Inclusion Criteria:

          1. Subjects with histologically confirmed diagnosis of inoperable locally advanced or
             metastatic TNBC.

          2. For Cohort 1 only, subjects must have received at least 1 prior line of systemic
             chemotherapy or immunotherapy that includes an approved regimen.

          3. For Cohort 2 only, subjects may only have received neoadjuvant and adjuvant treatment
             in the non-metastatic or operable disease setting and must not have progressed within
             6 months of last dose of (neo) adjuvant therapy.

          4. For both Cohorts 1 and 2, Subjects must have estrogen (ER) receptor and progesterone
             (PR) receptor staining <10% and be human epidermal growth factor receptor 2 (HER2)
             negative defined as immunohistochemistry (IHC) 0 to 1+

          5. For Cohort 2 only, subjects must have PD-L1 testing per Dako 22C3 Combined Positive
             Score (CPS) assay performed prior to dosing. Prior testing will be acceptable if
             completed per required assay. Otherwise recent or newly obtained biopsy at screening
             will be collected for central determination of PD-L1 expression.

          6. Subjects must not have disease that, in the opinion of the Investigator, is considered
             amenable to potentially curative treatment.

          7. Age ≥ 18 years of age of day of signing informed consent.

          8. Eastern Cooperative Oncology Group (ECOG) performance status 0-1.

          9. Life expectancy of at least 6 months.

         10. Have measurable disease based on RECIST v1.1, and at least one anatomically distinct
             lesion involving skin or subcutaneous tissue accessible for electroporation of ≥ 0.3
             cm and lesion must be accurately measured in at least one dimension (longest diameter
             in the plane of measurement is to be recorded).

         11. Demonstrate adequate organ function as defined below. All screening laboratories
             should be performed within 10 days of treatment initiation.

         12. For women of childbearing potential, negative serum or urine pregnancy test within 72
             hours prior to the first study drug administration. If the urine test is positive or
             cannot be confirmed as negative, a serum pregnancy test will be required.

         13. For women of childbearing potential, must be willing to use an adequate method of
             contraception from 30 days prior to the first study drug administration and 120 days
             following last day study drug administration (either tavo or pembrolizumab). Women may
             be surgically sterile or at least 1-year post-last menstrual period.

         14. Male subjects must be surgically sterile or must agree to use contraception during the
             study and at least 120 days following the last day of study drug administration.

         15. Able and willing to give informed consent and to follow study instructions.

        Exclusion Criteria:

          1. Subject has a known additional malignancy that is progressing or requires active
             treatment.

          2. Clinically active central nervous system (CNS) metastases. Subjects with previously
             treated brain metastases may participate provided they are radiologically stable,
             i.e., without evidence of progression for at least 4 weeks by repeat imaging (note
             that the repeat imaging should be performed during study screening), clinically stable
             and without requirement of steroid treatment for at least 14 days prior to first dose
             of study drug.

          3. For Cohort 2 only, less than 6-month disease free interval from the last dose of
             (neo)adjuvant therapy.

          4. Subject who had an allogenic tissue/solid organ transplant.

          5. Subjects with electronic pacemakers or defibrillators.

          6. Subject who have a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2
             antibodies).

          7. Subjects who are known to be positive for Hepatitis B antigen (HBsAg) or Hepatitis B
             virus (HBV) DNA or Hepatitis C antibody or RNA. Active Hepatitis C is defined by a
             known positive Hep C Ab result and known quantitative hepatitis C virus (HCV) RNA
             results greater than the lower limits of detection of the assay.

          8. Subject has a diagnosis of immunodeficiency or is receiving chronic systemic steroid
             therapy (in dosing exceeding 10 mg/day of prednisone or equivalent) or any other form
             of immunosuppressive therapy within 7 days prior to the first dose of study drug. The
             use of physiologic doses of corticosteroids may be approved after consultation with
             the Sponsor.

          9. Subjects who have received a live-virus vaccination within 30 days of the first dose
             of treatment. Seasonal flu vaccines that do not contain live virus are permitted.

         10. Subject has severe hypersensitivity (≥Grade 3) to pembrolizumab or other anti-PD-1
             monoclonal antibody therapy and/or any of its excipients.

         11. For Cohort 2 only: Subject has severe hypersensitivity (≥Grade 3) to nab-paclitaxel
             (Abraxane). Patient must be able to tolerate the trial approved chemotherapy.

         12. Subjects who have received transfusion of blood products (including platelets or red
             blood cells) or colony stimulating factors (including G-CSF, GM-CSF or recombinant
             erythropoietin) within 3 weeks prior to study Cycle 1, Day 1 (Baseline).

         13. Subject has a history of (non-infectious) pneumonitis that required steroids or
             current pneumonitis.

         14. Subject has a history of interstitial lung disease.

         15. Subject has an active infection requiring systemic therapy.

         16. Subject has a history or current evidence of any condition, therapy, or laboratory
             abnormality that might confound the results of the study, interfere with the subject's
             participation for the full duration of the study, or is not in the best interest of
             the subject to participate, in the opinion of the treating Investigator.

         17. Subject has not recovered (i.e., ≤ Grade 1 or at Baseline) from adverse events (AEs)
             due to a previously administered agent.

         18. Participation in another clinical study of an investigational anti-cancer agent or has
             used an investigational device within 30 days of screening.

         19. Subject has known psychiatric or substance abuse disorders that would interfere with
             the subject's ability to cooperate with the requirements of the study.

         20. Subjects who are pregnant or breastfeeding or expecting to conceive children within
             the projected duration of the study, starting with the Screening visit through 120
             days after the last dose of study treatment.