, pRCC, NSCLC, and CRC 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