An Extension Study of AK002 in Patients With Eosinophilic Gastritis and/or Eosinophilic Duodenitis

Inclusion Criteria: 1. Provide written informed consent. 2. Completed Study AK002-003, defined as having received 4 infusions of study drug and followed through Day 113 (±3 days) in Study AK002-003 or discontinued from treatment due to high eosinophil counts prior to infusions 2, 3, or 4 and willing to begin extended dosing on or about Day 113 (for AK002-003 completers) or within 6 months of last dosing for patients discontinued from treatment. 3. If patient is on pre-existing dietary restrictions, willingness to note any changes that occur from the Baseline diet, throughout the study. 4. Able and willing to comply with all study procedures. 5. Female patients must be either post-menopausal for at least 1 year or surgically sterile (tubal ligation, hysterectomy, or bilateral oophorectomy) for at least 3 months, or if of childbearing potential, have a negative pregnancy test and agree to use dual methods of contraception, or abstain from sexual activity until the end of the study, or for 120 days following the last dose of study drug, whichever is longer. 6. Male patients with female partners of childbearing potential must agree to use a highly effective method of contraception until the end of the study or for 120 days following the last dose of study drug, whichever is longer. All fertile men with female partners of childbearing potential should be instructed to contact the Investigator immediately if they suspect their partner might be pregnant at any time during study participation. Exclusion Criteria: 1. Poor tolerance to previous administration of AK002 in the opinion of the Investigator. 2. Known hypersensitivity to any constituent of the study drug. 3. Any disease, condition (medical or surgical), or cardiac abnormality, which, in the opinion of the Investigator, would place the patient at increased risk. 4. Vaccination with live attenuated vaccines within 30 days prior to initiation of treatment in the study, during the treatment period, or vaccination expected within 5 half-lives (4 months) of study drug administration. All types and formulations of vaccines (including live attenuated vaccines) authorized by FDA or other regulatory authority for the prevention of COVID-19 may be administered before, during, or after this study. The vaccine should not be administered within 7 days prior to and within 7 days after the administration of AK002 so that any side effects caused by either of the 2 medications can be more easily determined. 5. Women who are pregnant, breastfeeding, or planning to become pregnant while participating in the study. 6. Any other reason that, in the opinion of the Investigator or Medical Monitor, makes the patient unsuitable for enrollment. 7. Diagnosis of Hypereosinophilic Syndrome (HES), based on standard criteria (blood eosinophils \>1500/µL with involvement of either the heart, nervous system, and/or bone marrow).