• Participant's parent(s)/legal guardian(s) have provided written informed consent (and assent has been provided by the participant, depending on age) for the study.

• Participant is of any sex, ≤17 years of age.

• Participant has been diagnosed with CPT (with or without NF1).

• Participant has a non-healing Paley type 3 or 4 diaphyseal fracture.4

• Participant is a candidate for surgical treatment using an internal fixation approach (intramedullary rod) based on CPT fracture status and general health status.

• Participant has serology and molecular test results at Visits 1 and 2 excluding the presence of human T-cell lymphoma virus, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and syphilis.

• Participant can provide an adequate ATC sample volume.

• Participant weighs ≥5 kg/11 lb at Screening and on Day 1.

• Participant is not pregnant or lactating.

⁃ If participant is of childbearing potential, is practicing highly effective methods of birth control from Screening to the end of the study:

∙ Combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation:

⁃ Oral

• Intravaginal

• Transdermal

‣ Progestogen-only hormonal contraception associated with inhibition of ovulation:

⁃ Oral

• Injectable

• Implantable

‣ Intrauterine device

‣ Intrauterine hormone-releasing system

‣ Bilateral tubal occlusion

‣ Vasectomized partner

‣ Sexual abstinence, defined as refraining from heterosexual intercourse during study participation, is acceptable if this is the participant's usual lifestyle; periodic abstinence (calendar, symptothermal, post-ovulation methods), withdrawal (coitus interruptus), spermicides only, and the lactational amenorrhea method are not acceptable methods of contraception Note: A participant is considered to be of childbearing potential if they are postmenarchal and premenopausal, unless surgically sterile (permanent sterilization methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy).

⁃ If participant is sexually active and has a partner who may become pregnant (i.e., neither surgically sterile nor postmenopausal), agrees to use highly effective contraception (e.g., sterilization, birth control pills, Depo Provera injections, or contraceptive implants) from Screening to the end of the study.

⁃ Participant agrees to refrain from donating sperm or eggs from Screening to the end of the study.

⁃ Participant and parent(s)/legal guardian(s) are able to understand all study information provided and are willing to return to the study facility for all visits, including follow-up evaluations.