• Men or women aged 30 to 85 years (inclusive), at the time of informed consent.

• Body weight range of ≥40 kg (88 lbs) to ≤110 kg (242 lb) and a BMI of 18 to 34 kg/m2.

• Has symptomatic frontotemporal dementia (FTD), including mild behavioral, cognitive, motor or language impairment per Investigator's assessment (behavioral-variant FTD, primary progressive aphasia-FTD, FTD with corticobasal syndrome, or a combination of syndromes are allowed for enrollment).

• Score ≥0.5 and ≤15 on CDR plus NACC FTLD sum of boxes (Cohorts 1-4 only). Note: In Cohort 5 only patients with CDR plus NACC FTLD with sum of boxes ≥0.5 and ≤9 AND global score of 0.5 or 1 will be enrolled.

• Stable use of background medications at least 8 weeks prior to LY3884963 dosing.

• Carrier of a pathogenic progranulin gene (GRN) mutation.

• Negative screening test for Mycobacterium tuberculosis (MTB) or documented negative MTB test within 1year prior to screening.

• Age- and gender-appropriate cancer screenings are up-to-date and completed.

• Patient and/or patient's legally authorized representative has the ability to understand the purpose and risks of the study, and provide written informed consent and authorization to use protected health information.

• Women of nonchildbearing potential must be either surgically sterile (hysterectomy, bilateral tubal ligation, salpingectomy, and/or bilateral oophorectomy at least 26 weeks before Screening) or postmenopausal, defined as spontaneous amenorrhea for at least 2 years, with follicle stimulating hormone level in the postmenopausal range at Screening based on the central laboratory's range.

• Men and women of childbearing potential (i.e., ovulating, premenopausal, and not surgically sterile) must use a highly effective method of contraception consistently and correctly for the duration of the study, including the long term follow up. Highly effective methods of contraception are those that, alone or in combination, result in a failure rate of less than 1% per year when used consistently and correctly (i.e., perfect use) and include the following for female patients of childbearing potential:

‣ Combined (estrogen and progestogen containing) oral, intravaginal, or transdermal hormonal contraception associated with inhibition of ovulation.

⁃ Oral, injectable, or implantable progestogen-only hormonal contraception associated with inhibition of ovulation.

⁃ Intrauterine device.

⁃ Intrauterine hormone-releasing system.

⁃ Bilateral tubal ligation or bilateral tubal occlusion (performed at least 3 months prior to Screening).

⁃ Vasectomized partner (performed at least 3 months prior to Screening).

⁃ Sexual abstinence (no sexual intercourse), if in line with the patient's usual and preferred lifestyle.

• Acceptable forms of contraception for male patients include:

‣ Sexual abstinence (no sexual intercourse), if in line with the patient's usual and preferred lifestyle.

⁃ History of vasectomy (performed at least 3 months prior to Screening, with documented absence of sperm in the ejaculate) in combination with condom.

⁃ Condom with spermicide used together with highly effective female contraceptive methods if the female partner(s) is of childbearing potential (see above for list of acceptable female contraceptive methods).

∙ Note: Individuals who are in exclusively same sex relationships (as their preferred and usual lifestyle) are not required to use contraception.

• Men must agree to use a condom during any sexual intercourse (including male patients who have had a vasectomy) and abstain from sperm donation for the duration of the study, including long-term follow-up.

• Women must agree to abstain from egg donation for the duration of the study, including long-term follow-up.

• Women of childbearing potential cannot be pregnant or lactating/breastfeeding and must have a negative result for the serum pregnancy test (β-human chorionic gonadotropin) at Screening.

• Patient must agree to abstain from blood donation for the first year following gene transfer.

• Patient has a reliable study partner/informant (e.g. family member, friend) willing and able to participate in the study as a source of information on the patient's health status and cognitive and functional abilities.

• Patient is not dependent on a walker or wheelchair.

• Patient is living in the community (i.e. not in nursing home); some levels of assisted living may be permitted at the discretion of the investigator.

• Pneumococcal pneumonia and shingles vaccines are required within 10 years of Screening allowed to be performed during Screening but must be given at least 4 weeks prior to initiation of immunosuppressant regimen.