Flotetuzumab in Treating Patients With Recurrent or Refractory CD123 Positive Blood Cancer

PRIMARY OBJECTIVES:

I. Evaluate the anti-tumor activity of flotetuzumab in CD123-positive advanced acute
lymphoblastic leukemia (ALL) (Cohort A) and other hematological malignancies (Cohort B), as
assessed by complete remission (complete remission [CR]/complete remission with incomplete
count recovery [CRi]/complete remission with partial hematological recovery [CRh]) rate.

SECONDARY OBJECTIVES:

I. Evaluate toxicity profile of flotetuzumab. II. Evaluate remission duration among
responders. III. Estimate 1-year overall survival. IV. Evaluate minimal residual disease
(MRD) status in responders in the ALL cohort.

V. Evaluate the percentage of patients who receive subsequent allogeneic transplantation.

EXPLORATORY OBJECTIVES:

I. Examine immune profile pre- and post-treatment with flotetuzumab. II. Assess the
association between CD123 expression and tumor response. III. Assess the association between
alterations in tumor genetic or microenvironment with response.

IV. Assess cytokine levels during therapy.

OUTLINE:

Patients receive flotetuzumab intravenously (IV) continuously for 28 days. Patients who
achieve partial response or stable disease or any clinical benefit (partial remission [PR],
stable disease [SD]) that did not meet CR, CRi, CRh or morphologic leukemia free state (MLFS)
criteria receive a second 28-day continuous flotetuzumab IV infusion. Patients who achieve
CR/CRi/CRh/MLFS after course 1 or course 2 receive flotetuzumab IV at a 4 days on-3 days off
schedule. Treatment repeats every 28 days for up to 6 courses in the absence of disease
progression or unacceptable toxicity.

After completion of study treatment, patients are followed up at 30 days and then up to 1
year.

Inclusion Criteria:

- Documented informed consent of the participant and/or legally authorized
representative.

- Assent, when appropriate, will be obtained per institutional guidelines

- Agreement to allow the use of archival tissue from diagnostic tumor biopsies

- If unavailable, exceptions may be granted with study principal investigator (PI)
approval.

- Eastern Cooperative Oncology Group (ECOG) =< 2

- Histologically confirmed diagnosis of

- Cohort A. Acute lymphoblastic leukemia

- B-cell phenotype: patients with relapsed or refractory ALL who have received
at least 2 prior regimens and failed or are ineligible for CD19-based target
therapy

- T-cell phenotype: patients with relapsed or refractory who have received at
least 1 prior regimen

- Cohort B. Other CD123+ hematological malignancies that failed standard regimens,
excluding acute myeloid leukemia and myelodysplastic syndrome

- Blastic plasmacytoid dendritic cell neoplasm (BPDCN) patients who have
failed or relapsed after initial therapy

- Chronic myeloid leukemia (CML) patients who have failed or relapsed or
ineligible for third generation tyrosine kinase inhibitor (ponatinib)

- Hairy cell leukemia patients who have failed or progressed shortly after
purine analogs or failed 2 cycles of purine analog

- Systemic mastocytosis patients who have failed or progressed on midostaurin

- Hodgkin lymphoma patients who have failed or relapsed after PD-1/PD-L1-
inhibitors and brentuximab vedotin

- Advanced acute leukemia patients with ambiguous lineage or biphenotypic
leukemia that failed 2 lines of prior regimens

- Patients with any other advanced CD123+ hematological malignancy who have
failed standard therapy per the treating physician's judgement

- Relapsed or refractory disease as defined above

- Tumor cells expressing CD123 either by flow cytometry or immunohistochemistry staining
as defined below

- Measurable disease of at least 1.5 cm on computed tomography (CT)/magnetic resonance
imaging (MRI) for cases without bone marrow involvement

- Peripheral blast count < 20,000/ul at the time of initiation of infusion on cycle 1
day 1

- Life expectancy of at least 4 weeks

- Fully recovered from the acute toxic effects (except alopecia) to =< grade 1 to prior
anti-cancer therapy

- Absolute neutrophil count (ANC) >= 750/ul (to be performed within14 days prior to day
1 of protocol therapy unless otherwise stated)

- NOTE: Growth factor is not permitted within 14 days of ANC assessment unless
cytopenia is secondary to disease involvement

- Platelets >= 50,000/ul (to be performed within14 days prior to day 1 of protocol
therapy unless otherwise stated)

- NOTE: Platelet transfusions are not permitted within 14 days of platelet
assessment unless cytopenia is secondary to disease involvement

- Lumbar puncture to assess presence of central nervous system (CNS) disease if there
are symptoms and signs concerning for CNS involvement (to be performed within14 days
prior to day 1 of protocol therapy unless otherwise stated)

- Total bilirubin =< 1.5 X upper limit of normal (ULN) (unless has Gilbert's disease)
(to be performed within14 days prior to day 1 of protocol therapy unless otherwise
stated)

- Aspartate aminotransferase (AST) =< 2.5 x ULN (to be performed within14 days prior to
day 1 of protocol therapy unless otherwise stated)

- Alanine aminotransferase (ALT) =< 2.5 x ULN (to be performed within14 days prior to
day 1 of protocol therapy unless otherwise stated)

- Serum creatinine level =< 1.5 times the ULN or a calculated or measured creatinine
clearance of >= 50 mL/min per 24 hour urine test or the Cockcroft-Gault formula (to be
performed within14 days prior to day 1 of protocol therapy unless otherwise stated)

- Seronegative for human immunodeficiency virus (HIV) antigen (Ag)/antibody (Ab) combo,
hepatitis C virus (HCV)*, active hepatitis B virus (HBV) (surface antigen negative),
and syphilis (rapid plasma reagin [RPR]) (to be performed within14 days prior to day 1
of protocol therapy unless otherwise stated)

- If positive, hepatitis C ribonucleic acid (RNA) quantitation must be performed

- Meets other institutional and federal requirements for infectious disease titer
requirements

- Note Infectious disease testing to be performed within 28 days prior to day 1 of
protocol therapy

- Women of childbearing potential (WOCBP): negative urine or serum pregnancy test (to be
performed within14 days prior to day 1 of protocol therapy unless otherwise stated)

- If the urine test is positive or cannot be confirmed as negative, a serum
pregnancy test will be required

- Agreement by females and males of childbearing potential* to use an effective method
of birth control or abstain from heterosexual activity for the course of the study
through at least 6 months after the last dose of protocol therapy.

- Childbearing potential defined as not being surgically sterilized (men and women)
or have not been free from menses for > 1 year (women only)

Exclusion Criteria:

- Autologous or allogeneic hematopoietic cell transplant performed within 100 days prior
to study drug administration in day 1 of cycle 1 of protocol therapy. However,
patients who received allogeneic hematopoietic cell transplantation (HCT) more than
100 days are allowed if no active graft versus host disease (GVHD) > grade 1 and not
actively on systemic immunosuppressive therapy

- Chemotherapy, radiation therapy, biological therapy, within 14 days prior to day 1 of
protocol therapy. Maintenance-type ALL chemotherapies, including vincristine and
mercaptopurine are allowed up to 7 days before starting therapy. High dose steroids
are allowed up to 3 days before starting therapy. Cytoreduction with hydroxyurea is
allowed to control leukocytosis until to the day of starting therapy. Hydroxyurea can
be given during cycle 1 of flotetuzumab administration to control leukocytosis but
need to be discussed with the study PI

- Previous treatment with immunotherapeutic agents (for example chimeric antigen
receptor [CAR] T cells, long acting bispecific antibodies, etc) in the 28 days period
prior to study drug administration on day 1 cycle 1, with the exception of short-half
bispecific antibodies (blinatumomab) where the washout period is only 14 days

- Requirement, at the time of study entry, for concurrent steroid > 10 mg/day of oral
prednisone or the equivalent, except steroid inhaler, nasal spray or ophthalmic
solution

- Use of immunosuppressant medications (other than steroid as noted above) in the 2
weeks prior to study drug administration (cycle 1 day 1)

- Known central nervous system involvement. Patients with suspected CNS involvement must
be evaluated by lumber puncture and be free of CNS disease prior to study entry.
Previously treated CNS involvement is allowed provided adequate treatment has been
provided and the patient is free of CNS disease

- History of allergic reactions attributed to compounds of similar chemical or biologic
composition to flotetuzumab

- Any active untreated autoimmune disorders (with the exception of vitiligo)

- Dementia or altered mental status that would preclude sufficient understanding to
provide informed consent

- Second primary malignancy that requires active therapy. Adjuvant hormonal therapy is
allowed

- Active uncontrolled infection

- Significant pulmonary compromise

- Unstable angina or clinically significant heart disease

- Major trauma or surgery within 4 weeks before enrollment

- Clinically significant uncontrolled illness

- Known history of immunodeficiency virus (HIV) or hepatitis B or hepatitis C infection

- Females only: Pregnant or breastfeeding

- Any other condition that would, in the Investigator's judgment, contraindicate the
patient's participation in the clinical study due to safety concerns with clinical
study procedures

- Prospective participants who, in the opinion of the investigator, may not be able to
comply with all study procedures (including compliance issues related to
feasibility/logistics)