1. Able and willing to participate and comply with all study requirements and provide
             signed and dated informed consent prior to initiation of any study procedures;

          2. Histologically or cytologically confirmed advanced/metastatic extracranial solid tumor
             malignancy.

               1. Stages 1 and 2: Subject must have received, have been intolerant to, have been
                  ineligible for, or have declined all treatment known to confer clinical benefit
                  with the exception of subjects enrolled in combination cohorts with a PD-1i,
                  where a PD-1i is approved by the local regulatory agencies

               2. Stage 3: This stage may enroll subjects with the following cancers:

                  • 3L/4L PD-(L)1-naïve, platinum-resistant ovarian cancer

               3. Stage 4: This stage may enroll subjects with the following cancers:

                    -  2L/3L ccRCC. Subjects must have progressed on or after treatment with an
                       anti-PD-(L)1 agent in their most recent prior line of therapy

                    -  2L-4L TNBC. Subjects must have progressed on or after treatment with a prior
                       anti-PD-(L)1 therapy

                    -  1L, PD-(L)1-naïve, PD-L1+; combined positive score (CPS) ≥ 1% HNSCC

                    -  3L/4L, PD-(L)1-naïve, platinum-resistant ovarian cancer

                    -  2L/3L NSCLC; Subjects must have progressed on or after treatment with
                       platinum-based chemotherapy and an anti-PD-(L)1-containing therapy. The
                       anti-PD-(L)1 agent must have been a part of the most recent prior line of
                       therapy. Subjects with EGFR mutations and ALK rearrangements will be
                       excluded. Subjects with other targetable genomic aberrations for which FDA
                       approved therapies exist must have received appropriate FDA-approved
                       targeted therapy

                    -  2L/3L cSCC; Subjects must have progressed on or after treatment with an
                       anti-PD-(L)1 agent in their most recent prior line of therapy

                    -  2L-4L PD-(L)1-naïve UPS and LPS

          3. Measurable disease, according to the RECIST version 1.1, that has objectively
             progressed since (or on) previous treatment as assessed by the Investigator;

          4. ≥ 18 years of age;

          5. Eastern Cooperative Oncology Group performance status 0 or 1;

          6. Predicted life expectancy of ≥ 3 months;

          7. Have specified laboratory values (obtained ≤ 28 days prior to first dose) in
             accordance with the study protocol;

          8. For women of childbearing potential (WOCBP): negative serum pregnancy test during the
             Screening period and a negative urine pregnancy test up to 24 hours in advance of C1D1

          9. WOCBP and males whose partners are WOCBP must agree to use a highly effective method
             of birth control throughout their participation and for 5 months following the last
             study drug administration.

        Exclusion Criteria:

          1. Concurrent anticancer treatment, either FDA approved or investigational, for the
             cancer being evaluated in this study or for prior malignancies. A past history of
             other malignancies is allowed as long as the subject is not receiving treatment other
             than hormonal therapy and, in the judgment of the Investigator, is unlikely to have a
             recurrence. Of note, concurrent malignancies that do not require treatment and are
             clinically stable are allowed

          2. Prior infusion of JTX-8064, LILRB2, or ILT4-directed therapy;

          3. The therapies listed below within the specified timeframe:

               1. Immunotherapy or biologic therapy < 28 days prior to planned C1D1 or 5
                  half-lives, whichever is shorter

               2. Chemotherapy < 21 days prior to planned C1D1, or < 42 days for mitomycin or
                  nitrosoureas or 5 half-lives, whichever is shorter

               3. Targeted small molecule therapy < 14 days or 5 half-lives, whichever is shorter,
                  prior to planned C1D1

               4. Radiation therapy < 21 days prior to planned C1D1. Exception: Limited (e.g., pain
                  palliation) radiation therapy is allowed prior to and during study drug
                  administration as long as there are no acute toxicities, any AE due to prior
                  radiation therapy has recovered to < Grade 2, and the radiation is not
                  administered to a target lesion

          4. Symptomatic or uncontrolled brain metastases, leptomeningeal disease, or spinal cord
             compression not definitively treated with surgery or radiation (brain metastases that
             are stable and asymptomatic after prior treatment will be allowed);

          5. Women who are pregnant or breastfeeding or who plan to become pregnant/breastfeed
             while on study; men who plan to father children during the study

          6. Live vaccines ≤ 30 days of C1D1