• Life expectancy at least 12 weeks

• Histologically-confirmed MCL, with documentation of either overexpression of cyclin D1 or the presence of t(11:14)

• Relapsed (disease progression after the last treatment regimen) or refractory (failure to achieve a partial or complete response from the last treatment regimen) disease

• At least 1 line of prior systemic therapy including a BTK inhibitor and additional systemic therapy option

• Confirmed availability of tumor tissue, unless deemed unsafe per investigator assessment

• At least one bi-dimensionally measurable (defined as at least 1.5 cm) nodal lesion, or one bi-dimensionally measurable (at least 1 cm) extranodal lesion, as measured on CT scan

• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

• Negative HIV test at screening

• Adequate hematological function