Corporate Presentation

August 2020

Forward Looking Safe Harbor Statement

This presentation may contain “forward-looking statements” within the meaning of Section

27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934,

each as amended. These statements are often, but not always, made through the use of

words or phrases such as “anticipates”, expects”, plans”, believes”, “intends”, and similar

words or phrases. Such statements involve risks and uncertainties that could cause

Mustang Bio’s actual results to differ materially from the anticipated results and

expectations expressed in these forward-looking statements. These statements are only

predictions based on current information and expectations and involve a number of risks

and uncertainties. Actual events or results may differ materially from those projected in any

such statements due to various factors, including the risks and uncertainties inherent in

clinical trials, drug development, and commercialization. You are cautioned not to place

undue reliance on these forward-looking statements, which speak only as of the date

hereof. All forward-looking statements are qualified in their entirety by this cautionary

statement and Mustang Bio undertakes no obligation to update these statements, except

as required by law.

2

Mustang Bio:

Building a Fully

Integrated Gene & Cell

Therapy Company

▪ Mustang (NASDAQ:MBIO) is focused on developing next-generation therapies for patients with cancer and rare genetic diseases

▪ Transformational ex vivo lentiviral gene therapy for XSCID licensed from St. Jude

– Highly compelling results in 2 ongoing clinical trials led by St. Jude & NIH

– Targeting approval of Mustang INDs for both programs 2H2020

▪ Lead CAR-T targeting CD20 is generating early encouraging results in lymphoma

– Targeting disclosure of phase 1 data in December at ASH

– Anticipate filing Mustang IND 1Q2021 for pivotal phase 1/2 trial in NHL & CLL

– 5 COH CAR-Ts also in phase 1 trials; first Mustang IND trial targets CD123, now enrolling

▪ Phase 1 oncolytic virus from Nationwide to enhance CAR-T activity in glioblastoma

▪ 27,000 square foot cell processing & translational research facility on UMass Medical School campus with capacity to launch at commercial scale

▪ Team with extensive gene & cell therapy industry experience

3

Leadership Team with Extensive Gene, Cell & Rare Disease Therapy Experience

4

James Edinger, PhD

VP, Preclinical Sciences

Debra Manning, SPHR

VP, Human Resources

Knut Niss, PhD

Chief Technology Officer

Brian Achenbach, MBA

SVP, Finance & Corporate Controller

Manuel Litchman, MD

President & Chief Executive Officer

Greg Furrow, MS, FRQA

VP, Quality

Lynn E. Bayless, MS

Head, Regulatory Affairs

Regan Flynn, SHRM-CP

Executive Assistant / HR Generalist

John Bernard, MD

Senior Medical Director

Scott Smith, MBA

Senior Director, Alliance & Program Mgmt

▪ Technology licensed from City of Hope (COH), Fred Hutch Cancer Research Center (FHCRC), Nationwide Children’s Hospital, & St. Jude Children’s Research Hospital

▪ Research based on pioneering work by:

5

R&D Collaborators: World Class Team of Scientific Experts

Dr. Stephen Forman

City of Hope

Dr. Christine Brown

City of Hope

Dr. Brian Till

FHCRC

Dr. Kevin Cassady

Nationwide

Dr. Brian SorrentinoSJCRH

(1958-2018)

Therapeutic

Modality

Target

(Partner)2020 2021 2022 2023

Ex-vivo

Gene TherapyIL2RG

(St. Jude)

CAR-T

Therapy

He

ma

tolo

gic

Ma

lig

nan

cie

s CD123(COH)

CD20(FHCRC)

CS1(COH)

So

lid

Tu

mo

rs

IL13Rα2(COH)

C134 OV(Nationwide)

PSCA(COH)

HER2(COH)

Mustang files new IND

COH files new IND

Topline data available

Robust Pipeline of Therapies Addressing Highly Challenging Diseases

Pivotal Phase 1/2 Blastic plasmacytoid dendritic cell neoplasm (Mustang IND) [AML & hrMDS may be added at higher dose levels]

Phase 1 NHL at FHCRC Pivotal Ph 1/2 NHL & chronic lymphocytic leukemia (Mustang IND)

Phase 1/2 GBM: CAR-T + OV (Mustang IND)

Phase 1 Prostate cancer at COH* Phase 1/2 Prostate & pancreatic cancer (Mustang IND)

Phase 1 GBM at UAB*

Phase 1 GBM: CAR-T + nivolumab ± pretreatment with nivolumab and ipilimumab at COH*

Phase 1 GBM: CAR-T for leptomeningeal disease at COH

Phase 1/2 GBM: CAR-

T + OV at COH

Ph 1 Multiple myeloma (MM) at COH Pivotal Phase 1/2 Multiple myeloma (Mustang IND)

Phase 1 GBM & metastatic HER2+ cancer to brain at COH* Phase 1/2 Met. HER2+ cancer to brain (Mustang IND)

6

CMC Hold: Pivotal Phase 2 XSCID newly diagnosed (Mustang IND)

Pivotal Phase 2 XSCID previously transplanted (Mustang IND)Ph 1Ph 1 at NIH

Ph 1

St. Jude = St. Jude Children’s Research Hospital Nationwide = Nationwide Children’s Hospital hrMDS = High-risk myelodysplastic syndrome

NIH = National Institutes of Health UAB = University of Alabama at Birmingham NHL = Non-Hodgkin lymphoma

COH = City of Hope National Medical Center XSCID = X-linked severe combined immunodeficiency GBM = Glioblastoma multiforme

FHCRC = Fred Hutchinson Cancer Research Center AML = Acute myelogenous leukemia OV = Oncolytic virus

* Partially or totally supported by grants

7

▪ Facility was built & fully operational prior to enrolling first patient on Mustang IND trial

▪ Universal platform process developed for autologous CAR-Ts; 1st patient’s cells expected 3Q2020

▪ Deep expertise of our people leveraged to also process XSCID patients’ cells starting 4Q2020

Cell Processing: A Core Competency & Competitive Advantage

Leukapheresis Enrichment

Activation

Transduction

Wash

Expansion

Harvest

Fill

Cryopreservation

Shipment

Shipment Thawing

Infusion

Day 0Day -1 Day 2 Day 3 Day 7

CoA

Day 15+ Day 19+8-day sterility

0

20

40

60

80

100

120

A B C D E F MBIO

Direct RM Costs per RunDirect raw material cost (excl. LV)

Leading Companies & Academic Institutions

% C

om

pan

y A

CD123

CS1

Direct Labor (h) for 10 processes

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7

FTE

Sum

Process Day

8

Cleanroom space

Labs (QC/PD and Research)Office

Master Site File with FDA as part of MB-102 IND (open)

Mustang’s Manufacturing Site – Current West Wing SpaceEast Wing now office & storage space; clean rooms & labs to be build out in 2021

Landlord: UMass

Lease Start: Oct 2017

Duration: 9 years

Mustang Milestones over Next 12 Months

9

Therapy Type

Asset (Target)

Event Type

Expected Event Timing

Gene Therapy

MB-107, MB-207

Trial Start Resolve CMC hold, begin accrual to pivotal trial in newly diagnosed XSCID pts Q3, Q4

IND Filing File Mustang IND for pivotal trial in previously transplanted XSCID patients Q3

CAR-T

MB-106 (CD20)

Data Potential first data at ASH from FHCRC trial in NHL Q4

IND Filing Tech transfer from FHCRC and prepare for Mustang IND filing for NHL and CLL Q1’21

MB-105 (PSCA)

Data Potential first data from COH trial in prostate cancer Q1’21

MB-102 (CD123)

Trial Start Treat first patient in Mustang IND multicenter trial for BPDCN, AML, & hrMDS Q3

Data Potential follow-up data from COH trial in AML & BPDCN Q2’21

MB-101 (IL13Rα2)

IND Filing Support COH IND filing for combination trial with MB-108 oncolytic virus for GBM Q4

X-Linked Severe Combined Immunodeficiency (XSCID): Profound deficiency of T, B & NK Cell Immunity Due to Mutations in the IL2RG Gene1

10

βchain Common

chain

IL-2, 4, 7, 9, 15 or 21 X Mutated

c

XSCID

Interleukin receptor1. Fischer A et al. Nat Rev Dis Primers. 2015 (Oct 29);1:15061.

▪ IL2RG codes for common gamma chain (c) – critical for development of normal immune cells

▪ Early diagnosis & treatment possible in areas with newborn screening (NBS) or in patients with family history

▪ In the absence of NBS, most patients (almost all males) are diagnosed at 3 – 6 months when maternal immunity wanes

– Recurrent bacterial, viral and fungal infections

– Diarrhea, protein-losing enteropathy, failure to thrive

▪ Death by age 1 if untreated

▪ Standard of care is immune reconstitution via allogeneic hematopoietic stem cell transplant (HSCT)

XSCID Is the Most Common Form of Combined Immunodeficiency1

11

▪ US: ~20 new cases per year ▪ Rest of world: ~55 new cases per year in high/mid-income ex-US markets

Newly-diagnosed infants: Worldwide annual incidence of ~1:225,000 live births

“Reservoir” (patients with XSCID who have been previously treated with allogeneic HSCT and who therefore might be eligible for gene therapy now or in the future)

▪ US ≈ 400 patients ▪ High/mid-income ex-US markets ≈ 650 patients

1. Third-party analysis based on NBS data, medical literature, registry data & KOL interviews. Addressable ex-US markets include Canada & mid to high income countries in Europe, Asia, Latin America & Middle East.2. https://primaryimmune.org/idf-advocacy-center/idf-scid-newborn-screening-campaign.3. http://www.scid.net/the-scid-homepage/newborn-screening-where-it-began.4. Meehan C et al. Rev Paul Pediatr. 2018;36:388-397.

▪ Newborn screening for SCID is available in all 50 states, D.C., & Puerto Rico2,3

▪ Very few countries outside the US have nationwide newborn screening for SCID4

Collaboration with St. Jude Around XSCID Gene Therapy Leverages the Talent of Our Team As Well As the Capacity of Our Cell Processing Facility

12

▪ Ex vivo lentiviral transduction of patients’ hemato-poietic stem cells with normal copy of mutated c gene

▪ Process & supply chain are analogous to CAR-Ts

▪ Vector encodes normal ɣc receptor chain

– Strong preclinical efficacy & safety:no activation of LMO2 oncogene1

– Produced from a proprietary stable lentivirus producer cell line at St. Jude Vector Facility2

– Cell line licensed from CSL Behring in 2019

1. S. Zhou et al. Blood. 2010;116:900-908.2. RE Throm et al. Blood. 2009;113:5104-10.

1. Bone marrow harvest or apheresis

2. Lentiviral vector transduction

Cryopreservation

4. Low-dose busulfan

5. Cell infusion3. -160o C

MB-107

13

HSCT Remains Standard of Care, But Better Therapy Urgently Needed

1. Hacein-Bey-Abina S. NEJM. 2014;371:1407-1417.2. Heimall J. Expert Rev Clin Immunol. 2017;13:1029–1040.3. Pai S-Y. NEJM. 2014;371:434-446.4. Haddad E. Blood. 2018;132:1737-1749.5. Amatuni GS. Pediatrics. 2019;143(2): doi: 10.1542/peds.2018-2300.

Source: ASGCT presentation by MJ Cowan, May 2018.

MSD

MORD

MMRD

URD – UCB

URD

Years

MSD Matched sibling donorMORD Matched other related donorMMRD Mismatched related donorURD Unrelated donor – peripheral blood/bone

marrowURD – UCB Unrelated donor – umbilical cord blood

Pro

bab

ility

of

Surv

ival

Donor Type▪ Only 15% of patients have a matched sibling donor (MSD)

▪ Absent MSD, survival is lower & complications are higher

▪ Mortality ~50% if severe infections present at time of HSCT1

▪ Quality of life is poor due to late morbidities2

– 20% experience acute graft-vs-host disease, 15% chronic GVHD

– T-cell immunity decreases over time in ≥ 20%, leading to infections & diarrhea

– Up to 70% require lifelong intravenous immunoglobulin4,5

• Only 1/3 have sufficient B-cell reconstitution at 2 - 5 years4

– 20% require 2nd HSCT due to poor T-cell reconstitution3

MB-107: Impressive Results in Newborns Reported in April 2019 NEJMFollow-up data reported at ASH, December 2019

• Multicenter trial demonstrates first successful use of a lentiviral vector following targeted low-

exposure busulfan as first treatment for newly diagnosed infants with XSCID

• All patients experienced broad immune reconstitution with excellent safety profile

14Source: Mamcarz E et al. N Engl J Med. 2019;380:1525-1534.

MB-107: Clinical Outcome Continues to Be PromisingMedian follow-up = 23.6 months

15

Pt No.

Age (mos)

CD34+ Cell Dose(x106/kg)

VCN of Graft(VCN/cell)

Follow-up (mos)

Current Status

1 6 4.46 0.16 33.9Coronavirus & CMV resolved post boost; recent detection of CMV, now resolved;

developed autoimmune cytopenia, now resolved

2 3 8.67 1.13 32.1 Off IVIG, Immunized

3 4 9.26 0.80 29.1 Off IVIG, Immunized

4 14 6.93 0.35 26.1 Disseminated BCG & Legionella resolved; no response to immunizations

5 3 6.02 0.44 24.7 Off IVIG, Immunized

6 11 4.60 0.17 23.6 Disseminated BCG resolved; off IVIG; responded to polio vaccine

7 2 15.10 1.10 20.1 Outpatient

8 3 6.52 0.36 16.0 Outpatient; ulcers resolved

9 4 18.95 0.45 10.4 Outpatient; adenovirus & candidiasis resolved

10 7 11.01 1.09 6.5 Outpatient; off IVIG

11 6 10.05 0.57 1.5 Outpatient; BCG site quiescent

Source: Mamcarz E et al. Blood. (2019) 134 (Suppl 1): 2058. https://doi.org/10.1182/blood-2019-126746 [ASH 2019]

▪ All patients remain outpatient

▪ Patients with follow-up >3 months recovered from infections & are off isolation & protective antimicrobials

▪ Five patients off IVIG; 3 responded to vaccines

MB-107: Robust Functional Immune ReconstitutionPeripheral blood immune-cell subsets assessed by flow cytometry

9 patients, with 3 months’ follow-up, achieved normal for age T-cell & NK-cell numbers within 3-4 months

16

Patient #1 Patient #1

In all evaluable patients, IgM normalized by 6-12 months

• Patient #1 received boost @ 12 mos, then normalized T-cells in 3 mos

• Phytohemagglutinin (PHA) stimulation assays showed normal T-cell function

Source: Mamcarz E et al. Blood. (2019) 134 (Suppl 1): 2058. https://doi.org/10.1182/blood-2019-126746 [ASH 2019]

MB-107: Sustained Multi-Lineage Vector, Polyclonal Insertion

17

• In addition, vector insertion site analysis demonstrated polyclonality on all evaluated lineages

Source: Mamcarz E et al. Blood. (2019) 134 (Suppl 1): 2058. https://doi.org/10.1182/blood-2019-126746 [ASH 2019]

MB-107: Conclusions from Newborn Trial & Future Directions

• Clinical

– Low-exposure busulfan + LV vector gene therapy is well tolerated & results in development of a functional immune system

– No evidence of malignant transformation observed with median follow-up of ~2 years

– Results support Mustang’s goal to replace HSCT with gene therapy in newborns without matched sibling donor

• Regulatory

– Mustang filed MB-107 IND pivotal phase 2 trial 2Q2020

• Trial is on CMC hold

• St. Jude, UCSF & Seattle Children’s will continue to accrue patients until FDA approves Mustang’s IND

– Regenerative Medicine Advanced Therapy (RMAT) Designation – granted 3Q2019

• Will facilitate Mustang’s IND regulatory interactions for MB-107

– Requests for Rare Pediatric Disease (RPD) & Orphan Drug designations submitted 2Q2020

• RPD designation would qualify Mustang for Voucher at time of approval

– Mustang is lining up additional US sites & laying foundation for expansion to Europe in 2021

• ATMP Designation in Europe granted 2Q2020; requests planned for Orphan Drug & PRIME designations in Europe

18

Pt No.

Age (yrs)

CD34+ (106/kg)

VCN Cells Infused

Date Infused

PB Myeloid VCN @ 3 mos

1 23 18 0.27 Oct 2012 0.07

2 22 16 0.17 Jun 2013 0.06

3 7 20 0.31 Mar2015 0.07

4 16 22 0.57 Jul 2015 0.23

5 10 25 0.36 Jul 2015 0.29

6 23 22 0.41 Feb 2016 0.33

7 3 32 0.30 Sep 2016 0.04

8* 12 36 0.27 Oct 2016 0.05

19

Pt No.

Age (yrs)

CD34+ (106/kg)

VCN Cells Infused

Date Infused

PB Myeloid VCN @ 3 mos

9 19 5 3.19 Feb 2019 1.72

10 13 9 4.70 Mar 2019 3.59

11 25 25 14.28 Mar 2019 6.44

12 34 28 3.07 Apr 2019 6.42

13 24 17 4.22 Jul 2019 0.23

8* 15 10 4.78 Jun 2019 2.54

Original transduction (OT) regimen (2012-2016) Transduction Enhancers (TE) regimen (2019)

Source: De Ravin SS et al. Blood (2019) 134 (Suppl 1): 608. https://doi.org/10.1182/blood-2019-127439. [ASH 2019]

*Patient 8 retreated with boost of cells manufactured using TE regimen

MB-207: Equally Encouraging Results in Previously Transplanted PatientsTransduction enhancers added in 2019: LentiBOOST™ + 16,16-dimethyl Prostaglandin E2

~10x OT VCN

MB-207: Results in First 8 Patients Treated with OT Regimen1

Confirm & Extend Positive 2016 Findings2

• Safety profile maintained vs. 2016 paper

– No indication of possible pre-cancerous cell proliferation

– No vector insertional leukemogenesis to date

– 1 patient died from pre-existing lung damage >2 years post-therapy – highlights importance of early intervention

• Substantial clinical improvement over baseline

• Impressive biomarker improvement

20

1. De Ravin SS et al. Blood (2019) 134 (Suppl 1): 608. https://doi.org/10.1182/blood-2019-127439. [ASH 2019]

2. De Ravin SS et al. Sci Transl Med. 2016; 8(335):335ra57.

MB-207: Stable Gene Marking in First 2 OT Patients

21

Gene marking as VCN per genome after treatment

Source: SS De Ravin et al. Sci Transl Med. 2016; 8(335):335ra57.

Patient 1 Patient 2

MB-207: Despite Excellent Results with OT Regimen, NIH Noted Room for Improvement

• Patient #8 – like newborn patient #1 – failed to achieve any of the lab or clinical landmarks

• Pace to achieve lab & clinical landmarks was slow (2-3 years in most patients)

• Slow increase in peripheral blood NK cells; only patient #1 achieved normal range (at year 7)

• Vector amount used per patient was high, particularly for adults

22

Transduction Enhancers subsequently included in cell processing to address these challenges

Source: De Ravin SS et al. Blood (2019) 134 (Suppl 1): 608. https://doi.org/10.1182/blood-2019-127439. [ASH 2019]

MB-207: TE Regimen Resulted in Accelerated Increase in NK Cell Numbers & NK Cell VCN & in first 3 Months

23

OT ET

OT ET

Source: De Ravin SS et al. Blood (2019) 134 (Suppl 1): 608. https://doi.org/10.1182/blood-2019-127439. [ASH 2019]

MB-207: TE Regimen Resulted in Accelerated Clearance of Chronic Norovirus Infection

OT Regimen

• 6/7 patients with norovirus cleared infection

• Patients required 1 – 3 years post therapy to cure infection

• Patient 8 did not clear the infection

TE Regimen

• Patients 9 & 10 cured chronic norovirus infection by 6 months post therapy

• Patients 11, 12 & re-treated 8 with norovirus infection are symptom free @ 3 – 6 months

24

Source: De Ravin SS et al. Blood (2019) 134 (Suppl 1): 608. https://doi.org/10.1182/blood-2019-127439. [ASH 2019]

MB-207: Summary of Regimen With TEs & Future Plans

• Several advantages for regimen with TEs observed with limited follow-up

– Accelerated clearance of norovirus & GI symptoms

– Accelerated production of NK cells, spike in IgM

– Accelerated increase in vector marking, with uniformly higher transduction product VCN

– Vector requirement was ~1/8 to 1/12 OT regimen

• Safety profile of regimen thus far similar to OT regimen

• Mustang currently considering possibility of incorporating LentiBOOST™ alone in MB-207 pivotal trial

• IND filing expected 3Q2020

• Requests for Rare Pediatric Disease & Orphan Drug designations submitted 2Q2020

• Expect to submit request for ATMP designation in Europe 3Q2020, RMAT in US in 2021

25

MB-106: CAR T Therapy for B-cell NHL & CLL1,2

26

▪ CD20 is a commercially validated target,3 and CD20 CAR Ts have been active in small pilot trials 4,5

1. Lee SY et al. J Immunother. 2018;41:19-31.2. NHL = Non-Hodgkin lymphoma; CLL = Chronic lymphocytic leukemia3. https://www.genengnews.com/the-lists/the-top-15-best-selling-drugs-of-

2017/77901068?page=24. Till BG et al. Blood. 2012;119:3940-3950.5. Zhang W-y et al. Signal Transduction and Targeted Therapy. (2016) 1, 16002;

doi:10.1038/sigtrans.2016.226

Source: Brian Till, Fred Hutchinson Cancer Research Center, unpublished data.

Spacer (IgG2 hinge linker)

Co-stimulatory domains

(CD28 and 4-1BB)

Signaling domain (CD3ζ)

Fully human CD20 scFv

ζ ζ

CD19t

NSG mice were injected i.v. with Raji-ffLuc tumor cells, followed 2 days later by i.v. injection of central memory T cells transduced with MB-106, an anti-CD19 CAR-T, or an empty vector.

1. Tumor burden over time (bioluminescence imaging)

2. Overall survival (Kaplan‐Meier plot)

In vivo antitumor effect of MB-106 compared with CD19 CAR

MB-106: Little Competition in CD20-Targeted Cell Therapy Space

• Major investigational competition for target is in bispecific antibody space (Regeneron, Genmab, Roche)

• One early clinical-stage biotech CD20 CAR-T in the US: Precision BioSciences’ off-the-shelf PBCAR20A– 2 academic CD19/CD20 dual CAR-Ts

– Several clinical-stage CD20 CAR-Ts in China

• One preclinical CD20 gamma-delta CAR-T (Adicet Bio, ADI-001)

• FHCRC initiated a single-center investigator IND trial with MB-106 in B-cell NHL 4Q20171

27 1. https://clinicaltrials.gov/ct2/show/NCT03277729

MB-106: Background to Cohort 4▪ Due to safety concerns, trial started with cyclophosphamide alone as lymphodepleting (LD)

chemotherapy

▪ Little activity in first 3 cohorts

• Cohort 1 (no fludarabine): 3.3 x 105 CAR-T cells/kg

• Cohort 2 (no fludarabine): 1 x 106 CAR-T cells/kg

• Cohort 3 (cyclophosphamide + fludarabine): 3.3 x 105 CAR-T cells/kg

▪ In collaboration with Mustang CMC team, FHCRC optimized cell processing

▪ In vivo experiments at FHCRC demonstrated superiority of the new process, resulting in decision to amend the IND & implement the process starting with Cohort 4

▪ First patient then enrolled in Cohort 4

• Due to enhanced in vivo potency of CAR-T cells relative to prior cohorts, dose was reduced to starting level:3.3 x 105 CAR-T cells/kg

• Complete LD chemotherapy regimen administered: Cyclophosphamide + fludarabine28

2017

2018

2019

2020

MB-106: CR Achieved at Day 28 in FL Patient1st patient dosed after Mustang-led optimization of cell processing

• Disease was refractory to initial therapy & 2 salvage regimens

• Patient experienced no cytokine release syndrome (CRS) or neurotoxicity

• Good CAR-T expansion noted

• Awaiting further follow-up data; trial continues to accrue well

29

MB-106: Next Steps

• FHCRC: Continue dose escalation, submit abstract for ASH 2020 Annual Meeting

• Mustang

• Tech transfer to start 3Q2020; plan for process development to address CLL

• Anticipate pre-IND meeting 4Q2020, IND filing 1Q2021

MB-105: CAR-T Therapy for Prostate & Pancreatic Cancer1

30

1. Priceman SJ et al. Oncoimmunology. 2017 Oct 16;7(2):e1380764.2. Saeki N et al. Clin Cancer Res. 2010;16:3533-3538.3. Abate-Daga D. Human Gene Therapy. 2014;25:1003-1012.4. https://clinicaltrials.gov/ct2/show/NCT03873805

• Estimated new cases in U.S. in 2018: Prostate 164,000, pancreatic 55,000

• Target: Prostate stem cell antigen (PSCA) – overexpressed on numerous solid tumors2,3

• Little CAR-T competition for target, somewhat more for prostate-specific membrane antigen (PSMA)

– Bellicum: PSCA CAR-T (Ph 1, NCT02744287)

– Poseida: PSMA CAR-T (Ph 1, NCT04249947)

– Tmunity: PSMA CAR-T (Ph 1, NCT04227275) (Not recruiting)

– Autolus: PSMA CAR-T (to start phase 1 1H2021)

• Ph 1 prostate cancer trial at COH is currently enrolling 3rd cohort

• Awaiting grant funding in order to initiate phase 1 trial in pancreatic cancer

31

• 3 patients treated in 1st cohort @ 100M cells without lymphodepleting (LD) chemotherapy

• 1st patient in 2nd cohort – 100M cells with LD chemo – experienced significant PSA decline at 28 days + substantial improvement on scans

• Therapy well tolerated; cytokine release syndrome treated only with tocilizumab

• Trial continues to accrue well; may permit additional data disclosure 1Q2021

• Mustang is targeting IND filing for 4Q2021

MB-105: PSCA CAR-T Showed Substantial Activity in 1st

Patient with LD Chemo

• ~11,800 new patients diagnosed in the US annually;7% 5-year survival2

• IL13R⍺2 is an attractive target for CAR-T development – Overexpressed in >75% of GBM patients

– Not expressed on normal brain cells

• No CAR-T programs competing for target

• MB-101 is first CAR-T to demonstrate durable remission in solid tumor setting

• Complex ~60-patient phase 1 trial now complete4-1BBIgG4 CD3ζ

5’ 3’CD4

tm

human IL-

13

Mutated at (E13Y) to preferentially bind IL-13R⍺21. Brown CE et al. Mol Ther. 2018;26:1-14.2. Ostrom QT et al. Neuro-Oncology. 2019;21(S5):v1-v100. doi: 10.1093/neuonc/noz150.

32

Co-stimulatory domain (4-1BB)

Signaling domain (CD3ζ)

Fully human binder tohuman IL13Rα2

Spacer [ IgG4(∆CH2) ]

ζ ζ

MB-101: IL13Rα2 CAR-T Therapy for Glioblastoma (GBM)1

MB-101: Phase 1 Clinical Trial CompletedStudy has established foundation for patient selection & combination trials

33

Treatment maycontinue with

additional optional infusions

Cycle 1 Cycle 2+

DL1 2 x 106 CAR+ 10 x 106 CAR+

DL2 10 x 106 CAR+ 50 x 106 CAR+

DL3 20 x 106 CAR+ 100 x 106 CAR+

Phase 1 Dosing Regimen

Unique Features of Recommended Phase 2 Regimen

1. Repeat dosing

2. Intracerebroventricular dosing (into cerebrospinal fluid) – in addition to intracavitary dosing (site of resection of tumor recurrence)

3. Selection for highly active TN/MEM cells

4. No lymphodepleting chemotherapy

MB-101: ICV CAR-T Cells Achieved Dramatic Results in a Refractory GBM PatientTumor noted to be “hot” (high infiltration of T cells) with significant leptomeningeal disease

34

5 tumors followed

T4 T5 T6 T7 T8

400

0

300

200

100

0 100 150 200 300250

First ICV infusion

Max

imu

m L

esi

on

Are

a (m

m2)

Intracavitary Cycles 1 - 6

Intracerebroventricular (ICV)Cycles 12 - 16

ICVCycles 7 - 11

Source: Brown et al. NEJM. 2016;375:2561-9.

T6

T7

T6

T7

Pre-Therapy Post-Therapy

▪ Complete response sustained for 7.5 months

▪ Initial tumors did not recur

▪ New lesions had ↓ IL13Rα2 expression

Days after enrollment

Day

86

D

ay 1

08

Day

28

9

D

ay 2

95

MB-101: 3 Approaches at COH to Enhancing Efficacy

35

1. Shi T et al. Frontiers in Immunology. 28 April 2020, https://doi.org/10.3389/fimmu.2020.00683.2. Cassady KA et al. Mol Ther Oncolytics. June 2017, vol 5. https://doi.org/10.1016/j.omto.2017.02.001. 3. https://clinicaltrials.gov/ct2/show/NCT036575764. Shen SH et al. Expert Opinion on Biological Therapy. 2020 Jun;20(6):579-591. doi: 10.1080/14712598.2020.17274365. https://clinicaltrials.gov/ct2/show/NCT04003649

Leptomeningeal disease (CAR-T alone)

• Best opportunity for activation of CAR-T cells?

• Pilot trial to start 3Q2020

Combination Strategy

Combine with Oncolytic Virus (OV)

• Best opportunity to make cold tumors hot?1

• OV in-licensed from Nationwide 20192,3

• Pilot combination trial to start 4Q2020

Combine with Checkpoint Inhibitors

• Best opportunity to overcome PD-L1-mediated immunosuppression due to CAR-T administration? 4

• Pilot combination trial with nivolumab started 2Q20205

Patient Selection Strategy

MB-101 IL13Rα2-Directed CAR-T for GBM

• US incidence: AML ~20,000; MDS ~15,000; BPDCN ~500-1,000

– Mustang has Orphan Drug Designation for BPDCN & AML

• Target overexpressed in high percentage of patients4,5,6

– Cellectis’ CD123 CAR-T is in Ph 1 for AML

– Other CD123 competitors include ADCs, bispecifics

– Stemline’s ELZONRIS™ is approved for BPDCN

• Ph 1 at COH has reached highest planned dose (500M cells)8

• Mustang IND approved 3Q2019; expect treatment of 1st

BPDCN patient 3Q209

36

MB-102: CD123 CAR-T Therapy for BPDCN, AML & high-risk MDS1,2,3

Median survival for all 3 diseases is generally ≤ 1 year7

1. Mardiros A et al. Curr Opin Hematol. 2015;22:484-488.2. Jonnalagadda M et al. Mol Ther. 2015;23:757-768.3. Zhang W et al. Blood. 2017;130:1917.4. Also known as IL-3R⍺5. Testa U et al. Biomarker Research. 2014;2:4.

Murine anti-CD123 scFv

IgG4-Fc

CD3ζ

3’scFv IgG4-Fc CD28 CD3ζ T2A EGFRt5’

Sources: • Mardiros A et al. Blood. 2013;122:3138–3148. • Budde L et al. Blood. 2017;130 (Suppl 1): 811

[ASH 2017, abstract #811]

6. Stevens BM et al. Blood. 2015;126:4104. 7. American Cancer Society; https://www.cancer.org/cancer/acute-

myeloid-leukemia/about/key-statistics.html8. https://clinicaltrials.gov/ct2/show/NCT02159495 9. https://clinicaltrials.gov/ct2/show/NCT04109482

CD28

MB-102: AACR Tumor Immunology & Immunotherapy Meeting, November 20181: COH Reported 2 MRD Negative CRs in AML, 1 CR in BPDCN

37

Pt. No.

Age/SexDx

Prior Lines;Allo (donor)

BM Blasts; CD123

Cytogenetics/ Molecular

Lympho-depletion

CAR T dose Response at Day 28

1 44/FAML/MDS

6; Y (MRD) 20%;-ve to dim

-7, Inv(3) Flu/Cy 50MDonor

PD40% blasts

2 54/FAML/MPD

4; Y (MRD) 18%;Dim to mod

IDH1 Flu/Cy 50MDonor

Morphologic leukemic-free state (MLFS)

3 43/FAML

4; Y (MRD) 20%;Dim

Normal Flu/Cy 200MDonor

CRi(MRD-ve by flow on day 14)

4 54/FAML

7; Y (MUD) 37%;Mod

t(3;7), +21 Flu/Cy 200MDonor (DLI)

SD20% blasts

5 42/FAML/MDS

6; Y (MRD) 41%Mod

-7, +8 Flu/CyDecitabine

187MDonor (DLI)

SD46% blasts

6 28/MAML

7; Y (MRD) 3%Dim

ComplexFLT3-TKD, N-RAS

Flu/Cy 200MDonor

CR(MRD+, 0.10% day 28)

7 36/FAML

10; Y (MRD, MUD)) 0.64%Dim

Complex-7, inv(3)

Flu/CyDecitabine

200MAuto

MLFS(MRD-ve CR day 84)

1 Presented by Dr. Budde at AACR Tumor Immunology & Immunotherapy Conference, Nov. 30, 2018.

MRD = Matched related donorMUD = Matched unrelated donor

MRD = Minimalresidual disease

Pt. No.

Age/SexDx

Prior Lines;Allo (donor)

BM Blasts; CD123

Cytogenetics/ Molecular

Lympho-depletion

CAR T dose Response at Day 28

8 74/M; BPDCN 1 (SL-401 x 6 => PR; No NED Normal Flu/Cy 100M; Auto CR

9 BPDCN Flu/Cy 100M; Auto MRD+ CR

AM

LB

PD

CN

MB-102: CRS & Neurotoxicity So Far Easily Manageable1

38

Adverse Events Grade 2 Grade 3 Grade 4

Cytokine release syndrome 1 0 0

Febrile neutropenia 0 3 0

Chills 2 0 0

Fever 4 0 0

Alanine aminotransferase increased 0 1 0

Aspartate aminotransferase increased 0 1 0

Grade 2 & above toxicities (probably or definitely attributed to CAR-T cells)

▪ Maximum neurotoxicity grade 2 (dizziness, headache, somnolence)

▪ Patient 7 achieved full bone marrow recovery on day 56

▪ No grade 5 events or DLTs1. Presented by Dr. Budde at AACR Tumor Immunology &

Immunotherapy Conference, Nov. 30, 2018.

MB-102: Next Steps for Mustang Multicenter Trial

39

• Due to increased potency of cells processed by Mustang, dose reduced by 50% from highest safe dose achieved by COH at time of IND submission; starting dose will be 100M cells

• 4 sites: COH + major enrollers to Stemline’s pivotal BPDCN trial (MDACC, DFCI, Duke)1,2

• Anticipate treating first patient 3Q2020

1. https://ir.stemline.com/node/10281/pdf2. Pemmaraju N, et al. Blood. 2017;130:3855.

Board of Directors

Executive Title Previous Experience

Michael S. Weiss, JD Chairman

Lindsay A. Rosenwald, MD Director

Manuel Litchman, MDPresident & Chief Executive Officer

Adam J. Chill, JD Director

Neil Herskowitz DirectorReGen Group (ReGen Capital Investments LLC, Riverside Claims Investments LLC)

Michael J. Zelefsky, MD Director

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Financial Summary

▪ As of March 31, 2020, cash, cash equivalents and restricted cash of $56.8 million(1Q20 net loss of $11.9M)

▪ $35.0M gross proceeds in June 2020 from underwritten public offering, excluding exercise of the over-allotment option

▪ 2019 financing

▪ $20 million venture debt financing with Horizon Technology Finance announced April 2019

• $15 million funded at closing

• $5 million upon achieving certain milestones

▪ $31.6M gross proceeds in May 2019 from underwritten public offering, including full exercise of the over-allotment option

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Mustang Target Goals Through Mid-2021: 4 Open Mustang INDsAnticipate initiating pivotal XSCID trials & building on early indications of CAR-T activity

▪ Newly diagnosed XSCID: Once CMC hold resolved, begin accrual to Mustang IND trial 4Q2020

▪ Previously transplanted XSCID: File Mustang IND for multicenter trial 3Q2020

▪ CD20 CAR-T: Tech transfer & prepare for 1H2021 Mustang IND filing

▪ CD123 CAR-T: Treat first patient on Mustang IND multicenter CAR-T trial (NCT04109482) 3Q2020

▪ IL13Rα2 CAR-T: File COH IND for innovative combination trial in GBM (CAR-T + oncolytic virus) 4Q2020

▪ Possible data disclosures from collaboration partners’ trials

− Follow-up data from FHCRC CD20 CAR-T trial, COH CD123 CAR-T trial

− First data from COH PSCA trial, Nationwide OV trial

▪ Continue BD&L activities

− In-licensing opportunities to expand our ex vivo gene therapy franchise for rare diseases

− Partnering opportunities to access non-dilutive capital

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