Inclusion Criteria:

   - Diagnosis of multiple myeloma (MM) per the International Myeloma Working Group (IMWG)
   criteria

   - Eligible for autologous stem cell transplantation (ASCT) per institutional guidelines

   - Within 1 year of start of therapy for multiple myeloma

   - Cardiac and pulmonary status sufficient to undergo apheresis and transplantation per
   institutional transplant guidelines

   - Calculated creatinine clearance > 30 mL/min, according to the Modification of Diet in
   Renal Disease (MDRD) formula.

   - Absolute neutrophil count (ANC) > 1500 x 10e6/L

   - Platelet count > 100,000 x 10e6/L

   - Ability to understand and the willingness to sign a written informed consent document.

   - Agreement to use an approved form of contraception for male patients or female
   patients of childbearing potential.

Exclusion Criteria:

   - History of prior stem cell transplant for multiple myeloma or other indications

   - Planned tandem stem cell transplant

   - Prior history of failure to collect HSCs.

   - Total bilirubin > 1.5x upper limit of normal (ULN) in the absence of a documented
   history of Gilbert's syndrome

   - Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) > 3x ULN

   - Known allergy to MGTA-145 or plerixafor.

   - Lifetime exposure to lenalidomide or another immunomodulatory drug greater than 6
   cumulative months of treatment, ie, > 6 cycles of 28 days or > 8cycles of 21 days

   - Pregnant or lactating