Ipilimumab is a humanized antibody to CTLA4, used to treat cancers refractory to conventional treatment. We treated 21 patients with refractory melanoma or prostate cancer with anti-CTLA4 antibody (ipilimumab), with subsequent development of significant colitis in 9. Two of these nine did not respond rapidly to high-dose (2 mg/kg/day) glucocorticoids or infliximab. They required additional immunosuppression, and one ultimately died of opportunistic infection, representing a more refractory course than has previously been described complicating ipilimumab therapy. Both patients had received radiation to the pelvis for prostate cancer less than one year prior to receiving ipilimumab. We performed immunohistochemical analysis of colon biopsies from ipilimumab recipients to determine if colitis correlates with depletion of intramucosal FOXP3+ regulatory T cells (Tregs), which normally express CTLA4. However, we found no evidence of FOXP3+ T cell depletion in any of the 9 patients who developed colitis.

Previous studies suggest regulatory T cells (Tregs) inhibit graft versus host disease (GVHD) in mouse and human hematopoietic cell transplant (HCT) recipients. As the gastrointestinal tract represents one of the most common and severe sites of GVHD-related tissue damage, we sought to determine if a deficit in circulating or gastric mucosal Treg numbers correlates with the clinical onset of gastric GVHD. We used the marker FOXP3 to quantify Tregs in blood and in gastric antral biopsies in a cohort of 60 allogeneic HCT recipients undergoing endoscopy at a single center to evaluate symptoms suspicious for gastrointestinal GVHD. We show for the first time in the gastric mucosa and, contrary to existing reports, in the blood, that the percent of T cells expressing FOXP3 is at least as high in the presence as in the absence of GVHD involving the upper gut. There was no correlation of Treg frequency with the histological nor clinical severity of gastrointestinal GVHD. We conclude that Treg depletion is not a central feature in the pathogenesis of gastric GVHD in man.

Background B-lymphoblastic leukemia (BLL) is a B lineage neoplasm that expresses typical immature B cell markers, but may also express myeloid-associated antigens. Myeloperoxidase (MPO) is a heme-containing peroxidase, which has been used as the single most specific myeloid marker when assigning lineage to acute leukemia. MPO positivity by immunohistochemistry (IHC) in BLL has been historically described in a subset of patients; however, further detailed comparison of IHC to flow cytometry and IHC methodology is described herein. Design The University of Washington pathology database was searched for new or relapsed adult BLL from 2011–2019. Cases with blasts >30% of marrow cellularity by morphology were selected. MPO IHC was performed using the Dako, polyclonal antibody (rabbit) on a Ventana instrument with streptavidin-biotin (SB) detection method. MPO IHC SB positive cases were also stained using the same antibody and platform, but a different detection method, multimer-optiview (MO). MPO IHC was called positive when >10% of neoplastic blasts showed expression. MPO positive blast percentage, staining intensity and pattern were assessed. Intensity: 0=negative, 1=mild, 2=moderate, 3=bright/same level as myeloids. Cytoplasmic pattern: homogenous or granular. Concurrent flow cytometry results and cytogenetic and/or molecular studies were reviewed. Results 35 cases were identified. Positive MPO IHC expression was present in 7/35 cases by SB method, with the percentage of MPO positive blasts ranging from 20–90% (majority >70%), all ranged from 1 - 2+ intensity and most (5/7) were homogenous pattern. 4/5 MPO SB positive cases were negative by MO detection method. MPO evaluation by flow cytometry was negative in 3 of 3 cases and myeloid associated antigens were negative or low on a subset. 2/8 BLL, BCR-ABL1 cases were MPO IHC positive by SB. Conclusion MPO staining by IHC in BLL is present in 17% of cases, often present in the majority of blasts, and positive using the SB detection system. This aberrant staining can be negated in most cases with the MO detection system. MPO expression by flow cytometry in MPO IHC SB positive cases were negative (3/3) and were low to absent for other myeloid antigens. We agree with prior studies that MPO IHC using the SB method can be a confounder for lineage assignment in acute leukemia.