Inclusion criteria:

          -  Personally signed informed consent document

          -  Male or female, age ≥18 years

          -  Relapsed or refractory CLL/SLL or MCL:

               -  CLL/SLL patients on at least 2nd line therapy, with a partial response at
                  Screening to ≥12 months ongoing treatment with Bruton's tyrosine kinase inhibitor
                  (BTKi) or venetoclax ± anti-CD20 MAb

               -  MCL patients on at least 2nd line therapy, with a partial response at Screening
                  to ≥6 months ongoing treatment with a BTKi

          -  MCL and SLL patients must have archived tumor biopsy tissue available, or have a new
             biopsy unless blood or bone marrow tests at Screening show detectable ROR1

          -  ECOG performance status ≤2

          -  Adequate organ function

               -  Bilirubin ≤1.5 x ULN (unless Gilbert's syndrome)

               -  AST and ALT ≤2.5 x ULN (if no hepatic CLL or MCL), or AST and ALT ≤5 x ULN (if
                  hepatic CLL or MCL)

               -  APTT and PT ≤1.5 x ULN

               -  ANC ≥0.5 x 10^9 /L (without growth factors) and platelets ≥ 30 x 10^9 /L (without
                  transfusion)

               -  Serum creatinine ≤2 x ULN

               -  Estimated creatinine clearance ≥30 mL/min

          -  In females of childbearing potential, a negative serum pregnancy test

          -  For both males and females, willingness to use adequate contraception

          -  Willingness and ability to comply with study procedures

        Exclusion Criteria:

          -  Richter's transformation

          -  CNS or leptomeningeal lymphoma

          -  High tumour bulk as defined in the protocol

          -  Allogeneic or autologous hematopoietic stem cell transplant or donor lymphocyte
             infusion within prior 6 months.

          -  Uncontrolled autoimmune haemolytic anaemia or idiopathic thrombocytopenic purpura

          -  Clinically significant neurological disease

          -  Clinically significant cardiovascular disease or ECG abnormalities

          -  Severe chronic lung disease

          -  Positive test at Screening for Covid-19, HIV, hepatitis B or hepatitis C infection

          -  Presence of other major cancer

          -  Any other concurrent cancer treatments

          -  Recent or planned live vaccines

          -  Uncontrolled ongoing infection

          -  Recent major surgery

          -  Concurrent participation in another clinical trial, or experimental therapy within 5
             half-lives of Screening

          -  Pregnant or currently breastfeeding.

          -  Any other medical condition that in the opinion of the investigator contraindicates
             participation in the study