Relapse of acute myeloid leukemia after hematopoietic stem cell transplantation appears to be related to posttransplant changes in immune function that may be reversible with interferon-gamma therapy, investigators said.
Researchers performed a comparison of acute myeloid leukemia (AML) samples taken from patients before hematopoietic stem cell transplantation (HSCT) and at the time of relapse. They found that, while the general genomic changes seen at relapse resembled changes seen when patients experience relapse after chemotherapy, HSCT was associated with changes in genes believed to control both adaptive and innate immunity.
The findings suggest that transplantation results in a dampening of immune surveillance that could potentially be reversed with interferon gamma, an immunostimulatory cytokine, reported, from Washington University, St. Louis, and his colleagues.
“These changes appeared to be epigenetic in nature in at least some cases, which suggests that therapeutic strategies to resensitize AML cells to the graft-versus-leukemia effect may be feasible,” they wrote in the.
The researchers noted that, while the presence of certain AML mutations may predict risk for relapse following HSCT, “the mechanisms by which these mutations promote relapse remain unclear.”
To get a better sense of how genetic and epigenetic changes after transplantation may allow leukemic cells to avoid the graft-versus-leukemia effect – and to see whether immune-related genes are affected by HSCT – they performed enhanced exome sequencing, flow cytometry, and immunohistochemical analyses on samples from 15 patients with AML who had a relapse after receiving transplants from HLA-matched siblings, matched unrelated donors, or HLA-mismatched unrelated donors, and on paired samples from 20 patients who experienced relapses after chemotherapy.
To validate their findings, they also evaluated samples from 28 other patients with AML who had a relapse after transplantation.
They first looked for relapse-specific mutations, but found no driver mutations associated with relapse after transplantation. The mutations seen during relapse after transplantation were generally similar to those seen both before treatment and after relapse in patients who had undergone chemotherapy. The researchers could not identify any patterns of mutations related to relapse.
They then looked for, but did not find, relapse-specific mutations in genes involved in either modulation of immune checkpoints, antigen presentation, or cytokine signaling.
The researchers did, however, find evidence of epigenetic changes that were more common in the samples of patients with posttransplant relapses, compared with postchemotherapy relapses. Specifically, they found that major histocompatibility (MHC) class II genes were down-regulated 200%-1100% after transplant, compared with the pretransplant samples.
In samples from 17 of 34 patients who experienced a relapse after transplantation, both flow cytometry and immunohistochemical analyses confirmed that expression of MHC class II molecules were decreased at relapse.
To see whether this down-regulation was reversible, the researchers treated samples from three patients with posttransplant relapse with interferon gamma, which is known to up-regulate MHC class II protein on myeloid cells and other cell types.
“Culture of these cells with interferon-gamma rapidly induced MHC class II protein expression on leukemic blasts, with essentially full restoration of MHC class II protein expression in nearly all AML blasts after 72 hours,” they wrote, adding that the reversibility of down-regulation of MHC class II in these blasts “strongly suggests that this phenomenon is mediated by an epigenetic mechanism.”
The study was supported by grants to investigators from the National Institutes of Health, Leukemia & Lymphoma Society, and the Barnes-Jewish Hospital Foundation. Dr. Christopher and several coauthors reported receiving grants from the study funders but no other relevant conflicts of interest. Several coauthors reported receiving personal fees and/or research support from industry outside the submitted work.
SOURCE: Christopher MJ et al. N Engl J Med. 2018 Oct 31. doi: 10.1056/NEJMoa1808777.