Neihulizumab for Standard-Risk Acute Graft Versus Host Disease (GVHD)

Inclusion Criteria: 1. Patients aged ≥ 18 years. 2. Recipients of myeloablative and non-myeloablative, reduced-intensity conditioning allogeneic transplants. 3. Recipients of all donor sources, including sibling, unrelated donor, human leukocyte antigen (HLA) -haploidentical, and HLA-mismatched donors. 4. Patients must have initial presentation of standard-risk aGVHD according to refined Minnesota Criteria. Standard-risk aGVHD is defined as follows: Single organ involvement: * Stage 1-3 skin * Stage 1 upper GI * Stage 1-2 lower GI Multiple organ involvement: * Stage 1-3 skin plus stage 1 upper GI * Stage 1-3 skin plus stage 1 lower GI * Stage 1-3 skin plus stage 1 lower GI plus stage 1 upper GI * Stage 1-3 skin plus stage 1-4 liver * Stage 1 lower GI plus stage 1 upper GI 5. Patients must not have received prior systemic immune suppressive therapy for the treatment of active aGVHD (topical steroids and budesonide are permitted). 6. Biopsy confirmation of GVHD is not required, but encouraged. 7. Female patients must meet one of the following: * Postmenopausal for at least one year before the screening visit, or * Surgically sterile (i.e. undergone a hysterectomy or bilateral oophorectomy), or * If subject is of childbearing potential (defined as not satisfying either of the above two criteria), agree to practice two acceptable methods of contraception (combination methods requires use of two of the following: diaphragm with spermicide, cervical cap with spermicide, contraceptive sponge, male or female condom, hormonal contraceptive) from the time of signing of the informed consent form through 90 days after the last dose of study agent, AND o Agree to practice true abstinence when this is in line with the preferred and usual lifestyle of the subject. (Periodic abstinence \[e.g., calendar, ovulation, symptom-thermal, post ovulation methods\] and withdrawal are not acceptable contraception methods). 8. Male patients, even if surgically sterilized (i.e., status post vasectomy), must agree to one of the following: * Practice effective barrier contraception during the entire study period and through 60 calendar days after the last dose of study agent, OR * Must also adhere to the guidelines of any study-specific pregnancy prevention program, if applicable, OR o Agree to practice true abstinence when this is in line with the preferred and usual lifestyle of the subject. (Periodic abstinence \[e.g., calendar, ovulation, symptom-thermal, post ovulation methods\] and withdrawal are not acceptable methods of contraception.) 9. Ability to understand a written informed consent document, and the willingness to sign it. Exclusion Criteria: 1. Relapse of disease which was the primary indication for transplant. 2. Uncontrolled infections not responding to antimicrobial therapy. 3. Active and uncontrolled human immunodeficiency virus (HIV), or chronic Hepatitis B, or Hepatitis C. 4. Tuberculosis, history of tuberculosis or a known positive Quantiferon test. 5. Liver dysfunction not attributable to aGVHD evidenced by a Total Bilirubin ≥ 2 x upper limit of normal (ULN). 6. Creatinine clearance \< 40 mL/min calculated by Cockcroft-Gault equation. 7. Intestinal obstruction within three days of enrollment. 8. Life expectancy of less than 28 days, or Eastern Cooperative Oncology Group (ECOG) performance status of 4.