A Randomized, Partially Blinded, Placebo- and Comparator-Controlled, Multicenter, Phase 2a, Dose Ranging, Proof-of-Concept Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Efficacy of SPR720 as Compared With Placebo or Standard of Care for the Treatment of Patients With Mycobacterium Avium Complex (MAC) Pulmonary Disease
Phase: PHASE2
Conditions: Mycobacterium Avium Complex, Non-tuberculous Mycobacterium Pulmonary Disease
Sponsor: Spero Therapeutics

ClinicalTrials.gov Identifier:    NCT04553406

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INVESTIGATOR AGREEMENT
I have read the clinical study protocol and agree the trial will be carried out in accordance with 
Good Clinical Practice, with the Declaration of Helsinki (with amendments), and with the laws 
and regulations of the countries in which the study takes place. 
Signature: 
Date:
Name (print):

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azithromycin 250 to 500 mg once daily PLUS ethambutol HCl 
approximately 15 mg/kg once daily for 28 days. Optional rifampin 600 mg or 
rifabutin 300 mg once daily for up to 28 days may be added to the SOC 
regimen.
Inform the medical monitor of alternative SOC regimens and discuss concerns or
questions.  
Randomization will be stratified by diagnosis at enrollment as either 1) nodular-
bronchiectatic or 2) fibro-cavitary NTM-PD.
Clinic study visits will occur on Days 1, 7, 14, 21, and 28 (end-of-treatment 
[EOT] visit) (± 1 day). Patients in the double-blinded Treatment Arms 1, 2, and 
3 will be evaluated at a follow-up- visit on Day 56 (± 2 days). Patients in the 
open-label SOC Treatment Arm 4 will be discontinued from the study after the 
EOT visit.  
Patient-collected pooled expectorated sputum will be collected on Days -1, 6, 13, 
20, and 27 (i.e., the day before clinical study visits over an approximate 24-hour
(h) period) for all patients and, for patients in Treatment Arms 1, 2, and 3, on 
Day 55 (i.e., the day before the follow-up visit on Day 56). In all cases, the 
patient-collected sputum will be collected on the day before the actual clinic 
visit. Sputum will also be collected at each clinic visit using a standard induction 
protocol.
Patients in Treatment Arms 1, 2, and 3 will participate in the collection of blood 
samples for PK analysis as follows:
x At least 3 selected qualifying sites will enroll a total of at least 18 patients 
(at least 6 per treatment arm) for intensive PK evaluation. On Days 1 and 
28, blood samples for intense PK will be collected at pre-dose and post-
dose: 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h. On Days 7, 14, and 21, blood 
samples will be obtained at: pre-dose, 1 h post-dose, and just before 
discharge from the clinic. The acceptable windows for the PK collection are 
specified in the Schedule of Assessments (Table 2). 
x At all remaining sites, samples will be collected for sparse PK evaluation on 
Days 1, 7, 14, 21, and 28. Blood samples will be obtained at pre-dose, 1 h 
after the oral dose, and just before discharge from the clinic. 
x Patients randomized to the SOC arm will not participate in PK collection. 
Actual dates and times of blood sampling and dates and times of study drug 
administration will be recorded.
Planned Sample Size:
Approximately 90 patients at approximately 30 study sites in the United States
Medical Condition or 
Disease Under 
Investigation:
NTM-PD due to MAC
Key Patient Selection 
Criteria:
Inclusion Criteria
Patients meeting all the following inclusion criteria should be considered for 
admission to the study:
1.
Provided written informed consent
2.
Male or female, 18 years of age or older at the time of consent
3.
Has a diagnosis of NTM-PD due to MAC
4.
Had at least 1 prior positive culture (sputum or bronchoalveolar lavage) for 
MAC in the previous 6 months
5.
Has an induced sputum culture at screening positive for MAC by at least 
one of the following methods performed by the microbiology laboratory:
quantitative culture on solid agar or growth on liquid media (MGIT)  
6.
Is either treatment naïve and has not received any prior treatment for MAC, 

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OR if previously treated for MAC, has culture evidence of persistent, 
recurrent, or relapsed disease and has been off therapy for at least 6 months
7.
In the opinion of the Investigator, is ready to initiate treatment (treatment 
naïve) or reinitiate treatment (previously treated) within the next 3 months, 
and for whom a delay, in order to participate in a placebo-controlled clinical 
trial, is considered reasonable and clinically acceptable
8.
Had clinical signs and symptoms within the 6 weeks prior to consent that 
are consistent with NTM-PD with at least two of the following:
a. chronic cough
b. fatigue 
c. frequent throat clearing
d. shortness of breath (dyspnea) 
e. coughing up of blood (hemoptysis) 
f. excessive mucus (sputum) production 
g. fever 
h. night sweats 
i.
loss of appetite 
j.
unintended weight loss 
k. wheezing
l.
chest pain
9.
Has a measured forced expiratory volume in 1 second (% predicted FEV1) 
30% on pulmonary function test within 3 months prior to consent
10. Has a chest radiograph (CXR) or computed tomography (CT) scan within 
6 months prior to consent with findings consistent with NTM-PD. If no 
prior CXR or CT scan is available, a CXR or CT scan should be performed
at screening to confirm eligibility
11. If female, is of nonchildbearing potential (e.g., postmenopausal as 
demonstrated by follicle-stimulating hormone or surgical sterilization, i.e., 
tubal ligation or hysterectomy), or if of childbearing potential, is willing to 
commit to either sexual abstinence or use of at least 2 medically accepted, 
effective methods of birth control in combination (e.g., condom, spermicidal 
gel, oral contraceptive, indwelling intrauterine device, hormonal 
implant/patch, injections, approved cervical ring) from consent through 
follow-up. Patients randomized to the SOC arm will be followed until EOT
12. If male, is willing not to donate sperm and, if engaging in sexual intercourse 
with a female partner who could become pregnant, willing to use a condom 
in addition to having his female partner use a highly effective method of 
birth control (such as an intrauterine device, diaphragm, oral contraceptives, 
injectable progesterone, subdermal implants, or a tubal ligation) from 
consent through follow-up. Patients randomized to the SOC arm will be 
followed up until EOT 
13. Is willing and able to comply with all study assessments and adhere to the 
protocol schedule
Exclusion Criteria
Patients meeting any of the following exclusion criteria will not be enrolled in 
the study:
1.
In the opinion of the Investigator, is not a candidate for a 3-month delay in 
initiation of standard multidrug therapy in order to participate in a placebo-
controlled clinical trial or observation (e.g., severe symptoms, extensive 
disease burden) 
2.
Has disseminated or extrapulmonary NTM
3.
Has end-stage NTM-PD or treatment-refractory NTM-PD and is unlikely to 
respond to protocol-specified SOC treatment
4.
Had isolation on sputum cultures of any species of Mycobacterium other 
than a species included in MAC within the past 6 months

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5.
Had prior isolation of MAC with macrolide resistance 
6.
Has active tuberculosis at time of consent
7.
Has received any systemic (oral or intravenous) or inhaled antibiotic with 
activity against MAC between consent and randomization
8.
Has a potentially confounding underlying pulmonary disease, including but 
not limited to cystic fibrosis, active pulmonary malignancy (primary or 
metastatic), NTM-hypersensitivity disease pneumoconiosis, or another 
advanced lung disease with a % predicted FEV1<30%
9.
Has a history of a positive test for HIV, known CD4 count <200/mm3 within 
the last year before consent, or a diagnosis of AIDS
10. Has an immunodeficiency or an immunocompromised condition, including 
neutropenia (<1000 neutrophils/mm3 obtained from the central laboratory at 
screening), hematologic malignancy, a history of hematopoietic stem cell 
transplant, a history of solid organ transplant, is receiving 
immunosuppressive therapy (e.g., cancer chemotherapy, monoclonal 
antibodies for autoimmune disease, or medications to prevent transplant 
rejection), and has had long-term use of systemic corticosteroids (e.g., 
 mg/day of prednisone or systemic equivalent for at least 2 weeks)
11. Has a history of known or suspected C. diff infection
12. Has a history of epilepsy or known seizure disorder (excluding a history of 
childhood febrile seizures)
13. Has hepatic impairment at screening, as evidenced by alanine 
aminotransferase or aspartate aminotransferase >2 × upper limit of normal 
(ULN) or total bilirubin >1.5 × ULN, or clinical signs of cirrhosis or end-
stage hepatic disease (e.g., ascites, hepatic encephalopathy) 
14. Has renal impairment (creatinine clearance <50 mL/min) or end-stage renal 
disease requiring hemodialysis or peritoneal dialysis
15. If female, is pregnant or breastfeeding
16. Has a corrected QT (QTc) interval on electrocardiogram (ECG) >470 ms
17. Has consumed drugs or supplements that are strong cytochrome P450 
(CYP)3A4 enzyme inducers or strong CYP3A4 inhibitors (see Appendix 1)
within 4 weeks of randomization
18. Has consumed drugs or supplements that are substrates of the hepatic 
transporters OATP1B1 or OATP1B3 (see Appendix 2) within 1 week of 
randomization
19. Has a documented hypersensitivity reaction or anaphylaxis to SPR720 or 
any of the specified SOC medications
20. Has received any investigational medication in the year before the time of 
consent
21. Has any other condition or prior therapy, which, in the opinion of the 
Investigator, would make the patient unsuitable for this study, including 
compliance with all study assessments and adherence to the protocol 
schedule
Test Product, Dose, and 
Mode of Administration:
SPR720 500 mg dose administered by capsules po once daily for 28 days  
SPR720 1000 mg dose administered by capsules po once daily for 28 days
Recommended Reference 
Product, Dose, and Mode of 
Administration:
x
Placebo capsules administered po once daily for 28 days
x
Standard of Care regimen is at the Investigator’s discretion; 
recommended standard of care is as follows: 2-drug or 3-drug SOC 
administered po once daily for 28 days as follows
o
Clarithromycin 500-1000 mg, plus ethambutol HCl 15 mg/kg 
or
o
Azithromycin 250-500 mg, plus ethambutol HCl 15 mg/kg

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TABLE OF CONTENTS
SIGNATURE PAGE .......................................................................................................................2
INVESTIGATOR AGREEMENT...................................................................................................3
SYNOPSIS ......................................................................................................................................4
LIST OF ABBREVIATIONS AND DEFINITIONS OF TERMS ................................................15
SAFETY REPORTING CONTACT INFORMATION ................................................................17
1.
INTRODUCTION ......................................................................................................18
1.1.
Background .................................................................................................................18
1.1.1.
Nontuberculous Mycobacterial Pulmonary Disease ...................................................18
1.1.2.
Unmet Need ................................................................................................................19
1.1.3.
SPR720 .......................................................................................................................20
1.1.3.1.
SPR720 Nonclinical Development .............................................................................20
1.1.4.
SPR720 Clinical Development ...................................................................................20
1.2.
Risks and Benefits ......................................................................................................21
2.
STUDY OBJECTIVES ..............................................................................................22
2.1.
Primary Objective .......................................................................................................22
2.2.
Secondary Objective ...................................................................................................22
2.3.
Exploratory Objective .................................................................................................22
3.
INVESTIGATIONAL PLAN .....................................................................................23
3.1.
Overall Study Design and Plan ...................................................................................23
3.2.
Study Duration ............................................................................................................26
3.3.
Selection of Study Population ....................................................................................26
3.3.1.
Inclusion Criteria ........................................................................................................26
3.3.2.
Exclusion Criteria .......................................................................................................27
3.3.3.
Premature Discontinuation of Investigational Product ...............................................29
3.3.4.
Withdrawal from Study ..............................................................................................29
3.3.5.
Criteria for Stopping the Study ...................................................................................30
3.3.6.
Replacement of Patients .............................................................................................30
4.
INVESTIGATIONAL PRODUCT ............................................................................31
4.1.
Identity of the Investigational Product .......................................................................31
4.2.
Dosage Schedule .........................................................................................................31
4.3.
Treatment Assignment ................................................................................................32

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4.4.
Drug Packaging and Blinding .....................................................................................33
4.5.
Drug Inventory and Accountability ............................................................................33
4.6.
Treatment Compliance ................................................................................................33
4.7.
Concomitant Illnesses and Treatments .......................................................................34
4.7.1.
Concomitant Illnesses .................................................................................................34
4.7.2.
Concomitant Treatments .............................................................................................34
5.
ASSESSMENTS .........................................................................................................35
5.1.
Schedule of Assessments ............................................................................................35
5.2.
Screening (Day –42 to –1) ..........................................................................................39
5.3.
Pharmacokinetic Assessments ....................................................................................39
5.4.
Safety Assessments .....................................................................................................39
5.5.
Efficacy Assessments .................................................................................................41
5.6.
Appropriateness of Measurements .............................................................................42
6.
ASSESSMENT AND MANAGEMENT OF ADVERSE EVENTS .........................43
6.1.
Adverse Event Definitions ..........................................................................................43
6.2.
Evaluating Adverse Events and Serious Adverse Events ...........................................44
6.2.1.
Assessment of Intensity ..............................................................................................44
6.2.2.
Assessment of Causality .............................................................................................45
6.3.
Time Period, Frequency, and Method of Detecting Adverse Events .........................46
6.4.
Adverse Event Management .......................................................................................46
6.5.
Recording of Adverse Events and Serious Adverse Events .......................................47
6.6.
Serious Adverse Event Reporting ...............................................................................47
6.6.1.
Regulatory Reporting Requirements for Reporting of Serious Adverse 
Events .........................................................................................................................47
6.6.2.
Completion and Transmission of the Serious Adverse Event Reports .......................47
6.6.3.
Post-study Adverse Events and Serious Adverse Events ...........................................48
6.7.
Follow-up of Adverse Events and Serious Adverse Events .......................................48
6.8.
Clinical Laboratory Evaluations .................................................................................49
6.9.
Pregnancy ...................................................................................................................49
6.10.
Abuse, Misuse, Overdose, and Medication Error .......................................................49
6.11.
Reference Safety Information .....................................................................................50
7.
DATA MANAGEMENT ...........................................................................................51
7.1.
Data Management Considerations ..............................................................................51

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8.
STATISTICAL CONSIDERATIONS .......................................................................52
8.1.
Endpoints ....................................................................................................................52
8.1.1.
Primary .......................................................................................................................52
8.1.2.
Secondary ...................................................................................................................52
8.1.3.
Exploratory .................................................................................................................52
8.1.4.
Determination of Sample Size ....................................................................................53
8.1.5.
Analysis Populations ..................................................................................................53
8.1.6.
Protocol Deviations ....................................................................................................54
8.1.7.
Demographic and Baseline Characteristics ................................................................54
8.1.8.
Pharmacokinetic Analyses ..........................................................................................54
8.1.9.
Safety Analyses ..........................................................................................................54
8.1.9.1.
Extent of Exposure .....................................................................................................54
8.1.9.2.
Adverse Events ...........................................................................................................55
8.1.9.3.
Concomitant Medications ...........................................................................................55
8.1.9.4.
Laboratory Data ..........................................................................................................55
8.1.9.5.
Electrocardiographic Data ..........................................................................................55
8.1.9.6.
Vital Signs ..................................................................................................................55
8.1.9.7.
Physical Examinations ................................................................................................56
8.1.10.
Efficacy Analyses .......................................................................................................56
8.1.10.1.
Microbiological Response ..........................................................................................56
8.1.10.2.
Clinical Response .......................................................................................................56
9.
STUDY MANAGEMENT .........................................................................................57
9.1.
Regulations and Guidelines ........................................................................................57
9.2.
Sponsor’s Responsibilities ..........................................................................................57
9.2.1.
Good Clinical Practice ................................................................................................57
9.2.2.
Indemnity/Liability and Insurance ..............................................................................57
9.2.3.
Public Posting of Study Information ..........................................................................57
9.2.4.
Suspension, Discontinuation, and Completion of the Study ......................................57
9.3.
Investigator Responsibilities .......................................................................................58
9.3.1.
Good Clinical Practice Compliance ............................................................................58
9.3.2.
Protocol Adherence and Investigator Agreement .......................................................58
9.3.3.
Institutional Review Board .........................................................................................58

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9.3.4.
Informed Consent .......................................................................................................58
9.4.
Study Documentation .................................................................................................59
9.5.
Data Management and Quality Control ......................................................................59
9.5.1.
Electronic Case Report Forms ....................................................................................59
9.5.2.
Recording, Access, and Retention of Source Data and Study Documents .................59
9.5.3.
Study Monitoring and Quality Assurance ..................................................................59
9.5.4.
Financial Disclosure ...................................................................................................60
9.6.
Use of Study Findings ................................................................................................60
9.7.
Privacy and Confidentiality ........................................................................................60
9.8.
Publications .................................................................................................................61
10.
REFERENCES ...........................................................................................................62
APPENDIX 1.
PROHIBITED INHIBITORS AND INDUCERS OF CYP3A ..........................65
APPENDIX 2.
PROHIBITED SUBSTRATES OF THE HEPATIC TRANSPORTERS 
OATP1B2 OR OATP2B3 ...........................................................................................66
APPENDIX 3.
PATIENT-REPORTED OUTCOMES ..............................................................67
NTM-PD Symptom Questions .......................................................................................................67
NTM-PD Impact Questions ...........................................................................................................70
Patient Global Impression of Severity Questions ..........................................................................71
Patient Global Impression of Change Questions ...........................................................................72
LIST OF TABLES
Table 1: Study Treatments .............................................................................................................32
Table 2:
Schedule of Assessments ............................................................................................36
Table 3:
Clinical Laboratory Tests ...........................................................................................40
LIST OF FIGURES
Figure 1:
Study Design ...............................................................................................................25

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LIST OF ABBREVIATIONS AND DEFINITIONS OF TERMS
Abbreviation
Definition
AE
adverse event
ALT 
alanine aminotransferase
AST
aspartate aminotransferase
ATC 
Anatomical/Therapeutic/Chemical
AUClast
area under the concentration-time curve from zero to last concentration
AUC0-Ĳ
area under the concentration-time curve from zero to Ĳ, where Ĳ is the dosing 
interval
CFR
Code of Federal Regulations
CFU
colony-forming unit
Cmax
maximum plasma concentration
CRO
contract research organization
CS
clinically significant
CT
computed tomography
CTCAE
Common Terminology Criteria for Adverse Events
Ctrough
plasma concentration at the end of a dosing interval (taken directly before next 
administration)
CXR
chest radiograph
CYP
cytochrome P450
ECG
electrocardiogram
eCRF
electronic case report form
EDC 
electronic data capture
EOT 
end of treatment
FDA
Food and Drug Administration
FEV1
forced expiratory volume in 1 second
GCP
Good Clinical Practice
h 
hour
HCl
hydrochloride
HIPAA
Health Insurance Portability and Accountability Act
IB
investigator’s brochure
ICF
informed consent form
ICH
International Council for Harmonisation of Technical Requirements for 
Pharmaceuticals for Human Use
IP
investigational product
IRB
institutional review board

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Abbreviation
Definition
IRT
interactive randomization technology
ITT 
intent to treat
IV
intravenous
MAC
Mycobacterium avium complex
MAC-PD
Mycobacterium avium complex pulmonary disease
MedDRA
Medical Dictionary for Regulated Activities
MGIT
Mycobacteria Growth Indicator Tube
micro-ITT
microbiological intent to treat
NTM
nontuberculous mycobacteria
NTM-PD
nontuberculous mycobacteria pulmonary disease
PGI-C 
Patient Global Impression of Change
PGI-S 
Patient Global Impression of Severity
PK
pharmacokinetic(s)
po
orally
PRO
patient-reported outcome
QTc 
corrected QT
QTcF
corrected QT interval according to Fridericia’s formula
SAE
serious adverse event
SAP
statistical analysis plan
SOC
standard of care
SUSAR
suspected unexpected serious adverse reaction
TEAE 
treatment-emergent adverse event
Tmax
time to reach Cmax
TTP 
time to positivity
ULN 
upper limit of normal
US
United States

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1.
INTRODUCTION
1.1.
Background
1.1.1.
Nontuberculous Mycobacterial Pulmonary Disease
Nontuberculous mycobacterial pulmonary disease (NTM-PD) is a chronic, progressive disease 
that occurs through inhalation of pathogenic mycobacteria from environmental sources, 
including aerosols from water and dust from soil (Falkinham 2015). The most commonly 
reported nontuberculous mycobacterial (NTM) species causing NTM-PD in the United States
(US) and worldwide are Mycobacterium avium complex (MAC), which includes Mycobacterium 
avium, Mycobacterium intracellulare, Mycobacterium chimaera and several other species and 
subspecies, Mycobacterium kansasii, and Mycobacterium abscessus (Griffith et al 2007;
Falkinham 2015; Haworth et al 2017).
Nontuberculous mycobacterial pulmonary disease predominantly occurs in patients with 
underlying lung disease, including chronic obstructive pulmonary disease and bronchiectasis, 
patients with cystic fibrosis, older males, and nonsmoking women over the age of 50 years 
without previously diagnosed lung disease (Lady Windermere syndrome). Development of 
NTM-PD is based on a variety of pathogen and host-specific factors for which the 
pathophysiology is poorly understood (Griffith et al 2007). Risk factors for disease include 
underlying immunodeficiency, treatment with antitumor necrosis factor agents, and exposure to 
environmental water sources (Griffith et al 2007; Henkle and Winthrop 2015; Adjemian at al 
2017; Baldwin et al 2019). The natural history of this disease is varied based on pathogen and 
host factors, but 5-year mortality rates as high as 35% have been reported for M. abscessus
pulmonary disease. Risk factors for progressive lung disease include infection with 
M. abscessus, the presence of cavitary lung disease, and low body weight/body mass index 
(Dhillon and Watanakunakorn 2000; Lam et al 2006; Griffith et al 2007; Gochi et al 2015).
Based on the patient- and pathogen-specific factors contributing to development of disease, there 
is significant variability in the clinical presentation of patients with NTM-PD, and definitive 
diagnostic criteria are lacking. As a result, recommendations in current treatment guidelines for 
pulmonary NTM infections are based predominantly on observational clinical data supported by 
in vitro susceptibility data and expert opinion. Understanding the epidemiology and treatment of 
these infections is complicated by the large number of causative species, the varied clinical 
manifestations of disease (fibronodular, cavitary, bronchiectatic, etc), and geographical variation 
in the prevalence of infection (Fiske et al 2016; Adjemian et al 2017; Lande et al 2018).
Patients at the US Food and Drug Administration (FDA) NTM Open Public Meeting (CDER 
2016) described debilitating symptoms such as a relentless and severe deep cough, hemoptysis, 
progressive fatigue, stabbing chest pain, loss of appetite, along with fever, night sweats, and 
weight loss, which often indicate advanced disease (Baldwin et al 2019). In the results of a 
survey conducted by the NTM Info & Research patient advocacy group and presented at the 
FDA Workshop, Development of Antibacterial Drugs for Treatment of Nontuberculous 
Mycobacterial Disease (NTMir 2019), the top symptoms that plagued respondents and had the 
greatest impact on their lives were fatigue, cough, shortness of breath, night sweats, and weight 
loss. When asked about their preferences in treatment outcomes, the majority of the respondents 
selected improving quality of life, increasing energy, and reducing fatigue.  

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Clinical diagnosis of NTM-PD is based on assessment of specific clinical, radiographic and
microbiologic criteria as outlined in the 2007 American Thoracic Society and Infectious Disease 
Society of America treatment guidelines (Griffith et al 2007).  
1.1.2.
Unmet Need
Therapy for NTM infections generally requires prolonged treatment (months to years) with 
antibiotic combination regimens that are poorly tolerated and, in many cases, ineffective. The 
therapeutic regimens vary based on the specific causative pathogen (MAC, M. abscessus,
M. kansasii), the presence or absence of pulmonary cavities at the initiation of therapy, the 
response to prior attempts at therapy, comorbidities such as renal dysfunction, and the individual 
patient’s ability to tolerate oral, aerosolized, or intravenous (IV) therapy (Griffith et al 2007;
Griffith and Aksamit 2016; Haworth et al 2017; Lee et al 2019). There is currently only 1
antimicrobial agent, Arikayce®, that is approved for the treatment of NTM-PD. It is approved for 
patients with MAC pulmonary disease (MAC-PD) as part of a combination antibacterial drug 
regimen in adult patients who do not achieve negative sputum cultures after a minimum of 6 
consecutive months of a multidrug background regimen therapy and who have limited or no 
alternative treatment options (Insmed 2018). Current standard of care (SOC) therapy for MAC-
PD in the US, as outlined in the joint treatment guidelines developed in 2007 by the American 
Thoracis Society and Infectious Disease Society of America (Griffith et al 2007), recommends 
prolonged treatment with 3 or 4 antimicrobial agents in combination for up to 18 months, based 
on pathogen- and patient-specific factors. Suggested agents for MAC-PD include clarithromycin 
or azithromycin, rifampin or rifabutin and ethambutol, and IV streptomycin or amikacin (Griffith 
et al 2007; Haworth et al 2017). Among these agents, the macrolide component appears to be 
particularly important, as emergence of resistance to clarithromycin or azithromycin is a risk 
factor for disease progression and mortality. This complex multidrug therapy is often 
complicated by side effects and/or drug interactions that require discontinuation of one or more 
of the agents and predisposes patients to treatment failure and development of drug-resistant 
NTM, further complicating therapy (Wallace et al 1994; CDER 2016; Philley et al 2016).
Importantly, none of the guideline-based therapeutic options, as individual drugs or combination 
regimens, have been evaluated for safety and efficacy under controlled conditions in 
prospectively designed clinical studies in patients with NTM-PD and none are specifically 
approved for such use. 
In addition to complex antimicrobial therapy, patients diagnosed with NTM-PD are required to 
undertake aggressive daily respiratory hygiene regimens including chest physiotherapy and 
nebulizer treatments in order to clear copious pulmonary secretions and prevent atelectasis.
These adjunctive therapies are time-consuming and can have an adverse impact on patients’ 
quality of life (CDER 2016).
Although up to 86% of patients with pulmonary disease due to MAC may achieve sputum 
conversion (from positive to negative) on therapy (Wallace et al 2014), the translation of 
microbiological sputum clearance to immediate or long-term clinical outcomes is unclear since 
controlled and prospectively designed clinical studies to assess the link are lacking (Griffith et al 
2015; ALIS 2018). Once established, NTM-PD can cause progressive destruction of the 
pulmonary parenchyma, and, despite prolonged therapy, outcomes remain unsatisfactory, with 
high rates of reinfection and mortality (Jarand et al 2011; Wallace et al 2014). Mortality rates 

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due to NTM-PD range from 25% to 40% at 5 years (Cadelis et al 2017). The main factors of 
poor outcomes identified in mortality studies at 5 years corresponded to an advanced age, the 
existence of respiratory comorbidities, radiological cavity lesions, and specific mycobacterial 
species, including Mycobacterium xenopi (Cadelis et al 2017).  
The high rate of intrinsic resistance of NTM species to conventional antibiotics and 
antimycobacterial agents, as well as the poor tolerability exhibited to agents utilized in current 
SOC regimens, contributes to relatively high mortality rates for NTM-PD. The development and 
approval of novel drugs with demonstrated efficacy and improved tolerability for NTM-PD is
thus a critical research priority (Baldwin et al 2019).
1.1.3.
SPR720
Spero is developing SPR720 as an oral therapy for the treatment of patients with NTM-PD 
caused by MAC. SPR720 is a chemically stable phosphate prodrug that converts rapidly to 
SPR719, the active moiety, in vivo.  
SPR719 was identified and optimized through structure-guided design and iterative structure-
activity relationship studies; it is an aminobenzimidazole, a novel class of antibacterial agents 
that target the ATPase subunits of gyrase and, when present, topoisomerase. These enzymes are 
highly conserved and essential in bacteria for DNA replication (Locher et al 2015). In 
mycobacteria, only gyrase enzymes have been identified. The potent enzyme activity 
demonstrated by SPR719 translates to growth inhibition of a range of pathogens such as 
Mycobacterium tuberculosis (Locher et al 2015; O’Dowd et al 2015) and nontuberculosis 
mycobacteria such as MAC, M. abscessus complex, and M. kansasii, including isolates that are 
resistant to the current SOC agents amikacin, clarithromycin, and, importantly, the 
fluoroquinolones (Brown-Elliott et al 2018).
1.1.3.1.
SPR720 Nonclinical Development
Nonclinical studies conducted to date on SPR720 and/or its active moiety SPR719 have 
demonstrated acceptable safety and pharmacokinetic (PK) profiles. No adverse effect levels 
identified in repeat-dose toxicity studies of SPR720 in rats and in monkeys provide exposure 
multiples to the anticipated human therapeutic exposure, and, in rats, SPR720 was determined to 
be nongenotoxic. In safety pharmacology studies in vitro and in monkeys and rats, SPR720 
and/or its active moiety SPR719 exhibited no adverse effects on the normal functioning of the 
cardiovascular, respiratory, or central nervous systems. 
1.1.4.
SPR720 Clinical Development 
Spero has completed a single Phase 1 study in the United Kingdom in healthy volunteers to 
assess the safety, tolerability, and PK of SPR720 (Study SPR720-101). A comprehensive set of 
nonclinical studies has also been completed that evaluated the PK/metabolism, safety 
pharmacology, and toxicity of SPR720 (prodrug) and SPR719 (active moiety).  
The advancement of SPR720 into the Phase 1 clinical assessment was based on a favorable 
profile exhibited in a suite of preclinical in vitro and in vivo safety, toxicology, absorption, 
distribution, metabolism, and excretion studies, as well as its demonstration of 

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potency in vitro and in vivo activity versus multiple, clinically important species of NTM, 
including MAC and M. abscessus.  
1.2.
Risks and Benefits 
SPR720 has demonstrated in vitro and in vivo biological activity against a range of NTM
species, including MAC, the most common pathogen group in NTM-PD, and M. abscessus, a
highly resistant organism associated with a high rate of mortality.
The collective preclinical data to date suggests that SPR720 has an acceptable safety profile, 
encouraging target pathogen efficacy, drug distribution to key sites of infection such as the lung, 
and a wide therapeutic margin.
SPR720 has been successfully evaluated in a single-ascending-dose/multiple-ascending-dose 
Phase 1 study in humans (Study SPR720-101). SPR720 was safe and well tolerated in healthy 
volunteers at doses believed to be in the therapeutic range for up to 14 days of dosing. The 
safety, tolerability, and PK data from this Phase 1 study further support a favorable risk-benefit 
profile for SPR720. 
SPR720 is a novel agent with the potential to be the first oral antibiotic designed to treat NTM 
disease, a rare orphan disease.

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3.
INVESTIGATIONAL PLAN
3.1.
Overall Study Design and Plan
This is a Phase 2a, multicenter, randomized, partially blinded, placebo- and comparator-
controlled study to evaluate the safety, tolerability, PK, and efficacy of 2 dose levels of SPR720 
compared with placebo or SOC for the treatment of patients with NTM-PD due to MAC. The 
SPR720 and placebo arms will be double blinded, and the SOC arm will be open label.
Approximately 90 male and female patients 18 years of age and older with a diagnosis of NTM-
PD due to MAC will be enrolled and treated for 28 days. Treatment-naïve patients must be ready 
to initiate treatment within the next 3 months. Patients who have received prior treatment may be 
eligible if they have culture evidence of persistent, recurrent, or relapsed disease; have been off 
therapy for at least 6 months; and are likely to reinitiate or resume treatment.
For the sparse PK sites, enrolled patients will be randomly assigned 5:5:5:4 (Arm 1: Arm 2: 
Arm 3: Arm 4) into one of the following treatment arms until 72 patients are enrolled (19 to 20 
patients each for Treatment Arms 1, 2, and 3 and 15 to 16 patients for Arm 4). For the intense 
PK sites, enrolled patients will be randomly assigned 1:1:1 (Arm 1: Arm 2: Arm 3) into one of 
the following treatment arms (6 patients each for Treatment Arms 1, 2, and 3): 
x
Treatment Arm 1: SPR720 Low Dose: Double-blinded SPR720 investigational 
product (IP) 500 mg once daily for 28 days.
x
Treatment Arm 2: SPR720 High Dose: Double-blinded SPR720 IP 1000 mg once 
daily for 28 days.
x
Treatment Arm 3: Placebo: Double-blinded placebo once daily for 28 days.
x
Treatment Arm 4: SOC: At Investigator’s discretion. Recommended as follows: 2-
drug or 3-drug SOC, including clarithromycin 500 to 1000 mg PLUS ethambutol 
hydrochloride (HCl) approximately 15 mg/kg or azithromycin 250 to 500 mg once 
daily PLUS ethambutol HCl approximately 15 mg/kg once daily for 28 days. 
Optional rifampin 600 mg or rifabutin 300 mg once daily for up to 28 days may be 
added to the SOC regimen.
Inform the medical monitor of alternative SOC regimens and discuss concerns or questions.  
Randomization will be stratified by diagnosis at enrollment as either 1) nodular-bronchiectatic or 
2) fibro-cavitary NTM-PD.
Clinic study visits will occur on Days 1, 7, 14, 21, and 28 (end-of-treatment [EOT] visit) 
(± 1 day). Patients in the double-blinded Treatment Arms 1, 2, and 3 will be evaluated in a 
follow-up visit on Day 56 (± 2 days) (28 days after EOT). Patients in the open-label SOC 
Treatment Arm 4 will be discontinued from the study after the EOT visit.  
Baseline symptoms will include chronic cough, fatigue, frequent throat clearing, dyspnea, 
hemoptysis, excessive mucus (sputum) production, fever, night sweats, loss of appetite, 
unintended weight loss, wheezing, and chest pain. A multi-dimensional patient-reported outcome 
(PRO) (see Appendix 3) instrument assessing severity and changes in these baseline symptoms 

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will be administered at clinic visits on Days 1, 7, 14, 21, and 28 in all arms and Day 56 in 
Treatment Arms 1, 2, and 3. 
Patient-collected pooled expectorated sputum will be collected on Days –1, 6, 13, 20, and 27 
(i.e., the day before clinical study visits over an approximate 24-hour [h] period) for all patients 
and, for patients in Treatment Arms 1, 2, and 3, on Day 55 (i.e., the day before the follow-up 
visit on Day 56). In all cases, the patient-collected sputum will be collected on the day before the 
actual clinic visit. Sputum will also be collected at each clinic visit using a standard induction 
protocol. 
Patients in Treatment Arms 1, 2, and 3 will participate in the collection of blood samples for PK 
analysis as follows:
x
At least 3 selected qualifying sites will enroll a total of at least 18 patients (at least 6 
per treatment arm) for intensive PK evaluation. On Days 1 and 28, blood samples for 
intense PK will be collected at pre-dose and post-dose: 1 h, 2 h, 4 h, 8 h, 12 h, and 24 
h. On Days 7, 14, and 21, blood samples will be obtained at: pre-dose, 1 h post-dose, 
and just before discharge from the clinic. The acceptable windows for PK collection 
are specified in the Schedule of Assessments (Table 2). 
x
At all remaining, samples will be collected for sparse PK evaluation, on Days 1, 7, 
14, 21, and 28. Blood samples will be obtained at pre-dose, 1 h post-dose, and just 
before discharge from the clinic.  
x
Patients randomized to the SOC arm will not participate in PK collection.
Actual dates and times of blood samples as well as dates and times of study drug administration 
will be recorded. Please refer to the Schedule of Assessments (Table 2) for allowable windows.
A diagram of the study design is presented in Figure 1. 

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Figure 1: 
Study Design
Assessed for 
Eligibility 
Randomized 
(N=90)
Treatment Arm 1
SPR720 Low Dose 
QD 28 days
(n=25)
Treatment Arm 2
SPR720 High Dose
QD 28 days
(n=25)
Treatment Arm 3
Placebo
QD 28 days
(n=25)
Treatment Arm 4
Recommended SOC
QD 28 days
(n=15)
DB 500 mg QD
28 Days
DB 1000 mg QD
28 Days
DB Placebo
28 Days
OL 2-drug SOC
Up to 28 Days
or
OL 3-drug SOC
Up to 28 days
Clarithromycin 
500-1000 mg
Plus
Ethambutol HCl 
Approximately 15 mg/kg
QD for 28 days.
Plus Optional 
 Rifampin 600 mg or 
Rifabutin 300 mg QD
Up to 28 days
Azithromycin 
250-500 mg 
Plus 
Ethambutol HCl 
Approximately 15 mg/kg
QD for 28 days.
Plus Optional 
 Rifampin 600 mg or 
Rifabutin 300 mg QD
Up to 28 days
Clinic Visits: Days 1, 7, 
14, 21, and 28 EOT
Clinic Visits: Days 1, 7, 
14, 21, and 28 EOT
Clinic Visits: Days 1, 7, 
14, 21, and 28 EOT
Clinic Visits:
Days 1, 7, 14, 21, and 28 EOT
Follow-up Visit Day 56
Follow-up Visit Day 56
Follow-up Visit Day 56
Completed
Completed
Completed
Completed
Abbreviations: DB=double-blinded; EOT=end of treatment; HCl=hydrochloride; OL=open label; QD=once daily; SOC=standard of care. 

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3.2.
Study Duration
Patients will be screened within 42 days prior to the first dose of study drug. All patients will be 
treated for 28 days. Patients in Treatment Arms 1, 2, and 3, only, will have a follow-up visit 
28 days after the completion of therapy. The maximum duration of participation for each patient 
will be approximately 98 days (including a 42-day screening period, 28-day treatment period, 
and 28-day follow-up period) for Treatment Arms 1, 2, and 3, and approximately 70 days 
(including a 42-day screening period and 28-day treatment period) for Treatment Arm 4 SOC 
recipients. 
3.3.
Selection of Study Population
Approximately 90 male and female patients, 18 years of age and older, with a diagnosis of NTM-
PD due to MAC will be enrolled in the study. 
Specific entry criteria are detailed in Section 3.3.1 and Section 3.3.2.
3.3.1.
Inclusion Criteria
Patients meeting all the following inclusion criteria should be considered for admission to the 
study: 
1. Provided written informed consent 
2. Male or female, 18 years of age or older at the time of consent 
3. Has a diagnosis of NTM-PD due to MAC 
4. Had at least 1 prior positive culture (sputum or bronchoalveolar lavage) positive for 
MAC in the previous 6 months  
5. Has an induced sputum culture at screening positive for MAC by at least one of the 
following methods performed by the microbiology laboratory: quantitative culture on 
solid agar or growth on liquid media (MGIT) 
6. Is either treatment naïve and has not received any prior treatment for MAC, OR if 
previously treated for MAC, has culture evidence of persistent, recurrent, or relapsed 
disease and has been off therapy for at least 6 months
7. In the opinion of the Investigator, is ready to initiate treatment (treatment naïve ) or 
reinitiate treatment (previously treated) within the next 3 months, and for whom a delay,
in order to participate in a placebo-controlled clinical trial, is considered reasonable and 
clinically acceptable
8. Had clinical signs and symptoms within the 6 weeks before the date of consent that are 
consistent with NTM-PD with at least two of the following:
a.
chronic cough
b. fatigue 
c.
frequent throat clearing
d. shortness of breath (dyspnea) 
e.
coughing up of blood (hemoptysis) 

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f.
excessive mucus (sputum) production 
g. fever 
h. night sweats 
i.
loss of appetite 
j.
unintended weight loss 
k. wheezing
l.
chest pain
9. Has a measured forced expiratory volume in 1 second (% predicted FEV1) 30% on 
pulmonary function test within 3 months prior to consent
10. Has a chest radiograph (CXR) or computed tomography (CT) scan within 6 months prior 
to consent with findings consistent with NTM-PD. If no CXR or CT scan is available, a 
CXR or CT scan should be performed at screening to confirm eligibility.
11. If female, is of nonchildbearing potential (e.g. postmenopausal as demonstrated by 
follicle-stimulating hormone or surgical sterilization, i.e., tubal ligation or hysterectomy), 
or if of childbearing potential, be willing to commit to either sexual abstinence or use of 
at least 2 medically accepted, effective methods of birth control in combination (e.g., 
condom, spermicidal gel, oral contraceptive, indwelling intrauterine device, hormonal 
implant/patch, injections, approved cervical ring) from consent through follow-up. 
Patients randomized to the SOC arm will be followed up until EOT
12. If male, is willing not to donate sperm and, if engaging in sexual intercourse with a 
female partner who could become pregnant, a willingness to use a condom in addition to 
having his female partner use a highly effective method of birth control (such as an 
intrauterine device, diaphragm, oral contraceptives, injectable progesterone, subdermal 
implants, or a tubal ligation) from consent through follow-up. Patients randomized to the 
SOC arm will be followed up until EOT
13. Is willing and able to comply with all study assessments and adhere to the protocol 
schedule 
3.3.2.
Exclusion Criteria
Patients meeting any of the following exclusion criteria will not be enrolled in the study:
1. In the opinion of the Investigator, is not a candidate for a 3-month delay in initiation of 
standard multidrug therapy in order to participate in a placebo-controlled clinical trial or 
observation (e.g., severe symptoms, extensive disease burden) 
2. Has disseminated or extrapulmonary NTM
3. Has end-stage NTM-PD or treatment-refractory NTM-PD and is unlikely to respond to 
protocol-specified SOC treatment
4. Had isolation on sputum cultures of any species of Mycobacterium other than a species 
included in MAC within the past 6 months 
5. Had prior isolation of MAC with macrolide resistance 
6. Has active tuberculosis at the time of consent

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7. Has received any systemic (oral or IV) or inhaled antibiotic with activity against MAC 
between consent and randomization 
8. Has a potentially confounding underlying pulmonary disease, including but not limited to 
cystic fibrosis, active pulmonary malignancy (primary or metastatic), NTM-
hypersensitivity disease pneumoconiosis, or another advanced lung disease with a %
predicted FEV1<30%
9. Has a history of a positive test for HIV, known CD4 count <200/mm3 within the last year 
before time of consent, or a diagnosis of AIDS 
10. Has an immunodeficiency or an immunocompromised condition, including neutropenia 
(<1000 neutrophils/mm3 obtained from the central laboratory at screening), hematologic 
malignancy, a history of hematopoietic stem cell transplant, a history of solid organ 
transplant, is receiving immunosuppressive therapy (e.g., cancer chemotherapy, 
monoclonal antibodies for autoimmune disease, or medications to prevent transplant 
rejection), and has had long-term use of systemic corticosteroids (e.g. mg/day of 
prednisone or systemic equivalent for at least 2 weeks)
11. Has a history of known or suspected C. diff infection
12. Has a history of epilepsy or known seizure disorder (excluding a history of childhood 
febrile seizures)
13. Has hepatic impairment at screening, as evidenced by alanine aminotransferase (ALT) or 
aspartate aminotransferase (AST) >2 u upper limit of normal (ULN) or total bilirubin 
>1.5 u ULN, or clinical signs of cirrhosis or end-stage hepatic disease (e.g., ascites, 
hepatic encephalopathy) 
14. Has renal impairment (creatinine clearance <50 mL/min) or end-stage renal disease 
requiring hemodialysis or peritoneal dialysis
15. If female, is pregnant or breastfeeding
16. Has a corrected QT (QTc) interval on electrocardiogram (ECG) >470 ms
17. Has consumed drugs or supplements that are strong cytochrome P450 (CYP)3A4 enzyme 
inducers or strong CYP3A4 inhibitors (see Appendix 1) within 4 weeks of randomization 
18. Has consumed drugs or supplements that are substrates of the hepatic transporters 
OATP1B1 or OATP1B3 (see Appendix 2) within 1 week of randomization
19. Has a documented hypersensitivity reaction or anaphylaxis to SPR720 or any of the 
specified SOC medications
20. Has received any investigational medication in the year before the time of consent
21. Has any other condition or prior therapy, which, in the opinion of the Investigator, would 
make the patient unsuitable for this study, including compliance with all study 
assessments and adherence to the protocol schedule
Patients who are unable to comply with the requirements of the study or who in the opinion of 
the Investigator should not participate in the study are not eligible. 

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3.3.3.
Premature Discontinuation of Investigational Product
Premature discontinuation of the IP by the Investigator is an important discussion that should 
include the Medical Monitor, if feasible, before the IP is discontinued.
Possible reasons for premature discontinuation from IP due to safety reasons include, but are not 
limited to, the following:
x
Occurrence of an AE that, in the opinion of the Investigator, warrants the patient’s 
permanent discontinuation from IP administration
x
Hy’s law criteria are met, defined by at least 3-fold elevations of ALT or AST above 
the ULN, elevation of serum total bilirubin to >2 × ULN without elevated serum 
alkaline phosphatase, and no other disease or condition can be found to explain the 
liver test abnormalities
x
Known pregnancy or breastfeeding during the study drug administration period  
Possible reasons for discontinuation from the IP due to insufficient therapeutic effect include, but 
are not limited to, clinical worsening or lack of clinical progress. If the Investigator deems the 
benefit-to-risk ratio of IP continuance acceptable, study drug administration of at least 48 h is 
encouraged before discontinuation from IP therapy for insufficient effect.
3.3.4.
Withdrawal from Study
A patient will be considered to have completed the study when he or she completes the EOT visit 
for patients in Treatment Arm 4 and the follow-up visit on Day 56 (± 2 days) for patients in 
Treatment Arms 1, 2, and 3.  
Patients may withdraw from the study or be withdrawn at the request of the Investigator or 
Sponsor at any time. Examples of reasons for study withdrawal include the following: 
x
The patient withdraws consent or requests withdrawal from the study for any reason 
x
The patient is lost to follow-up 
x
The patient fails to comply with protocol requirements or study-related procedures
x
The Investigator determines that it is in the best interest of the patient to withdraw 
from the study protocol for reasons other than an adverse event (AE) 
x
The study is terminated or temporarily suspended by the Sponsor or a regulatory 
authority for any reason including, but not limited to, study drug-related unexpected 
life-threatening serious AEs (SAEs) detected during safety monitoring (e.g., torsade 
de pointes or other ventricular arrhythmias), and 2 or more of the same drug-related 
(possible or probable) treatment-emergent SAE 
Patients who wish to withdraw completely from this clinical study during the treatment period 
should be encouraged to undergo the EOT safety and efficacy assessments at the time of 
withdrawal as shown in the Schedule of Assessments (Table 2). For a patient who agrees to 
complete the EOT visit, blood draws for PK will not be conducted. In addition, for women of 
child-bearing potential a pregnancy test should be conducted at this visit. Once a patient 
withdraws consent, no further data will be collected.

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A patient is considered lost to follow-up if he or she fails to return to the study clinic for 
scheduled visits and is unable to be contacted by the study site. The site must attempt to contact 
the patient at least twice by phone or letter, and, if no response is obtained from the patient, a 
certified letter will be sent requesting that the patient contact the Investigator and asking that 
they return any unused IP and return to the site for a final evaluation. Documentation of these 
efforts to contact the patient must be recorded in the patient’s study file. 
3.3.5.
Criteria for Stopping the Study
The Sponsor, in consultation with the Medical Monitor, upon review of available data may stop 
the study. Possible reasons include, but are not limited to, the following: 
x
Occurrence of an SAE assessed as probably related to IP and resulting in death
x
Occurrence of 2 or more SAEs of the same character that are determined to be 
clinically significant (CS) and assessed as probably related to IP
x
Occurrence of 2 or more AEs of acute pancreatitis, defined as the presence of 
DEGRPLQDOSDLQHOHYDWHGSDQFUHDWLFHQ]\PHVDP\ODVHDQGOLSDVHî8/1DQG
determined to be CS, and an abdominal ultrasound with finding consistent with acute 
pancreatitis
x
Occurrence of 2 or more AEs of acute hepatitis meeting Hy’s Law criteria, defined by 
at least 3-fold elevations of ALT or AST above the ULN, elevation of serum total 
bilirubin to >2 × ULN without elevated serum alkaline phosphatase, and no other 
disease or condition can be found to explain the liver test abnormalities
3.3.6.
Replacement of Patients
Patients prematurely withdrawn from the study will not be replaced. Patients may be rescreened 
at the Investigator’s discretion.

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4.
INVESTIGATIONAL PRODUCT
4.1.
Identity of the Investigational Product
Investigational product refers to both SPR720 and placebo in this Investigational Product 
section.
SPR720 will be administered po as 250 mg capsules containing SPR720 as the active substance 
with no additional excipients. The capsules are white, opaque, size 0, hard gelatin capsules 
containing a white powder. Placebo doses will also be administered po as white, opaque, size 0, 
hard gelatin capsules containing an approximately equivalent weight of microcrystalline 
cellulose (white powder).  
SPR720 drug product and placebo are manufactured by Patheon UK Limited (Abingdon, 
Oxfordshire, UK) under Good Manufacturing Practice conditions and packaged, labeled, and 
distributed by Almac Clinical Services.
SPR720 and placebo are packaged in blister cards of 28 capsules each and then packaged into 
wallets that will be given to the patient. 
Additional information is provided in the investigator’s brochure (IB) and in the Pharmacy 
Manual. 
Standard of care (SOC) will be obtained by the study sites or by prescription. Refer to the 
Product Package Inserts for detailed information regarding SOC treatments.
4.2.
Dosage Schedule
Dosing for each treatment arm is displayed in Table 1. Study drug will be taken po once daily for 
28 days (Days 1 through 28). Dosing for Treatment Arms 1, 2, and 3 will take place at the clinic 
on study visit days. The clinic and patient should try to schedule clinic visits as early as possible 
in the morning to accommodate pre-dose study activities and dosing, preferably before a meal. 
Patients in Treatment Arms 1, 2, and 3 should make every effort to take the IP at the same time 
in the morning approximately an hour before a morning meal on an empty stomach. There are no 
liquid restrictions. Patients will receive a supply of IP and instructions for documenting at-home 
dosing. If a patient experiences IP tolerability issues while at home, the site should instruct the 
patient to call the Investigator. The Investigator may instruct the patient to take their dose with a 
snack or meal, if clinically indicated, to alleviate tolerability concerns. Dosing for Treatment 
Arm 4 (SOC) should occur per specific prescribing information instructions.

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Table 1: Study Treatments
Treatment Arm 1
Double-blinded SPR720 IP 500 mg (2 capsules of 250 mg SPR720 
and 2 capsules of placebo) po once daily
Treatment Arm 2
Double-blinded SPR720 IP 1000 mg (4 capsules of 250 mg SPR720) po once 
daily
Treatment Arm 3
Double-blinded placebo (4 capsules of placebo) po once daily
Treatment Arm 4
Standard of Care regimen is at the Investigator’s discretion; recommended 2-
drug or 3-drug SOC, consisting of either:
x
Clarithromycin 500-1000 mg, plus ethambutol HCl 15 mg/kg po once 
daily
or
x
Azithromycin 250-500 mg, plus ethambutol HCl 15 mg/kg po once 
daily
Optional rifampin 600 mg or rifabutin 300 mg po once daily may be added to 
the SOC regimen for up to 28 days.  
Inform the medical monitor of alternative SOC regimens and discuss concerns 
or questions.
Abbreviations: HCl=hydrochloride; IP=investigational product; po=orally; SOC=standard of care.
Note: Patients will be treated for 28 days.
4.3.
Treatment Assignment
Patients will be randomized (assigned to a treatment) by the site using interactive randomization 
technology (IRT).
Only the designated unblinded study personnel will have access to the randomization schedule 
until the study is completed and approval to unblind the treatment arm assignments has been 
made. Complete details regarding handling, storage, and security of the randomization schedule 
will be documented. 
At the sparse PK sites, patients will be randomized to 1 of 4 treatment arms in a ratio of 5:5:5:4
(SPR720 low dose, SPR720 high dose, placebo, and SOC). The SPR720 and placebo arms will 
be double blinded, and the SOC arm will be open label. At intense PK sites a total of at least 18 
patients will be randomized to Treatment Arms 1, 2, and 3 in a ratio of 1:1:1. 
The IRT will stratify randomization by diagnosis at enrollment as either 1) nodular-
bronchiectatic or 2) fibro-cavitary NTM-PD. 
Patients will be identified by a unique 10-digit patient identifier (e.g., 201-YYY-ZZZZ) in which 
the first 3 digits indicate the study identifier (e.g., 201), the second 3 digits indicate the site 
number, and the final 4 digits indicate the number assigned at randomization. For example, the 
first patient randomized at site 001 will be identified by the number 201-001-0001. Spero 
Therapeutics, Inc. will assign site numbers. As a double-blind study, the Investigators, the site 
staff, the Sponsor, and clinical monitors will not be aware of the treatment assigned to the 

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individual study patients except for Treatment Arm 4 (SOC), which is open label. Specific,
documented staff at the sponsor and contract research organization (CRO) will be unblinded to 
treatment assignments. 
4.4.
Drug Packaging and Blinding
The IP will be labeled in such a way that the blind is maintained.  
The Investigator can receive a patient’s assigned treatment through the IRT system if knowledge 
of the IP is necessary for emergency treatment. If possible, the Medical Monitor should be 
consulted before breaking the code. In any case, the Investigator must record the date, time, and 
reason for breaking the code. The Investigator, once unblinded, should not share the treatment 
assignment with site, Sponsor, or CRO personnel. The Sponsor must be notified as soon as 
possible if the blind must be broken. 
A copy of the randomization code will be maintained securely by the CRO. Designated 
unblinded personnel will be able to access the randomization code if needed.
Additional information can be found in the Pharmacy Manual. 
4.5.
Drug Inventory and Accountability
The Investigator must keep an accurate accounting of the number of IP units delivered to the site, 
dispensed to patients, returned to the Investigator by the patient, and returned to the Sponsor or 
destroyed locally or other disposition during and at the completion of the study.  
The IP is to be used in accordance with the protocol by patients who are under the direct 
supervision of the Investigator. The IP will be sent home with patients for drug administration 
between clinic visits. Investigators should maintain records that document adequately that the 
patients were provided the doses specified by the protocol and reconcile all IP received at the site 
before final disposition. Procedures for the return or destruction of both the used and unused IP 
will be described in the Pharmacy Manual.  
Investigators are required to report IP quality complaints to the Sponsor as described in the 
Pharmacy Manual.
Full details of IP receipt and storage will be documented in the Pharmacy Manual. 
4.6.
Treatment Compliance
All patients will be asked to document in a provided diary the date and time of each IP or SOC
dose taken at home, along with other requested information related to IP administration.
Patients will be required to bring the IP wallet the subsequent clinic visit including any 
remaining capsules that have not been taken. At each visit, the patient’s remaining capsules and 
the diary will be retrieved by the Investigator and compliance assessed. 
Investigational product wallets must be returned at each visit, as compliance will be assessed by 
capsule counts. Investigational product noncompliance for a patient is defined as taking less than 
80% or more than 120% of IP during the treatment period (Day 1 through EOT). Discontinuation 
for noncompliance is at the Investigator’s discretion and should be documented accordingly. 

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4.7.
Concomitant Illnesses and Treatments
4.7.1.
Concomitant Illnesses
Medical history, including significant illnesses, should be documented in the electronic case 
report form (eCRF) according to completion guidelines. 
Additional illnesses present at the time informed consent is given are to be regarded as
concomitant illnesses. Illnesses first occurring or detected after first dose and/or worsening of a 
concomitant illness during the study are to be documented as AEs in the eCRF.
4.7.2.
Concomitant Treatments
Concomitant medications and treatments, defined as treatments taken after the first dose of IP
and SOC, should be recorded in the eCRF according to completion guidelines. Medications and 
treatments taken before the first dose of IP or SOC will not be recorded in the eCRF.
Patients should not have used any systemic (po or IV) or inhaled antibiotic with activity versus
MAC between screening and randomization. Drugs or supplements that are strong CYP3A4 
enzyme inducers or inhibitors (see Appendix 1) within 4 weeks of randomization and during the 
study are prohibited. Hepatic transporters, OATP1B1 or OATP1B3, (see Appendix 2) within 
1 week of randomization and during the study are prohibited.  
Any medication or therapy that is taken by or administered to the patient during the study will be 
recorded (see completion guidelines for eCRF).

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5.
ASSESSMENTS
Unless otherwise indicated, all assessments will be performed by the Investigator or designated 
study personnel.  
5.1.
Schedule of Assessments
The procedures to be performed throughout the study are outlined in the Schedule of 
Assessments (Table 2 ). A detailed description of each assessment may be found in Section 5.2.  

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5.2.
Screening (Day -42 to -1) 
Before enrollment, patients will undergo screening to determine study eligibility. Screening 
procedures must be performed within 42 days before the first day of treatment (Day 1). 
Patients must sign and date the main full study informed consent form (ICF) before any 
screening procedures are performed. 
5.3.
Pharmacokinetic Assessments
Blood samples from patients in Treatment Arms 1, 2, and 3 will be obtained for plasma for PK 
analysis according to the following schedule. Allowable windows of time for the collection of 
blood samples are shown in the Schedule of Assessments (Table 2). 
At 3 or more selected sites, blood samples will be collected from at least 18 patients (at least 
6 per treatment arm) for intensive PK evaluation. Intense blood sampling for PK will occur in the 
clinic on Days 1 and 28 at the following times relative to the time of the daily oral dose 
administered in the clinic: pre-dose and 1, 2, 4, 8, 12, and 24 h post-dose. On Days 7, 14, and 21, 
blood samples will be obtained at the following times relative to the time of the daily oral dose 
administered in the clinic: pre-dose, 1 h post-dose, and just before discharge from the clinic.  
At all remaining sites for sparse PK evaluation, on Days 1, 7, 14, 21, and 28, blood samples will 
be obtained at the following times relative to the time of the daily oral dose administered in the 
clinic: pre-dose, 1 h post-dose, and just before discharge from the clinic. 
Instructions for sample collection, handling, storage, and shipping can be found in the 
Laboratory Manual. 
5.4.
Safety Assessments
Physical Examinations: Full physical examinations will be conducted at screening and Day 1,
and for patients in Treatment Arms 1, 2, and 3 at the follow-up visit 28 days after EOT. The full 
physical examination will include, at a minimum, assessment of the following systems: skin, 
head, ears, eyes, nose and throat, respiratory system, cardiovascular system, gastrointestinal 
system, neurological condition, blood and lymphatic systems, and the musculoskeletal system. 
Symptom-directed physical examinations will be conducted at study visits on Days 7, 14, 21, and 
28.
Any CS changes from baseline in physical examination findings after dosing will be recorded as 
AEs. Height without shoes will be recorded at screening. 
Vital Signs and Body Weight: Vital signs will be measured at each study visit for systolic and 
diastolic blood pressure, pulse, temperature (ºC), and respiratory rate. 
Body weight (kg) will be measured at screening and Days 1, 7, 14, 21, and 28. 
Electrocardiogram: Standard 12-lead ECGs will be measured at screening and Days 1, 14, and 
28, and, for patients in Treatment Arms 1, 2, and 3, at the follow-up visit 28 days after EOT.
Laboratory Parameters: The following clinical laboratory tests (Table 3) are to be performed 
as indicated in the Schedule of Assessments (Table 2).

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Table 3: 
Clinical Laboratory Tests
Serum Chemistry
Hematology (CBC)
Urinalysis
Albumin
Hematocrit
Color and clarity
Alkaline phosphatase
Hemoglobin
pH and specific gravity
ALT
Platelet count
Bilirubin
Amylase
RBC count
Protein
AST
RBC indices:
Glucose
Bicarbonate
    --MCH
Ketones
Bilirubin (total and conjugated)
    --MCHC
Leukocytes
Blood urea nitrogen
    --MCV
Microscopy (if clinically indicated): 
Calcium (total)
    --% Reticulocytes
   --Including bacteria, RBCs, 
Chloride
RDW
      WBCs per HCF
Cholesterol (total)
WBC count
   --Sediment
Creatinine
WBC w/differential (% and absolute):
Nitrites
Creatinine kinase
    --Basophils
Occult blood
GGT
    --Eosinophils
Urobilinogen
Globulins
    --Lymphocytes
Glucose
    --Monocytes
LDH
    --Neutrophils
Additional Tests
Lipase
Serum hCGa
Magnesium
Calculated creatinine clearance using 
measured serum creatinine with 
Cockcroft-Gault formula
Phosphorus
Potassium
Protein (total)
Coagulation
Sodium
aPTT
Triglycerides
PT
Uric acid
INR
Abbreviations: ALT=alanine aminotransferase; aPTT=activated partial thromboplastin time; AST=aspartate 
aminotransferase; CBC=complete blood count; EOT=end of treatment; GGT=gamma glutamyl transferase;
hCG=human chorionic gonadotropin; HPF=high-power field; INR=international normalized ratio; LDH=lactate 
dehydrogenase; MCH=mean corpuscular hemoglobin; MCHC=mean corpuscular hemoglobin concentration; 
MCV=mean corpuscular volume; PT=prothrombin time; RBC=red blood cell; RDW=red blood cell distribution 
width; WBC=white blood cell. 
a.
Female patients will have a serum pregnancy test at screening and Day 1, and, for patients in Treatment Arms 1, 
2, and 3, at the follow-up visit 28 days after EOT. 
Laboratory samples will be analyzed by a central laboratory to ensure consistent interpretation of 
results. Instructions for obtaining and handling laboratory samples are provided in the 
Laboratory Manual.
In the event of an unexplained clinically noteworthy abnormal laboratory test value, the test 
should be repeated immediately and followed up until it has returned to the normal range and/or 
an adequate explanation of the abnormality is found. 
Concomitant Medications and Adverse Events: Concomitant medications and AEs will be 
reviewed and recorded at all study visits. All AEs occurring after the first dose of IP and up to 
the last study event will be recorded. 

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6.
ASSESSMENT AND MANAGEMENT OF ADVERSE EVENTS
Throughout the course of the study, all AEs will be monitored and recorded in an AE page of the 
eCRF, including the AE’s description, start and end date, seriousness, severity, action taken, and 
relationship to the IP. If AEs occur, the first concern will be the safety of the study patients. All 
AEs will be followed until resolved or stable.
6.1.
Adverse Event Definitions
An AE is any untoward medical occurrence in a patient or clinical investigation patient
administered a pharmaceutical product, which does not necessarily have to have a causal 
relationship with the treatment. An AE can therefore be any unfavorable and unintended sign 
(including an abnormal laboratory finding), symptom, or disease temporally associated with the 
use of a medicinal (investigational/experimental) product, whether related to this product or not. 
This includes any newly occurring event or previous condition that has increased in severity or 
frequency since starting active or randomized treatment. 
An SAE is any AE occurring at any dose and regardless of causality that: 
x
Results in death
x
Is life-threatening (Note: The term “life-threatening” in the definition of “serious” 
refers to an event/reaction in which the patient was at risk of death at the time of the 
event/reaction; it does not refer to an event/reaction which hypothetically might have 
caused death, if it were more severe)
x
Requires inpatient hospitalization or prolongation of an existing hospitalization. 
Hospitalization admissions and/or surgical operations scheduled to occur during the 
study period, but planned prior to study entry, are not considered AEs if the illness or 
disease existed before the patient was enrolled in the study, provided that it did not 
deteriorate in an unexpected manner during the study (e.g., surgery performed earlier 
than planned). 
x
Results in persistent or significant disability/incapacity. Disability is defined as a 
substantial disruption of a person’s ability to conduct normal life functions. 
x
Is a congenital anomaly/birth defect
x
Is a medically important event or reaction
Medical and scientific judgment should be exercised in deciding whether other situations should 
be considered serious such as important medical events that may not be immediately 
life-threatening or result in death or hospitalization but might jeopardize the patient or might 
require medical or surgical intervention to prevent one of the other outcomes listed in the above 
definition. These should also be considered serious. Examples of such events are intensive 
treatment in an emergency room or at home for allergic bronchospasm, blood dyscrasias or 
convulsions that do not result in hospitalization, or development of drug dependency or drug 
abuse. The Investigator must review the laboratory report, document this review, and record any 
CS abnormal results in the AE section of the eCRF. The laboratory reports will be reviewed, 
filed, and handled in accordance with the site’s source data list.

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Clarification should be made between the terms “serious” and “severe” since the terms are not
synonymous. The term “severe” is often used to describe the intensity (severity) of a specific 
event (as in mild, moderate, or severe myocardial infarction); the event itself, however, may be 
of relatively minor medical significance (such as a severe headache). This is NOT the same as 
“serious,” which is based on patient/event outcome or action criteria described above and is 
usually associated with events that pose a threat to a patient’s life or functioning. A severe AE 
does not necessarily need to be considered serious. For example, persistent nausea of several 
hours’ duration may be considered severe nausea but not an SAE. However, a stroke resulting in 
only a minor degree of disability may be considered mild but would be defined as an SAE based 
on the above noted criteria. Seriousness (not severity) serves as a guide for defining regulatory 
reporting obligations. 
A suspected unexpected serious adverse reaction (SUSAR): An AE or suspected adverse 
reaction is considered "unexpected" if:
x
It is not listed in the IB
x
It is not listed at the specificity or severity that has been observed
x
The IB is not required or available or not consistent with the risk information 
described in the general investigational plan or elsewhere in the current application
For example, under this definition, hepatic necrosis would be unexpected (by virtue of greater 
severity) if the IB referred only to elevated hepatic enzymes or hepatitis. Similarly, cerebral 
thromboembolism and cerebral vasculitis would be unexpected (by virtue of greater specificity) 
if the IB listed only cerebral vascular accidents. "Unexpected," as used in this definition, also 
refers to AEs or suspected adverse reactions that are mentioned in the IB as occurring with a 
class of drugs or as anticipated from the pharmacological properties of the drug but are not 
specifically mentioned as occurring with the particular drug under investigation. 
Abnormal laboratory findings (e.g., serum chemistry, hematology, coagulation, and urinalysis) or 
other abnormal assessments (e.g., ECG parameters, vital signs) that are judged by the 
Investigator as CS will be recorded as AEs or SAEs if they meet the definitions stated above. 
Clinically significant abnormal laboratory findings or other abnormal assessments that are 
detected during the study or are present at baseline and significantly worsen following the first 
dose will be reported as AEs or SAEs. The Investigator will exercise his/her medical and 
scientific judgment in deciding whether an abnormal laboratory finding or other abnormal 
assessment is CS.
6.2.
Evaluating Adverse Events and Serious Adverse Events
6.2.1.
Assessment of Intensity
The Investigator will assess the intensity for each AE and SAE reported during the study. The 
assessment will be based on the Investigator’s clinical judgment using the latest version of the 
National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) v5.0 as a 
guideline, wherever possible. The intensity of each AE and SAE recorded should be assigned to 
one of the following categories: 

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x
Mild: An event that is easily tolerated by the patient, causing minimal discomfort and 
not interfering with everyday activities 
x
Moderate: An event that is sufficiently discomforting to interfere with normal 
everyday activities 
x
Severe: An event that prevents normal everyday activities. An AE that is assessed as 
severe should not be confused with an SAE. Severity is a category utilized for rating 
the intensity of an event; and both AEs and SAEs can be assessed as severe
x
Life-Threatening or Disabling: An event that poses an immediate risk of death from 
the reaction as it occurred
x
Death: The event resulted in death 
The following terms and definitions are used in assessing the final outcome of an AE:
x
Recovered/Resolved: The patient has fully recovered, or by medical or surgical 
treatment, the condition has returned to the level observed at the first study-related 
activity after the patient signed the informed consent 
x
Recovering/Resolving: This term is only applicable if the patient has completed the 
study or has died from another AE, the condition is improving, and the patient is 
expected to recover from the event
x
Recovered/Resolved with Sequelae: The patient has recovered from the condition, 
but with lasting effect due to a disease, injury, treatment, or procedure. If a sequela 
meets an SAE criterion, the AE must be reported as an SAE
x
Not Recovered/Not Resolved: The condition of the patient has not improved, and 
the symptoms are unchanged, or the outcome is not known at the time of reporting 
x
Fatal: This term is only applicable if the patient died from a condition related to the 
reported AE. Outcomes of other reported AEs in a patient before he/she died should 
be assessed as “recovered/resolved,” “recovering/resolving,” “recovered/resolved 
with sequelae,” or “not recovered/not resolved.” An AE with fatal outcome must be 
reported as an SAE 
x
Unknown: This term is only applicable if the patient is lost to follow-up 
6.2.2.
Assessment of Causality
The Investigator (or designee) will make an assessment as to the relationship between the study 
drug and the occurrence of each AE/SAE. The Investigator (or designee) will use clinical 
judgment to determine whether the AE/SAE is causally related to the study drug. Alternative 
causes, such as natural history of the underlying diseases, concomitant therapy, other risk factors, 
and the temporal relationship of the event to the study drug will be considered and investigated. 
The Investigator (or designee) will also consult the IB in the determination of his/her assessment. 
The causal relationship of the study drug to an AE will be rated according to the following 
4-point scale: 

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x
Unrelated: Clearly and incontrovertibly due only to extraneous causes and does not 
meet criteria listed under unlikely, possible, or probable 
x
Unlikely: Does not follow a reasonable temporal sequence from administration; may 
have been produced by the patient’s clinical state or by environmental factors or other 
therapies administered
x
Possible: Follows a reasonable temporal sequence from administration; may have 
been produced by the patient’s clinical state or by environmental factors or other 
therapies administered
x
Probable: Clear temporal association with improvement on cessation of study drug 
or reduction in dose; reappears upon rechallenge or follows a known pattern of 
response to the study drug 
There may be situations when an SAE has occurred and the Investigator (or designee) has 
minimal information to include in the initial report to the Sponsor. However, it is very important 
that the Investigator (or designee) always assess causality for every event before transmission of 
the SAE form to the Sponsor. The Investigator (or designee) may change his/her opinion of 
causality in light of follow-up information, amending the SAE form and the eCRF accordingly. 
The causality assessment is one of the criteria used when determining regulatory reporting 
requirements. The Investigator (or designee) will provide an assessment of causality as per 
instructions on the SAE form.
6.3.
Time Period, Frequency, and Method of Detecting Adverse Events 
As a consistent method of soliciting AEs, the patient shall be asked a nonleading question such 
as: "How do you feel?” 
Any preexisting conditions or signs and/or symptoms present in a patient before the start of the 
study (e.g., before informed consent) should be recorded as medical/surgical history. In addition, 
any change in health status, which is reported after informed consent is obtained but before
receipt of study drug, will be documented as medical/surgical history. 
Any medical occurrence reported or observed after the first dose of study drug will be recorded 
as an AE. Adverse events will be evaluated by the Investigator (or designee) and recorded. 
Any AEs already documented at a previous assessment and designated as ongoing, should be 
reviewed at subsequent assessments, as necessary. If these have resolved, this should be 
documented. 
6.4.
Adverse Event Management
The Investigator (or designee) will provide appropriate medical care for the clinical management 
of any AEs related to study participation, whether identified during or after the course of study 
participation. Evaluation and treatment of any AE (or CS laboratory abnormality) is at the 
discretion of the Investigator based on their clinical judgment. The applied measures should be 
recorded in the patient’s source documents and entered in the eCRF as applicable. Referral or 
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Section 6.7, the Sponsor may request additional supplemental investigations as needed to 
elucidate the nature and/or causality of an SAE. 
Serious AEs will be reported to competent authorities in accordance with national requirements.
6.5.
Recording of Adverse Events and Serious Adverse Events
When an AE/SAE occurs, it is the responsibility of the Investigator (or designee) to review all 
documentation (e.g., hospital progress notes, laboratory results, patient diaries, and diagnostics 
reports) relative to the event. The Investigator (or designee) will then record all relevant 
information regarding an AE/SAE in the eCRF. It is not acceptable for the Investigator (or 
designee) to send photocopies of the patient’s medical records to the Sponsor in lieu of 
completion of the appropriate AE/SAE eCRF pages. However, there may be instances when the 
Sponsor requests copies of medical records for certain cases. In this instance, all patient 
identifiers will be blinded on the copies of the medical records before submission to the Sponsor. 
The Investigator (or designee) will attempt to establish a diagnosis of the event based on signs, 
symptoms, and/or other clinical information. In such cases, the diagnosis should be documented 
as the AE/SAE and not the individual signs/symptoms. 
6.6.
Serious Adverse Event Reporting
6.6.1.
Regulatory Reporting Requirements for Reporting of Serious Adverse Events
The Investigator (or designee) will promptly report all SAEs to the Sponsor (or delegate). 
Prompt notification of SAEs by the Investigator (or designee) to the appropriate Sponsor (or 
delegate) contact for SAE receipt is essential so that the Sponsor may comply with its regulatory 
obligations. Serious AEs will be reported to regulatory authorities in accordance with national 
requirements.
The Sponsor is responsible for notifying the local regulatory authorities of all SAEs that occur at 
the site. It is the Sponsor’s responsibility to report all SUSARs promptly.
The Principal Investigator (or designee) is responsible for notifying the local institutional review 
board (IRB) or the relevant local regulatory authority of all SAEs that occur at his or her site as 
required. 
6.6.2.
Completion and Transmission of the Serious Adverse Event Reports
Once the Investigator (or designee) becomes aware that an SAE has occurred in a study patient,
he/she will report the information to the Sponsor (or delegate) and the Sponsor’s Medical 
Monitor within 24 h. The SAE form/eCRF will always be completed as thoroughly as possible 
with all available details of the event, signed by the Investigator (or designee), and forwarded to 
the Sponsor (or delegate) and the Sponsor’s Medical Monitor within the designated time frames. 
If the Investigator does not have all information regarding an SAE, he/she will not wait to 
receive additional information before notifying the Sponsor (or delegate) and the Sponsor’s 
Medical Monitor of the event and completing the form/eCRF. The form/eCRF will be updated as 
soon as possible when additional information becomes available. 
The Investigator will always provide an assessment of causality at the time of the initial report.

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Completion of the SAE form/eCRF in an electronic data capture (EDC) system is the preferred 
method to transmit this information to the Sponsor (or delegate) and the Sponsor’s Medical 
Monitor for SAE receipt. In rare circumstances, and in the absence of facsimile, computer and 
scanner equipment, notification by telephone is acceptable, with a copy of the SAE form sent by 
overnight mail. Initial notification via the telephone does not replace the need for the Investigator 
(or designee) to complete and sign the SAE form/eCRF within the outlined time frames.
Any event that in the opinion of the Investigator (or designee) may be of immediate or potential 
concern for the patient’s health or well-being will be reported to the Sponsor’s Medical 
Representative or emergency contact.
Adverse events will be classified as SUSARs if the AE or suspected adverse reaction meets the 
definition of “unexpected” in Section 6.1. All SUSARs should be reported to the ethics 
committee and regulatory authority in accordance with applicable regulatory requirements for 
expedited reporting. It is the Sponsor’s responsibility to report SUSARs to the ethics committee 
and regulatory authority. 
6.6.3.
Post-study Adverse Events and Serious Adverse Events
A post-study AE/SAE is defined as any event that occurs outside of the nominal AE/SAE study 
detection period.  
Investigators are not obligated to actively seek AE/SAE information in former study patients.
However, if the Investigator (or designee) learns of any SAE, including a death, at any time after 
a patient has completed the study and he/she considers the event reasonably related to the study 
drug, the Investigator will promptly notify the Sponsor. 
6.7.
Follow-up of Adverse Events and Serious Adverse Events
After the initial AE/SAE report, the Investigator (or designee) is required to proactively follow 
each patient and provide further information to the Sponsor on the patient’s condition. 
All AEs and SAEs documented at a previous visit/contact and are designated as ongoing will be 
reviewed at subsequent visits/contacts. All AEs must be followed until the patient has 
recovered/resolved and all queries have been resolved, or until deemed medically stable by the 
Investigator (or designee). For cases of chronic conditions or if the patient dies from another 
event, follow-up until the outcome category is “recovered/resolved” is not required, as these 
cases can be closed with an outcome of “recovering/resolving” or “not recovered/not resolved.” 
All patients with SAEs will be followed until they have recovered/resolved, recovered/resolved 
with sequelae, or the event was fatal, or until all queries have been resolved or the patient is lost 
to follow-up. Once resolved, the appropriate SAE report will be updated. The Investigator will 
ensure that follow-up includes any supplemental investigations as may be indicated to elucidate 
the nature and/or causality of the SAE. This may include additional laboratory tests or 
investigations, histopathological examinations, or consultation with other health care 
professionals. 
The Sponsor may request that the Investigator perform or arrange for the conduct of 
supplemental measurements and/or evaluations to elucidate as fully as possible the nature and/or 
causality of the SAE. If a patient dies during participation in the study or during a recognized 

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follow-up period, the Sponsor will be provided with a copy of any postmortem findings, 
including histopathology. 
New or updated information will be recorded on the originally completed SAE form and the 
eCRF, with all changes signed and dated by the Investigator. The Sponsor should be notified of 
the updated SAE form/eCRF. 
6.8.
Clinical Laboratory Evaluations
A change in the value of a clinical laboratory assessment can represent an AE if the change is 
clinically relevant or if, during treatment with the study drug, a shift of a parameter is observed 
from a normal value to an abnormal value, or a further worsening of an already abnormal value. 
When evaluating such changes, the extent of deviation from the reference range, the duration 
until return to the reference range, either while continuing treatment or after the treatment with 
study drug, and the range of variation of the respective parameter within its reference range, 
must be taken into consideration. 
The Investigator should decide, based on the above criteria and the clinical condition of a patient, 
whether a change in a clinical laboratory parameter is CS and therefore represents an AE.
6.9.
Pregnancy
Any report of pregnancy for any female study patient or male study patient’s partner must be 
reported within 1 business day to the Sponsor (or designee) and the Sponsor’s Medical Monitor. 
The female study patient must be withdrawn from the treatment.
A serum pregnancy test will be performed on all women of childbearing potential.  
Every effort should be made to gather information regarding the pregnancy outcome and 
condition of the infant. It is the responsibility of the Investigator to obtain this information within 
30 calendar days after the initial notification and approximately 30-calendar days postpartum.
Pregnancy complications such as spontaneous abortion/miscarriage or congenital abnormality 
are considered SAEs and must be reported to the Sponsor (or designee) and the Sponsor’s 
Medical Monitor. 
Pregnancy outcomes should be collected for female partners of any males who took the study 
drug if possible. Consent to report information regarding these pregnancy outcomes should be 
obtained from the mother.
Note: An elective abortion is not considered an SAE. 
In addition to the above, if the Investigator determines that the pregnancy meets serious criteria, 
it must be reported as an SAE. The test date of the first positive serum/urine ȕ-human chorionic 
gonadotropin test or ultrasound result will determine the pregnancy onset date.
6.10.
Abuse, Misuse, Overdose, and Medication Error
Abuse, misuse, overdose, or medication error (as defined below) must be reported to the Sponsor 
according to the SAE reporting procedure whether or not they result in an AE/SAE. Note: The 
1-business-day requirement for reporting SAEs does not apply to reports of abuse, misuse, 
overdose, or medication errors unless these result in an SAE. 

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The categories below are not mutually exclusive; the event can meet more than 1 category. 
x
Abuse: Persistent or sporadic intentional intake of study drug when used for a 
nonmedical purpose (e.g., to alter one’s state of consciousness or get high) in a 
manner that may be detrimental to the individual and/or society
x
Medication Error: An error made in prescribing, dispensing, administration, and/or 
use of a study drug (for studies, medication errors are reportable to the Sponsor) 
x
Misuse: Intentional use of study drug other than as directed or indicated at any dose 
(Note: this includes a situation where the study drug is not used as directed at the dose 
prescribed by the protocol) 
x
Overdose: Intentional or unintentional intake of a dose of a study drug exceeding a 
prespecified total daily dose of the product 
Cases of patients missing doses of product are not considered reportable as medication errors.
Medication errors should be collected/reported for all products under investigation. 
The administration and/or use of the unassigned treatment is always reportable as a medication 
error. The administration and/or use of an expired product should be considered as a reportable 
medication error.
Errors related to administration of study drug are reportable as medication errors.
Intentional overdosing of study drug is unlikely. In the event of overdose in general, treatment 
should be supportive and symptomatic according the patient's clinical presentation. 
6.11.
Reference Safety Information
The reference for safety information for this study is the IB, which the Sponsor has provided 
separately to all Investigators. 
The reference for safety information for the comparator in this study are Summary of Product 
Characteristics/Product Package Inserts.

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7.
DATA MANAGEMENT
7.1.
Data Management Considerations
Electronic case report forms will be employed for this study. Completed eCRFs for this study 
will be forwarded to the Sponsor or its representative where editing and construction of a 
quality-assured database will occur. Data will be quality checked and electronically verified after 
entry into the database. Queries will be issued for any inconsistencies, omissions, and 
discrepancies and will be resolved by the appropriate parties. The statistical analysis of these 
data will be performed by the Sponsor or its representative. All AEs will be coded using the 
Medical Dictionary for Regulated Activities (MedDRA). Concomitant medications will be coded 
using WHODrug Global. Data management details will be outlined in a separate data 
management plan. 

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8.1.9.2.
Adverse Events
All AEs occurring during the study will be recorded and classified using terminology from 
MedDRA. A treatment-emergent AE (TEAE) is defined as any AE that has an onset on or after 
the first dose of IP or any preexisting condition that has worsened on or after the first dose of IP.  
The incidence of TEAEs (number and percent of patients reporting the AE at least once during 
the study), SAEs, AEs related to study treatment, SAEs related to treatment, and AEs leading to 
study discontinuation will be summarized by treatment. Treatment-emergent AEs will also be 
summarized by severity and relationship to IP. When summarizing TEAEs by severity or 
relationship to IP, each patient will only be counted once within a system organ class or 
preferred term using the event with the greatest severity or causality, respectively, within each
category.  
A listing of patients who prematurely discontinue from the study due to AEs will be provided as 
well as a list of patients who reported SAEs. 
8.1.9.3.
Concomitant Medications
Concomitant medication verbatim terms in the eCRFs will be mapped to 
Anatomical/Therapeutic/Chemical (ATC) class and Preferred Names using WHODrug Global. 
Concomitant medications will be summarized by ATC class and preferred name. These 
summaries will present the number and percentage of patients using each medication. Patients 
may have more than 1 medication per ATC class and preferred name. At each level of 
summarization, a patient will be counted only once if he/she reported 1 or more medications at 
that level.
8.1.9.4.
Laboratory Data 
Laboratory results (hematology, serum chemistry, and urinalysis) will be summarized by 
treatment arm for each time point, change from baseline at each postbaseline time point, shifts 
from baseline for selected laboratory tests (aspartate aminotransferase, alanine aminotransferase, 
gamma-glutamyltransferase, alkaline phosphatase, total bilirubin, amylase, lipase, blood urea 
nitrogen, serum creatinine, creatinine clearance, hemoglobin, hematocrit, neutrophils, 
lymphocytes, and erythrocytes)using CTCAE v5.0, and CS out-of-normal range laboratory. In 
addition, scatterplots of key laboratory values over time will also be produced. 
8.1.9.5.
Electrocardiographic Data
Baseline and change from baseline in ECG parameters (heart rate, cardiac rhythm, PR interval, 
RR interval, QRS interval, QT interval, and QTc interval) will be summarized at each
postbaseline time point. At each time point, the number of patients with QTc according to 
Fridericia’s formula (QTcF) values of >450 ms, >480 ms, and >500 ms will be presented. At 
each postbaseline time point, the number of patients with change from baseline values in QTcF 
of >30 ms and >60 ms will be presented.  
8.1.9.6.
Vital Signs
Summary statistics for the absolute vital sign value and the changes from baseline will be 
presented by treatment arm for each visit.

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9.
STUDY MANAGEMENT
9.1.
Regulations and Guidelines
The study will be performed in accordance with this protocol, US investigational new drug 
regulations (US Title 21 Code of Federal Regulations [CFR] Part 312), International Council for 
Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines 
for Good Clinical Practice (GCP), and the regulations on electronic records and electronic 
signature (Title 21 CFR Part 11). 
9.2.
Sponsor’s Responsibilities
9.2.1.
Good Clinical Practice
The Sponsor and any third party to whom aspects of the study management or monitoring have 
been delegated will undertake their assigned roles for this study in compliance with all applicable 
industry regulations and ICH GCP Guideline E6(R2).
Representatives of the Sponsor and/or the company organizing/managing the research on behalf 
of the Sponsor to inspect study data, patients’ medical records, and eCRFs in accordance with 
current GCP and the respective government regulations and guidelines conduct visits to sites. 
Records and data may additionally be reviewed by auditors or by regulatory authorities. 
The Sponsor ensures that local regulatory authority requirements are met before the start of the 
study. The Sponsor (or designee) is responsible for the preparation, submission, and 
confirmation of receipt of any regulatory authority approvals required prior to release of IP for 
shipment to the site.
9.2.2.
Indemnity/Liability and Insurance
The Sponsor ensures that suitable clinical study insurance coverage is in place prior to the start 
of the study. An insurance certificate is supplied to the CRO/Investigator as necessary.
9.2.3.
Public Posting of Study Information
The Sponsor is responsible for posting appropriate study information on applicable websites.
Information included in clinical study registries may include participating Investigators’ names 
and contact information.  
9.2.4.
Suspension, Discontinuation, and Completion of the Study
The Sponsor reserves the right to suspend or discontinue the study or part of the study at any 
time for any reason. If the study is suspended or terminated, the Sponsor will ensure that 
applicable regulatory agencies and IRBs are notified as appropriate. Additionally, the 
discontinuation of a registered clinical study, which has been posted to a designated public 
website, will be updated accordingly. Should the study be terminated and/or a site closed, all IP 
pertaining to the study must be returned to the Sponsor or its representative.

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9.3.
Investigator Responsibilities
9.3.1.
Good Clinical Practice Compliance
The Investigator must undertake to perform the study in accordance with ICH GCP Guideline 
E6(R2) and applicable regulatory requirements and guidelines. 
It is the Investigator’s responsibility to ensure that adequate time and appropriately trained 
resources are available at the site prior to commitment to participate in this study. The 
Investigator should also be able to estimate or demonstrate a potential for recruiting the required 
number of suitable patients within the agreed recruitment period.
The Investigator will maintain a list of appropriately qualified persons to whom the Investigator 
has delegated significant study-related tasks. Curricula vitae for Investigators and 
Subinvestigators will be provided to the Sponsor (or designee) before starting the study. 
If a potential research patient has a primary care physician, the Investigator should, with the 
patient’s consent, inform them of the patient’s participation in the study.
9.3.2.
Protocol Adherence and Investigator Agreement
The Investigator and any Subinvestigators must adhere to the protocol as detailed in this 
document. The Investigator is responsible for enrolling only those patients who have met 
protocol eligibility criteria. Investigators are required to sign an Investigator Agreement to 
confirm acceptance and willingness to comply with the study protocol. 
If the Investigator suspends or terminates the study at their site, the Investigator will promptly 
inform the Sponsor and the IRB and provide them with a detailed written explanation. The 
Investigator will also return all IP, containers, and other study materials to the Sponsor. Upon 
study completion, the Investigator will provide the Sponsor, IRB, and regulatory agency with 
final reports and summaries as required by national regulations.
Communication with local IRBs, to ensure accurate and timely information is provided at all 
phases during the study, may be done by the Sponsor, CRO, or Investigator.
9.3.3.
Institutional Review Board
Conduct of the study must be approved by an appropriately constituted IRB, which operates in 
accordance with the principles and requirements described in the US Title 21 CFR Part 56, and 
the ICH guidelines. Approval is required for the study protocol, protocol amendments, ICFs,
patient information sheets, and advertising materials. 
9.3.4.
Informed Consent
For each trial patient, a written ICF will be obtained before any protocol-specific activities are 
performed. As part of this procedure, the Investigator or a designated representative must explain 
orally and in writing the nature, duration, and purpose of the study, and the action of the IP in 
such a manner that the patient and (if applicable) appointed guardian are aware of the potential 
risks, inconveniences, or adverse effects that may occur. Patients should be informed that they 
may withdraw from the study at any time. They will receive all information that is required by 
federal regulations and ICH guidelines. The Principal Investigator or a designated representative 

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will provide the Sponsor or its representative with a copy of the approved ICF before the start of 
the study.
The Sponsor’s indemnification of the Investigator and institution during the conduct of this study 
will be discussed in a separate document.
9.4.
Study Documentation
By signing a copy of Form FDA 1572, the Principal Investigator acknowledges that he/she has 
received a copy of the IB on SPR720 and assures the Sponsor that he/she will comply with the 
protocol and the provisions stated in Form FDA 1572. No changes in this protocol can be made 
without the Sponsor’s written approval.
9.5.
Data Management and Quality Control
9.5.1.
Electronic Case Report Forms
Electronic case report forms will be used to collect all patient data during the study. The 
Investigator is responsible for the accuracy and completeness of all data in the eCRFs. 
The Investigator is responsible for maintaining adequate and accurate medical records from 
which accurate information is recorded into the eCRFs, which have been designed to record all 
observations and other data pertinent to the clinical investigation. The Investigator or designee as 
stated in the site delegation log must complete eCRFs. 
9.5.2.
Recording, Access, and Retention of Source Data and Study Documents
Original source data to be reviewed during this study will include, but is not limited to the 
patient’s medical file, patient diaries, original clinical laboratory reports, and histology and 
pathology reports. All key data must be recorded in the patient’s medical records.
The Investigator must permit authorized representatives of the Sponsor, the respective national, 
local, or foreign regulatory authorities, the IRB, and auditors to inspect facilities and to have 
direct access to original source records relevant to this study, regardless of media.
The Study Monitor (and auditors, IRB or regulatory inspectors) may check the eCRF entries 
against the source documents. The consent form includes a statement by which the patient agrees 
to the monitor/auditor from the Sponsor or its representatives, national or local regulatory 
authorities, or the IRB having access to source data (e.g., patient’s medical file, appointment 
books, original laboratory reports, X-rays).  
These records must be made available within reasonable times for inspection and duplication, if 
required, by a properly authorized representative of any regulatory agency (e.g., the FDA or an 
auditor).
Essential documents must be maintained according to ICH GCP requirements and may not be 
destroyed without written permission from the Sponsor. 
9.5.3.
Study Monitoring and Quality Assurance
This study will be monitored for quality assurance at all stages of its development by the clinical 
research personnel employed by the Sponsor or its representative. Monitoring will include 

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personal visits and telephone communication to assure that the investigation is conducted 
according to the protocol, standard operating procedures, GCP guidelines, and applicable 
regulatory requirements. Quality control procedures will be applied to each stage of data 
handling to ensure that all data are reliable and have been processed correctly. On-site review of 
eCRFs will include a review of forms for completeness and clarity and consistency with source 
documents available for each patient. Note that a variety of original documents, data, and records 
will be considered as source documents in this trial. The eCRF itself is not to be used as a source 
document under any circumstances. 
By signing this protocol, the Investigator grants permission to personnel from the Sponsor, its 
representatives, and appropriate regulatory authorities, for on-site monitoring of all appropriate 
study documentation, as well as on-site review of the procedures employed in eCRF generation, 
where clinically appropriate.
All data collected in patient diaries, if applicable, of this study will be entered into a computer
database. Verification of entered data will be done by double-data entry procedure. An audit trail 
will trace every change made in the database. Data management will be performed according to 
Synteract’s standard operating procedures. 
The eCRFs for any patient leaving the study should be completed at the time of the final visit or 
shortly thereafter.
9.5.4.
Financial Disclosure
Upon submission of a marketing application to the FDA for any drug, Spero Therapeutics, Inc. 
must provide the FDA with a list of clinical investigators who conducted a sponsored clinical 
study and certify or disclose financial arrangements.
The Investigator is required to disclose any financial arrangement during the study and for 1 year 
following, whereby the value of the compensation for conducting the study could be influenced 
by the outcome of the study. The following information is collected: any significant payments 
from the Sponsor or subsidiaries such as a grant to fund ongoing research; compensation in the 
form of equipment; retainer for ongoing consultation or honoraria; any proprietary interest in IP;
and any significant equity interest in the Sponsor or subsidiaries as defined in 21 CFR 54 2(b) 
(1998). 
In consideration of participation in the study, the Sponsor pays the Investigator or nominated 
payee the sums set out in the payment schedule attached to the Investigator Agreement.
9.6.
Use of Study Findings
By signing the study protocol, the Investigator agrees to the use of results of the study for the 
purposes of national and international registration. If necessary, the authorities will be notified of 
the Investigator’s name, address, qualifications, and extent of involvement. Reports covering 
clinical and biometric aspects of the study will be prepared by the Sponsor or its representative.
9.7.
Privacy and Confidentiality
All US sites and laboratories or entities providing support for this study, must, where applicable, 
comply with the Health Insurance Portability and Accountability Act of 1996 (HIPAA). A site 

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that is not a Covered Entity as defined by HIPAA must provide documentation of this fact to the 
CRO/Sponsor. 
The confidentiality of records that may be able to identify patients will be protected in 
accordance with applicable laws, regulations, and guidelines.
After patients have consented to take part in the study, the Sponsor and/or its representatives 
review their medical records and data collected during the study. Others, including the following, 
may review these records and data: independent auditors who validate the data on behalf of the 
Sponsor; third parties with whom the Sponsor may develop, register, or market SPR720; and 
national or local regulatory authorities and the IRB, which gave approval for the study to 
proceed. The Sponsor and/or its representatives accessing the records and data will take all 
reasonable precautions in accordance with applicable laws, regulations, and guidelines to 
maintain the confidentiality of patients’ identities.
Patients will be assigned a unique identifying number. However, their initials and date of birth 
may also be collected and used to assist the Sponsor to verify the accuracy of the data, for 
example, to confirm that laboratory results have been assigned to the correct patient. 
The results of studies containing patients’ unique identifying number, relevant medical records, 
and possibly initials and dates of birth will be recorded. They may be transferred to, and used in, 
other countries that may not afford the same level of protection that applies within the countries 
where this study is conducted. The purpose of any such transfer would be to support regulatory 
submissions, to conduct new data analyses to publish or present the study results, or to answer 
questions asked by regulatory or health authorities. 
9.8.
Publications
As a multicenter trial, the Sponsor intends to publish clinical data from all centers participating 
in the investigation. A publication committee selected by the Sponsor will submit draft 
manuscripts to all participating Investigators for their comments. In conformity with the Uniform 
Requirements for Manuscripts Submitted to Biomedical Journals published by the International 
Committee of Medical Journal Editors (Kassirer and Angell 1991), Investigators whose 
contribution consists solely in the collection of data will not be named individually as authors. 
Rather, those Investigators will receive a collective authorship as the “SPR720 Study Group” and 
will be identified in a note.
Individual Investigators and/or their associates subsequently may publish additional findings of 
this study in scientific journals or present them at scientific meetings, provided that the Sponsor 
is given many opportunities to review any proposed abstract, manuscript, or slide presentation 
before its submission. This review is required to ensure that the Sponsor is aware of all written 
and oral presentations of the data and does not imply any editorial review or restriction of the 
contents of the presentation or use. 

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10.
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Griffith DE, Adjemian J, Brown-Elliott BA, Philley JV, Prevots DR, Gaston C, et al. 
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Griffith DE, Aksamit T, Brown-Elliott BA, Catanzaro A, Daley C, Gordin F, et al. An official 
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APPENDIX 1.
PROHIBITED INHIBITORS AND INDUCERS OF CYP3A
The following inhibitors and inducers of CYP3A are prohibited within 4 weeks before 
randomization and during the study: 
CYP3A Strong Inhibitors
CYP3A Strong Inducers
Boceprevir 
Cobicistat 
Conivaptan  
Danoprevir and ritonavir  
Elvitegravir and ritonavir
Grapefruit juice 
Indinavir and ritonavir
Itraconazole
Ketoconazole  
Lopinavir and ritonavir  
Paritaprevir and ritonavir and (ombitasvir 
and/or dasabuvir) 
Posaconazole
Ritonavir  
Saquinavir and ritonavir 
Telaprevir  
Tipranavir and ritonavir
Troleandomycin  
Voriconazole 
Clarithromycin
Diltiazem
Idelalisib
Nefazodone 
Nelfinavir
Carbamazepine
Enzalutamide 
Mitotane 
Phenytoin  
Rifampin 
St. John’s wort
Abbreviation: CYP=cytochrome P450

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APPENDIX 2.
PROHIBITED SUBSTRATES OF THE HEPATIC 
TRANSPORTERS OATP1B2 OR OATP2B3
The following substrates of the hepatic transporters OATP1B2 or OATP2B3 are prohibited 
within 1 week before randomization and during the study: 
Asunaprevir 
Atorvastatin
Bosentan
Danoprevir 
Docetaxel
Fexofenadine 
Glyburide 
Nateglinide
Paclitaxel
Pitavastatin
Pravastatin
Repaglinide 
Rosuvastatin
Simvastatin acid