Study of IMGN632 in Patients With Untreated BPDCN and Relapsed/Refractory BPDCN

Inclusion Criteria:

   1. Disease Characteristics:

   a. Confirmation of CD123 positivity by flow cytometry or IHC. Participants who
   received prior CD123-targeting agents will be allowed as long as the blasts still have
   detectable CD123 expression.

   2. Expansion inclusion:

      - Cohort 1 - Participants with relapsed or refractory blastic plasmacytoid
      dendritic cell neoplasm (BPDCN) with 1-3 prior lines of therapy

      - Cohort 2 - Participants with relapsed AML

      - Cohort 3 - Participants with relapsed relapsed or refractory ALL (including any
      subtypes: B-cell, T-cell, Ph+ and Ph-)

      - Cohort 4 - Participants with relapsed or refractory other hematologic
      malignancies not included in the cohorts above (eg, high risk/very high-risk MDS,
      MPN, CMML, BP-CML).

      - Cohort 5 - Participants with relapsed relapsed or refractory (to nonintense
      therapies) CD123+ AML.

      - Cohort 6 - Participants with frontline de novo BPDCN at screening who have not
      received prior systemic therapy and participants with frontline BPDCN who have
      PCHM and have not received prior systemic therapy.

Note: Participants in Cohort 6 may have received local therapy (radiotherapy, surgical
excision, photodynamic therapy). Eligible participants must have a recurrence or
progression in the field of local therapy OR disease outside the field of local therapy.

Exclusion Criteria:

   1. Participants who, in the judgment of their treating physician, have appropriate
   standard of care therapies will be excluded from Cohorts 1 through 5.

   2. Frontline BPDCN participants with central nervous system (CNS) disease will be
   excluded. A lumbar puncture must be performed during the 28-day screening period,
   prior to drug administration. Relapsed or refractory BPDCN participants with a known
   history of CNS disease must have been treated locally, have at least 1 lumbar puncture
   with no evidence of CNS disease, and must be clinically stable prior to first dose.
   Concurrent therapy for CNS prophylaxis or continuation of therapy for controlled CNS
   disease is permitted with the approval of the Sponsor.

   3. Participants with a history of veno-occlusive disease (sinusoidal obstruction
   syndrome) of the liver.

   4. Participants with a history of Grade 4 capillary leak syndrome, or non-cardiac Grade 4
   edema are ineligible, eg, related to tagraxofusp-erzs or other etiology.

   5. Interval from prior cancer therapy: 1. For frontline BPDCN participants with prior
   local therapy (eg, radiotherapy), participants must not have received treatment within
   14 days prior to drug administration on this study. 2. Relapsed or refractory BPDCN
   participants must not have received any anti-cancer therapy including chemotherapy,
   immunotherapy, radiotherapy, hormonal, biologic, or any investigational agents within
   14 days prior to drug administration on this study. Participants must have recovered
   to baseline from all acute toxicity from this prior therapy.

Note: the exception that participants who have received a checkpoint inhibitor must not
have received that therapy within 28 days prior to drug administration on this study.