Long-term Extension Study of Ulviprubart (ABC008) in Subjects with Inclusion Body Myositis

ABC008-IBM-202 is an open-label, multicenter study to evaluate the safety and efficacy of long-term administration of ulviprubart (ABC008) in subjects with IBM who have completed either Study ABC008-IBM-101 or Study ABC008-IBM-201. Subjects may be enrolled in this study if they meet study eligibility criteria and:

* Have completed the Part 2 (Multiple Ascending Dose \[MAD\]) End of-Treatment (EOT) Visit in Study ABC008-IBM-101; subjects who continued further on into Part 3 of the study (MAD Extension) prior to enrolling in this study are also eligible; OR
* Have completed the Week 80 Follow-up Visit in Study ABC008-IBM-201.

ABC008-IBM-202 is an open-label, multicenter study to evaluate the safety and efficacy of long-term administration of ulviprubart (ABC008) in subjects with IBM who have completed either Study ABC008-IBM-101 or Study ABC008-IBM-201. Subjects may be enrolled in this study if they meet study eligibility criteria and:

* Have completed the Part 2 (Multiple Ascending Dose \[MAD\]) End of-Treatment (EOT) Visit in Study ABC008-IBM-101; subjects who continued further on into Part 3 of the study (MAD Extension) prior to enrolling in this study are also eligible; OR
* Have completed the Week 80 Follow-up Visit in Study ABC008-IBM-201. Subjects will enter this study following their initial study such that dosing continues every eight weeks (Q8W) between the last dose in the initial study and the first dose in this long-term extension (LTE) Study IBM-202. Study subjects will continue to receive any ongoing concomitant medications from the initial study.

Subjects will be required to sign an informed consent form before undertaking any study-specific procedures or assessments. Screening is intended to be done at the final visit of the initial study, which will coincide with the Baseline (Day 1) Visit for this study; if this is not possible, the Baseline (Day 1) Visit for this study, including screening, may be conducted at a separate visit (provided it occurs within the visit window defined in Appendix 1 of the protocol). Subsequent study visits will occur every eight weeks until EOT at Week 156, or withdrawal from the study.

Eligibility Criteria:
Inclusion Criteria:

* 1. Able to read, understand, and provide signed informed consent prior to the performance of any study-related procedures.

  2. Has participated in and completed either Study ABC008-IBM-101 or Study ABC008-IBM-201; completion of the prior study will be defined as completion of the Part 2 (MAD) EOT Visit in Study ABC008-IBM-101 (subjects may have continued into Part 3 \[MAD Extension\]) or completion of the Week 80 Follow-up Visit in Study ABC008-IBM-201.

  3. Demonstrated adequate compliance, in the opinion of the Investigator, with the study procedures during Study ABC008-IBM-101 or Study ABC008-IBM-201.

  4. Willing and able to comply with the requirements of the protocol, including traveling to the site for study-related assessments and SC injections of ulviprubart.

  5. Women of childbearing potential (WOCBP) and male subjects with female partners who are WOCBP (based on sex assignation at birth) must agree to use highly effective (\< 1% failure rate) contraception for the duration of the study through 180 days after EOT/ETV.

  6. WOCBP (based on sex assignation at birth) must have a negative urine pregnancy test at the Baseline (Day 1) Visit.

  7. Male subjects (based on sex assignation at birth) must refrain from sperm donation for the duration of the study through 180 days after EOT/ETV.

Exclusion Criteria:

* 1. Has an unresolved clinically significant AE or a clinically significant finding on a clinical laboratory test, ECG, or physical examination during Study ABC008-IBM-101 or Study ABC008 IBM-201 that, in the Investigator's opinion, would limit the subject's ability to participate in or comply with this study.

  2. Participation in another investigational drug study (other than Study ABC008-IBM-101 or Study ABC008-IBM-201) within 30 days prior to the Baseline (Day 1) Visit or five times the half-life of the investigational drug, whichever is longer.

  3. Is not willing or able to comply with the restrictions regarding the use of prohibited medications throughout the study.

  4. Women who are pregnant, lactating, or who plan to become pregnant or initiate lactation during the study.