Inclusion Criteria:

          1. Male or female age 18 years or older.

          2. Refractory or relapsed lymphoma (per World Health Organization (WHO) Classification
             system)

          3. Pathologically confirmed relapsed or refractory lymphoma

          4. Availability of formalin-fixed paraffin-embedded (FFPE) tumor tissue block.

          5. Measurable disease, defined by the 2014 Lugano Classification Criteria and Global
             Response Score Grading Scales for cutaneous T-cell lymphoma (CTCL)

          6. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2.

          7. Absolute neutrophil count ≥1500/µL. Criterion not applicable to adult T cell
             leukemia/lymphoma (ATLL) patients.

          8. Platelet count of ≥75000/µL. Criterion not applicable to ATLL patients.

          9. Hemoglobin ≥9.0 g/dL without transfusion within the 2 weeks prior to Day 1.

         10. Serum/plasma creatinine ≤1.5 mg/dL, or if the participant has a creatinine > 1.5
             mg/dL, a measured creatinine clearance must be > 80 mL/min as calculated by the
             Cockcroft and Gault equation

         11. Serum alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase
             ≤2 times the upper limit of normal (ULN); ≤ 5 times ULN if there is liver or bone
             involvement.

         12. Total serum/plasma bilirubin ≤1.5 times ULN (participants with known Gilbert's
             syndrome may have a total bilirubin up to ≤3 times ULN)

         13. Women of childbearing potential must have a negative serum beta-human chorionic
             gonadotropin pregnancy test within 7 days prior to Day 1.

         14. Women of childbearing potential must agree to use a highly effective method of
             contraception. Men with female partners who are of childbearing potential must agree
             that they or their partners will use a highly effective method of contraception.

        Exclusion Criteria:

          1. Participants who have an option for any treatment with proven clinical benefit for
             their lymphoid malignancy at current state of disease.

          2. Active graft-versus-host disease.

          3. Autologous or allogenic transplant within the 60 days prior to Cycle 1 Day 1 (C1D1)

          4. Evidence of myelodysplasia or myeloid leukemia by morphology, immunostains, flow
             cytometry, or cytogenetics on a bone marrow aspirate or biopsy.

          5. Known history of positive serum human anti-drug antibody (ADA) or known allergy to any
             component of ADCT-301.

          6. History of symptomatic autoimmune disease (e.g., rheumatoid arthritis, systemic
             progressive sclerosis [scleroderma], systemic lupus erythematosus, Sjögren's syndrome,
             autoimmune vasculitis [e.g., Wegener's granulomatosis])

          7. History of neuropathy considered of autoimmune origin (e.g., polyradiculopathy
             including Guillain-Barré syndrome and myasthenia gravis); other central nervous system
             autoimmune disease (e.g., poliomyelitis, multiple sclerosis).

          8. History of recent infection (within 4 weeks of C1D1) considered to be caused by one of
             the pathogens listed: herpes simplex virus Type 1 (HSV1), herpes simplex virus Type 2
             (HSV2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV),
             measles, Influenza A, Zika virus, Chikungunya virus, mycoplasma pneumonia,
             Campylobacter jejuni, or enterovirus D68.

          9. Known seropositive for human immunodeficiency virus (HIV), hepatitis B surface antigen
             (HbsAg), or antibody to hepatitis C virus (anti-HCV) with confirmatory testing and
             requiring anti-viral therapy. Note: testing is not mandatory to be eligible.

             If participant is at risk for having undiagnosed hepatitis C virus (HCV) (e.g.,
             history of injection drug use), HCV testing should be considered.

         10. History of Steven's Johnson's syndrome or toxic epidermal necrolysis syndrome.

         11. Pregnant or breastfeeding women.

         12. Significant medical comorbidities, including uncontrolled hypertension (diastolic
             blood pressure > 115 mm Hg), unstable angina, congestive heart failure (greater than
             New York Heart Association class II), severe uncontrolled ventricular arrhythmias, or
             electrocardiographic evidence of acute ischemia, poorly controlled diabetes, severe
             chronic pulmonary disease, coronary angioplasty, or myocardial infarction within 6
             months prior to screening, or uncontrolled atrial or ventricular cardiac arrhythmias.

         13. Use of any other experimental medication(s) within 14 days or 5 half-lives, but in no
             case < 14 days prior to the start of study treatment on Cycle 1, Day 1, except if
             approved by the Sponsor.

         14. Major surgery, radiotherapy, chemotherapy, or other anti-neoplastic therapy (including
             prednisone ≥ 40 mg/day or equivalent) within 14 days or 5 half-lives (whichever is
             shorter) prior to Cycle 1, Day 1 treatment, except if approved by the Sponsor.

         15. Failure to recover (to Common Terminology Criteria for Adverse Events [CTCAE Version
             4.0] Grade 0 or Grade 1) from acute non-hematologic toxicity (except all grades of
             alopecia or Grade 2 or lower neuropathy), due to previous therapy, prior to Screening.

         16. Congenital long QT syndrome or a corrected QT interval (QTc)≥ 450 ms at screening
             (unless secondary to pacemaker or bundle branch block).

         17. Active second primary malignancy other than non-melanoma skin cancers, nonmetastatic
             prostate cancer, in situ cervical cancer, ductal or lobular carcinoma in situ of the
             breast, or other malignancy that Sponsor Medical Monitor and Investigator agree, and
             document should not be exclusionary.

         18. Any other significant medical illness, abnormality, or condition that would, in the
             Investigator's judgment, make the participant inappropriate for study participation or
             put the participant at risk.